JP2007114309A - Driving unit and driving method of light emitting display panel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a driving unit for a display panel capable of suppressing the output capacity of a power source circuit by controlling display luminance according to the lighting rate of a pixel, and a driving method. <P>SOLUTION: One frame period is divided to a plurality of sub-frames including a lighting period and non-lighting period of the pixel and gradation control is executed by totaling the lighting periods of the pixel within one frame period by selection of the sub-frame. In addition thereto, a light emission control circuit 1 calculates the lighting rate of the pixel from a video signal and operates so as to extract the video data at which the gradation lowers from a conversion table 4 when the lighting rate is high. Accordingly, the lighting period in one frame period of the pixel is shortened and the light emission luminance of the pixel is suppressed in the case the lighting rate of the pixel is high. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a display panel driving device in which a large number of light emitting elements are used as pixels and arranged in, for example, a matrix, and more particularly to a light emitting display panel driving device and a driving method for controlling display luminance in accordance with the lighting rate of the pixels. About.

  Development of a display panel in which a large number of light emitting elements are used as pixels and arranged in a matrix has been widely promoted. As one of such display panels, a display panel using an organic EL (electroluminescence) element using an organic material for a light emitting layer as a pixel has already been commercialized. This is also due to the fact that the use of an organic compound that can be expected to have good light-emitting characteristics for the light-emitting layer of the EL element has led to an increase in efficiency and longevity that can withstand practical use.

  As a display panel using such organic EL elements, for example, a passive matrix display panel in which EL elements are simply arranged in a matrix, and a lighting control of pixels by, for example, TFTs (Thin Film Transistors) in each of the EL elements arranged in a matrix. There has been proposed an active matrix type display panel to which an element is added.

  The former display panel has a relatively simple structure and can be manufactured at a low cost. On the other hand, the latter display panel can achieve low power consumption and can be used between pixels. Therefore, it is possible to realize a high-definition display panel that constitutes a large screen.

  In any of the above-described display panels, the EL element arranged in the display panel includes a light emitting element having an electrically diode characteristic and a parasitic capacitance component coupled in parallel to the light emitting element. Can be replaced. It is known that a light emission drive current flows in a state where a voltage equal to or higher than the light emission threshold voltage (= Vth) unique to the element is applied in the forward direction of the element, and emits light with an intensity substantially proportional to the drive current value. .

  As described above, in a display panel using an EL element as a display pixel, the light emission luminance has a characteristic depending on a current value. Therefore, the power consumption depends on the lighting rate of the pixel corresponding to the video signal to be displayed. Will change drastically. That is, as shown in FIG. 1, the light emission consumption current applied to the display panel is substantially proportional to the lighting rate (number of light emitting pixels) of the pixels in the display panel.

  Therefore, the power supply circuit that supplies the drive current to the display panel secures an output capacity sufficient to supply a predetermined drive current to each pixel when the lighting rate of the pixel is maximum (100%). Therefore, there is a problem that the parts used in the power supply circuit and the overall size are inevitably increased.

Therefore, Patent Document 1 discloses a PLE (Peak Luminance Enhancement) control method in which the lighting rate is controlled from display video data to suppress the amount of current supplied to the display panel.
JP 2005-189636 A

  The present invention basically follows the PLE control method and intends to provide a control mode that is not disclosed in the above-mentioned Patent Document 1, thereby increasing the size of the power supply component as described above. It is an object of the present invention to provide a driving device and a driving method of a light emitting display panel that can solve the problem.

  A preferred form of the driving device according to the present invention, which has been made in order to solve the above-described problems, is that, as described in claim 1, pixels each composed of a light-emitting element are arranged at intersections of a plurality of data lines and a plurality of scanning lines. A light emitting display panel driving apparatus for displaying an image by selectively driving the pixels to be lit, and calculating a lighting rate for calculating a lighting rate of the pixels in the display panel driven to be lit based on video data And brightness control means for controlling the light emission brightness of each pixel according to the lighting rate obtained by the lighting rate calculation means, and the brightness control means is configured to control the video data based on the lighting rate. By performing the conversion process, the light emission luminance of each pixel is controlled.

  According to another aspect of the present invention, there is provided a driving method according to the present invention, wherein a pixel composed of a light emitting element is arranged at each of intersections of a plurality of data lines and a plurality of scanning lines. A method of driving a light-emitting display panel that displays an image by selectively driving the pixels to light, and calculates and calculates the lighting rate of the pixels in the display panel that is lighted based on video data. Further, the present invention is characterized in that the light emission luminance of each pixel is controlled by executing conversion processing of the video data based on the lighting rate.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS A light emitting display panel driving apparatus according to the present invention will be described below based on the embodiments shown in the drawings. 2 to 4 show the first embodiment, which constitutes a drive device for an active matrix display panel.

