Source: https://patents.google.com/patent/KR101206629B1/en
Timestamp: 2019-11-18 01:55:54
Document Index: 516795291

Matched Legal Cases: ['art 16', 'art 16', 'art 16', 'art 16', 'art 16', 'Application No. 2008']

KR101206629B1 - A pixel driving device, light emitting device, and property parameter acquisition method in a pixel driving device - Google Patents
A pixel driving device, light emitting device, and property parameter acquisition method in a pixel driving device Download PDF
KR101206629B1
KR101206629B1 KR1020107021618A KR20107021618A KR101206629B1 KR 101206629 B1 KR101206629 B1 KR 101206629B1 KR 1020107021618 A KR1020107021618 A KR 1020107021618A KR 20107021618 A KR20107021618 A KR 20107021618A KR 101206629 B1 KR101206629 B1 KR 101206629B1
KR1020107021618A
KR20100123746A (en
?지 가시야마
마나부 다케이
쥰 오구라
2008-11-28 Priority to JPJP-P-2008-305714 priority
2009-11-27 Application filed by 가시오게산키 가부시키가이샤 filed Critical 가시오게산키 가부시키가이샤
2009-11-27 Priority to PCT/JP2009/070370 priority patent/WO2010061975A1/en
2010-11-24 Publication of KR20100123746A publication Critical patent/KR20100123746A/en
2012-11-30 Publication of KR101206629B1 publication Critical patent/KR101206629B1/en
The pixel driving device includes a voltage applying circuit 14 that outputs a reference voltage Vref exceeding the threshold voltage Vth of the driving transistor T3, a voltage measuring circuit 114, and characteristic parameters relating to electrical characteristics of the pixel. Has a characteristic parameter obtaining circuit 16 for obtaining. The pixel driving device applies a reference voltage on the pixel having the electroluminescent element 101 and the driving transistor. The voltage measuring circuit obtains the voltage of the signal line Ld as the measurement voltage after each of the plurality of settling times that elapse from the time when the reference voltage is cut off. The characteristic parameter obtaining circuit obtains the threshold voltage and the current amplification rate of the driving transistor as the characteristic parameters based on the values of the plurality of measured voltages obtained by the voltage measuring circuit.
A method for acquiring characteristic parameters of a pixel driving device, a light emitting device, and a pixel driving device {A PIXEL DRIVING DEVICE, LIGHT EMITTING DEVICE, AND PROPERTY PARAMETER ACQUISITION METHOD IN A PIXEL DRIVING DEVICE}
The present invention relates to a pixel driving device, a light emitting device and a method for obtaining characteristic parameters of the pixel driving device.
Recently, research and development of light emitting element type display devices (light emitting element type displays, light emitting devices) providing a display panel (pixel array) in which light emitting elements are arranged in a matrix form as a next generation display device following the liquid crystal display device have been developed. Actively done.
As such a light emitting element, a current driven light emitting element such as an organic electroluminescent element (organic EL element), an inorganic electroluminescent element (inorganic EL element), or a light emitting diode (LED) is known.
In particular, a light emitting device type display device employing an active matrix driving method has faster display response speed, no viewing angle dependence, and has high brightness, high contrast, and high resolution of display quality compared to known liquid crystal display devices.
In addition, since the light emitting element type display device does not display the backlight or the light guide plate, unlike the LCD device, the light emitting element type display device has an extremely superior feature that it is possible to remove a further thin film. . Therefore, application to this type of electronic device is expected in the future.
As such a light emitting device type display device, for example, an organic EL display device of an active matrix driving method for controlling current through a voltage signal is disclosed in Japanese Patent Laid-Open No. 2002-156923.
In the organic EL display device of this active matrix driving method, each pixel includes an organic EL element which is a light emitting element, and a pixel driving circuit having a thin film transistor for current control and a thin film transistor for switching in order to drive the organic EL element.
The thin film transistor for current control uses a gate voltage applied after a voltage signal having a predetermined voltage value (hereinafter referred to as "voltage value based on image data") is applied based on image data of each pixel. The current value of the current flowing between the drain and the source is controlled. This current is supplied to the organic EL element to cause the organic EL element to emit light. The switch thin film transistor performs switching for supplying a voltage signal based on image data to the gate of the current control thin film transistor.
The characteristics of the thin film transistor for current control of the display device constructed in this manner change over time with use. In particular, when the current control thin film transistor is formed of an amorphous TFT (thin film transistor), it is known that the threshold voltage Vth, which is one of the characteristics of the TFT, exhibits a relatively large change over time.
The threshold voltage Vth is applied even if a thin film transistor gate for current control having a voltage signal having the same voltage value is applied to the same gray value of the image data having the configuration of controlling the gray level of the image displayed by the voltage value of the voltage signal based on the image data. When is changed, the current value of the current flowing between the drain and the source of the current control thin film transistor is changed, and the luminance of light emitted from the organic EL element of the display pixel is changed for the same gray value of the image data.
Another characteristic of the current control thin film transistor is that, for example, irregular current amplification factor? Between pixels also affects the displayed image. The current value of the current flowing between the drain and the source of the current control thin film transistor is proportional to the current amplification factor β. Therefore, even if the threshold voltages of the current control thin film transistors of all the pixels are the same, or if an irregularity occurs in the value of the current amplification factor β due to the manufacturing process, for example, the current value of the current flowing between the drain and the source of the current control thin film transistor. Irregularities occur, and irregularities occur in the luminance of light emitted from the organic EL element.
The irregularity of this current amplification factor is due to the irregularity of mobility. The irregularities in mobility are particularly noticeable in low temperature polysilicon TFTs, while these irregularities in amorphous silicon TFTs are relatively low. However, the influence of mobility due to the manufacturing process, i.e., irregularity in the current amplification factor β, cannot be avoided.
In this way, the change in the threshold voltage Vth and the irregularity in the current amplification factor β occurring in the manufacturing process affect the reproducibility of the image data of the displayed image, that is, the image quality.
In order to control the deterioration of the image quality caused by such a change in the threshold voltage Vth and irregularities in the current amplification factor β generated in the manufacturing process, in the present invention, for example, the threshold voltage and the current amplification ratio β of each pixel are characteristic parameters. It is possible to correct the voltage signal supplied to each pixel based on the supplied image data and based on this characteristic parameter.
The pixel driving device according to the present invention is connected to a signal line, controls a light emitting element, a current supplied to the light emitting element, and one end of a driving transistor connected to one end of the current of the driving transistor and the driving transistor. A pixel driving device for driving a pixel having a pixel driving circuit having a holding capacitor for storing charges by a voltage applied to a control terminal, comprising: a voltage applying circuit for outputting a reference voltage, a voltage measuring circuit, and the voltage applying circuit And a switching circuit for switching a connection of one end of the signal line between the voltage measuring circuit and a characteristic parameter obtaining circuit for obtaining a characteristic parameter relating to an electrical characteristic of the pixel, wherein the reference voltage is the current of the driving transistor. The potential difference at one end relative to the other end of the furnace is critical for the drive transistor. Having a potential that is a value exceeding a voltage, the switching circuit connects one end of the signal line to the voltage application circuit, and after applying the reference voltage to the one end of the signal line by the voltage application circuit for a predetermined time, The connection between one end of the signal line and the voltage application circuit is cut off, and one end of the signal line is connected to the voltage measuring circuit after each of a plurality of predetermined settling times, and the voltage measuring circuit is connected to the switching circuit. Is connected to one end of the signal line, the voltage value of one end of the signal line is obtained as a measurement voltage, and the characteristic parameter obtaining circuit is configured to perform a plurality of measurements obtained by the voltage measuring circuit for the plurality of predetermined settling times. Based on the value of the voltage, the threshold voltage of the driving transistor and the effective of the pixel driving circuit The current amplification factor is obtained as a characteristic parameter.
A first light emitting device according to the present invention includes: a driving transistor connected to at least one signal line, controlling a light emitting element, a current supplied to the light emitting element, and one end of the driving transistor connected to one end of the light emitting element; At least one pixel having a pixel driving circuit having a storage capacitor for storing charge by a voltage applied to a control terminal of the driving transistor, a voltage applying circuit for outputting a reference voltage, a voltage measuring circuit, and a signal line A switching circuit for switching one end of the connection between the voltage measuring circuit and a characteristic parameter obtaining circuit for obtaining a characteristic parameter relating to an electrical characteristic of the pixel, wherein the reference voltage is one end and the other end of the driving transistor to the current. Has a potential whose potential difference is greater than a threshold voltage of the driving transistor, The switching circuit connects one end of the signal line to the voltage application circuit, and after applying the reference voltage to the one end of the signal line by the voltage application circuit for a predetermined time, between one end of the signal line and the voltage application circuit. And one end of the signal line is connected to the voltage measuring circuit after each of a plurality of predetermined settling times have elapsed, and the voltage measuring circuit is connected to one end of the signal line by the switching circuit. At this time, a voltage value of one end of the signal line is obtained as a measurement voltage, and the characteristic parameter acquisition circuit is configured to drive the drive based on the values of the plurality of measurement voltages obtained by the voltage measurement circuit for the plurality of predetermined settling times. The threshold voltage of the transistor and the effective current amplification factor of the pixel driving circuit are defined as characteristic parameters. It is obtained.
A method for obtaining characteristic parameters of a pixel driving apparatus according to the present invention includes: a driving transistor connected to a signal line, controlling a light emitting element and a current supplied to the light emitting element, and one end of the light emitting element connected to one end of the current; A method of acquiring a characteristic parameter of a pixel driving apparatus for driving a pixel having a pixel driving circuit having a holding capacitor for storing charges by a voltage applied to a control terminal of a driving transistor, the method comprising: connecting a voltage applying circuit to one end of the signal line; Thereby applying a reference voltage to one end of the signal line such that the potential difference of one end of the driving transistor with respect to the other end to the current becomes a value exceeding a threshold voltage of the driving transistor, and one end of the signal line; Breaks the connection between the voltage application circuits, and restores the predetermined A measurement voltage acquiring step of acquiring a voltage of one end of the signal line as a plurality of measured voltages after each elapse of another settling time, and based on the values of the plurality of measured voltages obtained for the predetermined plurality of different settling times And a characteristic parameter obtaining step of obtaining, as a characteristic parameter, a threshold voltage of the driving transistor and an effective current amplification ratio of the pixel driving circuit.
A second light emitting device according to the present invention is connected to a signal line, has a light emitting element, a current path and a control terminal, connects one end of the current path to one end of the light emitting element, and one end of the control terminal and the current path. A pixel having a driving transistor for controlling a current supplied to the light emitting element through the current path based on voltage data written therebetween, and a storage capacitor for storing charge determined by the voltage applied to the driving transistor And a voltage measuring circuit for acquiring a voltage value as a measurement voltage of one end of the signal line, and a characteristic parameter obtaining circuit for acquiring characteristic parameters relating to an electrical characteristic of the pixel. Between both ends of the signal transistor through one end of the signal line to exceed the threshold voltage of the drive transistor; After the voltage is applied, when the time elapsed from the moment when the applied voltage is stopped due to the presence of the high impedance state becomes the settling time t, the parasitic on the holding capacitor of the pixel connected by the signal line, the signal line In the case of the sum of the parasitic capacitances and the total capacitances of the light emitting element capacitances parasitic to the light emitting element, the voltage value of the voltage of one end of the signal line shown in equation (4) is obtained as the measurement voltage, and the characteristic parameter obtaining circuit When the settling time t is a plurality of different values satisfying the condition of (C / β) / t <1, the threshold voltage of the driving transistor and (C) are based on the plurality of measured voltages obtained by the voltage measuring circuit. / β) value as a characteristic parameter.
