JP2006119326A - Driver of display panel, electronic equipment mounted with this driver and driving method of display panel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a driver of a display panel having a pixel constitution in which numerical aperture of pixels and practical light emitting duty are sufficiently secured and a reverse bias voltage is effectively applied to a luminous element. <P>SOLUTION: Each pixel 10 is provided with a scanning selection transistor Tr2 which receives a scanning selection signal from a scanning driver 12 and writes electric charges, that are based on data signals supplied from a data driver 11, into a light emitting sustain capacitor C1, a light emitting drive transistor Tr1 which supplies a light emitting drive current to a luminous element E1 based on the electric charges written in the light emitting sustain capacitor C1 and an electric charge discharging element R1 which gradually discharges the electric charges that are based on the data signals written into the light emitting sustain capacitor C1. The light emitting drive transistor Tr1 is set to operate in a digital operating region where a switching function can be conducted for an "on" or an "off" operation around a prescribed voltage between the gate-source as a border. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a display panel that actively drives self-luminous elements constituting a pixel by, for example, a TFT (Thin Film Transistor), and more particularly to a display panel driving apparatus and driving method capable of improving the aperture ratio and light emission duty of a pixel. .

  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 to meet that requirement. On the other hand, in recent years, a display panel using an organic EL element taking advantage of the characteristic of being a self-luminous display element has been commercialized, and this is drawing attention as a next-generation display panel that replaces a conventional liquid crystal display panel. 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 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, 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.

  The above-described organic EL element can be replaced with a configuration of a light emitting element having an electrically diode characteristic and a parasitic capacitance component coupled in parallel to the light emitting element. The organic EL element is a capacitive light emitting element. Can be said. When a light emission driving voltage is applied to the organic EL element, first, a charge corresponding to the electric capacity of the element flows into the electrode as a displacement current and is accumulated. Subsequently, when a certain voltage specific to the element (light emission threshold voltage = Vth) is exceeded, a current starts to flow from one electrode (the anode side of the diode component) to the organic layer constituting the light emitting layer, and the intensity proportional to this current Can be considered to emit light.

  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

  FIG. 1 shows a circuit configuration corresponding to one pixel 10 formed in an already proposed active matrix display panel. The circuit configuration of the pixel 10 is a relatively basic pixel configuration in the case where an organic EL element called a SES (Simultaneous Erasing Scan) system capable of realizing time gray scale expression is used as a light emitting element. .

  In the configuration of the pixel 10, the data signal Vdata corresponding to the video signal from the data driver 11 is supplied to the scan selection transistor, that is, the source S of the data writing transistor Tr2 via the data line L11 arranged in the display panel. It is configured to be. Further, the gate G of the scanning selection transistor Tr2 is configured to be supplied with a scanning selection signal Select from the scanning driver 12 via a scanning selection line L12.

  The drain D of the scan selection transistor Tr2 is connected to the gate G of the light emission driving transistor Tr1 and to one terminal of the light emission maintaining capacitor C1. The source S of the light emission driving transistor Tr1 is connected to the other terminal of the capacitor C1 and to the anode power source Va. Further, the drain D of the light emission driving transistor Tr1 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 cathode side power source Vc.

  Further, the pixel configuration shown in FIG. 1 includes an erasing transistor Tr3, and the erasing signal Erase is supplied from the erasing driver 13 to the gate of the erasing transistor Tr3 via the erasing signal line L13. ing. The source S and drain D of the erasing transistor Tr3 are connected to the respective ends of the light emission maintaining capacitor C1.

  In the pixel 10 shown in FIG. 1, only the light emission driving transistor Tr1 is composed of a p-channel TFT, and the others are composed of n-channel TFTs. The pixel 10 having the above-described configuration is arranged at each intersection position of the data line, the scanning selection line, and the erasing signal line arranged in the row and column directions to constitute a dot matrix type display panel.

  In the configuration of the pixel 10 shown in FIG. 1, an on-voltage Select as a scanning signal is supplied from the scanning driver 12 to the gate of the scanning selection transistor Tr2 in the address period. As a result, a current corresponding to the data signal (analog data voltage) Vdata supplied from the data driver 11 flows through the light emission maintaining capacitor C1 through the source / drain of the scan selection transistor Tr2, and the capacitor C1 is charged with electric charge. Is done.

  Then, the charging voltage is supplied to the gate of the light emission driving transistor Tr1, and the transistor Tr1 is based on the gate voltage and the gate-source voltage (Vgs) based on the voltage from the anode power supply Va supplied to the source. A drain current Id is passed through the EL element E1, and the EL element E1 emits light.

