JP2010026209A - Display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To set a desired driving voltage of a driving transistor in a capacitive element which holds the driving voltage of the driving transistor in one display period without being affected by the ratio of the capacitance value of the capacitive element and the capacitance value of parasitic capacitance of a light emitting device. <P>SOLUTION: A signal corresponding to the threshold voltage of the driving transistor 11b is detected by detecting a voltage at the source terminal S of the driving transistor 11b when the parasitic capacitance 51 of the light emitting device 11a is charged. A data signal based upon the detected signal corresponding to the threshold voltage and the driving voltage of the driving transistor 11b corresponding to the light emission amount of the light emitting device 11a is supplied to the source terminal S of the driving transistor 11b through a data line 14 and a transistor 11e for threshold voltage detection. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a display device including a light emitting element driven by an active matrix method and a drive control method for the display device.

  Conventionally, display devices using light-emitting elements such as organic EL light-emitting elements have been proposed, and their use in various fields such as displays for televisions and mobile phones has been proposed.

  In general, an organic EL light emitting element is a current driven light emitting element. Therefore, unlike a liquid crystal display, a selection transistor that selects a pixel circuit as a driving circuit thereof, a storage capacitor that holds charges according to a display image, and organic EL light emission A driving transistor for driving the element is at least necessary (see, for example, Patent Document 1).

  Conventionally, a thin film transistor made of low-temperature polysilicon or amorphous silicon has been used in a pixel circuit of an active matrix organic EL display device.

  However, a low-temperature polysilicon thin film transistor can obtain high mobility and threshold voltage stability, but has a problem in uniformity of mobility. Amorphous silicon thin film transistors can achieve mobility uniformity, but have problems of low mobility and threshold voltage variation over time.

  The non-uniformity of mobility and the instability of the threshold voltage as described above appear as unevenness in the display image. Thus, for example, Patent Document 2 proposes a display device in which a diode connection type compensation circuit is provided in a pixel circuit.

  However, if the compensation circuit described in Patent Document 2 is provided, the pixel circuit becomes complicated, leading to an increase in cost due to a decrease in yield and a decrease in aperture ratio.

  Therefore, for example, Patent Document 3 proposes a method of correcting the threshold voltage of the driving transistor by performing a charging operation on the parasitic capacitance of the organic EL light emitting element and reducing the number of transistors used in the pixel circuit. ing.

  Here, the configuration and operation of the pixel circuit described in Patent Document 3 will be described below.

  As shown in FIG. 18, the pixel circuit 100 described in Patent Literature 3 includes an organic EL light emitting element 100a, a driving transistor 100b that causes a driving current and a detection current described later to flow through the organic EL light emitting element 100a, and a driving transistor 100b. The capacitor element 100c is connected between the gate terminal G and the source terminal S, and a selection transistor 100d.

  Next, the operation of the pixel circuit 100 will be described with reference to the timing chart shown in FIG. 19 and FIGS. 20 to 23. FIG. 19 shows voltage waveforms of the scanning signal Vscan, the power supply voltage Vddx, the data signal Vdata, the source voltage Vs, and the gate-source voltage Vgs.

  First, an on-scan signal as shown in FIG. 19 is output to the scan line 15 (time t1 in FIG. 19). Then, as shown in FIG. 20, the selection transistor 100d is turned ON in response to the ON scanning signal, and the gate terminal G of the driving transistor 100b and the data line 14 are short-circuited.

  First, a reset operation is performed (see t1 to t2 in FIG. 19 and FIG. 20). Specifically, the data bus signal VB is output from the data driving circuit to the data line 14.

  Here, assuming that the light emission threshold voltage of the organic EL light emitting element 100a is Vf0 and the threshold voltage Vth of the driving transistor 100b, the condition of the data bus signal VB is as follows. That is, the driving transistor 100b is turned on by the supply of the data bus signal VB, but the organic EL light emitting element 100a does not emit light because the data bus signal VB is smaller than Vf0 + Vth.

Vth <VB <Vf0 + Vth
Here, since the light emission period is immediately before the reset operation, some charge remains in the parasitic capacitance 102 of the organic EL light emitting element 100a. When the power supply voltage Vddx of the power supply line 105 changes from Vdd to 0V, the driving transistor 100b has the drain terminal D on the organic EL light emitting element 100a side and the source terminal S on the power supply line 105 side. The charge remaining in the parasitic capacitance 102 of the organic EL light emitting device 100a is discharged to the power supply line 105 via the source-drain of the driving transistor 100b, and finally the potential of the anode terminal of the organic EL light emitting device 100a is 0V.

  Then, a threshold voltage detection operation is performed (t2 to t3 in FIG. 19, see FIG. 21). Specifically, first, the power supply voltage Vddx of the power supply line 105 returns to Vdd, whereby the drive transistor 100b has the terminal on the power supply line 105 side as the drain terminal D and the terminal on the organic EL light emitting element 100a side as the source terminal. S.

  At this time, since the data bus signal VB is supplied to the gate terminal G of the driving transistor 100b, Vgs> Vth, and the detection current Idd corresponding to Vgs flows through the driving transistor 100b. Then, the parasitic capacitance 102 of the organic EL light emitting element 100a is charged by the detection current Idd, and the source voltage Vs of the source terminal S of the driving transistor 100b is increased.

  Since the data bus signal VB supplied to the gate terminal G of the driving transistor 100b is a fixed voltage, Vgs decreases and the detection current Idd decreases due to the increase of the source voltage Vs. When the voltage becomes sufficiently small, the increase in the source voltage Vs stops.

At this time, the inter-terminal voltage Vcs of the capacitive element 100c is
Vcs = Vgs = Vth
Thus, the threshold voltage Vth of the driving transistor 100b is held.

  Next, a program operation is performed (see t3 to t4 in FIG. 19, see FIG. 22). Specifically, the program data signal Vprg is output to the data line 14 and input to the pixel circuit 100.

Here, the program data signal Vprg is
Vprg = VB + Vod
It is. Vod is an overdrive voltage of the driving transistor 100b,
Vod = Vgs−Vth
It is. That is, Vod is a voltage value signal having a magnitude corresponding to the display image.

When the program data signal Vprg satisfying the above equation is input, the source voltage Vs of the driving transistor 100b is divided between the capacitance Cs of the capacitive element 100c and the capacitance Cd of the parasitic capacitance 102 of the organic EL light emitting element 100a.
Vs = (VB−Vth) + Vod × {Cs / (Cd + Cs)}
However, if Cs << Cd, Vod × {Cs / (Cd + Cs)} ≈0,
Vs≈VB-Vth
Thus, a voltage obtained by adding Vod to the threshold voltage Vth detected by the threshold voltage detection operation is set in the capacitive element 100c.

  Then, the light emission operation is performed (see FIG. 23 after t4 in FIG. 19). Specifically, an off scanning signal is output to the scanning line 15 (time t4 in FIG. 19).

  Then, as shown in FIG. 23, the selection transistor 100d is turned OFF in response to the OFF scanning signal, and the gate terminal G of the driving transistor 100b and the data line 14 are disconnected.

  Then, the gate-source voltage Vgs of the driving transistor 100b becomes Vod + Vth, and the driving current Idv flows between the drain and source of the driving transistor 100b.

The drive current Idv charges the parasitic capacitance 102 of the organic EL light emitting device 100a, and the source voltage Vs of the drive transistor 100b rises. However, the gate-source voltage Vgs is held by the hold voltage Vod + Vth of the capacitor 100c. Accordingly, the source voltage Vs eventually exceeds the light emission threshold voltage Vf0 of the organic EL light emitting element 100a, and the light emitting operation of the organic EL light emitting element 100a is performed at a constant current.
JP-A-8-234683 JP 2003-255856 A JP 2003-271095 A JP 2006-227237 A

  Here, in the pixel circuit 100 described in Patent Document 3, as described above, the driving voltage of the driving transistor during one display period is held in the capacitor 100c, but the capacitance necessary for the capacitor 100c. Cs is determined by the gate leakage current of the driving transistor 100b and the off-current of the selection transistor 100d.

