JP2011013293A - Electronic apparatus and method for driving electronic apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electronic apparatus and a method for driving an electronic apparatus that allows an OLED (organic electro-luminescence) to emit light at predetermined luminance.SOLUTION: The electronic apparatus includes a pixel circuit 11(i, j) including a transistor T4. The gate of the transistor T4 is connected to an auxiliary scanning line Ls2(j). When a transistor T2 is turned on and the transistor T4 is turned off, a capacitor Cs is disconnected from a gate-source line of a transistor T3. When a data driver supplies a gradation current to a data line Ld(i), an output voltage of the data driver immediately rises to become a voltage value obtained by adding the gradation voltage to the threshold voltage of the transistor T3. The data driver measures the voltage value and applies the voltage of the voltage value to the data line Ld(i). As the voltage is written in the capacitor Cs according to a voltage writing system, insufficient writing is eliminated even in a low gradation level. As the threshold voltage is added, the OLED 101 can emit light at a luminance corresponding to the preset gradation voltage.

Description

  The present invention relates to an electronic device and a method for driving the electronic device.

  OLED (Organic Electro-Luminescence) emits light by applying a DC voltage to a fluorescent organic compound that is excited by applying an electric field, and is attracting attention as a next-generation display device. There is a display device as an electronic apparatus in which a display panel is configured by arranging OLEDs in a matrix.

  This OLED is a current driving element and emits light with a luminance proportional to the flowing current. A display device including such an OLED includes a driving transistor configured by a field effect transistor (thin film transistor) in each pixel, and the driving transistor supplies a current to the OLED while controlling a current value.

  In addition, since the OLEDs are arranged in a matrix, a capacitor is connected between the gate and the source of the driving transistor, and a voltage corresponding to the gradation of the image data supplied from the outside is written into the capacitor. Hold this voltage.

  When a voltage is applied between the drain and the source of the driving transistor, the voltage held by the capacitor is set as a gate-source voltage (hereinafter referred to as “gate voltage”) Vgs, and the current value at the gate voltage Vgs. Is supplied to the OLED. The OLED emits light with a luminance corresponding to the supplied amount of current, and the display device displays an image.

  As a method for writing a voltage to the capacitor, a voltage writing method in which a specified voltage is applied to the source as the lower end of the current path of the driving transistor, and a specified current is supplied (drawn) to the source of the driving transistor. There is a current writing method (see, for example, Patent Document 1).

JP 2003-195810 A (page 11, FIG. 1, FIG. 5)

  However, both the voltage writing method and the current writing method have advantages and disadvantages. That is, in the voltage writing method, although the period for writing the voltage to the capacitor is short, the threshold voltage Vth of the driving transistor shifts with time, so correction corresponding to the shift amount of the threshold voltage Vth must be performed.

  Also, the threshold voltage Vth may vary between pixels, and correction corresponding to this variation must be performed. The correction corresponding to the shift amount of the threshold voltage Vth and the correction method corresponding to the variation are complicated, and if the correction is not properly performed, the image cannot be displayed with the correct gradation.

  On the other hand, in the current writing method, if a specified current flows, the voltage can be written regardless of the threshold voltage Vth shift of the driving transistor and the variation of the threshold voltage Vth among the pixels, so the accuracy of the voltage written to the capacitor is good. .

  However, with this current writing method, especially in the case of a low gradation image, the writing current is reduced, and a voltage corresponding to the gradation of the image data cannot be written to the capacitor within a certain period. The so-called writing voltage is insufficient, and the organic EL element cannot emit light with a preset brightness (gradation).

  The present invention has been made in view of such conventional problems, and an object of the present invention is to provide an electronic device capable of causing a light emitting element to emit light with a preset luminance and a method for driving the electronic device. .

In order to achieve this object, an electronic device according to the first aspect of the present invention provides:
A light emitting element that emits light at a luminance corresponding to the current value of the supplied current;
A lower end of a current path is connected to one end of the light emitting element, and a current is supplied to the light emitting element while controlling a current value of a current flowing through the current path based on a control voltage between a control end and the lower end of the current path. A driving transistor to be supplied;
A capacitor connected between the control end of the drive transistor and the lower end of the current path to hold the control voltage;
A switch transistor that disconnects or connects the capacitor between the control end of the drive transistor and the lower end of the current path;
A first driver for driving the switch transistor;
When the first driver drives the switch transistor and the capacitor is disconnected from between the control end of the drive transistor and the lower end of the current path, a current having a current value corresponding to the luminance of the light emitting element Is pulled from the current path of the drive transistor, the voltage value of the current path of the drive transistor is measured, and when the capacitor is connected between the control end of the drive transistor and the lower end of the current path A second driver that writes the voltage of the measured voltage value by applying it across the capacitor;
A third driver for causing the light emitting element to emit light by applying a voltage to an upper end of the current path of the driving transistor after the second driver writes a voltage across the capacitor; To do.

