Luminescent display panel drive unit and drive method thereof

BACKGROUND OF THE INVENTION

The present invention relates to a unit for driving a luminescent display panel using a capacitive luminescent element, such as an organic electro-luminescent element.

As a display which attains low power dissipation, high-quality display, and lower profile, an electro-luminescent display, in which a plurality of organic electro-luminescent elements are arranged in a matrix pattern, has attracted attention. As shown in

FIG. 1

, the organic electro-luminescent element is formed by means of stacking, on a transparent substrate

100

such as a glass plate on which a transparent electrode

101

is formed, at least one organic function layer

102

which is made up of an ion transport layer, a light-emitting layer; and a positive hole transport layer, and a metal electrode

103

. A positive voltage is applied to the anode of the transparent electrode

101

, and a negative voltage is applied to the cathode of the metal electrode

103

. A d.c. current is applied across the transparent electrode

101

and the metal electrode

103

, wherewith the organic function layer

102

illuminates. Use of an organic compound which can be expected to exhibit a superior luminous characteristic embodies a practicable electro-luminescent display.

The organic electro-luminescent element (hereinafter referred to simply as an “EL element”) can be electrically expressed as an equivalent circuit shown in FIG.

2

. As can be seen from the drawing, the EL element can be replaced with a capacitive component C and a diode component E which is connected in shunt with the capacitive component and has a diode characteristic. For this reason, the organic electro-luminescent element is considered to be a capacitive luminescent element. When a light-emitting d.c. drive voltage is applied across electrodes of the organic electro-luminescent element, electric charge is stored in the capacitive component C. When the light-emitting d.c. drive voltage exceeds a barrier voltage or threshold illumination voltage unique to the EL element, an electric current starts flowing from the electrode (i.e., the anode of the diode component E) to the organic function layer, which also acts as a light-emitting layer, whereupon the organic electro-luminescent element illuminates at an intensity proportional to the electric current.

As shown in

FIG. 3

, the characteristic of the EL element concerning a voltage V, a current I, and luminance L is analogous to that of a diode. The current I is considerably small at a voltage lower than the threshold illumination voltage V

th

and abruptly increases at a voltage higher than the threshold illumination voltage V

th

. The electric current I is substantially proportional to the luminance L. When a drive voltage exceeding the threshold illumination voltage V

th

is applied to the EL element, the EL element illuminates at an intensity proportion to the electric current corresponding to the drive voltage. If the drive voltage to be applied to the EL element is below the threshold illumination voltage V

th

no drive current flows through the EL element, and hence the luminous intensity of the EL element remains substantially zero.

A passive matrix drive method has hitherto been known as a method of driving a luminescent display panel using a plurality of EL elements.

FIG. 4

shows an example structure of a driver device of passive matrix drive type for driving a luminescent display panel. In a luminescent display panel, “n” cathode lines (i.e., metal electrodes) B

1

to B

n

are arranged in parallel with each other so as to extend in the lateral direction, and “m” anode lines (i.e., transparent electrodes) A

1

to A

m

are arranged in parallel with each other so as to extend in the longitudinal direction. In respective intersections (a total number of “n×m”) between the cathode lines and the anode lines, light-emission layers of EL elements E

1

to E

m

are sandwiched. The EL elements E

1

to E

m

, which serve as pixels, are arranged in a matrix pattern and are positioned in respective intersections between the anode lines A to A

h

and the cathode lines B

1

to B

n

. One end of the EL element (i.e., the anode of the diode component E of the equivalent circuit) is connected to the anode line, and the other end of the EL element (i.e., the cathode of the diode component E of the equivalent circuit) is connected to the cathode line. The cathode line is connected to and activated by a cathode line scanning circuit

1

, and the anode line is connected to and activated by an anode line drive circuit

2

.

The cathode line scanning circuit

1

has scan switches

5

1

to

5

n

assigned to respective cathode lines B

1

to B

n

for determining respective electric potentials thereof. Each of the scanning switches

51

to

5

n

connects to a corresponding cathode line either a reverse bias voltage (e.g., 10 volts) produced from a supply voltage, or a ground potential (e.g., 0 volt).

The anode drive circuit

2

has current sources

2

1

to

2

m

(e.g., constant-current sources) for supplying a drive current to respective EL elements, and drive switches

6

1

to

6

m

, which are assigned to the anode lines A

1

to A

m

. The drive switches

6

1

to

6

m

supply a current to the respective anode lines A

1

to A

n

by means of switching operations. A voltage source, such as a constant-voltage source, can be used as a drive source. The previously-described current-luminance characteristic is stable against temperature variations, whereas a voltage-luminance characteristic is unstable against temperature variations. For this reason, a current source (a source circuit which is to be controlled such that the amount of supply current assumes a desired value) is commonly used. The amount of current supplied from current sources

2

1

to

2

m

is the amount of current required for sustaining a state in which an EL element illuminates at desired instantaneous luminance (this state will hereinafter be referred to as a “steady luminous state”). When the EL element is in a steady luminous state, electric charge corresponding to the amount of supply current is charged into the capacitive component C of the EL element. The voltage across the EL element assumes a specified value Ve corresponding to instantaneous luminance (hereinafter referred to as a “specified illumination voltage”).

The anode lines A

1

to A

m

are connected to an anode line reset circuit

3

. The anode line reset circuit

3

has shunt switches

7

1

to

7

m

assigned to respective anode lines A

1

to A

m

. The anode lines A

1

to A

m

are brought into ground potential by means of selection of the shunt switches

7

1

to

7

m

. The cathode line scanning circuit

1

, the anode line drive circuit

2

, and the anode line reset circuit

3

are connected to an illumination control circuit

4

.

The illumination control circuit

4

controls the cathode line scanning circuit

1

, the anode line drive circuit

2

, and the anode line reset circuit

3

, to thereby display a video in accordance with a video signal supplied from an unillustrated video signal generation system. The illumination control circuit

4

sends a scanning line selection control signal to the cathode line scanning circuit

1

, to thereby perform operations for selecting a cathode line corresponding to a horizontal scanning period of a video signal and setting the thus-selected cathode line to ground potential. The scanning switches

5

1

to

5

n

are switched so as to apply a reverse bias voltage Vcc to the remaining cathode lines. The reverse bias voltage Vcc is applied from the constant-voltage line connected to the cathode line, in order to prevent illumination of EL elements connected to intersections between the anode line through which a drive current is flowing and cathode lines which are not selected for scanning, which would otherwise be caused by crosstalk. Here, the reverse bias voltage Vcc is usually set equal to the specified illumination voltage Ve. During each horizontal scanning period, the scanning switches

5

1

to

5

n

are sequentially switched to ground potential. The cathode line set to ground potential acts as a scanning line which enables illumination of an EL element connected to the cathode line.

The anode line drive circuit

2

controls illumination of the scanning line. The illumination control circuit

4

produces a drive control signal indicating a timing at which and a period of time during which the EL element connected to the scanning line is illuminated in accordance with the pixel information represented by a video signal. In accordance with the drive control signal, the anode line drive circuit

2

switches some of the drive switches

6

1

to

6

m

, thereby supplying a drive current to EL elements in accordance with pixel information by way of the anode lines A

1

to A

m

. The EL elements through which the drive current flows illuminate in accordance with the pixel information.

The anode line reset circuit

3

is reset in response to a reset control signal output from the illumination control circuit

4

. The anode line reset circuit

4

turns on some of the shunt switches

7

1

to

7

m

corresponding to the anode lines, which lines are represented by the reset control signal and are to be reset, and turns off the remaining shunt switches.

Japanese Patent Application Laid-Open No. 232074/1997 filed by the present inventor describes a drive method for a passive matrix luminescent display panel, in which a reset operation is performed for causing discharge of the electric charges stored in each of EL elements arranged into a matrix pattern immediately before scanning lines are switched (the method is hereinafter referred to as a “reset drive method”). The reset drive method is for speeding up illumination of an EL element when a scanning line is switched. The reset drive method for a passive matrix luminescent display panel will be described by reference to

FIGS. 4 through 6

.

Driving operations which will be described hereinbelow and are shown in

FIGS. 4 through 6

are directed to a case where, after EL elements E

1,1

and E

2,1

have been illuminated by means of scanning a cathode line B

1

, EL elements E

2,2

and E

3,2

are illuminated by means of scanning a cathode line B

2

. In order facilitate explanations, illuminating EL elements are depicted by diode symbols, and nonilluminating EL elements are depicted by capacitor symbols. The reverse bias voltage Vcc applied to the cathode lines B

1

to B

n

is equal to the specified illumination voltage Ve of the EL element; that is, 10 volts.

In

FIG. 4

, only a scanning switch

5

1

is switched to a ground potential of 0 volt, thereby scanning the cathode line B

1

. The reverse bias voltage Vcc is applied to the remaining cathode lines B

2

to B

n

by way of the scanning switches

5

2

to

5

n

. The anode line A

1

is connected to a current source

2

1

by way of a drive switch

6

1

, and the anode line A

2

is connected to a current source

2

2

by way of a drive switch

6

2

. The remaining anode lines A

3

to A

m

are brought into a ground potential of 0 volt by means of shunt switches

7

3

to

7

m

. In connection with the circuit diagram shown in

FIG. 4

, only the EL elements E

1,1

and E

2,1

are forwardly biased, and a drive current flows into the EL elements E

1,1

, and E

2,1

from respective current sources

2

1

and

2

2

, as depicted by arrows. As a result, solely the EL elements E

1.1

and E

2,1

are illuminated. In this state, nonilluminating and hatched EL elements E

3,2

to E

m,n

are charged with a polarity such as that illustrated in the drawing.

The following reset control operation is performed immediately before a scanning operation is performed for causing the next EL elements E

2,2

and E

3,2

to illuminate from the steady luminous state shown in FIG.

4

. Specifically, as shown in

FIG. 5

, all drive switches

6

1

to

6

m

are released, and all the scanning switches

5

1

to

5

n

and all the shunt switches

7

1

to

7

m

are brought into a ground potential of 0 volt. Further, all the anode lines A

1

to A

m

and cathode lines B

1

to B

n

are temporarily shunted to a ground potential of 0 volt, thus resetting the entire display. If the entire display is reset, all the anode and cathode lines are brought to a single voltage of 0. The electric charges stored in the EL elements are discharged by way of the route depicted by the arrows provided in the drawing. Thus, all the electric charges stored in the EL elements become momentarily empty.

After the electric charges stored in all the EL elements have been fully discharged, only the scanning switch

5

2

corresponding to the cathode line B

2

is switched to 0 volt, as shown in

FIG. 6

, thereby scanning the cathode line B

2

. Simultaneously, the drive switches

6

2

and

6

3

are closed, thereby connecting the current sources

2

2

and

2

3

to corresponding anode lines. The shunt switches

7

1

and

7

4

through

7

m

are turned on, thus bringing anode lines A

1

and A

4

through A

m

to 0 volt.

As mentioned above, according to the reset drive method, illumination is controlled by means of repetition of a scanning mode during which any of the cathode lines B

1

to B

n

are made active, and a subsequent reset mode. The display is brought into the scanning mode and the reset mode every horizontal scanning period (1H). If the display is brought directly into the state shown in

FIG. 6

from the state shown in

FIG. 4

, the drive current supplied from the current source

2

3

flows to an EL element E

3,2

and is consumed by means of canceling the reverse electric charges (illustrated in

FIG. 4

) stored in the EL elements E

3,3

to E

3,n

. For these reasons, time is consumed for bringing the EL element E

3.2

into a steady luminous state (bringing the voltage across the EL element E

3,2

to the specified luminous voltage Ve).

When the above-described reset control operation is performed, the anode lines A

2

and A

3

assume potentials close to Vcc at the moment at which the scanning line is switched to the cathode line B

2

. A charge current flows into EL elements E

2,2

and E

3,2

not only from the current sources

2

2

and

2

3

but also from a plurality of routes such as constant-voltage sources connected to cathode lines B

1

and B

3

to B

n

. Parasitic capacitance is charged with the charge current, and the specified luminous voltage Ve is momentarily reached. Thus, the EL elements E

2,2

and E

3,2

can instantaneously enter a steady luminous state. During a period of time in which the cathode line B

2

is scanned, the amount of current supplied from the current source is set to the minimum amount of current required for maintaining the EL element in a steady luminous state at the specified luminous voltage Ve. Therefore, the electric current supplied from the current sources

2

2

and

2

3

flows into solely the EL elements E

2,2

and E

3,2

. Thus, all the electric current is dissipated by illumination of the EL elements. As a result, the display is sustained in a luminous state shown in FIG.

6

.

As has been described above, according to the known reset drive method, before illumination of the next scanning lines is controlled, all the cathode and anode lines are temporarily connected and reset to a ground potential of 0 volts or a voltage equal to the reverse bias voltage Vcc. Consequently, when the current scanning line has been switched to the next scanning line, there can be speeded up the charging of the EL elements to the specified luminous voltage Ve, as well as the rise and illumination of EL elements, which are connected to the scanning line and are to be illuminated.

As shown in

FIGS. 4 and 6

, when some cathode lines are scanned by means of application of ground potential thereto, the voltage Vcc is applied to the cathode lines which are not scanned. Further, ground potential is applied to anode lines to which an electric current is not supplied from a current source. More specifically, in the case of the circuit diagram shown in

FIG. 4

, a reverse bias voltage substantially equal to the voltage Vcc is applied between the anode and cathode of each of the EL elements E

3,2

to E

m,n

. In the case of the circuit diagram shown in

FIG. 6

, a reverse bias voltage substantially equal to the voltage Vcc is applied between the anode and cathode of each of the EL elements E

1,1

, E

4,1

to E

m,1

, E

1,3

to E

1,n

, and E

4,3

to E

m,n

. The EL elements to which the reversely-biased voltage Vcc is applied are charged. The thus-charged electric charges are discharged for supplying ground potential to the cathode lines as well as for supplying an electric current from a current source. The electric charges that are charged in and discharged from the EL elements do not contribute to illumination of EL elements at all and are wasted. Power dissipation due to the charging and discharging operations of the EL elements increases in proportion to the number of EL elements. Therefore, useless power dissipation increases as the display area of a display panel increases.

SUMMARY OF THE INVENTION

The present invention is aimed at providing a luminescent display panel drive unit capable of diminishing useless power dissipation that does not contribute to illumination.