  Further, as described above, during the program operation, the capacitance Cs of the capacitive element 100c is required to be sufficiently smaller than the capacitance Cd of the parasitic capacitance 102 of the organic EL light emitting element 100a. When the premise of Cd >> Cs is broken, during the program operation, all of Vod is not set in the capacitive element 100c but is divided and set to the ratio of Cs and Cd, and a program error occurs.

  Therefore, Cd >> Cs is premised, which requires that the capacitance of the capacitive element 100c be reduced in accordance with the reduction of the parasitic capacitance of the organic EL light emitting element in the high-definition panel. It becomes a factor of deterioration of the holding characteristics of 100c.

  Further, in the threshold voltage detection operation of the pixel circuit 100 described in Patent Document 3, as described above, the detection current Idd flowing through the driving transistor 100b is sufficiently small, and the source voltage Vs of the driving transistor 100b is increased. Although Vgs at the time of stoppage is detected as the threshold voltage Vth, actually, the threshold voltage Vth detected as described above is theoretically determined by the current characteristics of the sub-threshold region of the thin film transistor constituting the driving transistor 100b. The magnitude is different from the threshold voltage Vth ′ obtained by the equation.

  Vod set in the program operation is a voltage calculated based on the threshold voltage Vth ′ obtained by a theoretical formula.

  Here, FIG. 24 shows the relationship between the driving current Id and the gate-source voltage Vgs of the thin film transistor having a small subthreshold region current and the large transistor. In order to clarify the difference between the two, FIG. 25 shows the relationship between √Id and Vgs. 24 and 25, the thick line indicates the current characteristic of the thin film transistor with a small subthreshold region current, and the thin line indicates the current characteristic of the thin film transistor with a large subthreshold region current. Furthermore, in FIG. 25, the current characteristic calculated | required from a theoretical formula is shown with the broken line.

  As can be seen from the current characteristics shown in FIG. 25, the threshold voltage Vth ′ obtained from the theoretical formula is higher than the value Von of Vgs at which current starts to flow through the thin film transistor.

Therefore, when the threshold voltage detection operation of the pixel circuit described above is performed, a voltage close to the threshold voltage Vth ′ shown in FIG. 25 should be detected. When a thin film transistor having a small subthreshold region current is used, the threshold voltage is detected. Von ₁ is detected as a voltage, and when a thin film transistor having a large subthreshold voltage is used, Von ₂ is detected as a threshold voltage. The difference from the threshold voltage Vth ′ obtained from the equation is different. As a result, an error occurs in each pixel circuit with respect to Vod calculated based on the threshold voltage Vth ′, resulting in a program error.

In addition, the parasitic capacitance 102 of the organic EL light emitting device 100a is usually about 150 pF to 300 pF / mm ² , but is determined by the dielectric constant and film thickness of the organic light emitting material.

  In general, in an active matrix substrate, pixel circuits are repeatedly arranged in the order of R, G, and B in a direction orthogonal to a scanning direction (a direction in which data lines extend) (a direction in which the scanning lines extend). Accordingly, since the pixel circuits connected to the same scanning line are controlled at the same timing, the threshold voltage detection operation is also performed at the same timing in the R, G, and B pixel circuits.

However, since the threshold voltage detection time is determined by the size of the parasitic capacitance 102 of the organic EL light emitting element 100a and the current characteristics of the driving transistor 100b, the threshold voltage detection time depends on the deviation of the parasitic capacitance of the R, G, B organic EL light emitting elements. A detection error of the threshold voltage of the transistor 100b occurs.

  Here, in a pixel circuit using a thin film transistor having a small sub-threshold region current as a driving transistor, the characteristics of the Vgs of the driving transistor when the capacitance value Cd of the parasitic capacitance of the organic EL light emitting element is set to 2 pF and 4 pF are simulated. The results are shown in FIG. In FIG. 26, the characteristic of Vgs when the capacitance value Cd is set to 2 pF is a thin line, the characteristic of Vgs when the capacitance value Cd is set to 4 pF is a thick line, and the threshold voltage 1.46 V obtained from the theoretical formula is It is indicated by a broken line.

  In addition, in a pixel circuit using a thin film transistor having a large sub-threshold region current as a driving transistor, the characteristics of the Vgs of the driving transistor were simulated when the capacitance value Cd of the parasitic capacitance of the organic EL light emitting element was set to 2 pF and 4 pF. The results are shown in FIG. In FIG. 27, the characteristic of Vgs when the capacitance value Cd is set to 2 pF is a thin line, the characteristic of Vgs when the capacitance value Cd is set to 4 pF is a thick line, and the threshold voltage 1.46 V obtained from the theoretical formula is It is indicated by a broken line.

  From the simulation results shown in FIG. 26, when a thin film transistor having a small sub-threshold region current is used as a driving transistor, for example, the threshold voltage detection period is set to about 50 μs based on a threshold voltage of 1.46 V obtained from a theoretical formula. If set, it can be seen that even if the capacitance value Cd changes, there is no change in Vgs at the time of 50 μs, that is, no large error occurs in the detection value of the threshold voltage.

  However, from the simulation results shown in FIG. 27, when a thin film transistor having a small sub-threshold region current is used as a driving transistor, for example, the threshold voltage detection period is set to 25 μs based on the threshold voltage of 1.46 V obtained from the theoretical formula. If it is set to about, it can be seen that when the capacitance value Cd changes, Vgs at 25 μs changes greatly, that is, a large error occurs in the detected value of the threshold voltage.

  In order to eliminate the problem of the parasitic capacitance deviation of the organic EL light emitting elements of R, G, and B as described above, for example, as shown in FIG. 28, the capacitance connected to the source terminal of the driving transistor 100b. It is conceivable that the correction capacitance element 100e is provided for each pixel circuit so that the capacitance values of R, G and B are the same among the pixel circuits.

  However, the provision of the correction capacitor element 100e decreases the aperture ratio, thereby reducing the life of the organic EL light emitting element. In addition, the yield is reduced and the cost is increased.

  In the pixel circuit described in Patent Document 3, it is necessary to use an N-type thin film transistor as a driving transistor, and an amorphous silicon thin film transistor is assumed as the N-type thin film transistor.

  However, an amorphous silicon thin film transistor has a problem that its threshold voltage shifts due to voltage stress caused by application of a gate voltage.

  In the threshold voltage detection operation in the pixel circuit described in Patent Document 3, it is necessary to charge the parasitic capacitance 102 without causing the organic EL light emitting element 100a to emit light. Therefore, as shown in FIG. The source voltage Vs (the voltage at the anode terminal of the organic EL light emitting device 100a) needs to be equal to or lower than the light emission threshold voltage Vf0 of the organic EL light emitting device 100a. As shown in FIG. 29, the source voltage Vs of the driving transistor is determined by the magnitude of the threshold voltage of the driving transistor 100b (minimum value Vthmin to maximum value Vthmax of the threshold voltage of the driving transistor 100b). As described above, if the threshold voltage is shifted due to the voltage stress, the accurate threshold voltage cannot be detected, and normal correction operation cannot be performed, leading to deterioration of the quality of the display image. . Note that VB in FIG. 29 indicates a fixed voltage applied to the gate terminal of the driving transistor, and ΔVth indicates the magnitude of variation in the threshold voltage of the driving transistor.

  Therefore, in Patent Document 4, immediately before the reset period for resetting data held in the pixel circuit, a voltage Vg lower than the source voltage Vs of the driving transistor is applied to the gate terminal to apply a reverse bias to the driving transistor. Thus, a method for suppressing the shift of the threshold voltage of the driving transistor has been proposed.

  However, the magnitude of the gate voltage Vg applied to the gate terminal of the driving transistor during the display operation depends on the display image, and the amount of shift of the threshold voltage of the driving transistor also changes depending on the magnitude of the gate voltage Vg. To do. On the other hand, since the reverse bias period and the reverse bias voltage performed in Patent Document 4 are common to all the pixels, the threshold voltage deviation of each driving transistor and the change in the threshold voltage shift amount due to the display image are changed. Can not cope with. When the threshold voltage of the driving transistor starts to shift due to insufficient reverse bias, the threshold voltage is accelerated. That is, with the method described in Patent Document 4, it is difficult to suppress the shift of the threshold voltage of the driving transistor when the display image is updated over a long period of time.