  When the address period elapses and the gate of the scan selection transistor Tr2 becomes an off voltage, the transistor Tr2 enters a so-called cut-off state. However, the gate voltage of the light emission drive transistor Tr1 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 until the period until the next address operation (for example, the next one frame period or the next one subframe period).

  On the other hand, in the middle of the lighting period of the EL element E1 (for example, in the middle of one frame period or one subframe period), an erase signal Erase for turning on the erase transistor Tr3 is supplied from the erase driver 13. When the erasing transistor Tr3 is turned on, the charge charged in the capacitor C1 is instantaneously erased (discharged). As a result, the light emission driving transistor Tr1 is cut off and the EL element E1 is immediately turned off. Is done.

  In other words, by controlling the output timing of the gate-on voltage from the erase driver 13 in one frame period or one subframe period, the lighting period of the EL element E1 is controlled, thereby realizing multi-tone expression. Can do.

  FIG. 2 shows an example in which time gradation expression is realized by driving the light emission drive transistor Tr1 constituting the pixel 10 shown in FIG. That is, in this case, the light emission driving transistor Tr1 shown in FIG. 1 functions as a voltage-controlled current source in which the drain current Id is determined by the gate-source voltage Vgs.

  FIG. 2 shows that when the voltage V1 is applied as the data voltage Vdata from the data driver 11 to the source of the data write transistor Tr2, the gate-source voltage in the light emission drive transistor Tr1 is -Vgs1. The case where a drain current as Id1 flows from the light emission driving transistor Tr1 by Vgs1 is illustrated. In FIG. 2, t1 and t2 indicate timings at which the above-described erasing transistor Tr3 is turned on.

  As described above, when the voltage V1 is supplied as the data voltage Vdata from the data driver 11, as shown in FIG. 2A, the gate-source voltage in the light emission driving transistor Tr1 is -Vgs1. . Therefore, the drain current Id1 corresponding to -Vgs1 is determined in accordance with the constant current drive characteristics of the transistor Tr1 shown in FIG. 2B, and the drive current due to Id1 is the EL as a self-light emitting element as shown in FIG. The EL element is supplied to the element E1, and emits light with a luminance proportional to Id1.

  In this case, when the erase signal Erase is supplied to the erasing transistor Tr3 from the erasing driver 13 at time t1, the -Vgs1 is erased at time t1, so after time t1 shown in FIG. The EL element E1 is turned off. That is, in this case, the area (a) in FIG. 2C indicates a gradation (brightness) expressed by one pixel.

  When the erase signal Erase is supplied from the erase driver 13 to the erase transistor Tr3 at time t2, the -Vgs1 is erased at time t2, so that the EL element E1 at time t2 shown in FIG. Is turned off. That is, in this case, the area (a) + (b) in FIG. 2C represents a gradation (brightness) expressed by one pixel.

  On the other hand, FIG. 3 shows an example in which the light emission driving transistor Tr1 constituting the pixel 10 shown in FIG. In this case, as shown in FIG. 3A, when the data voltage Vdata from the data driver 11 is V1, the gate-source voltage in the light emission drive transistor Tr1 is -Vgs1, and the data voltage It is assumed that the gate-source voltage of the transistor Tr1 when-is V2 is -Vgs2.

  Since the light emission driving transistor Tr1 is driven at a constant current, as shown in FIG. 3B, the drain current at −Vgs1 is set to Id1, and the drain current at −Vgs2 is set to Id2. That is, FIG. 3B shows Vgs-Id characteristics when the transistor Tr1 is driven at a constant current.

  Therefore, when the data voltage is V1, the gray level (brightness) represented by the organic EL element E1 as the light emitting element has an area (a) corresponding to Id1 as shown in FIG. It can be said that. When the data voltage is V2, as shown in FIG. 3C, the area (a) + (b) corresponding to Id2 is represented by the organic EL element E1 as the light emitting element. It can be said that (brightness).

  In the example shown in FIG. 3, the gradation is expressed according to the data voltages V1 and V2 supplied from the data driver 11, but in addition to this, the erasure from the erasure driver 13 is performed. By appropriately supplying the signal Erase to the erasing transistor Tr3, the time gray scale control can be used together.