To this end, the present invention provides a luminescent display panel drive unit including

a plurality of drive lines and a plurality of scanning lines, which intersect each other; and

a plurality of capacitive luminescent elements which are provided in respective intersections between the drive lines and the scanning lines and connected to the scanning lines and drive lines and which have polarities, the drive unit comprising:

control means for setting a scanning period during which a single scanning line is selected from the plurality of scanning lines in accordance with a scan timing of an input video signal, for specifying a light-emission drive line assigned to the capacitive luminescent element which is connected to the single scanning line and is to be illuminated in accordance with the input video signal during the scanning period, and for setting a reset period during an interval between scanning periods;

scanning means for applying a first potential lower than an illumination threshold voltage of the capacitive luminescent element to the single scanning line during the scanning period, for applying a second potential higher than the illumination threshold voltage to scanning lines other than the single scanning line, and for applying the second potential to all the scanning lines during the reset period; and

drive means for supplying a drive current to the illumination drive line for forwardly applying, during the scanning period, a positive voltage higher than the illumination threshold voltage to the capacitive luminescent element to be illuminated, for applying a third potential slightly lower than the illumination threshold voltage to the drive lines other than the illumination drive line, and for supplying during the reset period a fourth potential equal to the second potential to all the drive lines.

Further, according to the present invention, a first potential lower than an illumination threshold voltage is applied to a single scanning line selected for scanning, during a scanning period. A second potential higher than the illumination threshold voltage is applied to the scanning lines other than the single scanning line. A fourth potential slightly lower than the illumination threshold voltage is applied to the plurality of drive lines other than an illumination drive line connected to capacitive luminescent elements to be illuminated. Consequently, a comparatively-low reverse bias voltage is applied to respective capacitive luminescent elements located in intersections between scanning lines except the single scanning line and drive lines except the illumination drive line. Electric charges which are stored in the luminescent elements with the reverse bias voltage and which do not contribute to illumination are diminished as compared with those charged in luminescent elements in a known display panel, thus reducing useless power dissipation.

Accordingly, the present invention provides a luminescent display panel drive unit including

a plurality of drive lines and a plurality of scanning lines, which intersect each other; and

a plurality of capacitive luminescent elements which are provided in respective intersections between the drive lines and the scanning lines and connected to the scanning lines and drive lines and which have polarities, the drive unit comprising:

control means for setting a scanning period during which a single scanning line is selected from the plurality of scanning lines in accordance with a scan timing of an input video signal, for specifying a light-emission drive line assigned to the capacitive luminescent element which is connected to the single scanning line and is to be illuminated in accordance with the input video signal during the scanning period, for setting a reset period during an interval between scanning periods, and for specifying, as a non-reset drive line, at least the drive line having connected thereto the capacitive luminescent element to remain unilluminated during the scanning periods before and after the reset period;

scanning means for applying a first potential lower than an illumination threshold voltage of the capacitive luminescent element to the single scanning line during the scanning period, for applying a second potential higher than the illumination threshold voltage to scanning lines other than the single scanning line, and for applying the second potential to all the scanning lines during the reset period; and

drive means for supplying a drive current to the illumination drive line for forwardly applying, during the scanning period, a positive voltage higher than the illumination threshold voltage to the capacitive luminescent element to be illuminated, for applying a third potential slightly lower than the illumination threshold voltage to the drive lines other than the illumination drive line, for supplying during the reset period a fourth potential equal to the second potential to the plurality of drive lines exclusive of the non-reset drive line, and for applying the third potential to the non-reset drive line.

According to the present invention, a first potential lower than an illumination threshold voltage is applied to a single scanning line selected for scanning, during a scanning period. A second potential higher than the illumination threshold voltage is applied to the scanning lines other than the single scanning line. A fourth potential slightly lower than the illumination threshold voltage is applied to the plurality of drive lines other than an illumination drive line connected to capacitive luminescent elements to be illuminated. Consequently, a comparatively-low reverse bias voltage is applied to respective capacitive luminescent elements located in intersections between scanning lines except the single scanning line and drive lines except the illumination drive line. Electric charges which are stored in the luminescent elements with the reverse bias voltage and which do not contribute to illumination are diminished as compared with those charged in luminescent elements in a known display panel, thus reducing useless power dissipation.

Further, during the reset period, there is specified as a non-reset drive line at least the drive line connected to the capacitive luminescent element which is to remain unilluminated during the scanning periods before and after the reset period, and the second potential is applied to all the scanning lines. Moreover, a fourth potential equal to the second potential is applied to the plurality of drive lines exclusive of the non-reset drive line, and a third potential is applied to the non-reset drive line. The electric charges—which are stored in the capacitive luminescent elements connected to a non-reset drive line by means of the reverse bias voltage—are held without being discharged. Even when the reverse bias voltage is applied to the capacitive luminescent elements during the next scanning period, charging or discharging barely arises in the luminescent elements, thereby reducing useless power dissipation.

Further, accordingly, the present invention provides a luminescent display panel drive unit including

a plurality of drive lines and a plurality of scanning lines, which intersect each other; and

a plurality of capacitive luminescent elements which are provided in respective intersections between the drive lines and the scanning lines and connected to the scanning lines and rive lines and which have polarities, the drive unit comprising:

control means for setting a scanning period during which a single scanning line is selected from the plurality of scanning lines in accordance with a scan timing of an input video signal, for specifying a light-emission drive line assigned to the capacitive luminescent element which is connected to the single scanning line and is to be illuminated in accordance with the input video signal during the scanning period, for setting a reset period during an interval between scanning periods, and for specifying, as anon-reset drive line, only the drive line having connected thereto the capacitive luminescent element to remain unilluminated during the scanning periods before and after the reset period;

scanning means for applying a first potential lower than an illumination threshold voltage of the capacitive luminescent element to the single scanning line during the scanning period, for applying a second potential higher than the illumination threshold voltage to scanning lines other than the single scanning line, and for applying the second potential to all the scanning lines during the reset period; and

drive means for supplying a drive current to the illumination drive line for forwardly applying, during the scanning period, a positive voltage higher than the illumination threshold voltage to the capacitive luminescent element to be illuminated, for applying a third potential slightly lower than the illumination threshold voltage to the drive lines other than the illumination drive line, for supplying during the reset period a fourth potential equal to the second potential to the plurality of drive lines exclusive of the non-reset drive line, and for applying the third potential to the non-reset drive line.

According to the present invention, a first potential lower than an illumination threshold voltage is applied to a single scanning line selected for scanning, during a scanning period. A second potential higher than the illumination threshold voltage is applied to the scanning lines other than the single scanning line. A fourth potential slightly lower than the illumination threshold voltage is applied to the plurality of drive lines other than an illumination drive line connected to capacitive luminescent elements to be illuminated. Consequently, a comparatively-low reverse bias voltage is applied to respective capacitive luminescent elements located in intersections between scanning lines except the single scanning line and drive lines except the illumination drive line. Electric charges which are stored in the luminescent elements with the reverse bias voltage and which do not contribute to illumination are diminished as compared with those charged in luminescent elements in a known display panel, thus reducing useless power dissipation.

Further, during the reset period, there is specified as a non-reset drive line only the drive line connected to the capacitive luminescent element which is to remain unilluminated during the scanning periods before and after the reset period, and the second potential is applied to all the scanning lines. Moreover, a fourth potential equal to the second potential is applied to the plurality of drive lines exclusive of the non-reset drive line, and a third potential is applied to the non-reset drive line. The electric charges—which are stored in the capacitive luminescent elements connected to a non-reset drive line by means of the reverse bias voltage—are held without being discharged. Even when the reverse bias voltage is applied to the capacitive luminescent elements during the next scanning period, charging or discharging barely arises in the luminescent elements, thereby reducing useless power dissipation.

The present invention also provides a luminescent display panel drive unit including

a plurality of drive lines and a plurality of scanning lines, which intersect each other; and

a plurality of capacitive luminescent elements which are provided in respective intersections between the drive lines and the scanning lines and connected to the scanning lines and drive lines and which have polarities, the drive unit comprising:

control means for setting a scanning period during which a single scanning line is selected from the plurality of scanning lines in accordance with a scan timing of an input video signal, for specifying a light-emission drive line assigned to the capacitive luminescent element which is connected to the single scanning line and is to be illuminated in accordance with the input video signal during the scanning period, for setting a reset period during an interval between scanning periods, and for specifying, as a non-reset drive line, only the drive line having connected to the capacitive luminescent element to remain unilluminated during the scanning period subsequent to the reset period;

scanning means for applying a first potential lower than an illumination threshold voltage of the capacitive luminescent element to the single scanning line during the scanning period, for applying a second potential higher than the illumination threshold voltage to scanning lines other than the single scanning line, and for applying the second potential to all the scanning lines during the reset period; and

drive means for supplying a drive current to the illumination drive line for forwardly applying, during the scanning period, a positive voltage higher than the illumination threshold voltage to the capacitive luminescent element to be illuminated, for applying a third potential slightly lower than the illumination threshold voltage to the drive lines other than the illumination drive line, for supplying during the reset period a fourth potential equal to the second potential to the plurality of drive lines exclusive of the non-reset drive line, and for applying the third potential to the non-reset drive line.

According to the present invention, a first potential lower than an illumination threshold voltage is applied to a single scanning line selected for scanning, during a scanning period. A second potential higher than the illumination threshold voltage is applied to the scanning lines other than the single scanning line. A fourth potential slightly lower than the illumination threshold voltage is applied to the plurality of drive lines other than an illumination drive line connected to capacitive luminescent elements to be illuminated. Consequently, a comparatively-low reverse bias voltage is applied to respective capacitive luminescent elements located in intersections between scanning lines except the single scanning line and drive lines except the illumination drive line. Electric charges which are stored in the luminescent elements with the reverse bias voltage and which do not contribute to illumination are diminished as compared with those charged in luminescent elements in a known display panel, thus reducing useless power dissipation.

Further, during the reset period, there is specified as a non-reset drive line only the drive line connected to the capacitive luminescent element which is to remain unilluminated during a scanning period subsequent to the reset period, and the second potential is applied to all the scanning lines. Moreover, a fourth potential equal to the second potential is applied to the plurality of drive lines exclusive of the non-reset drive line, and a third potential is applied to the non-reset drive line. The electric charges—which are stored in the capacitive luminescent elements connected to non-reset drive line by means of the reverse bias voltage—are held without being discharged. Even when the reverse bias voltage is applied to the capacitive luminescent elements during the next scanning period, charging or discharging barely arises in the luminescent elements, thereby reducing useless power dissipation.

Further, the present invention provides a luminescent display panel drive unit including

a plurality of drive lines and a plurality of scanning lines, which intersect each other; and

a plurality of capacitive luminescent elements which are provided in respective intersections between the drive lines and the scanning lines and are connected to the scanning lines and drive lines and which have polarities, the drive unit comprising:

determination means for distinguishing, as real scanning lines from the plurality of scanning lines, scanning lines which are connected to capacitive luminescent elements to be illuminated during each scanning period;

control means which sequentially specifies one scanning line from the real scanning lines and specifies light-emission drive lines assigned to the capacitive luminescent elements to be illuminated every time one scanning line is specified, the luminescent elements being connected to the specified scanning line; and

drive means for forwardly supplying a drive current to the capacitive luminescent elements to be illuminated, by way of the scanning line and the light-emission drive line every time one scanning line is specified.

Further, the present invention also provides a method of driving a luminescent display panel including

a plurality of drive lines and a plurality of scanning lines, which intersect each other; and

a plurality of capacitive luminescent elements which are provided in respective intersections between the drive lines and the scanning lines and are connected to the scanning lines and drive lines and which have polarities, the method comprising the steps of:

distinguishing, as real scanning lines from the plurality of scanning lines, scanning lines which are connected to capacitive luminescent elements to be illuminated during each scanning period;

sequentially specifying one scanning line from the real scanning lines and specifies light-emission drive lines assigned to the capacitive luminescent elements to be illuminated every time one scanning line is specified, the luminescent elements being connected to the specified scanning line; and

forwardly supplying a drive current to the capacitive luminescent elements to be illuminated, by way of the scanning line and the light-emission drive line every time one scanning line is specified.

By means of the configuration embodied by the present invention, scanning lines to which capacitive luminescent elements to be illuminated are connected are scanned, and the remaining scanning lines are not scanned. Useless power dissipation can be diminished, by the amount corresponding to the power required for scanning the scanning lines to which capacitive luminescent elements to be illuminated are not connected.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1

is a cross-sectional view of an EL element;

FIG. 2

is an equivalent circuit of the EL element;

FIG. 3

is a plot schematically showing a drive voltage-current-luminous brightness characteristic of the EL element;

FIG. 4

is a block diagram for describing a reset drive method applied to a known luminescent display panel drive unit using EL elements;

FIG. 5

is a block diagram for describing a reset drive method applied to a known luminescent display panel drive unit using EL elements;

FIG. 6

is a block diagram for describing a reset drive method applied to a known luminescent display panel drive unit using EL elements;

FIG. 7

is a block diagram showing the configuration of a luminescent display panel drive unit according to the present invention;

FIG. 8

is a block diagram specifically showing a luminescent display panel, a cathode line scanning circuit, and an anode line drive circuit of the drive unit shown in

FIG. 7

;

FIG. 9

is a flowchart for describing an illumination drive operation performed by a light-emission control circuit;

FIG. 10

is an illustration showing the relationship between scanning periods and reset periods;

FIG. 11

is a block diagram for describing the illumination drive operation shown in

FIG. 9

;

FIG. 12

is a block diagram for describing the illumination drive operation shown in

FIG. 9

;

FIG. 13

is a block diagram for describing the illumination drive operation shown in

FIG. 9

;

FIG. 14

is a block diagram showing the configuration of a luminescent display panel drive unit according to the present invention;

FIG. 15

is a block diagram specifically showing a luminescent display panel, a cathode line scanning circuit, and an anode line drive circuit of the drive unit shown in

FIG. 14

;

FIG. 16

is a flowchart for describing an illumination drive operation performed by a light-emission control circuit;

FIG. 17

is a block diagram for describing the illumination drive operation shown in

FIG. 16

;

FIG. 18

is a block diagram for describing the illumination drive operation shown in

FIG. 16

;

FIG. 19

is a block diagram for describing the illumination drive operation shown in

FIG. 16

;

FIG. 20

is a block diagram specifically showing a luminescent display panel, a cathode line scanning circuit, and an anode line drive circuit of the drive unit shown in

FIG. 7

;

FIG. 21

is a block diagram for describing the illumination drive operation shown in

FIG. 9

;

FIG. 22

is a block diagram for describing the illumination drive operation shown in

FIG. 9

;

FIG. 23

is a block diagram for describing the illumination drive operation shown in

FIG. 9

;

FIG. 24

is a flowchart for describing another example of illumination drive operation performed by a light-emission control circuit;

FIG. 25

is a block diagram for describing the illumination drive operation shown in

FIG. 24

;

FIG. 26

is a block diagram for describing the illumination drive operation shown in

FIG. 24

;

FIG. 27

is a block diagram for describing the illumination drive operation shown in

FIG. 24

;

FIG. 28

is a block diagram showing the configuration of a luminescent display panel drive unit according to the present invention;

FIG. 29

is a block diagram specifically showing a luminescent display panel, a cathode line scanning circuit, and an anode line drive circuit of the drive unit shown in

FIG. 7

;

FIG. 30

is a flowchart for describing a light-emission determination operation performed by a control circuit;

FIG. 31

is a flowchart for describing a light-emission drive operation performed by a control circuit;

FIG. 32

is an illustration showing an example of scanning operation performed by the drive unit shown in

FIG. 7

;

FIG. 33

is a block diagram specifically showing a luminescent display panel, a cathode line scanning circuit, and an anode line drive circuit of a luminescent panel drive unit according to another embodiment of the present invention;

FIG. 34

is a block diagram for describing the light-emission determination operation shown in

FIG. 33

;

FIG. 35

is a block diagram specifically showing a luminescent display panel, a cathode line scanning circuit, and an anode line drive circuit of a luminescent panel drive unit according to yet another embodiment of the present invention; and

FIG. 36

is a block diagram for describing the light-emission determination operation shown in FIG.