The second driver is:
A current output drawn from the current path of the drive transistor when the first driver drives the switch transistor and the capacitor is disconnected from between the control end of the drive transistor and the lower end of the current path; And
A voltage measuring unit that measures the line voltage of the signal line between the current path of the drive transistor and the lower end of the current path as the voltage of the current path of the drive transistor when the current output unit draws the current;
When the first driver drives the switch transistor and the capacitor is connected between the control end of the drive transistor and the lower end of the current path, the voltage of the voltage value measured by the voltage measurement unit is obtained. And a voltage output unit that applies and writes to both ends of the capacitor.

The first driver is:
The switch transistor is turned off to disconnect the capacitor from between the control end of the drive transistor and the lower end of the current path, and the switch transistor is turned on to connect the capacitor to the control end of the drive transistor and the current. You may make it connect between a road lower end.

The switch transistor as a first switch transistor,
A plurality of pixel circuits having the light emitting element, the driving transistor, the capacitor, the first switch transistor, and a second switch transistor that is turned on when a row selection signal is supplied are arranged in a matrix.
The first driver selects a row by supplying a row selection signal to the second switch transistor via a scanning line, and performs drive control via the auxiliary scanning line during a selection period in which the row is selected. The first switch transistor may be driven on and off by supplying a signal to the first switch transistor in the selected row.

An electronic device driving method according to a second aspect of the present invention includes:
A light emitting element that emits light at a luminance corresponding to the current value of the supplied current;
A lower end of a current path is connected to one end of the light emitting element, and a current is supplied to the light emitting element while controlling a current value of a current flowing through the current path based on a control voltage between a control end and the lower end of the current path. A driving transistor to be supplied;
A capacitor connected between the control end of the drive transistor and the lower end of the current path to hold the control voltage;
Separating the capacitor from between the control end of the drive transistor and the lower end of the current path;
Drawing a current having a current value corresponding to the luminance of the light emitting element from the current path of the driving transistor;
Measuring a voltage value of the current path of the drive transistor;
Connecting the capacitor between the control end of the driving transistor and the lower end of the current path;
Applying and writing the voltage of the measured voltage value across the capacitor;
And a step of applying a voltage to the upper end of the current path of the driving transistor to cause the light emitting element to emit light after writing a voltage across the capacitor.

  According to the present invention, the light emitting element can emit light with a preset brightness.

It is a block diagram which shows the structure of the display apparatus which concerns on embodiment of this invention. FIG. 2 is a circuit diagram illustrating a configuration of each pixel circuit illustrated in FIG. 1. FIG. 2 is a block diagram illustrating a configuration of a data driver illustrated in FIG. 1. FIG. 3 is a diagram showing a relationship between a drain voltage (gate voltage) and a gradation current of the driving transistor shown in FIG. 3 is a timing chart illustrating an operation of the display device illustrated in FIG. 1. 3 is a timing chart showing detailed operations of the display device shown in FIG. 1. It is a figure which shows the relationship between the drain voltage (gate voltage) of a drive transistor, and a gradation current when a threshold voltage shifts.

  Hereinafter, a display device according to an embodiment of the present invention will be described with reference to the drawings. In the present embodiment, the electronic apparatus is described as a display device including a TFT-OLED (Thin Film Transistor-Organic light-emitting diode).

FIG. 1 shows the configuration of the display device 1 according to the present embodiment.
The display device 1 according to this embodiment includes a TFT panel 11, a scan driver 12, an anode driver 13, a data driver 14, and a control unit 15.

  The TFT panel 11 includes a plurality of pixel circuits 11 (i, j) (i = 1 to m, j = 1 to n, m, n: natural numbers).

  Each of the pixel circuits 11 (i, j) is a circuit corresponding to one pixel of the two-dimensional display data Pic, and is arranged in a matrix. As shown in FIG. 2, each pixel circuit 11 (i, j) includes an OLED 101, transistors T1 to T4, and a capacitor Cs.

  The OLED 101 is a light emitting element that emits light with a luminance corresponding to a current value of a supplied current, and has a structure in which a pixel electrode, an organic EL layer including a plurality of carrier transport layers, and a counter electrode are stacked. A ground voltage GND is applied to the counter electrode (cathode electrode).

  The transistors T1 to T4 are polysilicon or amorphous silicon thin film transistors (TFTs) formed of n-channel FETs (Field Effect Transistors).

  The transistor T3 is a drive transistor that supplies a current to the OLED 101 while controlling a current value based on a gate-source voltage (hereinafter referred to as “gate voltage”) Vgs as a control voltage.

  The gate as the control end of the transistor T3 is connected to the source of the transistor T1 and one end of the capacitor Cs, the drain as the upper end of the current path is connected to the anode line La (j), and the source as the lower end of the current path is the transistor T2. , The source of the transistor T4, and the anode (electrode) of the OLED 101.

