JP2005189381A - Display device and method for driving display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To correctly correct threshold voltage even when not regulating a period correcting the threshold voltage of a transistor driving a light emitting element. <P>SOLUTION: The display device corrects irregularity of a transistor TR2 and sets gradation by setting a signal level of a signal line SIG after setting the threshold voltage of the transistor TR2 in the capacitor Cs2 for holding a signal level provided between gate sources of the transistor TR2 to the transistor TR2 driving by current the light emitting element 12. It discharges accumulation charge of the transistor TR2 through the light emitting element 12, and is held at the threshold voltage of the transistor TR2 by supplying lowering of voltage between the gate sources by lowering of terminal voltage due to discharge of the accumulation charge of the light emitting element 12 after the voltage between the gate sources lowers down to the threshold voltage of the transistor TR2. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a display device and a display device driving method, and can be applied to, for example, a display device using an organic EL (Electro Luminescence) element. The present invention relates to a transistor for driving a light emitting element with a source follower circuit configuration, and after setting a threshold voltage of a transistor in a signal level holding capacitor provided between the gate and source of the transistor, By setting the signal level of the transistor, the variation of the transistor is corrected to set the gradation, the accumulated charge of the transistor is discharged through the light emitting element, and the gate-source voltage of the transistor is set to the threshold value of the transistor. After the voltage drops to the voltage, the gate-source voltage is compensated for by the reduction of the terminal voltage due to the discharge of the accumulated charge of the light emitting element, and the gate-source voltage of the transistor is maintained at the threshold voltage of the transistor. Therefore, the threshold voltage of the transistor driving the light emitting element is corrected. , Even without adjusting the length of time to correct the threshold voltage, to be able to properly correct the threshold voltage.

  Conventionally, in organic EL display devices, various applications to display devices have been proposed, for example, in US Pat. No. 5,684,365 and JP-A-8-234683.

  That is, as shown in FIG. 11, in this type of display device 1, the pixel unit 2 has scanning lines SCN provided in the horizontal direction in units of lines with respect to the pixels (PX) 3 arranged in a matrix. A signal line SIG is provided in the vertical direction for each column so as to be orthogonal to the scanning line SCN. For the pixel portion 2 formed in this way, the display device 1 drives the scanning line SCN by the vertical drive circuit 4 to sequentially select the pixels 3 of the pixel portion 2 in units of lines, and this pixel 3 The gray level of each pixel 3 is set by driving the signal line SIG by the horizontal drive circuit 5 so as to correspond to the selection.

  For this reason, the vertical drive circuit 4 generates a write signal ws for sequentially instructing writing to each pixel 3 in line units by the write scan circuit (WSCN) 4A, and outputs the write signal ws to the scan line SCN. The setting of gradation in the pixel 3 is controlled. The horizontal drive circuit 5 generates a drive signal in accordance with the gradation data D1 indicating the gradation of each pixel 3, distributes this drive signal to each signal line SIG by the horizontal selector (HSEL) 5A, and outputs it. Thus, the display device 1 is configured to set the gradation of each pixel 3 in line units.

  In the display device of an organic EL element, each pixel 3 driven in this way is an organic EL element that is a self-luminous element driven by current, and a driving circuit for each pixel that drives the organic EL element (hereinafter, referred to as an organic EL element). , Referred to as a pixel circuit).

  In the display device thus formed, each pixel circuit is formed by an n-channel MOS type TFT (Thin Film Transistor), and the anode of the organic EL element is connected to the transistor. By driving with current, an organic EL element and a pixel circuit can be integrally formed on a glass substrate by applying an amorphous silicon process. As a result, as shown in FIG. It is conceivable to drive the element 12.

  That is, the display device 11 shown in FIG. 12 is formed in each pixel 3 so that the organic EL element 12 is current-driven by the transistor TR2 having a source follower circuit configuration in which the source is connected to the anode of the organic EL element 12. A signal level holding capacitor C1 is provided at the gate of the transistor TR2. The display device 11 outputs the write signal ws from the write scan circuit 4A provided in the vertical drive circuit 4, and this signal level holding capacitor C1 by the switch circuit by the transistor TR1 that is turned on by the write signal ws. Is connected to the signal line SIG, whereby the gate Vg of the transistor TR2 is set by the signal level of the drive signal output to the signal line SIG in response to the write signal ws. As a result, the display device 11 drives the organic EL element 12 with a current corresponding to the gate voltage Vg set in this way, and emits the organic EL element 12 of each pixel 3 with a gradation corresponding to the gradation data D1. Thus, a desired image can be displayed.

  However, in the organic EL element, as shown in FIG. 13, the voltage-current characteristic changes in a direction in which current hardly flows by use. In FIG. 13 and FIG. 14, the symbol L1 indicates the initial characteristics, and the symbol L2 indicates the characteristics due to the change with time. On the other hand, in the driving by the sofa follower circuit described above with reference to FIG. 12, the characteristic curve due to the load intersects the characteristic curve of the drain-source voltage Vds−the drain source current Ids of the transistor TR2 as shown in FIG. The intersecting point becomes the operating point. As a result, when the voltage-current characteristics change in the organic EL element, the current flowing through the organic EL element is reduced by that amount, thereby causing a problem that the luminance of each pixel is gradually lowered to deteriorate the image quality.

As one method for solving this drawback, a method of controlling the drive current of the organic EL element 12 by setting the gradation by the gate-source voltage Vgs instead of simply setting the gradation by the gate voltage Vg can be considered. That is, in the drain current Ids of the TFT, it is expressed by (1/2) × μ × (W / L) Cox (Vgs−Vth) ² (1), thereby setting the gradation by the gate-source voltage Vgs. Thus, it is possible to prevent a change in drive current due to a change with time. Here, μ is the carrier mobility, W is the gate width, L is the gate length, Cox is the gate capacitance per unit area, and Vth is the threshold voltage.

  However, when the gradation is set by the gate-source voltage Vgs in this way, as is clear from the equation (1), if the threshold voltage Vth of the transistor that drives the organic EL element varies, the corresponding amount in each pixel. There is a drawback in that the drive current varies, and the image quality deteriorates. Accordingly, as a method for eliminating this drawback, a threshold voltage Vth of the transistor is set in advance in a capacitor for holding the signal level for gradation setting, and the capacitor for holding the signal level is set by this threshold voltage. It is conceivable to correct the terminal voltage.

  FIG. 15 is a block diagram showing a display device considered to be able to eliminate these drawbacks by contrast with FIG. In this display device 31, in each pixel 33, a signal level holding capacitor Cs2 is arranged between the gate and source of the transistor TR2 in place of the arrangement of the signal level holding capacitor C1 between the gate and drain of the transistor TR2. The terminal voltage of the signal level holding capacitor Cs2 is set according to the signal level of the signal line SIG. Further, when a switch circuit composed of a transistor TR3 which is turned on by the drive scan signal ds1 is connected to the source of the transistor TR2, the terminal voltage of the signal level holding capacitor Cs2 is set by the signal level of the signal line SIG. The source side end of the signal level holding capacitor Cs2 is held at a constant potential. In FIG. 15, this constant potential is the ground potential.