35

.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will be described hereinbelow in detail by reference to the accompanying drawings.

FIG. 7

schematically shows the configuration of a display which is embodied by application of the present invention to a luminescent display panel using EL elements as capacitive luminescent elements. The display comprises a capacitive luminescent display panel

11

; a light-emission control section

12

; a cathode line scanning circuit

13

; an anode drive circuit

14

; and an anode line potential output circuit

15

.

As shown in

FIG. 8

, the luminescent display panel

11

comprises a plurality of EL elements E

I,j

(1≦i≦m, 1≦j≦n). As in the case of the EL elements shown in

FIGS. 4 through 6

, the plurality of EL elements are arranged in a matrix pattern at respective intersections between anode lines A

1

to A

m

serving as drive lines and cathode lines B

1

to B

n

serving as scanning lines. The EL elements are connected to the scanning lines and the drive lines. In other words, the EL elements are located at respective intersections between a plurality of drive lines extending substantially in parallel with each other and a plurality of scanning lines extending substantially at right angles to the drive lines. Each of the EL elements is connected to the scanning line and the drive line. The EL elements E

I,j

shown in

FIG. 8

are depicted by capacitor symbols.

In the luminescent display panel

11

, the cathode lines B

1

to B

n

are connected to the cathode line scanning circuit

13

, and the anode lines A

1

to A

m

are connected to the anode line drive circuit

14

. The cathode line scanning circuit

13

has scanning switches

16

1

to

16

n

assigned to the respective cathode lines B

1

to B

n

. Each of the scanning switches

16

1

to

16

n

supplies to a corresponding cathode line ground potential or a reverse bias voltage Vcc. Under control of the light-emission control section

12

, the scanning switches

16

1

to

16

n

are sequentially switched to ground potential every horizontal scanning period. Accordingly, the cathode lines B

1

to B

n

set to ground potential act as scanning lines which enable illumination of EL elements connected to the cathode lines B

1

to B

n

.

The anode line drive circuit

14

has current sources

17

1

to

17

m

and drive switches

18

1

to

18

m

. Each of the drive switches

18

1

to

18

m

corresponds to a changeover switch having two stationary contacts and a neutral position. An electric current is supplied from one of the current sources

17

1

to

17

m

to a corresponding anode line by way of one of the two stationary contacts. Further, a voltage Vcc is supplied by way of the remaining stationary contact. The voltage Vcc is supplied from an unillustrated voltage source.

The anode line potential output circuit

15

has potential application switches

19

1

to

19

m

and voltage sources

20

1

to

20

m

, which are provided so as to correspond to the respective anode lines A

1

to A

m

. A voltage V

L

develops between the positive and negative terminals of each of the voltage sources

20

1

to

20

m

. The voltage V

L

is lower than and close to a threshold illumination voltage V

th

. Switching operations of each of the potential application switches

19

1

to

19

m

are controlled by the light-emission control section

12

. When the potential application switches

19

1

to

19

m

are in an ON state, the positive terminals of the respective voltage sources

20

1

to

20

m

are connected to the anode lines A

1

to A

m

. The negative terminals of the voltage sources

20

1

to

20

m

are grounded.

The light-emission control section

12

controls the cathode line scanning circuit

13

, the anode line drive circuit

14

, and the anode line potential output circuit

15

so as to cause the luminescent display panel to display an image in accordance with a video signal supplied from an unillustrated video signal generation system. Such a control operation is performed while being divided into a reset period and a scanning period.

The light-emission control section

12

sends a scanning line selection control signal to the cathode line scanning circuit

13

during the scanning period. The scanning switches

16

1

to

16

n

are switched such that one from the cathode lines B

1

to B

n

corresponding to the horizontal scanning period of a video signal is selected and set to ground potential and such that a reverse bias voltage Vcc is applied to the remaining cathode lines. In order to prevent illumination of EL elements connected to the intersections between the anode lines to which the drive current is applied and the cathode lines which are not selected for scanning, which would otherwise be caused by crosstalk, a constant-voltage source (not shown) connected to the cathode lines supplies the reverse bias voltage Vcc. Since the scanning switches

16

1

to

16

n

are sequentially switched to ground potential during every horizontal scanning period, the cathode lines B

1

to B

n

set to ground potential act as scanning lines which enable illumination of the EL elements connected to the cathode lines B

1

to B

n

.

The light-emission control section

12

produces a drive control signal indicating that one among the EL elements connected to a scanning line is to be illuminated, at any timing and for any period of time, in accordance with pixel information represented by a video signal during a scanning period. The thus-produced drive control signal is delivered to the anode line drive circuit

14

. In response to the drive control signal, the anode line drive circuit

14

switches, to the current source side, the one among the drive switches

18

1

to

18

m

assigned to the anode line connected to the EL elements to be illuminated. By way of the corresponding one of the anode lines A

1

to A

m

, a drive current corresponding to the pixel information is supplied to the EL elements. The remaining drive switches

18

are switched to neutral positions. The anode line potential output circuit

15

turns off some of the potential application switches

20

1

to

20

m

corresponding to anode lines connected to EL elements to be illuminated, in accordance with the drive control signal. The remaining potential application switches are turned on, and the voltage V

L

is supplied to corresponding anode lines.

The light-emission control section

12

produces a reset signal during a reset period, and the thus-produced reset signal is delivered to the cathode line scanning circuit

13

, the anode line drive circuit

14

, and the anode line potential output circuit

15

. The cathode line scanning circuit

13

performs a control operation for switching the scanning switches

16

1

to

16

n

such that a reverse bias voltage Vcc is applied to all the cathode lines B

1

to B

n

in accordance with the reset signal. The anode line drive circuit

14

performs a control operation for switching the drive switches

18

1

to

18

n

such that a voltage Vcc is applied to the anode lines A

1

to A

n

in accordance with the reset signal. The anode line potential output circuit

15

turns off the potential application switches

20

1

to

20

m

in accordance with the reset signal.

The internal circuit of the light-emission control circuit

12

is configured as shown in FIG.

7

. As shown in

FIG. 7

, a synch separation circuit

41

extracts horizontal and vertical synch signals from a supplied input video signal. The thus-extracted horizontal and vertical synch signals are supplied to a timing pulse signal generation circuit

42

. On the basis of the thus-extracted horizontal and vertical synch signals, the timing pulse signal generation circuit

42

produces a synch signal timing pulse signal. The thus-produced synch signal timing pulse signal is supplied to an analog-to-digital converter

43

, a control circuit

45

, and a scan timing signal generation circuit

47

. The analog-to-digital converter

43

converts an input video signal into digital pixel data on a per-pixel basis, in synchronism with the synch signal timing pulse signal. The input video signal is supplied to the memory

44

. The control circuit

45

supplies a write signal and a read signal, which are synchronized with the synch signal timing pulse signal, to the memory

44

according to a drive method to be described later. In response to the write signal, the memory

44

sequentially captures the pixel data supplied from the analog-to-digital converter

43

. Further, in response to the read signal, the memory

44

sequentially reads pixel data stored therein and supplies the thus-read pixel data to an output processing circuit

46

provided in a subsequent stage. The scan timing signal generation circuit

47

produces various timing signals for controlling a scanning switch and a drive switch and delivers the thus-produced signals to the cathode line scanning circuit

13

and the output processing circuit

46

. As a result, the scan timing signal generation circuit

47

supplies a scan selection control signal to the cathode line scanning circuit

13

. In synchronism with a timing signal output from the scan timing signal generation circuit

47

, the output processing circuit

46

supplies, to the anode line drive circuit

14

and the anode line potential output circuit

15

, a drive control signal corresponding to the pixel data supplied from the memory

44

. During a reset period, the control circuit

45

supplies a reset signal to the anode line drive circuit

14

and the anode lines potential output circuit

15

by way of the output processing circuit

46

, as well as to the cathode line scanning circuit

13

by way of the scan timing signal generation circuit

47

.

The drive operation of the capacitive luminescent display panel performed by the control circuit

45

of the light-emission control section

12

will now be described by reference to a flowchart shown in FIG.

9

.

The control circuit

45

executes a light-emission control routine for every horizontal scanning period of the supplied pixel data. In the light-emission control routine, pixel data corresponding to a horizontal scanning period are acquired from RAM 44 (step S

1

). In accordance with pixel information represented by the pixel data corresponding to a horizontal scanning period, the scan selection control signal and the drive control signal are supplied (step S

2

).

The scan selection control signal is delivered to the cathode line scanning circuit

13

. The cathode line scanning circuit

13

switches, to ground, a scanning switch (a single scanning switch

16

s

in the range of

16

1

to

16

n

, where “S” designates a numeral in the range of 1 to “n”) assigned to one of the cathode lines B

1

to B

n

, which cathode line corresponds to the current horizontal scanning period represented by the scan selection control signal.

The drive control signal is supplied to the anode line drive circuit

14

and the anode line potential output circuit

15

. In the anode line drive circuit

14

, a drive switch (any one of the drive switches

18

1

to

18

m

) is switched to a second stationary contact connected to a current source (i.e., the corresponding one of the current sources

17

1

to

17

m

). Here, the drive switch is assigned to one of the anode lines A

1

to A

m

,_which anode line is connected to an EL element to be illuminated Luring the current horizontal scanning period represented by the drive control signal. Drive switches

18

assigned to the remaining anode lines A are switched to the first stationary contacts connected to voltage sources (corresponding ones of voltage sources

20

1

to

20

m

). The anode line potential output circuit

15

turns off some of the potential application switches (some of the application switches

19

1

to

19

m

) corresponding to anode lines connected to the EL elements to be illuminated, during the current horizontal scanning period represented by the drive control signal. The potential application switches corresponding to the remaining anode lines are turned on.

For example, in a case where the drive switch

18

1

is switched to a current source

17

1

, a drive current flows from the current source

17

1

to a drive switch

18

1

, the anode line A

1

, an EL element E

1,s

a cathode line B

s

, a scanning switch

16

s

, and ground. The EL element E

1,s

to which the drive current is supplied illuminates in accordance with the pixel data.

If the drive switch switched to the neutral position is assigned

18

3

, the potential application switch

19

3

is turned on. The voltage Vcc is applied to an anode line A

3

from a voltage source

20

3

by way of the potential application switch

19

3

. The voltage VCC-V

L

is applied to EL elements E

3,1

to E

3,n

exclusive of an EL element E

3,s

.

After having performed processing pertaining to step S

2

, the control circuit

45

determines whether or not a preset scanning period T has elapsed (step S

3

). The scanning period T is set in accordance with, for example, brightness information included in the pixel data and a preset horizontal scanning period. The scanning period is determined through use of an unillustrated internal counter.

The control circuit

45

produces a reset signal if the scanning period T has elapsed (step S

4

). The reset signal is delivered to the cathode line scanning circuit

13

, the anode line drive circuit

14

, and the anode line potential output circuit

15

. The cathode line scanning circuit

13

switches the movable contacts of all the scanning switches

16

1

to

16

n

in accordance with the reset signal. The anode line drive circuit

14

switches the movable contacts of all the drive switches

18

1

to

18

n

to the stationary contacts of Vcc in accordance with the reset signal. The anode line potential output circuit

15

turns off the potential application switches

20

1

to

20

m

, in accordance with the reset signal. As a result, a voltage Vcc develops between the terminal of each of the EL elements i,j, and the electric charge stored in the EL elements is discharged.

The reset period may be constant or may change in accordance with the scanning period T.

After having performed processing pertaining to step S

5

, the control circuit

45

terminates the light-emission control routine and Enters a standby state until the next horizontal scanning period begins. Even during a period in which the control circuit

45

awaits the beginning of the next horizontal scanning period, processing pertaining to steps S

1

to S

4

is repeated.

FIG. 10

shows the relationship between the scanning period and the scanning period of the light-emission drive operation.

By reference to

FIGS. 11 through 13

, next will be described a case where, after a cathode line B

1

has been scanned by means of the control operation of the control circuit

45

, to thereby cause elements E

1.1

and E

2.1

to illuminate, a cathode line B

2

is scanned, to thereby cause elements E

2.2

and E

3.2

to illuminate. In order to facilitate explanations, illuminating EL elements shown in

FIGS. 11 through 13

are depicted by diode symbols, and nonilluminating EL elements are depicted by capacitor symbols.

In connection with

FIG. 11

, only a scanning switch

16

1

is switched to a ground potential of 0 volt, thereby scanning a cathode line B

1

. A reverse bias voltage Vcc is applied to the remaining cathode lines B

2

to B

n

by way of corresponding scanning switches

16

2

to

16

n

. Simultaneously, the anode line A

1

is connected to the current source

17

1

by way of the drive switch

18

1

, and the anode line A

2

is connected to the current source

17

2

by way of the drive switch

18

2

. The drive switches

18

3

to

18

m

are placed in neutral positions. The voltage V

L

is applied to the remaining anode lines A

3

to A

m

by way of the potential application switches

19

3

to

19

m

. In the circuit configuration shown in

FIG. 11

, only the EL elements E

1,1

and E

2,1

are forwardly biased, and a drive current flows into the EL elements E

1,1

and E

2,1

from the current sources

17

1

and

17

2

, as designated by arrows. As a result, only the elements E

1,1

and E

2,1

are illuminated. In an illuminated state, a reverse bias voltage Vcc-V

L

is applied between the anode and cathode electrodes of each of nonilluminating and hatched EL elements E

3,2

to E

m,n

. The EL elements E

3,2

to E

m,n

are charged with illustrated polarities, respectively. Since the voltage Vcc-V

L

is sufficiently low, the electric charges stored in the EL element are smaller than those charged in an EL element of a known flat display panel. Although the voltage V

L

is forwardly applied between the anode and cathode electrodes of each of the hatched and nonilluminating EL elements E

3.1

to E

m.i

, the voltage V

L

is lower than the illumination threshold voltage V

th

, and hence the EL elements E

3.1

to E

m.i

remain unilluminated and are charged solely.