  The transistor T1 is a transistor for applying the voltage of the signal Vscan1 (j) to one end of the capacitor Cs.

  In the pixel circuit 11 (i, j), the source of the transistor T1 is connected to the gate of the transistor T3 and one end of the capacitor Cs, and the drain is connected to the drain of the transistor T3.

  The gates of the transistors T1 of the pixel circuits 11 (1, j),..., 11 (m, j) are connected to the scanning line Ls1 (j), respectively. When the VscanH level signal Vscan1 (j) is output to the scanning lines Ls1 (1),..., Ls1 (n), respectively, the pixel circuits 11 (1, j),. , j) is turned on.

  In the case of the pixel circuit 11 (1,1), when a VscanH level signal is output from the scan driver 12 to the scanning line Ls1 (1), the transistor T1 is turned on, and a VscanL level signal is output to the scanning line Ls1 (1). When output, the transistor T1 is turned off. When the transistor T1 is turned off, the charge charged in the capacitor Cs is held.

  The transistor T2 is a switch transistor that is selected and turned on and off by the scan driver 12 to conduct and cut off between the data line Ld (i) and the sources of the transistors T3 and T4 and the OLED 101.

  The drain of the transistor T2 of each pixel circuit 11 (i, j) is connected to the sources of the transistors T3 and T4 and the anode (electrode) of the OLED 101, and the source is connected to the data line Ld (i).

  The gates of the transistors T2 of the pixel circuits 11 (1,1) to 11 (m, 1) are connected to the scanning line Ls1 (1). Similarly, the gate of the transistor T2 of each of the pixel circuits 11 (1,2) to 11 (m, 2) is connected to the scanning line Ls1 (2),..., And each pixel circuit 11 (1, n) to 11 (m , n) of the transistor T2 is connected to the scanning line Ls1 (n).

  Further, the source as the other end of the transistor T2 of each pixel circuit 11 (1,1) to 11 (n, 1) is connected to the data line Ld (1). Similarly, the source of the transistor T2 of each pixel circuit 11 (2,1) to 11 (2, n) is connected to the data line Ld (2),..., And each pixel circuit 11 (m, n) to 11 (11). The source of the transistor T2 of m, n) is connected to the data line Ld (m).

  In the case of the pixel circuit 11 (1, 1), the transistor T2 is turned on when a signal of VscanH level is output from the scan driver 12 to the scanning line Ls1 (1), and the source of the transistors T3 and T4, the anode of the OLED 101, and the data. Connect the line Ld (1).

  Further, when a VscanL level signal is output to the scanning line Ls1 (1), the transistor T2 is turned off, and the sources of the transistors T3 and T4, the anode of the OLED 101, and the data line Ld (1) are cut off.

  The transistor T4 is a switch transistor that disconnects or connects the capacitor Cs from the gate to the source of the transistor T3.

  The transistor T4 has a drain connected to the other end of the capacitor Cs, and a source connected to the drain of the transistor T2, the source of the transistor T3, and the anode of the OLED 101.

  The gate of the transistor T4 is connected to the auxiliary scanning line Ls2 (j), and the gate is supplied with the Vscan'L level signal Vscan2 (j) to be turned off, and the Vscan'H level signal Vscan2 (j) is supplied. Supplied and turned on.

  The capacitor Cs has an auxiliary capacity for holding the gate voltage Vgs of the transistor T3, and one end thereof is connected to the gate of the transistor T3 and the source of the transistor T1. The capacitor Cs holds the gate voltage Vgs of the transistor T3 when the transistors T1 and T2 are turned off.

  Returning to FIG. 1, the scan driver 12 is supplied with the clock signal DotCLK, the vertical control signal Vsync, and the horizontal control signal Hsync from the control unit 15, and in accordance with these supplied control signals, the pixel circuit 11 (1) in the j-th row. , j) to 11 (m, j), and the transistors T4 of the pixel circuits 11 (1, j) to 11 (m, j) in the selected j-th row are turned on and off.

  The scan driver 12 sequentially outputs the VscanH level signals Vscan1 (1) to Vscan1 (n) to the scanning lines Ls1 (1),..., Ls1 (n), whereby the pixel circuit in the first row. 11 (1,1) to 11 (m, 1),..., Nth row pixel circuits 11 (1, n) to 11 (m, n) are selected. The period during which the VscanH level signal Vscan1 (j) is output is the selection period of the jth row.

  Further, the scan driver 12 uses Vscan as a drive control signal for turning off the transistors T4 of the pixel circuits 11 (1, j) to 11 (m, j) in the selected j-th row in the first half of the selection period. A signal Vscan2 (j) of 'L (<VscanH) level is output to the auxiliary scanning line Ls2 (j). The first half of this selection period is defined as period Tm1.