  Thereby, in the transistor TR2, the organic EL element 12 can be driven by the gate-source voltage Vgs based on the inter-terminal voltage held in the signal level holding capacitor Cs2, and the voltage-current characteristics of the organic EL element 12 change over time. Even so, it is possible to prevent the deterioration of the image quality by preventing the change of the drive current due to the change with time.

  The display device 31 is provided with a coupling capacitor Cs1 between the signal level holding capacitor Cs2 and the transistor TR1, so as to set the gradation by setting the gate-source voltage Vgs. The terminal voltage of the signal level holding capacitor Cs2 is set by the signal level Vin of the signal line SIG via the coupling capacitor Cs1. In this case, the voltage between the terminals of the signal level holding capacitor Cs2 due to the connection to the signal line SIG via the capacitor Cs1 is the voltage ΔVin = Vin obtained by dividing the signal level Vin of the signal line SIG by the capacitors Cs1 and Cs2. (Cs1 / (Cs1 + Cs2))... (2). Accordingly, the signal line SIG is driven by the horizontal drive circuit 35 in consideration of this relational expression.

  Further, the display device 31 is connected to the reference voltage by the switch circuit by the transistor TR4 that stops the supply of the power source Vcc to the transistor TR2, the switch circuit by the transistor TR5 that short-circuits the gate and source of the transistor TR2, and the transistor TR1 side end of the capacitor Cs1. A switch circuit comprising a transistor TR6 is provided. Even in the reference voltage related to the transistor TR6, the display device 31 is set to the ground potential.

  Accordingly, as shown in FIGS. 16 and 17A, the display device 31 current-drives the organic EL element 12 with the transistor TR2 by the gate-source voltage Vgs by the signal level holding capacitor Cs2, and generates the write signal ws. Immediately before setting the gradation of the pixel 33, with the power supply Vcc supplied to the transistor TR2, the transistor TR5 is turned on by the control signal az and the transistor TR2 is diode-connected, and the coupling capacitor Cs1 is connected. The signal line side end is set to a predetermined reference potential (FIGS. 16A, 16B, and 17B). After that, the supply of power Vcc to the transistor TR2 is stopped by the transistor TR4, and the source of the transistor TR2 is connected to the reference voltage by the transistor TR3 (FIGS. 16C, 16D, and 17C). As a result, in this display device 31, even if the voltage across the terminals of the signal level holding capacitor Cs2 is equal to or lower than the threshold voltage Vth of the transistor TR2, the display device 31 once exceeds the threshold voltage Vth of the transistor TR2. The gate-source voltage Vgs of the transistor TR2 is raised and then converged to the threshold voltage Vth, so that the threshold voltage Vth of the transistor TR2 is set in the signal level holding capacitor Cs2. Has been made. (FIGS. 16E and 16F).

  When the threshold voltage Vth is set to the signal level holding capacitor Cs2 in this manner, the display device 31 causes the control signal az to fall while the source of the transistor TR2 is connected to the reference voltage by the transistor TR3. Thus, the diode connection by the transistor TR5 is stopped, and the connection of the coupling capacitor Cs1 to the reference voltage by the transistor TR6 is stopped (FIGS. 16B and 17D). Subsequently, the transistor TR1 is controlled by the rising of the write signal ws to connect the signal line SIG to the coupling capacitor Cs1, thereby holding the source side end of the signal level holding capacitor Cs2 at the reference voltage. In this state, the terminal voltage of the signal level holding capacitor Cs2 is set by the signal level Vin of the signal line SIG through the coupling capacitor Cs1, and thereby, between the gate and source of the transistor TR2 used for driving the organic EL element 12 The voltage Vgs is set (FIGS. 16C and 17D). In this case, since the threshold voltage Vth of the transistor TR2 is set in advance in the signal level holding capacitor Cs2, the threshold voltage Vth of the signal level holding capacitor Cs2 is set. The voltage between the terminals is set by a voltage that is higher by a corresponding amount, so that the term of -Vth in parentheses in the equation (1) is set to be canceled, and the organic EL element 12 is driven by the transistor TR2. This prevents variations in drive current due to variations in the threshold voltage Vth of the transistor TR2.

  Thus, in the display device 31, after the transistors TR1 and TR3 are returned to the original settings, the supply of the power supply Vcc is started by the transistor TR4, so that the signal level holding capacitor Cs2 thus set is connected between the terminals. The organic EL element 12 is current-driven by the voltage (FIG. 17E).

  In the display device 31 (FIG. 15), in addition to the write scan circuit 24A that outputs the write signal ws, the output of the write signal ws by this write scan circuit 24A corresponds to the configuration of the pixel unit 32 by such pixels 33. The vertical drive circuit 34 is provided with a drive scan circuit (DSCN) 34B, a drive scan circuit (DSCN2) 34C, and an auto zero circuit (ZERO) 34D that output a drive scan signal ds1, a drive scan signal ds2, and a control signal az, respectively. . The horizontal drive circuit 35 generates a drive signal so as to correspond to these configurations.

  By doing so, it is possible to prevent deterioration in image quality due to changes over time of the organic EL element 12 and variations in the threshold voltage Vth of the transistor TR2 that drives the organic EL element 12.

  However, in a TFT made of amorphous silicon, generally, even when the gate-source voltage Vgs becomes a threshold voltage Vth and is cut off, an off-current continues to flow if the cut-off voltage is high. Thus, in the case of correcting the threshold voltage Vth of the transistor TR2 that drives the organic EL element 12 with the configuration of FIG. 15, even after the gate-source voltage Vgs of the transistor TR2 becomes the threshold voltage Vth. When the gate voltage Vg of the transistor TR2 gradually decreases and the period T for raising the control signal az and correcting the threshold voltage Vth as shown in FIG. 18 by comparison with FIG. 14 becomes longer. Therefore, the gate voltage of the transistor TR2 falls to the source potential. In addition to TFTs made of amorphous silicon, for example, some transistors made of polysilicon also have a large off-current, and the same problem occurs in such transistors.

  Accordingly, in the configuration shown in FIG. 15, there is a problem that the threshold voltage Vth of the transistor TR2 cannot be corrected correctly unless the period for correcting the threshold voltage Vth is set appropriately. In the case where the threshold voltage Vth of the transistor TR2 cannot be corrected correctly, in the display device, variations in the threshold voltage Vth of the transistor TR2 assigned to each pixel 33 and variations in the variation amount of the threshold voltage Vth are caused. The display is affected, and a so-called surface roughness is generated in which the display screen is rough, resulting in deterioration of uniformity.

However, in this type of display device, since the characteristics of the transistor TR2 are different for each product, if the period for correcting the threshold voltage Vth is appropriately set, the adjustment can be made for each product. This requires a lot of time for this adjustment work, and the configuration of the display device becomes complicated as the adjustment is possible. Thus, it is desired that no adjustment be made during the period for correcting the threshold voltage Vth.
USP 5,684,365 JP-A-8-234683

  The present invention has been made in consideration of the above points, and corrects the threshold voltage of the transistor that drives the light emitting element, and corrects the threshold voltage without adjusting the period for correcting the threshold voltage. It is an object of the present invention to propose a display device and a display device driving method capable of correcting a threshold voltage.