If the illuminated state of the EL elements shown in

FIG. 11

have been effected for only the scanning period T, a reset control operation is performed before there is effected the next scanning operation for causing the EL elements E

2,2

and E

3,2

to illuminate. As shown in

FIG. 12

, all the drive switches

18

1

to

18

3

and all the scanning switches

16

1

to

16

n

are switched to the potential Vcc. Since all the potential application switches

19

1

to

19

m

are turned off, the positive lines A

1

to A

3

and the negative lines B

1

to B

n

are made equal to the potential Vcc. Through such a reset control operation, all the anode and cathode lines are made equal to the potential Vcc. The electric charge stored in the EL elements are discharged by way of the path such as that designated by an arrow, whereby the electric charge stored in all the EL elements disappears immediately.

When the next horizontal scanning period beings after the electric charges stored in the EL elements have been discharged to zero, only a scanning switch

16

2

corresponding to a cathode line B

2

is switched to 0 voltage, thus scanning the cathode line B

2

. Simultaneously, the drive switches

18

2

and

18

3

are switched to the current sources

17

2

and

17

3

, and the output terminals of the current sources are connected to the corresponding anode lines. Further, the remaining drive switches

18

1

and

18

4

to

18

m

are switched to neutral positions. The potential application switches

19

1

to

19

4

to

19

m

are turned, to thereby impart the potential V

L

to the anode lines A

1

and A

4

to A

m

. In connection with the circuit configuration shown in

FIG. 13

, only the EL elements E

2,2

and E

3,2

are forwardly biased, so that a drive current flows from current sources

17

2

and

17

3

to the EL elements E

2,2

and E

3,2

thereby causing only the elements E

2,2

and E

3,2

to illuminate. In such an illuminated state, the reverse bias voltage VCC-V

L

is applied, in a reversely-biased manner, between the anode and cathode electrodes of each of hatched and nonilluminating EL elements E

1,1

, E

1,3

to E

1,n

, E

4,1

to E

m,1

, and E

4,3

to E

m,n

. The EL elements are charged with polarities, as illustrated. Since the voltage VCC-V

L

is sufficiently low, the electric charge stored in the EL elements is smaller than that stored in EL elements of a known display. Although the voltage VCC-V

L

is forwardly applied between the anode and cathode electrodes of each of hatched and nonilluminating EL elements E

1,1

and E

4,1

to E

m,1

. Since the voltage V

L

is lower than the illumination threshold voltage V

th

, the EL elements E

1,2

and E

4,2

to E

m,2

remain unilluminated and are charged only.

As mentioned above, the reverse bias voltage VCC-V

L

applied to the nonilluminating EL elements during the scanning period is lower than that employed in the known display panel.

In the previous embodiment, the first potential is made equal to ground potential, and the second and fourth potentials are set to a potential Vcc which is substantially equal to the specified illumination voltage Ve of a capacitive luminescent element. However, the present invention is not limited to such an embodiment.

Although in the previous embodiment the anode line drive circuit

14

and the anode line potential output circuit

15

are formed separately, there may be formed the anode line drive circuit

14

including the configuration of the anode line potential output circuit

15

without formation thereof.

In the previous embodiment the reset period is set so as to follow the scanning period during the light-emission control operation. However, the reset period may be set such that the scanning period follows the reset period.

The present invention also provides a luminescent display panel-drive unit including

a plurality of drive lines and a plurality of scanning lines, which intersect each other; and

a plurality of capacitive luminescent elements which are provided in respective intersections between the drive lines and the scanning lines and connected to the scanning lines and drive lines and which have polarities, the drive unit comprising:

control means for setting a scanning period during which a single scanning line is selected from the plurality of scanning lines in accordance with a scan timing of an input video signal, for specifying a light-emission drive line assigned to the capacitive luminescent element which is connected to the single scanning line and is to be illuminated in accordance with the input video signal during the scanning period, for setting a reset period during an interval between scanning periods, and for specifying, as a non-reset drive line, only the drive line having connected to the capacitive luminescent element to remain unilluminated during the scanning period subsequent to the reset period;

scanning means for applying a first potential lower than an illumination threshold voltage of the capacitive luminescent element to the single scanning line during the scanning period, for applying a second potential higher than the illumination threshold voltage to scanning lines other than the single scanning line, and for applying the second potential to all the scanning lines during the reset period; and

drive means for supplying a drive current to the illumination drive line for forwardly applying, during the scanning period, a positive voltage higher than the illumination threshold voltage to the capacitive luminescent element to be illuminated, for applying a third potential slightly lower than the illumination threshold voltage to the drive lines other than the illumination drive line, for supplying during the reset period a fourth potential equal to the second potential to the plurality of drive lines exclusive of the non-reset drive line, and for applying the third potential to the non-reset drive line.

According to the present invention, a first potential lower than an illumination threshold voltage is applied to a single scanning line selected for scanning, during a scanning period. A second potential higher than the illumination threshold voltage is applied to the scanning lines other than the single scanning line. A fourth potential slightly lower than the illumination threshold voltage is applied to the plurality of drive lines other than an illumination drive line connected to capacitive luminescent elements to be illuminated. Consequently, a comparatively-low reverse bias voltage is applied to respective capacitive luminescent elements located in intersections between scanning lines except the single scanning line and drive lines except the illumination drive line. Electric charges which are stored in the luminescent elements with the reverse bias voltage and which do not contribute to illumination are diminished as compared with those charged in luminescent elements in a known display panel, thus reducing useless power dissipation.

Further, during the reset period, there is specified as a non-reset drive line only the drive line connected to the capacitive luminescent element which is to remain unilluminated during a scanning period subsequent to the reset period, and the second potential is applied to all the scanning lines. Moreover, a fourth potential equal to the second potential is applied to the plurality of drive lines exclusive of the non-reset drive line. As a result, the electric charges—which are stored in the capacitive luminescent elements connected to non-reset drive line by means of the reverse bias voltage—are held during the current reset period without being discharged. Even when the reverse bias voltage is applied to the capacitive luminescent elements during the next scanning period, charging or discharging barely arises in the luminescent elements, thereby reducing useless power dissipation.

Further, an embodiment of the present invention will be described hereinbelow in detail by reference to the accompanying drawings.

FIG. 14

schematically shows the configuration of a display which is embodied by application of the present invention to A luminescent display panel using EL elements as capacitive luminescent elements. The display comprises a capacitive luminescent display panel

211

; a light-emission control section

212

; a cathode line scanning circuit

213

; and an anode drive circuit

214

.

As shown in

FIG. 15

, the luminescent display panel

211

comprises a plurality of EL elements E

I,j

(1≦i≦m, 1≦j≦n). As in the case of the EL elements shown in

FIGS. 4 through 6

, the plurality of EL elements are arranged in a matrix pattern at respective intersections between anode lines A

1

to A

m

serving as drive lines and cathode lines B

1

to B

n

serving as scanning lines. The EL elements are connected to the scanning lines and the drive lines. In other words, the EL elements are located at respective intersections between a plurality of drive lines extending substantially in parallel with each other and a plurality of scanning lines extending substantially at right angles to the drive lines. Each of the EL elements is connected to the scanning line and the drive line. The EL elements E

I,j

shown in

FIG. 15

are depicted by capacitor symbols.

In the luminescent display panel

211

, the cathode lines B

1

to B

n

are connected to the cathode line scanning circuit

213

, and the anode lines A

1

to A

m

are connected to the anode line drive circuit.

214

. The cathode line scanning circuit

213

has scanning switches

216

1

to

216

n

assigned to the respective cathode lines B

1

to B

n

. Each of the scanning switches

216

1

to

216

n

supplies to a corresponding cathode line ground potential or a reverse bias voltage Vcc. Under control of the light-emission control section

212

, the scanning switches

216

1

to

216

n

are sequentially switched to ground potential every horizontal scanning period. Accordingly, the cathode lines B

1

to B

n

set to ground potential act as scanning lines which enable illumination of EL elements connected to the cathode lines B

1

to B

n

.

The anode line drive circuit

214

has current sources

217

1

to

217

m

, drive switches

218

1

to

218

m

, and voltage sources

220

1

to

220

m

, which are provided so as to correspond to the anode lines A

1

to A

m

. A voltage V

L

develops between the positive and negative terminals of each of the voltage sources

220

1

to

220

m

. The voltage V

L

is lower than and close to the threshold illumination voltage V

th

. Each of the drive switches

218

1

to

218

m

corresponds to a changeover switch having three stationary contacts. A moving contact of each of the drive switches

218

1

to

218

m

is connected to a corresponding one of the anode lines A

1

to A

m

. A first stationary contact of each of the drive switches

218

1

to

218

m

is connected to a positive terminal of a corresponding one of the voltage sources

220

1

to

220

m

. A second stationary contact of each of the drive switches

218

1

to

218

m

is connected to an output terminal of a corresponding one of the current sources

217

1

to

217

m

. Further, a voltage Vcc is applied to the third stationary contact of each of the drive switches

218

1

to

218

m

. The negative terminal of each of the voltage sources

220

1

to

220

m

is connected to ground. Moreover, the voltage Vcc is output from an unillustrated voltage source.

The light-emission control section

212

controls the cathode line scanning circuit

213

and the anode line drive circuit

214

, so as to cause the luminescent display panel

211

to display an image in accordance with a video signal supplied from an unillustrated video signal generation system. Such a control operation is performed while being divided into a reset period and a scanning period.

The light-emission control section

212

produces a reset signal during a reset period, and the thus-produced reset signal is delivered to the cathode line scanning circuit

213

and the anode line drive circuit

214

. The cathode line scanning circuit

213

performs a control operation for switching the scanning switches

216

1

to

216

n

such that a reverse bias voltage Vcc is applied to all the cathode lines B

1

to B

n

in accordance with the reset signal. The anode line drive circuit

214

performs a control operation for switching the drive switches

218

1

to

218

n

such that a voltage Vcc is applied to the anode lines A

1

to A

n

in accordance with the reset signal. As will be described later, the drive switches

218

1

to

218

m

are controlled such that a voltage V

L

is applied to the anode lines not connected to the EL elements which have been illuminated during the previous scanning period or which are to illuminate during the current scanning period (i.e., non-reset drive lines).

The light-emission control section

212

sends a scanning line selection control signal to the cathode line scanning circuit

213

during the scanning period. The scanning switches

216

1

to

216

n

are switched such that any one of the cathode lines B

1

to B

n

corresponding to the horizontal scanning period of a video signal is selected and set to ground potential and such that a reverse bias voltage Vcc is applied to the remaining cathode lines. In order to prevent illumination of EL elements connected to the intersections between the anode lines to which the drive current is applied and the cathode lines which are not selected for scanning, which would otherwise be caused by crosstalk, a constant-voltage source (not shown) connected to the cathode lines supplies the reverse bias voltage Vcc. Since the scanning switches

216

1

to

216

n

are sequentially switched to ground potential during every horizontal scanning period, the cathode lines B

1

to B

n

set to ground potential act as scanning lines which enable illumination of the EL elements connected to the cathode lines B

1

to B

n

.

The light-emission control section

212

produces a drive control signal indicating that one among the EL elements connected to a scanning line is to be illuminated, at any timing and for any period of time, in accordance with pixel information represented by a video signal during a scanning period. The thus-produced drive control signal is delivered to the anode line drive circuit

214

. In response to the drive control signal, the anode lines drive circuit

214

switches, to the current source side, the ones among the drive switches

218

1

to

218

m

assigned to the anode line connected to the EL elements to be illuminated. By way of the corresponding one of the anode lines A

1

to A

m

, a drive current corresponding to the pixel information is supplied to the EL elements. The remaining drive switches

18

are switched to the first stationary contacts, and the voltage V

L

is supplied to the drive switches from the voltage sources

220

1

to

220

m

.

The internal circuit of the light-emission control circuit

212

is configured as shown in FIG.

14

. As shown in

FIG. 14

, a such separation circuit

241

extracts horizontal and vertical synch signals from a supplied input video signal. The thus-extracted horizontal and vertical synch signals are supplied to a timing pulse signal generation circuit

242

. On the basis of the thus-extracted horizontal and vertical synch signals, the timing pulse signal generation circuit

242

produces a synch signal timing pulse signal. The thus-produced synch signal timing pulse signal is supplied to an analog-to-digital converter

243

, a control circuit

245

, and a scan timing signal generation circuit

247

. The analog-to-digital converter

243

converts an input video signal into digital pixel data on a per-pixel basis, in synchronism with the synch signal timing pulse signal. The input video signal is supplied to the memory

244

. The control circuit

245

supplies a write signal and a read signal, which are synchronized with the synch signal timing pulse signal, to the memory

244

according to a drive method to be described later. In response to the write signal, the memory

244

sequentially captures the pixel data supplied from the analog-to-digital converter

243

. Further, in response to the read signal, the memory

244

sequentially reads pixel data stored therein and supplies the thus-read pixel data to an output processing circuit

246

provided in a subsequent stage. The scan timing signal generation circuit

247

produces various timing signals for controlling a scanning switch and a drive switch and delivers the thus-produced signals to the cathode line scanning circuit

213

and the output processing circuit

246

. As a result, the scan timing signal generation circuit

247

supplies a scan selection control signal to the cathode line scanning circuit

213

. In synchronism with a timing signal output from the scan timing signal generation circuit

247

, the output processing circuit

246

supplies, to the anode line drive circuit

214

, a drive control signal corresponding to the pixel data supplied from the memory

244

. During a reset period, the control circuit

245

supplies a reset signal to the anode line drive circuit

214

by way of the output processing circuit

246

, as well as to the cathode line scanning circuit

213

by way of the scan timing signal generation circuit

247

.

The drive operation of the capacitive luminescent display panel performed by the control circuit

245

of the light-emission control section

212

will now be described by reference to a flowchart shown in FIG.

16

.

