JP2004078210A - Drive circuit for active matrix type organic el panel and organic el display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a drive circuit for an active matrix type organic EL which can initially charge an OEL element of an active matrix type organic EL panel, can improve the luminance of the OEL element and is suitable for high luminance color display. <P>SOLUTION: This drive circuit is provided with many current drive circuits and a write control circuit. The current drive circuits are provided so as to correspond to a data line or a column pin of an organic EL display panel, and each of the current drive circuits has an output pin connected to the data line or the column pin, generates current for charging to charge a capacitor of a pixel cell circuit to a voltage value through the data line or the column pin and generates current for charging to initially charge the organic EL element. The write control circuit controls write for storing the voltage value into the capacitor and also controls the resetting of the voltage value of the written capacitor. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to a drive circuit for an active matrix organic EL panel and an organic EL display device, and more specifically, in an apparatus such as a mobile phone or PHS, the organic EL element of the active matrix organic EL panel is initially charged (emits light emission at an early stage). Suitable for high-luminance color display that can reduce the writing time of the driving current value to the capacitor of the pixel circuit and improve the luminance of the organic EL element. The present invention relates to an active matrix organic EL display device.

The organic EL display device is capable of high-luminance display by self-light emission, and is therefore suitable for display on a small screen, and is a next-generation display device mounted on a mobile phone, PHS, DVD player, PDA (portable terminal device), etc. Is currently attracting attention. When this organic EL display device is driven by voltage like a liquid crystal display device, the luminance variation increases, and there is a difference in sensitivity between R (red), G (green), and B (blue). There is a problem that becomes difficult.
Therefore, recently, an organic EL display device using a current-driven driver has been proposed. For example, Japanese Patent Laid-Open No. 10-112391 describes a technique for solving the problem of luminance variation by current driving (Patent Document 1).
An organic EL display panel of a mobile phone or an organic EL display device for PHS has been proposed in which a column line has 396 (132 × 3) terminal pins and a row line has 162 terminal pins. Line terminal pins tend to increase further.

The output stage of the current drive circuit of such an organic EL display panel is provided with a drive circuit of a current source, for example, an output circuit using a current mirror circuit, corresponding to a terminal pin, regardless of whether it is an active matrix type or a simple matrix type.
In the active matrix type, a pixel circuit including a capacitor and a current-driven transistor is provided for a display cell (pixel), and the transistor is driven according to the voltage stored in the capacitor, and the organic EL element is passed through the transistor. (Hereinafter referred to as OEL element) is current driven. As the driving method, there are digital driving for controlling the OEL element by binary ON / OFF and analog driving for controlling the driving current of the OEL element by analog input data. In the case of digital driving, the display area is controlled by providing sub-pixels in the pixel, or the gradation of the display pixel is controlled according to the driving time difference by time-dividing the light emission time. In the case of analog drive, there are voltage specification type (voltage programming method) and current specification type (current programming method). In the case of voltage specification type, the capacitor terminal voltage of each pixel circuit is set by voltage signal, In the case of the current designation type, the terminal voltage of the capacitor is set by a current signal.
By the way, Patent Document 1 discloses an EL element drive circuit in which EL elements arranged in a matrix are driven by current and the anode and cathode of the EL element are dropped to the ground for resetting. Patent Document 2 discloses a technique for driving an EL element with low power consumption using a DC-DC converter.

Japanese Patent Application Laid-Open No. 9-232074 JP 2001-143867 A

In such an active matrix type, luminance unevenness is likely to occur due to variations in the operation threshold value of the driving transistor for each pixel circuit. Since it is difficult to make the operation thresholds of the drive transistors of the display element uniform in the manufacturing process, it is considered to suppress the luminance unevenness by controlling the voltage of the capacitor of each pixel circuit. Therefore, a threshold compensation circuit is provided in the pixel circuit. Examples of the compensation circuit include the voltage program circuit and the current program circuit.
The former voltage programming method uses four transistors and two capacitors for each pixel circuit. In addition to the data line and the selection line, two voltage programming methods are used to compensate for variations in the operating threshold of the driving transistor. A line is provided. Then, by applying a control signal to these two lines and charging the two capacitors at a predetermined timing, current driving is performed without the influence of the threshold value of the driving transistor.
The latter current programming method is composed of three transistors including a driving transistor and a switch transistor for setting a specific voltage. A data line, two selection lines, and a power supply line (source line) of a specific voltage Vdd are provided. First, the drive transistor is disconnected by the switch transistor and the capacitor is charged by current drive. After that, the drive transistor is connected to the capacitor by the switch transistor and power is supplied from the source line to the drive transistor to drive the OEL element with current. .

