JP2006284712A - Driving method and driving device of light emitting display panel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a driving device of a light emitting display panel, which is capable of achieving multi-gradation representation including a γ characteristic with a high precision without increasing power consumption. <P>SOLUTION: A unit frame period of a video signal is divided into a plurality of sub-frame periods, and lighting of a light emitting element is controlled every sub-frame period to represent a gradation. In the case of gradation expression in a low-gray level region, first lighting control accompanying an extinguishing operation of the light emitting element is executed within each sub-frame period. In the case of gradation representation in a high-gray level region, the first lighting control and the second lighting control performing lighting control of the light emitting element are executed per sub-frame. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a drive device for an active drive type display panel in which a light emitting element constituting a pixel is selectively driven to emit light by, for example, a TFT (Thin Film Transistor) and displays an image, and without particularly increasing power consumption. The present invention relates to a driving method and a driving device of a light emitting display panel that can realize multi-gradation expression including γ characteristics with high accuracy.

  With the widespread use of mobile phones and personal digital assistants (PDAs), there is an increasing demand for display panels that have high-definition image display functions and that can be thin and have low power consumption. Display panels have been adopted in many products as display panels that meet these requirements. On the other hand, recently, a display panel using an organic EL (electroluminescence) element utilizing the characteristic of being a self-luminous display element has been put into practical use, and this is drawing attention as a next-generation display panel that replaces a conventional liquid crystal display panel. ing. 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 functional layer of the device has led to higher efficiency and longer life that can withstand practical use.

  The organic EL element described above is basically configured by sequentially laminating a transparent electrode made of, for example, ITO, a light emitting functional layer made of an organic material, and a metal electrode on a transparent substrate such as glass. The light emitting functional layer is a single layer of an organic light emitting layer, or a two-layer structure comprising an organic hole transport layer and an organic light emitting layer, or a three layer comprising an organic hole transport layer, an organic light emitting layer and an organic electron transport layer. The structure may be a multilayer structure in which an electron or hole injection layer is inserted between these appropriate layers.

  As a display panel using such an organic EL element, a passive matrix display panel in which EL elements are simply arranged in a matrix, and an active matrix type in which, for example, active elements such as TFTs are added to each of the EL elements arranged in a matrix. A display panel has been proposed. The latter active matrix display panel can realize lower power consumption and has less crosstalk between pixels than the former passive matrix display panel. Suitable for high-definition displays that make up

  By the way, as one of the gradation expressions when the above active matrix display panel is driven to be lit, one frame period of the video signal is divided into a plurality of equally spaced subframes, and the light emitting elements are lit in units of the subframes. There has been proposed time gradation control that is controlled. FIG. 1 shows an example. As shown in FIG. 1, gradation control for controlling lighting of light emitting elements in units of subframes is called a simple subframe method, and the relationship between gradation and light emission luminance is controlled almost linearly (γ = 1). The However, it is said that the ideal gradation and luminance characteristics are based on a γ characteristic curve of γ = 1.8 to 2.2.

  Therefore, for example, in the case where the gradation control based on the γ characteristic curve of about γ = 2.0 is to be realized, the luminance difference between gradations on the high gradation side is relatively large, whereas the low gradation side The difference in brightness between gradations is extremely small. Therefore, in order to precisely control the luminance difference in accordance with the luminance difference between gradations on the low gradation side, high resolution is required, and as a result, it is necessary to speed up the clock signal that controls the entire drive circuit. Will occur. When the clock signal is increased in this way to increase the operation speed of the circuit, there is a problem that the power consumption of the entire circuit increases.

Therefore, as described above, as means for executing gradation control without increasing the speed of the clock signal, gradation control using analog gradation control in addition to the above-described time gradation control is disclosed in Patent Document 1 shown below. Is disclosed.
JP 2000-56727 A

  By the way, according to the gradation control system disclosed in Patent Document 1, in addition to the time gradation control, the light emission luminance of the element is controlled by changing the power supply voltage for driving the light emitting element in an analog manner. I have to. According to this, although it is not necessary to speed up the clock signal to some extent as described above, it is possible to realize multi-gradation expression including ideal γ characteristics under the influence of variations in characteristics of TFTs constituting the pixels. Is difficult.