  FIG. 4 shows an example in which the light emission driving transistor Tr1 constituting the pixel 10 shown in FIG. 1 is driven at a constant voltage and time gradation expression is realized. In this case, the light emission driving transistor Tr1 shown in FIG. 1 is controlled to perform a switching operation according to the level of its gate voltage as shown in FIG. 4B. That is, at a level deeper in the negative direction than -Vgst with a predetermined gate-source voltage -Vgst as a boundary, the light emission drive transistor Tr1 is turned on. In this operating region, the gate-source voltage is turned on. Regardless of the value of, the value of the drain current Id acts to be substantially constant. In the following, this operation area shown in FIG. 4B is expressed as a digital operation area.

  Here, when the voltage V1 is supplied as the data voltage Vdata from the data driver 11, as shown in FIG. 4A, the gate-source voltage in the light emission driving transistor Tr1 is set to -Vgs1. As a result, the transistor Tr1 driven at a constant voltage is turned on as shown in FIG. 4B, and a drain current Id1 flows as shown in FIG. 4C. Therefore, the EL element emits light with a luminance corresponding to the drain current Id1.

  In this case, when the erase signal Erase is supplied to the erase transistor Tr3 from the erase driver 13 at time t1, the light emission drive transistor Tr1 is turned off at time t1, so the time shown in FIG. 4C. After t1, the EL element E1 is turned off. Therefore, in this case, the area (a) in FIG. 4C indicates a gradation (brightness) expressed by one pixel.

  Further, when the erase signal Erase is supplied to the erasing transistor Tr3 from the erasing driver 13 at time t2, the light emission driving transistor Tr1 is turned off at time t2, as shown in FIG. At time t2, the EL element E1 is turned off. That is, in this case, the area (a) + (b) in FIG. 4C represents a gradation (brightness) expressed by one pixel.

  As described above, when the self-light-emitting element represented by the EL element E1 is driven to be lit, a configuration in which the light-emitting drive transistor Tr1 is driven at a constant current and a configuration in which the light-emitting drive transistor Tr1 is driven at a constant voltage can be selected. When the light emission driving transistor is driven at a constant current, it has an advantage that it is not easily influenced by, for example, the characteristics of the self-light-emitting element, the wiring resistance to the anode side power supply Va, the wiring resistance to the cathode side power supply Vc, and the like. .

  On the other hand, in the manufacturing process, the light emitting drive transistor Tr1 that performs the constant current operation together with the scan selection transistor Tr2 and the erase transistor Tr3 that are driven at a constant voltage (switching operation) is formed in the same pixel. Several technical challenges arise that must be overcome.

  On the other hand, in the above-described organic EL element, it is known that the light emission lifetime of the element can be extended by periodically applying a reverse bias voltage to the element. However, in a light emission driving transistor that performs a constant current operation, an electrical resistance value between the source and the drain is large, and therefore, even if a reverse bias voltage is applied to the organic EL element through the light emission driving transistor, A sufficient life extension effect of the EL element cannot be obtained.

  Therefore, in order to overcome the above-described problem, the pixel configuration shown in FIG. 5 can be recalled. The configuration shown in FIG. 5 is basically the same as the configuration shown in FIG. 1. When the reverse bias voltage is applied by switching the anode side power supply Va and the cathode side power source Vc, the light emission drive transistor Tr1 is bypassed. The diode D1 having a function is further added. When the diode D1 is further added as shown in FIG. 5, it is inevitable that problems such as a decrease in the aperture ratio of the pixel and a complicated manufacturing process of each pixel occur.

By the way, paying attention to the aperture ratio of the above-mentioned pixel, when trying to increase the aperture ratio, it is conceivable to adopt the pixel configuration shown in FIG. In FIG. 6, parts that perform the same functions as the parts shown in FIG. 1 already described are denoted by the same reference numerals, and therefore detailed descriptions thereof are omitted. The pixel configuration shown in FIG. 6 is disclosed in Patent Document 1. However, Patent Document 1 does not particularly mention the point of improving the aperture ratio of the pixel.
JP 2004-126139 A

  In the configuration shown in FIG. 6, as compared with the configuration shown in FIG. 1, the resistor R1 is connected to both ends of the light emission maintaining capacitor C1 instead of the erasing transistor. According to the configuration shown in FIG. 6 shown in Patent Document 1, the light emission drive transistor Tr1 is configured to perform a constant current operation.

  FIG. 7 shows the lighting drive characteristics of the pixel in the pixel configuration shown in FIG. As shown in FIG. 7A, the gate-source voltage in the light emission drive transistor Tr1 when the data voltage Vdata from the data driver is V1 is -Vgs1, and the transistor Tr1 when the data voltage is V2. It is assumed that the voltage between the gate and the source at −Vgs2 is −Vgs2.