The control circuit

245

executes a light-emission control routine for every horizontal scanning period of the supplied pixel data. In the light-emission control routine, pixel data corresponding to a horizontal scanning period are acquired (step S

201

). A determination is made as to whether or not an anode line (non-reset drive line) to which the voltage V

L

has been applied during the previous scanning period is included in the anode lines to which the voltage V

L

is to be applied during a current scanning period in accordance with the pixel data (step S

202

). When the voltage V

L

has been applied to an anode line during the previous scanning period and is to be applied to the anode line during the current scanning period, all the EL elements connected to the anode line remain extinct during both the previous and current scanning periods. In connection with the determination, a determination may be made as to whether or not a drive switch which have been switched to the first stationary contact during the previous scanning period is included in the drive switches to be switched to the first stationary contact during the current scanning period.

If there is no anode line to which the voltage V

L

has been applied during either the previous scanning period and is to be applied during current scanning period, there is issued a reset signal for applying a voltage Vcc to all the positive lines A

1

to A

m

and all the cathode lines B

1

to B

n

(step S

203

). In contrast, if there is an anode line to which the voltage V

L

has been applied during the previous scanning period and is to be applied during the current scanning period, there is produced a reset signal for releasing the anode line, for applying the voltage V

L

to the anode line, and for applying the voltage Vcc to the remaining positive lines and all the cathode lines B

1

to B

n

(step S

204

). The reset signal is supplied to the cathode line scanning circuit

213

and the anode line drive circuit

214

.

In the case of the reset signal produced in step S

203

, the cathode line scanning circuit

213

switches movable contacts of all the scanning switches

216

1

to

216

n

to the stationary points of voltage Vcc in accordance with the reset signal. In accordance with the reset signal, the anode line drive circuit

214

switches the movable contacts of all the drive switches

218

1

to

218

n

to the third stationary contacts of voltage Vcc. As a result, the voltage developing across each EL element E

I,j

becomes equal to the voltage Vcc, thereby discharging the electric charges stored in the EL elements.

In the case of the reset signal produced in step S

204

, the cathode line scanning circuit

213

switches the movable contacts of all the scanning switches

216

1

to

216

n

to the stationary contacts of voltage Vcc in accordance with the reset signal. In the anode line drive circuit

214

, drive switches corresponding to the anode lines—to which the voltage V

L

has been applied during the previous scanning period and is to be applied during the current scanning period—are switched to the fourth stationary contact. The drive switches corresponding to the remaining anode lines are switched to third stationary contacts of voltage Vcc. Provided that there is an anode line A

k

(“k” corresponds to at least one numeral in the range of 1 through “mm”) to which the voltage V

L

has been applied during the previous scanning period and to which the voltage V

L

is to be applied during the current scanning period, a voltage developing across EL elements E

I,j

excluding the EL element E

k,j

becomes equal to the voltage Vcc. The electric charges stored in the EL elements are discharged. A voltage Vcc-V

L

is applied between the terminals of each of the EL element E

k.j

connected to the anode line A

k

in a reversely-biased manner.

The reset period may be constant or may vary in length in accordance with a scanning period T.

The control circuit

245

produces a scan selection control signal and a drive control signal in accordance with pixel information represented by the pixel data, which data have been captured in step S

201

and correspond to a single horizontal scanning period (step S

205

).

The scan selection control signal is delivered to the cathode line scanning circuit

213

. The cathode line scanning circuit

213

switches, to ground, a scanning switch (a single scanning switch

216

S

in the range of

216

1

to

216

n

, where “S” designates a numeral in the range of 1 to “n”) assigned to one of the cathode lines B

1

to B

n

, which cathode line corresponds to the current horizontal scanning period represented by the scan selection control signal.

The drive control signal is supplied to the anode line drive circuit

214

. In the anode line drive circuit

214

, a drive switch (any one of the drive switches

218

1

to

218

m

) is switched to a second stationary contact connected to a current source (i.e., the corresponding one of the current sources

217

1

to

217

m

). Here, the drive switch is assigned to one of the anode lines A

1

to A

m

, which anode line is connected to an EL element to be illuminated during the current horizontal scanning period represented by the drive control signal. Drive switches

218

assigned to the remaining anode lines A are switched to the first stationary contacts connected to voltage sources (corresponding ones of voltage sources

220

1

to

220

m

).

For example, in a case where the drive switch

218

1

is switched to a current source

217

1

, a drive current flows from the current source

217

1

to a drive switch

218

1

, the anode line A

1

, an EL element E

1,s

, a cathode line B

s

, a scanning switch

216

S

, and ground. The EL element E

1,s

to which the drive current is supplied illuminates in accordance with the pixel data.

If the drive switch switched to the first contact is assigned

218

3

, the voltage V

L

is applied to an anode line A

3

from a voltage source

220

3

by way of a drive switch. The voltage Vcc-V

L

is applied to EL elements E

3,1

to E

3,n

exclusive of an EL element E

3,s

in a reversely-biased manner. The voltage V

L

lower than the illumination threshold voltage V

th

is forwardly applied to the EL element E

3,s

, wherewith the EL elements E

3,1

, to E

3,n

are charged with an applied voltage.

After having performed processing pertaining to step S

205

, the control circuit

245

determines whether or not a preset scanning period T has elapsed (step S

206

). The scanning period T is set in accordance with, for example, brightness information included in the pixel data and a preset horizontal scanning period. The scanning period is determined through use of an unillustrated internal counter.

If the scanning period T has elapsed, processing proceeds to step S

207

, where the control circuit

245

produces a drive stop signal, to thereby terminate the light-emission control routine. The control circuit

245

enters a stand-by state until the next horizontal scanning period begins. When the next horizontal scanning period begins, processing pertaining to steps S

201

to S

207

is repeated.

FIG. 10

shows the relationship between a reset period and a scanning period T, which are required for the foregoing illumination and drive operations. The scanning period T shown in

FIG. 10

designates a period starting from the end of the reset period to the start of the next horizontal scanning period. As mentioned above, if the scanning period T continues to the start of the next horizontal scanning period, steps S

206

and S

207

may be omitted.

By reference to

FIGS. 17 through 19

, next will be described a case where, after a cathode line B

1

has been scanned by means of the control operation of the control circuit

245

, to thereby cause elements E

1.1

and E

2.1

to illuminate, a cathode line B

2

is scanned, to thereby cause elements E

2.2

and E

3.2

to illuminate. In order to facilitate explanations, illuminating EL elements shown in

FIGS. 17 through 19

are depicted by diode symbols, and nonilluminating EL elements are depicted by capacitor symbols.

In connection with

FIG. 17

, only a scanning switch

216

1

is switched to a ground potential of 0 volt, thereby scanning a cathode line B

1

. A reverse bias voltage Vcc is applied to the remaining cathode lines B

2

to B

n

by way of corresponding scanning switches

216

2

to

216

n

. Simultaneously, the anode line A

1

is connected to the current source

217

1

by way of the drive switch

218

1

, and the anode line A

2

is connected to the current source

217

2

by way of the drive switch

218

2

. The voltage V

L

is applied to the remaining anode lines A

3

to A

m

by way of the drive switches

218

3

to

218

m

. In the circuit configuration shown in

FIG. 17

, only the EL elements E

1,1

and E

2,1

are forwardly biased, and a drive current flows into the EL elements E

1,1

, and E

2,1

from the current sources

217

1

and

217

2

, as designated by arrows. As a result, only the elements E

1,1

, and E

2,1

are illuminated. In an illuminated state, a reverse bias voltage Vcc-V

L

is applied between the anode and cathode electrodes of each of nonilluminating and hatched EL elements E

3,2

to E

m,n

. The EL elements E

3,2

lo E

m,n

are charged with illustrated polarities, respectively. Since the voltage VCC-V

L

is sufficiently low, the electric charges stored in the EL element are smaller than those charged in an EL element of a known flat display panel. Although the voltage V

L

is forwardly applied between the anode and cathode electrodes of each of the hatched and nonilluminating EL elements E

3.1

to E

m.i

, the voltage V

L

is lower than the illumination threshold voltage V

th

, and hence the EL elements E

3.1

to E

m.i

remain unilluminated and are charged solely.

If the illuminated state of the EL elements shown in

FIG. 17

have been effected for only the scanning period T, a reset control operation is performed before illumination of the EL elements E

2,2

and E

3,2

during the next horizontal scanning period. As shown in

FIG. 18

, the drive switches

218

1

to

218

3

and all the scanning switches

216

1

to

216

n

are switched to the potential Vcc. Accordingly, the positive lines A

1

to A

3

and the negative lines B

1

to B

n

are made equal to the potential Vcc. Through such a reset control operation, the electric charges stored in the respective EL elements E

1,1

to E

3,n

are discharged by way of the path designated by arrows in the drawing, wherewith the electric charges stored in all the EL elements become momentarily zero. Even during the current scanning period, no drive current for illumination purpose is supplied to the anode lines A

4

to A

m

. Hence, the anode lines A

4

to A

m

are released by way of drive switches

218

4

to

218

m

. Accordingly, the voltage Vcc is applied to the cathode of each of the EL elements E

4,1

to E

m,n

. The anodes of the EL elements A

4,1

to E

m,n

are commonly connected to respective anode lines A

4

to A

m

. Therefore, there is discharged the electric charge that has been stored in the EL elements E

4,1

to E

m,1

as a result of forward application of the voltage V

L

during the scanning period shown in FIG.

17

. An electric current further flows into and are charged into the EL elements E

4,3

to E

m,1

. The electric charge that has been stored during the scanning period shown in

FIG. 17

are held in the EL elements E

4,2

to E

m,n

exclusive of the EL elements E

4,1

to E

m,1

. Consequently, the EL elements E

4,1

to E

m,1

are equally charged with the polarities such as those shown in FIG.

18

.

When the next horizontal scanning period beings after the electric charges stored in the EL elements E

1,1

to E

3,n

have been discharged to zero, only a scanning switch

216

2

corresponding to a cathode line B

2

is switched to 0 volt, thus scanning the cathode line B

2

. Simultaneously, the drive switches

218

2

and

218

3

are switched to the current sources

217

2

and

2

17

3

, and the output terminals of the current sources

217

2

and

217

3

are connected to the corresponding anode lines A

2

and A

3

. The remaining drive switches

218

1

and

218

4

to

218

m

are switched to the first stationary contact of potential V

L

, and the voltage V

L

is supplied to the anode lines A

1

and A

4

through A

m

. In connection with the circuit configuration shown in

FIG. 19

, only the EL elements E

2,2

and E

3,2

are forwardly biased, so that a drive current flows from current sources

217

2

and

217

3

to the EL elements E

2,2

and E

3,2

, thereby causing only the elements E

2,2

and E

3,2

to illuminate. In such an illuminated state, the reverse bias voltage VCC-V

L

is applied across the anode and cathode electrodes of each of hatched and nonilluminating EL elements E

1,1

, E

1,3

to E

1,n

, E

4,1

to E

m,1

, and E

4,3

to E

m,n

. The EL elements E

1,1

, and E

1,3

to E

1,n

are newly charged with polarities, as illustrated. Since the electric charges are held in the EL elements E

4,3

to E

m,n

, the electric charge are continuously sustained without application of a voltage VCC-V

L

even when the voltage VCC-V

L

is applied to the EL elements E

4,3

to E

m,n

.

As mentioned above, the reverse bias voltage VCC-V

L

applied to the nonilluminating EL elements during the scanning period is lower than that employed in the known display panel. The electric charges which are charged by the reverse bias voltage VCC-V

L

and do not contribute to illumination are diminished as compared with those which arise in the conventional display panel. In connection with anode lines (non-reset drive lines) to which the voltage V

L

has been applied during the previous scanning period and the voltage V

L

is to be applied during the current scanning period, none of the EL elements are connected to the non-reset drive line illuminate during the previous and current scanning periods. The electric charges charged with the reverse bias voltage VCC-V

L

are held without being discharged during the current reset period. Therefore, in the foregoing example, the total of electric charge charged with the reverse bias voltage Vcc-V

L

during the current scanning period can be diminished by the amount of electric charge corresponding to that stored in the EL elements E

4,3

to E

m,n

.

In the previous embodiment, the first potential is made equal to ground potential, and the second and fourth potentials are set to a potential Vcc which is substantially equal to the specified illumination voltage Ve of a capacitive luminescent element. However, the present invention is not limited to such an embodiment.

Of the anode lines to which the voltage V

L

is to be applied during a single horizontal scanning period (i.e., a current scanning period), the anode line to which the voltage V

L

has been applied during the previous scanning period is specified as a non-reset drive line by the light-emission control routine in the previous embodiment. Alternatively, the anode lines to which the voltage V

L

is to be applied during a single horizontal scanning period may be specified as non-reset drive lines. In such a case, in step S

202

a determination may be made as to whether or not there is an anode line to which the voltage V

L

is to be applied during the current scanning period.

Further, an embodiment of the present invention will be described hereinbelow in detail by reference to the accompanying drawings.

FIG. 7

schematically shows the configuration of a display which is embodied by application of the present invention to a luminescent display panel using EL elements as capacitive luminescent elements. The display comprises a capacitive luminescent display panel

311

; a light-emission control section

312

; a cathode line scanning circuit

313

; and an anode drive circuit

314

.

As shown in

FIG. 20

, the luminescent display panel

311

comprises a plurality of EL elements E

I,j

(1≦i≦m, 1≦j≦n). As in the case of the EL elements shown in

FIGS. 4 through 6

, the plurality of EL elements are arranged in a matrix pattern at respective intersections between anode lines A

1

to A

n

serving as drive lines and cathode lines B

1

to B

n

serving as scanning lines. The EL elements are connected to the scanning lines and the drive lines. In other words, the EL elements are located at respective intersections between a plurality of drive lines extending substantially in parallel with each other and a plurality of scanning lines extending substantially at right angles to the drive lines. Each of the EL elements is connected to the scanning line and the drive line. The EL elements E

I,j

. Shown in

FIG. 20

are depicted by capacitor symbols.