  FIG. 2 shows the overall configuration of the driving apparatus. An analog / digital (A / D) conversion circuit 2, an image memory 3, and a video data conversion table 4 are connected to the light emission control circuit 1. In the embodiment shown in FIG. 2, an analog video signal is supplied to the light emission control circuit 1 and the A / D conversion circuit 2. The light emission control circuit 1 generates a clock signal CK for the A / D conversion circuit 2, a write signal W and a read signal R for the image memory 3, based on horizontal and vertical synchronization signals in the analog video signal.

  The A / D conversion circuit 2 samples the input analog signal based on the clock signal supplied from the light emission control circuit 1, converts it into pixel data for each pixel, and supplies it to the image memory 3. Acts as follows. The image memory 3 operates to sequentially write each pixel data supplied from the A / D conversion circuit 2 to the image memory 3 in accordance with a write signal W from the light emission control circuit 1.

  A frame memory is used as the image memory 3, and data for one screen is written on a display panel described later by the above-described writing operation. Then, in a state where the writing of data for one screen has been completed, an operation is performed so as to obtain a ratio (lighting rate) of pixels to be controlled for light emission based on the pixel data written in the memory 3. That is, the light emission control circuit 1 also functions as a lighting rate calculation unit.

  The light emission control circuit 1 operates to generate a synchronization signal for the scanning driver 6 and the data driver 7 based on the horizontal and vertical synchronization signals in the video signal. Further, the light emission control circuit 1 operates to obtain the pixel lighting rate from the pixel data written in the memory 3 and to read out the pixel data from the memory 3 by the read signal R supplied from the light emission control circuit 1. .

  In the embodiment shown in FIG. 2, a video data conversion table 4 is externally attached to the light emission control circuit 1, and the light emission control circuit 1 refers to the video data conversion table 4 based on the lighting rate. As a result, conversion processing of video data for changing the gradation value of the input video signal is executed based on the lighting rate. That is, the light emission control circuit 1 extracts the video data whose gradation value has been changed from the table 4 based on the lighting rate, and the display panel 10 to be described later based on the video data whose gradation value has been changed. It operates so as to realize PLE control for controlling the light emission luminance of each of the arranged pixels 11.

  Reference numeral 10 shown in FIG. 2 indicates a display panel in which a large number of pixels 11 each including a light emitting element are arranged in a matrix. In the display panel 10, scanning lines 13 and data lines 14 connected to the scanning driver 6 and the data driver 7 are arranged in directions orthogonal to each other, and pixels including the light emitting elements at intersections thereof. 11 are arranged respectively. Each pixel 11 is configured to be supplied with a lighting driving voltage for the pixel from the power supply circuit 9 via the power supply line 16.

  FIG. 3 shows a circuit configuration corresponding to one pixel arranged in the display panel 10 described above, and this shows the most basic pixel configuration when an EL element is used as a light emitting element. A data signal Vdata corresponding to the video signal from the data driver 7 is supplied to the pixel 11 via the data line 14 arranged on the display panel to the control TFT, that is, the source of the data write transistor Tr1. It is configured.

  A scanning signal Select (also referred to as a writing pulse) is supplied to the gate of the data writing transistor Tr1 through a scanning line 13 connected to the scanning driver 6. The drain of the data writing transistor Tr1 is connected to a lighting driving TFT, that is, a gate of the lighting driving transistor Tr2, and is connected to one terminal of the charge holding capacitor C1.

  Further, the source of the lighting drive transistor Tr2 is connected to the other terminal of the capacitor C1, and the drive voltage Vcc is supplied from the power supply circuit 9 through the power supply line 16. . The drain of the lighting drive transistor Tr2 is connected to an anode terminal of an organic EL element E1 as a light emitting element, and a cathode terminal of the organic EL element E1 is connected to a reference potential point (ground).

  In the circuit configuration of the pixel 11 shown in FIG. 3, the data write transistor Tr1 is configured by an n-channel TFT, and the drive transistor Tr2 is configured by a p-channel TFT. A large number of pixels 11 having the above-described configuration are arranged in a matrix in the row and column directions as shown in FIG.