  Since the gate-source voltage in the light emission driving transistor Tr1 is gradually discharged by the resistor R1, the negative bias shown by -Vgs1 and -Vgs2 shown in FIG. 7A gradually shifts to a shallower direction. In this case, since the Vgs-Id characteristic is as shown in FIG. 7B, when the data voltage is V1, the area (a) corresponding to Id1 is as shown in FIG. 7C. It can be said that the gradation (brightness) is expressed by the organic EL element E1 as the light emitting element.

  Similarly, in the case where the data voltage is V2, as shown in FIG. 7C, the area (a) + (b) corresponding to Id2 is expressed by the organic EL element E1 as the light emitting element. It can be said that (brightness). The lighting operation of this pixel is repeated based on the data voltage supplied every frame or every subframe.

  According to the configuration shown in FIG. 6, the erasing transistor can be omitted as compared with the pixel configuration shown in FIG. 1, and the erasing signal line L13 can also be omitted based on this. Therefore, the aperture ratio of the pixel can be improved, and it can contribute to improving the manufacturing yield of the element. However, the pixel configuration shown in FIG. 6 has the following technical problems.

  That is, according to the pixel configuration shown in FIG. 6, since the charge in the capacitor C1 is discharged by the time constant circuit of the capacitor C1 and the resistor R1, the charge is not completely discharged in one frame or one subframe period. The remaining charge affects the luminance in the period of the next one frame or one subframe. In order to avoid such a problem, the time constant must be set small so that the charge in the capacitor C1 can be discharged quickly.

  Incidentally, when the time constant by the capacitor C1 and the resistor R1 is set small as described above, there arises a problem that the light emission duty of each pixel is lowered by the action as shown in FIG.

  FIG. 8 exemplifies the light emission luminance characteristics of the EL element according to −Vgs1 and −Vgs2 shown in FIG. The example shown in FIG. 8 shows a case where the light emission degree of each pixel is controlled every frame period. Here, in the case where the time constant is set so that the electric charge is completely discharged in the period of one frame, the charge / discharge characteristics as illustrated as light emission by -Vgs2 in FIG. Is determined. That is, the area of the charge / discharge characteristics shown in FIG. 8 indicates the brightness of the pixel.

  The light emission characteristic due to -Vgs2 in FIG. 8 is an example in the case where the maximum luminance characteristic (gradation) is given under the above-mentioned conditions. The area occupied by can not be made larger than the state shown in the figure. In other words, the substantial light emission duty of the pixel is inevitably lowered, and the substantial luminance of the pixel is lowered.

  Therefore, it is conceivable to adopt means for compensating for a substantial decrease in luminance of the pixel by setting a large value of the light emission drive current supplied to the EL element as the light emitting element during the light emitting operation. However, in this case, there is a risk of shortening the lifetime of the light emitting element.

  On the other hand, in the pixel configuration shown in FIG. 6, since the light emission driving transistor Tr1 is driven at a constant current, for the reason already described, it is possible to effectively apply a reverse bias voltage to the EL element as the light emitting element. Impossible.

  The present invention has been made by paying attention to the technical problems described above, and can sufficiently ensure the aperture ratio of the pixel and the substantial light emission duty, and is effective for the self light emitting element. It is an object of the present invention to provide a driving device and a driving method for a display panel having a pixel configuration capable of applying a reverse bias voltage.

  The display panel drive device according to the present invention, which has been made to solve the above-described problems, has a self-luminous element at each intersection of a plurality of scan selection lines and a plurality of data lines. The display panel driving device is configured by arranging the pixels included in the matrix in a matrix, and each pixel receives a scanning selection signal from the scanning driver and is based on a data signal supplied from the data driver. A scan selection transistor that writes charge to the light emission maintaining capacitor; a light emission drive transistor that supplies a light emission drive current to the self-light emitting element based on the charge written to the light emission maintenance capacitor; and the light emission maintenance capacitor. A charge discharge element for gradually discharging charges based on the written data signal, and the light emission drive transistor is a digital It is set to operate in Le operating region, characterized in that the switching function that operates on or off by the boundary of a predetermined gate-source voltage is configured to be fulfilled.