By the way, the current drive circuit of the simple matrix type organic EL display panel uses a drive current having a peak current to initially charge an OEL element having a characteristic that becomes a capacitive load to emit light early and suppress luminance unevenness. It is done. In this regard, the active matrix type temporarily writes and stores a voltage value corresponding to the drive current value in the capacitor of the pixel circuit, and then generates a drive current value corresponding to the stored voltage value. Therefore, the active matrix type OEL element is not driven by the peak current. As a result, the OEL element cannot emit light as early as the simple matrix type, and a drive current value writing period is also required.
The drive current value is written by charging the capacitor of the pixel circuit of several hundred pF with a current of about 0.1 μA to 10 μA. Therefore, the write time to the capacitor of the pixel circuit is 10% of the entire scanning period. It occupies a relatively large proportion of about or above. Accordingly, the light emission period is shortened and the luminance is lowered. In particular, when the number of display pixels becomes high, for example, VGA, XGA, etc., the current programming circuit needs to perform timing control within a limited time, so the above-described drawbacks are problematic. Become.
The object of the present invention is to solve such problems of the prior art, and it is possible to initially charge the OEL element of the active matrix organic EL panel and to improve the luminance of the OEL element. An object of the present invention is to provide a drive circuit for an active matrix organic EL panel suitable for luminance color display.
Another object of the present invention is to provide an organic EL display device capable of initially charging an OEL element of an active matrix organic EL panel and improving the luminance of the OEL element.
Still another object of the present invention is to provide an active matrix organic EL panel driving circuit and an organic EL display device capable of reducing the writing time of the driving current value to the capacitor of the pixel circuit and improving the luminance of the OEL element. It is to provide.

The active matrix organic EL panel drive circuit and the organic EL display device according to the first aspect of the present invention for achieving such an object are provided corresponding to the data lines or column pins of the organic EL display panel, and the data A line or an output pin connected to the column pin for generating a current for charging a capacitor of a pixel circuit to the voltage value via the data line or the column pin and for initially charging the organic EL element A plurality of current drive circuits for generating a current; and a write control circuit for performing a write control for storing the voltage value in the capacitor and a control for resetting the voltage value of the written capacitor. Is.
According to a second aspect of the present invention, the capacitor of the pixel circuit is initialized to charge the capacitor of the pixel circuit to which the current driving circuit is connected to the voltage value in a short time. A current for charging is generated.

As described above, in the first invention, the current driving circuit outputs a current for charging the capacitor of the pixel circuit to a voltage value corresponding to the driving current value of the OEL element, and further, an electric current for initially charging the OEL element. Thus, the OEL element can be initially charged even in the active matrix organic EL panel. In addition, since the OEL element is initially charged from the outside of the pixel circuit, a large current value for the initial charging of the OEL element can be taken. As a result, the OEL element can be made to emit light at an early stage by the driving current of the pixel circuit, so that the OEL element emission period can be lengthened accordingly.
In the second aspect of the invention, since the current driving circuit further outputs a current for initially charging the capacitor of the pixel circuit, the writing time for storing the driving current value in the capacitor of the pixel circuit is shortened. Can do.
As a result, the luminance of the OEL element can be improved, and an active matrix organic EL panel drive circuit and an organic EL display device suitable for high luminance color display can be realized.

FIG. 1 is a block diagram of an embodiment to which the active matrix type organic EL display device of the first and second inventions is applied, and FIG. 2 is a timing control table of scanning target lines in Y direction (low direction) scanning. FIG. 3 is a block diagram of another embodiment of the present invention, and FIG. 4 is an explanatory diagram of a specific example of a display cell driving circuit in still another embodiment of the present invention. It is a block diagram of the principal part of the conventional defect inspection apparatus.
In FIG. 1, reference numeral 1 denotes an active matrix organic EL display device, which includes a data electrode driver 2, a write control circuit 3, a pixel circuit 4, a control circuit 5, a register 6, a low side scanning circuit 7, and an MPU 8. Etc. A large number of pixel circuits 4 are provided corresponding to the intersections of the X and Y matrix wirings, but only one of them is shown as a representative thereof. The data electrode driver 2 is a column driver (driver in the horizontal scanning direction) of a so-called organic EL driving circuit, and the display cell driving circuit 10 provided corresponding to each data line (or each column pin, the same hereinafter) is replaced with the number of data lines. Built in minutes. The output pin 9 of each display cell driving circuit 10 is connected to each data line (X electrode = X1, X2, X3,... Xn) of the active matrix type X and Y matrix wiring (data line, scanning line). ) Are connected to each.

Here, each display cell driving circuit 10 provided corresponding to the data line (column pin) initially charges the current value writing capacitor and the OEL element 4a of the pixel circuit 4 serving as a capacitive load, and drives the current. This is a circuit for discharging the residual charge of the element 4a. A capacitor Cp indicated by a dotted line provided in parallel with the OEL element 4a is a parasitic capacitor formed by the junction capacitance of the OEL element 4a.
The display cell driving circuit 10 includes a push-pull circuit, and includes a push-side current source 11 and pull-side current sources 12 and 13. The push-side current source 11 is output via the switch circuit SW1. The current sources 12 and 13 on the pull side connected to the pin 9 are connected to the output pin 9 via the switch circuits SW2 and SW3, respectively. The output pin 9 is connected to the data line X1 via the terminal 1b of the organic EL panel.
Here, the push-side current source 11 generates a current for initially charging the OEL element 4a. The pull-side current source 12 generates a current for initially charging the capacitor C, and also serves as a current source for resetting the OEL element 4a. The pull-side current source 13 generates a current for writing a predetermined voltage value to the capacitor C.
The other display cell driving circuit 10 connected to other than the data line X1 has the same configuration as the display cell driving circuit 10 connected to the data line X1, and therefore the description thereof is omitted.
The switch circuits SW1 to SW3 are turned on / off by “H” and “L” signals of the control signals S1, S2, and S3 from the control circuit 5. The current values of the pull-side current sources 12 and 13 receive a current from the D / A conversion circuit 14 and become a constant current source having a current value corresponding to the current. The current generated in the D / A conversion circuit 14 is generated by receiving the display data DAT set in the register 6 from the MPU 8 and converting this data value.
A specific circuit of the constant current source and the D / A converter circuit in the drive circuit of the active matrix type organic EL panel is the same as the US application, application number 10,360,715 or application number 10, One example is disclosed in US Pat.