  In view of the above circumstances, the present invention is not affected by the ratio between the capacitance value of the capacitive element that holds the driving voltage of the driving transistor during one display period and the capacitance value of the parasitic capacitance of the light emitting element. It is an object of the present invention to provide a display device capable of setting a desired drive voltage of a driving transistor in an element and a drive control method for the display device.

  In addition, the threshold voltage close to the threshold voltage obtained from the theoretical formula for each pixel circuit is detected and the program error is suppressed without being affected by the sub-threshold region current characteristics of the thin film transistors constituting the driving transistors of each pixel circuit. For the purpose.

  It is another object of the present invention to detect an appropriate threshold voltage without being affected by a deviation in parasitic capacitance of a light emitting element of each pixel circuit.

  It is another object of the present invention to appropriately suppress a threshold voltage shift due to voltage stress of a driving transistor.

  According to the display device drive control method of the present invention, a light emitting element, a driving transistor in which a source terminal is connected to an anode terminal of the light emitting element, and a driving current is supplied to the light emitting element, and a gate terminal and a source terminal of the driving transistor are interposed. A connected capacitive element; a selection switch connected between a gate terminal of the driving transistor and a voltage source supplying a predetermined voltage; and a source terminal of the driving transistor and a data line supplying a predetermined signal A drive control method for a display device having an active matrix substrate in which a plurality of pixel circuits having threshold voltage detection switches connected therebetween are arranged, wherein the current flows through the drive transistor by supplying the predetermined voltage. By detecting the voltage at the source terminal of the driving transistor when the parasitic capacitance of the light emitting element is charged, the driving transistor is detected. A signal corresponding to the threshold voltage of the star is detected, and a data signal based on the signal corresponding to the detected threshold voltage and the driving voltage of the driving transistor corresponding to the light emission amount of the light emitting element is used as the data line and the threshold voltage detecting switch. And output to the source terminal of the driving transistor.

  The display device of the present invention includes a light emitting element, a driving transistor in which a source terminal is connected to an anode terminal of the light emitting element, and a driving current is supplied to the light emitting element, and a capacitor connected between the gate terminal and the source terminal of the driving transistor. A selection switch connected between the element, a gate terminal of the driving transistor and a voltage source supplying a predetermined voltage, and a connection between the source terminal of the driving transistor and a data line supplying a predetermined signal; A plurality of pixel circuits each having a threshold voltage detection switch, an active matrix substrate having a data line provided for each column of the pixel circuits, and a light emitting element by a current flowing through the driving transistor by supplying the predetermined voltage By detecting the voltage of the source terminal of the driving transistor when charging the parasitic capacitance of the driving transistor, A threshold detection unit for detecting a signal corresponding to the value voltage, and a data signal based on the signal corresponding to the threshold voltage and the driving voltage of the driving transistor corresponding to the light emission amount of the light emitting element via the data line and the threshold voltage detecting switch And a data driving circuit having a data signal output unit for outputting to the source terminal of the driving transistor.

  In the display device of the present invention, the threshold detection unit detects the source voltage of the driving transistor before the increase in the source voltage of the driving transistor is saturated by charging the parasitic capacitance of the light emitting element. be able to.

  In addition, a correction capacitor element for correcting the deviation of the parasitic capacitance of the light emitting element can be provided for each data line.

  Further, the data drive circuit may further include a reverse bias voltage output unit that supplies a reverse bias voltage having a magnitude corresponding to the drive voltage of the drive transistor to the gate terminal of the drive transistor.

  Further, the driving transistor can be formed of a thin film transistor having a current characteristic with a negative threshold voltage.

  Further, the driving transistor can be formed of a thin film transistor made of IGZO (InGaZnO).

  According to the display device and the driving control method thereof of the present invention, the light emitting element, the driving transistor in which the source terminal is connected to the anode terminal of the light emitting element, and the driving current is supplied to the light emitting element, the gate terminal and the source terminal of the driving transistor, A capacitor connected between the gate, a selection switch connected between a gate terminal of the driving transistor and a voltage source supplying a predetermined voltage, and data supplying a predetermined signal to the source terminal of the driving transistor In a display device including an active matrix substrate in which a large number of pixel circuits each having a threshold voltage detection switch connected to a line are arranged, the current flowing in the driving transistor by the supply of the predetermined voltage is used to By detecting the voltage at the source terminal of the driving transistor when the parasitic capacitance is charged, the driving transistor is A signal corresponding to the threshold voltage of the star is detected, and a data signal based on the signal corresponding to the detected threshold voltage and the driving voltage of the driving transistor corresponding to the light emission amount of the light emitting element is used as the data line and the threshold voltage detecting switch. Since the data signal is supplied to the source terminal of the driving transistor without being divided into the capacitive element and the parasitic capacitance of the light emitting element, the data signal is supplied to the source terminal of the driving transistor via the capacitor. A desired driving voltage of the driving transistor can be set in the capacitor element without being affected by the ratio between the capacitance value of the element and the parasitic capacitance value of the light emitting element.

  In the display device of the present invention, the threshold detection unit detects the source voltage of the driving transistor before the increase of the source voltage of the driving transistor is saturated by charging the parasitic capacitance of the light emitting element. Can detect a threshold voltage close to the threshold voltage obtained from the theoretical formula for each pixel circuit without being affected by the sub-threshold region current characteristics of the thin film transistors that constitute the driving transistor of each pixel circuit. Errors can be suppressed.

  Further, when a correction capacitance element for correcting the deviation of the parasitic capacitance of the light emitting element is provided for each data line, the data line is appropriately affected without being affected by the deviation of the parasitic capacitance of the light emitting element of each pixel circuit. A threshold voltage can be detected.

  In addition, when the data drive circuit is further provided with a reverse bias voltage output unit for supplying a reverse bias voltage having a magnitude corresponding to the drive voltage of the drive transistor to the gate terminal of the drive transistor, the drive transistor The threshold voltage shift due to the voltage stress can be appropriately suppressed.

  In addition, when the reverse bias voltage is supplied to the driving transistor as described above, the reverse bias voltage needs to be set to a level at which the light emitting element does not emit light. In the case of high luminance display, the reverse bias voltage is insufficient.

  Therefore, when the driving transistor is constituted by a thin film transistor having a current characteristic of threshold voltage Vth <0, a voltage of both positive and negative polarity is applied as Vgs in the display operation. The voltage also has both positive and negative polarities, and the reverse bias shortage due to the limit value of the reverse bias voltage can be reduced.

  Further, when the driving transistor is formed of a thin film transistor made of IGZO (InGaZnO), the reversible threshold voltage shift characteristic of the thin film transistor made of IGZO can be used. That is, the threshold voltage of a thin film transistor made of IGZO shifts due to voltage stress caused by application of a gate voltage, but unlike an amorphous silicon thin film transistor, it returns to its initial value by applying a zero bias. By utilizing this characteristic, for example, the threshold voltage can be returned to the initial value during a non-display period such as when a black screen is displayed or when the power is turned off. it can.

  Hereinafter, an organic EL display device to which a first embodiment of a display device of the present invention is applied will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of an organic EL display device to which the first embodiment of the present invention is applied.

  As shown in FIG. 1, the organic EL display device according to the first embodiment of the present invention holds charges according to the data signal output from the data drive circuit 12 and drives according to the held charge amount. An active matrix substrate 10 in which a large number of pixel circuits 11 that flow current to the organic EL light emitting elements are arranged in a two-dimensional manner, a data drive circuit 12 that outputs a data signal to each pixel circuit 11 of the active matrix substrate 10, and an active matrix substrate And a scanning drive circuit 13 for outputting a scanning signal to each of the ten pixel circuits 11.

  The active matrix substrate 10 supplies a number of data lines 14 that supply the data signal output from the data driving circuit 12 to each pixel circuit column and a scanning signal output from the scan driving circuit 13 to each pixel circuit row. And a large number of scanning lines 15. The data lines 14 and the scanning lines 15 are provided in a lattice shape so as to be orthogonal to each other. A pixel circuit 11 is provided in the vicinity of the intersection of the data line 14 and the scanning line 15.

