Liquid-crystal display apparatus

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to liquid-crystal display (LCD) apparatuses, and more particularly, to an active-matrix liquid-crystal display apparatus using time-division driving.

2. Description of the Related Art

Active-matrix liquid-crystal display (LCD) apparatuses have been mainly used in personal computers and word processing units. Active-matrix LCD apparatuses are superior in terms of response speed and image quality, and are best suited to in improving recent color display. In such a display apparatus, a nonlinear device such as a transistor and diode is used in each pixel of the LCD panel. Specifically, thin film transistors (TFTs) are formed on a transparent insulating substrate such as a glass substrate.

For active-matrix LCD apparatuses, it is said that a so-called dot-inversion driving method, in which the polarities of voltages to be applied to adjacent dots (pixels) are inverted, is good in improving image quality. This is because inverting the polarities of voltages to be applied to adjacent dots cancels potentials jumped from signal lines, which are caused by capacitors formed at the crossover points of signal lines and gate lines, and thereby stable pixel potentials are input to reduce flickers in LCD display.

On the other hand, if the dot-inversion driving method is not employed, the ground level of gate lines fluctuates and thereby the gate switches of TFTs cannot hold off states. Consequently, held pixel potentials are discharged. The transmission factors of pixels decrease and their contrast is also reduced. In addition, since potentials having the same polarity are jumped from signal lines, pixel contrast becomes conspicuous between alternate lines. Even if an image having the same graduation is displayed, different graduations are shown in alternate lines.

Since the dot-inversion driving method solves these inconveniences, it is an effective driving method for LCD apparatuses to improve image quality.

The outputs of an external driver IC for driving an LCD panel usually correspond to the signal lines of the LCD panel in a one-to-one correspondence relationship. In other words, each output of the driver IC is sent to the corresponding signal line. On the other hand, to make the driver IC compact, there has been known a so-called time-division driving method as an LCD-panel driving method which allows the number of the output pins (output terminals) of the driver IC to be reduced.

In this time-division driving method, a plurality of signal lines are handled as one block, a driver IC outputs a signal to a plurality of signal lines in one division block in a time sequential manner, time-division switches are provided for an LCD panel in units of division blocks, and the time-sequential signal output from the driver IC is time-divided by the time-division switches and sequentially sent to a plurality of signal lines.

When time-division driving is applied to a general driver IC used for dot-inversion driving, however, since the output signals of the driver IC used for dot-inversion driving change their polarities between odd-numbered lines and even-numbered lines, it may occur that dot-inversion driving cannot be used in time-division driving. With divided-by-two time-division driving being taken as an example, this issue will be described below.

As an example of divided-by-two time-division driving, a system shown in

FIG. 17

is formed such that two adjacent signal lines

71

-

1

and

71

-

2

,

71

-

3

and

71

-

4

, . . . are handled as blocks irrespective of the corresponding colors, red (R), green (G), and blue (B), and the time-division switches

72

-

1

and

72

-

2

,

72

-

3

and

72

-

4

, . . . connected to these signal lines divide in time time-sequential signals sent through output lines

73

-

1

,

73

-

2

, . . . from a not-shown driver IC and sequentially send to the signal lines

71

-

1

and

71

-

2

,

71

-

3

and

71

-

4

, . . .

In divided-by-two time-division driving in the system configured as described above, since signal voltages inverted in polarity between odd-numbered and even-numbered output terminals of the driver IC are distributed to odd-numbered and even-numbered actual pixels and their polarities are inverted in alternate lines, it is clear from

FIG. 18

, which shows signal-voltage write conditions, that the polarities of the voltages applied to adjacent pixels in one line cannot be inverted in the entire pixel area, namely, dot inversion cannot be achieved in the entire pixel area.

In

FIG. 18

, the horizontal direction indicates a scanning order and the vertical direction indicates the order in which the time-division switches operate. A high-voltage write condition is indicated by H, and a low-voltage write condition is indicated by L.

As another example of divided-by-two time-division driving, a system shown in

FIG. 19

is formed such that two adjacent signal lines

81

-

1

and

81

-

4

,

81

-

2

and

81

-

5

,

81

-

3

and

81

-

6

, . . . for each color of R, G, and B are handled as blocks, and the time-division switches

82

-

1

and

82

-

4

,

82

-

2

and

82

-

5

,

82

-

3

and

82

-

6

, . . . connected to these signal lines divide in time time-sequential signals sent through output lines

83

-

1

,

83

-

2

, . . . from a not-shown driver IC and sequentially send to the signal lines

81

-

1

and

81

-

4

,

81

-

2

and

81

-

5

,

81

-

3

and

81

-

6

, . . .