As shown in FIG. 1, three data lines X1, X2, X3,... Xn arranged in the column direction, and a large number of scanning lines Y arranged in the row direction (selection line Y1, selection line Y2, erase line Y3). Pixel circuits (display cells) 4 are provided corresponding to the intersections connecting the X and Y matrix wirings, each of which is a unit line. In the pixel circuit 4, for example, a P-channel MOS transistor Tr 1 having a gate and a drain connected to each line at the intersection of the selection line Y 1 and the data line X 1 is disposed as shown in the figure. The source of the transistor Tr1 is connected to the gate of the P-channel transistor Tr3 for driving the OEL element through the drain-source of the P-channel MOS transistor Tr2.
A capacitor C for storing a drive current value is connected between the source and gate of the transistor Tr3. The source of the transistor Tr3 is connected to a power supply line + Vcc of about +7 V, for example, and its drain is provided downstream thereof. The P-channel transistor Tr4 for driving the OEL element is connected to the source. The drain of the transistor Tr4 is connected to the anode of the OEL element 4a.
The cathode of the OEL element 4a is connected to the input / output terminal 7a of the push-pull switch circuit 70 of the low-side scanning circuit 7 through the terminal 1a of the organic EL panel, and the ground GND or the power supply is connected through this switch circuit 70. Selectively connected to line + Vcc.

The gate of the transistor Tr2 is connected to the selection line Y2, and the selection line Y2 is further connected to the gate of the transistor Tr4 via the inverter 4b. Further, a reset P-channel MOS transistor Tr5 having a source and a drain connected to both terminals of the capacitor C is provided in parallel with the capacitor C, and the gate of this transistor is connected to the erase line Y3.
The selection line Y1, the selection line Y2, and the erase line Y3 are connected to the write control circuit 3 through the terminal 1c, the terminal 1d, and the terminal 1e of the organic EL panel, respectively, and the selection line Y1, the selection line Y2, and the erase line Y3. Are sequentially scanned in accordance with the control signal of the writing control circuit 3, and scanning in the Y direction (low direction) is performed in synchronization with the scanning of the low side scanning circuit 7.
By the way, in the active matrix type, there are a case where the reset is performed after the OEL elements for the entire screen are caused to emit light, and a case where the reset is performed before the voltage value is written to the capacitor C of the pixel circuit corresponding to the row line scanning. is there. Since only one pixel circuit is shown in FIG. 1, the case of resetting after light emission will be described as an example in order to simplify the description of resetting.

As shown in the table of FIG. 2, the selection line Y1, the selection line Y2, and the erase line Y3 are the high level (hereinafter “H”) or the low level (hereinafter “L”). ”). As a result, the transistors Tr1 to Tr5 are turned ON / OFF. At the same time, the display cell driving circuit 10 receives "H" and "L" signals of the control signals S1, S2, and S3 from the control circuit 5 and, as shown in FIG. 1, to the capacitor C through the current path (1). Initial charge (peak current drive) is performed, then the current value is written to the capacitor C in the current path (2), and then the OEL element 4a is initially charged in the current path (3). Subsequently, the OEL element 4a is driven to emit light by the pixel circuit 4 through the current path (4). Finally, the capacitor is reset in (5) in the current path. As a result, the scanning of the Y line currently being scanned is completed. In addition, about the said current path | route (1)-current path | route (5), it shows with the numerals 1-5 with (circle) in each figure.
Similarly, the scanning of the next Y line starts from the current path (1) and ends through the current path (2) to the current path (5), and such scanning is present in the Y direction (low direction). This is repeated sequentially from one scanning line to the next.
Note that the Y lines including the selection line Y1, the selection line Y2, and the erase line Y3 are provided for the pixel circuit (for the number of scanning lines) in the row direction (vertical direction), and these are connected to the write control circuit 3. However, here, only the relationship for one pixel circuit scanned in the row direction is shown as in the switch circuit 70 of the row side scanning circuit 7. Other circuits are omitted.

In the switch circuit 70 of the low-side scanning circuit 7, the driving current value for one line corresponding to one line in the horizontal scanning direction of R, G, B is written in the capacitor C of each pixel circuit (display cell) 4. Later, the switch 71 of the switch circuit 70 of the low-side scanning circuit 7 is turned on, the cathode of the OEL element 4a is connected to the ground GND, and the OEL elements 4a for one line in the horizontal scanning direction are simultaneously driven.
A number of push-pull switch circuits 70 are provided in the row-side scanning circuit 7 corresponding to the scanning lines in the row direction. In the switch circuit 70 connected to the Y line to be scanned, the pull-side switch 71 is turned on and the push-side switch 72 is turned off. As a result, the cathode of the OEL element 4a is connected to the ground GND. At this time, the switch 71 on the pull side of the switch circuit 70 immediately before the end of scanning is turned off, and the scanning line on which the scanning is finished by turning on the switch 72 on the push side is pulled up to “H”.