Where t is the settling time
Vmeas (t): measured voltage obtained by the voltage measuring circuit at elapsed settling time t
C: total capacity (C = Cs + Cp + Cel)
Cel: light emitting device capacity
β: effective current gain
The present invention can provide a parameter obtaining method in a pixel driving device, a light emitting device and a pixel driving device which can acquire characteristics of a pixel for correcting a voltage value of a voltage signal based on image data.
In addition, the present invention can provide a parameter driving method in a pixel driving device, a light emitting device, and a pixel driving device capable of controlling pixel degradation.
1 is a block diagram showing a configuration of a display device according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating a configuration of an organic EL panel and a data driver shown in FIG. 1. FIG.
3A and 3B are diagrams and graphs for explaining voltage / current characteristics when writing a pixel driving circuit;
4A and 4B are graphs for explaining a voltage measurement method of a data line when the auto zero method is used according to the present embodiment.
FIG. 5 is a block diagram showing the detailed configuration of the data driver shown in FIG. 1; FIG.
6 (a) and 6 (b) are diagrams for explaining the structure and function of the DVAC and ADC shown in FIG. 5;
FIG. 7 is a block diagram showing the configuration of the control unit shown in FIG. 1; FIG.
FIG. 8 is a diagram showing each storage area of the memory shown in FIG. 7; FIG.
9A and 9B are graphs showing examples of image data conversion characteristics of the LUT shown in FIG.
10A and 10B are diagrams for explaining image data conversion characteristics of the LUT shown in FIG. 7;
Fig. 11 is a timing chart showing the operation of each part in the case where voltage measurement is performed by the auto zero method.
12 (a) and 12 (b) are diagrams showing a connection relationship of respective switches when outputting data from a data driver to a control unit.
13 (a), 13 (b) and 13 (c) are diagrams showing a connection relationship of each switch when voltage measurement is performed by the auto zero method;
14 is a diagram for explaining a driving sequence executed by a control unit when a characteristic parameter for correction is obtained;
Fig. 15 is a view for explaining a driving sequence executed by a control unit when a voltage signal based on supplied image data is output to a data driver after correction.
Fig. 16 is a timing chart showing the operation of each part in the actual operation.
Fig. 17 is a diagram showing a connection relationship of each switch when a voltage signal is written.
Fig. 18 is a diagram showing a connection relationship of each switch when data is input to a data driver from a control unit.
EMBODIMENT OF THE INVENTION Hereinafter, the pixel drive device, the light emitting device, and the characteristic parameter acquisition method in the pixel drive device which concern on this invention are demonstrated with reference to embodiment shown in drawing. In the present embodiment, the light emitting device is described as a display device.
1 shows a configuration of a display device according to the present embodiment.
The display device (light emitting device) 1 according to the present embodiment includes a panel module 11, an analog power supply (voltage application unit) 14, a logic power supply 15, and a control unit (parameter acquisition circuit and signal correction circuit) ( It consists of 16).
The panel module 11 includes an organic EL panel (pixel array) 21, a data driver (signal line driving circuit) 22, an anode circuit (power supply driving circuit) 12, and a selection driver (selection driving circuit) 13. It is provided.
The organic EL panel 21 includes a plurality of data lines (signal lines) Ldi (i = 1 to m) arranged in the column direction, a plurality of selection lines (scan lines) Lsj (j = 1 to n) arranged in the row direction A plurality of anode lines La arranged in the direction and a plurality of pixels 21 (i, j) (i = 1 to m, j = 1 to n, m, n; natural numbers). The pixels 21 (i, j) are arranged near the intersection of the data line Ldi and the selection line Lsj, and are connected to these lines, respectively.
FIG. 2 shows the details of the configuration of the panel module 11 shown in FIG. 1. Each pixel 21 (i, j) represents image data of one pixel of an image, and as shown in FIG. 2, it is composed of an organic EL element (light emitting element) 101, transistors T1 to T3, and a storage capacitor Cs. The pixel drive circuit DC is provided.
The organic EL element 101 is a self-luminous display element that uses a phenomenon of emitting light through an exciton generated by recombination of electrons and holes injected into an organic compound. Light is emitted at a luminance determined by the current value of the current supplied to the organic EL element 101.
The pixel electrode is formed in the organic EL element 101, and the hole injection layer, the light emitting layer, and the counter electrode are formed in this order on this pixel electrode. The hole injection layer has a function of supplying holes to the light emitting layer.
The pixel electrode is made of a transparent or translucent conductive material, for example, indium tin oxide (ITO), zinc oxide (ZnO), or the like. Each pixel electrode is insulated from the pixel electrodes of other adjacent pixels by an interlayer insulating film.
The hole injection layer is composed of a transportable (hole injection / transport material) organic polymer material. Moreover, as an organic compound containing liquid containing the hole injection / transport material of organic polymer, For example, Aqueous PEDOT / PSS which disperse | distributed polyethylene dioxythiophene (PEDOT), a dopant, and polystyrene sulfonic acid (PSS) which are conductive polymers to an aqueous solvent. Dispersion is used.
The light emitting layer is formed on the interlayer, for example. The pixel electrode and the counter electrode are an anode electrode and a cathode electrode, respectively. The light emitting layer has a function of emitting light to apply a predetermined voltage between the anode electrode and the cathode electrode.
The light emitting layer is a red (R), green (G), blue (B) containing a conjugated double bond polymer such as a known polymer light emitting material capable of emitting fluorescence or phosphorescence, such as polyparaphenylenevinylene or fluorine. It is formed of a light emitting material that emits light.
In addition, this light emitting material is a solution of the above-described light emitting material dissolved (or dispersed) in a suitable aqueous solvent or an organic solvent such as tetraine, tetramethylbenzene, mesitylene, xylene, etc. on the interlayer by a nozzle coating method, an inkjet method, or the like. It is formed by applying (dispersion liquid) and then evaporating the solvent.
When the light emitting layer consists of three primary color light emitting materials of red (R), green (G), and blue (B), each light emitting material is generally applied in rows.
The counter electrode is a two-layer structure consisting of a layer made of a conductive material, for example, a material having a low work function such as Ca or Ba, and a light reflective conductive layer such as Al.
The current flows from the pixel electrode to the opposite electrode, that is, from the anode electrode to the cathode electrode, and does not flow in the reverse direction. The cathode voltage Vcath is applied to the cathode electrode. In this embodiment, the cathode voltage Vcath is set to GND (ground potential).
In addition, the organic EL element 101 has an organic EL pixel capacitance (light emitting element capacitance) Cel. This organic EL pixel capacitor Cel is connected between the cathode and the anode of the organic EL element 101 on an equivalent circuit.
The selection driver 13 outputs a Gate (j) signal to each selection line Lsj, and selects the pixels 21 (i, j) (j = 1 to n) for each row. The selection driver 13 includes a shift register, for example, which shifts the start pulse SP1 supplied from the control unit 16 continuously, as shown in FIG. 2 in accordance with the supplied clock signal. The selection driver 13 outputs a high level signal VgH or a low level signal VgL to the continuously shifted start pulse SP1 as the Gate (1) to Gate (n) signals. .
The data driver 22 measures the voltage of each data line Ldi (i = 1 to m), obtains the voltage Vmeas (t) measured at time t, and corrects it based on the measured voltage Vmeas (t). A voltage signal having the specified voltage value Vdata is applied to each data line Ldi.
The anode circuit 12 applies a voltage to the organic EL panel 21 through each anode line La. As shown in FIG. 2, the anode circuit 12 is controlled by the controller 16 and switches the voltage applied on the anode line La to the voltage ELVDD or ELVSS.
The voltage ELVDD is a display voltage applied to the anode line La when the organic EL element 101 of each pixel 21 (i, j) emits light. The voltage ELVDD is a voltage having a positive potential higher than the ground potential in this embodiment.
The voltage ELVSS is a voltage applied to the anode line La when the pixel driving circuit DC is set to the write operation state described later and executed by the autozero method described later. The voltage ELVSS is set to the same voltage as the cathode voltage Vcath of the organic EL element 101 in this embodiment.
In each pixel 21 (i, j), the transistors T1 to T3 of the pixel driving circuit DC are TFTs composed of n-channel FETs (field effect transistors), for example, amorphous silicon or polysilicon TFTs. do.
The transistor T3 includes a current control thin film transistor and a drive transistor (first thin film transistor) which supply current to the organic EL element 101 by controlling the amount of current based on the gate-source voltage Vgs (hereinafter referred to as gate voltage Vgs). to be.
For the transistor T3, while the drain-source is a current, the gate is a control terminal, the drain (terminal) is connected to the anode line La, and the source (terminal) is connected to the anode (electrode) of the organic EL element 101. .
The transistor T1 is a switch transistor (second thin film transistor) for connecting a diode to the transistor T3 when the write operation described later is performed.
The gate (terminal) of the transistor T1 of each pixel 21 (1, j) to 21 (m, j) is connected to the selection line Lsj (j = 1 to n).
When the high level gate (1) signal VgH is output from the selection driver 13 to the selection line Ls1 as the Gate (1) signal for the pixel 21 (1,1), the transistor T1 is turned on. .
When the low-level Gate 1 signal VgL is output from the selection driver 13 as the Gate 1 signal to the selection line Ls1, the transistor T1 is turned off.
The transistor T2 is a switch transistor (third thin film transistor) for conducting or interrupting the anode circuit 12 and the data driver 22. This transistor T2 is in an on or off state depending on selection by the selection driver 13. The on or off state determines the conduction or interruption mode between the anode circuit 12 and the data driver 22. The situation is the same for the other pixels 21 (i, j).
The drain of the transistor T2 of each pixel 21 (i, j) is connected to the anode (electrode) of the organic EL element 101 similarly to the source of the transistor T3.
The gate of transistor T2 of each pixel 21 (1, j) to 21 (m, j) is connected to the selection line Lsj (j = 1 to n).
In addition, the source of the transistor T2 of each pixel 21 (i, 1) to 21 (i, n) is connected to the data line Ldi (i = 1 to m).
With respect to the pixel 21 (1, 1), the transistor T2 is turned on when the high level Gate (1) signal VgH is output as the Gate (1) signal to the selection line Ls1, similarly to the source of the transistor T3. The anode of the organic EL element 101 and the data line Ld1 are connected.
When the low level signal VgL is output as the Gate (1) signal to the selection line Ls1, the transistor T2 is turned off and, like the source of the transistor T3, between the anode line and the data line Ld1 of the organic EL element 101. Block the connection.
The holding capacitor Cs is a capacitor for holding the gate voltage Vgs of the transistor T3, and a source of the transistor T1 and a gate of the transistor T3 are connected to one end thereof, and a source of the transistor T3 and an anode of the organic EL element 101 are connected to the other end thereof. do.
In transistor T3, the source and the drain of transistor T1 are connected to the gate and the drain thereof, respectively. A voltage ELVSS is applied to the anode line La by the anode circuit 12, a high level signal VgH is applied as the Gate 1 signal to the selection line Ls1 by the selection driver 13, and a voltage signal to the data line Ld1. When is applied, transistors T1 and T2 are in the on state.
At this time, the transistor T3 is in a diode-connected state by the connection between the gate and the drain via the transistor T1.
