JP5015428B2 - Display device - Google Patents

Description

  The present invention relates to an active organic EL display device that uses a transistor to drive a current-driven light-emitting element such as an electroluminescence (EL) element.

  An organic EL display device using an organic electroluminescence (EL) element that emits light by itself does not require a backlight necessary for a liquid crystal display device and is optimal for thinning the device, and there is no restriction on the viewing angle. It is expected to be put to practical use as a next generation display device. In addition, the organic EL light emitting element used for the organic EL display device is different from a liquid crystal display device or the like in which the liquid crystal cell is controlled by voltage in that it is controlled by a current value through which the luminance of each light emitting element flows.

  FIG. 9 shows a pixel circuit in another active matrix organic EL display device in the prior art. Such a pixel circuit in the prior art has an organic EL light emitting element 204 whose cathode side is connected to the negative power supply line 209, a driver element 202 whose source electrode is connected to the anode electrode of the organic EL light emitting element 204, and a drain electrode whose positive power is supplied. Connected to the line 208, the source electrode is connected to the drain electrode of the driver element 202, the gate electrode is connected between the switching element 203 connected to the control line 210, and the gate electrode and the source electrode of the driver element 202. A structure having an electrostatic capacitance 205, and a switching element 201 whose source or drain electrode is connected to the gate electrode of the driver element 202, whose drain or source electrode is connected to the signal line 207, and whose gate electrode is connected to the scanning line 206. Take. Here, the switching element 201, the switching element 203, and the driver element 202 are field-effect thin film transistors (TFTs).

  The operation of the pixel circuit will be described below. It is assumed that a voltage higher than the threshold voltage of the driver element 202 is stably held between the gate and source electrodes of the driver element 202 by the electrostatic capacitance 205, and the switching element 203 is held in the ON state by the control line 210. Accordingly, the driver element 202 is on.

  In this state, the negative power supply line 209 is set to a level higher than the potential GND of the positive power supply line 208 to keep the driver element 202 in an on state, and the potential of the anode electrode of the organic EL light emitting element 204 is equal to the potential GND of the positive power supply line 208. A reverse bias voltage is applied to and held at the organic EL light emitting element 204 so as to have the same potential. Next, after the scanning line 206 is set to a high level and the switching element 201 is turned on, the potential of the signal line 207 is applied to the gate electrode of the driver element 202. The potential of the signal line 207 is the same as the potential GND of the positive power supply line 208. At this time, the potential of the anode electrode of the organic EL light emitting element 204 becomes lower than the potential of the positive power supply line 208 according to the capacitance ratio of the electrostatic capacitance component of the organic EL light emitting element 204 and the electrostatic capacity 205. The driver element 202 is turned off through the above steps.

  Next, when the negative power supply line 209 is set to the same potential GND as that of the positive power supply line 208, the source potential of the driver element 202 decreases according to the voltage drop of the negative power supply line 209, but the gate potential of the driver element 202 is GND. 202 is turned on. Therefore, a current is supplied from the positive power supply line 208 to the anode electrode of the organic EL light emitting element 204 through the driver element 202 and the switching element 203, and the potential of the anode electrode of the organic EL light emitting element 204 gradually becomes the gate electrode of the driver element 202. And the potential difference between the anode electrode potential of the organic EL light emitting element 204 and the threshold voltage of the driver element 202 continue to rise.

  After that, the potential of the scanning line 206 is set to a low level, and the threshold voltage of the driver element 202 can be held on the source electrode of the driver element 202 by the electrostatic capacitance 205 and the electrostatic capacitance component of the organic EL light emitting element 204. This process is hereinafter referred to as “threshold voltage detection”.

  Next, the switching element 203 is turned off by the control line 210, the scanning line 206 is set to the high level, the voltage of the signal line 207 is applied to the gate electrode of the driver element 202, and the data voltage Vdata (luminance voltage) is applied to the signal line 207. Is supplied, the source electrode of the driver element 202 changes depending on the capacitance ratio of the electrostatic capacity 205 and the organic EL light emitting element 204, and the potential between the gate and source electrodes of the driver element 202 is as follows.

Vgs = {Cs / (Cs + Coled)} Vdata + Vt (Expression 1)
This potential difference Vgs is stably held by the capacitance 205. The process of adding the data voltages is hereinafter referred to as “writing”.