In the active matrix type, since the capacitor C stores the drive current value, the drive current value for one screen is not used for one horizontal line, but the capacitor C of each pixel circuit for one screen as described above. Then, the switch 71 of the switch circuit 70 of each scanning line may be turned on and the switch 72 may be turned off. In this case, it is only necessary to provide one switch circuit 70, and it is not necessary to use the low-side scanning circuit 7. Further, when one screen of R, G, B is driven in a time-sharing manner, the one screen is provided corresponding to R, G, B. Therefore, the switch circuit 70 is provided with R, G, B. A total of three are provided, one for each screen.
The charge written in the capacitor C is set to “L” by the write control circuit 3 so that the scanning line Y3 connected to the write control circuit 3 turns on the transistor Tr5. Discharged at high speed. Thereby, the voltage of the capacitor C is reset. As described above, this reset may be performed in the blanking period before the voltage value is written to the capacitor C of the pixel circuit in response to the row line scanning.
The selection line Y1, the selection line Y2, and the erase line Y3 are scanned by receiving timing signals T1 and T2 from the write control circuit 3, respectively. The write control circuit 3 that performs the scanning as described above is controlled by the control circuit 5.

FIG. 2 is a timing control table for scanning target lines in Y-direction (low-direction) scanning. “H” and “L” signals of the control signals S1, S2 and S3 of the control circuit 5, and the selection line Y1, selection line Y2 and erase line Y3 of the write control circuit 3 are set to “H” and “L”. The generation timing of the control signal is shown corresponding to the control contents. The last column of the table shows the initial charge (peak current drive) to the capacitor C in the current path (1) (see dotted line) formed according to these control signals, and the current path (2) (see dotted line). Current value writing to capacitor C, initial charging (peak current drive) to OEL element 4a in current path (3) (see thin line) in display period, and OEL element 4a in current path (4) (see dotted line) Corresponding to the light emission drive and the reset operation of the capacitor C in the reset period, the reset operation of the OEL element 4a in the current path (5) (see the thin line) is associated.
First, initial charging (peak current driving) to the capacitor C shown in the first row of this table is performed by setting the selection line Y1 = “L”, the selection line Y2 = “L”, and the erase line Y3 = “H” to the transistor Tr1. , Tr2 is turned ON, and Tr4 and Tr5 are turned OFF. Then, the control signals S1 = "L", S2 = "H", and S3 = "H" are set so that both the switch circuits SW2 and SW3 are turned on and the switch circuit SW1 is kept off.
Note that the switch circuits SW1 to SW3 are turned ON at "H" here. In the initial state, the control signals S1 = "L", S2 = "L", S3 = "L", and the switch circuits SW1 to SW3 are OFF.
As a result, the drive currents from the constant current sources 12 and 13 flow from the power supply line + Vcc through the switch circuits SW2 and SW3 that are turned on and the transistors Tr1 and Tr2 that are turned on to the current path (1). At this time, a large charging current corresponding to the peak current flows in a short time, and the capacitor C is initially charged early. As a result, the transistor Tr3 is also turned on.

In the second row, the current value writing to the capacitor C performed subsequently is maintained with the selection line Y1 = "L", the selection line Y2 = "L", and the erase line Y3 = "H". The transistors Tr1 to Tr3 are kept ON, and Tr4 and Tr5 are kept OFF. In this state, the control signal S2 is set to "L" and the switch circuit SW2 is turned off. At this time, the control signals are the control signals S1 = "L", S2 = "L", S3 = "H", the switch circuit SW1 remains OFF, and the switch circuit SW3 remains ON.
As a result, the constant current source 13 passes through the switch circuit SW3 that is turned on, the output pin 9, and the transistors Tr1 and Tr2 that are turned on, along the path shown as the current path (2) from the power line + Vcc of the pixel circuit 4. Drive current flows. Thereby, a charging current corresponding to the drive current value of the OEL element flows through the capacitor C, and the capacitor C is set to a voltage value corresponding to the drive current value.
The initial charge (peak current drive) to the next OEL element 4a shown in the third row is control for setting the selection line Y2 to "H", turning off the transistor Tr2, and turning on the transistor Tr4. At this time, the selection lines are selected line Y1 = "L", selection line Y2 = "H", and erase line Y3 = "H", so that transistor Tr1 remains ON and transistor Tr5 remains OFF. .

In this state, initial charging (peak current drive) is further performed by setting the control signal S1 to "H" and the control signal S3 to "L" to turn on the switch circuit SW1 for a certain period of peak occurrence and turn off the switch circuit SW3. To do. At this time, the control signals are the control signals S1 = "H", S2 = "L", S3 = "L", and the switch circuit SW2 remains OFF. At the same time, the low-side scanning circuit 7 enters a display period in which the switch 71 on the pull side of the switch circuit 70 is turned on and the switch 72 is turned off to cause the OEL element 4a to emit light.
As a result, the constant current source is connected through the switch circuit SW1 that is turned on, the output pin 9, and the transistors Tr1 and Tr4 that are turned on to the power line + Vcc of the pixel circuit (display cell) 4 as a current path (3). 11 is driven. As a result, a large current corresponding to the peak current flows in the OEL element 4a in a short period of time, and the OEL element 4a is initially charged at an early stage. A drive current corresponding to the voltage value of the current flows to the OEL element 4a, and light emission of the OEL element 4a starts.

