Patent Application
20100110055
The present invention relates to a display apparatus of an active matrix type having a pixel circuit on a pixel-by-pixel basis, and more particularly, to one which causes luminance changes by controlling the light emission strength of a pixel with a pixel signal current.
Practical use of an organic EL display apparatus employing a spontaneously light-emitting organic electroluminescent (EL) element is expected as a next-generation display apparatus, as it requires no backlight which is needed in a liquid crystal display apparatus, so as to be most suited for a reduction in apparatus thickness, and has an unlimited viewing angle. In the organic EL element employed in an organic EL display apparatus, the luminance of each light-emitting element is controlled by the current value that flows therein, and the organic EL element differs in this respect from the crystal liquid cell in which control is made by the voltage applied.
The active matrix method in a display apparatus with an organic EL element is an effective method over a passive matrix method in lengthening the life of an organic EL element and making a large-sized screen, and is being the subject of active research and development activities. Active matrix methods are grouped into a voltage writing method and a current writing method, depending on the type of a signal written into each pixel.
In an organic EL display apparatus according to the active matrix method, the brightness of each pixel is determined by the current value that flows to the organic EL element implemented in each pixel, and a control for the current value is performed by the voltage applied between the gate and the source electrodes of a drive transistor connected in series to the organic EL element. Generally, in many cases, the threshold voltage and mobility, the electric and physical characteristics of a drive transistor, vary in stability and uniformity among pixels, depending on the production process, material composition, and structure of the transistor. Therefore, reports are actively being made on the research to introduce a pixel compensation circuit and enhance the uniformity among the pixels.
With the above voltage writing method, compensation may be made only for the threshold voltage of the drive transistor, while with the above current writing method both the threshold voltage and the mobility may be compensated. In principle, the current writing method, capable of compensation for both the threshold voltage and the mobility, can easily realize display characteristics of high uniformity as compared with the voltage writing method.
A conventional pixel compensation circuit according to the current writing method is disclosed in patent document 1.
Immediately before the time period A shown in
Vds=√{square root over ( )}(2Idata/β)+Vth Equation (1)
where β is a value proportional to the mobility of the driver element 103 and is represented by the following equation (2).
β=μCox(W/L) Equation (2)
where μ is the mobility of the driver element 103, Cox is the gate oxide film capacity of the driver element 103, W is the channel width of the driver element 103, L is the channel length of the driver element 103, and Vth is the threshold voltage of the driver element 103.
Thereafter, if the first scan line 107 is turned to a low voltage state to turn off the first switching element 101 and the second switching element 102, and the second power line 109 is turned to a high voltage state such that the driver element 103 operates in the saturation region during the time period B, the current Ipix that flows to the light-emitting element 105 is made:
Ipix=Idata Equation (3)
owing to the potential between the gate electrode and the source electrode of the driver element 103 that is being maintained at the value of the equation (1) by the luminance signal retention capacitor 104. Therefore, the current Ipix that flows to the light-emitting element 105 does not contain the characteristic values of β and Vth of the driver element 103. Accordingly, it becomes possible to compensate for variations in the mobility and threshold voltage of the driver element 103 as well as for variations in transistor geometries.
Patent document 1: Japanese Patent Application Publication No. 2003-195810 (page 21; FIGS. 5 and 7)
Even in an active matrix organic EL display apparatus with an amorphous silicon transistor, such as the one in patent publication 1, which is rated as having a relatively high in-plane uniformity of mobility, the temperature dependency of the mobility is high. Because of this, there arises a problem that the luminance of a light-emitting element varies if the temperature changes depending on the place of its display area, or if the temperature of its usage environment changes. Furthermore, there is also a problem that, due to the misalignment of a mask on a production lot basis, which mask is used during the light exposure process when producing transistor substrates, variations in the transistor geometries and the like occur. In consideration of these, the development of a highly reliable compensation circuit according to the current writing method is important.
Moreover, also in the active matrix organic EL display apparatus that employs a polysilicon transistor with a large in-plane mobility variation, it is preferable to use a compensation circuit according to the current writing method as a means for correcting the variations in mobility.