  Therefore, it is conceivable to use the gradation control by the simple subframe shown in FIG. 1 together with the conversion means for converting the linear gradation data into the pseudo γ gradation in software. The conversion means for converting the linear gradation data into the pseudo γ gradation is, for example, a means for converting the linear gradation data into the pseudo γ gradation using a lookup table, or a linear gradation by calculation using software. A means for converting the data into pseudo γ gradation can be employed.

  The above-described configuration in which pseudo-γ gradation conversion means is used in combination with gradation control by simple subframes can avoid the problem of being affected by variations in TFT characteristics due to the analog operation described above, but FIG. As shown in FIG. 4, the luminance adjustment amount for gradation control is restricted by the number of subframes that divide one frame period, and for example, as shown in gradations 4 to 6, gradation jumps and collapses occur. There is a problem that the brightness cannot be adjusted with high accuracy.

  Therefore, as shown in FIG. 3, one frame period is time-divided into equal subframe periods, and the charge stored in the charge holding capacitors provided in each pixel is changed in the course of each subframe period. It is conceivable to employ a lighting control method in which the light emitting element is turned off by discharging. As one of such lighting control methods, a SES (Simultaneous Erasing Scan) driving method is generally known. In the SES driving method, basically, three pixels including an erasing transistor are included in each pixel as described later. A TFT is configured.

  In the case of adopting the lighting control method in which the light emitting element is turned off in the course of each subframe period described above, the light emitting period of the light emitting element in each subframe period can be finely adjusted. In addition, it is possible to realize gradation control based on non-linear characteristics with high accuracy in luminance characteristics, that is, the ideal γ characteristic curve described above. FIG. 4 shows an example in which gradation display having a γ characteristic is realized by adopting a lighting control method in which the light emitting element is turned off in the course of each subframe period.

  However, according to the lighting control method in which the light emitting element is turned off in the course of each subframe period, data (charge) is written to the charge holding capacitors provided in each pixel as shown in FIG. In addition, since the charge erasing operation is executed for each subframe, the power consumption increases.

  The present invention has been made based on the above-described technical point of view, and is a driving method of a light-emitting display panel capable of accurately realizing multi-gradation expression including γ characteristics without causing an increase in power consumption. It is another object of the present invention to provide a driving device.

  The driving method according to the present invention, which has been made to solve the above-described problem, is that, as described in claim 1, a plurality of pixels provided with light emitting elements are arranged in a matrix, and a plurality of subframes are provided in one frame period. A light-emitting display panel that performs gradation control by driving the light-emitting elements for each subframe, wherein the one frame period includes a lighting period and a non-lighting period in the subframe. Including a first period composed of a plurality of subframes, and a second period composed of a plurality of subframes not including an extinguishing period in the subframe, wherein the first period or the second period It is characterized in that the step of performing gradation control is performed in a period including at least one of the periods.

  The drive device according to the present invention, which has been made to solve the above-described problems, includes a plurality of pixels provided with light emitting elements arranged in a matrix, and a plurality of pixels in one frame period. A light-emitting display panel driving device that includes subframes and performs gradation control by driving and driving the light-emitting elements for each subframe, wherein the one-frame period includes a lighting period and a non-lighting period during the subframe. Including a first period composed of a plurality of subframes including a period and a second period composed of a plurality of subframes not including an extinguishing period in the subframe, the first period or the first The gradation control is performed in a period including at least one of the two periods.

  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. FIG. 5 shows the form of one pixel arranged in an active matrix light-emitting display panel that is lit and driven by the drive device according to the present invention. This shows a pixel configuration in the SES driving method described above.

  In FIG. 5, the control TFT, that is, the gate of the data writing transistor Tr <b> 1 is connected to a scanning line (hereinafter also referred to as a scanning line) 2, and its source is connected to a data line (hereinafter also referred to as a data line) 3. Has been. The drain of the writing transistor Tr1 is connected to the lighting driving TFT, that is, the gate of the driving transistor Tr2, and to one terminal of the charge holding capacitor C1.