In divided-by-two time-division driving in the system configured as described above, since signal voltages inverted in polarity between odd-numbered and even-numbered output terminals of the driver IC are distributed to odd-numbered and even-numbered actual pixels and their polarities are inverted in alternate lines, it is clear from

FIG. 20

, which shows signal-voltage write conditions, that dot inversion cannot be achieved at boundaries of division blocks in one line. Since the definition of dot inversion does not cover the case which happened at the boundaries of the division blocks, pixel potentials fluctuate and vertical lines appear.

In

FIG. 20

, the horizontal direction indicates a scanning order and the vertical direction indicates the order in which the time-division switches operate. A high-voltage write condition is indicated by H, and a low-voltage write condition is indicated by L.

In other words, when a time-division number is even, the polarity of the signal voltage A first written in a division block is opposite that of the signal voltage B last written in

FIGS. 18 and 20

. Since signal voltages sent from the driver IC are inverted between odd-numbered dots and even-numbered dots, signal voltages B

1

, B

2

, . . . written last in division blocks have the same polarities as signal voltages A

2

, A

3

, . . . written first in the following division blocks.

Therefore, in the first example of divided-by-two time-division driving, dot inversion cannot be achieved in the entire pixel area, and in the second example of divided-by-two time-division driving, dot inversion cannot be achieved at the boundaries of division blocks. Hence, image quality is reduced. Polarity inversion, however, can be achieved with chroma signals being rotated. As will be described later, this makes data re-arrangement processing complicated and increases the size of a processing circuit.

SUMMARY OF THE INVENTION

The present invention has been made in consideration of the above inconveniences. Accordingly, it is an object of the present invention to provide an LCD apparatus which allows time-division driving to be implemented without reducing image quality.

The foregoing object is achieved according to the present invention through the provision of a liquid-crystal display apparatus including: a display section formed of a plurality of row gate lines, a plurality of column signal lines, and a plurality of pixels two-dimensionally arranged at the intersections of the plurality of row gate lines and the plurality of column signal lines; a transparent substrate on which the display section is formed; a second transparent substrate having an opposite electrode, connected to the transparent substrate with a predetermined gap placed therebetween; liquid crystal held in the gap; a driver circuit for outputting a time-sequential signal corresponding to a predetermined time-division number; and a time-division switch for time-dividing the time-sequential signal output from the driver circuit and for sending them to the corresponding signal lines among the plurality of column signal lines, wherein the time-division number used in the time-division switch is set odd.

In the LCD apparatus having the above configuration, the driver circuit outputs a time-sequential signal corresponding to the time division number to allow time-division driving. The time-sequential signals, for example, in dot-inversion driving, are signals having different polarities alternately (dot-inversion signals). Time-division switches apply time division to the time-sequential signals with an odd time-division number and send them to the corresponding signal lines. With this operation, the voltages applied to adjacent pixels in one line do not have the same polarity, and dot inversion driving is achieved in the entire pixel area.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1

is a wiring diagram of a liquid-crystal display section in an active-matrix liquid-crystal display apparatus according to the present invention.

FIG. 2

is a circuit diagram of pixels.

FIG. 3

is a block diagram of a configuration example of a driver IC.

FIG. 4

is a configuration view showing the connections of time-division switches in first divided-by-three time-division driving according to a first embodiment.

FIG. 5

is a view showing signal-voltage write conditions on pixels in the first divided-by-three time-division driving.

FIG. 6

is a timing chart of each signal in the first divided-by-three time-division driving.

FIG. 7A

is a structural cross section of a thin film transistor having a bottom gate structure, and

FIG. 7B

is a structural cross section of a thin film transistor having a top gate structure.

FIG. 8

is a configuration view showing the connections of time-division switches in second divided-by-three time-division driving according to the first embodiment.

FIG. 9

is a view showing signal-voltage write conditions on pixels in the second divided-by-three time-division driving.

FIG. 10

is a timing chart of each signal in the second divided-by-three time-division driving.

FIG. 11

is a configuration view showing the connections of time-division switches in divided-by-nine time-division driving according to the first embodiment.

FIG. 12

is a view showing signal-voltage write conditions on pixels in the divided-by-nine time-division driving.

FIG. 13

is a configuration view showing the connections of time-division switches in divided-by-five time-division driving according to the first embodiment.

FIG. 14

is a view showing signal-voltage write conditions on pixels in the divided-by-five time-division driving.