On the other hand, there exists the instability of an element called threshold voltage shifts in an amorphous silicon transistor, and there exist threshold voltage variations as well as mobility variations in a polysilicon transistor. With the conventional technique as shown in
The present invention has been made in view of these circumstances, and an object thereof is to provide an active matrix type display apparatus which enables a reduction in the design withstand voltage of the output stage of a signal line drive circuit by correcting the threshold voltage on a pixel-by-pixel basis.
In order to solve the above problem, the present invention provides an active matrix type display apparatus including a plurality of pixels disposed in a matrix arrangement, each of the pixels including: a light-emitting element which emits light in response to a supplied current; a signal line connected to a signal line drive circuit which supplies a luminance signal corresponding to a luminance of light emission of the light-emitting element, the luminance signal being a current signal; a driver element which controls a current value of the luminance signal supplied to the light-emitting element; a luminance signal retention capacitor which retains, as a luminance signal voltage, a potential difference generated between a drain electrode and a source electrode of the driver element when the luminance signal is supplied to the driver element via the signal line; and a threshold voltage detection and addition unit which detects a threshold voltage of the driver element and causes a voltage obtained by adding the luminance signal voltage being retained in the luminance signal retention capacitor to the detected threshold voltage to be applied at a gate electrode of the driver element.
Furthermore, the present invention also provides an active matrix type display apparatus including a plurality of pixels disposed in a matrix arrangement, each of the pixels including: a light-emitting element having a first electrode and a second electrode, which emits light in response to a current supplied via the first and second electrodes; a first power line connected to the first electrode of the light-emitting element; a second power line; a signal line connected to a signal line drive circuit which supplies a luminance signal corresponding to a luminance of light emission of the light-emitting element, the luminance signal being a current signal; a first switching element, one of a drain electrode and a source electrode of which is connected to the signal line, and which has a gate electrode connected to a first scan line; a driver element, one of a drain electrode and a source electrode of which is connected to the other of the drain electrode and the source electrode of the first switching element, and the other of which is connected to the second electrode of the light-emitting element or to the second power line; a luminance signal retention capacitor having a first electrode and a second electrode, the second electrode being connected to the source electrode of the driver element; a second switching element, one of a drain electrode and a source electrode of which is connected to the first electrode of the luminance signal retention capacitor, and the other of which is connected to the signal line or to the drain electrode of the driver element; and a threshold voltage detection and addition unit having a first terminal connected to the gate electrode of the driver element, a second terminal connected to the first electrode of the luminance signal retention capacitor, and a third terminal connected to a second scan line, which detects a threshold voltage of the driver element and causes a voltage obtained by adding the threshold voltage to a potential of the second terminal to be applied at the first terminal.
According to the above configurations of the present invention, by correcting the threshold voltage on a pixel-by-pixel basis, a reduction can be made in the design withstand voltage of the output stage of the signal line drive circuit.
Here, the threshold voltage detection and addition unit may include a threshold voltage retention capacitor having a first electrode connected to the first terminal and a second electrode connected to the second terminal.
Furthermore, the driver element may be an n-channel type transistor, the threshold voltage detection and addition unit may include: a first diode element having an anode terminal connected to the first terminal and a cathode terminal connected to the second terminal; and a second diode element having an anode terminal connected to the third terminal and a cathode terminal connected to the first terminal, and a threshold voltage of the first diode element may be controlled such that a value obtained by dividing an absolute value of the threshold voltage of the first diode element by an absolute value of the threshold voltage of the driver element becomes a positive value of 1 or less.
The driver element may be a p-channel type transistor, the threshold voltage detection and addition unit may include: a first diode element having a cathode terminal connected to the first terminal and an anode terminal connected to the second terminal; and a second diode element having a cathode terminal connected to the third terminal and an anode terminal connected to the first terminal, and a threshold voltage of the first diode element may be controlled such that a value obtained by dividing an absolute value of the threshold voltage of the first diode element by an absolute value of the threshold voltage of the driver element becomes a positive value of 1 or less.