  In order to solve such a problem, in the invention of claim 1, the pixel is applied to a display device having a pixel portion in which pixels driven by current drive are arranged in a matrix and a drive circuit for driving the pixel portion. A transistor having a signal level holding capacitor between a light emitting element and a gate source, a transistor having a source follower circuit that drives the light emitting element by a gate-source voltage by a voltage between terminals of the signal level holding capacitor, and one end of the transistor A coupling capacitor connected to the gate, a signal line switch circuit for connecting the other end of the coupling capacitor to the signal line, a short-circuit switch circuit for short-circuiting the gate drain of the transistor, and a coupling Switch for the capacitor side reference voltage that connects the other end of the capacitor to a predetermined reference voltage. Circuit, and a power supply switch circuit for stopping the supply of power to the transistor, and the drive circuit is driven by the signal line switch circuit, and the signal is transmitted according to the signal level of the signal line through the coupling capacitor. By setting the terminal voltage of the capacitor for holding the level, the voltage between the gate and the source of the transistor used to drive the light emitting element is set. In setting the terminal voltage of the capacitor for holding the signal level, the switch for the capacitor side reference voltage The circuit and the short-circuit switch circuit are set to the on state, and the power supply switch circuit is set to the off state, so that the accumulated charge of the transistor is discharged through the light emitting element to gradually increase the gate-source voltage of the transistor. The gate-source voltage of the transistor is reduced to the threshold voltage of the transistor. After that, the decrease in the gate-source voltage of the transistor is compensated by the decrease in the terminal voltage due to the discharge of the accumulated charge of the light emitting element, so that the gate-source voltage of the transistor is maintained at the threshold voltage of the transistor. The switch circuit for the reference voltage on the capacitor side and the switch circuit for the short circuit are set to the OFF state, and then the signal line switch circuit is turned ON during the period in which the source-to-source voltage is maintained at the transistor threshold voltage. The terminal voltage of the capacitor for holding the signal level is set according to the signal level of the signal line.

  According to a fifth aspect of the present invention, the pixel is applied to a display device in which pixels driven by current are arranged in a matrix, and the pixel holds a signal level holding capacitor between the light emitting element and the gate source, A transistor by a source follower circuit that drives a light emitting element by a gate-source voltage by a voltage between terminals of a capacitor for holding a signal level set by a signal level of the line, a coupling capacitor having one end connected to the gate of the transistor, After the other end of the coupling capacitor is connected to a predetermined reference voltage, the transistor is switched to the off state when the gate-source voltage of the transistor is almost the threshold voltage of the transistor, and the coupling capacitor Switch circuit for capacitor-side reference voltage that separates the other end of the capacitor from the reference voltage In response to the connection to the reference voltage by the short-circuit switch circuit that short-circuits the gate drain of the transistor and the switch circuit for the capacitor-side reference voltage, the transistor is switched on in conjunction with the source-side reference voltage switch. By stopping the supply of power to the capacitor-side reference voltage switch circuit and short-circuit switch circuit, the accumulated charge of the transistor is discharged through the light emitting element until the gate source of the transistor is discharged. After the voltage between the gate and source of the transistor has dropped to the threshold voltage of the transistor, the voltage between the gate and source of the transistor is reduced due to the discharge of the accumulated charge of the light emitting element. The transistor gate voltage is almost compensated by the transistor threshold voltage. The switch circuit for the power supply that starts the supply of power to the transistor and the switch circuit for the capacitor side reference voltage are turned off by setting the voltage between the terminals of the capacitor for holding and holding the signal level according to the signal level of the signal line After that, the other end of the coupling capacitor is connected to the signal line, and the terminal voltage of the signal level holding capacitor is set through the coupling capacitor according to the signal level of the signal line. And a signal line switch circuit for setting a voltage between terminals of the signal level holding capacitor according to the signal level.

  In the invention of claim 8, the pixel is applied to a display device in which pixels of organic EL elements are arranged in a matrix, and the pixel holds a signal level holding capacitor between the organic EL element and the gate source. A transistor having a source follower circuit that drives an organic EL element by a gate-source voltage by a voltage between terminals of a signal level holding capacitor set by a signal level of the signal line, and a coupling having one end connected to the gate of the transistor After connecting the other capacitor and the other end of the coupling capacitor to the specified reference voltage, the transistor is switched to the OFF state when the gate-source voltage of the transistor is almost equal to the threshold voltage of the transistor. Separate the other end of the ring capacitor from the reference voltage. In response to the connection to the reference voltage by the switch circuit for short circuit that shorts the gate drain of the transistor and the switch circuit for capacitor side reference voltage By stopping the power supply to the transistor, the accumulated charge of the transistor is discharged through the organic EL element until the switch circuit for the reference voltage on the capacitor side and the switch circuit for the short circuit are turned off. After the voltage between the gate and source of the transistor is gradually reduced and the voltage between the gate and source of the transistor is reduced to the threshold voltage of the transistor, the decrease in the voltage between the gate and source of the transistor is caused by discharging the accumulated charge of the organic EL element. The voltage between the gate and the source of the transistor The switch circuit for power supply that starts supply of power to the transistor by setting the voltage across the terminals of the capacitor for holding the signal level according to the signal level of the signal line, and the capacitor side reference voltage After the switch circuit for turning off, connect the other end of the coupling capacitor to the signal line, and set the terminal voltage of the signal level holding capacitor via the coupling capacitor according to the signal level of the signal line. Thus, a signal line switch circuit for setting a voltage between terminals of the signal level holding capacitor according to the signal level of the signal line is provided.

  According to another aspect of the invention, the pixel holds a signal level holding capacitor between the light emitting element and the gate source when applied to a driving method of a display device in which pixels driven by current are arranged in a matrix. A transistor using a source follower circuit that drives a light emitting element by a gate-source voltage by a voltage between terminals of a signal level holding capacitor, a coupling capacitor having one end connected to the gate of the transistor, and a coupling capacitor Signal line switch circuit for connecting the other end of the transistor to the signal line, switch circuit for short-circuiting the gate and drain of the transistor, and capacitor side reference for connecting the other end of the coupling capacitor to a predetermined reference voltage Switch circuit for voltage and power supply for stopping supply of power to transistor The display device is driven by the signal line switch circuit, and the terminal voltage of the signal level holding capacitor is set according to the signal level of the signal line via the coupling capacitor. To set the gate-source voltage of the transistor used to drive the light-emitting element, and set the capacitor-side reference voltage switch circuit and the short-circuit switch circuit to the ON state when setting the terminal voltage of the signal level holding capacitor At the same time, by setting the switch circuit for power supply to the OFF state, the accumulated charge of the transistor is discharged through the light emitting element, and the gate-source voltage of the transistor is gradually lowered. After the voltage drops to the threshold voltage of the transistor, The drop in the source-to-source voltage is compensated by the drop in the terminal voltage due to the discharge of the accumulated charge of the light emitting element, so that the gate-source voltage of the transistor is maintained at the threshold voltage of the transistor. The capacitor side reference voltage switch circuit and short circuit switch circuit are set to the OFF state during the period when the threshold voltage is maintained, and then the signal line switch circuit is set to the ON state, and the signal level of the signal line is set. Thus, the terminal voltage of the signal level holding capacitor is set.