  In addition, the scan driver 12 uses Vscan as a drive control signal for turning on the transistor T4 of the pixel circuit 11 (1, j) to 11 (m, j) in the selected j-th row in the latter half of the selection period. The 'H level signal Vscan2 (j) is output to the auxiliary scanning line Ls2 (j). The latter half of the selection period is referred to as period Tm2.

  The anode driver 13 is a driver that supplies current between the drain and the source as a current path of the transistor T3 of each pixel circuit 11 (i, j).

  The anode driver 13 is supplied with the clock signal DotCLK, the vertical control signal Vsync, and the horizontal control signal Hsync from the control unit 15, and in synchronization with these supplied control signals, the anode lines La (1) to La (n). In addition, signals Vanode (1) to Vanode (n) of the voltage VanodeH or the ground voltage GND are output, respectively.

  The anode driver 13 has a power supply of voltage VanodeH-GND and a power supply of GND-Vss (negative voltage). In this embodiment, the voltage VanodeH is set to + 15V, for example.

  The data driver 14 sequentially supplies the gradation voltages Vdata (1) to Vdata (1) to Vdata (1) from the first row to the nth row as voltages having a voltage value corresponding to the gradation of the display data Pic. m) is supplied, and voltages based on the gradation voltages Vdata (1) to Vdata (m) are applied to the pixel circuits 11 (1,1) to 11 (1, m),. The driver writes to each capacitor Cs of n) to 11 (m, n).

  The data driver 14 is supplied with the clock signal DotCLK, the vertical control signal Vsync, and the horizontal control signal Hsync from the control unit 15, and operates according to these supplied control signals.

  As shown in FIG. 3, the data driver 14 includes a shift register 21, a data register 22, and blocks 23 (1) to 23 (m).

  The shift register 21 sequentially shifts the supplied gradation voltages Vdata (1) to Vdata (m) as digital data from the control unit 15, and the shifted gradation voltages Vdata (1) to Vdata (m). ) Is supplied to the data register 22.

  The data register 22 holds the voltage values of the gradation voltages Vdata (1) to Vdata (m) supplied from the shift register 21. The data register 22 is supplied with the gradation current Idata (i) corresponding to the gradation voltage Vdata (i) from each block 23 (i) (i = 1 to m) to the data line Ld (i). Line voltage VLd (i) is supplied, and the voltage value of the gradation voltage Vdata (i) is rewritten to the voltage value of the line voltage VLd (i).

  The block 23 (i) includes D / A converters 31 (i) and 32 (i), a current output unit 33 (i), a voltage measurement unit 34 (i), and an A / D converter 35 ( i), a voltage output unit 36 (i), a changeover switch Sw (i), and a changeover control unit 37 (i).

  The D / A converter 31 (i) and the current output unit 33 (i) are configured to write a voltage to the capacitor Cs of the selected pixel circuit 11 (i, j) according to the current writing method.

  The D / A converter 32 (i) and the voltage output unit 36 (i) are configured to write a voltage to the capacitor Cs of the selected pixel circuit 11 (i, j) according to the voltage writing method. .

  The D / A converters 31 (i) and 32 (i) convert the digital data of the gradation voltage Vdata (i) held in the data register 22 into an analog gradation voltage Vdata (i). .

  The current output unit 33 (i) converts the gradation voltage Vdata (i) converted by the D / A converter 31 (i) into the gradation current Idata (i), and the converted gradation current Idata (i). The data line Ld (i) is supplied.

  The current output unit 33 (i) generates a gray-scale current Idata when the capacitor Cs of the pixel circuit 11 (i, j) is disconnected from the drain-source of the transistor T3 in the selected period Tm1 of the j-th row. By supplying (i) to the data line Ld (i), a current is drawn from between the drain and source of the transistor T3.

  One end of the current output unit 33 (i) is connected to one end of the changeover switch Sw (i) on the current output unit 33 (i) side, and the other end is connected to the negative voltage Vss line.

  The gradation current Idata (i) of the current output unit 33 (i) corresponds to the drain current Id of the transistor T3.

  The voltage measuring unit 34 (i) measures the voltage value (analog) of the line voltage VLd (i) of the data line Ld (i) when the current output unit 33 (i) draws a current. If the line resistance of the data line Ld (i) is ignored, the line voltage VLd (i) corresponds to the drain voltage Vds (or gate voltage Vgs) of the transistor T3.

  If the line resistance is known in advance, a voltage obtained by subtracting the voltage drop due to the line resistance from the line voltage VLd (i) becomes the drain voltage Vds of the transistor T3.

  The drain current Id and the drain voltage Vds of the transistor T3 have a relationship as shown in FIG. As shown in FIG. 4, when the drain voltage Vds when the drain current Id flows by the current value a1 is Vd1, the voltage value Vd1 includes the threshold voltage (value) Vth1.