The threshold voltage detection and addition unit may further include: a fourth terminal connected to the source electrode of the driver element, and each of the pixels may include: a third switching element, either one of a drain electrode and a source electrode of which is connected to the first terminal, and the other of which is connected to the fourth terminal, and which has a gate electrode connected to the third terminal.
The threshold voltage detection and addition unit may further include: a fourth terminal connected to the drain electrode of the driver element, and may further include: a third switching element, one of a drain electrode and a source electrode of which is connected to the first terminal, and the other of which is connected to the fourth terminal.
The threshold voltage detection and addition unit may further include: a fifth terminal; and a fourth switching element, one of a drain electrode and a source electrode of which is connected to the second terminal, and the other of which is connected to the fifth terminal.
Moreover, the present invention also provides an active matrix type display apparatus including a plurality of pixels disposed in a matrix arrangement, each of the pixels including: a light-emitting element having a first electrode and a second electrode, which emits light in response to a current supplied via the first and second electrodes; a first power line connected to the first electrode of the light-emitting element; a second power line; a signal line connected to a signal line drive circuit which supplies a luminance signal corresponding to a luminance of light emission of the light-emitting element, the luminance signal being a current signal; a first switching element, one of a drain electrode and a source electrode of which is connected to the signal line, and which has a gate electrode connected to a first scan line; a reference driver element, one of a drain electrode and a source electrode of which is connected to the other of the drain electrode and the source electrode of the first switching element, and the other of which is connected to the second power line; a driver element having a source electrode connected to the second power line, a gate electrode connected to the gate electrode of the reference driver element, and a drain electrode connected to the second electrode of the light-emitting element; a luminance signal retention capacitor having a first electrode and a second electrode, the second electrode being connected to the source electrode of the reference driver element; a second switching element, one of a drain electrode and a source electrode of which is connected to the first electrode of the luminance signal retention capacitor, and the other of which is connected to the signal line or to the drain electrode of the reference driver element; and a threshold voltage detection and addition unit having a first terminal connected to the gate electrode of the reference driver element, a second terminal connected to the first electrode of the luminance signal retention capacitor, and a third terminal connected to a second scan line, which detects a threshold voltage of the reference driver element and causes a voltage obtained by adding the threshold voltage to a potential of the second terminal to be applied at the first terminal.
According to the above configuration of the present invention, by correcting the threshold voltage on a pixel-by-pixel basis, a reduction can be made in the design withstand voltage of the output stage of the signal line drive circuit.
Here, the threshold voltage detection and addition unit may include: a threshold voltage retention capacitor having a first electrode connected to the first terminal and a second electrode connected to the second terminal.
Furthermore, the reference driver element may be an n-channel type transistor, the threshold voltage detection and addition unit may include: a first diode element having an anode terminal connected to the first terminal and a cathode terminal connected to the second terminal; and a second diode element having an anode terminal connected to the third terminal and a cathode terminal connected to the first terminal, and a threshold voltage of the first diode element may be controlled such that a value obtained by dividing an absolute value of the threshold voltage of the first diode element by an absolute value of the threshold voltage of the reference driver element becomes a positive value of 1 or less.
The reference driver element may be a p-channel type transistor, the threshold voltage detection and addition unit may include: a first diode element having a cathode terminal connected to the first terminal and an anode terminal connected to the second terminal; and a second diode element having a cathode terminal connected to the third terminal and an anode terminal connected to the first terminal, and a threshold voltage of the first diode element may be controlled such that a value obtained by dividing an absolute value of the threshold voltage of the first diode element by an absolute value of the threshold voltage of the reference driver element becomes a positive value of 1 or less.
The threshold voltage detection and addition unit may further include: a fourth terminal connected to the source electrode of the reference driver element, and each of the pixels may include: a third switching element, either one of a drain electrode and a source electrode of which is connected to the second terminal, and the other of which is connected to the fourth terminal, and which has a gate electrode connected to the third terminal.
The threshold voltage detection and addition unit may further include: a fourth terminal connected to the drain electrode of the driver element, and may further include: a third switching element, one of a drain electrode and a source electrode of which is connected to the first terminal, and the other of which is connected to the fourth terminal.