  Then, the switching element 203 is turned on by the control line 210, and the negative power supply line 209 is set so that the potential difference between the positive power supply line 208 and the negative power supply line 209 is sufficiently larger than the light emission start voltage of the organic EL light emitting element 204. When the voltage is lowered, the driver element 202 controls the current flowing through the organic EL light emitting element 204 according to the voltage held in the capacitance 205 in the above process, and the organic EL light emitting element 204 emits light with luminance according to the current value. Continue.

  As described above, in the pixel circuit shown in FIG. 9, once the luminance information is written, the organic EL light emitting element 204 continues to emit light at a constant luminance until the next writing is performed.

  As described above, in the pixel circuit shown in FIG. 9, once the data voltage is written, the organic EL light-emitting element 204 continues to emit light at a constant luminance until the next writing state is canceled (for example, Patent Document 1).

US2004 / 0174349A1 (2nd page, Fig. 1)

  However, in the threshold voltage detection step, the signal applied to the signal line 207 must be switched to a signal different from the luminance signal applied to each pixel, and the signal driving circuit that drives the signal line 207 must be operated at high speed. There will be an increase in power consumption. In addition, since the time required for the threshold voltage detection process occupies a large proportion of the time of one frame, the signal line 207 needs to be shared by a plurality of scanning lines in the threshold voltage detection process. Accordingly, the ratio of the time during which the organic EL light emitting element 204 emits light is about 60% at the maximum, and the current value that flows through the organic EL light emitting element 204 instantaneously increases in order to realize the necessary luminance, and the organic EL light emission. There was a problem that the life of the element 204 was shortened.

  In the present invention, a capacitance is provided between the gate electrode and the drain electrode of a driver element made of an FET such as a TFT when the light emitting element emits light, and a switching element is provided between the gate electrode and the reference power source to emit light. The threshold voltage between the gate and drain electrodes of the driver element when the element emits light is detected, and the voltage in the direction in which the driver element is turned off from the potential applied to the gate electrode of the driver element when the threshold voltage is detected is used as the pixel signal. In the signal writing process, it is possible to superimpose the luminance data on the threshold voltage without losing the threshold voltage of the driver element held in the capacitance, and at the same time, increase the ratio of the light emission time of the light emitting element. Made possible.

The present invention relates to a data writing means for writing a voltage corresponding to light emission luminance, a current value control means for controlling a driving current in accordance with the voltage written by the data writing means, and a drive controlled by the current value control means. A light emitting means that emits light upon receiving a current supply, and a power line control means for setting the voltage written by the data writing means to a state unrelated to the data voltage written before the voltage writing, In an active matrix display device that performs display by controlling light emission for each pixel arranged in a matrix, the data writing means includes a signal line for supplying a data voltage corresponding to light emission luminance, and a pixel on the signal line. A signal line driving circuit for supplying each data voltage, and a first for controlling the data voltage of the signal line to be taken into the pixel. An switching element, a scanning line for controlling the first switching element, and a scanning line driving circuit for controlling the scanning line, wherein the current value control means is responsive to a data voltage taken in by the first switching element. A driver element for flowing a driving current, a second switching element in which either a drain electrode or a source electrode is connected to a gate electrode of the driver element, and a gate electrode is connected to a reset line; A capacitance provided between a gate electrode and a drain electrode and holding a threshold voltage of the driver element and a voltage corresponding to the data voltage; a reset line for controlling the second switching element; and a reference voltage for the first voltage. A reference power line for supplying to the gate electrode of the driver element through two switching elements, The light emitting means includes a light emitting element connected to a drain electrode of the driver element, and the power supply line control means includes a positive power supply line and a negative power supply line for supplying a driving current to the light emitting element. Controlling the potential of the pair of power supply lines and the pair of power supply lines, and setting the positive power supply line on the drain electrode side of the driver element to a potential equal to or lower than the potential of the power supply line on the source electrode side of the driver element, The threshold voltage of the driver element is generated such that a potential obtained by subtracting the maximum value of the threshold voltage range of the driver element from the potential of the negative power supply line on the source electrode side of the driver element is generated at the drain electrode of the driver element. A power supply circuit for executing a detection step , wherein the data writing means is configured such that, after the threshold voltage detection step, the potential of the scanning line is electrically connected to the first switching element. And writing a pixel signal to each pixel is performed .
The display device according to the present invention includes a light emitting element that emits light according to a driving current, a driver element that is connected in series to the light emitting element and controls the driving current of the light emitting element, the light emitting element, and the driver element. Data voltage is supplied to the positive and negative power supply lines connected to both ends of the series connection, the capacitance connected between the drain electrode and the gate electrode of the driver element, and the gate electrode of the driver element. A first switching element connected to a signal line to be connected, and a second switching element connecting a gate electrode of the driver element to a reference power supply line to which a constant reference voltage is supplied. By changing the voltage or the negative voltage of the negative power supply line, the voltage of the positive power supply line is set to a voltage lower than the voltage of the negative power supply line, and the light emitting element is reverse-biased. 1 switching element is turned off, the second switching element is turned on, a voltage corresponding to the threshold voltage of the driver element is generated between the drain electrode and the gate electrode of the driver element, and the capacitance is charged, The threshold voltage detection step of the driver element is executed, and then the second switching element is turned off and the first switching element is turned on, so that the data voltage is superimposed on the gate electrode of the driver element and the static voltage is applied. Drive controlled by the driver element by charging the capacitance, executing a pixel signal writing process to each pixel, and then returning the voltages of the positive power supply line and the negative power supply line to positive voltage and negative voltage, respectively. A current is supplied to the light emitting element.