At this time, when the voltage signal is applied to the data line Ld1 by the data driver 22, the voltage signal is applied to the source of the transistor T3 through the transistor T2, and the transistor T3 is in the on state. Subsequently, a current determined by the voltage signal flows from the anode circuit 12 through the anode line La, the transistor T3, and the transistor T2 toward the data line Ld1. The holding capacitor Cs is charged by the gate voltage Vgs of the transistor T3 at this time, and the electric charge thereof is stored in the holding capacitor Cs.
When the low level signal VgL is applied as the Gate 1 signal to the selection line Ls1 by the selection driver 13, the transistors T1 and T2 are turned off. At this time, the holding capacitor Cs holds the gate voltage Vgs of the transistor T3. The situation is the same for the other pixels 21 (i, j).
In addition, the wiring parasitic capacitance Cp also exists in the organic EL panel 21. This wiring parasitic capacitance Cp is mainly generated at the intersection of the data lines Ld1 to Ldm and the selection lines Ls1 to Lsn.
The display device 1 according to the present embodiment measures the data line voltage as a characteristic value of the pixel drive circuit DC of each pixel 21 (i, j) using the auto zero method. By this measurement, irregularities of the threshold voltage Vth of the transistor T3 of each pixel 21 (i, j) and the current amplification factor β of the pixel driving circuit DC can be obtained as correction parameters of the image data of the common circuit.
3A and 3B are diagrams and graphs for explaining voltage / current characteristics when writing image data of a pixel driving circuit. FIG. 3A is a diagram showing voltages and currents of respective portions of the pixel 21 (i, j) at the time of writing.
As shown in Fig. 3A, the high level signal VgH is applied to the selection line Lsj by the selection driver 13 at the time of writing. Thereafter, the transistors T1 and T2 are turned on, and the transistor T3 which is a thin film transistor for current control is diode-connected.
Subsequently, the voltage driver of the voltage value Vdata determined by the image data is applied to the data line Ldi by the data driver 22. At this time, the voltage ELVSS is applied to the anode line La by the anode circuit 12.
Thereafter, the current Id defined by the voltage signal flows from the anode circuit 12 through the pixel driving circuit DC through the transistors T2 and T3 toward the data line Ldi.
The current value of this current Id is represented by the following equation (101). Β in equation (101) is a current amplification factor, and Vth is a threshold voltage of transistor T3.
Here, the voltage Vds applied between the source and the drain of the transistor T3 is the voltage of the drain-source of the transistor T2 (between the contact N13 and the contact N12) at the absolute value of the voltage Vdata when the voltage ELVSS of the anode line La is regarded as 0V. Voltage minus voltage).
That is, equation (101) shows the voltage / current characteristics of the transistor T3, and shows the characteristic when the pixel driving circuit DC functions substantially as one element, and β is the effective current amplification factor of the pixel driving circuit DC. .
FIG. 3B is a graph showing the change of the current Id with respect to the absolute value of the voltage value Vdata.
In the case where the transistor T3 has the characteristics of the initial state, the threshold voltage Vth has the initial value Vth0, and the current amplification factor β of the pixel driving circuit DC has the initial value β0 (reference value), it is shown in FIG. It is represented by the voltage / current characteristic VI_0 shown.
Here, β0 as the reference value of β is set to, for example, a design value or a typical value of the pixel drive circuit DC.
When the transistor T3 deteriorates over time and the threshold voltage Vth is shifted (increased) by ΔVth, the voltage / current characteristic is the voltage / current characteristic VI_3 shown in Fig. 3B.
In addition, when the value of the current amplification ratio β is β1 (= β0-Δβ) smaller than β0 due to the irregularity from β0 (standard value), the voltage / current characteristic becomes the voltage-current characteristic VI_1, and the current amplification ratio β If the value of is β2 (= β0 + Δβ) larger than β0, the voltage / current characteristic is the voltage / current characteristic VI_2.
Next, the auto zero method will be described.
The auto zero method first applies a reference voltage Vref to the gate-source of the pixel driving circuit DC transistor T3 of the pixel 21 (i, j) through the data line Ldi at the time of the above-described writing. The reference voltage is set to a voltage at which the absolute value of the potential difference with respect to the voltage ELVSS of the anode line La exceeds the threshold voltage Vth. Thereafter, the data line Ldi is in a high impedance state. By doing this, the voltage of the gate data line Ldi naturally decreases (decreases). After the natural degradation ends, the voltage of the data line Ldi is measured, and the measured voltage is regarded as the threshold voltage Vth.
Compared with the general auto zero method described above, the auto zero method according to the present embodiment measures the voltage of the data line Ldi at the timing before the above-described natural degradation is completely completed. Details will be described later.
4A and 4B are graphs for explaining the voltage measuring method of the data line when using the auto zero method according to the present embodiment. FIG. 4A is a graph showing the time variation (settlement characteristic) of the data line Ldi when the data line Ldi is in a high impedance state after applying the reference voltage Vref as described above.
The voltage of the data line Ldi is obtained by the data driver 22 as the measurement voltage Vmeas (t). This measured voltage Vmeas (t) is generally the same voltage as the gate voltage Vgs of transistor T3.
FIG. 4B is a graph for explaining the influence of the data line voltage (measurement voltage Vmeas (t)) when there is β irregularity shown in FIG. 3B. 4A and 4B, the vertical axis represents the absolute value of the data line Ldi voltage (measurement voltage Vmeas (t)). The horizontal axis represents the time t (settling time) elapsed from the time, and becomes a high impedance state by applying the reference voltage Vref, after which the application of the reference voltage Vref is stopped.
The measurement of the data line voltage according to the auto zero method will be described in more detail.
In the write state, first, the absolute value of the potential difference with respect to the voltage ELVSS of the anode line LA exceeds the threshold voltage Vth of the transistor T3, and a negative reference voltage Vref having a potential smaller than the voltage ELVSS is defined by the data line Ldi. The pixel driving circuit DC pixel T3 of the pixel 21 (i, j) is applied to the gate-source. In this way, the current defined by the reference voltage Vref flows from the anode circuit 12 through the anode line La, the transistor T3, and the transistor T2 toward the data line Ldi.
At this time, the holding capacitor Cs connected to the gate-source (between the contacts N11 and N12 in Fig. 3A) of the transistor T3 is charged to a voltage based on the reference voltage Vref.
Next, the data input side (data driver 22 side) of the data line Ldi is set to a high impedance (HZ) state. Immediately after setting to the high impedance state, the voltage charged in the storage capacitor Cs is maintained at a voltage based on the reference voltage Vref, and the gate-source voltage of the transistor T3 is maintained at the voltage charged in the storage capacitor Cs.
As a result, immediately after the high impedance state is set, the transistor T3 is kept in the on state, and a current continues to flow through the drain-source of the transistor T3.
As a result, the potential of the source terminal side (contact point N12) of the transistor T3 gradually increases so as to approach the potential of the drain terminal side with the passage of time. As a result, the value of the current flowing between the drain and the source of the transistor T3 decreases.
In connection with this, part of the electric charge accumulated in the storage capacitor Cs is discharged. When the charge accumulated in the storage capacitor Cs is gradually discharged, the voltage between both ends of the storage capacitor Cs gradually decreases.
As a result, the gate voltage Vgs of the transistor T3 gradually decreases. As a result, as shown in FIG. 4A, the absolute value of the voltage of the data line Ldi gradually decreases.
Finally, if no current flows between the drain and the source of the transistor T3, the discharge from the holding capacitor Cs is stopped. At this time, the gate voltage Vgs of the transistor T3 becomes the threshold voltage Vth of the transistor T3.
At this time, since no current flows between the drain and the source of the transistor T2, the voltage between the drain and the source of the transistor T2 is almost zero. As a result, the voltage of the data line Ldi becomes approximately equal to the threshold voltage Vth of the transistor T3.
As shown in Fig. 4A, the voltage of the data line Ldi gradually approaches this threshold voltage Vth with time (settling time). However, this voltage approaches the threshold voltage Vth indefinitely, but theoretically, no matter how long the settling time is set, it does not become exactly equal to the threshold voltage Vth.
Thereby, in this embodiment, the control part 16 in the display apparatus 1 is set to a high impedance state, and the settling time t which measures the voltage of the data line Ldi is preset. Thereafter, the voltage (measurement voltage Vmeas (t)) of the data line Ldi is measured at the settling time t, and based on the measured voltage Vmeas (t), the threshold voltage Vth of the transistor T3 and the current amplification factor of the pixel driving circuit DC Obtain β.
The relationship between the settling time t of this measured voltage Vmeas (t) can be expressed by the following equation (102).
Then, if the settling time t is set to a value satisfying the condition of (C / β) / t <1 (that is, (C / β) <t), the measured voltage Vmeas (t) becomes the following at the settling time t. It can be represented by equation (103).
If the settling time tx shown in FIG. 4B satisfies the condition of (C / β) / t = 1, the time exceeding the settling time tx satisfies the condition of (C / β) / t <1. It becomes settling time to let. This settling time tx is the time at which the measured voltage Vmeas (t) is typically approximately 30% of the reference voltage Vref, more specifically generally between 1 ms and 4 ms.
Next, Vmeas_0 (t) shown by the solid line in FIG. 4B shows the condition of β with respect to the voltage / current characteristic VI_0 shown in FIG. 3B when the current amplification ratio β is the initial value β0 (reference value). Voltage fixing characteristic of the data line Ldi).
Vmeas_2 (t) shown in FIG. 4B is a condition of β of voltage / current characteristic VI_1 shown in FIG. 3B when the value of current amplification factor β is β1 (= β0-Δβ) smaller than β0. Voltage fixing characteristic of the data line Ldi). Vmeas_3 (t) represents the data line Ldi in the case where the value of the current amplification ratio β is β2 (= β0 + Δβ) larger than β0 (same as the condition of β of the voltage / current characteristic VI_2 shown in Fig. 3B). The fixing characteristics of the voltage are shown.
In the initial stage, such as when the display device 1 is shipped, two different times t1 and t2 exceeding the settling time tx are set as the settling time for satisfying the above condition (C / β) / t <1. The voltage of the data line Ldi is measured at two timings of the settling times t1 and t2 after the reference voltage Vref is applied to the data line Ldi by the above-described autozero method. The initial threshold voltages Vth, that is, Vth0 and (C / β) can be obtained based on the voltage value of the data line obtained by the measurement of the settling times t1 and t2 and the above expression (103).
Thereafter, the threshold voltages Vth0 and (C / β) for each of all the pixels 21 (i, j) of the organic EL panel 21 are obtained by the above-described method. Then, the average value (<C / β>) of (C / β) of each pixel 21 and its deviation are calculated.
Then, this deviation is within the allowable range of the threshold voltage Vth measurement, and the shortest settling time t0 that satisfies (C / β) / (βt) <1 is determined.
When the image data is supplied at the time of operation, using the obtained measured voltage Vmeas (t0), the threshold voltage Vth at the time of operation can be obtained from the following equation (104) modified in equation (103).
The arithmetic mean value (<C / β>) of (C / β) of each pixel 21 may be used as the mean value (<C / β>) of (C / β) of each pixel 21, but each The median value of (C / β) of the pixel 21 may be used.
Here, the value of the second part on the right side in the equation (104) is defined as the offset voltage Voffset.
Next, the current amplification factor β of the pixel driving circuit DC of the pixel 21 (i, j) is a deviation within the range of Δβ around β0 as indicated by β0 ± Δβ = β0 (1 ± Δβ / β0).
The change amount ΔVmeas (t) attributable to Δβ of the voltage (measurement voltage Vmeas (t)) of the data line Ldi at this time can be expressed by the following equation (106).