The threshold voltage detection and addition unit may further include: a fifth terminal; and a fourth switching element, one of a drain electrode and a source electrode of which is connected to the second terminal, and the other of which is connected to the fifth terminal.
The switching element or the driver element may be constituted by a field-effect transistor.
The field-effect transistor may be constituted by a thin-film transistor.
Furthermore, the light-emitting element may be an organic EL element.
The above object, other objects, features and advantages of the present invention will become apparent from the following detailed description of its preferred embodiments with reference made to the accompanying drawings.
According to an active matrix type display apparatus of the present invention, it becomes possible to set the design withstand voltage value of the output stage of the signal line drive circuit without depending on the allowable threshold voltage value of the driver element provided in each pixel, thereby realizing the lowering of the withstand voltage of the signal line drive circuit.
In addition, with the lowering of the withstand voltage of the signal line drive circuit, the downsizing and price reduction of the signal line drive circuit can also be realized.
a is a block diagram showing the configuration of an active matrix type display apparatus according to an embodiment 1 of the present invention.
b is a block diagram showing the configuration of a light-emitting element circuit included in the display apparatus according to the embodiment 1 of the present invention.
a is a circuit diagram showing the configuration of a light-emitting element circuit where the light-emitting element circuit of
b is a circuit diagram showing the configuration of a light-emitting element circuit where the light-emitting element circuit of
c is a circuit diagram showing the configuration of a light-emitting element circuit where the light-emitting element circuit of
a is a circuit diagram showing the configuration of a light-emitting element circuit where the light-emitting element circuit of
b is a circuit diagram showing the configuration of a light-emitting element circuit where the light-emitting element circuit of
1 first switching element
2 second switching element
3 third switching element
4 fourth switching element
5 fifth switching element
6 driver element
7 threshold voltage retention capacitor
8 luminance signal retention capacitor
9 light-emitting element
10 first scan line
10
b first scan line
11 second scan line
12 third scan line
13 signal line
14 first power line
15 second power line
20 threshold voltage detection and addition unit
21 current retention unit
22 reference driver element
23 signal line drive circuit
24 data writing unit
30 active matrix type display apparatus
50 pixel circuit (light-emitting element circuit)
200 first diode element
201 second diode element
Preferred embodiments of the present invention will now be described with reference to the drawings.
[Configuration of Display Apparatus]
a is a block diagram showing the configuration of an active matrix type display apparatus (hereinafter simply referred to as “display apparatus”) according to an embodiment 1 of the present invention. As illustrated in
The display panel 27 is a display device of an active matrix drive type. This display panel 27 and the signal line drive circuit 23 are connected via a plurality of signal lines, and the display panel 27 and the scan line drive circuit 25 are connected via a plurality of scan lines. Although not shown in
The signal lines and the scan lines are respectively driven by the signal line drive circuit 23 and the scan line drive circuit 25. Additionally, the signal line drive circuit 23 and the scan line drive circuit 25 are controlled by the control circuit 26 which receives the video signals.
[Configuration of Light-Emitting Element Circuit]
Next, a description will be made of the configuration of the light-emitting element circuits disposed, as mentioned above, in the matrix arrangement.
b is a block diagram showing the configuration of a light-emitting element circuit included in the display apparatus according to the embodiment 1 of the present invention. As illustrated in
When the first switching element 1 is turned on while the fifth switching element 5 is in an off state, the current signal outputted to the signal line 13 by the signal line drive circuit 23 is supplied to the current retention unit 21. The function of the current retention unit 21 is to retain the potential difference generated between the drain electrode and the source electrode of the driver element 6 as a luminance signal voltage, and further to add the threshold voltage of the driver element 6 to the above luminance signal voltage and cause the resultant voltage to be applied at the gate electrode of the driver element 6.
A data writing means 24 is made up of the above signal line drive circuit 23 and first switching element 1.
A further detailed configuration of the light-emitting element circuit is shown in
When the first switching element 1 is in the on state and the fifth switching element 5 is in the off state, the signal current outputted by the signal line drive circuit 23 flows through the driver element 6 by way of the signal line 13. At this time, because the second switching element 2 is in the on state, the voltage generated between the drain electrode and the source electrode of the driver element 6 is transmitted to the luminance signal retention capacitor 8. Thereafter, by turning the second switching element 2 off, the voltage is retained in the luminance signal retention capacitor 8.