In the light emission driving of the next OEL element 4a shown in the fourth row, the selection line Y1 is set to "H" and the transistor Tr1 is turned off. At this time, the selection lines Y1 = “H”, selection line Y2 = “H”, and erase line Y3 = “H”, and the transistors Tr2 and Tr5 remain OFF. As a result, the drive current according to the voltage stored in the capacitor C flows through the current path (4) through the transistors Tr3 and Tr4 which are turned on from the power supply line + Vcc of the pixel circuit 4. As a result, a predetermined drive current is supplied to the OEL element 4a, and the drive OEL element 4a continues to emit light with a luminance according to the predetermined drive current. The pixel circuit 4 is disconnected from the output pin 9 by turning off the transistor Tr1.
At this time, the control signals S1 = “L”, S2 = “L”, S3 = “L”, the switch circuits SW1 to SW3 are turned OFF, and the display cell driving circuit 10 has no current. Does not flow.
When the display period for causing the OEL element 4a to emit light ends and the pull-side switch 71 of the switch circuit 70 that has been scanned by the low-side scanning circuit 7 is turned off and the push-side switch 72 is turned on, the capacitors C and OEL The period for resetting the element 4a is entered.

In the reset operation, as shown in the fifth row, the selection line Y1 is set to “L”, the erase line Y3 is set to “L”, the transistors Tr1 and Tr5 are turned ON, and the transistor Tr3 is turned OFF. At this time, the selection lines Y1 = "L", selection line Y2 = "H", and erase line Y3 = "L" are selected, and the transistor Tr2 remains OFF.
Although the transistor Tr4 is ON, since the transistor Tr3 is OFF, no drive current flows from the pixel circuit 4 to the OEL element 4a. Further, during this reset period, the pull-side switch 71 of the switch circuit 70 is held ON. In this reset operation, in this state, the control signal S2 is further set to "H" to turn on the switch circuit SW2.
As a result, the charge of the capacitor C is rapidly discharged through the transistor Tr5 that is turned on. At the same time, the charge of the capacitor Cp of the OEL element 4a also flows to the ground GND through the transistor Tr1, the output pin 9, the ON switch circuit SW2, and the constant current source 12 through the path indicated as the current path (5). It is rapidly discharged.
The control signals at this time are the control signals S1 = "L", S2 = "H", and S3 = "L", and the switch circuits SW1 and SW3 remain OFF.

By the way, when the scanning method of the organic EL panel sequentially scans the row line by the row-side scanning circuit 7, the reset is performed before the voltage value is stored in the capacitor C in the reset period as described above. There are many. In this case, the switch circuit 71 is turned on after the reset period for discharging the charges of the capacitor C and capacitor Cp in the currently scanned line, and the OEL element in the scanning line is controlled to emit light. After this light emission, the next scanning line reset period starts. At this time, the cathode side of the OEL element connected to the row line where scanning is completed is pulled up to “H”, and scanning on the row side of that line is completed.
In such low-side scanning, the reset period is before the light emission period (display period). Therefore, the capacitor and the OEL element connected to the scanning target line are reset first in the current path (5) in the table of FIG. 2 and thereafter in the current paths (1) to (4). As a result, the reset of the capacitor and OEL element of a certain pixel circuit starts from the reset period (current path (5)) in the table of FIG.

When the reset period is after the light emission period of the light emission period, the Y line for which the low-side scanning is completed returns to the initial state, and the control signals are the control signals S1 = "L" and S2 = " L ", S3 =" L ". As a result, the switch circuits SW1 to SW3 are turned off during the switching period (return line period) of the low-side scan line provided after the reset period, and are in the initial state.
Note that, for example, when row lines are not sequentially scanned by the row-side scanning circuit 7 such as when scanning for one screen of R, G, and B, all row lines are pulled down to “L” when the OEL element emits light. And pulled up to “H” after the end of light emission.

In this embodiment, for the initial charging of the OEL element 4a, the peak current is generated by combining the drive current from the pixel circuit 4 and the drive current supplied from the constant current source 11. As a result, the OEL element 4a is driven to start light emission from the OEL element 4a. However, it is not always necessary to drive the peak current by simultaneously generating the initial charging current and the driving current. The drive current from the pixel circuit 4 may flow after initial charging.
In this case, the switch circuit SW1 is turned ON for a predetermined period for the initial charge in order to supply the current for the initial charge from the constant current source 11 first. Thereafter, the pull-side switch 71 of the switch circuit 70 of the low-side scanning circuit 7 is turned on, and the switch 72 is turned off. Thereby, it is possible to enter a display period in which the OEL element 4a emits light after the initial charging.
Similarly, in this embodiment, for the initial charging of the capacitor C, as shown in the table of FIG. 2, the switch circuits SW2 and SW3 are turned on, the initial charging current is added to the write current, and these are combined. Although peak current driving is performed, this is also not the peak current driving that simultaneously generates the initial charging current and the writing current, but only the initial charging current is passed first, and then the writing current is allowed to flow. May be.
In this case, the control signals S1 = “L”, S2 = “H”, S3 = “L” are set to the respective control signals, and only the switch circuit SW2 is turned on, and the capacitor C is initially driven by current drive by the constant current source 12. After charging, the control signal S2 is set to "L" to turn off the switch circuit SW2, and then the control signal S3 is set to "H" to turn on the switch circuit SW3. Thereby, the current value can be written to the capacitor C by the current drive by the constant current source 13 after the initial charging.