  The source of the driving transistor Tr2 is connected to the other terminal of the capacitor C1 and to the power supply line 4. The drain of the drive transistor Tr2 is connected to the anode terminal of the organic EL element E1 as a light emitting element, and the cathode terminal of the organic EL element E1 is connected to the reference potential point of the display panel.

  The source and drain of an erasing transistor Tr3 as an erasing TFT are connected to both ends of the capacitor C1, and the gate of the erasing transistor Tr3 is connected to an erasing signal line (hereinafter also referred to as erasing line) 5. Has been.

  In the configuration of the pixel 1 described above, when the on voltage Select is supplied to the gate of the writing transistor Tr1 via the scanning line 2 in the address period, the writing transistor Tr1 is turned on. Then, in response to the data voltage Vdata corresponding to the write data from the data line 3 supplied to the source of the write transistor Tr1, a current corresponding to the write transistor Tr1 data voltage Vdata flows from the source to the drain. Therefore, the capacitor C1 is charged while the gate of the write transistor Tr1 is on-voltage.

  On the other hand, a charge voltage charged in the capacitor C1 is supplied to the drive transistor Tr2 as a gate voltage, and the drive voltage Vcc supplied from the power supply line 4 which is the gate voltage and the source voltage to the drive transistor Tr2. Current flows from the drain to the EL element E1, and the EL element E1 is driven to emit light by the drain current of the driving transistor Tr2.

  Here, when the addressing operation corresponding to one scanning line 2 is completed and the gate of the write transistor Tr1 becomes an off voltage, the write transistor Tr1 becomes a so-called cutoff, and the drain side of the transistor Tr1 is opened. However, the gate voltage of the driving transistor Tr2 is held by the charge accumulated in the capacitor C1, and the light emitting state of the EL element E1 is continued.

  The light emission driving operation of the EL element E1 by the writing transistor Tr1 and the driving transistor Tr2 described above is based on a pixel configuration called a known conductance control method, and in this embodiment, there is no erasing period described later. This is used when the gradation control operation by the subframe, that is, the gradation control by the simple subframe is executed.

  On the other hand, the erase signal Erase is supplied to the gate of the erase transistor Tr3 through the erase line 5. Thereby, the electric charge charged in the capacitor C1 is erased (discharged) instantaneously. As a result, the drive transistor Tr2 is cut off, and the EL element E1 is immediately turned off. Therefore, the lighting period of the EL element E1 is controlled by controlling the supply timing of the erase signal Erase supplied to the gate of the erase transistor Tr3, and the EL element is in the course of the subframe period shown in FIG. The lighting control method for executing the turn-off operation is realized.

  The pixel 1 shown in FIG. 5 is arranged in a matrix on the light emitting display panel 10 shown in FIG. 6 to form a dot matrix type display panel. Each pixel 1 includes each scanning line 2 and each data. They are formed at the intersections of the line 3 and the erase signal line 5, respectively. FIG. 6 is a block diagram showing the configuration of the light emitting display panel 10 and its driving circuit.

  The video signal displayed on the light emitting display panel 10 is supplied to the light emission control circuit 11 shown in FIG. The light emission control circuit 11 converts the input video signal into pixel data corresponding to each pixel by performing sampling processing or the like based on the horizontal synchronization signal and the vertical synchronization signal in the video signal, and performs one scan. Each data is supplied to the data driver 12. With the above-described action, the data voltage Vdata corresponding to the pixel data is individually supplied to the source of the data write transistor Tr1 constituting each pixel 1. The above-described operation is repeated for each scan in the address period.

  Further, the light emission control circuit 11 supplies a scan clock signal corresponding to the horizontal synchronizing signal to the scan driver 13 in the address period. As a result, the ON voltage Select described above is sequentially supplied to the gate of the data write transistor Tr1 constituting each pixel 1 for each scanning line.

  The light emission control circuit 11 sends a command signal corresponding to the gradation control to the erasing driver 14, and the erasing driver 14 is in the middle of the lighting period of the EL element E1 (in the middle of one subframe period). The erasing signal Erase for turning on Tr3 is supplied.