  According to the configuration of claim 1, the pixel is applied between a light emitting element and a gate source when applied to a display device having a pixel portion in which pixels driven by current are arranged in a matrix and a driving circuit for driving the pixel portion. A transistor with a source follower circuit that drives a light emitting element by a gate-source voltage by a voltage between terminals of the capacitor for holding a signal level, and a terminal connected to the gate of the transistor. Capacitor, a signal line switch circuit for connecting the other end of the coupling capacitor to the signal line, a short-circuit switch circuit for short-circuiting the gate drain of the transistor, and the other end of the coupling capacitor Switch circuit for the capacitor side reference voltage connected to the reference voltage of A power supply switch circuit that stops the supply of the signal, and the drive circuit is driven by the signal line switch circuit, and the terminal of the signal level holding capacitor by the signal level of the signal line through the coupling capacitor By setting the voltage, the voltage between the gate and source of the transistor used to drive the light emitting element is set, and in setting the terminal voltage of the capacitor for holding the signal level, the switch circuit for the capacitor side reference voltage, the switch circuit for short circuit Is turned on and the switch circuit for the power supply is turned off to discharge the accumulated charge of the transistor through the light emitting element and gradually reduce the gate-source voltage of the transistor. Even when the gate-source voltage of the transistor becomes the threshold voltage and is cut off, The discharge of the product charge source voltage of the transistor is a gradual drop. As a result, even when the transistor is cut off and the current flows out, a drop in the gate-source voltage due to the current outflow can be compensated. Thus, after the gate-source voltage of the transistor has decreased to the threshold voltage of the transistor, the decrease in the gate-source voltage of the transistor is compensated by the decrease in the terminal voltage due to the discharge of the accumulated charge of the light emitting element. Switch circuit for capacitor-side reference voltage, switch for short circuit during the period in which the source-to-source voltage is held approximately at the threshold voltage of the transistor and the gate-source voltage of the transistor is held approximately at the threshold voltage of the transistor After setting the circuit to the OFF state, the signal line switch circuit is set to the ON state, and the terminal voltage of the capacitor for holding the signal level is set according to the signal level of the signal line. Increase the period of time around the threshold voltage, and increase the signal level holding capacitor. After setting the threshold voltage of the transistor, the signal level of the signal line can be set, thereby correcting the threshold voltage of the transistor driving the light emitting element, and correcting the threshold voltage Even without adjusting the threshold voltage, the threshold voltage can be corrected correctly.

  Thus, according to the configurations of claims 5, 6 and 8, the threshold voltage is corrected by correcting the threshold voltage of the transistor driving the light emitting element and the organic EL element. It is possible to provide a display device and a display device driving method that can correct the threshold voltage correctly without adjusting the threshold voltage.

  According to the present invention, it is possible to correct the threshold voltage correctly without correcting the threshold voltage correction period by correcting the threshold voltage of the transistor that drives the light emitting element. Display device and display device driving method can be provided.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate.

(1) Configuration of Embodiment FIG. 2 is a block diagram showing a display device according to Embodiment 1 of the present invention. In the display device 51, the pixel unit 52 includes red, green, and blue pixels (PXR, PXG, and PXB) 53 that are current-driven and arranged in a matrix. For these pixels 53, five scanning lines SCN are provided. , SCN2R, SCN2G, SCN2B, and SCN3 are provided in the horizontal direction in units of lines. A signal line SIG is provided in the vertical direction for each column so as to be orthogonal to these scanning lines SCN, SCN2R, SCN2G, SCN2B, and SCN3. With respect to the pixel portion 52 formed as described above, the display device 51 is provided in the pixel 53 sequentially in line units by driving the scanning lines SCN, SCN2R, SCN2G, SCN2B, and SCN3 by the vertical drive circuit 54. The operation of the pixel circuit is controlled, and the signal line SIG is driven by the horizontal drive circuit 55 so as to correspond to the control of the pixel circuit, and the gradation of each pixel 53 is set.

  Therefore, the vertical drive circuit 54 generates a write signal ws for sequentially instructing writing to each pixel 53 in line units by the write scan circuit (WSCN) 54A, and emits light from each pixel 53 in synchronization with the write signal ws. The drive scan signal ds2 for controlling the non-light emission is generated by the drive scan circuit (DSCN2) 54C, and the write signal ws and the drive scan signal ds2 are output to the scan lines SCN, SCN2R, SCN2G, and SCN2B. It is designed to control key settings. A control signal az for instructing correction of the threshold voltage Vth of the organic EL element is generated by an auto zero circuit (ZERO) 54D, and this control signal az is output to the scanning line SCN3. In such a control, the drive scan signal ds2 is generated for each of the red, green, and blue pixels 53 and is output to the corresponding scan lines SCN2R, SCN2G, and SCN2B of the pixel 53, thereby the display device 51. In this case, the color balance is adjusted by controlling light emission and non-light emission in each of the red, green, and blue pixels 53.

  In the horizontal drive circuit 55, a drive signal is generated according to the gradation data D1 indicating the gradation of each pixel 53, and this drive signal is distributed to each signal line SIG by a horizontal selector (HSEL) 55A and output. It is made like that.

  FIG. 1 is a connection diagram showing each pixel 53 of the display device 51 in comparison with FIG. In the pixel 53 according to the display device 51, the switch circuit including the transistor TR3 that connects the source of the transistor TR2 to the reference voltage is controlled by the write signal ws of the signal line transistor TR1 used for connection to the signal line SIG. Except for the point that the driving timing of each of the transistors TR1 to TR6 by the vertical drive circuit 54 is different, the pixel 33 is configured in the same manner as that described above with reference to FIG.

  Thus, in this embodiment, the scanning line of the drive scan signal ds1 related to the transistor TR3 is omitted, and the number of scanning lines can be reduced accordingly. The transistors TR1 to TR6 constituting the pixel 53 are n-channel MOS type TFTs, and are integrally formed on the glass substrate together with the horizontal drive circuit 55 and the vertical drive circuit 54 by an amorphous process.

  Accordingly, in each pixel 53, as shown in FIG. 3 and FIG. 4A, the organic EL element 12 is driven by the transistor TR2 by the gate-source voltage Vgs based on the voltage across the terminals of the signal level holding capacitor Cs2. Even when the voltage-current characteristics of the organic EL element 12 change over time, the change in drive current due to the change over time can be prevented to prevent image quality deterioration (FIG. 3D). And (E)). 4A to 4E correspond to periods TA to TE in FIG. 3, respectively.

  Thus, the organic EL element 12 is driven by the transistor TR2 in this way, and the drive scan signal ds2 is lowered in the display device 51 for a predetermined period before and after the horizontal scanning period related to the pixel 53, and the organic EL element 12 is organic. The light emission of the EL element 12 is stopped (FIG. 3C), and the period during which the light emission of the organic EL element 12 by the drive scan signal ds2 is stopped is set for each of the red, green, and blue pixels 53 and desired. The color balance is set.

  In this display device 51, immediately before the drive scan signal ds2 is thus lowered, the control signal az is raised, whereby the signal line side end of the coupling capacitor Cs2 is grounded by the transistor TR6 as a reference voltage. Connected to. In addition, the gate and drain of the transistor TR2 are short-circuited by the transistor TR5 (FIGS. 3B and 4B). Thereby, in the display device 51, even when the voltage between the terminals of the signal level holding capacitor Cs2 has been set to be equal to or lower than the threshold voltage Vth of the transistor TR2 to display the gray level according to the black level, The gate-source voltage Vgs of the transistor TR2 is once raised above the threshold voltage Vth of the transistor TR2 (FIGS. 3D and 3E).