Further, during the reset period in which the voltage value is stored in the capacitor C, the switch circuit SW2 is ON, so that the control signals S1 = "L", S2 = "L", and S3 = "L" Without setting the initial state, the transistors Tr1 and Tr2 are turned ON by simply setting the selection lines Y1 = "L", the selection lines Y2 = "L", and the erase lines Y3 = "H". , Tr4 and Tr5 can be turned off, and the initial charge of the capacitor C can be started along the current path (1) following the discharge of the residual charge of the OEL element 4a.
FIG. 3 shows an embodiment in which the transistor Tr5 is omitted and the electric charge of the capacitor C is discharged through the transistor Tr3. As a result, the reset period is slightly longer than that of the embodiment of FIG. 1, but the number of transistors constituting the pixel circuit 4 is only four, and the erase line Y3 is unnecessary.

The reset operation of the capacitor C and the OEL element 4a in this embodiment will be described. During the reset operation, the selection line Y1 is set to "H" and the selection line Y2 is set to "L". As a result, the transistor Tr1 is turned off, the transistor Tr2 is turned on, and the transistor Tr4 is turned off. At this time, since the transistor Tr3 is turned on with the voltage stored in the capacitor C, the charge of the capacitor C is discharged through the transistor Tr3 and the turned on transistor Tr2.
Note that during this reset period, the control signals S1 = "L", S2 = "H", S3 = "L", the switch circuit SW2 is turned on, and the switch circuits SW1, SW3 Remains off. Therefore, at the timing after the electric charge of the capacitor C is discharged, the selection line Y1 = "L" and the selection line Y2 = "H" are set. As a result, the transistor Tr2 is turned off and the transistors Tr1 and Tr4 are both turned on. Further, when the discharge of the capacitor C is completed, the transistor Tr3 is turned off. Therefore, as described above, the charge of the capacitor Cp of the OEL element 4a is rapidly discharged to the ground GND through the transistor Tr1, the output pin 9, the switch circuit SW2, and the constant current source 12.

FIG. 4 is an explanatory diagram of a specific example of a display cell driving circuit in still another embodiment of the present invention.
The display cell driving circuit 100 of FIG. 4 can be used in place of the display cell driving circuit 10 of FIG. 1 or FIG.
In the display cell driving circuit 100, the pull-side current source 12 in the display cell driving circuit 10 is omitted. Instead, a constant voltage source 101 (voltage follower) is provided, and the constant voltage circuit 101 is connected to the output pin 9 via the switch circuit SW2.
The control is the same from the writing of the current value to the capacitor C in the second to fourth rows in the table of FIG. 2 to the initial charging of the OEL element 4a. The control of the selection lines and erase lines in the first and fifth rows is the same. The only difference is the control for turning on / off each switch circuit when initially charging the capacitor C in the first row in FIG. 2 and when resetting the capacitor in the fifth row.
This will be described. The control signals at the time of initial charging of the capacitor C in the first row are S1 = "L", S2 = "H", and S3 = "H" in FIG. The signals are set to S1 = "L", S2 = "H", and S3 = "L". As a result, the switch circuits SW1 and SW3 are turned off and the switch circuit SW2 is turned on.

The control signals at the time of reset in the fifth row are S1 = "L", S2 = "H", and S3 = "L". Instead, the control signals are S1 = "L", S2 = " L ", S3 =" H ". As a result, the switch circuits SW1 and SW2 are turned off and the switch circuit SW3 is turned on.
The ON / OFF control of each transistor of the pixel circuit 4 is not different from the embodiment of FIGS.
Therefore, from the initial charging of the capacitor C, the switch circuits SW1 and SW3 are turned OFF and the switch circuit SW2 is turned ON by the ON / OFF control of each switch circuit. Therefore, the voltage from the constant voltage source 101 is applied to the capacitor C through the data line X1 and the transistors Tr1 and Tr2 that are turned on. As a result, the capacitor C is set to the voltage of the constant voltage source 101. Therefore, when the voltage of the constant voltage source 101 is higher than the voltage of the capacitor C when reset, a current of a voltage difference flows out from the output pin 9. On the contrary, when the voltage of the constant voltage source 101 is lower than the voltage of the capacitor C when reset, the current of the voltage difference is drawn to the output pin 9. At this time, the amount of current that moves is smaller than in the case of FIGS.

Note that the voltage of the constant voltage source 101 can be adjusted by externally setting data to the programmable voltage generation circuit 102 in accordance with the threshold values of the transistors Tr3 and Tr4 of the pixel circuit 4. This voltage adjustment can suppress uneven brightness and the like.
Next, resetting of the capacitor C and the OEL element 4a will be described. By the ON / OFF control of each switch circuit, the switch circuit SW3 is turned on and the switch circuits SW1 and SW2 are turned off. Therefore, the OEL element 4a includes the transistors Tr4 and Tr1, the output pin 9 and the current that are turned on. Reset via source 13. The resetting of the capacitor C is the same as in the case of FIGS. 1 and 3, and is performed by the transistor Tr5 being turned on or the transistors Tr2 and Tr3 being turned on.
In this embodiment, initial charging of the capacitor C is performed by voltage setting by the constant voltage source 101. As shown in the figure, the constant voltage source 101 is built in a display cell driving circuit 100 provided corresponding to the pixel circuit 4.