FIG. 15

is a rough configuration view of an active-matrix liquid-crystal display apparatus according to a second embodiment of the present invention.

FIG. 16

is a timing chart of operations of the active-matrix liquid-crystal display apparatus according to the second embodiment.

FIG. 17

is a configuration view showing the connections of time-division switches in first divided-by-two time-division driving.

FIG. 18

is a view showing signal-voltage write conditions on pixels in the first divided-by-two time-division driving.

FIG. 19

is a configuration view showing the connections of time-division switches in second divided-by-two time-division driving.

FIG. 20

is a view showing signal-voltage write conditions on pixels in the second divided-by-two time-division driving.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described in detail by referring to the drawings.

FIG. 1

is a wiring diagram of a liquid-crystal display section of an active-matrix liquid-crystal display (LCD) apparatus according to a first embodiment of the present invention.

In the active-matrix LCD apparatus according to the first embodiment, a plurality of row gate lines

11

-

1

,

11

-

2

,

11

-

3

, . . . and a plurality of column signal lines

12

-

1

,

12

-

2

,

12

-

3

, . . . are arranged in matrix on a transparent substrate made, for example, from glass, and a back light formed, for example, of a cold-cathode tube is disposed at the rear side of the transparent substrate. Pixels are disposed at the intersections of the gate lines

11

-

1

,

11

-

2

,

11

-

3

, . . . made, for example, from polycrystalline silicon, and the signal lines

12

-

1

,

12

-

2

,

12

-

3

, . . . made, for example, from Aluminum to form a LCD panel (display section)

10

. The configuration of the pixels will be described below.

One end of each of the plurality of row gate lines

11

-

1

,

11

-

2

,

11

-

3

, . . . is connected to the output end in the corresponding row of a vertical driving circuit

13

. The vertical driving circuit

13

is disposed on the same substrate as the LCD panel

10

, and sequentially sends selection pulses to the gate lines

11

-

1

,

11

-

2

,

11

-

3

, . . . to select pixels in units of rows for vertical scanning.

A driver IC

14

is provided as an external circuit of the LCD panel

10

and sends signal potentials to the signal lines

12

-

1

,

12

-

2

,

12

-

3

, . . . according to an image data. Digital image data which allows display with eight or more graduations and 512 colors or more, for example, is input to the driver IC

14

. A general dot-inversion driving IC is used as the driver IC

14

. The driver IC

14

outputs signal voltages in which the potentials are inverted between odd-numbered dots and even-numbered dots to implement dot-inversion driving.

In addition, to implement time-division driving, the driver IC

14

time-sequentially outputs signals to pluralities of signal lines with a plurality of signal lines being handled as one block. A time-division switch section

16

is provided between the output lines

15

-

1

,

15

-

2

,

15

-

3

, . . . of the driver IC

14

and the signal lines

12

-

1

,

12

-

2

,

12

-

3

, . . . The configurations of the driver IC

14

and the time-division switch section

16

will be described later.

FIG. 2

is a circuit diagram of pixels. As clearly shown in the figure, each pixel

20

is formed of a thin film transistor

21

, an additional capacitor

22

, and a liquid-crystal capacitor

23

. The thin film transistors

21

are connected to gate lines

11

m

−1,

11

m

,

11

m

+1, . . . at their gate electrodes and connected to signal lines (source lines)

12

n

−1,

12

n

, 12

n

+1, . . . at their source electrodes.

In this pixel structure, the liquid-crystal capacitor

23

indicates a capacitor generated between a pixel electrode formed of the thin film transistor

21

and the opposite electrode formed correspondingly. An “H” potential or an “L” potential is written into and held at the pixel electrode, where “H” indicates a high-voltage write condition and “L” indicates a low-voltage write condition.

The potential (common potential Vcom) of the opposite electrode is, for example, set to a DC potential of 6 V and a signal voltage is periodically changed between a high voltage “H” and a low voltage “L” at an interval of one field to implement alternate liquid-crystal driving. The alternate driving reduces polarization of liquid-crystal molecules and prevents the liquid-crystal molecules or an insulating film made, for example, from organic macromolecules and disposed at an electrode surface from being charged.

In the pixel

20

, when the thin film transistor

21

is turned on, the optical transmission factor of the pixel changes and the additional capacitor

22

is charged. With this charging, even if the thin film transistor

21

is turned off, the optical transmission factor of the pixel set by the charged voltage of the additional capacitor

22

is maintained until the thin film transistor

21

is turned on next time. With this method, the quality of an image displayed on the LCD panel

10

is improved.