  That is, if this voltage value Vd1 can be acquired, the compensation process for the threshold voltage Vth1 becomes unnecessary. If the voltage of the voltage value Vd1 is written into the capacitor Cs according to the voltage writing method, the OLED 101 can emit light with the luminance corresponding to the gradation of the display data Pic, and the lack of writing is solved even at a low gradation. Is done.

  The A / D converter 35 (i) converts the analog voltage value Vdx of the line voltage VLd (i) measured by the voltage measuring unit 34 (i) into digital data. The A / D converter 35 (i) supplies the digital data of the converted voltage value Vdx to the data register 22.

  The voltage output unit 36 (i) outputs an analog signal converted by the D / A converter 32 (i). One end of the voltage output unit 36 (i) is connected to one end of the changeover switch Sw (i) on the voltage output unit 36 (i) side, and the other end is connected to the negative voltage Vss line.

  The changeover switch Sw (i) is a switch for connecting or disconnecting the current output unit 33 (i) and the data line Ld (i), or the voltage output unit 36 (i) and the data line Ld (i). is there.

  The switching control unit 37 (i) is supplied with the switching control signal Csw from the control unit 15, and controls switching of the switching switch Sw (i) according to the supplied switching control signal Csw.

  When the switching control signal Csw (I) is supplied from the control unit 15 as the switching control signal Csw, the switching control unit 37 (i) connects the current output unit 33 (i) and the data line Ld (i). In this manner, the changeover switch Sw (i) is controlled.

  When the switching control signal Csw (V) is supplied from the control unit 15 as the switching control signal Csw, the switching control unit 37 (i) connects the voltage output unit 36 (i) and the data line Ld (i). In this manner, the changeover switch Sw (i) is controlled.

  The control unit 15 controls each of these drivers by supplying control signals to the scan driver 12, the anode driver 13, and the data driver 14.

  The control unit 15 is supplied with control signals such as a clock signal DotCLK, a vertical control signal Vsync, and a horizontal control signal Hsync as control signals from the outside, and supplies these control signals to the scan driver 12, the anode driver 13, and the data driver 14. To do.

  Further, the control unit 15 is supplied with two-dimensional display data Pic from the outside, and the pixel circuits 11 (1,1) to 11 (m, 1),..., 11 (1, n) to 11 (m , n) digital data of gradation voltages Vdata (1) to Vdata (m) corresponding to each gradation degree is generated, and the generated gradation voltages Vdata (1) to Vdata (m) are generated for each row by the data driver 14. To supply.

  Further, the control unit 15 supplies a switching control signal Csw to the data driver 14 as a control signal.

  The control unit 15 supplies the switching control signal Csw to the data driver 14, thereby controlling the switching control unit 37 (i) and the changeover switch Sw (i).

Next, the operation of the display device 1 according to this embodiment will be described.
As shown in FIG. 5, the control unit 15 supplies control signals such as the clock signal DotCLK, the vertical control signal Vsync, and the horizontal control signal Hsync to the scan driver 12, the anode driver 13, and the data driver 14 at time t10.

  The scan driver 12, the anode driver 13, and the data driver 14 each start to operate in synchronization with the supplied control signal.

  The anode driver 13 outputs the signals Vanode (1) to Vanode (n) of the ground voltage GND to the anode lines La (1) to La (n) at times t10 to t17, respectively.

  At times t10 to t12, the scan driver 12 outputs a VscanH level signal Vscan1 (1) to the scanning line Ls1 (1). These times t10 to t12 are the selection period of the pixel circuits 11 (1,1) to 11 (m, 1), and the pixel circuits 11 (1,1) to 11 (m, 1) in the first row are selected. .

  Each of the transistors T1 and T2 of the pixel circuits 11 (1,1) to 11 (m, 1) in the first row has a VscanH level signal Vscan1 (1) as a gate via the scanning line Ls1 (1). Supplied and turned on.

  Times t10 to t11 are a period Tm1 in the first half of the selection period of the first row, and the scan driver 12 outputs a signal Vscan2 (1) of Vscan'L level to the auxiliary scanning line Ls2 (1) in this period Tm1. .

  Each transistor T4 of the pixel circuits 11 (1,1) to 11 (m, 1) in the first row supplies the gate with the Vscan'L level signal Vscan2 (1) through the auxiliary scanning line Ls2 (1). Then, the other end of each capacitor Cs is disconnected from the drain of the transistor T2, the source of the transistor T3, and the anode of the OLED 101.

  The control unit 15 sequentially supplies the gradation voltages Vdata (1) to Vdata (m) of the pixel circuits 11 (1,1) to 11 (m, 1) in the first row to the data driver 14 as digital data. To do.

  The shift register 21 sequentially shifts the gradation voltages Vdata (1) to Vdata (m) supplied from the control unit 15 and supplies them to the data register 22, which in turn supplies the supplied gradation voltages Vdata. (1) to Vdata (m) are retained.