  Thus, according to the present invention, the first switching element, the second switching element, the driver element, the capacitance, and the light emitting element are provided. Then, a capacitance is installed between the gate electrode and the drain electrode of the driver element when the light emitting element emits light, and a threshold voltage between the gate and drain electrodes of the driver element when the light emitting element emits light is detected, This is charged into the electrostatic capacitance provided between the gate and drain electrodes of the driver element. Thereafter, by supplying a data voltage to the gate of the driver element, a voltage obtained by superimposing the luminance data on the threshold voltage to the voltage between the gate and drain of the driver element is obtained. Therefore, variations in the threshold voltage of the driver element can be compensated. Furthermore, by setting the reset selection switching element between the gate and source of the driver element during the reset period, the reset process, writing process, and light emission period can be sequentially scanned, and the light emission period can be secured very long. become.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the scope of the invention is not limited to the illustrated examples.

[First Embodiment]
FIG. 1 shows a display device according to a first embodiment to which the present invention is applied, and FIG. 2 shows a timing chart thereof.

  As shown in FIG. 1, the pixel circuits 1 are arranged in a matrix, and each pixel circuit has a positive power supply line 17 from the scanning line driving circuit 3 and a negative power supply line 18 from the constant power supply circuit 4. It is connected. Thus, the positive power supply line 17 and the negative power supply line 18 extend along each horizontal line, and each positive power supply line 17 and negative power supply line 18 are connected to the pixels in each row. As shown in FIGS. 4 and 5, the power supply line driven by the scanning line drive circuit 3 for each row may be a negative power supply line 18, in which case the positive power supply line 17 is a constant power supply circuit. 4 is connected.

  A scanning line 16 and a reset line 19 from the scanning line driving circuit 3 are arranged along each row in the horizontal direction, and each scanning line 16 and each reset line 19 are connected to each pixel circuit in the corresponding row. A signal line 15 from the signal line driving circuit 2 is arranged along each column in the vertical direction, and each signal line 15 is connected to each pixel circuit in the corresponding column. The scanning line 16 and the reset line 19 are sequentially selected for each row, and the data voltage for the pixels in the selected row is supplied to the signal line 15.

  Next, the configuration of the pixel circuit 1 will be described. An anode electrode of a current-driven light emitting element 14 such as an organic EL light emitting element is connected to the positive power supply line 17. The cathode electrode of the light emitting element 14 is connected to the drain electrode of the driver element 12, and the source electrode of the driver element 12 is connected to the negative power supply line 18. A capacitance 13 is connected between the gate electrode and the drain electrode of the driver element 12. The source or drain electrode of the first switching element 11 is connected to the gate electrode of the driver element 12, the drain or source electrode of the first switching element 11 is connected to the signal line 15, and the gate electrode is the scanning line 16. It is connected to the. A drain or source electrode of the second switching element 20 is also connected to the gate electrode of the driver element 12, a negative power supply line 18 is connected to the source or drain electrode of the second switching element 20, and the gate electrode is the reset line 19. It is connected to the.