FIG. 3

is a block diagram of a configuration example of the driver IC

14

. As clearly shown in

FIG. 3

, the driver IC

14

includes a horizontal shift register circuit

31

, a sampling switch set

32

, a level shifting circuit

33

, a data latch circuit

34

, and a digital-analog conversion circuit

35

. In this example, five-bit digital image data, data

1

to data

5

, and power voltages Vdd and Vss, for example, are input to the horizontal shift register circuit

31

in both shift directions.

In the driver IC

14

configured as described above, the horizontal shift register circuit

31

sequentially outputs a horizontal scanning pulse to perform horizontal scanning (row scanning). Each sampling switch in the sampling switch set

32

sequentially samples the input digital image data data

1

to data

5

according to the corresponding horizontal scanning pulse sent from the horizontal shift register circuit

31

.

The level shifting circuit

33

increases in voltage the 5-V digital data, for example, sampled by the sampling switch set

32

to digital data having a liquid-crystal driving voltage. The data latch circuit

34

is a memory that accumulates the digital data of which the voltage has been increased by the level shifting circuit

33

, for one horizontal scanning period. The digital-analog conversion circuit

35

converts the digital data for one horizontal scanning period output from the data latch circuit

34

to an analog signal and outputs it.

The driver IC

14

outputs dot-inversion signals in which the polarities are inverted between odd-numbered output terminals and even-numbered output terminals and the polarities are further inverted every one horizontal scanning period (1H) to implement the above-described dot-inversion driving. The driver IC

14

time-sequentially outputs signals from the output terminals to the signal lines with a plurality of signal lines in the LCD panel

10

being handled as one block to implement time-division driving.

A first embodiment of the present invention to which dot-inversion driving is applied will be described below.

FIG. 4

is a configuration view showing a first example of the connections of the time-division switch section

16

. This view, for example, shows a first example applied to divided-by-three time-division driving corresponding to R, G, and B. In this example, the driver IC

14

time-sequentially outputs signals from the output terminals through the output lines

15

-

1

,

15

-

2

,

15

-

3

, . . . with one signal corresponding to adjacent three pixels in the same color, R, G, or B, namely three every third pixels.

Specifically, as shown in a timing chart of

FIG. 6

, the driver IC

14

outputs a signal for R

1

, R

2

, and R

3

pixels from an odd-numbered output terminal through the output line

15

-

1

, a signal for G

1

, G

2

, and G

3

pixels from an even-numbered output terminal through the output line

15

-

2

, a signal for B

1

, B

2

, and B

3

pixels from an odd-numbered output terminal through the output line

15

-

3

, . . .

Time-division switches

16

-

1

,

16

-

4

, and

16

-

7

are provided between the output line

15

-

1

and three signal lines

12

-

1

,

12

-

4

, and

12

-

7

, time-division switches

16

-

2

,

16

-

5

, and

16

-

8

are provided between the output line

15

-

2

and three signal lines

12

-

2

,

12

-

5

, and

12

-

8

, time-division switches

16

-

3

,

16

-

6

, and

16

-

9

are provided between the output line

15

-

3

and three signal lines

12

-

3

,

12

-

6

, and

12

-

9

, . . .

These time-division switches

16

-

1

,

16

-

4

,

16

-

7

,

16

-

2

,

16

-

5

,

16

-

8

,

16

-

3

,

16

-

6

,

16

-

9

, . . . are formed in the LCD panel

10

together with pixel switches (transistors) and transistors constituting the vertical driving circuit

13

, by polycrystalline TFTs having, for example, a bottom gate structure shown in

FIG. 7A

or a top gate structure shown in FIG.

7

B.

In a TFT having the bottom gate structure shown in

FIG. 7A

, a gate electrode

42

made, for example, from Mo is formed on a glass substrate

41

, a polycrystalline silicon (poly-Si) layer

44

is formed thereon through a gate insulating film

43

made, for example, from SiO

2

, and an inter-layer insulating film

45

made, for example, from SiO

2

is further formed thereon. On the gate insulating film

43

positioned at the sides of the gate electrode

42

, a source area

46

and a drain area

47

formed of N

+

diffusion layers are disposed. A source electrode

48

and a drain electrode

49

made, for example, from aluminum are connected to the areas

46

and

47

, respectively.

In a TFT having the top gate structure shown in

FIG. 7B

, a polycrystalline silicon layer

52

is formed on a glass substrate

51

, a gate electrode

54

is formed thereon through a gate insulating film

53

made, for example, from SiO

2

, and an inter-layer insulating film

55

made, for example, from SiO

2

is further formed thereon. At the sides of the polycrystalline silicon layer

52

on the glass substrate

51

, a source area

56

and a drain area

57

formed of N

+

diffusion layers are disposed. A source electrode

58

and a drain electrode

59

made, for example, from aluminum are connected to the areas

56

and

57

, respectively.