  The data register 22 supplies the supplied gradation voltages Vdata (1) to Vdata (m) to the blocks 23 (1) to 23 (m), respectively.

  The D / A converter 31 (i) of the block 23 (i) converts the digital data of the gradation voltage Vdata (i) supplied from the shift register 21 into an analog gradation voltage Vdata (i).

  The control unit 15 supplies the data driver 14 with a switching control signal Csw (i). When this switching control signal Csw (i) is supplied, the switching control unit 37 (i) of the block 23 (i) of the data driver 14 controls the switching switch Sw (i), and switches the switching switch Sw (i). The current output unit 33 (i) is connected to the data line Ld (i).

  When the current output unit 33 (i) and the data line Ld (i) are connected, the drain driver of each transistor T3 and the drain of the transistor T2 of the selected pixel circuit 11 (i, 1) are connected from the anode driver 13. A closed circuit is formed that returns to the anode driver 13 via the source, the data line Ld (i), and the current output unit 33 (i).

  The other end of the capacitor Cs is disconnected from the drain of the transistor T2, the source of the transistor T3, and the anode of the OLED 101. However, since the transistor T is on, the transistor T3 has a gate voltage Vgs between the gate and the source. Applied to conduct.

  The current output unit 33 (i) converts the analog gradation voltage Vdata (i) converted by the D / A converter 31 (i) into a gradation current Idata (i). Then, when the current output unit 33 (i) supplies the gradation current Idata (i) to the data line Ld (i), a current flows through the formed closed circuit.

  When a current flows through the formed closed circuit, the parasitic capacitance of the transistor T3 and the wiring capacitance existing in the closed circuit are immediately charged. Further, when a current flows through the closed circuit, a drain voltage Vds is applied between the drain and source of the transistor T3.

  As shown in FIG. 6A, the threshold voltage Vth of the transistor T3 of the block 23 (i) is Vth1, and the voltage value of the gradation voltage Vdata (i) supplied from the control unit 15 is Vd0. After Tm11 has elapsed, the gradation current Idata (i) output from the current output unit 33 (i) reaches the current value a1, and the voltage value Vdx of the line voltage VLd (i) becomes the voltage value Vd1.

  The voltage measuring unit 34 (i) measures the voltage value Vd1 of the line voltage VLd (i) at the time t13 before the time t11 after the period Tm11 elapses.

  The voltage value Vd1 is a value obtained by adding a threshold voltage (value) Vth1 to the voltage value Vd0. Further, as described above, the voltage value Vd1 becomes the drain voltage Vds (or gate voltage Vgs) of the transistor T3 if the line resistance of the data line Ld (i) is ignored.

  On the other hand, when the gradation of the display data Pic remains the same and the threshold voltage Vth is shifted by ΔVth from Vth1 to the threshold voltage Vth2 as shown in FIG. 7, even in this case, the gradation current Idata (i) The current value remains at a1.

  In this case, when the current output unit 33 (i) supplies the gradation current Idata (i) having the current value a1 to the data line Ld (i), the gradation current Idata (i) is as shown in FIG. In addition, after the period Tm12 has elapsed from time t10, the current value a1 is reached, and the voltage value Vdx of the line voltage VLd (i) becomes the voltage value Vd2. The voltage value Vd2 is a value obtained by adding the threshold voltage (value) Vth2 to the voltage value Vd0, and is also a value obtained by adding the shift amount ΔVth of the threshold voltage Vth to the voltage value Vd1, as shown in FIG.

  The voltage measuring unit 34 (i) measures the voltage value Vdx of the line voltage VLd (i) at time t13 before time t11 after the period Tm12 has elapsed.

  The voltage measuring unit 34 (i) supplies the measured voltage value Vdx to the A / D converter 35 (i), and the A / D converter 35 (i) converts the analog voltage value Vdx into digital data. And supplied to the data register 22.

  The data register 22 rewrites the voltage values of the gradation voltages Vdata (1) to Vdata (m) to the voltage value Vdx of the line voltage VLd (i) supplied from the block 23 (i).

  At time t11, the scan driver 12 outputs the Vscan'H level signal Vscan2 (j) to the auxiliary scanning line Ls2 (j), and each transistor of the pixel circuits 11 (1,1) to 11 (m, 1). Turn on T4. These times t11 to t12 become a period Tm2 in the latter half of the selection period of the first row.

  When the transistor T4 is turned on, the capacitor Cs is connected between the gate and the source of the transistor T3.

  The D / A converter 32 (i) of the block 23 (i) converts each voltage value of the gradation voltage Vdata (i) held in the data register 22 as digital data into an analog value, and outputs a voltage output unit. 36 (i).

  Further, the control unit 15 supplies a switching control signal Csw (V) to the data driver 14. When the switching control signal Csw (V) is supplied, the switching control unit 37 (i) of the block 23 (i) switches so that the voltage output unit 36 (i) and the data line Ld (i) are connected. The switch Sw (i) is controlled, and the voltage output unit 36 (i) and the data line Ld (i) are connected via the changeover switch Sw (i).