  As shown in FIG. 2, each pixel circuit 11 has an organic EL light emitting element 11a and a source terminal S connected to the anode terminal of the organic EL light emitting element 11a. A driving transistor 11b to be flown, a capacitive element 11c connected between a gate terminal G and a source terminal S of the driving transistor 11b, one end of the capacitive element 11c, a gate terminal G of the driving transistor 11b, and the data line 14 And a threshold voltage detecting transistor 11e connected between the source terminal S of the driving transistor 11b and the data line 14.

  The organic EL light emitting element 11 a includes a light emitting unit 50 that emits light by a driving current passed by the driving transistor 11 b and a parasitic capacitance 51 of the light emitting unit 50. The cathode terminal of the organic EL light emitting element 11a is connected to the ground potential.

  The driving transistor 11b and the selection transistor 11d are N-type thin film transistors. As a kind of the thin film transistor of the driving transistor 11b, an amorphous silicon thin film transistor or an inorganic oxide thin film transistor can be used. As the inorganic oxide film thin film transistor, for example, a thin film transistor made of an inorganic oxide film made of IGZO (InGaZnO) can be used. However, not only IGZO but also IZO (InZnO) can be used.

  As shown in FIG. 2, a predetermined fixed voltage Vdd is supplied to the drain terminal D of the driving transistor 11b. The fixed voltage VB is supplied to the terminal of the selection transistor 11d that is not connected to the gate terminal G of the driving transistor 11b. The magnitude of the fixed voltage VB will be described in detail later.

  The scanning drive circuit 13 uses an on-scan signal Vscan (on) for turning on the selection transistor 11d and the threshold voltage detection transistor 11e of the pixel circuit 11 and an off-scan signal Vscan (off) for turning off each scanning line. 15 are sequentially output.

  FIG. 3 shows a detailed configuration diagram of the data driving circuit 12. The data driving circuit 12 includes a large number of circuits shown in FIG. 3, and the circuit shown in FIG. 3 is connected to each data line 14 of the active matrix substrate 10.

  As shown in FIG. 3, the data driving circuit 12 includes a reset fixed voltage source 12a that supplies a reset signal VA, a sample and hold circuit 12b that detects a signal corresponding to the threshold voltage of the driving transistor 11b, and a display image. The pixel data corresponding to the constituent pixels is input, the DA data is converted into an analog signal and the overdrive voltage Vod is output, and the signal corresponding to the threshold voltage output from the sample hold circuit 12b is converted to DA. A subtractor 12d that subtracts the overdrive voltage output from the converter 12c and outputs it as a program data signal Vprg corresponding to the display image, and a first switch 12e that switches connection between the reset fixed voltage source 12a and the data line 14. And the connection between the subtractor 12d and the data line 14 is switched. And a second switch 12f. The detailed operation of the data driving circuit 12 will be described later.

  Next, the operation of the organic EL display device of the first embodiment will be described with reference to the timing chart shown in FIG. 4 and FIGS. 5 to 8. In FIG. 4, the scanning signal Vscan output from the scanning driving circuit 13, the data signal Vdata output from the data driving circuit 12, the gate voltage Vg, the source voltage Vs, and the gate-source voltage Vgs of the driving transistor 11b are shown. The voltage waveform is shown.

  In the organic EL display device of the present embodiment, pixel circuit rows connected to each scanning line 15 of the active matrix substrate 10 are sequentially selected, and a predetermined operation is performed in the selection period in units of one row. Here, an operation performed in the selected period in the selected predetermined pixel circuit row will be described.

  First, a predetermined pixel circuit row is selected by the scanning drive circuit 13, and an on-scan signal as shown in FIG. 4 is output to the scanning line 15 to which the pixel circuit row is connected (time t1 in FIG. 4).

  Then, as shown in FIG. 5, the selection transistor 11d and the threshold voltage detection transistor 11e are turned on in response to the ON scanning signal output from the scanning driving circuit 13, and the gate terminal G of the driving transistor 11b and the fixed voltage VB are turned on. Are connected to the source terminal S of the driving transistor 11b, one end of the capacitive element 11c, and the anode terminal of the organic EL light emitting element 11a, and the data line 14.

  First, a reset operation is performed (see t1 to t2 in FIG. 4 and FIG. 5). Specifically, the first switch 12e in the data drive circuit 12 is turned on, the second switch 12f is turned off, and the reset fixed voltage source 12a of the data drive circuit 12 and the data line 14 are connected. The reset signal VA is output to the data line 14 from the reset fixed voltage source 12a. The reset signal VA output from the reset fixed voltage source 12a is input to each pixel circuit 11 in the selected pixel circuit row.

  Then, by the operation as described above, the gate voltage Vg = VB, the source voltage Vs = VA, and the gate-source voltage Vgs = VB-VA of the driving transistor 11b are reset.

  Here, the fixed voltage VB supplied to the gate terminal G of the driving transistor 11b is set to a magnitude that satisfies the following expression.

VB ≧ VA + Vthmax
However, Vthmax is the maximum value of the threshold voltage of the driving transistor 11b. Therefore, the gate-source voltage Vgs of the driving transistor 11b is
Vgs = VB−VA ≧ Vthmax
Thus, some drive current Id flows toward the data line 14 in the drive transistor 11b.

  Here, immediately before this reset operation, since each pixel circuit 11 in the pixel circuit row is in the light emission period, some charges remain in the parasitic capacitance 51 and the capacitance element 11c of the organic EL light emitting element 11a. This charge is also swept out toward the data line 14 by the action.

  As the value of the fixed voltage VB, 0 V can be used, and the reset signal VA at this time is a negative voltage. Further, 0V may be used as the reset signal VA, and the fixed voltage VB may be set to a positive voltage. In the following description, it is assumed that VB = 0V and VA <0.

  Next, a threshold voltage detection operation is performed (t2 to t3 in FIG. 4, see FIG. 6). Specifically, first, the first switch 12e of the data driving circuit 12 is turned off to cut off the supply of the reset signal VA to the data line. As a result, the data line 14 is in a high impedance (Hi-Z) state.

  At this time, since the source voltage Vs of the driving transistor 11b is VA, the gate-source voltage of the driving transistor 11b is Vgs = Vg−Vs = VB−VA ≧ Vthmax, and the detection current is supplied to the driving transistor 11b. Idd flows.

  Then, the parasitic current 51 of the organic EL light emitting element 11a is charged by the detection current Idd, and the source voltage Vs of the source terminal S of the driving transistor 11b increases.

  Since the fixed voltage VB is supplied to the gate terminal G of the driving transistor 11b, Vgs decreases and the detection current Idd decreases due to the increase of the source voltage Vs.

  The source voltage Vs of the drive transistor 11b is input to the sample hold circuit 12b of the data drive circuit 12 via the threshold voltage detection transistor 11e and the data line 14, and the sample hold circuit 12b of the data drive circuit 12 is The source voltage Vs at the time when the set charging time has elapsed is held as a signal corresponding to the threshold voltage Vth of the driving transistor 11b (time t3 in FIG. 4). The preset charging time is a time before the increase in the source voltage of the driving transistor 11b is saturated by charging the parasitic capacitance 51 of the organic EL light emitting element 11a, and the charging time of the sub-threshold region of the driving transistor 11b. It is determined in advance from the current characteristics, the capacitance value of the parasitic capacitance, and the initial Vgs voltage.

  At this time, the gate voltage Vg of the driving transistor 11b is Vg = VB, and the source voltage Vs is VB−Vth. In order to appropriately detect the threshold voltage Vth of the driving transistor 11b, the source voltage Vs of the driving transistor 11b needs to be equal to or lower than the light emission threshold of the organic EL light emitting element 11a.

  Therefore, the source voltage Vs needs to satisfy the following formula.

Vs = VB−Vthmin ≦ Vf0
However, Vthmin is the minimum value of the threshold voltage of the driving transistor 11b, and Vf0 is the light emission threshold voltage of the organic EL light emitting element 11a.

  Therefore, the fixed voltage VB needs to have a magnitude that satisfies the following expression.