  In the configuration of the pixel 11 shown in FIG. 3, a write pulse Select as a scanning signal is supplied from the scanning driver 6 to the gate of the control transistor Tr1 during the address period. At this time, when the data signal Vdata supplied from the data driver 7 is data for lighting the pixel, a current corresponding to the data signal Vdata flows to the capacitor C1 via the source / drain of the control transistor Tr1, and the capacitor C1 is charged.

  Then, the charging voltage is supplied to the gate of the driving transistor Tr2, and the transistor Tr2 supplies a current corresponding to the gate voltage and the driving voltage Vcc supplied to the drain to the EL element E1, whereby the EL element E1 emits light. To do.

  When application of the write pulse to the gate of the control transistor Tr1 is stopped, the transistor Tr1 becomes a so-called cutoff. However, the gate voltage of the drive transistor Tr2 is held by the electric charge accumulated in the capacitor C1, thereby maintaining the drive current to the EL element E1.

  Therefore, the EL element E1 can continue the lighting state corresponding to the data signal Vdata during the period until the next address operation. Therefore, in the address period described above, the lighting or extinguishing of the pixels is controlled in accordance with the data signal Vdata supplied from the data driver 7, whereby the lighting period in the unit period of each pixel is individually controlled to control the gradation. Is realized.

  In the embodiment shown in FIGS. 2 and 3, in order to realize the PLE control described above, one frame period is divided into a plurality of subframes, and pixel lighting or non-lighting is controlled for each subframe. Thus, a gradation control means that realizes gradation control by the cumulative number of lighting periods of pixels within one frame period is employed.

  FIG. 4 shows an example of the gradation control. In this example, in order to simplify the explanation, one frame period is divided into seven subframes, and “0” to “0” are calculated by simple accumulation of the subframe periods. A simple sub-frame method expressing 8 gradations of “7” is shown. In this example, for each subframe period, at the start of the subframe period, the data signal Vdata for controlling the pixels to be turned on or off is supplied from the data driver 7 described above.

  Here, in all of the first to seventh sub-frames constituting one frame period, when a data signal for controlling the pixel to be non-lighted is supplied, the gradation “0” is realized as shown in FIG. Then, in all of the first to seventh subframes, when a data signal for controlling the pixel to the lighting state is supplied, the gradation “7” is realized as shown in FIG.

  As described above, the light emission control circuit 1 refers to the video data conversion table 4 on the basis of the lighting rate of the pixel, and when the lighting rate increases, the video data in which the gradation is lowered is extracted from the table 4. Operates to perform data conversion processing. Accordingly, when the lighting rate is in a state close to 100%, for example, the gradation is reduced by n stages (n is an integer) with respect to the gradation based on the video signal input to the light emission control circuit 1. . Therefore, when the lighting rate is high, the lighting period in one frame period of the pixel is reduced, and the light emission luminance of the pixel is suppressed.

  As described above, when the lighting rate of the pixel is high, the maximum driving current supplied from the power supply circuit to the display panel is suppressed because the light emission luminance of the pixel is controlled by controlling the gradation to be low. The Therefore, the problem that the size of each component used in the power supply circuit and the entire power supply circuit is increased can be solved.

  FIG. 5 shows a second embodiment of a drive device for a light emitting display panel according to the present invention, which constitutes a drive device for a passive matrix display panel. In addition, the structure shown with the code | symbol 1-4 shown in FIG. 5 fulfill | performs the same function as the structure shown in FIG. 2 already demonstrated, Therefore Therefore the detailed description is abbreviate | omitted.

  On the display panel 21 shown in FIG. 5, anode lines A1 to Am as m data lines are arranged in the vertical direction (column direction), and cathode lines K1 to Kn as n scanning lines are arranged in the horizontal direction (row direction). ) And organic EL elements as light-emitting elements indicated by diode symbol marks are connected between each anode line and the scanning line at each intersecting portion (total m × n locations). Yes. The anode lines A1 to Am are connected to an anode line drive circuit 22 as a data driver, and the cathode lines K1 to Kn are similarly connected to and driven by a cathode line scanning circuit 23 as a scan driver.

  The anode line drive circuit 22 includes constant current sources I1 to Im and drive switches Sa1 to Sam that operate using a drive voltage VH. The drive switches Sa1 to Sam include the constant current sources I1 to Im. By being connected to the side, the current from the constant current sources I1 to Im acts so as to be supplied to the individual EL elements arranged corresponding to the cathode lines. The drive switches Sa1 to Sam are configured so that the anode lines can be connected to the ground as a reference potential point when the currents from the constant current sources I1 to Im are not supplied to the individual EL elements. Yes.