  Thereby, the electric charge charged in the capacitor C1 is erased (discharged) instantaneously. As a result, the drive transistor Tr2 is cut off, and the EL element E1 is immediately turned off. In other words, by controlling the output timing of the gate-on voltage (erase signal Erase) from the erase driver 14, the lighting period of the EL element E1 during the subframe period is controlled, thereby realizing multi-gradation expression. To be made.

  In the embodiment shown in FIG. 6, the light emission control circuit 11 is connected to a data memory 16 for constructing a look-up table, which is used when gradation control is performed by a simple subframe as will be described later. It is used to convert linear gradation data into pseudo γ gradation data.

  FIG. 7 explains the gradation control operation performed by the configuration shown in FIGS. 5 and 6 described above. In the display panel driving method according to the present invention, one frame period is time-divided into a plurality of subframe periods, and gradation expression is performed by controlling lighting of the light emitting elements for each subframe period. As shown in FIG. 5, when the gradation expression of the low gradation region (A) is performed, the first lighting control with the light-off operation of the light emitting element is controlled within each subframe period. In addition, when performing gradation expression of the high gradation region (B), control is performed so as to execute the first lighting control and the second lighting control for performing the lighting control of the light emitting element in each subframe unit. .

  According to this control mode, in the gradation control of the low gradation region (A), an ideal γ characteristic using the erasing transistor Tr3 can be obtained. In the gradation control of the high gradation region (B), the gradation control using the erasing transistor Tr3 and the gradation control by a simple subframe without the light-off operation are used in combination. This is because, in the high gradation region (B), the luminance characteristics with respect to the gradation are closer to linear as compared with the low gradation region (A), so the gradation control by the simple subframe without the light-off operation is used. However, it is possible to obtain an ideal γ characteristic. In this manner, since the operation is performed so as to use the simple subframe not accompanied by the turn-off operation according to the degree of gradation, it is possible to obtain an ideal γ characteristic without increasing the power consumption so much. In addition, since the light emission duty is increased as compared with the case where only the gradation control based on the simple subframe accompanied by the turn-off operation is used, the burden on the light emitting element is reduced.

  In this embodiment, as shown in FIG. 8, in order to bring about the above-described operation and effect, one frame period is a first period composed of a plurality of subframes including a lighting period and a non-lighting period in the subframe. Then, a second period constituted by a plurality of subframes that do not include the turn-off period in the subframe is set. Then, gradation control is performed in at least one of the first period and the second period.

  As shown in FIG. 8, in the first period, all the subframe periods are set to be equal, and the lighting period in each subframe period is set to be different. This is achieved by turning on the erasing transistor Tr3 shown in FIG. 5 during each subframe period, thereby realizing ideal γ characteristic gradation control.

  On the other hand, all the subframe periods are set to be equal in the second period shown in FIG. In the case where the gradation control is executed by the simple subframe shown as the second period, the linear gradation data is converted into the pseudo γ gradation data using the data memory 16 shown in FIG. Gradation control by simple subframe is executed. As a result, it is possible to approach the ideal γ gradation characteristics while executing gradation control by simple subframes.

  It should be noted that for the second period described above, it is possible to adopt a subframe configuration in which the subframe periods are different instead of using simple subframes in which all subframe periods are set equal. For example, FIG. 9 shows a weighted subframe method in which the ratio of subframe periods is set to a power of 2, and such a weighted subframe method can be used for the second period described above. .

It is a frame block diagram explaining a simple sub-frame system. It is a brightness | luminance characteristic figure explaining the example of a gradation control by the simple sub-frame which used the conversion means of the pseudo | simulation gamma gradation together. It is a frame block diagram explaining the sub-frame system with a light extinction operation | movement in a sub-frame. FIG. 4 is a luminance characteristic diagram for explaining gradation expression by the subframe method shown in FIG. 3. It is a block diagram of a pixel suitably used in the present invention. FIG. 6 is a block diagram illustrating a configuration of a display panel in which pixels illustrated in FIG. 5 are arranged and a driving circuit. It is a characteristic view explaining the degree of gradation and the control operation. It is a block diagram of the sub-frame in 1 frame period. It is a frame block diagram explaining the weighting sub-frame system which can be utilized in this invention.