  Here, the first switching element 11 and the second switching element 20 are n-type or p-type TFTs (n-type in the illustrated example), and the driver element 12 is an n-type TFT.

  The operation of the pixel circuit will be described with reference to the timing chart of FIG. 2 and FIGS. 3-1 (FIGS. 3-1, 3-1-2) to 3-3.

"Reset (threshold voltage detection) process"
First, by setting the reset line 19 to a high level, the second switching element 20 is turned on, and the gate of the driver element 12 is conducted to the negative power supply line 18, whereby the potential difference between the gate and source electrodes of the driver element 12 is reduced. 0V is turned off. Thereafter, the positive power supply line 17 is set to a potential Vp that is equal to or lower than the potential VSS of the negative power supply line 18.

  The potential of the drain electrode of the driver element 12 at the moment when the potential of the positive power supply line 17 becomes Vp is VDD-Voled + {Coled / (Cs + Coled)} (Vp-VDD) (FIG. 3-1-1). Coled is the capacitance value of the capacitive component 14 ′ of the light emitting element 14.

Here, when the maximum value of the threshold voltage range of the driver element 12 to be compensated is Vt (TFT) (> 0),
VSS-Vt (TFT) ≧ VDD-Voled
+ {Coled / (Cs + Coled)} (Vp−VDD) (Formula 2)
Vp is set so that

  The threshold voltage detection of the driver element 12 is started from the moment when the positive power supply line 17 becomes Vp. Then, a potential of VSS-Vt is generated at the drain electrode of the driver element 12 (FIG. 3-1-2).

"Writing process"
Next, after the potential of the signal line 15 is set to Vdata, the scanning line 16 is set to a high level so that the switching element 11 becomes conductive, and the pixel signal writing process (2) to each pixel is started. When the gate potential of the driver element 12 is Vdata (<VSS), the drain electrode of the driver element 12 becomes VSS−Vt + {Cs / (Cs + Coled)} (Vdata−VSS) (FIG. 3-2).

"Light emission process"
Next, the positive power supply line 17 is set to VDD so that the voltage applied to the light emitting element 14 is sufficiently larger than the threshold voltage of the light emitting element 14. Accordingly, a drive current flows through the driver element 12 in accordance with the gate-source voltage Vgs of the driver element at that time, and the light emitting element 14 emits light.

The potential difference between the gate and source electrodes of the driver element 12 is then
Vgs = VDD−VSS−Voled + (Vdata−VSS) {Coled / (Cs + Coled)} + Vt (Expression 3)
(FIG. 3-3).

Therefore, the current flowing through the driver element 12 is
id = (β / 2) (Vgs−Vt) ² = (β / 2) (VDD−VSS−Voled + (Vdata−VSS) {Coled / (Cs + Coled)}) ² (Formula 4)

  As described above, the drive current id of the light emitting element 14 flowing through the driver element 12 is not affected by the threshold voltage Vt of the driver element 12, and the threshold voltage of the driver element 12 is compensated.

  As shown in FIG. 2, the positive power supply line 17, the reset line 19, and the scanning line 16 are controlled independently for each row. That is, the signal lines 15 are arranged in the column direction, and the data voltage supplied for each horizontal period is sequentially changed. On the other hand, the positive power supply line 17, the reset line 19, and the scanning line 16 are provided in each row, and signals may be switched in units of one frame. Therefore, as shown in FIG. 2, for a specific n rows of pixels, a reset (threshold voltage detection) step, a writing step, and a light emitting step may be sequentially performed in accordance with the timing of the writing step. For this reason, it is not necessary to drive the signal line 15 at high speed, and an increase in power consumption can be suppressed. In addition, since a sufficient light emission period can be secured, a supply current to the light emitting element 14 necessary for obtaining a certain luminance can be sufficiently reduced, and the life of the light emitting element can be extended.

  The pixel circuit operates in the same manner according to the timing chart as shown in FIG. In other words, in this example, the positive power supply line 17 is kept constant at a high level VDD by the constant power supply circuit 4 ′, while the negative power supply line 18 is positively connected to the positive power supply line 3 ′ by the scanning line drive circuit 3 ′. While the power supply line 17 is maintained at Vp, it is maintained at a voltage equal to or higher than VDD. As a result, the same operation as in the above-described FIG. 2 can be obtained.