(Δβ / β) is a deviation parameter representing a deviation of current characteristics with respect to the pixel driving circuit DC of each pixel 21 (i, j), and ΔVmeas (t) is a deviation Δβ (or a deviation parameter) of the voltage of the data line Ldi. (Δβ / β)) is shown. That is, as shown in equation (106), the voltage of the data line Ldi only varies ΔVmeas (t) due to the deviation of β.
As shown in Fig. 4B, the settling time t can be set to a value t3 smaller than the settling time tx ((C / β) / t ≧ 1, t = t3).
As shown in Fig. 4B, at the fixing time t3, the voltage of the data line Ldi is rapidly fixed (decreased). As a result, the dependence of the deviation? Of the voltage (measurement voltage Vmeas (t)) of the data line Ldi becomes relatively large.
For this reason, when ΔVmeas (t) is measured at settling time t3, ΔVmeas (t) can be obtained as a larger value than when measured at settling time t1 or t2, and the measured voltage Vmeas ( The change in t) can be easily identified. This is the reason why Vmeas (t) was acquired by the settling time t3. ΔVmeas (t) is obtained from this Vmeas (t), and (Δβ / β) can be obtained from equation (106).
Next, the correction for the voltage value Vdata of the voltage signal applied to the data line Ld1 based on the supplied image data will be described. The purpose of this correction is to reduce the influence on the display image caused by the variation of the threshold voltage and the variation of the current amplification ratio β.
The voltage before correction based on image data is regarded as Vdata0 and the voltage value Vdata0 is corrected based on the deviation parameter (Δβ / β) of the current characteristic of the pixel drive circuit DC of each pixel 21 (i, j). The value Vdata1 is represented by the following equation (107) obtained by differentiating the equation (106) by the voltage.
The threshold voltage Vth is represented by the following equation 108 by the auto zero method of the settling time t0 using the offset voltage Voffset defined in equation (105).
The voltage value (correction voltage) Vdata in the voltage value Vdata based on the image data corrected based on the deviation parameter (Δβ / β) of the current characteristic of the pixel drive circuit DC and the threshold voltage Vth is expressed by the following equation (109). It is represented by
This voltage value Vdata is the voltage value of the voltage signal (drive signal) applied by the data driver 22 to the data line Ld1.
(109)... Vdata = Vdata1 + Vth
Next, the details of the configuration of the data driver 22 will be described.
FIG. 5 is a block diagram showing a specific configuration of the data driver 22 shown in FIG.
As shown in Fig. 5, the data driver 22 includes a shift register 111, a data register block 112, buffers 113 (1) to 113 (m), 119 (1) to 119 (m), ADC 114 (1) -114 (m), level shift circuit (shown as "LS" in the figure) (115 (1) -115 (m), 117 (1) -117 (m)), data Latch circuit (shown as "D-latch" in the figure) (116 (1) to 116 (m)), VDAC (118 (1) to 118 (m)), switch (Sw1 (1) to Sw1 (m) ), Sw2 (1) to Sw2 (m), Sw3 (1) to Sw3 (m), Sw4 (1) to Sw4 (m), Sw5 (1) to Sw5 (m) and SW6.
Sw3 (1) to Sw3 (m) correspond to a switch circuit.
The shift register 111 generates shift signals by shifting the start pulse SP2 supplied from the sequential control section 16 in response to a clock signal, and supplies these shift signals to the sequential data register block 112.
The data register block 112 is composed of m registers. The digital data Din (i) (i = 1 to m) generated based on the image data is supplied from the control unit 16 to the data register block 112. The data register block 112 holds these digital data Din (i) (i = 1 to m) sequentially in each of the m registers in accordance with the shift signal supplied from the shift register 111.
The buffer 113 (i) (i = 1 to m) is for applying the voltage of the data line Ldi (i = 1 to m) to the ADC 114 (i) (i = 1 to m) as analog data, respectively. It is a buffer circuit.
ADC 114 (i) (i = 1 to m) is an analog-to-digital converter that converts an analog voltage into a digital signal. ADC 114 (i) converts the analog data applied by buffer 113 (i) into digital data output signal Dout (i). The ADC 114 (i) is used as a measuring instrument (voltage measuring circuit) for measuring the voltage of the data line Ldi (i = 1 to m).
The level shift circuit 115 (i) level shifts the digital data of the ADC 114 (i) generated through the conversion to confirm the power supply voltage of the circuits i = 1 to m.
The digital data Din (i) is held in each register of the data register block 112. The data latch circuit 116 (i) holds the digital data Din (i) supplied from each register of the data register block 112. The data latch circuit 116 (i) latches and holds the digital data Din (i) at a timing at which the data latch pulse DL (pulse) supplied from the controller 16 rises.
The level shift circuit 117 (i) level shifts the digital data Din (i) held by the data latch circuit 106 (i) to confirm the power supply voltage of the circuits i = 1 to m. .
VDAC 118 (i) (i = 1 to m) is a digital-to-analog converter that converts digital signals into analog voltages. The VDAC 118 (i) converts the digital data Din (i) level-shifted by the level shift circuit 117 (i) into an analog voltage, and converts the buffer 119 (i) (i = 1 to m). To the data line Ldi. The VDAC 118 (i) corresponds to a drive signal application circuit that generates drive signals and applies them to the next circuit.
The buffer 119 (i) is a buffer circuit for outputting an analog voltage, that is, outputting from the VDAC 118 (i) to the data line Ldi (i = 1 to m).
6A and 6B are views for explaining the structure and function of the VDAC 118 shown in FIG.
FIG. 6A shows the general structure of the VDAC 118, and FIG. 6B shows the structure of the VD1 setting circuit 118-3 and the VD1023 setting circuit 118-4 included in the VDAC 118. FIG. Indicates.
As shown in Fig. 6A, the VDAC 118 (i) has a gray voltage generation circuit 118-1 and a gray voltage selection circuit 118-2.
The gray voltage generation circuit 118-1 generates a predetermined number of gray voltages (analog voltages) determined by the number of bits of the digital signal input to the VDAC 118. When the digital signal to be input is 10 bits (D0-D9) as shown in Fig. 6A, the gradation voltage generation circuit 118-1 generates 1024 gradation voltages VD0 to VD1023.
The gray scale voltage generation circuit 118-1 includes a VD1 setting circuit 118-3, a VD1023 setting circuit 118-4, a resistor R2, and a ladder resistor circuit 118-5.
The VD1 setting circuit 118-3 is a circuit for setting the voltage value of the gradation voltage VD1 based on the control signal VL_SEL supplied from the control unit 16, and the voltage VD0 is applied. The voltage VD0 is the minimum gradation voltage and is set to the same voltage as the power supply voltage ELVSS, for example.
As shown in Fig. 6B, the VD1 setting circuit 118-3 includes resistors R3, R4-1 to R4-127, and a VD1 selection circuit 118-6.
The resistors R3, R4-1 to R4-127 are voltage divider resistors connected in series in this order. The voltage VD0 is applied to one end of the resistor R3 connected in series. One end of the resistor R4-127 side connected in series is connected to one end of the resistor R2. The voltage at the connection point between the resistor R3 and the resistor R4-1 is the voltage VA0, the voltage at the connection point between the resistor 4-i and the resistor 4-i + 1 is VAi (i = 1 to 126), and the resistors R4-127 and the resistor R2 The voltage at the junction of is VA127.
The VD1 selection circuit 118-6 selects some voltages among the voltages VA0 to VA127 based on the control signal VL_SEL supplied from the control unit 16, and outputs the selected voltage as the gradation voltage VD1. The VD1 setting circuit 118-3 sets the gray voltage VD1 to a value corresponding to the threshold voltage Vth0.
The VD1023 setting circuit 118-4 is a circuit for setting the voltage value of the maximum gradation voltage VD1023 based on the control signal VH_SEL supplied from the control unit 16 and the voltage DVSS applied by the analog power supply 14.
As shown in Fig. 6B, the VD1023 setting circuit 118-4 includes resistors R5-1 to R5-127 and R6, and a VD1023 selecting circuit 118-7.
The resistors R5-1 to R5-127 and R6 are divided resistors connected in series in this order. One end of the resistor R5-1 side of the resistor connected in series is connected to the other end of the resistor R2, and a voltage DVSS is applied to one end of the resistor R6 side of the resistor connected in series. The voltage at the junction of these resistors R2 and R5-1 is the voltage VB0, the voltage at the junction of the resistors R5-i and R5-i + 1 is the voltage VBi (i = 1 to 126) and the junction of the resistors R5-127 and R6. The voltage at is the voltage VB127.
The VD1023 selection circuit 118-7 selects some voltages from the voltages VB0 to VB127 based on the control signal VH_SEL supplied from the control unit 16, and outputs the selected voltage as the gradation voltage VD1023.
The ladder resistor circuit 118-5 includes, for example, a plurality of ladder resistors of R1-1 to R1-1022 connected in series. Each ladder resistor R1-1 to R1-1022 has the same resistance value.
One end of the resistor R1-1 side of the ladder resistor circuit 118-5 is connected to the output terminal of the VD1 setting circuit 118-3, and the voltage VD1 is applied to this terminal. One end of the resistor R-1022 side of the ladder resistor circuit 118-5 is connected to the output terminal of the VD1023 setting circuit 118-4, and a voltage VD1023 is applied to this terminal.
The ladder resistors R1-1 through R1-1022 divide the voltages VD1-VD1023 evenly. The ladder resistance circuit 118-5 outputs the voltage divided evenly to the gray voltage selection circuit 118-2 as gray voltages VD2 to VD1022.
The digital signal level-shifted by the level shift circuit 117 (i) is input to the gray voltage selection circuit 118-2 as digital signals D0 to D9. Thereafter, the gray voltage selection circuit 118-2 selects a voltage corresponding to the values of the digital signals D0 to D9 input from the respective gray voltages VD0 to VD1023 supplied from the gray voltage generation circuit 118-1, and VDAC. The gray scale voltage is output as the output voltage VOUT of 118.
As described above, the VDAC 118 (i) converts the input digital signal into an analog voltage corresponding to the gray value of the digital signal.
In this embodiment, the value of the digital signal input to the VDAC 118 is set to a range narrower than the entire gradation range determined by the number of bits of the image data, and the output voltage output by the VDAC 118 (i). The voltage range of VOUT is set to a range of a part of the entire gradation voltages VD0 to VD1023 generated by the gradation voltage generation circuit 118-1.
As described above, in this embodiment, correction is performed on the image data supplied based on the value of the threshold voltage Vth obtained at that time in order to reduce the deviation of the image data due to the deviation of the threshold voltage Vth. By performing this correction, the width of the voltage range of the output voltage VOUT of all the gradation voltages of the image data does not change, but the lower limit voltage value within the voltage range of the first gradation of the image data is the variation amount of the threshold voltage Vth ((ΔVth) Only the value corresponding to is shifted in. Therefore, the voltage range of the output voltage VOUT with respect to all the gray scale values of the image data shifts within all the gray scale voltages VD0 to VD1023.
Here, the respective gradation voltages VD1 to VD1023 set by the gradation voltage generation circuit 118-1 are set to values at uniform intervals. That is, even if the voltage range of the output voltage VOUT shifts, the change characteristic of the output voltage of the VDAC 118 (i) corresponding to the gray value of the image data can be kept constant.