  Thereafter, in the display device 51, the supply of the power source Vcc to the transistor TR2 is stopped by the fall of the drive scan signal ds2, and thereby the source terminal of the transistor TR2 is not held at a constant potential, and the organic EL element 12 is interposed. With the source terminal grounded, correction of the threshold voltage Vth of the transistor TR2 is started (FIG. 4C). As a result, in the organic EL element 12, the accumulated charge charged and held in a capacity of several to several tens [pF] is discharged, and the voltage at the transistor TR2 side end gradually decreases.

  Here, as shown in FIGS. 5A and 5B, in the organic EL element 12, an equalization circuit can be represented by a diode or a diode-connected transistor. As shown in FIG. It has voltage-current characteristics similar to those of a diode-connected transistor, and the current stops when the terminal voltage reaches the threshold voltage VthEL of the organic EL element 12. Thereby, in the source voltage Vs of the transistor TR2, the speed of the voltage drop decreases as the source voltage Vs approaches the threshold voltage VthEL, and is eventually held at a constant voltage by the threshold voltage VthEL of the organic EL element 12. Will be.

  On the other hand, in the transistor TR2, the gate voltage Vg gradually decreases due to the discharge of the accumulated charge, and when the gate and drain are short-circuited in this way, the transistor TR2 exhibits voltage-current characteristics based on ideal diode characteristics. When the gate-source voltage Vgs decreases to the threshold voltage Vth of the transistor TR2, the decrease of the gate voltage Vg stops. As a result, in the signal level holding capacitor Cs2, the voltage between the terminals of the transistor TR2 is reduced. The threshold voltage Vth is held. In this case as well, in the transistor TR2, the voltage drop speed decreases as the gate-source voltage Vgs approaches the threshold voltage Vth.

  However, in the TFT transistor, even if the gate voltage Vg is gradually decreased so that the gate-source voltage Vgs becomes the threshold voltage Vth, the source current Is flows slightly, which results in FIG. As shown in the figure, when the transistor TR3 is set to the ON state, the gate voltage Vg gradually decreases due to this slight current even after the gate-source voltage Vgs reaches the threshold voltage Vth. The gate voltage Vg becomes the ground potential.

  However, as shown in FIG. 6B, when the source current IS is allowed to flow out through the organic EL element 12 without setting the transistor TR3 to the on state, the organic EL element 12 is more preferable than the transistor TR2. Since the capacitance is large and a large amount of accumulated charge is held, the transistor TR2 falls to the threshold voltage Vth earlier, and after falling to the threshold voltage Vth in this way, the organic EL element 12 Due to the decrease in the terminal voltage due to the discharge of the accumulated charge, the gate-source voltage Vgs of the transistor TR2 is held at the threshold voltage Vth.

  That is, in the organic EL element 12, the accumulated charge is discharged, so that the voltage at the source side end of the transistor TR2 gradually drops. As a result, the gate-source voltage Vgs of the transistor TR2 temporarily changes to the threshold voltage. Even after Vth is reached, the voltage thereafter becomes equal to or higher than the threshold voltage Vth. In this case, in the transistor TR2, the outflow of current starts, the gate-source voltage Vgs falls, and then falls back to the threshold voltage Vth. Further, even when the current flows out from the transistor TR2 due to the cutoff, it functions to prevent the terminal voltage from dropping due to the discharge of the organic EL element 12.

  Accordingly, in this embodiment, when the period T during which the gate-source voltage Vgs of the transistor TR2 is held in the vicinity of the threshold voltage Vth of the transistor TR2 is increased and the source terminal of the transistor TR2 is simply grounded by the transistor TR3. In contrast, such a period T can be extended significantly, thereby correcting the threshold voltage Vth of the transistor TR2 that drives the organic EL element 12 that is a light emitting element. The threshold voltage Vth can be corrected correctly without adjusting the period for correcting the threshold voltage Vth.

  Therefore, in this embodiment, as shown in FIG. 3, after the supply of the power source Vcc is stopped by the control of the transistor TR4, the gate-source voltage Vgs of the transistor TR2 is thus held in the vicinity of the threshold voltage Vth. When a sufficient period elapses, the transistors TR5 and TR6 are turned off by the rise of the control signal az, and the setting of the threshold voltage Vth to the signal level holding capacitor Cs2 is completed (FIG. 3 ( B)). In this embodiment, after the supply of the power supply Vcc is stopped by the control of the transistor TR4 as described above, the setting of the threshold voltage Vth to the signal level holding capacitor Cs2 is completed by the rise of the control signal az. This period T is set to a period sufficient to hold the gate-source voltage Vgs of the transistor TR2 in the vicinity of the threshold voltage Vth even when the threshold voltage Vth of the transistor TR2 varies between products. Has been made.

  Thereafter, in the display device 51, the transistor TR3 is set to the on state by the rise of the write signal ws, whereby the source terminal of the transistor TR2 is grounded, and the ground side terminal of the signal level holding capacitor Cs2 is set to the ground potential. Retained. At the same time, the transistor TR1 is set to the ON state, and the signal level holding capacitor Cs2 in which the ground side end is held at the ground potential in this way is connected to the signal level of the signal line SIG via the coupling capacitor Cs1. Thus, the signal level of the signal line SIG is set in the signal level holding capacitor Cs2.

  As a result, in the display device 51, after the transistors TR1 and TR3 are subsequently turned off, the transistor TR4 starts to supply power to the transistor TR2, and the gate source due to the voltage across the terminals of the signal level holding capacitor Cs2 The organic EL element 12 is driven by the transistor TR2 by the inter-voltage Vgs (FIG. 4E), and the gradation data is effectively avoided by the variation of the organic EL element 12 over time and the variation due to the threshold voltage Vth of the transistor TR2. The organic EL element 12 can be made to emit light by the gradation based on D1.

  In this embodiment, the vertical drive circuit 54 outputs a write signal ws, a drive scan signal ds2, and a control signal az so as to correspond to the drive of the pixel 53, and the horizontal drive circuit 55 , (2), as described above, the drive signal is generated so as to correspond to the setting of the signal level to the signal level holding capacitor Cs2 via the coupling capacitor Cs1.

(2) Operation of the embodiment In the above configuration, the display device 51 (FIG. 2) is driven by the horizontal drive circuit 55 sequentially in line units by driving the scanning lines SCN, SCN2R, SCN2G, SCN2B, and SCN3 by the vertical drive circuit 54. The signal level of the signal line SIG to be driven is set in each pixel 53. In the display device 51, each pixel 53 emits light according to the signal level set for each pixel 53, and a desired image is displayed.

  In the display device 51, in each pixel 53, a signal level holding capacitor Cs1 is provided between the gate and source of the transistor TR2 having a source follower circuit configuration for driving the organic EL element 12, and a coupling circuit is provided by a switch circuit by the transistor TR1. By connecting the capacitor Cs2 to the signal line SIG, the signal level Vin of the signal line SIG is set to the signal level holding capacitor Cs2 via the coupling capacitor Cs1. Further, the organic EL element 12 is driven by the transistor TR2 by the gate-source voltage Vgs by the signal level holding capacitor Cs2 set in this way. As a result, in the display device 51, it is possible to prevent a change in drive current due to a change with time of the voltage / current characteristics of the organic EL element 12, and to effectively avoid deterioration of image quality due to a change with time of the organic EL element 12. Further, each pixel 53 is formed by an n-channel MOS transistor, and the organic EL element 12 can be driven from the anode side by the transistor TR2. With these, an amorphous silicon process is applied to form the organic EL element and the pixel circuit. It can be integrally formed on a glass substrate.