  When the voltage output unit 36 (i) and the data line Ld (i) are connected, the drain driver of each transistor T3 and the drain of the transistor T2 of the selected pixel circuit 11 (i, 1) are connected from the anode driver 13. A closed circuit returning to the anode driver 13 is formed via the source, the data line Ld (i), and the voltage output unit 36 (i).

  When the voltage output unit 36 (i) applies the gradation voltage Vdata (i) to the data line Ld (i), a current flows through the formed closed circuit, and the voltage is written into the capacitor Cs according to the voltage writing method.

  Immediately after time t11, a current flows through the capacitor Cs via the drain-source of the transistor T1, and this current fluctuates as shown in FIGS. 6 (a) and 6 (b). Since a voltage is written in Cs, the current value immediately becomes the same current value a1 as the gradation current Idata (i).

  Since the drain current Id of this current value a1 flows also between the drain and source of the transistor T3, as shown in FIG. 6A, in the case of the threshold voltage Vth1 of the transistor T3, the voltage value of the voltage written to the capacitor Cs. Vdx becomes the voltage value Vd1, and in the case of the threshold voltage Vth2, the voltage value Vdx becomes the voltage value Vd2.

  At time t12, the scan driver 12 outputs a VscanL level signal Vscan1 (1) to the scanning line Ls1 (1). When the signal level of the scanning line Ls1 (1) becomes the VscanL level, the transistors T1 and T2 are turned off, the selection period of the first row ends, and each capacitor Cs uses the written voltage as the gate voltage of each transistor T3. Hold as Vgs.

  When the selection period of the pixel circuits 11 (1,1) to 11 (m, 1) in the first row is completed, the scan driver 12 sequentially outputs the pixel circuits 11 (1,2) to 11 (m, 2), ..., 11 (1, n) to 11 (m, n) are selected.

  In the same manner, the display device 1 sequentially selects the selected pixel circuits 11 (1, 2) to 11 (m, 2), ..., 11 (1, n) to 11 (m, n). A voltage is written to each capacitor Cs.

  As shown in FIG. 5, when the voltage writing to the capacitors Cs of the pixel circuits 11 (1, n) to 11 (m, n) is completed and the time t17 is reached, the anode driver 13 causes the signal Vanode ( 1) to Vanode (n) are output to the anode lines La (1) to La (n), respectively.

  When i = 1 to m and j = 1 to n and the anode driver 13 outputs a signal Vanode (j) of VscanH to the anode line La (j), the anode driver La outputs the anode line La (j) and the pixel circuit. A closed circuit is formed that returns to the anode driver 13 via the drain-source of the 11 (i, j) transistor T3, the anode-cathode of the OLED 101, and the ground voltage GND line.

  Each transistor T3 of each pixel circuit 11 (i, j) is controlled to a current value corresponding to the gate voltage Vgs held in the capacitor Cs and supplies a current to the OLED 101.

  6A and 6B, in the case of the threshold voltage Vth1, the voltage value of the drain voltage Vds (gate voltage Vgs) of the transistor T3 becomes the voltage value Vd1, and in the case of the threshold voltage Vth2, the voltage value. Since it becomes Vd2, the current of the current value a1 is supplied to the OLED 101 regardless of the voltage value of the threshold voltage Vth.

  The OLED 101 of each pixel circuit 11 (i, j) emits light with a luminance corresponding to the current value of the supplied current.

  As described above, according to the present embodiment, the display device 1 includes the transistor T4 in each pixel circuit 11 (i, j), and the capacitor Cs is provided in the first half period Tm1 of the selection period of the j-th row. The transistor T3 is separated from the gate and source, and the gradation current Idata (i) is supplied to the data line Ld (i) according to the current writing method, and the voltage measuring unit 34 (i) measures the line voltage VLd (i). .

  In the second half of the selection period Tm2, the measured line voltage VLd (i) is written to the capacitor Cs according to the voltage writing method.

  Therefore, by separating the capacitor Cs from the gate and source of the transistor T3, the source voltage of each transistor T3 can be rapidly converged to a constant voltage (= line voltage VLd (i)). Since the line voltage VLd (i) includes the threshold voltage Vth, complicated correction processing of the threshold voltage Vth of each transistor T3 is not necessary.

  In the period Tm2, the line voltage VLd (i) is written to the capacitor Cs according to the voltage writing method. Therefore, even when the gradation is low, the OLED 101 is set at a preset luminance corresponding to the gradation of the display data Pic. Can emit light.

  Although the transistor T4 is added to each pixel circuit 11 (i, j) and the auxiliary scanning line Ls2 (j) is added, it flows between the drain and source of the transistor T4 and the auxiliary scanning line Ls2 (j). Since the current value of the current is small, the size of the transistor T4 may be increased, and the influence on the pixel aperture ratio is small.