  The display panel driving method according to the present invention, which has been made to solve the above-described problems, is characterized in that, as described in claim 9, a self-light emitting element is provided at each intersection of a plurality of scanning selection lines and a plurality of data lines. A display panel driving method in which pixels each including a pixel are arranged in a matrix, wherein each pixel receives a scanning selection signal from a scanning driver and receives a data signal supplied from a data driver. A scanning selection transistor for writing the charge based on the light-emission maintaining capacitor, a light-emission driving transistor for supplying a light-emission driving current to the self-light-emitting element based on the charge written to the light-emission maintaining capacitor, and A charge discharge element for gradually discharging charges based on the data signal written in the capacitor, and the light emission driving transistor. By being set to operate in the digital operating region, characterized in that it is controlled to perform a switching function that operates on or off by the boundary of a predetermined gate-source voltage.

  Hereinafter, a display panel and a driving device thereof according to the present invention will be described based on embodiments shown in FIG. In the drawings described below, parts having the same functions as the parts already described are denoted by the same reference numerals, and detailed description thereof will be omitted as appropriate.

  The display panel employed in the present invention employs the pixel configuration shown in FIG. 9, and the light emission drive transistor Tr1 is driven to be switched by a constant voltage operation. That is, the pixel configuration shown in FIG. 9 is the same as the already described pixel configuration shown in FIG. 6 in terms of circuit configuration, but in the pixel configuration shown in FIG. 9, the light emission drive transistor Tr1 is shown in FIG. The operating point is set in the digital operation area already described based on the above. As a result, the light emission driving transistor Tr1 is turned on at a level deeper in the negative direction than the above-Vgst with a predetermined gate-source voltage -Vgst as a boundary. In this operating region, the gate-source voltage is turned on. Regardless of the value of, the value of the drain current Id acts to be substantially constant.

  In the pixel configuration shown in FIG. 9, the scan selection signal Select is supplied from the scan driver 12 to the scan selection transistor Tr2 in the address period for each frame or subframe period. The transistor Tr2 that has received the scan selection signal Select supplies a current corresponding to the data voltage Vdata supplied from the data driver 11 to the light emission maintaining capacitor C1, and the capacitor C1 is charged with a charge corresponding to the data voltage Vdata. Is done.

  Then, after the address period has elapsed, the charge charged in the capacitor C1 is gradually discharged through a charge discharge element connected in parallel to the capacitor C1, that is, the resistance element R1. This is shown in FIG. As shown in FIG. 10A, the capacitor C1 has a write voltage controlled in accordance with the data voltages supplied from the data driver 11, for example, V1 and V2, thereby causing the capacitor C1 to be connected to the gate of the light emission driving transistor Tr1. On the other hand, gate-source voltages indicated by -Vgs1 and -Vgs2 are applied.

  The -Vgs1 and -Vgs2 are discharged based on the time constant of the capacitor C1 and the resistor R1, as shown in FIG. FIG. 10B shows the switching characteristics of the light emission drive transistor Tr1 corresponding to -Vgs1 and -Vgs2. The transistor Tr1 is operated in the digital operation region as described above, and is turned on or off with a predetermined gate-source voltage -Vgst as a boundary. That is, at a level deeper in the negative direction than -Vgst, the light emission driving transistor Tr1 is turned on, and at a level shallower than that, it is turned off.

  Accordingly, the voltage written as -Vgs1 to the capacitor C1 in the address period becomes a level shallower than -Vgst at the elapse of t1 in FIG. 10A, and the time t1 as shown in FIG. 10C. Thereafter, the EL element E1 is turned off. That is, in this case, the area (a) in FIG. 10C represents a gradation (brightness) expressed by one pixel.

  Further, the voltage written as -Vgs2 to the capacitor C1 in the address period becomes a level shallower than -Vgst at the elapse of t2 in FIG. 10A, and the time t2 as shown in FIG. 10C. Thereafter, the EL element E1 is turned off. That is, in this case, the area (a) + (b) in FIG. 10C represents a gradation (brightness) expressed by one pixel.

  FIG. 11 shows an example of gradation control by a sub-frame method performed using a display panel having the pixel configuration shown in FIG. In the gradation control shown in FIG. 11, one frame period is divided into 10 subframe periods and two dummy subframe periods. In the example shown in FIG. 11, a discharge control pulse is output at each start time of the first to tenth subframes and at the start time of the dummy subframe, and the charge remaining in the light emission sustaining capacitor C1. The operation of discharging is performed. Such an operation is sequentially executed for each of the first selection line (1st line) to the Nth line (Nth line) of the scanning selection lines arranged on the display panel.