In the luminescent display panel

311

, the cathode lines B

1

to B

n

are connected to the cathode line scanning circuit

313

, and the anode lines A

1

to A

1

are connected to the anode line drive circuit

314

. The cathode line scanning circuit

313

has scanning switches

316

1

to

316

1

assigned to the respective cathode lines B

1

to B

n

. Each of the scanning switches

316

1

to

316

n

suppliers to a corresponding cathode line ground potential or a reverse bias voltage Vcc. Under control of the light-emission control section

312

, the scanning switches

316

1

to

316

1

are sequentially switched to ground potential every horizontal scanning period. Accordingly, the cathode lines B

1

to B

n

set to ground potential act as scanning lines which enable illumination of EL elements connected to the cathode lines B

n

to Br, The anode line drive circuit

314

has current sources

317

1

to

317

w, drive switches

318

1

to

318

m

, and voltage sources

320

1

to

320

, which are provided so as to correspond to the anode lines A

1

to A

m

. A voltage V

L

develops between the positive and negative terminals of each of the voltage sources

320

1

to

320

m

The voltage V

L

is lower than and close to the threshold illumination voltage V

th

. Each of the drive switches

318

1

to

318

m

corresponds to a changeover switch having three stationary contacts. A moving contact of each of the drive switches

318

1

to

318

is connected to a corresponding one of the anode lines A

1

to PA. A first stationary contact of each of the drive switches

318

, to

318

m

is connected to a positive terminal of a corresponding one of the voltage sources

320

1

to

320

m

. A second stationary contact of each of the drive switches

318

1

to

318

m

is connected to an output terminal of a corresponding one of the current sources

317

1

to

317

m

Further, a voltage Vcc is applied to the third stationary contact of each of the drive switches

318

1

to

318

m

. The negative terminal of each of the voltage sources

320

1

to

320

m

is connected to ground. Moreover, the voltage Vcc is output from an unillustrated voltage source.

The light-emission control section

312

controls the cathode line scanning circuit

313

and the anode line drive circuit

314

, so as to cause the luminescent display panel

311

to display an image in accordance with a video signal supplied from an unillustrated video signal generation system. Such a control operation is performed while being divided into a reset period and a scanning period.

The light-emission control section

312

produces a reset signal during a reset period, and the thus-produced reset signal is delivered to the cathode line scanning circuit

313

and the anode line drive circuit

314

. The cathode line scanning circuit

313

performs a control operation for switching the scanning switches

316

1

to

316

n

such that a reverse bias voltage Vcc is applied to all the cathode lines B

1

to B

n

in accordance with the reset signal. The anode line drive circuit

314

performs a control operation for switching the drive switches

318

1

to

318

n

such that a voltage Vcc is applied to the anode lines A

1

to A

n

in accordance with the reset signal. As will be described later, the drive switches

318

1

to

318

m

are controlled such that a voltage V

L

is applied to the anode lines not connected to the EL elements which have been illuminated during the previous scanning period or which are to illuminate during the current scanning period (i.e., non-reset drive lines).

The light-emission control section

312

sends a scanning line selection control signal to the cathode line scanning circuit

313

during the scanning period. The scanning switches

316

1

to

316

n

are switched such that any one of the cathode lines B

1

to B

n

corresponding to the horizontal scanning period of a video signal is selected and set to ground potential and such that a reverse bias voltage Vcc is applied to the remaining cathode lines. In order to prevent illumination of EL elements connected to the intersections between the anode lines to which the drive current is applied and the cathode lines which are not selected for scanning, which would otherwise be caused by crosstalk, a constant-voltage source (not shown) connected to the cathode lines supplies the reverse bias voltage Vcc. Since the scanning switches

316

1

to

316

n

are sequentially switched to ground potential during every horizontal scanning period, the cathode lines B

1

to B

n

set to ground potential act as scanning lines which enable illumination of the EL elements connected to the cathode lines B

1

to B

n

.

The light-emission control section

312

produces a drive control signal indicating that one among the EL elements connected to a scanning line is to be illuminated, at any timing and for any period of time, in accordance with pixel information represented by a video signal during a scanning period. The thus-produced drive control signal is delivered to the anode line drive circuit

314

. In response to the drive control signal, the anode line drive circuit

314

switches, to the current source side, the one among the drive switches

318

1

to

318

m

assigned to the anode line connected to the EL elements to be illuminated. By way of the corresponding one of the anode lines A

1

to A

m

, a drive current corresponding to the pixel information is supplied to the EL elements. The remaining drive switches

318

are switched to the first stationary contacts, and the voltage V

L

is supplied to the drive switches from the voltage sources

320

1

to

320

m

.

The internal circuit of the light-emission control circuit

312

is configured as shown in FIG.

7

. As shown in

FIG. 7

, a synch separation circuit

341

extracts horizontal and vertical synch signals from a supplied input video signal. The thus-extracted horizontal and vertical synch signals are supplied to a timing pulse signal generation circuit

342

. On the basis of the thus-extracted horizontal and vertical synch signals, the timing pulse signal generation circuit

342

produces a synch signal timing pulse signal. The thus-produced synch signal timing pulse signal is supplied to an analog-to-digital converter

343

, a control circuit

345

, and a scan timing signal generation circuit

347

. The analog-to-digital converter

343

converts an input video signal into digital pixel data on a per-pixel basis, in synchronism with the synch signal timing pulse signal. The input video signal is supplied to the memory

344

. The control circuit

345

supplies a write signal and a read signal, which are synchronized with the synch signal timing pulse signal, to the memory

344

according to a drive method to be described later. In response to the write signal, the memory

344

sequentially captures the pixel data supplied from the analog-to-digital converter

343

. Further, in response to the read signal, the memory

344

sequentially reads pixel data stored therein and supplies the thus-read pixel data to an output processing circuit

346

provided in a subsequent stage. The scan timing signal generation circuit

347

produces various timing signals for controlling a scanning switch and a drive switch and delivers the thus-produced signals to the cathode line scanning circuit

313

and the output processing circuit

346

. As a result, the scan timing signal generation circuit

347

supplies a scan selection control signal to the cathode line scanning circuit

313

. In synchronism with a timing signal output from the scan timing signal generation circuit

347

, the output processing circuit

346

supplies, to the anode line drive circuit

314

, a drive control signal corresponding to the pixel data supplied from the memory

344

. During a reset period, the control circuit

345

supplies a reset signal to the anode line drive circuit

314

by way of the output processing circuit

346

, as well as to the cathode line scanning circuit

313

by way of the scan timing signal generation circuit

347

.

The drive operation of the capacitive luminescent display panel performed by the control circuit

345

of the light-emission control section

312

will now be described by reference to a flowchart shown in FIG.

21

.

The control circuit

345

executes a light-emission control routine for every horizontal scanning period of the supplied pixel data. In the light-emission control routine, pixel data corresponding to a horizontal scanning period are acquired (step S

301

). A determination is made as to whether or not an anode line (non-reset drive line) to which the voltage V

L

has been applied during the previous scanning period is included in the anode lines to which the voltage V

L

is to be applied during a current scanning period in accordance with the pixel data (step S

302

). When the voltage V

L

has been applied to an anode line during the previous scanning period and is to be applied to the anode line during the current scanning period, all the EL elements connected to the anode line remain extinct during both the previous and current scanning periods. In connection with the determination, a determination may be made as to whether or not a drive switch which have been switched to the first stationary contact during the previous scanning period is included in the drive switches to be switched to the first stationary contact during the current scanning period.

If there is no anode line to which the voltage V

L

has been applied during either the previous scanning period and is to be applied during current scanning period, there is issued a reset signal for applying a voltage Vcc to all the positive lines A

1

to A

m

and all the cathode lines B

1

to B

n

(step S

303

). In contrast, if there is an anode line to which the voltage V

L

has been applied during the previous scanning period and is to be applied during the current scanning period, there is produced a reset signal for applying the voltage V

L

to the anode line and applying the voltage Vcc to the remaining positive lines and all the cathode lines B

1

to B

n

(step S

304

). The reset signal is supplied to the cathode line scanning circuit

313

and the anode line drive circuit

314

.

In the case of the reset signal produced in step S

303

, the cathode line scanning circuit

313

switches movable contacts of all the scanning switches

316

1

to

316

n

to the stationary points of voltage Vcc in accordance with the reset signal. In accordance with the reset signal, the anode line drive circuit

314

switches the movable contacts of all the drive switches

318

1

to

318

n

to the third stationary contacts of voltage Vcc. As a result, the voltage developing across each EL element E

I,j

becomes equal to the voltage Vcc, thereby discharging the electric charges stored in the EL elements.

In the case of the reset signal produced in step S

304

, the cathode line scanning circuit

313

switches the movable contacts of all the scanning switches

316

1

to

316

n

to the stationary contacts of voltage Vcc in accordance with the reset signal. In the anode line drive circuit

314

, drive switches corresponding to the anode lines—to which the voltage V

L

has been applied during the previous scanning period and is to be applied during the current scanning period—remain in contact with the first stationary contacts of voltage V

L

. The drive switches corresponding to the remaining anode lines are switched to third stationary contacts of voltage Vcc. Provided that: there is an anode line A

k

(“k” corresponds to at least one numeral in the range of 1 through “m”) to which the voltage V

L

has been applied during the previous scanning period and to which the voltage V

L

is to be applied during the current scanning period, a voltage developing across EL elements E

I,j

excluding the EL element E

k,j

becomes equal to the voltage Vcc. The electric charges stored in the EL elements are discharged. A voltage Vcc-V

L

is applied to the EL element E

k.j

in a reversely-biased manner.

The reset period may be constant or may vary in length in accordance with a scanning period T.

The control circuit

345

produces a scan selection control signal and c, drive control signal in accordance with pixel information represented by the pixel data, which data have been captured in step S

301

and correspond to a single horizontal scanning period (step S

305

).

The scan selection control signal is delivered to the cathode line scanning circuit

313

. The cathode line scanning circuit

313

switches, to ground, a scanning switch (a single scanning switch

316

s

in the range of

316

1

to

316

n

, where “S” designates a numeral in the range of 1 to “n”) assigned to one of the cathode lines B

1

to B

n

, which cathode line corresponds to the current horizontal scanning period represented by the scan selection control signal.

The drive control signal is supplied to the anode line drive circuit

314

. In the anode line drive circuit

314

, a drive switch (any one of the drive switches

318

1

to

318

m

) is switched to a second stationary contact connected to a current source (i.e., the corresponding one of the current sources

317

1

to

317

m

) Here, the drive switch is assigned to one of the anode lines A

1

to A

m

, _which anode line is connected to an EL element to be illuminated during the current horizontal scanning period represented by the drive control signal. Drive switches

318

assigned to the remaining anode lines A are switched to the first stationary contacts connected to voltage sources (corresponding ones of voltage sources

320

1

to

320

m

).

For example, in a case where the drive switch

318

1

is switched to a current source

317

1

, a drive current flows from the current source

317

1

to a drive switch

318

1

, the anode line A

1

, an EL element E

1,s

, a cathode line B

s

, a scanning switch

316

s

, and ground. The EL element E

1,s

to which the drive current is supplied illuminates in accordance with the pixel data.

If the drive switch switched to the first contact is assigned

318

3

, the voltage V

L

is applied to an anode line A

3

from a voltage source

320

3

by way of a drive switch. The voltage Vcc-V

L

is applied to EL elements E

3,1

to E

3,n

exclusive of an EL element E

3,s

. The voltage V

L

lower than the illumination threshold voltage V

th

is forwardly applied to the EL element E

3,s

, wherewith the EL elements E

3,1

to E

3,n

are charged with an applied voltage.

After having performed processing pertaining to step S

305

, the control circuit

345

determines whether or not a preset scanning period T has elapsed (step S

306

). The scanning period T is set in accordance with, for example, brightness information included in the pixel data and a preset horizontal scanning period. The scanning period is determined through use of an unillustrated internal counter.

If the scanning period T has elapsed, a drive stop signal is produced (step S

307

). If the scanning period T has elapsed, processing proceeds to step S

307

, where the control circuit

345

produces a drive stop signal, to thereby terminate the light-emission control routine. The control circuit

345

enters a stand-by state until the next horizontal scanning period begins. When the next horizontal scanning period begins, processing pertaining to steps S

301

to S

307

is repeated.

FIG. 10

shows the relationship between a reset period and a scanning period T, which are required for the foregoing illumination and drive operations. The scanning period T shown in

FIG. 10

designates a period starting from the end of the reset period to the start of the next horizontal scanning period. As mentioned above, if the scanning period T continues to the start of the next horizontal scanning period, steps S

306

and S

307

may be omitted.

By reference to

FIGS. 21 through 23

, next will be described a case where, after a cathode line B

1

has been scanned by means of the control operation of the control circuit

345

, to thereby cause elements E

1,1

and E

2.1

to illuminate, a cathode line B

2

is scanned, to thereby cause elements E

2.2

and E

3.2

to illuminate. In order to facilitate explanations, illuminating EL elements shown in

FIGS. 21 through 23

are depicted by diode symbols, and nonilluminating EL elements are depicted by capacitor symbols.

In connection with

FIG. 21

, only a scanning switch

316

1

is switched to a ground potential of 0 volt, thereby scanning a cathode line B

1

. A reverse bias voltage Vcc is applied to the remaining cathode lines B

2

to B

n

by way of corresponding scanning switches

316

2

to

316

n

. Simultaneously, the anode line A

1

is connected to the current source

317

1

by way of the drive switch

318

1

, and the anode line A

2

is connected to the current source

317

2

by way of the drive switch

318

2

. The voltage V

L

is applied to the remaining anode lines A

3

to A

m

by way of the drive switches

318

3

to

318

m

. In the circuit configuration shown in

FIG. 21

, only the EL elements E

1,1

, and E

2,1

are forwardly biased, and a drive current flows into the EL elements E

1,1

and E

2,1

from the current sources

317

1

and

317

2

, as designated by arrows. As a result, only the elements E

1,1

and E

2,1

are illuminated. In an illuminated state, a reverse bias voltage Vcc-V

L

is applied between the anode and cathode electrodes of each of nonilluminating and hatched EL elements E

3,2

to E

m,n

. The EL elements E

3,2

to E

m,n

are charged with illustrated polarities, respectively. Since the voltage VCC-V

L

is sufficiently low, the electric charges stored in the EL element are smaller than those charged in an EL element of a known flat display panel. Although the voltage V

L

is forwardly applied between the anode and cathode electrodes of each of the hatched and nonilluminating EL elements E

3.1

to E

m.i

, the voltage V

L

is lower than the illumination threshold voltage V

th

, and hence the EL elements E

3.1

to E

m.i

remain unilluminated and are charged solely.