VB ≦ Vf0 + Vthmin
On the other hand, the relationship between the reset signal VA and the fixed voltage VB is VB ≧ VA + Vthmax because of the condition in the reset operation described above.
VA ≦ VB−Vthmax
It is. Therefore, the condition of the reset signal VA is as follows:
VA ≦ Vf0 + Vthmin−Vthmax = Vf0−ΔVth
It becomes. Note that ΔVth is a variation in threshold voltage of the driving transistor 11b.

  Next, a program operation is performed (see t3 to t4 in FIG. 4 and FIG. 7). Specifically, the second switch 12f in the data driving circuit 12 is turned ON, the subtractor 12d and the data line 14 are connected, and a program data signal is output from the subtractor 12d to the data line 14. The program data signal Vprg output from the data driving circuit 12 is input to each pixel circuit 11 in the selected pixel circuit row.

  Here, the sample hold circuit 12b in the data drive circuit 12 holds the source voltage Vs of the drive transistor 11b as a signal corresponding to the threshold voltage as described above, and at this time, the source voltage Vs = VB−Vth. . Therefore, VB−Vth is output from the sample hold circuit 12b to the subtractor 12d. On the other hand, pixel data constituting a display image is input to the DA converter 12c of the data drive circuit 12, and the DA converter 12c converts this pixel data into an overdrive voltage Vod of the drive transistor 11b, and this overdrive voltage. Vod is output to the subtractor 12d.

  Then, in the subtracter 12d, the overdrive voltage Vod output from the DA converter 12c is subtracted from the signal VB-Vth corresponding to the threshold voltage output from the sample hold circuit 12b, and the program data signal Vprg expressed by the following equation is obtained. Is output.

Vprg = VB−Vth−Vod = VB− (Vth + Vod)
By the operation as described above, the gate voltage Vg = VB and the source voltage Vs = VB− (Vth + Vod) of the driving transistor 11b are set, and the gate-source voltage Vgs = Vth + Vod of the driving transistor 11b is set.

  As a result, a voltage obtained by adding Vod to the threshold voltage Vth detected by the threshold voltage detection operation is set in the capacitive element 11c.

  Next, a light emission operation is performed (see FIG. 8 after t4 in FIG. 4). Specifically, an off scanning signal is output from the scanning drive circuit 13 to each scanning line 15 (time t4 in FIG. 4). Then, as shown in FIG. 8, the selection transistor 11d and the threshold voltage detection transistor 11e are turned off in response to the off-scan signal output from the scan drive circuit 13, and the gate terminal G of the drive transistor 11b and the fixed voltage VB. Is disconnected from the source terminal S of the driving transistor 11b, one end of the capacitive element 11c, the anode terminal of the organic EL light emitting element 11a, and the data line 14.

  Then, the gate-source voltage Vgs of the driving transistor 11b becomes Vod + Vth, and the driving current Idv according to the following TFT current equation flows between the drain and source of the driving transistor 11b.

Idv = μ × Cox × (W / L) × (Vgs−Vth) ²
= Μ × Cox × (W / L) × Vod ²
Where μ is the electron mobility, Cox is the gate oxide film capacity per unit area, W is the gate width, and L is the gate length.

  The drive current Idv charges the parasitic capacitance 51 of the organic EL light emitting element 11a, and the source voltage Vs of the drive transistor 11b rises, but the gate-source voltage Vgs is held by the holding voltage Vod + Vth of the capacitance element 11c. Accordingly, the source voltage Vs eventually exceeds the light emission threshold voltage Vf0 of the organic EL light emitting element 11a, and the light emitting operation of the organic EL light emitting element 11a is performed with a constant current.

  In addition, after the application of Vod is completed, before the source voltage Vs rises due to the drive voltage Idv flowing between the drain and source of the drive transistor 11b, the voltage between the terminals of the parasitic capacitance 51 of the organic EL light emitting element 11a rises. Therefore, it is necessary to output an off-scan signal from the scanning drive circuit 13 to each scanning line 15 and turn off the selection transistor 11d and the threshold voltage detection transistor 11e.

  Then, a predetermined pixel circuit row is sequentially selected by the scanning drive circuit 13, and the operations from the reset operation to the light emission operation are performed on each pixel circuit row, and a desired display image is displayed.

  Further, in the organic EL display device according to the first embodiment, as shown in FIG. 9, a correction capacitor element 16 may be provided for each data line 14. The correction capacitance element 16 is for correcting a deviation of the parasitic capacitance 51 of the organic EL light emitting element 11a for each pixel circuit column connected to each data line. For example, when an R organic EL light emitting element, a G organic EL light emitting element, and a B organic EL light emitting element are repeatedly arranged in this order in a direction perpendicular to the data line 14, the parasitic of the organic EL light emitting element is used. Capacitance color (RGB) deviation can be corrected. The capacitance value of the correction capacitance element 16 is set so that the sum of the parasitic capacitance 51 and the capacitance value of the capacitance element 61 in each pixel circuit row becomes the same capacitance value.

  Note that the correction capacitor element 16 can be simply configured by crossing the data line 14 and the ground line outside the range where the pixel circuits in the active matrix substrate 10 are arranged. Can be realized without significantly expanding

  Further, when the correction capacitive element 16 is provided as described above, the threshold voltage detection transistor 11e is turned on during the threshold voltage detection operation, and the current flowing in the drive transistor 11b is changed to the organic EL light emitting element. The current flows through both the parasitic capacitance 51 of 11a and the correction capacitive element 16 to be charged.

  Next, an organic EL display device to which the second embodiment of the display device of the present invention is applied will be described.

  The organic EL display device according to the second embodiment is obtained by applying a reverse bias voltage to the driving transistor 11b in the organic EL display device according to the first embodiment. The configuration of the organic EL display device of the second embodiment is different from the configuration of the organic EL display device of the first embodiment to the configuration of the data drive circuit. Since other configurations are the same, only the configuration of the data driving circuit will be described.

  As shown in FIG. 11, the data drive circuit 17 of the organic EL display device of the second embodiment outputs a signal corresponding to the threshold voltage of the reset fixed voltage source 17a for supplying the reset signal VA and the drive transistor 11b. From the sample hold circuit 17b to be detected, the pixel data corresponding to the pixels constituting the display image, the DA converter 17c that converts the pixel data into an analog signal and outputs the overdrive voltage Vod, and the sample hold circuit 12b A first subtracter 17d that subtracts the overdrive voltage output from the DA converter 17c from the signal corresponding to the output threshold voltage and outputs it as a program data signal Vprg corresponding to the display image; A second subtracter 17e for subtracting the output of the subtractor 17d, and a second subtractor 17 The adder 17g for adding the fixed voltage VB to the output of the output, the first switch 17h for switching the connection between the reset fixed voltage source 17a and the data line 14, and the connection between the first subtractor 17d and the data line 14. A second switch 17i for switching and a third switch 17j for switching the connection between the adder 17g and the data line 14 are provided.

  Next, the operation of the organic EL display device of the second embodiment will be described with reference to the timing chart shown in FIG. In FIG. 12, the scanning signal Vscan output from the scanning driving circuit 13, the data signal Vdata output from the data driving circuit 17, the gate voltage Vg, the source voltage Vs, and the gate-source voltage Vgs of the driving transistor 11b are shown. The voltage waveform is shown. The operation of each pixel circuit is the same as that of the organic EL display device according to the first embodiment except for the period in which the reverse bias voltage is applied. For the operation of the pixel circuit, refer to FIGS. While explaining.

  Also in the organic EL display device of the second embodiment, the pixel circuit rows connected to each scanning line 15 of the active matrix substrate 10 are sequentially selected as in the organic EL display device of the first embodiment. A predetermined operation is performed in the selection period in units. Here, an operation performed in the selected period in the selected predetermined pixel circuit row will be described.

  First, a predetermined pixel circuit row is selected by the scanning drive circuit 13, and an on-scan signal as shown in FIG. 12 is output to the scanning line 15 to which the pixel circuit row is connected (time t1 in FIG. 12).

  Then, as shown in FIG. 5, the selection transistor 11d and the threshold voltage detection transistor 11e are turned on in response to the ON scanning signal output from the scanning driving circuit 13, and the gate terminal G of the driving transistor 11b and the fixed voltage VB are turned on. Are connected to the source terminal S of the driving transistor 11b, one end of the capacitive element 11c, and the anode terminal of the organic EL light emitting element 11a, and the data line 14.