  FIG. 12 shows the potential state of the pixel for setting the charge discharge period for discharging the charge remaining in the capacitor C1. In this charge discharge period, the anode side power supply Va is supplied to the source of the scan selection transistor Tr2, and the scan selection signal Select for turning on the transistor Tr2 is supplied to the gate of the transistor Tr2. Therefore, both ends of the capacitor C1 are set to the same potential by the anode side power supply Va, and the electric charge in the capacitor C1 is discharged.

  By performing such an operation, it is possible to prevent the remaining charge in the lighting control of the EL element in the previous subframe from being discharged and affecting the lighting luminance of the pixel in the next one subframe period. be able to.

  Returning to FIG. 11, in each subframe, the write control pulse is output immediately after the discharge control pulse is output. As a result, the scan selection transistor Tr2 shown in FIG. 9 is brought into the scan selection state (ON state), and the operation voltage corresponding to the data voltage Vdata from the data driver 11 (applied to the light emission driving transistor Tr1) is applied via the transistor Tr2. (The gate-source voltage) is written into the light emission sustaining capacitor C1. As described above, the on period of the light emission driving transistor Tr1 is set according to the level of the operating voltage written at this time, and the gradation control is realized.

  On the other hand, in the dummy sub-frame period shown in FIG. 11, each pixel is in a non-lighting state over two sub-frame periods, and in the period in which all the pixels are in a non-lighting state, as shown in FIG. A bias application period is set. FIG. 13 shows the potential setting state of the pixel during the reverse bias application period. In this state, the potential of the cathode side power source Vc is applied to the source side of the light emission driving transistor Tr1, and the EL element E1 is applied. The potential of the anode-side power supply Va is applied to the cathode side.

  At this time, the scan selection signal Select for turning on the gate is supplied to the gate of the scan selection transistor Tr2, and the potential at which the light emission driving transistor Tr1 is turned on, that is, the transistor Tr1 is supplied to the source of the transistor Tr2. For example, a data voltage giving −Vgs2 shown in FIG. 9 is supplied between the gate and the source.

  Therefore, the light emission driving transistor Tr1 is brought into a very low resistance value between its source and drain by constant voltage operation, and is effectively reverse-biased for each frame period with respect to the EL element E1 as a self-light emitting element. Voltage can be applied. Therefore, the life extension effect of the self-luminous element represented by the EL element can be expected.

  FIG. 14A shows the discharge operation of the light emission sustaining capacitor C1 for each subframe as described with reference to FIG. 11, and the subsequent data for writing the charge corresponding to the data voltage Vdata to the capacitor C1. A preferable light emission driving state of a pixel in a case where an address period is provided is shown. FIG. 14B shows the switching characteristics of the light emission driving transistor Tr1 operating in the above-described digital operation region at this time, and this shows the same characteristics as already described with reference to FIG. 10B.

  In the example shown in FIG. 14, the discharge characteristic of the time constant circuit formed by the capacitor C1 and the resistor R1 is equal to or longer than the period of one subframe in the state of the maximum amount of charge written to the light emission maintaining capacitor C1. Is set to That is, in FIG. 14A, when it is assumed that the maximum amount of charge written in the capacitor C1 corresponds to -Vgs2, the discharge characteristic of -Vgs2 is preferably at the end of one subframe. The level corresponding to the switching operation point −Vgst of the light emission driving transistor Tr1 is set to remain.

  According to the setting state as described above, when the maximum amount of charge −Vgs2 is written to the capacitor C1, as shown in FIG. 14 (A), over the period from the data writing time to the time t2. A light emission driving current by a constant voltage operation can be supplied to the EL element as the self-light emitting element. That is, as shown in FIG. 14A, when the period of one subframe is c, the period d corresponding to the area (a) + (b) can be set as the light emission duty, and the duty ratio is d / C.

  As shown in FIG. 14A, for example, when a charge amount -Vgs1 is written to the capacitor C1, the constant voltage operation is performed on the EL element over a period from the data writing time to time t1. The light emission driving current can be supplied. In this case, it can be said that the area (a) is a gradation (brightness) represented by this pixel.

  According to the lighting operation of the pixel shown in FIG. 14, although the operation of discharging the charge of the capacitor C1 every subframe is required, the light emission duty of the EL element can be greatly improved. In this case, regardless of the discharge of the charge accumulated in the capacitor C1, if the charge amount is not less than a predetermined value (the absolute value is not less than the level corresponding to the switching operation point -Vgst), a substantially constant drive current ( A drain current Id) can be passed through the EL element.