If the illuminated state of the EL elements shown in

FIG. 21

have been effected for only the scanning period T, a reset control operation is performed before illumination of the EL elements E

2,2

and E

3,2

during the next horizontal scanning period. As shown in

FIG. 22

, the drive switches

318

1

to

318

3

and all the scanning switches

316

1

to

316

n

are switched to the potential Vcc. Accordingly, the positive lines A

1

to A

3

and the negative lines B

1

to N

n

are made equal to the potential Vcc. Through such a reset control operation, the electric charges stored in the respective EL elements E

1,1

, to E

3,n

are discharged by way of the path designated by arrows in the drawing, wherewith the electric charges stored in all the EL elements become momentarily zero. Even during the current scanning period, no drive current for illumination purpose is supplied to the anode lines A

4

to A

m

. Hence, the voltage V

L

is applied to the anode lines A

4

to A

m

by way of drive switches

318

4

to

318

m

. Since the voltage Vcc-V

L

is applied to the EL elements E

4,1

to E

m,n

the electric charges which have been stored in the EL elements E

4,2

to E

m,n

during the scanning period shown in

FIG. 21

are held as they are. The electric charges stored in the EL elements E

4,1

to E

m,1

are immediately discharged, and the EL elements E

4,1

to E

m,1

are charged with the applied voltage Vcc-V

L

.

When the next horizontal scanning period beings after the electric charges stored in the EL elements E

1.1

to E

3,n

have been discharged to zero, only a scanning switch

316

2

corresponding to a cathode line B

2

is switched to ground potential, thus scanning the cathode line B

2

. Simultaneously, the drive switches

318

2

and

318

3

are switched to the current sources

317

2

and

317

3

, and the output terminals of the current sources

317

2

and

317

3

are connected to the corresponding anode lines A

2

and A

3

. Further, the drive switch

318

1

is newly switched to the first stationary contact of potential V

L

, and the voltage V

L

is supplied to the anode lines A

1

and A

4

through A

m

. In connection with the circuit configuration shown in

FIG. 23

, only the EL elements E

2,2

and E

3,2

are forwardly biased, so that a drive current flows from current sources

317

2

and

317

3

to the EL elements E

2,2

and E

3,2

, thereby causing only the elements E

2,2

and E

3,2

to illuminate. In such an illuminated state, the reverse bias voltage Vcc-V

L

is applied across the anode and cathode electrodes of each of hatched and nonilluminating EL elements E

1,1

, E

1,3

to E

1,n

, E

4,1

to E

m,1

and E

4,3

to E

m,n

. The EL elements El, and E

1,3

to E

1

, are newly charged with polarities, as illustrated. Since the electric charges are held in the EL elements E,

3

to E

m,n

charging or discharging barely arises in the EL elements E

4,3

to E

m,n

even when the voltage VCC-V

L

is applied to the EL elements E

4,3

to E

m,n

.

As mentioned above, the reverse bias voltage VCC-V

L

applied to the nonilluminating EL elements during the scanning period is lower than that employed in the known display panel. The electric charges which are charged by the reverse bias voltage Vcc-V

L

and do not contribute to illumination are diminished as compared with those which arise in the conventional display panel. In connection with anode lines (non-reset drive lines) to which the voltage V

L

has been applied during the previous scanning period and the voltage V

L

is to be applied during the current scanning period, none of the EL elements are connected to the non-reset drive line illuminate during the previous and current scanning periods. The electric charges charged with the reverse bias voltage VCC-V

L

are held without being discharged during the current reset period. Therefore, in the foregoing example, the total of electric charge charged with the reverse bias voltage Vcc-V

L

during the current scanning period can be diminished by the amount of electric charge corresponding to that stored in the EL elements E

4,3

to E

m,1

.

In the foregoing embodiment, in step S

302

a determination is made as to whether or not an anode line (non-reset drive line) to which the voltage V

L

has been applied during the previous scanning period is included in the anode lines to which the voltage V

L

is to be applied during the current scanning period. However, as shown in

FIG. 24

, in step S

302

a determination may be made as to whether or not there is an anode line (non-reset drive line) to which the voltage V

L

is to be applied during the current scanning period. If there is not any anode line to which the voltage V

L

is to be applied during the current scanning period, processing proceeds to step S

303

. In contrast, if there is an anode line to which the voltage V

L

is to be applied during the current scanning period, processing proceeds to step S

304

.

FIGS. 25 through 27

show an operating state of a display panel in which, after the cathode line B

1

has been scanned through the control operation shown in

FIG. 24

, to thereby cause elements E

1,1

and E

2,1

to illuminate, the cathode line B

2

is scanned so as to cause elements E

2,2

and E

3,2

to illuminate.

FIG. 25

shows a scanning period during which the EL elements E

1,1

, and E

2,1

are illuminated, as in the case of that shown in FIG.

21

.

If the illuminating state of the EL elements shown in

FIG. 25

has been effected only for the scanning period T, a reset control operation is performed before the next cathode line is scanned for causing the EL elements E

2,2

and E

3,2

to illuminate during the next horizontal scanning period. As shown in

FIG. 26

, the drive switches

318

2

and

318

3

and all the scanning switches

316

1

to

316

n

are switched to the voltage Vcc, and hence the voltages of the anode lines A

2

and A

3

and the voltages of the cathode lines B

1

to B

n

are made equal to the voltage Vcc. By means of such a reset control operation, the electric charges stored in the respective EL elements E

2,1

to E

2,n

and E

3,1

to E

3,n

are discharged by way of the path designated by arrows shown in the drawing, wherewith the electric charges stored in all the EL elements become momentarily zero. Even during the current scanning period, a drive current for illumination purpose is not supplied to the anode lines A

1

and A

4

to A

m

. The voltage V

L

is applied to the anode lines A

1

and A

4

to A

m

by way of the drive switches

318

1

and

318

4

to

318

m

. As a result, the voltage VCC-V

L

is applied to the EL elements E

1,1

to E

1,n

and E

4,1

to E

m,n

. The electric charges stored in the EL elements E

4,2

to E

m,1

during the scanning period shown in

FIG. 21

are held as they are. The electric charges which have been stored in the EL elements E

1,1

and E

4,1

to E

m,1

thus far are discharged immediately, and the EL elements E

1,1

, and E

4,1

are charged with the applied voltage Vcc-V

L

.

When the next horizontal scanning period beings after the electric charges stored in the EL elements E

2,1

to E

3,n

have been discharged to zero in the manner as mentioned above, only the scanning switch

316

2

assigned to the cathode line B

2

is switched to ground potential, whereby the cathode line B

2

is scanned. Simultaneously, the drive switch

318

2

is switched to the current source

317

2

, and the drive switch

318

3

is switched to the current source

317

3

, as in the case shown in FIG.

23

. Only the EL elements E

2,2

and E

3,2

are forwardly biased, and a drive current flows into the EL elements E

2,2

and E

3,2

from the current sources

317

2

and

317

3

, as indicated by arrows, thereby causing only the EL elements E

2,2

and E

3,2

to illuminate, as in the case shown in FIG.

23

. In the illuminated state of these EL elements, a reverse bias voltage Vcc-V

L

is applied between the anode and cathode electrodes of each of hatched and nonilluminating EL elements E

1,1

, E

1,3

to E

1,n

, E

4,1

to E

m,1

and E

4,3

to E

m,n

. Since the electric charges are held in the EL elements E

1,1

, E

1,3

to E

1,n

and E

4,3

to E

m,n

, charging or discharge barely arises in the L elements even when the voltage Vcc-V

L

is applied to the EL elements.

In the previous embodiment, the first potential is made equal to ground potential, and the second and fourth potentials are set to a potential Vcc which is substantially equal to the specified illumination voltage Ve of a capacitive luminescent element. However, the present invention is not limited to such an embodiment.

Further, an embodiment of the present invention will be described hereinbelow in detail by reference to the accompanying drawings.

FIG. 28

schematically shows the configuration of a display which is embodied by application of the present invention to a luminescent display panel using EL elements as capacitive luminescent elements. The display comprises a capacitive luminescent display panel

411

; a light-emission control section

412

; a cathode line scanning circuit

413

; and an anode drive circuit

414

.

As shown in

FIG. 29

, the luminescent display panel

411

comprises a plurality of EL elements E

I,j

(1≦i≦m, 1≦j≦n). As in the case of the EL elements shown in

FIGS. 4 through 6

, the plurality of EL elements are arranged in a matrix pattern at respective intersections between anode lines A

1

to A

m

serving as drive lines and cathode lines B

1

to B

n

serving as scanning lines. The EL elements are connected to the scanning lines and the drive lines. In other words, the EL elements are located at respective intersections between a plurality of drive lines extending substantially in parallel with each other and a plurality of scanning lines extending substantially at right angles to the drive lines. Each of the EL elements is connected to one of the scanning lines and one of the drive lines. The EL elements E

I,j

shown in

FIG. 29

are depicted by capacitor symbols.

In the luminescent display panel

411

, the cathode lines B

1

to B

n

are connected to the cathode line scanning circuit

413

, and the anode lines A

1

to A

m

are connected to the anode line drive circuit

414

. The cathode line scanning circuit

413

has a scanning switches

416

1

to

416

n

assigned to the respective cathode lines B

1

to B

n

, and a voltage source

417

. Each of the scanning switches

416

1

to

416

n

corresponds to a changeover switch having two stationary contacts. One of the stationary contacts is rounded, and movable contacts of the scanning switches

416

1

to

416

n

are connected to the respective cathode lines B

1

to B

n

. The voltage source

417

produces a voltage V

M

for producing a reverse bias voltage V

M

. The positive terminal of the voltage source

417

is connected to the remaining stationary contact of each of the scanning switches

416

1

to

416

n

. The negative terminal of the voltage source

417

is grounded. Each of the scanning switches

416

1

to

416

n

supplies to a corresponding one of the cathode lines B

1

to B

n

ground potential or a reverse bias voltage V

M

, which is the positive potential of the voltage source

417

. Under control of the light-emission control section

412

, the scanning switches

416

1

to

416

n

are switched to ground potential, in scanning sequence, during each horizontal scanning period. The cathode lines B

n

to B

n

set to ground potential act as scanning lines which enable illumination of EL elements connected to the cathode lines B

n

to B

n

.

The anode line drive circuit

414

has variable current sources

418

1

to

418

m

, drive switches

419

1

to

419

m

, a voltage source

420

, and a variable voltage source

421

, the variable current sources and the drive switches being provided so as to correspond to the anode lines A

1

to A

m

. The voltage source

420

produces a voltage Vcc, and the positive terminal of the voltage source

420

is connected to the input terminals of the current sources

418

1

to

418

m

. The negative terminal of the voltage source

420

is grounded. Each of the drive switches

419

1

to

419

m

corresponds to a changeover switch having two stationary contacts. Movable contacts of the drive switches

419

1

to

419

m

are connected to the respective anode lines A

1

to A

m

. One of the two stationary contacts belonging to each of the drive switches

419

1

to

419

m

is grounded, and the remaining contact is connected to an output terminal of the corresponding one of the current sources

418

1

to

418

m

. The positive terminal of the variable voltage source

421

is connected to the current control terminal of each of the current sources

418

1

to

418

m

. The negative terminal of the variable voltage source

421

is grounded. The voltage output from the variable voltage source

421

is controlled by the light-emission control section

412

.

The light-emission control section

412

controls the cathode line scanning circuit

413

and the anode line drive circuit

414

, so as to cause the luminescent display panel

411

to display an image in accordance with a video signal supplied from an unillustrated video signal generation system. Such a control operation is performed while being divided into a reset period and a scanning period.

The light-emission control section

412

produces a reset signal during a reset period, and the thus-produced reset signal is delivered to the cathode line scanning circuit

413

and the anode line drive circuit

414

. The cathode line scanning circuit

413

performs a control operation for switching the scanning switches

416

1

to

416

n

such that a reverse bias voltage V

M

is applied to all the cathode lines B

1

to B

n

in accordance with the reset signal. The anode line drive circuit

414

performs a control operation for switching the drive switches

419

1

to

419

n

such that ground potential is applied to the anode lines A

1

to A

n

in accordance with the reset signal.

The light-emission control section

412

sends a scanning line selection control signal to the cathode line scanning circuit

413

during the scanning period. The scanning switches

416

1

to

416

n

are switched such that any cathode line corresponding to the horizontal scanning period of the video signal is selected from the cathode lines B

1

to B

n

, and the thus-selected cathode line is set to ground potential, and such that the reverse bias voltage V

M

is applied to the remaining cathode lines The reverse bias voltage V

M

is applied from the constant-voltage source

417

connected to the cathode line, in order to prevent illumination of EL elements connected to intersections between the anode line through which a drive current is flowing and cathode lines which are not selected for scanning, which would otherwise be caused by crosstalk. During each horizontal scanning period, the scanning switches

416

1

to

416

n

are sequentially switched to ground potential. The cathode lines B

1

to B

n

set to ground potential act as scanning lines which Enable illumination of EL elements connected to the cathode lines B

1

to B

n

.

The light-emission control section

412

produces a drive control signal indicating that one from the EL elements connected to a scanning line is to be illuminated, at any timing and for any period of time, in accordance with pixel information represented by a video signal during a scanning period. The thus-produced drive control signal is delivered to the anode line drive circuit

414

. In response to the drive control signal, the anode line drive circuit

414

switches, to the current source side, any one of the drive switches

419

1

to

419

m

assigned to the anode line connected to the EL elements to be illuminated. By way of the corresponding one of the anode lines A

1

to A

m

, a drive current corresponding to the pixel information is supplied to the EL elements. The remaining drive switches

419

are switched to grounded contacts, and ground potential is supplied to the remaining drive switches

419

.

The internal circuit of the light-emission control section

412

is configured as shown in FIG.

28

. As shown in

FIG. 28

, a synch separation circuit

441

extracts horizontal and vertical synch signals from a supplied input video signal. The thus-extracted horizontal and vertical synch signals are supplied to a timing pulse signal generation circuit

442

. On the basis of the thus-extracted horizontal and vertical synch signals, the timing pulse signal generation circuit

442

produces a synch signal timing pulse signal. The thus-produced synch signal timing pulse signal is supplied to an analog-to-digital converter

443

, a control circuit

445

, and a scan timing signal generation circuit

447

. The analog-to-digital converter

443

converts an input video signal into digital pixel data on a per-pixel basis, in synchronism with the synch signal timing pulse signal. The input video signal is supplied to memory

444

. The memory

444

has at least a storage area for storing pixel data corresponding to one screen of the luminescent display panel

411

. The control circuit

445

supplies a write signal and a read signal, which are synchronized with the synch signal timing pulse signal, to the memory

444

. In response to the write signal, the memory

444

sequentially captures the pixel data supplied from the analog-to-digital converter

443

. Further, in response to the read signal, the memory

444

sequentially reads pixel data stored therein and supplies the thus-read pixel data to an output processing circuit

446

provided in a subsequent stage. The scan timing signal generation circuit

447

produces various timing signals for controlling a scanning switch and a drive switch and delivers the thus-produced signals to the cathode line scanning circuit

413

and the output processing circuit

446

. As a result, the scan timing signal generation circuit

447

supplies a scan selection control signal to the cathode line scanning circuit

413

. In synchronism with a timing signal output from the scan timing signal generation circuit

447

, the output processing circuit

446

supplies, to the anode line drive circuit

414

, a drive control signal corresponding to the pixel data supplied from the memory

444

. During a reset period, the control circuit

445

supplies a reset signal to the anode line drive circuit

414

by way of the output processing circuit

446

, as well as to the cathode line scanning circuit

413

by way of the scan timing signal generation circuit

447

.