  First, a reset operation is performed (t1 to t2 in FIG. 12, see FIG. 5). Specifically, the first switch 17h in the data driving circuit 17 is turned on, and the second and third switches 17i and 17j are turned off, so that the reset fixed voltage source 17a and the data line 14 of the data driving circuit 17 are turned on. And the reset signal VA is output to the data line 14 from the reset fixed voltage source 17a. The reset signal VA output from the reset fixed voltage source 17a is input to each pixel circuit 11 in the selected pixel circuit row.

  Then, by the operation as described above, the gate voltage Vg = VB, the source voltage Vs = VA, and the gate-source voltage Vgs = VB-VA of the driving transistor 11b are reset.

  The fixed voltage VB supplied to the gate terminal G of the driving transistor 11b is the same as that of the organic EL display device of the first embodiment.

The gate-source voltage Vgs of the driving transistor 11b is
Vgs = VB−VA ≧ Vthmax
As a result, some driving current Id flows through the driving transistor 11b toward the data line 14, so that the charge remaining in the parasitic capacitance 51 and the capacitive element 11c of the organic EL light emitting element 11a is also swept toward the data line 14. Is issued.

  Then, a threshold voltage detection operation is performed (t2 to t3 in FIG. 12, see FIG. 6). Specifically, first, the first switch 17h of the data driving circuit 17 is turned off to cut off the supply of the reset signal VA to the data line. As a result, the data line 14 is in a high impedance (Hi-Z) state.

  At this time, since the source voltage Vs of the driving transistor 11b is VA, the gate-source voltage of the driving transistor 11b is Vgs = Vg−Vs = VB−VA ≧ Vthmax, and the detection current is supplied to the driving transistor 11b. Idd flows.

  Then, the parasitic current 51 of the organic EL light emitting element 11a is charged by the detection current Idd, and the source voltage Vs of the source terminal S of the driving transistor 11b increases.

  Since the fixed voltage VB is supplied to the gate terminal G of the driving transistor 11b, Vgs decreases and the detection current Idd decreases due to the increase of the source voltage Vs.

  The source voltage Vs of the drive transistor 11b is input to the sample hold circuit 17b of the data drive circuit 17 via the threshold voltage detection transistor 11e and the data line 14, and the sample hold circuit 17b of the data drive circuit 17 is The source voltage Vs at the time when the set charging time has elapsed is held as a signal corresponding to the threshold voltage Vth of the driving transistor 11b (time t3 in FIG. 12).

  Note that the conditions of the fixed voltage VB and the reset signal VA at this time are the same as those of the organic EL display device of the first embodiment.

  Then, a reverse bias operation is performed (t3 to t4 in FIG. 12). Specifically, after the above-described reset operation, the third switch 17j in the data driving circuit 17 is turned on, the adder 17g and the data line 14 are connected, and the reverse bias voltage Vrv is connected from the adder 17g to the data line 14. Is output. The reverse bias voltage Vrv output from the data drive circuit 17 is input to each pixel circuit 11 in the selected pixel circuit row.

  More specifically, first, the sample hold circuit 17b in the data drive circuit 17 holds the source voltage Vs of the drive transistor 11b as a signal corresponding to the threshold voltage as described above. At this time, the source voltage Vs = VB-Vth. Therefore, VB−Vth is output from the sample hold circuit 17b to the first subtractor 17d. On the other hand, pixel data constituting a display image is input to the DA converter 12c of the data drive circuit 17, and the DA converter 12c converts the pixel data into an analog signal to obtain an overdrive voltage Vod of the driving transistor 11b. Vod is output to the first subtractor 17d.

  Then, in the first subtracter 17d, the overdrive voltage Vod output from the DA converter 17c is subtracted from the signal VB-Vth corresponding to the threshold voltage output from the sample and hold circuit 17b, and the program data represented by the following equation: A signal Vprg is output.

Vprg = VB−Vth−Vod = VB− (Vth + Vod)
The program data signal Vprg output from the first subtractor 17d is output to the second subtractor 17e. On the other hand, a voltage source that supplies a fixed voltage VB is connected to the second subtractor 17e, and the second subtractor 17e subtracts the program data signal Vprg from the fixed voltage VB and obtains the subtracted value. A signal K × (Vth + Vod) multiplied by a predetermined gain constant is output. The gain constant corresponds to the reverse bias coefficient and is set in advance.

  Then, the signal K × (Vth + Vod) output from the second subtractor 17e is input to the adder 17g. Then, the adder 17g adds the fixed voltage VB to the output signal K × (Vth + Vod) of the second subtractor 17e to generate a reverse bias voltage Vrv represented by the following equation.

Vrv = VB + K × (Vth + Vod)
Then, the reverse bias voltage Vrv generated in the adder 17g is output to the data line 14 via the third switch 17j.

The reverse bias voltage Vrv output to the data line 14 is applied to the source terminal S of the driving transistor 11b via the threshold voltage detecting transistor 11e. Therefore, since the source voltage Vs of the driving transistor 11b is Vs = VB + K × (Vth + Vod) and the gate voltage Vg is the fixed voltage VB, the gate-source voltage Vgs of the driving transistor 11b is
Vgs = −K × (Vth + Vod)
It becomes.

  Therefore, a reverse bias voltage corresponding to the gate-source voltage Vgs set to the driving transistor 11b, that is, Vth + Vod, is set to the driving transistor 11b in the program operation described later, and the display operation is performed for each pixel circuit. The reverse bias voltage corresponding to the generated voltage stress can be set, and the threshold shift of the driving transistor 11b can be appropriately suppressed.

  Next, a program operation is performed (see t4 to t5 in FIG. 12, see FIG. 7). Specifically, the third switch 17j in the data driving circuit 17 is turned off, the second switch 17i is turned on, the adder 17g and the data line 14 are disconnected, and the first subtractor 17d and the data The line 14 is connected, and the program data signal Vprg is output from the first subtractor 17 d to the data line 14. The program data signal Vprg output from the data driving circuit 12 is input to each pixel circuit 11 in the selected pixel circuit row. The program data signal Vprg output from the first subtractor 17d is the same as the reverse bias operation described above.

  Then, the gate voltage Vg = VB and the source voltage Vs = VB− (Vth + Vod) of the driving transistor 11b are set, and the gate-source voltage Vgs = Vth + Vod of the driving transistor 11b is set.

  As a result, a voltage obtained by adding Vod to the threshold voltage Vth detected by the threshold voltage detection operation is set in the capacitive element 11c.

  Then, a light emission operation is performed (see FIG. 8 after t5 in FIG. 12). Specifically, an off scanning signal is output from the scanning drive circuit 13 to each scanning line 15 (time t5 in FIG. 12). Then, as shown in FIG. 8, the selection transistor 11d and the threshold voltage detection transistor 11e are turned off in response to the off-scan signal output from the scan drive circuit 13, and the gate terminal G of the drive transistor 11b and the fixed voltage VB. Is disconnected from the source terminal S of the driving transistor 11b, one end of the capacitive element 11c, the anode terminal of the organic EL light emitting element 11a, and the data line 14.

  Then, the gate-source voltage Vgs of the driving transistor 11b becomes Vod + Vth, and the driving current Idv according to the following TFT current equation flows between the drain and source of the driving transistor 11b.

Idv = μ × Cox × (W / L) × (Vgs−Vth) ²
= Μ × Cox × (W / L) × Vod ²
Where μ is the electron mobility, Cox is the gate oxide film capacity per unit area, W is the gate width, and L is the gate length.

  The drive current Idv charges the parasitic capacitance 51 of the organic EL light emitting element 11a, and the source voltage Vs of the drive transistor 11b rises, but the gate-source voltage Vgs is held by the holding voltage Vod + Vth of the capacitance element 11c. Accordingly, the source voltage Vs eventually exceeds the light emission threshold voltage Vf0 of the organic EL light emitting element 11a, and the light emitting operation of the organic EL light emitting element 11a is performed with a constant current.

  Then, a predetermined pixel circuit row is sequentially selected by the scanning drive circuit 13, and the operations from the reset operation to the light emission operation are performed on each pixel circuit row, and a desired display image is displayed.