  Therefore, the area shown in (a) and (b) that contributes to the gradation expression of the pixel as shown in FIG. 14 can be secured, and the charge / discharge characteristics by the quadratic curve as shown in FIG. Compared with the accompanying gradation control, the substantial light emission duty of the pixel can be further greatly improved. In addition, since each pixel can have a relatively simple circuit configuration as shown in FIG. 9, a sufficient aperture ratio of the pixel can be secured.

  Next, FIG. 15A shows that the discharge of the time constant circuit by the capacitor C1 and the resistor R1 is intentionally terminated within one subframe period in the state of the maximum amount of charge written in the light emission maintaining capacitor C1. The example set to do is shown. Note that FIG. 15B shows the switching characteristics of the light emission drive transistor Tr1 operating in the digital operation region at this time, and this shows the same characteristics as FIG. 10B already described.

  According to the operation example shown in FIG. 15, when a charge corresponding to -Vgs2 which is the maximum amount of charge is written to the capacitor C1, as shown in FIG. Over the period up to time t2, the light emission driving current by the constant voltage operation can be supplied to the EL element as the self light emitting element. That is, as shown in FIG. 15A, when the period of one subframe is c, the period d ′ corresponding to the area (a) + (b) can be set as the light emission duty, and the duty ratio is It can be said that d ′ / c.

  As shown in FIG. 15A, when a charge amount corresponding to, for example, -Vgs1 is written to the capacitor C1, the EL element is constant over the period from the data write time to time t1. A light emission driving current by voltage operation can be supplied. In this case, it can be said that the area (a) is a gradation (brightness) expressed by this pixel.

  According to the lighting operation of the pixel shown in FIG. 15, the operation of discharging the charge remaining in the capacitor C1 every subframe becomes unnecessary, and therefore the lighting control of the pixel can be simplified. On the other hand, in the lighting operation of the pixel shown in FIG. 15, it is unavoidable that the light emission duty is reduced to some extent as compared with the lighting operation of the pixel shown in FIG. However, the light emission luminance of the EL element based on a substantially constant driving current (drain current Id) can be ensured during the lighting period of the pixel. Therefore, the substantial light emission duty of the pixel can be significantly improved as compared with the gradation control with charge / discharge characteristics by the quadratic curve as shown in FIG.

  In the embodiment described above, a p-channel TFT is used as the light emission drive transistor Tr1 as shown in FIG. 9, but an n-channel TFT can be used instead. FIG. 16 shows a pixel configuration that can be employed in that case. An EL element E1 as a self-luminous element is inserted and connected between the drain of the light emission driving transistor Tr1 made of an n-channel TFT and the anode side power supply Va, and the source of the transistor Tr1 is connected to the cathode side power supply Vc. It is connected. The light emission maintaining capacitor C1 and the resistor R1 are connected between the gate and the source of the transistor Tr1, respectively.

  In the above-described embodiment, as shown in FIGS. 11 and 14, the charge remaining in the light emission maintaining capacitor C1 is discharged at the beginning of one subframe. The discharge operation may be executed at the end of one subframe. Further, in the above-described embodiment, one frame period is divided into a plurality of subframes, and pixel lighting control is executed for each subframe. However, this is executed for each frame period. You can also.

  Furthermore, in the embodiment described above, an organic EL element is used as the self-light-emitting element. However, the self-light-emitting element is not limited to the organic EL element, and a current whose light emission luminance is determined according to the drive current. Even when a dependent element is used, the same effect as described above can be obtained. The above-described display panel driving device can be applied to various electronic devices that require this type of display device in addition to the mobile phone and the portable information terminal described at the beginning, so that the functions and effects described above can be obtained. You can enjoy it as it is.

It is the circuit block diagram which showed the example of the pixel by the conventional SES drive system. FIG. 2 is a lighting drive characteristic diagram showing an example in which time gradation expression is realized by driving a light emission drive transistor in the pixel configuration shown in FIG. 1 at a constant current. FIG. 2 is a lighting drive characteristic diagram showing an example in which the light emission drive transistor in the pixel configuration shown in FIG. FIG. 2 is a lighting drive characteristic diagram showing an example in which a light emission driving transistor in the pixel configuration shown in FIG. 1 is driven at a constant voltage and time gradation expression is realized. It is the circuit block diagram which showed the example of the pixel structure which aims at the life extension effect of the self-light-emitting element which comprises a pixel. It is a circuit block diagram which showed the other conventional pixel structural example. FIG. 7 is a lighting drive characteristic diagram in the pixel configuration shown in FIG. 6. FIG. 7 is a lighting drive characteristic diagram illustrating a state of light emission duty in the pixel configuration illustrated in FIG. 6. It is a circuit block diagram which showed the pixel structure employ | adopted as the display panel concerning this invention. FIG. 10 is a lighting drive characteristic diagram in the pixel configuration shown in FIG. 9. FIG. 10 is a timing diagram illustrating an example of gradation control by a subframe method performed using a display panel having the pixel configuration illustrated in FIG. 9. FIG. 10 is a state diagram of a charge discharge period performed in the pixel configuration shown in FIG. 9. FIG. 10 is a state diagram of a reverse bias voltage application period performed in the pixel configuration illustrated in FIG. 9. FIG. 10 is a first lighting drive characteristic diagram made in the pixel configuration shown in FIG. 9. FIG. 10 is a second lighting drive characteristic diagram made in the pixel configuration shown in FIG. 9. FIG. 10 is a circuit configuration diagram illustrating an example of another pixel configuration in place of the pixel configuration illustrated in FIG. 9.