These time-division switches

16

-

1

,

16

-

4

,

16

-

7

,

16

-

2

,

16

-

5

,

16

-

8

,

16

-

3

,

16

-

6

,

16

-

9

, . . . are sequentially turned on according to gate selection signals s

1

, s

2

, and s

3

(see the timing chart of

FIG. 6

) sent from the outside to divide by three in one horizontal scanning period time-sequential signals output from the driver IC

14

through the output lines

15

-

1

,

15

-

2

,

15

-

3

, . . . and to send them to the corresponding signal lines.

In this way, signal potentials which, for example, allow display with eight or more graduations and 512 colors or more are sent from the driver IC

14

to the signal lines

12

-

1

,

12

-

2

,

12

-

3

, . . . through the output lines

15

-

1

,

15

-

2

,

15

-

3

, . . . and the time-division switches

16

-

1

,

16

-

2

,

16

-

3

, . . . In this case, the time-sequential signals output from the external driver IC

14

are sent to the time-division switches

16

-

1

,

16

-

2

,

16

-

3

, . . . in the order of R, G, and B.

A time-division number should be odd, and is preferably the n-th power of three (n: natural number) or a multiple of three. This is because, since one pixel is formed of three R, G, and B dots, the R

1

, R

2

, and R

3

pixel outputs can correspond to odd-numbered outputs and even-numbered outputs inverted each other and sent from the external driver IC

14

. It is a matter of course that this also applies to G

1

, G

2

, and G

3

, and B

1

, B

2

, and B

3

.

It is also clear from the above descriptions that the driver IC

14

outputs R, G, and B signals in synchronization from the corresponding output terminals to the output lines

15

-

1

,

15

-

2

,

15

-

3

, . . . Therefore, the signal potentials output from the external driver IC

14

do not need to be rotated. In addition, without re-arranging data complicatedly, data can be re-arranged successively. Therefore, memory control for data re-arrangement can be made simple.

Signal rotation refers to a state in which R, G, and B signals are not output in synchronization, but output in the order of R, G, and B from a certain output terminal, output in the order of G, B, and R from another output terminal, and output in the order of B, R, and G from yet another output terminal. To allow this, color-signal data needs to be re-arranged in advance before input to the driver IC

14

, and to be accumulated in a buffer memory.

As described above, the signal voltages output from the driver IC

14

inverted in polarity between the odd-numbered output terminals and the even-numbered output terminals are distributed to actual pixel odd-numbered lines and even-numbered lines, and the polarity is inverted in each line. In a case of divide-by-three time-division driving, since a time-division number is odd, signal voltages B

1

, B

2

, . . . written last into division blocks have different polarities from signal voltages A

2

, A

3

, . . . written first into the following division block as clearly shown in FIG.

5

. In other words, dot-inversion driving is achieved in the entire pixel area.

FIG. 5

shows signal-voltage write conditions in pixels in divided-by-three time-division driving shown in FIG.

4

. In

FIG. 5

, the horizontal direction indicates a scanning order and the vertical direction indicates the order in which the time-division switches operate. A high-voltage write condition is indicated by H, and a low-voltage write condition is indicated by L.

FIG. 8

is a configuration view showing a second example of the connections of the time-division switch section

16

. This view, for example, shows a second example applied to divided-by-three time-division driving corresponding to R, G, and B. In this example, the driver IC

14

time-sequentially outputs signal potentials for three R, G, and B pixels from output terminals through the output lines

15

-

1

,

15

-

2

,

15

-

3

, . . .

Specifically, as shown in a timing chart of

FIG. 10

, the driver IC

14

outputs a signal for R

1

, G

1

, and B

1

pixels from an odd-numbered output terminal through the output line

15

-

1

, a signal for R

2

, G

2

, and B

2

pixels from an even-numbered output terminal through the output line

15

-

2

, a signal for R

3

, G

3

, and B

3

pixels from an odd-numbered output terminal through the output line

15

-

3

. . .

Time-division switches

16

-

1

,

16

-

2

, and

16

-

3

are provided between the output line

15

-

1

and three signal lines

12

-

1

,

12

-

2

, and

12

-

3

, time-division switches

16

-

4

,

16

-

5

, and

16

-

6

are provided between the output line

15

-

2

and three signal lines

12

-

4

,

12

-

5

, and

12

-

6

, time-division switches

16

-

7

,

16

-

8

, and

16

-

9

are provided between the output line

15

-

3

and three signal lines

12

-

7

,

12

-

8

, and

12

-

9

, . . .