  In the display device 51, in setting the terminal voltage of the signal level holding capacitor Cs2 based on the signal level Vin of the signal line SIG, the transistors TR5 and TR6 are turned on by the control signal az while the transistor TR2 remains connected to the power source. The transistor TR2 is set to diode connection, and the signal line side end of the coupling capacitor Cs1 is connected to the reference voltage, and the gate-source voltage Vgs of the transistor TR2 is once raised.

  Thereafter, the transistor TR4 stops the supply of the power source Vcc to the transistor TR2, thereby discharging the accumulated charge of the transistor TR2 through the organic EL element 12, and the voltage across the terminals of the signal level holding capacitor Cs2 Is set to the threshold voltage Vth of the transistor TR2. In the display device 51, the accumulated charge of the transistor TR2 is thereby discharged through the light emitting element, so that the gate-source voltage Vgs of the transistor TR2 gradually decreases, and the gate-source voltage Vgs of the transistor TR2 becomes the threshold of the transistor TR2. After decreasing to the value voltage Vth, the decrease in the gate-source voltage Vgs of the transistor TR2 is compensated for by the decrease in the terminal voltage due to the discharge of the accumulated charge of the light emitting element, so that the gate-source voltage Vgs of the transistor TR2 is substantially equal to that of the transistor TR2. It is held at the threshold voltage Vth.

  As a result, the display device 51 has a period during which the gate-source voltage Vgs of the transistor TR2 is held in the vicinity of the threshold voltage Vth of the transistor TR2 as compared with the case where the source end of the transistor TR2 is simply grounded by the transistor TR3. Even when the threshold voltage Vth of the transistor TR2 varies among the products, and even when the variation amount of the threshold voltage Vth varies, the control of the transistor TR4 is possible. A period T (FIG. 3B) for correcting the threshold voltage Vth until the setting of the threshold voltage Vth to the signal level holding capacitor Cs2 is completed after the supply of the power source Vcc is stopped by The threshold voltage Vth is set longer than the conventional one and the threshold voltage Vth is reliably set to the signal level holding capacitor Cs2. It can be. As a result, the threshold voltage Vth of the transistor TR2 that drives the organic EL element 12 that is a light emitting element is corrected, and the threshold value is correctly corrected without adjusting the period T for correcting the threshold voltage Vth. The voltage Vth can be corrected, thereby preventing variation in uniformity among products.

  In the display device 51, after that, after the transistors TR5 and TR6 are set to the off state, the transistors TR1 and TR3 are set to the on state by the write signal ws, and the ground side end of the signal level holding capacitor Cs2 is set to the ground potential. The coupling capacitor Cs1 is set and connected to the signal line SIG, so that the signal level holding capacitor Cs2 obtained by setting the threshold voltage Vth of the transistor TR2 in advance becomes the signal level Vin of the signal line SIG. Is set.

  As a result, in the display device 51, the organic EL element 12 is made to have a current by the transistor TR2 by the source follower circuit in which the voltage between the terminals of the signal level holding capacitor Cs2 set in this way is set to the gate-source voltage Vgs. Driven, variation in drive current due to variation in threshold voltage Vth of transistor TR2 is prevented, and image quality degradation is effectively avoided.

  In the case of an amorphous silicon TFT, the threshold voltage Vth of the transistor changes with use. However, according to this embodiment, it is possible to cope with such a change in the threshold voltage Vth, and thus it is possible to omit the readjustment work due to such a change in the threshold voltage Vth.

(3) Advantages of the embodiment With the above configuration, the signal level holding signal provided between the gate and the source of the transistor is driven with respect to the transistor that drives the organic EL element, which is a light emitting element, by the source follower circuit configuration. After setting the threshold voltage of the transistor to the capacitor, the signal level of the signal line is set to correct the transistor variation and set the gradation, and the accumulated charge of the transistor through this light emitting element After the gate-source voltage of the transistor has decreased to the threshold voltage of the transistor, the decrease in the gate-source voltage is compensated by the decrease in the terminal voltage due to the discharge of the accumulated charge of the light emitting element. By maintaining the gate-source voltage at approximately the threshold voltage of the transistor, the light emitting device is driven. The threshold voltage can be corrected correctly without adjusting the threshold voltage correction period by correcting the threshold voltage of the moving transistor.

  Further, a source-side reference voltage switch circuit for connecting the source of the transistor TR2 to a predetermined reference voltage is formed by the transistor TR3, and the source-side reference voltage is set during the period when the switch circuit of the signal line is set to the ON state. By setting the switch circuit for switching to the ON state and holding the source of the transistor at the reference voltage, in setting the terminal voltage of the capacitor for holding the signal level according to the signal level of the subsequent signal line, this reference potential is used as a reference. Thus, the gradation of each pixel can be set with high accuracy by the signal level of the signal line.

  FIG. 7 is a time chart showing the driving timing of each pixel in the display device according to the second embodiment of the present invention. In the display device according to this embodiment, the driving of the transistor TR3 in the display device 51 according to the first embodiment is executed by a dedicated control signal, and the signal level of the signal line SIG is maintained for the signal level by the write signal ws. The display device 51 is configured in the same manner as the display device 51 according to the first embodiment except that the transistor TR3 is held in the ON state during the period set in the capacitor Cs2.

  As a result, each pixel has the same connection relationship as that of the display device 31 described above with reference to FIG. 15, and the vertical drive circuit also includes a drive scan circuit that outputs a drive scan signal ds1 that is a control signal of the transistor TR3. It is made to be provided.

  As in this embodiment, during the period in which the transistor TR3 that connects the source of the transistor TR2 to the reference voltage is controlled by a dedicated control signal and the signal level of the signal line SIG is set in the signal level holding capacitor Cs2. Even if the source of the transistor TR2 is connected to the reference voltage, the same effect as in the first embodiment can be obtained.

  FIG. 8 is a block diagram showing a display apparatus according to the third embodiment of the present invention in comparison with FIG. In this display device 71, in each pixel 73, the transistor TR3 that connects the source of the transistor TR2 to the reference voltage is omitted. Corresponding to the omission of the transistor TR3, the vertical drive circuit 74 is provided with a write scan circuit 74A, a drive scan circuit 74C, and an auto zero circuit 74D, and corresponds to driving of the pixel 73 by the vertical drive circuit 74. As described above, the drive signal of the signal line is generated by the horizontal drive circuit 75 and is distributed to each signal line SIG by the horizontal selector 75A.

  FIG. 9 is a time chart used for driving the pixel 73 by the vertical drive circuit 74. In this display device 51, as shown in FIG. 10A, as in the first embodiment, an organic EL element is formed by a transistor TR2 by a source follower circuit using a gate-source voltage Vgs based on a terminal voltage of a signal level holding capacitor Cs2. 12 is driven by current to cause each pixel 73 to emit light. Further, the light emission and non-light emission of each pixel 73 is controlled by the drive scan signal ds2 (FIG. 9C).