Explanation of symbols

1 pixel 2 scan line (scan line)
3 data lines (data lines)
4 Power supply line 5 Erase line (erase signal line)
DESCRIPTION OF SYMBOLS 10 Light emission display panel 11 Light emission control circuit 12 Data driver 13 Scan driver 14 Erase driver 15 Power supply circuit 16 Data memory C1 Capacitor E1 Light emitting element (EL element)
Tr1 Write transistor Tr2 Drive transistor Tr3 Erase transistor

Claims (16)

A light-emitting display panel in which a plurality of pixels provided with light-emitting elements are arranged in a matrix, includes a plurality of sub-frames in one frame period, and performs gradation control by driving the light-emitting elements to light for each sub-frame. Driving method,
The one frame period includes a first period composed of a plurality of subframes including a lighting period and a light extinction period in the subframe;
Including a second period constituted by a plurality of subframes not including an extinguishing period in the subframe;
A method for driving a light-emitting display panel, comprising performing gradation control in a period including at least one of the first period and the second period.   In the first period, all the subframe periods are set to be equal, and at least two subframes having different lighting periods are set to be included, and the light emission is performed in the lighting period for each subframe. 2. The light emitting display panel according to claim 1, wherein a step of performing lighting drive control by converting linear grayscale image information into γ grayscale image information by driving the element to light is executed. Driving method. In each pixel, at least a light emitting element, a driving transistor for controlling lighting of the light emitting element, and an electric capacity charged with electric charge for holding a voltage applied to the gate of the driving transistor during the lighting period And
3. The driving method of the light emitting display panel according to claim 1, wherein a step of discharging the electric charge charged in the electric capacity is performed in the extinguishing period.   In the second period, lighting control is performed by converting linear gradation image information into pseudo γ gradation image information by pseudo γ gradation conversion means for converting linear gradation data into pseudo γ gradation data. The method of driving a light emitting display panel according to claim 1, wherein the step of performing is performed.   5. The method of driving a light emitting display panel according to claim 4, wherein in the second period, all the subframe periods are set to be equal.   The light emitting display panel driving method according to claim 4, wherein in the second period, at least two of the subframe periods are set to different periods.   The method of driving a light emitting display panel according to claim 6, wherein in the second period, a ratio of the plurality of subframe periods is set to a power of two.   The method for driving a light-emitting display panel according to claim 1, wherein the light-emitting element is an organic EL element. A light-emitting display panel in which a plurality of pixels provided with light-emitting elements are arranged in a matrix, includes a plurality of sub-frames in one frame period, and performs gradation control by driving the light-emitting elements to light for each sub-frame. Drive device
The one frame period includes a first period composed of a plurality of subframes including a lighting period and a light extinction period in the subframe;
Including a second period constituted by a plurality of subframes not including an extinguishing period in the subframe;
A driving device for a light-emitting display panel, wherein gradation control is performed in a period including at least one of the first period and the second period.   In the first period, all the subframe periods are set to be equal, and at least two subframes having different lighting periods are set to be included, and the light emission is performed in the lighting period for each subframe. 10. The drive device for a light emitting display panel according to claim 9, wherein lighting drive control is performed by converting the image information of linear gradation into image information of γ gradation by driving the element to light. In each pixel, at least a light emitting element, a driving transistor for controlling lighting of the light emitting element, and an electric capacity charged with electric charge for holding a voltage applied to the gate of the driving transistor during the lighting period And
11. The driving device of a light emitting display panel according to claim 9, wherein the electric charge charged in the electric capacity is discharged in the extinguishing period. A pseudo γ gradation converting means for converting linear gradation data into pseudo γ gradation data;
10. The lighting drive control is performed in the second period by converting the linear gradation image information into pseudo γ gradation image information by the pseudo γ gradation conversion means. Drive device for a light emitting display panel.   13. The light emitting display panel driving device according to claim 12, wherein in the second period, all the subframe periods are set to be equal.   13. The light emitting display panel driving device according to claim 12, wherein in the second period, at least two of the subframe periods are set to different periods.   15. The driving device of a light emitting display panel according to claim 14, wherein a ratio of the plurality of subframe periods is set to a power of 2 in the second period.   The driving device of the light emitting display panel according to claim 9, wherein the light emitting element is an organic EL element.

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