In this case, the gate-source voltage Vgs of the driver element 12 of the above-described formula 3 is
Vgs = VDD−VSS−Voled + (Vdata−Vp) {Coled / (Cs + Coled)} + Vt (Expression 3)
It becomes.

[Second Embodiment]
FIG. 6 shows another pixel circuit to which the present invention is applied. This pixel circuit includes a light emitting element 34 connected to a positive power supply line 137, a driver element 32 having a drain electrode connected to a cathode electrode and a source electrode of the light emitting element 34, and a gate electrode of the driver element 32. The capacitance 33 connected between the drain electrode and the drain electrode, the source or drain electrode is connected to the gate electrode of the driver element 32, the drain or source electrode is connected to the signal line 135, and the gate electrode is connected to the scanning line 136. The drain or source electrode is connected to the gate electrode of the first switching element 31 and the driver element 32 connected to each other, the source or drain electrode is connected to the reference power supply line 140, and the gate electrode is connected to the reset line 139. A second switching element 35 is included. The first switching element 31 and the second switching element 35 are n-type or p-type TFTs (n-type in the illustrated example), and the driver elements 32 are n-type TFTs.

  As described above, in the second embodiment of FIG. 6, the reference power supply line 140 that is maintained at the reference voltage Vr lower than VSS by the reference power supply circuit is provided, and the second switching element 35 is provided in the reference power supply line 140. Source or drain is connected.

The pixel circuit operates according to the timing chart of FIG. As a result, the voltage applied between the gate and source electrodes of the driver element 32 is
Vgs = VDD−VSS−Voled + (Vdata−Vr) {Coled / (Cs + Coled)} + Vt (Formula 5)
It becomes.

Therefore, the current flowing through the driver element 12 is
id = (β / 2) (Vgs−Vt) ² = (β / 2) (VDD−VSS−Voled + (Vdata−Vr) {Coled / (Cs + Coled)}) ² (Equation 6)
Thus, as in the first embodiment, the threshold voltage of the driver element 32 is compensated. In this example, the voltage of the positive power supply line 137 is switched between VDD and Vp. When switching the voltage of the negative power supply line 138, it is necessary to switch the reference voltage in the same manner as the voltage of the negative power supply line 138.

[Third Embodiment]
FIG. 7 shows another pixel circuit to which the present invention is applied, and FIG. 8 shows a timing chart thereof. In this way, the light emitting element 44 whose cathode electrode is connected to the negative power supply line 148, the driver element 42 whose drain electrode is connected to the anode electrode of the light emitting element 44 and whose source electrode is connected to the positive power supply line 147, and the driver element The capacitance 43 connected between the gate electrode and the drain electrode of 42, the source or drain electrode is connected to the gate electrode of the driver element 42, the drain or source electrode is connected to the signal line 145, and the gate electrode is The drain or source electrode is connected to the first switching element 41 connected to the scanning line 146, the gate electrode of the driver element 42, the source or drain electrode is connected to the positive power line 147, and the gate electrode is connected to the reset line 149. The second switching element 45 is provided.

  The first switching element 41 and the second switching element 45 are n-type or p-type TFTs (n-type in the illustrated example), while the driver elements 42 are p-type TFTs.

The operation of the pixel circuit will be described with reference to the timing chart of FIG. 8 and FIG. First, the reset line 149 is set to a potential at which the second switching element 45 becomes conductive, the potential difference between the source and gate electrodes of the driver element 42 is set to 0 V, and the driver element 42 is turned off. Vp is higher than the power supply potential VDD. The potential of the drain electrode of the instantaneous driver element 42 when the potential of the negative power supply line 148 becomes Vp is Voled + VSS + {Coled / (Cs + Coled)} (Vp−VSS). Here, if the threshold voltage range of the driver element 42 to be compensated is Vt (TFT) (<0),
VDD−Vt (TFT) ≦ Voled + VSS + {Coled / (Cs + Coled)} (Vp−VDD) (Expression 7)
Vp is set so that