These time-division switches

16

-

1

,

16

-

2

,

16

-

3

,

16

-

4

,

16

-

5

,

16

-

6

,

16

-

7

,

16

-

8

,

16

-

9

, . . . are formed in the same way as in the previous application example in the LCD panel

10

by polycrystalline TFTs having a gate structure shown in

FIG. 7A

or FIG.

7

B. These time-division switches are sequentially turned on according to gate selection signals s

1

, s

2

, and s

3

(see the timing chart of

FIG. 10

) sent from the outside to divide by three in one horizontal scanning period time-sequential signals output from the driver IC

14

through the output lines

15

-

1

,

15

-

2

,

15

-

3

, . . . and to send them to the corresponding signal lines.

Also in the divide-by-three time-division driving described above, since a time-division number is odd, signal voltages B

1

, B

2

, . . . written last into division blocks have different polarities from signal voltages A

2

, A

3

, . . . written first into the following division blocks as clearly shown in FIG.

9

. In other words, dot-inversion driving is achieved in the entire pixel area. Since an R output is followed by a G output, and then by a B output as clearly shown in

FIG. 10

, signal rotation is not required for the signal potentials output from the external driver IC

14

and complicated data re-arrangement is not required, either, in the same way as in the previous application example.

FIG. 9

shows signal-voltage write conditions in pixels in the divided-by-three time-division driving shown in FIG.

8

. In

FIG. 9

, the horizontal direction indicates a scanning order and the vertical direction indicates the order in which the time-division switches operate. A high-voltage write condition is indicated by H, and a low-voltage write condition is indicated by L.

Since complete dot-inversion driving is achieved in the active-matrix LCD apparatus employing dot inversion driving even if time-division driving is applied, as described above, the numbers of horizontal driving circuits and their output ICs in the LCD apparatus are not increased but reduced when the apparatus is used with display methods which have been increasing in display pixels such as super XGA (SXGA) and ultra XGA (UXGA). Stable, good image quality is provided in dot inversion display. An LCD apparatus according to the present invention can be made compact as an LCD module and multi-color display is implemented with an inexpensive LCD panel.

In the above application examples, the time-division number is set to three. The time-division number is not limited to three. When it is set to the n-th power of three (n: natural number) such as nine and

27

, inverted signals output from odd-numbered terminals and even-numbered terminals of the driver IC

14

are synchronized with the inversion signals corresponding to pixel arrangement in each time division.

FIG. 11

is a configuration view showing a case in which divided-by-nine time-division driving is applied.

FIG. 12

shows signal-voltage write conditions in pixels in the divided-by-nine time-division driving. Also in the divide-by-nine time-division driving, since the time-division number is odd, it is clearly understood from

FIG. 12

that signal voltages B

1

, B

2

, . . . written last into division blocks have different polarities from signal voltages A

2

, A

3

, . . . written first into the following division blocks, and dot-inversion driving is achieved in the entire pixel area.

Since signals are handled in units of R, G, and B pixels with the time-division number being set to the n-th power of three, signal processing becomes simple and the amount of memory data can be reduced in a signal processing system. The present invention is not limited to a case in which the time-division number is set to the n-th power of three. The time-division number is set odd to implement dot inversion in the entire pixel area.

FIG. 13

is a configuration view showing a case in which divided-by-five time-division driving is applied.

FIG. 14

shows signal-voltage write conditions in pixels in the divided-by-five time-division driving. Also in the divide-by-five time-division driving, since the time-division number is odd, it is clearly understood from

FIG. 14

that signal voltages B

1

, B

2

, . . . written last into division blocks have different polarities from signal voltages A

2

, A

3

, . . . written first into the following division blocks, and dot-inversion driving is achieved in the entire pixel area.

In the above first embodiment, under a prerequisite condition of dot-inversion driving, the time-division number is set odd, especially set to the n-th power of three to implement complete dot-inversion driving. Not only in dot-inversion driving but also in common (VCOM) inversion driving or 1H inversion driving, divide-by-three time-division driving corresponding to R, G, and B implements time-division driving without causing image-quality deterioration.

The common (VCOM) inversion driving refers to a driving method in which a common voltage VCOM applied to the opposite electrode of each pixel in common is alternately inverted every 1H. 1H inversion driving refers to a driving method in which the polarity of image data sent to each pixel is inverted against a common voltage VCOM every 1H.