While a signal current Idata is flowing through the driver element 6, the potential of the gate electrode of the driver element 6 is maintained by the threshold voltage detection and addition unit 20 at a higher level than the drain potential of the driver element 6 by as much as the threshold voltage of the driver element 6. Accordingly, the voltage generated and retained across both electrodes ends of the luminance signal retention capacitor 8 is represented by the following equation (4). It should be noted that B is calculated using the above equation (2).
√{square root over ( )}(2Idata/β) Equation (4)
From this, it turns out that the output voltage at the current output stage of the signal line drive circuit 23 is unaffected by the threshold voltage of the driver element 6.
An example is shown in
In addition, in the example illustrated in
Furthermore, in the example illustrated in
In the example illustrated in
The on-off operations of the first switching element 1 and the second switching element 2 are controlled by a first scan line 10, and the on-off operations of the third switching element 3 and the fourth switching element 4 are controlled by a second scan line 11. Additionally, the on-off operations of the fifth switching element 5 are controlled by a third scan line 12. These first to third scan lines 10 to 12 are driven by a scan line drive circuit.
Also in the examples shown in
The configurations shown in
Furthermore, the configuration shown in
Although an illustration and detailed description is omitted here, even a later-described configuration (embodiment 4) with the employment of a reference driver element may also incorporate such first and second diode elements as mentioned above. In this case, the threshold voltage of the first diode element may be controlled such that the value obtained by dividing an absolute value of the threshold voltage of the first diode element by an absolute value of the threshold voltage of the reference driver element becomes a positive value of 1 or less.
With the light-emitting element circuit in
As illustrated in
Then, the third scan line 12 is put in a low voltage state. The fifth switching element 5 is hereby turned off, initiating the time period C. At this point in time of the beginning of the time period C, because the potential difference between the gate electrode and the source electrode of the driver element 6 is maintained sufficiently large by the threshold voltage retention capacitor 7, the driver element 6 is in the on state.
The current that flows through the driver element 6 flows via the fourth switching element 4 to the threshold voltage retention capacitor 7, because the first switching element 1 and the fifth switching element 5 are in the off state. As a result, the potential difference that has been stored in the threshold voltage retention capacitor 7 gradually gets smaller until it eventually becomes the threshold voltage of the driver element 6. At this point in time, the driver element 6 becomes off. Now, by putting the second scan line in a low voltage state and turning the third switching element 3 and the fourth switching element 4 to an off state, the recording of the threshold voltage of the driver element 6 on the threshold voltage retention capacitor 7 is completed, and the time period C ends. At this time, the potential difference stored between both electrodes of the luminance signal retention capacitor 8 is 0 volt.
Then, the first scan line 10 is turned to a high voltage state to start a time period A. Assuming that the output current of the signal line drive circuit 23 is Idata, Idata is supplied to the current retention unit 21 via the first switching element 1 during the time period A. At this time, because the second switching element 2 is in the on state, the potential difference between the drain electrode and the source electrode of the driver element 6 is transmitted to the luminance signal retention capacitor 8. This potential difference Vds is represented by the following equation (5).
Vds=√{square root over ( )}(2Idata/β) Equation (5)
In other words, the potential difference Vgs between the gate electrode and the source electrode of the driver element 6 is made by the threshold voltage retention capacitor 7 and the luminance signal retention capacitor 8:
Vgs=√{square root over ( )}(2Idata/β)+Vth Equation (6)
The amplitude of Vds, determined by the amplitude of Idata of 0-max(Idata) obtained from the above equation (5), is the voltage width that the signal line drive circuit 23 needs to output. This voltage width, unlike the voltage width of the conventional technique obtained in accordance with the above equation (1), is not dependent on the threshold voltage of the driver element 6.