Explanation of symbols

10 pixels 11 data drivers 12 scan drivers 13 erasure drivers C1 light emission maintaining capacitors E1 self-luminous elements (organic EL elements)
L11 Data line L12 Scan selection line L13 Erase signal line R1 Resistance Tr1 Light emission drive transistor Tr2 Scan selection transistor (data write transistor)
Tr3 erase transistor

Claims (10)

A drive device for a display panel configured by arranging pixels each including a self-luminous element in a matrix at each intersection of a plurality of scanning selection lines and a plurality of data lines, each pixel including:
A scan selection transistor that receives a scan selection signal from the scan driver and writes a charge based on the data signal supplied from the data driver to the light emission maintaining capacitor;
A light emission drive transistor for supplying a light emission drive current to the self light emitting element based on the charge written in the light emission maintaining capacitor;
A charge discharge element that gradually discharges the charge based on the data signal written to the capacitor for maintaining light emission,
The display is characterized in that the light emission driving transistor is set so as to operate in a digital operation region, and is configured to perform a switching function of turning on or off with a predetermined gate-source voltage as a boundary. Panel drive device.   The charge discharge element is a resistance element connected in parallel to a light emission maintaining capacitor, and the resistance element constitutes a time constant circuit together with the light emission maintenance capacitor, and the charge in the state of the maximum amount of charge written to the capacitor 2. The display panel driving device according to claim 1, wherein the discharge characteristic of the time constant circuit is set to be equal to or longer than a period of one frame or one subframe.   The light emission period of the self-light emitting element is determined within a period of one frame or one subframe according to the electric charge written in the light emission maintaining capacitor based on the data signal. The display panel drive device according to claim 1 or 2.   The charge discharge period for discharging the charge of the light emission sustaining capacitor is set to the light emission sustaining capacitor immediately before the charge based on the data signal is written. The display panel driving device according to any one of claims 3 to 4.   5. The display panel according to claim 4, wherein in the charge discharging period, an operation of applying a potential at which both ends of the light emission sustaining capacitor have the same potential is performed through the scan selection transistor. Drive device.   A reverse bias voltage application period is set for turning on the light emission driving transistor and applying a potential in the opposite direction to the light emission of the self light emitting element via the light emission driving transistor. 6. The display panel drive device according to claim 1, wherein the display panel drive device is configured as described above.   The display panel drive according to claim 1, wherein the self-light-emitting element is configured by an organic EL element having at least one light-emitting functional layer. apparatus.   An electronic device comprising the display panel driving device according to claim 1. A driving method of a display panel configured by arranging pixels each including a self-light emitting element in a matrix at each intersection of a plurality of scanning selection lines and a plurality of data lines, each pixel including:
A scan selection transistor that receives a scan selection signal from the scan driver and writes a charge based on the data signal supplied from the data driver to the light emission maintaining capacitor;
A light emission drive transistor for supplying a light emission drive current to the self light emitting element based on the charge written in the light emission maintaining capacitor;
A charge discharge element that gradually discharges the charge based on the data signal written to the capacitor for maintaining light emission,
The light emission driving transistor is set to operate in a digital operation region, and is controlled to perform a switching function of turning on or off with a predetermined gate-source voltage as a boundary. Driving method of display panel.   The charge discharge element is a resistance element connected in parallel to a light emission maintaining capacitor, and the resistance element constitutes a time constant circuit together with the light emission maintenance capacitor, and the charge in the state of the maximum amount of charge written to the capacitor 10. The display panel driving method according to claim 9, wherein the discharge characteristic of the time constant circuit is set to be equal to or longer than a period of one frame or one subframe.

Images