In carrying out the present invention, various forms are conceivable and the present invention is not limited to the above embodiment.
For example, in the above embodiment, the transistor T4 is connected between the other end of the capacitor Cs and the source of the transistor T3. However, the transistor T4 may be connected between the gate of the transistor T3 and one end of the capacitor Cs.

  In the present embodiment, each pixel circuit 11 (i, j) has been described as including transistors T1 to T3. However, the present invention is not limited to this, and each pixel circuit 11 (i, j) may include a transistor T3, a row selection transistor, and a transistor T4.

  The display device 1 has been described as including a TFT-OLED. However, the display device 1 is not limited to this, and may be a liquid crystal display device. Further, the electronic device is not limited to the display device, and may be an electrophotographic device, for example.

  DESCRIPTION OF SYMBOLS 1 ... Display apparatus, 11 (i, j) ... Pixel circuit, 101 ... OLED, T1-T4 ... Transistor, Cs ... Capacitor, 14 ... Data driver, 31 (i) 32 (i) ... D / A converter, 33 (i) ... current output unit, 36 (i) ... voltage output unit, Sw (i) ... switch, 37 (i) ... Switch control unit, 15 ... Control unit

Claims (5)

A light emitting element that emits light at a luminance corresponding to the current value of the supplied current;
A lower end of a current path is connected to one end of the light emitting element, and a current is supplied to the light emitting element while controlling a current value of a current flowing through the current path based on a control voltage between a control end and the lower end of the current path. A driving transistor to be supplied;
A capacitor connected between the control end of the drive transistor and the lower end of the current path to hold the control voltage;
A switch transistor that disconnects or connects the capacitor between the control end of the drive transistor and the lower end of the current path;
A first driver for driving the switch transistor;
When the first driver drives the switch transistor and the capacitor is disconnected from between the control end of the drive transistor and the lower end of the current path, a current having a current value corresponding to the luminance of the light emitting element Is pulled from the current path of the drive transistor, the voltage value of the current path of the drive transistor is measured, and when the capacitor is connected between the control end of the drive transistor and the lower end of the current path A second driver that writes the voltage of the measured voltage value by applying it across the capacitor;
A third driver that causes the light emitting element to emit light by applying a voltage to the upper end of the current path of the drive transistor after the second driver writes a voltage across the capacitor;
An electronic device characterized by that. The second driver is:
A current output drawn from the current path of the drive transistor when the first driver drives the switch transistor and the capacitor is disconnected from between the control end of the drive transistor and the lower end of the current path; And
A voltage measuring unit that measures the line voltage of the signal line between the current path of the drive transistor and the lower end of the current path as the voltage of the current path of the drive transistor when the current output unit draws the current;
When the first driver drives the switch transistor and the capacitor is connected between the control end of the drive transistor and the lower end of the current path, the voltage of the voltage value measured by the voltage measurement unit is obtained. A voltage output unit for applying and writing to both ends of the capacitor, and
The electronic device according to claim 1. The first driver is:
The switch transistor is turned off to disconnect the capacitor from between the control end of the drive transistor and the lower end of the current path, and the switch transistor is turned on to connect the capacitor to the control end of the drive transistor and the current. Connect between the bottom of the road,
The electronic device according to claim 1, wherein the electronic device is an electronic device. The switch transistor as a first switch transistor,
A plurality of pixel circuits having the light emitting element, the driving transistor, the capacitor, the first switch transistor, and a second switch transistor that is turned on when a row selection signal is supplied are arranged in a matrix.
The first driver selects a row by supplying a row selection signal to the second switch transistor via a scanning line, and performs drive control via the auxiliary scanning line during a selection period in which the row is selected. Supplying a signal to the first switch transistor in the selected row to drive the first switch transistor on and off;
The electronic device according to any one of claims 1 to 3, wherein A light emitting element that emits light at a luminance corresponding to the current value of the supplied current;
A lower end of a current path is connected to one end of the light emitting element, and a current is supplied to the light emitting element while controlling a current value of a current flowing in the current path based on a control voltage between a control end and the lower end of the current path. A driving transistor to be supplied;
A capacitor connected between the control end of the drive transistor and the lower end of the current path to hold the control voltage;
Separating the capacitor from between the control end of the drive transistor and the lower end of the current path;
Drawing a current having a current value corresponding to the luminance of the light emitting element from the current path of the driving transistor;
Measuring a voltage value of the current path of the drive transistor;
Connecting the capacitor between the control end of the driving transistor and the lower end of the current path;
Applying and writing the voltage of the measured voltage value across the capacitor;
After writing a voltage across the capacitor, applying a voltage to the upper end of the current path of the drive transistor to cause the light emitting element to emit light,
A method for driving an electronic device.

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