  The cathode line scanning circuit 23 includes scanning switches Sk1 to Kn corresponding to the cathode lines K1 to Kn, and functions as a non-scanning selection potential to prevent crosstalk light emission or a reverse bias voltage source VM or scanning. One of the ground potentials functioning as the selection potential acts to connect to the corresponding cathode line. Thus, the EL elements are selectively emitted by connecting the constant current sources I1 to Im to the desired anode lines A1 to Am while setting the cathode lines to the reference potential point (ground potential) at a predetermined cycle. It works to let you.

  In the embodiment shown in FIG. 5, a scanning synchronization signal is supplied from the light emission control circuit 1 to the cathode line scanning circuit 23, whereby the cathode lines K1 to Kn are sequentially set to the ground potential (scanning selection potential). Repeated. Further, the light emission control circuit 1 supplies video data to the anode line drive circuit 22 for each scanning line in synchronization with the scanning synchronization signal. Accordingly, each of the EL elements is selectively turned on, and an image based on the video signal is displayed on the display panel 21.

  In the configuration shown in FIG. 5 as well, a PWM gradation control method that expresses 8 gradations by setting the lighting period in one scanning period to, for example, a period of 7 stages is adopted.

  That is, as in the example shown in FIG. 2, the light emission control circuit 1 shown in FIG. 5 refers to the video data conversion table 4 based on the lighting rate of the pixel, and the gradation is lowered when the lighting rate is increased. The video data is extracted from the table 4. Accordingly, when the lighting rate is in a state close to 100%, for example, the gradation is reduced by n stages (n is an integer) with respect to the gradation based on the video signal input to the light emission control circuit 1. .

  Therefore, when the lighting rate is high, the lighting period in one frame period of the pixel is reduced, and the light emission luminance of the pixel is suppressed. Therefore, also in the drive device intended for the passive matrix display panel shown in FIG. 5, the same effects as those of the first embodiment shown in FIGS. 2 to 4 can be obtained.

  In the embodiment described above, an example in which gradation control is performed in 8 stages is shown, but practical gradation control such as 32 stages or 64 stages is adopted as necessary. be able to. In the above description, an example in which an organic EL element is used as a light-emitting element constituting each pixel is shown. However, other light-emitting elements whose light emission luminance depends on a drive current can also be used.

It is the characteristic view which showed the relationship between the lighting rate of the pixel by the conventional drive device, and light emission consumption current. 1 is a block diagram showing a first embodiment of a display panel drive device according to the present invention; FIG. FIG. 3 is a circuit configuration diagram illustrating a configuration example of pixels arranged in the display panel illustrated in FIG. 2. FIG. 3 is a timing diagram for explaining gradation control means employed in the configuration shown in FIG. 2. It is the block diagram which showed 2nd Embodiment in the drive device of the display panel concerning this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light emission control circuit 2 A / D conversion circuit 3 Image memory 4 Image | video data conversion table 6,23 Scan driver 7,22 Data driver 9 Power supply circuit 10,21 Display panel 11 Pixel 13, K1-Kn Scan line 14, A1- Am data line 16 power supply line C1 charge holding capacitor E1 EL element (light emitting element)
I1 to Im constant current source Tr1 data write transistor Tr2 lighting drive transistor

Claims (4)

A driving device for a light emitting display panel, in which pixels each composed of a light emitting element are arranged at intersections of a plurality of data lines and a plurality of scanning lines, and an image is displayed by selectively driving the pixels to light.
A lighting rate calculating means for calculating a lighting rate of a pixel in the display panel driven to be lit based on video data, and a luminance for controlling the light emission luminance of each pixel according to the lighting rate obtained by the lighting rate calculating means Control means,
The drive device of the light emitting display panel, wherein the luminance control means is configured to control the light emission luminance of each pixel by executing the conversion process of the video data based on the lighting rate.   2. The drive device for a light emitting display panel according to claim 1, wherein the conversion processing of the video data is executed so that a gradation value is changed based on the lighting rate. A driving method of a light-emitting display panel, in which pixels each composed of a light-emitting element are arranged at intersections of a plurality of data lines and a plurality of scanning lines, and an image is displayed by selectively lighting the pixels,
The lighting luminance of each pixel is calculated by calculating the lighting rate of the pixel in the display panel that is driven to be lit based on the video data, and executing the conversion process of the video data based on the calculated lighting rate. A method for driving a light-emitting display panel, characterized by controlling the above.   4. The method of driving a light emitting display panel according to claim 3, wherein the light emission luminance of each pixel is controlled to decrease as the lighting rate increases.

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