  In the display device 71, immediately before the power supply to the transistor TR2 is stopped by the drive scan signal ds2 and the light emission of the pixel 73 is stopped, the transistors TR4 and TR5 are set to the on state by the control signal az (FIG. 9 ( (B) and FIG. 10 (B)), the gate-source voltage Vgs of the transistor TR2 is once raised, and then the supply of power is stopped (FIG. 10 (C)).

  Thereby, also in this embodiment, the accumulated charge of the transistor TR2 is discharged through the organic EL element 12, and the gate-source voltage Vgs of the transistor TR2 gradually decreases. After the voltage reaches the threshold voltage Vth, the gate-source voltage Vgs of the transistor TR2 is substantially compensated by compensating for the decrease in the gate-source voltage Vgs by the decrease in the terminal voltage due to the discharge of the accumulated charge of the organic EL element 12. The threshold voltage Vth of TR2 is held.

  As a result, when a sufficient period of time has passed for the display device 51 to maintain the gate-source voltage Vgs of the transistor TR2 in the vicinity of the threshold voltage Vth, the transistors TR4 and TR5 are switched to the off state and the threshold voltage Vth is reached. Then, the write signal ws is raised and the transistor TR1 is turned on, and the signal level of the signal line is changed to the signal level holding capacitor Cs2 via the coupling capacitor Cs1. (FIG. 10D).

  In this embodiment, the processing for setting the signal level of the signal line to the signal level holding capacitor Cs2 in this way is performed by grounding the ground side end of the signal level holding capacitor Cs2 via the organic EL element 12. It is executed depending on the state. In this case, the threshold voltage Vth of the organic EL element 12 is held at the ground side end of the signal level holding capacitor Cs2 by the correction of the threshold voltage Vth executed before this. It will be.

  Thus, in this embodiment, when the signal level of the signal line is set to the signal level holding capacitor, the threshold voltage VthEL of the organic EL element 12 is set as a reference, and the signal level holding capacitor Cs2 is set. The gradation of each pixel 73 can be set with sufficient accuracy even if the transistor TR3 having a constant potential at its ground end is omitted. Thus, in this display device 71, the organic EL element 12 is driven by the transistor TR2 by the voltage across the terminals of the signal level holding capacitor Cs2 in which the signal level of the signal line is set in this way, so that each pixel 73 has a signal level. A gradation is set (FIG. 10E). The horizontal drive circuit 75 generates a drive signal in anticipation of a voltage increase corresponding to the threshold voltage VthEL of the organic EL element 12.

  According to this embodiment, even when the signal level of the signal line is set to the signal level holding capacitor with reference to the threshold voltage VthEL of the organic EL element 12, the accumulated charge of the transistor is reduced via the light emitting element. After the discharge, the gate-source voltage of the transistor is reduced to the threshold voltage of the transistor, and this decrease in the gate-source voltage is compensated by the decrease in the terminal voltage due to the discharge of the accumulated charge of the light emitting element. By maintaining the source-to-source voltage substantially at the threshold voltage of the transistor, the same effect as in the first embodiment can be obtained.

  Further, in this way, by setting the signal level of the signal line to the signal level holding capacitor with reference to the threshold voltage VthEL of the organic EL element 12, the transistor for connecting the signal level holding capacitor to the reference voltage TR3 can be omitted, and the configuration of the pixel and the vertical drive circuit can be simplified accordingly.

  In the above-described embodiment, the case where an organic EL element and a pixel circuit are formed on a glass substrate by applying an amorphous silicon process has been described. However, the present invention is not limited to this, and a transistor made of polysilicon is formed. In this case, the present invention can be widely applied to a case where a driver circuit is formed separately from the pixel portion using a silicon substrate and then connected to the pixel portion to be integrated.

  In the above-described embodiments, the case where the light emitting element by the organic EL element is current-driven has been described. However, the present invention is not limited to this, and can be widely applied to display devices using various light-emitting elements related to current driving. .

  The present invention relates to a display device and a display device driving method, and can be applied to a self-luminous display device driven by current, such as an organic EL display device.

It is a connection diagram which shows the pixel circuit of the display apparatus which concerns on Example 1 of this invention with a periphery structure. It is a block diagram which shows the display apparatus by the pixel circuit of FIG. 2 is a time chart for explaining the operation of the pixel circuit of FIG. 1. FIG. 4 is a connection diagram for explaining the time chart of FIG. 3. It is a figure where it uses for description of the characteristic of an organic EL element. It is a connection diagram with which it uses for description of the electric charge discharge through an organic EL element. It is a time chart with which it uses for description of operation | movement of the display apparatus which concerns on Example 2 of this invention. It is a block diagram which shows the display apparatus which concerns on Example 3 of this invention. 9 is a time chart for explaining the operation of the display device of FIG. 8. FIG. 10 is a connection diagram for explaining the time chart of FIG. 9. It is a block diagram which shows the structure of a display apparatus. FIG. 12 is a connection diagram illustrating a pixel circuit of the display device of FIG. 11 together with a peripheral configuration. It is a characteristic curve figure which shows the characteristic of an organic EL element. It is a characteristic curve figure with which it uses for description of the change of the operating point of an organic EL element. FIG. 3 is a connection diagram illustrating a pixel circuit having a source follower circuit configuration along with a peripheral configuration. 16 is a time chart for explaining the operation of the pixel circuit of FIG. FIG. 17 is a connection diagram for explaining the time chart of FIG. 16. It is a time chart with which it uses for description of the change of the gate source voltage of a transistor.

Explanation of symbols

1, 11, 31, 51, 71 ... display device, 2, 32, 52, 72 ... pixel unit, 3, 33, 53, 73 ... pixel, 4, 34, 54, 74 ... vertical drive circuit, 4A, 34A, 54A, 74A: write scan circuit, 5, 35, 55, 75 ... horizontal drive circuit, 12 ... organic EL element, 34B, 34C, 54C, 74C ... drive scan circuit, 34D, 54D, 74D: Auto zero circuit, C1, Cs1, Cs2: Capacitor, TR1 to TR6: Transistor

Claims (9)