In addition, when the gray value of the image data is zero, the VDAC 118 (i) outputs the minimum gray voltage VD0 corresponding to the zero gray level. At this time, since the organic EL element 101 is not made to emit light as a black display, it is not necessary to perform correction based on the above-described value of the threshold voltage Vth. Therefore, the gradation voltage VD0 is set to a fixed voltage value.
The ADC 114 (i) and the VDAC 118 (i) have the same bit width, for example, and the voltage width corresponding to one gradation is set to the same value.
The switches Sw1 (i) (i = 1 to m) are switches for connecting or disconnecting between the data line Ldi and the output terminal of the buffer 119 (i), respectively.
When a voltage signal having a voltage value Vdata is applied to the data line Ldi, each switch Sw1 (i) is turned on (closed) after the On1 signal is supplied from the controller 16 as the switch control signal S1, and the buffer ( The output terminal of 119 (i) and the data line Ldi are connected.
After application of the voltage signal of the voltage value Vdata to the data line Ldi, each switch Sw1 (i) is turned off (open) when the Off1 signal is supplied from the controller 16 as the switch control signal S1, and the buffer 119 (i Disconnect the connection between the output terminal of)) and the data line Ldi.
Each switch Sw2 (i) (i = 1 to m) is a switch for connecting or disconnecting between the data line Ldi and the input terminal of the buffer 119 (i).
When performing voltage measurement on the data line Ldi by the auto zero method, each switch Sw2 (i) is turned on (closed) when the On2 signal is supplied from the controller 16 as the switch control signal S2, and the data line Ldi The input terminal of the buffer 113 (i) is connected.
After the voltage measurement of the data line Ldi is finished, each switch Sw2 (i) is turned off when the Off2 signal is supplied from the control unit 16 as the switch control signal S2, so that the data line Ldi and the buffer 113 (i). Disconnect the connection between the output terminals.
Each switch Sw3 (i) is a switch for connecting or disconnecting between the data line Ldi and the output terminal of the reference voltage Vref of the analog power supply 14.
When the reference voltage Vref is applied to the data line Ldi, each switch Sw3 (i) is turned on when the On3 signal is supplied from the control unit 16 as the switch control signal S3, so that the data line Ldi and the analog power supply 14 Connect the output of the reference voltage Vref.
In order to measure the voltage by the above-described auto zero method, the On3 signal is supplied to the switch Sw3 (i) only for a short period of applying the reference voltage Vref. Subsequently, each switch Sw3 (i) is turned off when the Off3 signal is supplied from the control unit 16 as the switch control signal S3, so that the switch Sw3 (i) is turned off. The connection between the output terminals of the reference voltage Vref is cut off.
The switch Sw4 (1) is a switch for switching the connection between the output terminal of the data latch circuit 116 (1) and one end of the switch Sw6 or the level shift circuit 117 (1). This switch has a front terminal connected to one end of the switch Sw6 and a DAC side terminal connected to the level shift circuit 117 (1).
Each switch Sw4 (i) (i = 2 to m) is connected between the output terminal of the data latch circuit 116 (i) and one end of the switch Sw5 (i-1) or the level shift circuit 117 (i). Switch to switch. This switch has a DAC side terminal connected to the level shift circuit 117 (i) and a front terminal connected to one end of the switch Sw5 (i-1).
When outputting the measurement voltage Vmeas (t) to the control unit 16 from the data driver 22 as output signals Dout (1) to Dout (m), each switch Sw4 (i) (i = 1 to m) is controlled. From 16, the Connect_front signal is supplied as the switch control signal S4.
The switch Sw4 (i) (i = 1 to m) connects the front terminal via the output terminal of the data latch circuit 116 (i) and the Connect_front signal supplied from the control unit 16.
When a voltage signal having a voltage value Vdata is applied to each data line Ldi, Connect_DAC is supplied from the controller 16 as a switch control signal S4 to each switch Sw4 (i) (i = 1 to m). This switch Sw4 (i) connects the output terminal of the data latch circuit 116 (i) and the DAC side terminal via a Connect DAC signal.
Each switch Sw5 (i) (i = 1 to m) includes an input terminal of the data latch circuit 116 (i), a data register block 112, a level shift circuit 115 (i), and a switch Sw4 (i). It is a switch to switch the connection between either.
The switch Sw5 (i) is input to the data latch circuit 116 (i) and the level shift circuit 115 (i) when the Connect_ADC signal is supplied from the controller 16 to the switch SW5 (i) as the switch control signal S5. Connect the output terminal of.
The switch Sw5 (i) is a switch control signal S5 from the control unit 16, when the Connect_rear signal is supplied to the switch Sw5 (i), the front of the input terminal of the data latch circuit 116 (i) and the switch Sw4 (i + 1). Connect the terminal.
The switch Sw5 (i) switches the input terminal of the data latch circuit 116 (i) and the output terminal of the data register block 112 when the Connect_DRB signal is supplied from the controller 16 to the switch Sw5 (i) as the switch control signal S5. Connect.
The switch Sw6 is a switch for connecting or disconnecting between the front terminal of the switch Sw4 (1) and the control unit 16.
When outputting the measurement voltage Vmeas (t) to the controller 16 as output signals Dout (1) to Dout (m), the switch Sw6 is supplied with the On6 signal from the controller 16 to the switch Sw6 as the switch control signal S6. It turns on at the time, and connects between the front terminal of switch Sw4 (1), and the control part 16. FIG.
When the measurement voltage Vmeas (t) is completely output, the switch Sw6 is turned off when the Off6 signal is supplied from the controller 16 to the switch control signal S6 to Sw6, so that the front terminal and the controller 16 of the switch Sw4 (1). Block the connection between.
The analog power supply 14 is a power supply for applying the reference voltage Vref, the voltage DVSS, and the DV0 to the data driver 22.
The reference voltage Vref is applied to the data driver 22 to draw current from each pixel (21 (i, j)) at the time of measuring the voltage of the data line Ld1 by the auto zero method. The power supply voltage ELVSS of the negative voltage applied by the circuit 12 on each pixel circuit DC, and the absolute value of the potential difference with respect to the power supply voltage ELVSS is the threshold voltage Vth of the transistor T3 of each pixel 21 (i, j). It is set to a value larger than the absolute value of.
The analog voltages DVSS and VD0 are analogs for driving the buffer 113 (i), the buffer 119 (i), the ADC 114 (i) and the VDAC 118 (i) (i = 1 to m). Voltage. The analog voltage DVSS is a negative voltage with respect to the power supply voltage ELVSS applied by the anode circuit 12 to the anode line La, and is set at, for example, about -12V.
The logic power supply 15 is a power supply for applying voltages LVSS and LVDD to the data driver 22. The voltages LVSS and LVDD are logical voltages for driving the data latch circuit 116 (i (i = 1 to m), the data register block, and the shift register of the data driver 22. Here, the voltages DVSS, VD0, LVSS, and LVDD are set to satisfy a condition, for example, (DVSS-VD0) <(LVSS-LVDD).
The control unit 16 stores each data, and controls each unit based on the stored data. As described above, the control unit 16 according to the present embodiment stores the digital data Din (i) (i = 1 to m) generated through various corrections to the image data of the supplied digital signal. Has a structure to be supplied to the control unit, and processing such as calculations in the control unit 16 is performed on the digital value. In addition, the following description is made by comparing a digital signal with an analog voltage value for a suitable reason.
For example, the controller 16 controls each unit at an initial stage such as shipment of the display device 1, measures the voltage of the data line Ldi by the auto zero method through the data driver 22, and controls all the pixels ( The measured voltages Vmeas (t1), Vmeas (t2), and Vmeas (t3) are obtained for 21 (i, j)).
Thereafter, the control unit 16 performs calculation according to equation (103) using the measurement voltage Vmeas (t1), similarly to Vmeas (t2), so that each pixel 21 (i, j) is a characteristic parameter. The (initial) threshold voltage Vth0 of the transistor T3 and the C / β value of the pixel driving circuit DC are obtained. In addition, the controller 16 obtains an average value <C / β> of C / β of all the pixels 21 (i, j). In addition, a settling time t0 for the actual operation is determined, and an offset voltage Voffset is obtained by calculation according to equation (105).
Further, the controller 16 calculates ΔVmeas (t3) by using the measured voltage Vmeas (t3), and obtains the deviation parameter Δβ / β as an attribute parameter by the calculation according to equation (106).
Subsequently, in the operation of supplying the image data, the control unit 16 controls each unit and measures the voltage of the data line Ldi by the auto zero method while the settling time is t0 through the data driver 22, The measurement voltage Vmeas (t0) of all the pixels 21 (i, j) is obtained.
The control unit 16 obtains the voltage value Vdata0 by converting a later-described data value (voltage amplitude) corresponding to the gradation value of the image data on the basis of the gradation voltage data corresponding to the supplied image data.
In color display, the white display required for each RGB needs to be the maximum gray scale. However, the organic EL element 101 of each RGB color of the pixel 21 (i, j) usually has a characteristic of light emission luminance with respect to a current value of a supplied current.
As a result, the control unit (10) can make the current value of the current supplied to the organic EL element 101 of each RGB color with respect to the gradation value of the image data to be a different value which becomes white display when each RGB is the maximum gradation. 16), the voltage amplitude is converted to the gradation value of the image data for each RGB.
The control unit 16 acquires the voltage value Vdata0 by performing such conversion of the voltage amplitude on all the pixels 21 (i, j).
After acquiring the voltage value Vdata0, the control unit 16 obtains the correction voltage value Vdata1 based on (Δβ / β) according to equation (107).
The control unit 16 obtains the correction voltage value Vdata based on the threshold voltage Vth as the final output voltage according to equations (108) and (109). Specifically, the controller 16 corrects the voltage value Vdata1 by bit addition of the corresponding threshold voltage Vth to obtain the voltage value Vdata.
The control unit 16 outputs the corrected image data Vdata of all the pixels 21 (i, j) to the data driver 22 for each row as digital data Din (i) (i = 1 to m).
7 is a block diagram showing the configuration of the control unit shown in FIG. 1.
FIG. 8 is a diagram illustrating each storage area of the memory shown in FIG. 7.
The control unit 16 includes a CPU (Central Processing Unit) 121, a memory 122, and a LUT (Look Up Table) 123 as shown in FIG. 7 to execute the above-described processing.
The CPU 121 controls the anode circuit 12, the selection driver 13, and the data driver 22 and executes each of the various operations.
The memory 122 includes a read only memory (ROM), a random access memory (RAM), and the like, and stores each processing program executed by the CPU 121 and stores various data required for processing.
The memory 122 is an area for storing various types of data. As shown in FIG. 8, the memory 122 includes a pixel data storage area 122a, a <C / β> storage area 122b, and a Voffset storage area 122c.
The pixel data storage area 122a includes the measurement voltages Vmeas (t1), Vmeas (t2), Vmeas (t3), ΔVmeas, threshold voltages Vth0, Vth, C / β, and the like for each pixel 21 (i, j). , Area for storing each data of Δβ / β.
The <C / β> storage area 122b is an area for storing the average value <C / β> of each pixel 21 (i, j) C / β.
The Voffset storage area 122c is an area for storing the offset voltage Voffset defined by equation (105).
The LUT 123 is a table set in advance for converting data values of respective RGB colors for the supplied image.
The control unit 16 converts the data value for each RGB to the image data value supplied by referring to this LUT 123.
9A and 9B show examples of conversion characteristics of image data in the LUT shown in FIG. 7 when data conversion is performed when the VDAC 118 (i) is 10 bits. It is a graph.
10A and 10B are graphs for explaining image data conversion characteristics in the LUT. In this example, the post-conversion data values differ in the order of blue (B)> red (R)> green (G).