The threshold voltage detection step (1) of the driver element 42 is started from the moment when the negative power supply line 148 becomes Vp. A potential of VDD-Vt is generated at the drain electrode of the driver element 42. Next, the reset line 149 is set to a potential at which the second switching element 45 is turned off, the potential of the signal line 145 is set to Vdata, and then the scanning line 146 is turned on to turn off the first switching element 41. The pixel signal writing process (2) starts. When the scanning line 146 is set so that the first switching element 41 becomes conductive and the gate potential of the driver element 42 is Vdata (> VDD), the drain electrode of the driver element 42 is VDD + {Cs / (Cs + Coled)} ( Vdata−VDD) −Vt. Next, the negative power supply line 148 is set to VSS so that the voltage applied to the light emitting element 44 is sufficiently larger than the threshold voltage of the light emitting element 44. The potential difference between the source and gate electrodes of the driver element 42 is then
Vsg = VDD−Voled−VSS + (Vdata−VDD) {Coled / (Cs + Coled)} − Vt (Equation 8)
It becomes.

Therefore, the current flowing through the driver element 42 is id = (β / 2) (Vsg + Vt) ² = (β / 2) (VDD−Voled−VSS + (Vdata−VDD) {Coled / (Cs + Coled)}) ² (Formula 9)
It becomes.

  Therefore, also in this embodiment, the threshold voltage of the driver element 42 is compensated as in the case described above. Furthermore, a reference power supply line that supplies a reference voltage higher than the voltage of the positive power supply line 147 may be provided separately to connect the second switching element 45 to the reference power supply line.

  Similarly to the above, the voltage of the negative power supply line 148 may be changed to make the voltage of the positive power supply line 147 constant. When the power supply voltage of the negative power supply line 148 is changed using the reference power supply line, the voltage of the reference power supply line may be changed in conjunction with the voltage of the negative power supply line 148.

  As described above, according to each of the above-described embodiments, the first switching element, the second switching element, the driver element, the capacitance, and the current-emitting light emitting element such as the organic EL light emitting element are included in one pixel. Provided. Then, a capacitance is installed between the gate electrode and the drain electrode of the driver element when the light emitting element emits light, and a threshold voltage between the gate and drain electrodes of the driver element when the light emitting element emits light is detected, This is charged into the electrostatic capacitance provided between the gate and drain electrodes of the driver element. Thereafter, by supplying a data voltage to the gate of the driver element, a voltage obtained by superimposing the luminance data on the threshold voltage to the voltage between the gate and drain of the driver element is obtained. Therefore, variations in the threshold voltage of the driver element can be compensated. Furthermore, by setting the reset selection switching element between the gate and source of the driver element during the reset period, the reset process, writing process, and light emission period can be sequentially scanned, and the light emission period can be secured very long. Became.

It is a figure which shows the whole structure of the 1st Embodiment of this invention. It is a timing chart of embodiment of FIG. It is a figure explaining the state of the reset (threshold voltage detection) initial stage of FIG. It is a figure explaining the state of the reset (threshold voltage) detection process final stage of FIGS. It is a figure explaining the state of the writing process of FIGS. It is a figure explaining the state of the light emission process of FIGS. It is a figure explaining other embodiment of FIG. 5 is a timing chart of the embodiment of FIG. It is a figure explaining the 2nd Embodiment of this invention. It is a figure explaining the 3rd Embodiment of this invention. It is a timing chart of embodiment of FIG. It is a figure which shows the conventional pixel circuit.

Explanation of symbols

  1 pixel circuit, 2 signal line drive circuit, 3 scanning line drive circuit, 4 constant power supply circuit, 5 negative power supply circuit, 11, 31, 41 first switching element, 12, 32, 42, 202 driver element, 13, 33, 43, 205 Capacitance, 14, 34, 44, 204 Light emitting element, 15, 135, 145, 207 Signal line, 16, 136, 146, 206 Scan line, 17, 137, 147, 208 Positive power supply line, 18, 138, 148, 209 Negative power line, 19, 139, 149 Reset line, 20, 35, 45 Second switching element, 140 Reference power line, 201, 203 Switching element, 210 Control line.