The drive operation of the capacitive luminescent display panel performed by the control circuit

445

of the light-emission control section

412

will now be described by reference to flowcharts shown in

FIGS. 30 and 31

.

During each vertical scanning period of supplied pixel data (i.e., a period of a single frame), the control circuit

445

executes a light-emission determination routine. As shown in

FIG. 30

, during the light-emission determination routine, the control circuit

445

sets count C to a value of 1 and count D to a value of 0 (step S

401

). Count C designates a numeral determined by means of counting up in the sequence in which a single screen is scanned, and count D represents the number of scanning lines. Pixel data corresponding to a C

th

horizontal scanning period are captured from the memory

444

in the order of scanning (step S

402

). Since the pixel data corresponding to a single screen are stored in the memory

444

by means of the write signal, the control circuit

445

captures the pixel data corresponding to one horizontal scanning period, in the order of scanning. The control circuit

445

determines whether or not pixel data indicating illumination are included in the pixel data corresponding to the C

th

horizontal scanning period (step S

403

). If the pixel data indicating illumination are included, the C

th

cathode line Bc is considered to be a real scanning line. Therefore, a scanned/unscanned flag F(C) is set to a value of 0, which value indicates that scanning is effected (step S

404

). Count D is incremented by only one (step S

405

). In contrast, if the pixel data indicating illumination are not included, the scanned/unscanned flag F(C) is set to a value of 1, which value indicates that scanning is not effected (step S

406

). Count D is left, as is. The scanned/unscanned flag F(C), count C, and count D are preserved in memory (not shown) provided in the control circuit

404

. Scanned/unscanned flags are formed as F(

1

), F(

2

), F(

3

), . . . , F(n).

After processing pertaining to step S

405

or S

406

has been performed, a determination is made as to whether or not count C has reached the number of cathode lines (n) (step S

407

). If C<n, count C is incremented by only one (step S

408

), and processing returns to step S

2

. In contrast, if C=n, the voltage output from the variable voltage source

421

is set in accordance with count D (step S

409

). There is output a voltage control signal for adjusting the voltage output from the variable voltage source

421

to the thus-set voltage (step S

410

). When count C assumes “n,” count D represents the number of scanning lines of the current frame. In step S

409

, there is adjusted the voltage output from the variable voltage source

421

for setting the Electric current output from the current sources

418

1

to

418

m

corresponding to the number of scanning lines. The relationship between count D and the voltage output from the variable voltage source

421

is stored in the internal memory of the control circuit

445

in the form of a data table. Through use of the data table, the output voltage of the variable voltage source

421

is set so as to correspond to count D. The greater the value of count D, the higher the output voltage of the variable voltage source

421

, thereby increasing the current output from the current sources

418

1

to

418

m

.

After the processing pertaining to step S

410

has been performed, a single scanning period T is set in accordance with count D (step S

411

). Provided that the period of a frame is constant, as count D becomes smaller, a single scanning period T is set to become longer. Since the relationship between count D and the single scanning period T has been stored beforehand in the internal memory of the control circuit

445

in the form of a data table, a single scanning period T corresponding to count D is set through use of the data table.

After having executed the light-emission determination routine, the control circuit

445

repeatedly executes a light-emission control routine. As shown in

FIG. 31

, during the light-emission control routine, the control circuit

445

sets count E to a value of 1 in the manner as shown in

FIG. 31

(step S

421

) and determines whether or not a scanned/unscanned flag F(E) assumes a value of 1 (step S

422

) As the scanned/unscanned flag F(E), the flag used in step S

404

or S

406

of the light-emission determination routine is used. If F(E)=1, the cathode line is not scanned. A determination is made as to whether or not count E has reached the number of cathode Lines (n) (step S

423

). If E<n, count E is incremented by only one (step S

424

), and processing returns to step S

422

. In contrast, if E=n, the routine is terminated.

If in step S

422

it is determined that F(E)=0, there is produced a reset signal for applying ground potential to all the anode lines A

1

to A

m

and the cathode lines B

1

to B

n

(step S

425

). As a result of production of the reset signal, a reset period R of predetermined duration is produced. The reset signal is supplied to the cathode line scanning circuit

413

and the anode line drive circuit

414

. In response to the reset signal, the cathode line scanning circuit

413

switches the movable contacts of all the scanning switches

416

1

to

416

n

to grounded stationary contacts. In response to the reset signal, the anode line drive circuit

414

switches the movable contacts of all the drive switches

419

1

to

419

n

to grounded stationary contacts. As a result, the voltage developing across each of the EL elements E

i,j

becomes equal to ground potential, and the electric charge stored in the EL elements is discharged.

After the end of the reset period R, the control circuit

445

captures pixel data corresponding to the E

th

horizontal scanning period from the memory

444

(step S

426

). In accordance with the pixel information represented by the thus-captured pixel data, the control circuit

445

produces a scan selection control signal and a drive control signal (step S

427

).

The scan selection control signal is supplied to the cathode line scanning circuit

413

. The cathode line scanning circuit

413

switches to ground the scanning switch (a scanning switch

416

E

of the scanning switches

416

1

to

416

n

) assigned to a cathode line B (one of the cathode lines B

1

to B

n

) corresponding to the current: horizontal scanning period represented by the scan selection control signal. The cathode line scanning circuit

413

switches to the voltage source

417

the scanning switches (all the scanning switches

416

1

to

416

n

exclusive of the scanning switch

416

E

) for applying the reverse bias voltage V

M

to the remaining cathode lines.

The drive control signal is supplied to the anode line drive circuit

414

. In the anode line drive circuit

414

, a drive switch (any one of the drive switches

419

1

to

419

m

) is switched to the stationary contact connected to a current source (i.e., the corresponding one of the current sources

418

1

to

418

m

) Here, the drive switch is assigned to the one of the anode lines A

1

to A

m

that is connected to an EL element to be illuminated during the current horizontal scanning period represented by the drive control signal. Drive switches

418

assigned to the remaining anode lines are switched to grounded stationary contacts.

For example, in a case where the drive switch

419

1

is switched to a current source

418

1

, a drive current flows from the current source

418

1

to a drive switch

419

1

, the anode line A

1

, an EL element E

1,s

a cathode line B

S

, a scanning switch

416

s

, and to ground. Since the electric current flowing through the EL element is proportional to illumination brightness, the EL element E

1,s

to which the drive current is supplied illuminates in accordance with the pixel information.

After having performed processing pertaining to step S

427

, the control circuit

445

determines whether or not the single scanning period T has elapsed (step S

428

). The scanning period T is set in accordance with, for example, brightness information included in the pixel data and a preset horizontal scanning period. The scanning period is determined through use of an unillustrated internal counter.

If the single scanning period T has elapsed, processing proceeds to step S

429

, where the control circuit

445

produces a drive stop signal for stopping illumination of the display panel. Subsequently, processing proceeds to step S

423

, which has been described above. A cathode line to which EL elements to be illuminated next are connected is scanned, and processing pertaining to steps S

423

to S

429

is iterated.

As shown in

FIG. 32

, in a case where a single frame is formed from a total number of “n” scanning lines and where the EL elements connected to the first through k

th

cathode lines are illuminated, the first through k

th

cathode lines are scanned. Subsequently, the next frame is scanned without involvement of scanning of the remaining k+1

th

to n

th

cathode lines.

FIG. 10

shows the relationship between a reset period R and a scanning period T, which are determined for the foregoing illumination and drive operations. The scanning period T charges in accordance with count D, that is, the number of scanning lines of a current luminescent display frame.

In a case where all the cathode lines B

1

to B

n

of a single frame are sequentially scanned in the same manner as in a known display panel, one of the scanning switches

416

1

to

416

n

is switched to ground. Even if no EL elements to illuminate are connected to a cathode line assigned to the scanning switch, the reverse bias voltage V

M

is applied to and charged in the EL elements connected to the cathode lines assigned to the remaining scanning switches. However, the thus-stored electric charge is discharged during the reset period D which immediately follows the charging operation. Thus, the electric charges do not directly contribute to illumination and is uselessly dissipated. However, the present invention prevents scanning of cathode lines to which no EL elements to be illuminated are connected. Therefore, there can be diminished useless power dissipation, which would otherwise be caused by charging or discharging such EL elements.

According to the present invention, as the number of scanning lines becomes smaller, the duration of the single scanning period T can be made longer. Therefore, even if a reduction arises in the instantaneous brightness of the EL elements, sufficient per-frame brightness can be ensured. As the number of scanning lines becomes smaller, the drive current output from the current sources

418

1

to

418

m

can be made smaller, thus saving power.

In the previous embodiment, the voltage source

420

outputs a constant voltage. However, as show in

FIG. 33

, the voltage source

420

may be replaced with a variable voltage source

420

. The output voltage of the variable voltage source

420

is controlled in accordance with the voltage control signal output from the control circuit

445

. If in step S

407

of the light-emission determination routine it is determined that C=n, as shown in

FIG. 34

, the control circuit

445

sets the output voltage of the variable voltage source

420

and the output voltage of the variable voltage source

421

in accordance with count D (step S

412

). Further, the control circuit

445

outputs a control signal for adjusting the variable voltage source

420

to the thus-set voltage and a control signal for adjusting the variable voltage source

421

to the thus-set voltage (step S

413

). In step S

412

the output voltage of the variable voltage source

420

and the output voltage of the variable voltage source

421

are set through use of individual data tables. As count D becomes greater, the output voltage of the variable voltage source

420

is set higher. In other respects, operations pertaining to the light-emission determination routine and the light-emission control routine are the same as those shown in

FIGS. 30 and 31

.

If the current flowing through the EL elements is diminished for reducing the instantaneous illumination brightness in accordance with a reduction in the number of scanning lines, the forward voltage applied to the EL elements is also decreased, as can be seen from the voltage V-current I characteristic of an EL element shown in FIG.

3

. Accordingly, even if the output voltage of the variable voltage source

420

is reduced, a desired current flows from the current sources

418

1

to

418

m

to EL elements to be illuminated. Thus, the voltage applied to the EL elements to be illuminated can be ensured. As mentioned above, the output voltage of the variable voltage source

420

, which is the drive source of the EL elements, is diminished, thereby reducing power to be dissipated by the current sources

418

1

to

418

m

.

The previous embodiment has described a drive unit of current drive method which supplies, from current sources, an electric current to EL elements to be illuminated. However, the present invention may also be applied to a drive unit of voltage drive method which applies a voltage, from a voltage source, directly to EL elements to be illuminated.

FIG. 35

shows a display equipped with a drive unit employing the voltage drive method. In this unit, one of stationary contacts of each of the drive switches

419

1

to

419

m

is grounded. The remaining stationary contact is connected directly to the positive terminal of the variable voltage source

420

. In other respects, the display is identical in structure with that shown in FIG.

29

. If in step S

407

of the light-emission determination routine it is determined that C=n, as shown in

FIG. 36

, the control circuit

445

sets the output voltage of the variable voltage source

420

in accordance with count D (step S

414

) and outputs a voltage control signal for adjusting the variable voltage source

420

to the thus-set voltage (step S

415

). In other respects, operations pertaining to the light-emission determination routine and the light-emission control routine are the same as those shown in

FIGS. 30 and 31

.

In the previous embodiment, a video signal having a constant frame period is supplied to a drive unit. However, the present invention is not limited to such an embodiment. In a case where an image pertaining to a single video signal is repeatedly displayed until the content of video data is changed, the frame period does not need to have a constant length. According to the present invention, a frame frequency can be increased.

As mentioned above, according to the present invention, a comparatively-low reverse bias voltage is applied to respective capacitive luminescent elements located in intersections between scanning lines except one scanning line and drive lines except an illumination drive line. Electric charges which are stored in the luminescent elements with the reverse bias voltage and which do not contribute to illumination are diminished as compared with those charged in luminescent elements in a known display panel, thus reducing useless power dissipation.

As mentioned above, according to the present invention, a comparatively-low reverse bias voltage is applied to respective capacitive luminescent elements located in intersections between scanning lines except one scanning line and drive lines except an illumination drive line. Electric charges which are stored in the luminescent elements with the reverse bias voltage and which do not contribute to illumination are diminished as compared with those charged in luminescent elements in a known display panel, thus reducing useless power dissipation.

According to the present invention, the electric charges—which are stored in the capacitive luminescent elements connected to non-reset drive lines by means of the reverse bias voltage—are held without being discharged. Even when the reverse bias voltage is applied to the capacitive luminescent elements during the next scanning period, charging or discharging barely arises in the luminescent elements, thereby reducing useless power dissipation.

As mentioned above, according to the present invention, a comparatively-low reverse bias voltage is applied to respective capacitive luminescent elements located in intersections between scanning lines except one scanning line and drive lines except an illumination drive line. Electric charges which are stored in the luminescent elements with the reverse bias voltage and which do not contribute to illumination are diminished as compared with those charged in luminescent elements in a known display panel, thus reducing useless power dissipation.

According to the present invention, the electric charges—which are stored in the capacitive luminescent elements connected to non-reset drive lines by means of the reverse bias voltage—are held without being discharged. Even when the reverse bias voltage is applied to the capacitive luminescent elements during the next scanning period, charging or discharging barely arises in the luminescent elements, thereby reducing useless power dissipation.

As has been mentioned above, according to the present invention, scanning lines to which capacitive luminescent elements to be illuminated are connected are scanned, and the remaining scanning lines are not scanned. Useless power dissipation can be diminished, by the amount corresponding to the power required for scanning the scanning lines to which capacitive luminescent elements to be illuminated are not connected.

Number	Date	Country
11-285104	Oct 1999	JP
11-285105	Oct 1999	JP
11-285106	Oct 1999	JP
11-289194	Oct 1999	JP

Number	Name	Date	Kind
4686426	Fujioka et al.	Aug 1987	A
5404074	Watanabe et al.	Apr 1995	A
6111557	Koyama et al.	Aug 2000	A

Luminescent display panel drive unit and drive method thereof

Information

Patent Number

Date Filed

Date Issued

Inventors

Original Assignees

Examiners

CPC

US Classifications

Field of Search

US

International Classifications

Abstract

Description

Claims

Priority Claims (4)

US Referenced Citations (3)