  In the organic EL display device according to the second embodiment, a correction capacitor element 16 may be provided for each data line 14 as shown in FIG.

  Here, the reverse bias voltage in the organic EL display device of the second embodiment will be considered.

In the organic EL display device of the second embodiment, the voltage stress of the driving transistor 11b due to the display operation is Vgs × Tdsp. Tdsp is a display period. When the reverse bias voltage application period is Trv, the necessary reverse bias voltage Vrv is
Vrv = Vgs × Tdsp / Trv
It becomes. By applying this reverse bias voltage, the voltage stress on the average of one frame is equalized between positive and negative and becomes zero.

That is, the reverse bias coefficient K in the organic EL display device of the second embodiment is
K = Tdsp / Trv
However, the reverse bias period Trv is a part of the program period Tprg and is naturally much shorter than the display period Tdsp. Therefore, the reverse bias coefficient K increases and the reverse bias voltage Vrv also becomes a high voltage.

  On the other hand, in the organic EL display device of the second embodiment, it is necessary to prevent the organic EL light emitting element 11a from emitting light during the reverse bias operation period, and the reverse applied to the source terminal S of the driving transistor 11b. The bias voltage Vrv needs to be equal to or lower than the light emission threshold voltage Vf0 of the organic EL light emitting element 11a.

  For example, when the fixed voltage VB = 0, Vrv ≦ Vf0, and even if a negative voltage is set as the fixed voltage VB, there is a limit value for the reverse bias voltage Vrv.

  Therefore, as shown in FIG. 13, a limiter circuit 17k may be provided at the output terminal of the adder 17g. As the limiter circuit 17k, for example, a diode element whose limit value Vrvmax of the reverse bias voltage is supplied to the cathode terminal can be used.

  However, when the limiter circuit 17k is provided as shown in FIG. 13, for example, the voltage stress at the time of high luminance display is not offset by the reverse bias voltage, and there is a possibility that the reverse bias voltage is insufficient.

  Therefore, in order to solve this problem, the driving transistor 11b may be formed of a thin film transistor having a current characteristic of the threshold voltage Vth <0. FIG. 14 shows an example of current characteristics of a driving transistor with a threshold voltage Vth <0.

  When the threshold voltage Vth of the driving transistor 11b is set to a negative voltage, a positive and negative voltage is applied as Vgs in the display operation, so that the reverse bias voltage also has both a positive and negative polarity. Thus, the shortage of reverse bias due to the limit value of the reverse bias voltage can be reduced.

  In the organic EL display device according to the second embodiment, the threshold voltage of the driving transistor 11b can be detected regardless of whether the threshold voltage is positive or negative. As a result, the reverse bias voltage setting range can be expanded and long-term stability can be improved.

  In the organic EL display devices of the first and second embodiments, an N-type thin film transistor made of amorphous silicon or an inorganic oxide film can be used as a driving transistor as described above. It is desirable to use an N-type thin film transistor as a driving transistor.

  By utilizing the reversible threshold voltage shift characteristic of a thin film transistor made of IGZO, for example, the threshold voltage can be returned to the initial value during a non-display period such as a period when a black screen is displayed or when the power is turned off. The shift of the threshold voltage can be further suppressed. Also, the negative voltage of the threshold voltage of the driving transistor 11b can be easily realized.

  Further, the configuration of the pixel circuit in the organic EL display devices of the first and second embodiments is not limited to the configuration shown in FIG. 2, but for example, an anode common type organic EL light emitting element as shown in FIG. It is good also as a structure using 21a. Specifically, as shown in FIG. 15, the pixel circuit 21 includes an organic EL light emitting element 21a having a light emitting part 52 and a parasitic capacitance 53 of the light emitting part 52, and a source terminal S at the cathode terminal of the organic EL light emitting element 21a. A driving transistor 21b connected to flow a driving current to the organic EL light emitting element 21a, a capacitive element 21c connected between the gate terminal G and the drain terminal D of the driving transistor 21b, one end of the capacitive element 21c, and driving A selection transistor 21e connected between the gate terminal G of the transistor 21b and the data line 14, and a threshold voltage detection transistor 21d connected between the drain terminal D of the drive transistor 21b and the data line 14. And a light emitting operation transistor 21f connected to the drain terminal D of the driving transistor 21b. The driving transistor 11b is composed of a P-type thin film transistor.

  Further, as shown in FIG. 15, a predetermined fixed voltage Vdd is supplied to the anode terminal of the organic EL light emitting element 21a. The fixed voltage VB is supplied to the terminal not connected to the gate terminal G of the driving transistor 21b of the selection transistor 21e.

  Further, when the pixel circuit 21 having the above-described configuration is used, it is necessary to provide a threshold voltage detection capacitive element 22 in each data line 14. Further, it is necessary to further provide a switch control line 18 for supplying a switch control signal for turning off the light emission operation transistor 21f during the threshold voltage detection operation and turning on the light emission operation transistor 21f during the light emission operation.

  In the threshold voltage detection operation, the threshold voltage of the driving transistor 21b is detected by turning off the light emitting operation transistor 21f and charging the threshold voltage detection capacitor element 22 with the detection current flowing through the driving transistor 21b. During the light emission operation, the organic EL light emitting element 21a is caused to emit light by turning on the light emission operation transistor 21f and causing a driving current to flow in the driving transistor 21b.

  Further, the pixel circuit is configured such that, as in the pixel circuit 11 shown in FIG. 2, a predetermined voltage is supplied to the gate terminal G of the driving transistor 11b, and current supplied to the driving transistor 11b by the supply of the voltage is used. Any other pixel circuit may be used as long as the capacitive element (parasitic capacitance) 55 connected to the source terminal S of the driving transistor 11b is charged to cause the capacitive element 11c to hold the threshold voltage of the driving transistor 11b. May be used.

  For example, a pixel circuit 31 as shown in FIG. 16 may be used. Specifically, the pixel circuit 31 illustrated in FIG. 16 includes an organic EL light emitting element 31a having a light emitting unit 54 and a parasitic capacitance 55 of the light emitting unit 54, and a source terminal S connected to an anode terminal of the organic EL light emitting element 31a. A driving transistor 31b for passing a driving current and a detection current to the organic EL light emitting element 31a, a capacitive element 31c connected between the gate terminal G and the source terminal S of the driving transistor 31b, one end of the capacitive element 31c, and driving A selection transistor 31e connected between the gate terminal G of the transistor 31b and the data line 14, and a threshold voltage detection transistor 31d connected between the source terminal S of the drive transistor 31b and the data line 14. And a resetting transistor 31f connected to the source terminal S of the driving transistor 31b.

  In the pixel circuit 31, during the reset operation, the reset transistor 31f is turned on in response to the reset control signal supplied from the reset control line, and remains in the capacitive element 31c and the parasitic capacitance 55 via the reset transistor 31f. The charge is discharged.

  Further, for example, a pixel circuit 41 as shown in FIG. 17 may be used. Specifically, the pixel circuit 41 shown in FIG. 17 includes an organic EL light emitting element 41a having a light emitting part 56 and a parasitic capacitance 57 of the light emitting part 56, and a source terminal S connected to the anode terminal of the organic EL light emitting element 41a. A driving transistor 41b for supplying a driving current and a detection current to the organic EL light emitting element 41a, a capacitive element 41c connected between the gate terminal G and the source terminal S of the driving transistor 41b, one end of the capacitive element 41c, and driving A selection transistor 41e connected between the gate terminal G of the transistor 41b and the data line 14, and a threshold voltage detection transistor 41d connected between the source terminal S of the drive transistor 41b and the data line 14. It has. The selection transistor 41e of the pixel circuit 41 of FIG. 17 is turned on / off in response to the first scanning signal supplied to the first scanning line 15, and the threshold voltage detection transistor 41d is This is turned ON / OFF according to the second scanning signal supplied to the second scanning line 20.

  As described above, the selection transistor 41e and the threshold voltage detection transistor 41d are independently controlled, and the opening timing of the selection transistor 41e is delayed from the opening timing of the threshold voltage detection transistor 41d. It is also possible to correct the mobility μ corresponding to that described in the publication.