Claims (13)

Data writing means for writing a voltage corresponding to the emission luminance;
Current value control means for controlling the drive current according to the voltage written by the data writing means;
A light emitting means for emitting light upon receiving a drive current controlled by the current value control means;
Power supply line control means for bringing the voltage written by the data writing means into a state unrelated to the data voltage written before the voltage writing;
In an active matrix display device that performs display by controlling light emission for each pixel arranged in a matrix,
The data writing means includes
A signal line for supplying a data voltage corresponding to the emission luminance;
A signal line driving circuit for supplying a data voltage for each pixel to the signal line;
A first switching element for controlling the data voltage of the signal line to be taken into the pixel;
A scanning line for controlling the first switching element;
A scanning line driving circuit for controlling the scanning line;
With
The current value control means includes
A driver element for passing a driving current in accordance with the data voltage captured by the first switching element;
A second switching element having a drain electrode or a source electrode connected to the gate electrode of the driver element and a gate electrode connected to the reset line;
A capacitance that is provided between the gate electrode and the drain electrode of the driver element and holds a threshold voltage of the driver element and a voltage corresponding to the data voltage;
A reset line for controlling the second switching element;
A reference power line for supplying a reference voltage to the gate electrode of the driver element through the second switching element;
With
The light emitting means includes
A light emitting element connected to the drain electrode of the driver element;
With
The power line control means includes:
A pair of power supply lines, each consisting of a positive power supply line and a negative power supply line, for supplying a drive current to the light emitting element;
By controlling the potential of the pair of power supply lines, the positive power supply line on the drain electrode side of the driver element is set to a potential equal to or lower than the potential of the power supply line on the source electrode side of the driver element, and the drain electrode of the driver element A power supply for performing the threshold voltage detection step of the driver element by generating a potential of a value obtained by subtracting the maximum value of the threshold voltage range of the driver element from the potential of the negative power supply line on the source electrode side of the driver element A supply circuit;
Equipped with a,
The data writing means executes a step of writing a pixel signal to each pixel by setting the potential of the scanning line to the conductive state after the threshold voltage detecting step so that the first switching element is in a conductive state. A display device characterized by that.   The display device according to claim 1, wherein the power supply line control unit switches a potential of one of a positive power supply line and a negative power supply line.   The display device according to claim 2, wherein the driver element is n-type, a drain electrode is connected to the light emitting element, and a source electrode is connected to the negative power supply line.   The display device according to claim 3, wherein the reference power supply line is connected to the negative power supply line. The display device according to claim 2, wherein the driver element is p-type, a drain electrode is connected to the light emitting element, and a source electrode is connected to the negative power supply line.   The display device according to claim 5, wherein the reference power supply line is connected to the positive power supply line.   7. The pixel voltage writing performed by the data writing unit and the threshold voltage detection performed by the current value control unit are performed by sequential scanning for each scanning line. The display device described in one.   The voltage held in the capacitance is a difference voltage between the potentials of the gate electrode and the drain electrode of the driver element, and holds a voltage corresponding to a threshold voltage of the driver element and the data voltage. The display device according to any one of claims 1 to 7.   The display device according to claim 1, wherein the driving threshold voltage is a driving threshold voltage between a gate electrode and a drain electrode of the driver element.   The display device according to claim 1, wherein the first switching element, the second switching element, and the driver element are field effect transistors.   The display device according to claim 10, wherein the field effect transistor is a thin film transistor.   The display device according to claim 1, wherein the light emitting element is an organic EL. A light emitting element that emits light according to a drive current;
A driver element that is connected in series to the light emitting element and controls the drive current of the light emitting element;
A positive power line and a negative power line connected to both ends of the series connection of these light emitting elements and driver elements,
A capacitance connected between a drain electrode and a gate electrode of the driver element;
A first switching element connecting a gate electrode of the driver element to a signal line to which a data voltage is supplied;
A second switching element for connecting a gate electrode of the driver element to a reference power supply line to which a constant reference voltage is supplied;
Including
The positive voltage of the positive power supply line or the negative voltage of the negative power supply line is changed so that the voltage of the positive power supply line is lower than the voltage of the negative power supply line, and the light emitting element is reverse-biased. The device is turned off, the second switching device is turned on, a voltage corresponding to the threshold voltage of the driver device is generated between the drain electrode and the gate electrode of the driver device, the electrostatic capacity is charged, and the driver Execute the threshold voltage detection process of the element,
Next, by turning off the second switching element and turning on the first switching element, the data voltage is superimposed on the gate electrode of the driver element to charge the capacitance, and the pixel signal to each pixel Execute the writing process of
After that, by returning the voltages of the positive power supply line and the negative power supply line to positive voltage and negative voltage, respectively, a driving current controlled by the driver element is supplied to the light emitting element.

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