When voltage is set for the capacitor C as described above, the constant voltage source 101 is not necessarily provided in each display cell driving circuit 100. For example, a total of three may be provided, one for each of the R, G, and B data electrode drivers 2. Alternatively, one may be provided as a whole.
By the way, in the embodiment of FIGS. 1 to 4, the charge of the OEL element 4a is reset before or after light emission. In the active organic EL panel, the reset of the OEL element 4a is a passive organic EL panel. Not so much needed.

As described above, when the capacitor C is initially charged, the input capacitance parasitic on the gate of the transistor Tr3 is also initially charged. Further, initial charging of the input capacitance of the transistor connected to the drive line of the capacitor C and the parasitic capacitance of X1 is also performed at this time. As a result, the time from driving the OEL element 4a to light emission can be shortened, and the initial drive characteristics until light emission can be improved.
The display cell driving circuit 10 of the embodiment is configured by a push-pull current driving circuit, and initially charges the capacitor Cp of the OEL element 4a by the push-side current, and the driving current value storage capacitor C by the pull-side current. Is initially charged, and the drive current value is written. However, depending on the configuration of the pixel circuit, for example, the P-channel MOS transistor is replaced with the N-channel MOS transistor, conversely, the capacitor C is initially charged with the push-side current and further written with the current value, The capacitor Cp of the OEL element 4a can be initially charged by the current.

Further, the display cell driving circuit 10 of the embodiment is provided with switch circuits SW1, SW2, SW3 in series with the current sources 11, 12, 13 or the voltage source 101 connected to the output pin 9, respectively. Then, current is supplied from the current source 11 (or voltage source 101) to the output pin 9 by ON / OFF of the switch circuits SW1, SW2, and SW3, or output from the current source 12 (or voltage source 101) and current source 13. Current is sinked from pin 9. However, this is a description of the circuit configuration in principle, and each current source (voltage source) is directly controlled without providing switch circuits SW1, SW2, and SW3 in series with each current source (voltage source). Of course, a circuit configuration may be adopted in which each current is generated by selectively starting in response to the signals S1, S2, and S3, or the generated current is stopped.
In the embodiment, a push-pull switch circuit is used as the switch circuit of the low-side scanning circuit 7. However, if the charge discharge path of the capacitor Cp of the OEL element 4a is separately formed, It may simply be a switch circuit connected to the ground GND. Further, the low-side scanning circuit 7 may be built in the organic EL panel similarly to the pixel circuit 4.

Furthermore, since the current drive circuit of the embodiment may be a monochrome display, it may not be provided corresponding to each of R, G, and B.
In the embodiment, the MOSFET transistor is mainly used, but it is needless to say that the bipolar transistor may be mainly used. In addition, the N-channel transistor (or npn-type) in the embodiment can be replaced with a P-channel (or pnp-type) transistor, and the P-channel transistor can be replaced with an N-channel (or npn-type) transistor. In this case, the power supply voltage is negative, and the transistor provided upstream is provided downstream.
Of course, the output pins in the present invention include output terminals formed as bumps connected to the pads of the IC.

FIG. 1 is a block diagram of an embodiment to which an active matrix organic EL display device according to the first and second inventions is applied. FIG. 2 is an explanatory diagram of a timing control table for scanning target lines in Y-direction (low-direction) scanning. FIG. 3 is a block diagram of another embodiment of the present invention. FIG. 4 is an explanatory diagram of a specific example of a display cell driving circuit in still another embodiment of the present invention. It is a block diagram of the principal part of the conventional defect inspection apparatus.

Explanation of symbols

1 ... Active matrix type organic EL display device,
2 ... Data electrode driver, 3 ... Write control circuit,
4 ... Pixel circuit, 4a ... Organic EL element, 4b ... Inverter,
5 ... Control circuit,
6 ... register, 7 ... low side scanning circuit,
70: Switch circuit,
8 ... MPU, 9 ... Output pin,
10, 100 ... display cell driving circuit,
11 ... Push-side current source,
12, 13 ... Pull-side current source,
14 ... D / A conversion circuit,
70, SW1 to SW3 ... switch circuit,
71, 72 ... switches,
101 ... Constant voltage circuit,
S1, S2, S3 ... control signals,
C, Cp ... capacitor
Tr1 to Tr5: Transistors.

Claims (18)