Especially where the current writing method is accomplished using an amorphous silicon TFT, because of the significant phenomenon of shifts in threshold voltage, the design of a signal line drive circuit must be made on the assumption of a large threshold voltage value in the conventional technique. In contrast, with the signal line drive circuit 23 in the present embodiment, because the threshold voltage of the driver element 6 needs not be compensated for, but only its mobility needs to be compensated, it becomes possible to lower the design withstand voltage value.
The light-emitting element circuit included in a display apparatus according to an embodiment 2, unlike in the case of the embodiment 1, has a fifth switching element 5 provided between the current retention unit and the second power line. A description will now be made of the configuration of this light-emitting element circuit in the embodiment 2.
The rest of the configuration of the light-emitting element circuit is the same as in the case of the embodiment 1, and thus its description will be omitted.
With this light-emitting element circuit, if the first switching element 1 is turned on while the fifth switching element 5 is in an off state, the current signal outputted to the signal line 13 by the signal line drive circuit 23 is supplied to the current retention unit 21. The current retention unit 21 retains the potential difference then generated between the drain electrode and the source electrode of the driver element 6 as a luminance signal voltage, and causes the value obtained by adding the threshold voltage of the driver element 6 to the luminance signal voltage to be applied at the gate electrode of the driver element 6.
A further detailed configuration of the light-emitting element circuit is shown in
Also in this embodiment 2, as in the case of the embodiment 1, when the first switching element 1 is in an on state and the fifth switching element 5 is in an off state, the signal current outputted by the signal line drive circuit 23 flows through the driver element 6 by way of the signal line 13. At this time, because the second switching element 2 is in the on state, the voltage generated between the drain electrode and the source electrode of the driver element 6 is transmitted to the luminance signal retention capacitor 8. Thereafter, by turning the second switching element 2 off, the voltage is retained in the luminance signal retention capacitor 8.
While a signal current Idata is flowing through the driver element 6, the potential of the gate electrode of the driver element 6 is maintained by the threshold voltage detection and addition unit 20 at a higher level than the drain potential of the driver element 6 by as much as the threshold voltage of the driver element 6. Accordingly, the voltage generated and retained across both electrodes ends of the luminance signal retention capacitor 8 is represented by the above equation (4).
Therefore, also in the embodiment 2, the output voltage of the current output stage of the signal line drive circuit 23 is unaffected by the threshold voltage of the driver element 6.
An example is shown in
Additionally, in the example illustrated in
In the example illustrated in
The on-off operations of the first switching element 1 and the second switching element 2 are controlled by a first scan line 10, and the on-off operations of the third switching element 3 and the fourth switching element 4 are controlled by a second scan line 11. Additionally, the on-off operations of the fifth switching element 5 are controlled by a third scan line 12. These first to third scan lines 10 to 12 are driven by a scan line drive circuit.
Also in the examples shown in
The operations of these light-emitting element circuits in
Also in the embodiment 2, as in the case of embodiment 1, the voltage width that the signal line drive circuit 23 needs to output is not dependent on the threshold voltage of the driver element 6. Consequently, the signal line drive circuit 23 needs not compensate for the threshold voltage of the driver element 6, but only needs to compensate for the mobility, making it possible to lower its design withstand voltage value.
The light-emitting element circuit included in a display apparatus according to an embodiment 3, unlike in the case of the embodiment 1, is not provided with a fifth switching element. A description will now be made of the configuration of the light-emitting element circuit in this embodiment 3.
The rest of the configuration of the light-emitting element circuit is the same as in the case of the embodiment 1, and thus its description will be omitted.
With this light-emitting element circuit, if the first switching element 1 is turned on, the current signal outputted to the signal line 13 by the signal line drive circuit 23 is supplied to the current retention unit 21. The current retention unit 21 causes the value obtained by adding the threshold voltage of the driver element 6 to the potential generated between the drain electrode and the source electrode of the driver element 6 to be applied at the gate electrode of the driver element 6, and allows the summed value to be retained by a capacitor.
A further detailed configuration of the light-emitting element circuit is shown in
If the first switching element 1 is turned on, and the first power line 14 or the second power line 15 is at a potential which causes the light-emitting element 9 to be turned off, the signal current which the signal line drive circuit 23 outputs flows through the driver element 6 by way of the signal line 13. At this time, because the second switching element 2 is in an on state, the voltage generated between the drain electrode and the source electrode of the driver element 6 is transmitted to the luminance signal retention capacitor 8. Thereafter, by turning the second switching element 2 to the off state, the voltage is retained in the luminance signal retention capacitor 8.