A second embodiment of the present invention to which common (VCOM) inversion driving is applied will be described below.

FIG. 15

is a rough configuration view of an active-matrix LCD apparatus according to a second embodiment of the present invention. The configuration of the active-matrix LCD apparatus according to the second embodiment is basically the same as that of the active-matrix LCD apparatus according to the first embodiment.

In the effective screen area of a color LCD panel

60

, groups of three R, G, and B dots disposed at intersections of gate lines

61

m

−1,

61

m

,

61

m

+1, . . . and R, G, and B signal lines

62

Rn,

62

Gn,

62

Bn, . . . form pixels. A common-voltage generation circuit

64

applies a common voltage VCOM alternately inverted, for example, every 1H to the opposite electrodes of the pixels by Cs lines

63

m

−1,

63

m

,

63

m

+1. Common (VCOM) inversion driving is thus implemented.

One end of each of the gate lines

61

m

−1,

61

m

,

61

m

+1, . . . is connected to the output end in the corresponding row in a vertical driving circuit

65

. The vertical driving circuit

65

is disposed on the same substrate (a transparent insulating substrate such as a glass substrate) as the color LCD panel

60

, and sends selection pulses in the order of the gate lines to select pixels in units of rows for vertical scanning.

On the substrate on which the color LCD panel

60

is disposed, the analog switches

66

Rn,

66

Gn,

66

Bn, . . . corresponding to the signal lines

62

Rn,

62

Gn,

62

Bn, . . . are further formed. These analog switches

66

Rn,

66

Gn,

66

Bn, are also made from polycrystalline TFTs having a gate structure shown in

FIG. 7A

or

7

B in the same way as in the first embodiment.

One end of each of the analog switches

66

Rn,

66

Gn,

66

Bn, . . . is connected to the corresponding signal line

62

Rn,

62

Gn,

62

Bn, or . . . , and the other end is connected in common with three R, G, and B switches being handled as one set. In other words, ends of each set are connected in common in such a manner that ends of the analog switches

66

Rn,

66

Gn, and

66

Bn are connected in common as a set, and ends of the analog switches

66

Rn+1,

66

Gn+1, and

66

Bn+1 are connected in common as another set.

These analog switches

66

Rn,

66

Gn,

66

Bn, . . . are connected to the corresponding output ends of a driver IC

67

at the common connection points of the sets, and are turned on (closed) and off (open) in the order of R, G, and B by switch control pulses SL

1

, SL

2

, and SL

3

output from a switch control circuit

68

. The outputs of the driver IC

67

are thus divided and sent to three R, G, and B signal lines, such as the signal lines

62

Rn,

62

Gn, and

62

Bn. The analog switches

66

R,

66

G,

66

B serve as time-division switches.

The switch control circuit

68

may be formed on an external substrate separated from the substrate for the, color LCD panel

60

, together with the driver IC

67

by a single-crystal silicon chip. Alternatively, the switch control circuit

68

may be formed on the substrate on which the color LCD panel

60

is disposed, by polycrystalline TFTs.

The driver IC

67

includes sets of circuits, each for three signal lines

62

R,

62

G, and

62

B for vertical pixel columns in the color LCD panel

60

. Specifically, a set of circuits for the n-th column, for example, is formed of a sampling circuit

671

n

for sampling input image data, a memory

672

n

for holding the image data sampled by the sampling circuit

671

n

, a D-A converter

673

n

for digitizing the data held by the memory

672

n

, and an output circuit

674

n.

In the driver IC

67

, the sampling circuit

671

n

corresponds to the horizontal shift register circuit

31

, the sampling switch set

32

, and the level shifting circuit

33

in

FIG. 3

, the memory

672

n

corresponds to the data latch circuit

34

, and the D-A converter

673

n

corresponds to the digital-analog conversion circuit

35

. The circuit section corresponding to the output circuit

674

n

is omitted in FIG.

3

.

Since, with the use of divide-by-three time-division driving implemented by the analog switches

62

Rn,

62

Gn,

62

Bn, . . . , the driver IC

67

only needs to have one set of a sampling circuit

671

, a memory

672

, a D-A converter

673

, and an output circuit

674

for three signal lines

62

R,

62

G, and

62

B, the driver IC

67

requires a smaller space, is made more inexpensive, and needs less power consumption.

The driver IC

67

sequentially samples input image data at an interval of 1H (one horizontal scanning period), and writes the image data into the pixels of the row selected by the vertical driving circuit

65

. The image data input to the driver IC

67

is inverted in polarity every 1H against the common voltage VCOM. In this way, 1H inversion driving is implemented.