In a display device having a pixel portion in which pixels driven by current are arranged in a matrix and a drive circuit for driving the pixel portion,
The pixel is
A light emitting element;
A transistor having a source follower circuit that holds a signal level holding capacitor between a gate and a source and drives the light emitting element by a gate-source voltage based on a voltage between terminals of the signal level holding capacitor;
A coupling capacitor having one end connected to the gate of the transistor;
A signal line switch circuit for connecting the other end of the coupling capacitor to the signal line;
A switch circuit for short-circuiting to short-circuit the gate drain of the transistor;
A capacitor side reference voltage switch circuit for connecting the other end of the coupling capacitor to a predetermined reference voltage;
A power supply switch circuit for stopping supply of power to the transistor,
The drive circuit is
By driving the signal line switch circuit, the terminal voltage of the signal level holding capacitor is set according to the signal level of the signal line via the coupling capacitor, so that the light emitting element is driven. Set the gate-source voltage of the transistor,
In setting the terminal voltage of the signal level holding capacitor,
The capacitor-side reference voltage switch circuit and the short-circuit switch circuit are set to an on state, and the power supply switch circuit is set to an off state, whereby the accumulated charge of the transistor through the light emitting element is set. After the gate-source voltage of the transistor is gradually reduced to the threshold voltage of the transistor, the gate-source voltage of the transistor is reduced. Complementing with a decrease in terminal voltage due to the discharge of the accumulated charge of the light emitting element, the gate-source voltage of the transistor is held approximately at the threshold voltage of the transistor,
The signal after the capacitor-side reference voltage switch circuit and the short-circuit switch circuit are turned off in a period in which the gate-source voltage of the transistor is substantially held at the threshold voltage of the transistor. A display device, wherein a line switch circuit is set to an on state, and a terminal voltage of the signal level holding capacitor is set according to a signal level of the signal line. The pixel is
A switch circuit for a source-side reference voltage that connects a source of the transistor to a predetermined reference voltage;
The drive circuit is
The source-side reference voltage switch circuit is set to an on state during a period in which the switch circuit of the signal line is set to an on state, and the source of the transistor is held at the reference voltage. The display device according to claim 1. The drive circuit is
The display device according to claim 2, wherein the switch circuit for the signal line and the switch circuit for the source side reference voltage are controlled by the same control signal. The display device according to claim 1, wherein the transistor and each switch circuit are formed by an n-channel MOS transistor. In a display device in which pixels driven by current are arranged in a matrix,
The pixel is
A light emitting element;
A source follower circuit that holds a signal level holding capacitor between a gate and a source and drives the light emitting element by a gate-source voltage by a voltage between terminals of the signal level holding capacitor set by a signal level of a signal line A transistor,
A coupling capacitor having one end connected to the gate of the transistor;
After the other end of the coupling capacitor is connected to a predetermined reference voltage, when the gate-source voltage of the transistor is almost equal to the threshold voltage of the transistor, the coupling capacitor is switched off. A capacitor side reference voltage switch circuit for separating the other end of the ring capacitor from the reference voltage;
A short-circuit switch circuit that switches to an on state in conjunction with the source-side reference voltage switch circuit and short-circuits the gate drain of the transistor;
In response to the connection to the reference voltage by the switch circuit for the capacitor side reference voltage, by stopping the supply of power to the transistor, the switch circuit for the capacitor side reference voltage, the switch circuit for the short circuit, Until the off operation is performed, the accumulated charge of the transistor is discharged through the light emitting element to gradually reduce the gate-source voltage of the transistor, and the gate-source voltage of the transistor is the threshold voltage of the transistor. After that, the gate-source voltage of the transistor is compensated for by the decrease of the terminal voltage due to the discharge of the accumulated charge of the light emitting element, so that the gate-source voltage of the transistor is substantially equal to the threshold voltage of the transistor. And a signal level holding capacitor according to the signal level of the signal line. By setting the voltage across the terminals of the support, and a switch circuit for power supply to start power supply to the transistors,
After the off operation of the capacitor-side reference voltage switch circuit, the other end of the coupling capacitor is connected to the signal line, and the signal level holding capacitor terminal is connected via the coupling capacitor. And a signal line switch circuit for setting a voltage between terminals of the signal level holding capacitor according to the signal level of the signal line by setting the voltage according to the signal level of the signal line. apparatus. While the other end of the coupling capacitor is connected to the signal line by the signal line switch circuit, the light emitting element side end of the signal level holding capacitor is connected to a predetermined reference voltage. The display device according to claim 5, further comprising a switch circuit for a source side reference voltage. The display device according to claim 5, wherein the transistor and each switch circuit are formed by an n-channel MOS transistor. In a display device in which pixels by organic EL elements are arranged in a matrix,
The pixel is
The organic EL element;
A source follower circuit that holds a signal level holding capacitor between a gate and a source and drives the organic EL element by a gate-source voltage based on a voltage between terminals of the signal level holding capacitor set by a signal level of a signal line And transistor by
A coupling capacitor having one end connected to the gate of the transistor;
After the other end of the coupling capacitor is connected to a predetermined reference voltage, when the gate-source voltage of the transistor is almost equal to the threshold voltage of the transistor, the coupling capacitor is switched off. A capacitor side reference voltage switch circuit for separating the other end of the ring capacitor from the reference voltage;
A short-circuit switch circuit that switches to an on state in conjunction with the source-side reference voltage switch circuit and short-circuits the gate drain of the transistor;
In response to the connection to the reference voltage by the switch circuit for the capacitor side reference voltage, by stopping the supply of power to the transistor, the switch circuit for the capacitor side reference voltage, the switch circuit for the short circuit, Until the transistor is turned off, the accumulated charge of the transistor is discharged through the organic EL element to gradually reduce the gate-source voltage of the transistor, and the gate-source voltage of the transistor is reduced to the threshold value of the transistor. After the voltage drops to the voltage, the gate-source voltage of the transistor is compensated for by the drop of the terminal voltage due to the discharge of the accumulated charge of the organic EL element, so that the gate-source voltage of the transistor is substantially the threshold of the transistor. For holding the signal level according to the signal level of the signal line. By setting the terminal voltage of the capacitor, and a switch circuit for power supply to start power supply to the transistors,
After the off operation of the capacitor-side reference voltage switch circuit, the other end of the coupling capacitor is connected to the signal line, and the signal level holding capacitor terminal is connected via the coupling capacitor. And a signal line switch circuit for setting a voltage between terminals of the signal level holding capacitor according to the signal level of the signal line by setting the voltage according to the signal level of the signal line. apparatus. In a driving method of a display device in which pixels driven by current are arranged in a matrix,
The pixel is
A light emitting element;
A transistor having a source follower circuit that holds a signal level holding capacitor between a gate and a source and drives the light emitting element by a gate-source voltage based on a voltage between terminals of the signal level holding capacitor;
A coupling capacitor having one end connected to the gate of the transistor;
A signal line switch circuit for connecting the other end of the coupling capacitor to the signal line;
A switch circuit for short-circuiting to short-circuit the gate drain of the transistor;
A capacitor side reference voltage switch circuit for connecting the other end of the coupling capacitor to a predetermined reference voltage;
A power supply switch circuit for stopping supply of power to the transistor,
The driving method of the display device is:
By driving the signal line switch circuit, the terminal voltage of the signal level holding capacitor is set according to the signal level of the signal line via the coupling capacitor, so that the light emitting element is driven. Set the gate-source voltage of the transistor,
In setting the terminal voltage of the signal level holding capacitor,
The capacitor-side reference voltage switch circuit and the short-circuit switch circuit are set to an on state, and the power supply switch circuit is set to an off state, whereby the accumulated charge of the transistor through the light emitting element is set. After the gate-source voltage of the transistor is gradually reduced to the threshold voltage of the transistor, the gate-source voltage of the transistor is reduced. Complementing with a decrease in terminal voltage due to the discharge of the accumulated charge of the light emitting element, the gate-source voltage of the transistor is held approximately at the threshold voltage of the transistor,
The signal after the capacitor-side reference voltage switch circuit and the short-circuit switch circuit are turned off in a period in which the gate-source voltage of the transistor is substantially held at the threshold voltage of the transistor. A display device driving method comprising: setting a line switch circuit to an ON state, and setting a terminal voltage of the signal level holding capacitor according to a signal level of the signal line.

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