While a signal current Idata is flowing through the driver element 6, the potential of the gate electrode of the driver element 6 is maintained by the threshold voltage detection and addition unit 20 at a higher level than the drain potential of the driver element 6 by as much as the threshold voltage of the driver element 6. Thus, the voltage generated and retained across both electrodes ends of the luminance signal retention capacitor 8 is represented by the above equation (4).
Therefore, also in the embodiment 2, the output voltage of the current output stage of the signal line drive circuit 23 is unaffected by the threshold voltage of the driver element 6.
An example is shown in
In addition, in the example illustrated in
Furthermore, in the example illustrated in
In the example illustrated in
The on-off operations of the first switching element 1 and the second switching element 2 are controlled by the first scan line 10, and the on-off operations of the third switching element 3 and the fourth switching element 4 are controlled by the second scan line 11. These first and second scan lines 10 and 11 are driven by a scan line drive circuit.
Also in the examples shown in
The configuration shown in
With the light-emitting element circuit illustrated in
As illustrated in
Then, by turning the second power line to a low voltage state such that the potential difference between the first power line and the second power line becomes equal to or lower than the rectification starting voltage of the light-emitting element 9, the light-emitting element 9 is turned off and the time period C begins. At this point in time of the beginning of the time period C, because the potential difference between the gate electrode and the source electrode of the driver element 6 is maintained sufficiently large by the threshold voltage retention capacitor 7, the driver element 6 is in the on state.
The current that flows through the driver element 6 flows via the fourth switching element 4 to the threshold voltage retention capacitor 7 and to the light-emitting element 9, because the first switching element 1 is in the off state. As a result, the potential difference that has been stored in the threshold voltage retention capacitor 7 gradually gets smaller until it eventually becomes the threshold voltage of the driver element 6. At this point in time, the driver element 6 becomes off. Now, by putting the second scan line in a low voltage state and turning the third switching element 3 and the fourth switching element 4 to an off state, the recording of the threshold voltage of the driver element 6 on the threshold voltage retention capacitor 7 is completed, and the time period C ends. At this time, the potential difference stored between both electrodes of the luminance signal retention capacitor 8 is 0 volt.
Then, the first scan line 10 is turned to a high voltage state to start a time period A. Assuming that the output current of the signal line drive circuit 23 is Idata, Idata is supplied to the current retention unit 21 via the first switching element 1 during the time period A. At this time, because the second switching element 2 is in the on state, the potential difference between the drain electrode and the source electrode of the driver element 6 is transmitted to the luminance signal retention capacitor 8. This potential difference Vds is represented by the above equation (5), and the potential difference Vgs between the gate electrode and the source electrode of the driver element 6 is represented by the above equation (6).
Thus, also in the embodiment 3, as in the case of embodiment 1, the voltage width that the signal line drive circuit 23 needs to output is not dependent on the threshold voltage of the driver element 6. Consequently, the signal line drive circuit 23 needs not compensate for the threshold voltage of the driver element 6, but only needs to compensate for the mobility, making it possible to lower its design withstand voltage value.
In the case of the light-emitting element circuit shown in
The light-emitting element circuit included in a display apparatus according to an embodiment 4, unlike in the case of the embodiment 1, is not provided with a fifth switching element, but includes, along with a driver element, a reference driver element having characteristics equivalent to this driver element. A description will now be made of the configuration of the light-emitting element circuit in this embodiment 4.
The rest of the configuration of the light-emitting element circuit is the same as in the case of the embodiment 1, and thus its description will be omitted.
With this light-emitting element circuit, if the first switching element 1 is turned on, the current signal outputted to the signal line 13 by the signal line drive circuit 23 is supplied to the current retention unit 21. The current retention unit 21 causes the value obtained by adding the threshold voltage of the reference driver element 22 to the potential generated between the drain electrode and the source electrode of the reference driver element 22 to emerge at the gate electrode of the driver element and of the reference driver element 22, and causes the summed value to be retained by a capacitor.