First, the horizontal axes in FIGS. 9A and 9B are input data, that is, gray scale values of image data, and the image data is 10 bits. The vertical axis in FIGS. 9A and 9B represents a gray value of converted data in which image data is converted by the LUT 123. In the data driver 22, the voltage amplitude of RGB is set based on this converted data. In addition, the conversion characteristic of the gray value of the conversion data with respect to the gray value of the image data is preset in the LUT 123. FIG. 9A illustrates a case where the gray value of the converted data is set in a linear relationship with respect to the gray value of the image data. 9B shows a case where the gray value of the converted data is set to have a curved gamma characteristic with respect to the gray value of the image data. The relationship between the gray scale value of the converted data and the gray scale value of the image data in the LUT 123 can be freely set as necessary.
Here, when the VDAC 118 (i) of the data driver 22 has a 10-bit configuration, it can receive input data of 0 to 1023. However, the converted data after being converted by the LUT 123 is set to about 0 to 600. This is based on the following reasons.
10A and 10B, the abscissa represents input data similarly to FIGS. 9A and 9B. 10A and 10B show the digital data Din (i) input to the data driver 22 from the control unit 16 corresponding to the gradation value of the image data.
Here, FIG. 10 (a) is based on FIG. 9 (a), and FIG. 10 (b) is based on FIG. 9 (b). As described above, in the present embodiment, correction is performed on the image data supplied based on the evaluation value of the threshold voltage Vth of the control unit 16.
This correction includes correction based on the variation of the current amplification factor β with respect to the image data, as shown in equation (109), and correction which adds an amount corresponding to the threshold voltage Vth of the data obtained as a result of the correction. .
Here, as described above, the gradation voltage VD1 in the VDAC 118 of the data driver 22 is set to a value when the threshold voltage Vth is the initial value Vth0, so the amount to be added with respect to the correction of the gradation voltage VD1 is This is an amount corresponding to ΔVth, which is an amount of change from the initial value Vth0 of the threshold voltage Vth.
Here, the gradation value of the digital data Din (i) output from the control unit 16 must be within the inputtable range (0 to 1023) of the VDAC 118 (i) of the data driver 22.
That is, the maximum value of the gradation value of the converted data after being converted by the LUT 123 is a value obtained by subtracting the amount added by the correction from the input possible range of the VDAC 118 (i) of the data driver 22 in advance. Is set.
Here, the amount added by the correction is not a fixed amount because it is determined according to the change amount [Delta] Vth of the threshold voltage Vth, and gradually increases with the use time.
That is, the maximum value of the gradation value of the conversion data by the LUT 123 is determined by estimating the maximum value of the amount added by correction based on the expected usage time of the display apparatus 1, for example.
In addition, when the gradation value of the image data is zero and black display, the organic EL element 101 is in a non-luminescing state. Therefore, it is not necessary to carry out the above correction at this time. As a result, when the image data of the black display has zero gray scale, the controller 16 supplies the zero gray scale to the data driver 22 as it is without referring to the LUT 123 and without performing the threshold deviation correction. .
Next, the operation of the display device 1 according to the present embodiment will be described.
In the initial stage, when the voltage measurement of each data line Ldi is performed by the auto zero method, the control unit 16 controls the anode circuit 12 to apply the voltage ELVSS to the anode line La.
Fig. 11 is a timing chart showing the operation of each unit in the case where voltage measurement is performed by the auto zero method.
As shown in FIG. 11, the control unit 16 supplies a start pulse to the selection driver 13 at time t10. At this time, the selection driver 13 outputs the Gate 1 signal of the VgH level to the selection line Ls1.
When the selection driver 13 outputs the gate (1) signal having the VgH level to the selection line Ls1, the transistors T1 and T2 of the pixels 21 (i, j) (i = 1 to m) in the first row are turned on. It is in a state. When the transistor T1 is in the on state, the gate-drain of the transistor T3 is connected, and the transistor T3 is in a diode connected state.
Moreover, the control part 16 supplies each data of Off1, Off2, On3, Connect_front, Connect_ADC, and Off6 to the data driver 22 as switch control signals S1-S6 at the time t10.
12 (a) and 12 (b) are diagrams showing a connection relationship with respect to each switch when data is supplied to the control unit 16 in the data driver.
At this time, as shown in Fig. 12A, the switch Sw4 (i) is supplied with the Connect_front signal from the control unit 16, and the output terminal of the data latch circuit 116 (i) and the front terminal i = 1 to m) is connected.
At this time, as shown in Fig. 12A, the Connect_ADC signal is supplied from the control unit 16 to input the level of the data latch circuit 116 (i) and the level shift circuit 115 (i) (i = 1). Connect the output terminal of ~ m).
13 (a), 13 (b) and 13 (c) are diagrams illustrating a connection relationship of each switch when voltage measurement is performed by the auto zero method.
The switches Sw1 (i) and Sw2 (i) are turned off when Off1 and Off2 signals are supplied from the control unit 16, respectively. Further, the switch Sw3 (i) (i = 1 to m) is turned on when the On3 signal is supplied from the control unit 16.
Since the reference voltage Vref of the analog power supply 14 has a negative voltage, when the transistors T1 to T3 are in the on state, the analog power supply 14 is the pixels 21 (i, 1) in the i-th column (i = 1). The current Id is drawn through the data line Ldi from ˜m).
At this time, in the organic EL element 101 of the pixels 21 (i, 1) (i = 1 to m) in the first row, the potential of the cathode is Vcath, and the anode is of a lower potential than Vcath. Since the current does not flow and does not emit light.
In addition, since the switches Sw1 (i) and Sw2 (i) (i = 1 to m) are in an off state, the current Id drawn by the analog power supply 14 is equal to the buffers 113 (i) and 119 (i). It does not flow at (i = 1 to m).
As a result, as shown in Fig. 13A, the current Id passes through the data lines Ldi from the transistors T3 and T2 of the pixels 21 (i, 1) (i = 1 to m) in the first row. It flows into the analog power supply 14.
When the current Id flows, the holding capacitor Cs of each pixel 21 (i, 1) (i = 1 to m) is charged at a voltage determined by the reference voltage Vref.
Subsequently, at the time t11, when charging of these capacities ends, the control unit 16 supplies the data driver 22 with the Off3 signal as the switch control signal S3.
When the Off3 signal is supplied from the control unit 16, as shown in FIG. 13B, the switch Sw3 (i) is turned off. At this time, each of the switches Sw1 (i) and Sw2 (i) remains in the off state. That is, the connection between the organic EL panel 21 and the data driver 22 is cut off by switching the switch Sw3 (i) to the off state. As a result, the data line Ldi becomes a high impedance (HZ) state.
Immediately after the high impedance state is reached in the data line Ldi, the charge accumulated in the storage capacitor Cs is held at the previous value, whereby the on state in the transistor T3 is maintained.
As a result, current continues to flow between the drain and the source of the transistor T3, and gradually increases so that the potential at the source terminal side of the transistor T3 approaches the potential at the drain terminal side. As a result, the current value of the current flowing between the drain and the source of the transistor T3 continues to decrease.
In connection with this, part of the electric charge accumulated in the storage capacitor Cs is discharged, and the voltage between both ends of the storage capacitor Cs continues to decrease. As a result, the gate voltage Vgs of the transistor T3 gradually decreases, so that the absolute value of the voltage of the data line Ldi gradually decreases from the reference voltage Vref.
At time t12, which is the time when the preset fixing time t elapses from time t11, the control unit 16 supplies the data driver 22 with the On2 signal as the switch control signal S2. This settling time t is set to satisfy the condition of C / (βt) &lt;
At this time, as shown in Fig. 13C, the switch Sw2 (i) is turned on with the On2 signal supplied from the controller 16, and the ADC 114 (i) changes the voltage value of the data line Ldi. Obtained as measurement voltage Vmeas (t1) (i = 1 to m).
The level shift circuit 115 (i) level shifts the measured voltage Vmeas (t1) obtained by the ADC 114 (i) (i = 1 to m).
As shown in Fig. 12A, since the input terminal of the data latch circuit 116 (i) and the output terminal of the level shift circuit 115 (i) are respectively connected via the switch Sw5 (i), each level The measurement voltage Vmeas (t1) level-shifted by the shift circuit 115 (i) is supplied to the data latch circuit 116 (i) (i = 1 to m).
The control unit 16 outputs the data latch pulse DL (pulse) to the data driver 22, and after receiving this pulse, each data latch circuit 116 (i) (i = 1 to m) is supplied with the measured voltage. Hold Vmeas (t1).
At time t13 when the Gate 1 signal falls, the control unit 16 supplies the data driver 22 with the On6 signal as the switch control signal S6. After reception of this signal, the switch Sw6 is shown in FIG. As shown by), it turns on.
As shown in FIG. 12B, the control unit 16 is connected to the output terminal of the data latch circuit 116 (1) and one end of the switch Sw6 (i) via the front terminal of the switch Sw4 (1). Connect-rear signal is supplied from the switch Sw4 (i) to the output terminal of the data latch circuit 116 (i) and the input terminal of the switch Sw5 (i-1) is connected to the switch Sw4 (i) (i = 2 to m). It is connected via the front terminal.
For this reason, the data latch circuit 116 (i) has the first row of pixels 21 (i, 1) held by the data latch circuit 116 every time DL (pulse) is supplied from the control unit 16. The measured voltage Vmeas (t1) of the data line Ldi is sequentially transmitted to the control unit 16 (i = 1 to m) as the data Dout (i).
The control unit 16 obtains this data Dout (i) (i = 1 to m) and stores this data in the pixel data storage area 122a of the memory 122 shown in FIG. In this way, the voltage measurement of the pixels 21 (i, 1) (i = 1 to m) in the first row is completed.
If the Gate 2 signal rises at time t20, the control unit 16 supplies the switch control signals S1 to S6 to the data driver 22 in the same manner as described above, whereby the second row of pixels ( The voltage measurement of the data line Ldi (i = 1 to m) for 21 (i, 2) is performed.
This measurement is repeated for every row, and after performing the voltage measurement of the data line Ldi (i = 1 to m) for the pixels 21 (i, n) in the nth row, all the voltage measurements at time t1. This ends.
Thereafter, the control unit 16 sets the fixing time t to t2 by the same method, and sets the data line Ldi for each pixel 21 (i, j) (i = 1 to m, j = 1 to n). Perform the voltage measurement of. The controller 16 acquires the measurement voltage Vmeas (t2) of the data line Ldi for each pixel 21 (i, j) at the settling time t2, and stores the memory 122 (i = 1 to m, j = 1 to n). ) Is stored in the pixel data storage area 122a.
Next, the control unit 16 sets the settling time t to t3 by the same method, and the data line Ldi for each pixel 21 (i, j) (i = 1 to m, j = 1 to n). Perform the voltage measurement of. The controller 16 acquires the measurement voltage Vmeas (t3) of the data line Ldi for each pixel 21 (i, j) at the settling time t3, and stores the memory 122 (i = 1 to m, j = 1 to n). ) Is stored in the pixel data storage area 122a.
14 is a diagram for explaining a driving sequence executed by the control unit when a correction parameter is obtained.
The control unit 16 obtains the measurement voltages Vmeas (t1), Vmeas (t2), and Vmeas (t3), stores them in the pixel data storage regions 122a of the memory 122, and then displays the drive sequence shown in FIG. 14. By calculating according to the above, a correction parameter is obtained.