A pixel circuit having an organic EL element, a capacitor for storing a voltage value corresponding to a current value of a driving current of the organic EL element, and a transistor for outputting the driving current to the organic EL element according to the voltage value In an active matrix organic EL panel drive circuit for driving an organic EL display panel arranged in a matrix,
The organic EL display panel is provided corresponding to a data line or a column pin, and has an output pin connected to the data line or the column pin, and the capacitor of the pixel circuit is connected to the voltage via the data line or the column pin. A plurality of current driving circuits for generating a current for charging the value and generating a current for initially charging the organic EL element;
A drive circuit for an active matrix organic EL panel, comprising: a write control circuit that performs write control for storing the voltage value in the capacitor and resets the voltage value of the written capacitor. Further, the current driving circuit is configured to initially charge the capacitor of the pixel circuit in order to charge the capacitor of the pixel circuit to which the self is connected via the output pin to the voltage value in a short time, or 2. The organic EL drive circuit of an active matrix organic EL panel according to claim 1, further comprising a charging circuit that generates a voltage. Further, the current for charging the capacitor to the voltage value is generated according to either the current discharged from the output pin to the pixel circuit or the current drawn from the pixel circuit to the output pin, 2. The active matrix organic material according to claim 1, wherein a current for initially charging the EL element is generated in accordance with one of another current discharged from the output pin or another current drawn into the output pin. EL panel drive circuit. Further, the current driving circuit is configured to initially charge the capacitor of the pixel circuit in order to charge the capacitor of the pixel circuit to which the self is connected via the output pin to the voltage value in a short time, or 4. The organic EL driving circuit for an active matrix organic EL panel according to claim 3, further comprising a charging circuit for generating a voltage. The current driving circuit includes a push-pull current output circuit. The push-side circuit of the current output circuit operates to discharge current from the output pin to the pixel circuit, and the pull-side circuit of the current output circuit 5. The drive circuit for an active matrix organic EL panel according to claim 4, wherein an operation of drawing current from the pixel circuit to the output pin is performed. The write control circuit resets the capacitor before writing to store the voltage value, and the current driving circuit also resets the organic EL element before driving the organic EL element. 5. A drive circuit for an active matrix organic EL panel according to 5. 7. The active matrix organic material according to claim 6, wherein the voltage of the organic EL element of the pixel circuit is reset when the current driving circuit to which the pixel circuit of the pixel circuit is connected draws current into the output pin of the pixel circuit. EL panel drive circuit. The drive circuit for an active matrix organic EL panel according to claim 6, wherein the voltage value of the capacitor is reset by turning on a transistor provided in parallel with the capacitor. The push side circuit has a first current source for initially charging the organic EL element connected to the output pin via a first switch circuit, and the pull side circuit is connected to the output pin. A second current source connected via a second switch circuit; and a third current source connected to the output pin via a third switch circuit, wherein the second current source is 9. The active matrix organic EL panel according to claim 8, wherein the charging circuit generates a current for initially charging a capacitor, and the third current source generates a current for writing the voltage value to the capacitor. Drive circuit. The push side circuit has a first current source for initially charging the organic EL element connected to the output pin via a first switch circuit, and the pull side circuit is connected to the output pin. A second current source connected via a second switch circuit, the second current source generating a current for writing the voltage value to the capacitor; and a third current source at the output pin. 9. A drive circuit for an active matrix organic EL panel according to claim 8, comprising a voltage source connected via a switch circuit, wherein the voltage source serves as the charging circuit for generating a current for initially charging the capacitor. . An organic EL display device having a drive circuit for an active matrix organic EL panel according to any one of claims 1 to 10. 10. An active matrix organic EL panel drive circuit and a controller according to claim 9, wherein the controller causes the first current source to operate to initially charge the organic EL element, and the controller performs the second and third operations. An organic EL display device in which the voltage value is stored while the capacitor of the pixel circuit is initially charged by operating the current source. 11. An active matrix organic EL panel driving circuit and a controller according to claim 10, wherein the controller causes the first current source to operate to initially charge the organic EL element, and the controller causes the voltage source to operate. The capacitor of the pixel circuit is initially charged, and the second current source is operated by the controller to store the voltage value. The pixel circuit has first, second, third, and fourth P-channel MOS transistors, and the first transistor has a gate and a drain on each line at the intersection of the selection line and the data line, respectively. The source of the first transistor is connected to the gate of the third transistor via the drain-source of the second transistor, and the capacitor C is connected between the source-gate of the third transistor. Connected, a source of the third transistor is connected to a power supply line, a drain thereof is connected to a source of the fourth transistor, and a drain of the fourth transistor is connected to an anode of the organic EL element. The organic EL display device according to claim 11. The write control circuit initially charges the organic EL element by turning on the first and fourth transistors and passing the current for charging the organic EL element to charge the first and fourth transistors. The organic EL display device according to claim 14, wherein the capacitor is initially charged by turning on the transistor 2 and sinking current from the output pin, and the voltage value is written to the capacitor. 16. The organic EL device according to claim 15, further comprising a P-channel MOS fifth transistor arranged in the capacitor, wherein the write control circuit turns on the fifth transistor to reset the voltage value of the capacitor. Display device. The pixel circuit includes a series circuit composed of first and second MOS transistors for driving the organic EL element, and third and fourth MOS transistors for writing the voltage value to the capacitor. ,
The capacitor is connected between the gate of the first MOS transistor and one of the source and drain electrodes of the first MOS transistor;
One of a source and a drain of the second transistor is connected to an anode of the organic EL element;
The third MOS transistor is connected between the gate of the first MOS transistor and the other of the source and drain electrodes of the first MOS transistor;
The fourth MOS transistor is connected between the other electrode of the first MOS transistor and the output pin of the current driving circuit; and
Either one of the gate of the second MOS transistor and the gate of the third MOS transistor is connected to either one via an inverter,
The write control circuit sends a control signal to the gate of the fourth MOS transistor and the gate connected to the input side of the inverter to turn on / off the second, third, and fourth transistors. The organic EL display device according to claim 11, wherein the writing control is performed by controlling the address. The pixel circuit further includes a fifth MOS transistor connected in parallel to the capacitor to discharge the charge of the capacitor, and the write control circuit turns on the fifth MOS transistor. The organic EL display device according to claim 17, wherein the voltage value of the capacitor written in the reset is reset.

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