A further detailed configuration of the light-emitting element circuit is shown in
When the first switching element 1 is turned on, the signal current which the signal line drive circuit 23 outputs flows through the reference driver element 22 by way of the signal line 13. At this time, because the second switching element 2 is in the on state, the voltage generated between the drain electrode and the source electrode of the reference driver element 22 is transmitted to the luminance signal retention capacitor 8. By thereafter turning the second switching element 2 off, the voltage is retained in the luminance signal retention capacitor 8.
While a signal current Idata is flowing through the reference driver element 22, the potential of the gate electrode of the reference driver element 22 is maintained by the threshold voltage detection and addition unit 20 at a higher level than the drain potential of the reference driver element 22 by as much as the threshold voltage of the reference driver element 22. Accordingly, the voltage generated and retained across both electrodes ends of the luminance signal retention capacitor 8 is represented by the above equation (4).
Therefore, also in the embodiment 2, the output voltage of the current output stage of the signal line drive circuit 23 is unaffected by the threshold voltage of the reference driver element 22.
An example is shown in
In addition, in the example illustrated in
In the example illustrated in
The on-off operations of the first switching element 1 and the second switching element 2 are controlled by the first scan line 10 and the third scan line 12, respectively. Additionally, the on-off operations of the third switching element 3 and the fourth switching element 4 are controlled by the second scan line 11. These first to third scan lines 10 to 12 are driven by a scan line drive circuit.
Also in the examples shown in
Taking the light-emitting element circuit of
As illustrated in
Then, by turning the third scan line 12 to a low voltage state, the second switching element 2 becomes off and the time period C starts. At this point in time of the beginning of the time period C, because the potential difference between the gate electrode and the source electrode of the reference driver element 22 is maintained sufficiently large by the threshold voltage retention capacitor 7, the reference driver element 22 is in the on state.
The current that flows through the reference driver element 22 flows into the threshold voltage retention capacitor 7 via the fourth switching element 4, because the first switching element 1 is in the off state. As a result, the potential difference that has been stored in the threshold voltage retention capacitor 7 gradually gets smaller until it eventually becomes the threshold voltage of the reference driver element 22. Now, by putting the second scan line in a low voltage state and turning the third switching element 3 and the fourth switching element 4 to an off state, the recording of the threshold voltage of the reference driver element 22 in the threshold voltage retention capacitor 7 is completed, and the time period C ends. At this time, the potential difference stored between both electrodes of the luminance signal retention capacitor 8 is 0 volt.
Next, the first scan line 10 is turned to a high voltage state to start a time period A. Assuming that the output current of the signal line drive circuit 23 is Idata, Idata is supplied to the current retention unit 21 via the first switching element 1 during the time period A. At this time, because the second switching element 2 is in the on state, the potential difference between the drain electrode and the source electrode of the reference driver element 22 is transmitted to the luminance signal retention capacitor 8. This potential difference Vds is represented by the above equation (5), and the potential difference Vgs between the gate electrode and the source electrode of the reference driver element 22 is represented by the above equation (6).
Thus, also in the embodiment 4, as in the case of embodiment 1, the voltage width that the signal line drive circuit 23 needs to output is not dependent on the threshold voltage of the reference driver element 22. Consequently, the signal line drive circuit 23 needs not compensate for the threshold voltage of the reference driver element 22, but only needs to compensate for the mobility, making it possible to lower its design withstand voltage value.
From the foregoing description, various improvements and other embodiments of the present invention will be apparent to a person skilled in the art. Accordingly, the above description should be construed as examples only, it being provided for the purpose of offering the skilled person the best mode for carrying out the invention. A substantial change can be made in the particulars of the structure and/or function of the present invention without departing from its spirit.
The active matrix type display apparatus of the present invention enables to make a reduction in the design withstand voltage of a signal line drive circuit, and is useful as an organic EL display apparatus and various other display apparatuses, and the like.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-327432 | Dec 2007 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2008/003776 | 12/16/2008 | WO | 00 | 8/3/2009 |