The control unit 16 reads the measurement voltages Vmeas (t1) and Vmeas (t2) of the data lines Ldi for the pixels 21 (1,1) from each pixel data storage region 122a of the memory 122 ( Step S11).
In addition, the control unit 16 obtains the threshold voltages Vth0 and C / β for the pixels 21 (1, 1) by calculating according to the equation (103) (step S12).
The control unit 16 performs this process for all the pixels 21 (i, j) (i = 1 to m, j = 1 to n), and the threshold voltages for all the pixels 21 (i, j). Once Vth0 and C / β are acquired, the average value <C / β> of C / β of all the pixels 21 (i, j) is obtained (step S13), and the settling time t = t0 is set at the time of actual operation. do.
The control unit 16 obtains the offset voltage Voffset defined by equation (105) using this settling time t0 (step S14).
The control unit 16 stores the obtained average value <C / β> and the offset voltage Voffset in the <C / β> storage region 122b and the offset voltage storage region 122c of the memory 122, respectively. The control unit 16 also measures the measured voltage Vmeas (t3) of the pixel 21 (i, j) from each pixel data storage region 122a of the memory 122 (i = 1 to m, j = 1 to n). ) Is read (step S15).
The control unit 16 transforms equation (106) using Vth0 previously obtained as the Vth of the measured voltage Vmeas (t3) of each pixel 21 (i, j), and calculates each pixel 21 (i, j). (DELTA) β / (beta) of (i = 1-m, j = 1-n) is acquired (step S16).
The controller 16 stores the obtained Δβ / β in each pixel data storage area 122a of the memory 122.
FIG. 15 is a diagram for explaining a driving sequence executed by the control unit 16 when a voltage signal based on supplied image data is output to the data driver after correction.
In the actual operation, the image data is supplied to the control unit 16. The control unit 16 corrects the image data in accordance with the drive sequence 2 shown in FIG. 15.
The control part 16 controls each part according to the timing chart shown in FIG. 11, and acquires the measured voltage Vmeas (t0) in the settling time t = t0 determined with respect to actual operation from the data driver 22 (step S21). ). Thereafter, the controller 16 stores the obtained measured voltage Vmeas (t0) in the pixel data storage region 122a of the memory 122.
When a digital signal of image data is input, the control unit 16 controls each RGB image referring to the LUT 123 of the image data 21 (i, j) (i = 1 to m, j = 1 to n). Convert the gradation value for. This converted gradation value is designed as the voltage value Vdata0, and consists of an original gradation signal for each pixel 21 (i, j) (step S22).
As described above, the maximum value of the original gradation signal is equal to or less than the maximum value in the input range of the VDAC 118 (i) minus the correction amount based on the characteristic parameter such as the threshold voltage Vth described above. Is set.
The control unit 16 obtains a signal corresponding to the voltage value Vdata1 by calculating according to equation (107) using Δβ / β as a correction parameter of the deviation of β (step S23).
The control unit 16 reads the offset voltage Voffset from the offset voltage storage region 122c of the memory 122 and calculates the offset voltage Voffset using the measured voltage Vmeas (t0) and the offset voltage Voffset according to equation (108). The threshold voltage Vth as a correction amount is obtained (step S24).
The control unit 16 acquires a signal corresponding to the voltage value Vdata as the correction gradation signal by adding the voltage value Vdata1 and the threshold voltage Vth according to equation (109) (step S25).
The control unit 16 executes this drive sequence 2 for each pixel. The control unit 16 also outputs a signal corresponding to the voltage value Vdata to the data driver 22 for each row as data Din (1) to Din (m).
Fig. 16 is a timing diagram showing the operation of each part in the actual operation.
The control part 16 controls each part according to the data output timing diagram shown in FIG. 16, and outputs data Din (1) -Din (m) to the data driver 22. FIG.
The control unit 16 supplies Off1, Off2, Off3, Connect_DAC, Connect_DRB, and Off6 signals to the data driver 22 as the switch control signals S1 to S6 at time t30.
As shown in FIG. 17, Sw2 (i) and Sw3 (i) enter the off state when the signals Off2 and Off3 are supplied from the control unit 16, respectively, and the buffer 113 (i) and the data line Ldi are separated. And the connection between the analog power supply 14 and the data line Ldi.
Each switch Sw1 (i) is turned on when the On1 signal is supplied from the controller 16, and the VDAC 118 (i) and the data line Ldi are connected through the buffer 119 (i).
FIG. 18 is a diagram illustrating a connection relationship of each switch when inputting data to the data driver 22 from the control unit 16.
As shown in Fig. 18, each switch Sw5 (i) switches the input terminal of the data latch circuit 116 (i) and the output terminal of the data register block 112 when the Connect_DRB signal is supplied from the controller 16 to each of them. Connect.
Each switch Sw4 (i) connects the output terminal of the data latch circuit 116 (i) and the DAC side terminal when the Connect_DAC signal is supplied from the control unit 16 to each of them.
The switch Sw6 is turned off when the Off6 signal is supplied from the control unit 16, and cuts off the connection between the data latch circuit 116 (1) and the control unit 16.
The control unit 16 raises the start pulse SP2 at time t31 and drops the start pulse SP2 to the low level at time t32.
When the start pulse SP2 falls to the low level, the shift register 111 of the data driver 22 generates a shift signal by sequentially shifting this start pulse SP2 in accordance with a clock signal, as shown in FIG. The generated shift signal is supplied to block 112.
The data register block 112 sequentially fetches the data Din (1) to Din (m) by synchronizing with the supplied shift signal.
When the Gate 1 signal rises to the VgH level at time t33, the transistors T1 and T2 of the pixels 21 (i, j) (i = 1 to m) are turned on.
The control unit 16 raises the data latch pulse DL (pulse), and the data latch circuit 116 (i) (i = 1 to m) of the data driver 22 raises the data latch pulse DL (pulse) when the data latch pulse DL (pulse) is raised. The data is latched at the timing.
The level shift circuit 117 (i) performs a level shift on the data latched by the data latch circuit 116 (i), and converts the level shifted data into the VDAC 118 (i) (i = 1 to m). Supplies).
The VDAC 118 (i) converts this digital data into a negative analog voltage and applies the converted negative analog voltage to the data line Ldi through the buffer 118 (i) (i = 1 to m).
When a negative analog voltage is applied to the data line Ldi, the organic EL element 101 of each pixel 21 (i, 1) (i = 1 to m) becomes reverse biased and interrupts the current flow. The current flows from the anode circuit 12 to the VDAC 118 (i) of the data driver 22 through the transistors T3 and T2 of the pixels 21 (i, 1) (i = 1 to m) and the data line Ldi. Flow.
Since the transistor T1 of each pixel 21 (i, 1) (i = 1 to m) is in the on state, the transistor T3 is connected to the gate-drain and diode-connected. For this reason, transistor T3 operates in a saturation region, and drain current Id according to diode characteristics flows through transistor T3.
Since the transistor T1 is in the on state and the drain current Id flows through the transistor T3, the gate voltage Vgs of the transistor T3 is set to a voltage defining the drain current Id, and the holding capacitor Cs is charged by the gate voltage Vgs.
In this manner, the data driver 22 extracts the current corrected based on the correction parameter from the transistor T3 of each pixel 21 (i, 1) (i = 1 to m) as shown in FIG. In the holding capacitor Cs, the gate voltage Vgs of the transistor T3 based on the voltage value Vdata is held.
In this manner, writing of data to the storage capacitor Cs of each pixel 21 (i, 1) (i = 1 to m) in the first row is completed.
The control unit 16 raises the start pulse SP at the time t34 by the falling of the DL (pulse), drops the start pulse SP2 at the time t35, and displays each pixel 21 (i, 2) in the second row ( i = 1 to m)) is written into the holding capacitor Cs.
In the same way, the control unit 16 sequentially controls pixels 21 (i, 3) (i = 1 to m),. , The voltage based on the voltage value Vdata is written into the holding capacitor Cs of 21 i, n) (i = 1 to m).
After writing the voltage value Vdata to the storage capacitors Cs of all the pixels 21 (i, j), if the Gate (n) signal is VgL, the transistors T1 and T2 of all the pixels 21 (i, j) It turns off.
When the transistors T1 and T2 are turned off for all the pixels 21 (i, j), the transistor T3 is turned off. When the transistor T3 is in the unselected state, the gate voltage Vgs of the transistor T3 is maintained at the voltage written in the holding capacitor Cs.
The control unit 16 controls the anode circuit 12 so that the voltage ELVDD is applied to the anode line La. This voltage ELVDD is set to 15V, for example.
At this time, since the gate voltage Vgs of the transistor T3 is held by the holding capacitor Cs, the drain current Id of the value equivalent to the current flowing when the current value Vdata is written into the holding capacitor Cs flows between the drain-source of the transistor T3. .
Since the transistor T2 is in the off state and the potential at the anode side of the organic EL element 101 is higher than the potential at the cathode side, this drain current Id is supplied to the organic EL element 101.
At this time, the current Id flowing in the organic EL element 101 of each pixel 21 (i, j) is corrected on the basis of an imbalance between the variation of the threshold voltage Vth and β, and the organic EL element 101 corrects this. Emits light at the given current.
As described above, the display device 1 according to the present embodiment selects t1 and t2 satisfying (C / β) / t <1 as the settling time, for example, the settling time t, and by the auto zero method, The voltage measurement of each data line Ldi is performed at a time number corresponding to the selected settling time number.
The display device 1 selects a time t3 that satisfies (C / β) / t≥1 as the settling time t, performs a voltage measurement on each data line by the auto zero method, and executes a pixel drive circuit for each pixel. (Δβ / β) indicating a deviation of the current amplification ratio β of is obtained.
Therefore, the display device 1 can correct the voltage value Vdata0 based on the image data supplied in the actual operation based on the obtained (Δβ / β), and obtain the corrected voltage value Vdata1. In addition, the corrected voltage value Vdata1 may be corrected based on the obtained threshold voltage Vth, and the voltage value Vdata may be obtained.
In this method according to the present embodiment, an image supplied at the time of actual operation in order to reduce the influence of the variation of the threshold voltage and the difference between pixels on the current amplification ratio of each display pixel 21 (i, j). A pixel driving device for correcting the current supplied to the organic EL element 101 based on the data can be realized. Therefore, in this pixel drive device, the display device 1 devising such an imbalance and a deviation can control the deterioration of the image quality of the display image.
In addition, the display device 1 according to the present embodiment acquires (Δβ / β) indicating the threshold voltage Vth, the (C / β) value, and the deviation of β as a characteristic parameter of each pixel in the common circuit of the pixel driving device. do.
For this reason, the display device 1 of the pixel drive device or the display device 1 which performs the above-described correction without having to separately provide a circuit for measuring the deviation of β or a circuit for measuring the threshold voltage Vth. The configuration can be simplified.
In addition, various aspects of embodiment of this invention can be considered without being limited to said embodiment.
For example, in the above embodiment, the organic EL device has been described as a light emitting device. However, the light emitting element is not limited to the organic EL element, and may be, for example, an inorganic EL element or an LED.
Moreover, although the said embodiment demonstrated the case where this invention was applied to the display apparatus 1 which has the organic electroluminescent panel 21, this invention is not limited to this example. For example, there is provided a light emitting element array in which a plurality of pixels having light emitting elements (organic EL element 101, etc.) are arranged in a single direction, and the light emitted from the light emitting element array on the photosensitive drum is based on image data. You may apply to the exposure apparatus which irradiates and exposes the photosensitive member of a drum. The exposure apparatus to which the present embodiment is applied can control the deterioration of the exposure state due to the deterioration of the image quality over time and the characteristic variation between the pixels.