  In the embodiment of the present invention, the display device of the present invention is applied to an organic EL display device. However, the light emitting element is not limited to the organic EL light emitting element, and for example, an inorganic EL element is used. It may be.

  The display device of the present invention has various uses. For example, a portable information terminal (electronic notebook, mobile computer, mobile phone, etc.), a video camera, a digital camera, a personal computer, a television, etc. are mentioned.

1 is a schematic configuration diagram of an organic EL display device to which a first embodiment of a display device of the present invention is applied. The figure which shows the structure of the pixel circuit of the organic electroluminescence display to which 1st Embodiment of the display apparatus of this invention is applied. The figure which shows the structure of the data drive circuit of the organic electroluminescent display apparatus to which 1st Embodiment of the display apparatus of this invention is applied. The timing chart for demonstrating the effect | action of the organic electroluminescence display to which 1st Embodiment of the display apparatus of this invention is applied. The figure for demonstrating the effect | action of the reset operation | movement of the organic electroluminescence display of the 1st Embodiment of this invention. The figure for demonstrating the effect | action of the threshold voltage detection operation | movement of the organic electroluminescence display of the 1st Embodiment of this invention. The figure for demonstrating the effect | action of the program operation | movement of the organic electroluminescence display of the 1st Embodiment of this invention. The figure for demonstrating the light emission operation | movement of the organic electroluminescence display of the 1st Embodiment of this invention. The figure which shows the modification of the organic electroluminescence display of the 1st Embodiment of this invention. The figure for demonstrating the threshold voltage detection operation | movement of the organic electroluminescence display shown in FIG. The figure which shows the structure of the data drive circuit of the organic electroluminescence display to which 2nd Embodiment of the display apparatus of this invention is applied. Timing chart for explaining the operation of the organic EL display device to which the second embodiment of the display device of the present invention is applied The figure which shows the modification of the data drive circuit of the organic electroluminescence display of the 2nd Embodiment of this invention. The figure which shows an example of the current characteristic of the drive transistor whose threshold voltage Vth is a negative voltage The figure which shows schematic structure of the organic electroluminescent display apparatus provided with the pixel circuit which has an organic electroluminescent element of an anode common type The figure which shows the other structure of a pixel circuit The figure which shows the other structure of a pixel circuit The figure which shows the structure of the conventional pixel circuit Timing chart for explaining the operation of a conventional organic EL display device The figure for demonstrating the effect | action of the reset operation | movement of the conventional organic electroluminescence display. The figure for demonstrating the effect | action of the threshold voltage detection operation | movement of the conventional organic electroluminescence display. The figure for demonstrating the effect | action of the program operation | movement of the conventional organic electroluminescence display. The figure for demonstrating the light emission operation | movement of the conventional organic electroluminescence display. The figure which shows the relationship between the drive current Id and gate-source voltage Vgs of a thin film transistor with a small subthreshold area | region current and a large transistor The figure which shows the relationship between the drive current (root) Id of a thin-film transistor with a small subthreshold area | region current, and a large transistor, and gate-source voltage Vgs. In a pixel circuit using a thin film transistor having a small sub-threshold region current as a driving transistor, the result of simulating the characteristics of Vgs of the driving transistor when the capacitance value Cd of the parasitic capacitance of the organic EL light emitting element is set to 2 pF and 4 pF. Illustration In a pixel circuit using a thin film transistor having a large sub-threshold region current as a driving transistor, the result of simulating the characteristics of Vgs of the driving transistor when the capacitance value Cd of the parasitic capacitance of the organic EL light emitting element is set to 2 pF and 4 pF. Illustration The figure which shows the structure which provided the correction capacity | capacitance element in the pixel circuit The figure which shows the relationship between the source voltage Vs of the transistor for a drive in the case of threshold voltage detection operation, and the light emission threshold voltage of an organic electroluminescent light emitting element.

Explanation of symbols

10 active matrix substrate 11 pixel circuit 11a organic EL light emitting element 11b driving transistor 11c capacitive element 11d selection transistor 11e threshold voltage detection transistor 12 data driving circuit 12a reset fixed voltage source 12b sample hold circuit 12c converter 12d subtractor 12e first 1 switch 12f second switch 13 scan drive circuit 14 data line 15 scan line 16 correction capacitive element 17 data drive circuit 17a fixed voltage source for reset 17b sample hold circuit 17c converter 17d first subtractor 17e second subtractor 17g adder 17h first switch 17i second switch 17k limiter circuit 18 switch control line 20 second scanning line 21 pixel circuit 21 driving transistor 21a organic EL light emitting element 21b driving Transistor 21c Capacitance element 21d Threshold voltage detection transistor 21e Selection transistor 21f Light emission operation transistor 22 Threshold voltage detection capacitance element 31 Pixel circuit 31a Organic EL light emission element 31b Drive transistor 31c Capacitance element 31d Threshold voltage detection transistor 31e Selection Transistor 31f Reset transistor 41 Pixel circuit 41a Organic EL light emitting element 41b Driving transistor 41c Capacitance element 41d Threshold voltage detection transistor 41e Selection transistor 50 Light emitting part 51 Parasitic capacitance 52 Light emitting part 53 Parasitic capacitance 54 Light emitting part 55 Parasitic capacitance 56 Light emission Part 57 parasitic capacitance 61 capacitive element

Claims (7)

A light emitting element, a driving transistor in which a source terminal is connected to an anode terminal of the light emitting element, and a driving current flows to the light emitting element, a capacitive element connected between a gate terminal and a source terminal of the driving transistor, and the driving A selection switch connected between the gate terminal of the transistor for driving and a voltage source for supplying a predetermined voltage, and a threshold connected between the source terminal of the driving transistor and a data line for supplying a predetermined signal A drive control method for a display device comprising an active matrix substrate in which a number of pixel circuits having voltage detection switches are arranged,
According to the threshold voltage of the driving transistor by detecting the voltage of the source terminal of the driving transistor when the parasitic capacitance of the light emitting element is charged by the current flowing through the driving transistor by supplying the predetermined voltage. Detected signal,
A data signal based on the detected signal corresponding to the threshold voltage and the driving voltage of the driving transistor corresponding to the light emission amount of the light emitting element is transmitted to the driving transistor via the data line and the threshold voltage detecting switch. A drive control method for a display device, wherein the output is output to a source terminal of the display device. A light emitting element, a driving transistor in which a source terminal is connected to an anode terminal of the light emitting element, and a driving current flows to the light emitting element, a capacitive element connected between a gate terminal and a source terminal of the driving transistor, and the driving A selection switch connected between the gate terminal of the transistor for driving and a voltage source for supplying a predetermined voltage, and a threshold connected between the source terminal of the driving transistor and a data line for supplying a predetermined signal An active matrix substrate having a plurality of pixel circuits having voltage detection switches and data lines provided for each column of the pixel circuits;
According to the threshold voltage of the driving transistor by detecting the voltage of the source terminal of the driving transistor when the parasitic capacitance of the light emitting element is charged by the current flowing through the driving transistor by supplying the predetermined voltage. A threshold value detection unit for detecting the received signal, a data signal based on the signal corresponding to the threshold voltage and the driving voltage of the driving transistor corresponding to the light emission amount of the light emitting element, the data line and the threshold voltage detecting switch. And a data driving circuit having a data signal output section for outputting to the source terminal of the driving transistor.   The threshold detection unit detects a source voltage of the driving transistor before a rise in the source voltage of the driving transistor is saturated by charging of the parasitic capacitance of the light emitting element. 2. The display device according to 2.   The display device according to claim 2, wherein a correction capacitor element for correcting a deviation in parasitic capacitance of the light emitting element is provided for each data line.   3. The data drive circuit further includes a reverse bias voltage output unit that supplies a reverse bias voltage having a magnitude corresponding to a drive voltage of the drive transistor to a gate terminal of the drive transistor. 5. The display device according to any one of 4 to 4.   6. The display device according to claim 5, wherein the driving transistor is a thin film transistor having a current characteristic with a negative threshold voltage.   The display device according to claim 2, wherein the driving transistor is a thin film transistor made of IGZO (InGaZnO).