In addition to this 1H inversion driving, common inversion driving is implemented by generating the common voltage VCOM alternately inverted every 1H by the common-voltage generation circuit

64

, as described above. With common inversion driving being used together with 1H inversion driving, the common voltage VCOM is inverted every 1H in polarity and alternate inversion driving is performed. Since the power voltage of the driver IC

67

can be reduced, low power consumption and low cost become possible.

An operation of the active-matrix LCD apparatus according to the second embodiment will be described next by referring to a timing chart shown in FIG.

16

.

Image data input to the driver IC

67

includes R, G, and B data arranged in series in 1H. The image data is sampled (O(n)) three times in 1H for the R, G, and B data by the sampling circuit

671

, held (P(n)) by the memory

672

, and output (Q(n)) through the D-A converter

673

and the output circuit

674

. These signals have the same polarity as the common voltage VCOM within 1H.

The output (Q(n)) of the driver IC

67

is inverted in polarity every 1H. It is divided and sent to three signal lines

62

R,

62

G, and

62

B by turning on (closed) and off (open) control of the analog switches (time-division switches)

66

R,

66

G, and

66

B caused by the switch control pulses SL

1

, SL

2

, and SL

3

sent from the switch control circuit

68

.

As a result, with the n-th column being taken as an example, the potentials CRn, CGn, and CBn of the R, G, and B signal lines

62

Rn,

62

Gn, and

62

Bn change as shown in

FIG. 16

, and the display data is written into the signal lines

62

Rn,

62

Gn, and

62

Bn. The vertical driving circuit

65

performs vertical scanning and the written display data is written into the pixels on the row selected by a selection pulse Vg.

In this embodiment,-common (VCOM) inversion driving in which the polarity of the common voltage (VCOM) is inverted every 1H is applied. When the common voltage VCOM is fixed to a certain DC voltage, 1H inversion driving is implemented. 1H inversion driving can also be applied.

Since the time-division number is set to three corresponding to R, G, and B in common (VCOM) inversion driving or 1H inversion driving as described above, the following advantages are obtained.

The potentials written into the signal lines

62

R,

62

G, and

62

B by the switch control pulses SL

1

, SL

2

, and SL

3

sent from the switch control circuit

68

shift due to the effect of various capacitance coupling in the LCD panel

60

in a high-impedance period after the analog switches

66

R,

66

G, and

66

B are opened. The potential last written into each pixel is determined at the instant when the selection pulse Vg sent from the vertical driving circuit

65

falls.

Therefore, as a result, the potential of the pixel corresponding to the signal line written first in a horizontal scanning period differs from that of the pixel corresponding to the signal line written last. Consequently, in divide-by-two time-division driving, described before, since one pixel does not correspond to one set of R, G, and B, the fluctuations of the potentials of the signal lines for each color are not constant and a problem may occur in terms of the sense of sight, such as color unevenness (vertical stripe) in the vertical direction.

On the other hand, as in the present embodiment, when the time-division number is set to three corresponding to R, G, and B, and data written into signal lines at different timing correspond to R, G, and B, the fluctuations of the potentials of the signal lines in each color is almost constant. In other words, the potentials fluctuate in colors, and this potential difference does not appear as a luminance difference. In terms of the sense of sight, only a minute color difference appears, and it practically causes no problem.

As described above, according to the present invention, when time-division driving, which allows the number of output pins of a driver IC to be reduced, is applied to an active-matrix LCD apparatus, since the time-division number is set to an odd number, voltages having different polarities can be applied to adjacent dots (pixels) in one line. Therefore, even if time-division driving is applied, complete dot-inversion driving can be performed. Flickers are reduced and a contrast difference between lines in liquid crystal is eliminated. Consequently, time-division driving is implemented without reducing image quality.

Number	Date	Country	Kind
10-069625	Mar 1998	JP
10-241393	Aug 1998	JP

Number	Name	Date	Kind
5781164	Jacobsen et al.	Jul 1998	A
5798744	Tanaka et al.	Aug 1998	A
6075505	Shiba et al.	Jun 2000	A
6160535	Park	Dec 2000	A
6175351	Matsuura et all.	Jan 2001	B1
6268841	Cairns et al.	Jul 2001	B1
6310592	Moon et al.	Oct 2001	B1

Liquid-crystal display apparatus

Information

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Date Filed

Date Issued

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Agents

CPC

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Abstract

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Priority Claims (2)

US Referenced Citations (7)