In the above embodiment, two t1 and t2 can be set as the settling time t that satisfies (C / β) / t <1. However, three or more settling times that satisfy this condition can also be set.
In the above embodiment, the control unit 16 performs conversion for each RGB using the LUT 123 of the supplied image data. However, instead of using the LUT 123, the control unit 16 may perform such conversion on the image data by introducing and calculating an expression.
Various embodiments and modifications are possible without departing from the spirit and scope of the invention. The above-described embodiments are intended to illustrate the present invention and are not intended to limit the scope of the present invention. The scope of the invention is indicated by the appended claims rather than the examples. Changes within the meaning equivalent to the claims of the present invention and within the claims of the present invention are considered within the scope of the present invention.
This application claims priority in accordance with Japanese Patent Application No. 2008-305714 for which it applied on November 28, 2008, and includes specification, a claim, a drawing, and a summary. The description of this patent application is incorporated by reference in its entirety.
One… Display device 11... Panel module, 12... Anode circuit, 13... Select driver, 14... Analog power supply, 16... Control unit 21. Organic EL panel, 21 (i, j) (i = 1 to m, j = 1 to n). Pixel, 22... Data driver, 101... Organic EL element (light emitting element), 114 (1) to 114 (m). ADC, 118 (1)-118 (m)... VDAC, Sw1 (1) to Sw1 (m), Sw2 (1) to Sw2 (m), Sw3 (1) to Sw3 (m), Sw4 (1) to Sw4 (m), Sw5 (1) to Sw5 (m ), Sw6... Switch, 121... CPU, 122... Memory, 123... LUT, T1 to T3... Transistor, Cs... Holding capacity, Cel… Organic EL pixel capacity, Cp... Wiring parasitic capacitance
A driving transistor T3 and the driving transistor connected to a signal line Ld, which controls the light emitting element 101 and the current supplied to the light emitting element, and one end of the current of the driving transistor is connected to one end of the light emitting element. A pixel driving device for driving a pixel 21 (i, j) having a pixel driving circuit DC having a holding capacitor Cs for storing charge by a voltage applied to a control terminal of
A voltage applying circuit 14 for outputting a reference voltage Vref;
The voltage measuring circuit 114,
A switching circuit Sw3 for switching one end of the signal line between the voltage applying circuit and the voltage measuring circuit;
A characteristic parameter obtaining circuit 16 for obtaining a characteristic parameter relating to an electrical characteristic of the pixel,
The reference voltage has a potential at which the potential difference of the one end with respect to the other end of the driving transistor to the current exceeds a threshold voltage Vth of the driving transistor,
The switching circuit connects one end of the signal line to the voltage application circuit, and after applying the reference voltage to the one end of the signal line by the voltage application circuit for a predetermined time, between one end of the signal line and the voltage application circuit. Is set to interrupt the connection of the signal line, and one end of the signal line is connected to the voltage measuring circuit after each of a plurality of predetermined
When the voltage measuring circuit is connected to one end of the signal line by the switching circuit, the voltage measuring circuit acquires a voltage value of one end of the signal line as a measurement voltage,
The characteristic parameter obtaining circuit calculates the threshold voltage of the driving transistor and the effective current amplification ratio of the pixel driving circuit based on the values of the plurality of measuring voltages obtained by the voltage measuring circuit for the plurality of predetermined settling times. And a pixel driving device as a characteristic parameter.
The plurality of predetermined settling times are set to a value larger than (C / β 0), where C is a total capacitance that is a sum of parasitic capacitances parasitic on the signal line, holding capacitors, and light emitting element capacitances parasitic on the light emitting element, β0 is a reference value of the effective current amplification factor).
And the reference value of the effective current amplification ratio is a design value or a typical value of the effective current amplification ratio.
The characteristic parameter obtaining circuit, when each of the plurality of predetermined settling times is t, sets the measured voltage to Vmeas (t), the threshold voltage to Vth, and the effective current amplification factor to be β, respectively. And substituting a predetermined settling time and a value of each of the plurality of measured voltages into equation (1) to obtain the threshold voltage and the effective current amplification factor.
A signal correction circuit 16 for correcting the supplied image data and generating a corrected gradation signal on the basis of the characteristic parameters obtained by the characteristic parameter obtaining circuit;
And a driving signal applying circuit (118) for generating a driving signal based on the corrected gradation signal and applying a driving signal to one end of the signal line.
A driving transistor T3 connected to at least one signal line Ld, controlling a light emitting element 101 and a current supplied to the light emitting element, and one end of the driving transistor being connected to one end of the light emitting element; At least one pixel 21 (i, j) having a pixel driving circuit DC having a holding capacitor Cs for storing charge by a voltage applied to a control terminal of the driving transistor;
A switching circuit Sw3 for switching the connection of one end of the signal line and the voltage measuring circuit;
The reference voltage has a potential at which a potential difference between one end and the other end of the current path of the driving transistor exceeds a threshold voltage of the driving transistor,
The characteristic parameter obtaining circuit calculates the threshold voltage of the driving transistor and the effective current amplification ratio of the pixel driving circuit based on the values of the plurality of measuring voltages obtained by the voltage measuring circuit for the plurality of predetermined settling times. Obtaining as a characteristic parameter.
A plurality of said signal lines are arranged along a first direction,
Has at least one scan line arranged along a second direction orthogonal to the first direction,
Each of the plurality of pixels is arranged near each intersection of the scan line and the plurality of signal lines,
The light emitting device has a selection driving circuit which sets a selection state for the plurality of pixels connected to the scanning line by applying a selection signal to the scanning line,
And the characteristic parameter obtaining circuit acquires the characteristic parameters of the plurality of pixels in a selected state by the selection driving circuit.
A first thin film transistor T3 having a connection point at which a predetermined power supply voltage is applied to one end of the current path, and the other end of the current path is connected to one end of the light emitting element;
A second thin film transistor in which a control terminal is connected to the scan line, one end of the current path is connected to one end of the current path of the first thin film transistor, and the other end of the current path is connected to a control terminal of the first thin film transistor ( T1),
A control terminal is connected to the scan line, one end of the current path is connected to the signal line, and the other end of the current path includes a third thin film transistor T2 connected to the connection point,
The first thin film transistor corresponds to the driving transistor,
When the pixel is in the selected state by the selection driving circuit, the second thin film transistor and the third thin film transistor enter an on state, and at one end of the first thin film transistor to the current path of the first thin film transistor, A control terminal is connected, and the signal line is connected to the connection point through the current path of the third thin film transistor, whereby the reference voltage supplied from the voltage application circuit is applied to the connection point through the third thin film transistor,
The voltage measuring circuit obtains the voltage of the connection point of each pixel arranged in the second direction in the selected state following the passage of each of the plurality of predetermined settling times through the third thin film transistor and each signal line as a measurement voltage. Light emitting device.
The plurality of predetermined settling times are (C / β0) (where C is a total capacitance that is the sum of the parasitic capacitance parasitic on the signal line, the storage capacitance, and the light emitting element capacitance parasitic on the light emitting element, and β0 is the effective current. And a plurality of prescribed different values larger than the reference value of the amplification factor).
And the reference value of the effective current amplification factor is a design value or a typical value of the effective current amplification factor.
The characteristic parameter acquisition circuit calculates Vmeas (t), the threshold voltage Vth, and the effective current amplification ratio β when each of the plurality of predetermined settling times is t. And the threshold voltage and the effective current amplification rate are obtained by calculating the plurality of predetermined settling times t and the values of the plurality of measured voltages Vmeas (t).
A signal correction circuit 16 for correcting supply-acquired image data and generating a corrected gradation signal based on the characteristic parameter obtained by the characteristic parameter obtaining circuit;
And a drive signal applying circuit (118) for generating a drive signal based on the corrected gradation signal and applying a drive signal to one end of the signal line.
A driving transistor T3 and a control terminal of the driving transistor, which are connected to the signal line Ld and which control the light emitting element 101 and the current supplied to the light emitting element, and one end of the light emitting element is connected to one end of the current. A method of obtaining a characteristic parameter of a pixel driving apparatus for driving a pixel 21 (i, j) having a pixel driving circuit DC having a holding capacitor Cs for storing electric charges by a voltage applied thereto,
By connecting the voltage application circuit 14 to one end of the signal line, a reference voltage is provided at one end of the signal line so that the potential difference of one end with respect to the other end of the drive transistor to a current exceeds a threshold voltage of the drive transistor. A reference voltage applying step of applying (Vref),
A measurement voltage acquiring step of interrupting a connection between one end of the signal line and the voltage application circuit and acquiring a voltage of one end of the signal line as a plurality of measured voltages after each of a plurality of predetermined different settling times after the interruption; ,
A characteristic parameter obtaining step of obtaining, as a characteristic parameter, a threshold voltage of the driving transistor and an effective current amplification factor of the pixel driving circuit based on values of the plurality of measured voltages obtained for the predetermined plurality of different settling times; Characteristic parameter acquisition method of the pixel drive device comprising a.
The measuring voltage acquiring step is a sum of the predetermined plurality of different settling times (C / β 0), where C is the sum of the parasitic capacitance parasitic on the signal line, the holding capacitance, and the light emitting element capacitance parasitic on the light emitting element. And? 0, which is a capacitance, and is set to a predetermined plurality of values larger than the effective current amplification factor).
The characteristic parameter obtaining step
When each of the predetermined plurality of different settling times is t, the measured voltage is Vmeas (t), the threshold voltage is Vth, and the effective current amplification factor is β, the values of the plurality of measured voltages and the predetermined Substituting each of a plurality of different settling times t into Vmeas (t) shown in equation (3),
Obtaining the threshold voltage and the effective current amplification rate by performing an operation based on the values of the plurality of measured voltages represented by the formula (3) and the predetermined plurality of different settling times. Characteristic parameter acquisition method of the pixel drive device characterized in that.
It is connected to the signal line Ld, has a light emitting element 101, a current path and a control terminal, and connects one end of the current path to one end of the light emitting element, and is written between the control terminal and one end of the current path. On the basis of the voltage data, a driving transistor T3 for controlling a current supplied to the light emitting element through the current path, and a holding capacitor Cs for storing charge determined by the voltage applied to the driving transistor. The pixels 21 (i, j) to have,
A voltage measuring circuit 114 for obtaining a voltage value as a measuring voltage of one end of the signal line;
A light emitting device comprising: a characteristic parameter obtaining circuit 16 for obtaining characteristic parameters relating to electrical characteristics of the pixel,
The voltage measuring circuit may stop the applied voltage due to the presence of a high impedance state after a voltage is applied between the both ends of the driving transistor through the one end of the signal line to exceed the threshold voltage of the driving transistor. When the time elapsed from the instant of time becomes the settling time t, the total capacitance that is the sum of the holding capacitance of the pixel connected by the signal line, the parasitic capacitance parasitic on the signal line, and the light emitting element capacitance parasitic on the light emitting element. In the case of, the voltage value of the voltage of one end of the signal line shown in equation (4) is obtained as a measurement voltage,
The characteristic parameter obtaining circuit is based on the plurality of measured voltages obtained by the voltage measuring circuit when the settling time t satisfies a condition of (C / β) / t <1, and thus the driving transistor. And a threshold voltage and a value of (C / β) as characteristic parameters.
And the characteristic parameter obtaining circuit acquires the characteristic parameter by using equation (5) changed from equation (4).
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