JP2008015178A - Organic el display device and organic el drive method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently and rapidly approximate the current flowing through an organic EL element within each pixel. <P>SOLUTION: The organic EL display device includes a comparison amplification circuit 2 which applies a voltage to a gate electrode of a thin film transistor for current control within each pixel 21, a feedback circuit 5 which feeds back the voltage proportional to the current flowing in the organic EL element within each pixel 21 to the comparison amplification circuit 2, and a slew rate switching circuit 1 which switches the slew rate of the voltage that the comparison amplification circuit 2 applies to each pixel 21. The comparison amplification circuit 2 applies the voltage to each pixel 21 based on a target voltage (image signal voltage) and a voltage proportional to the current flowing in the organic EL element within each pixel 21 fed back from the feedback circuit 5. The slew rate switching circuit 1 switches the slew rate of the voltage that the comparison amplification circuit 2 applies to each pixel 21 based on a target voltage (image signal voltage) and a voltage proportional to the current flowing in the organic EL element within each pixel 21 fed back from the feedback circuit 5. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an organic EL display device that performs display by using self-luminous organic EL elements for pixels and arranges them in a matrix, and an organic EL driving method for driving the organic EL display device. In particular, the present invention relates to an organic EL display device having a function of suppressing luminance variations and luminance reduction caused by long-time light emission, and an organic EL driving method for driving the organic EL display device.

  A display device using an organic EL element has a feature that an LCD (Liquid Crystal Display) does not require a backlight because the organic EL element is a self-luminous element and is suitable for low power consumption. In addition, since it has characteristics of a high-speed response and a wide viewing angle, and since the element itself is solid, it has any advantages that can be applied to flexible applications.

  In general, the luminance of an organic EL element is proportional to the value of current flowing through the element regardless of the current-voltage characteristics of the element. Therefore, in order to suppress the luminance variation for each pixel, it is necessary not to make the voltage applied to the organic EL element of each pixel uniform, but to make the current flowing through the organic EL element of each pixel uniform. . Similarly, in order to suppress a decrease in luminance due to light emission for a long time, the voltage applied to the organic EL element of each pixel is not constant, but the current flowing through the organic EL element of each pixel is constant. It is necessary to.

  As shown in FIG. 13, conventionally, an organic EL display device driving circuit for driving a plurality of pixels 21 is connected to each pixel 21 and applies a voltage to a gate electrode of a current control thin film transistor in each pixel 21. A comparison amplifier circuit 2; a feedback circuit 5 that is connected to the comparison amplifier circuit 2 and each pixel 21, detects a current flowing through the organic EL element in each pixel 21, converts it to a voltage value, and feeds it back to the comparison amplifier circuit 2; It has. Each pixel 21 is connected to a scanning signal generation circuit 22, and the scanning signal generation circuit 22 switches the pixel 21 to which a voltage is applied by the comparison amplification circuit 2.

  Such a comparison amplifier circuit 2 is configured so that each pixel is based on a target voltage (image signal voltage) and a voltage (feedback voltage) proportional to the current flowing through the organic EL element in each pixel 21 fed back from the feedback circuit. A voltage is applied to the gate electrode of the current control thin film transistor 21.

  However, according to the organic EL display device drive circuit as shown in FIG. 13, a phenomenon occurs in which the feedback voltage vibrates as shown in FIG. Since the feedback voltage is proportional to the current flowing through the organic EL element in each pixel 21, this phenomenon indicates that the current flowing through the organic EL element in each pixel 21 vibrates. When this vibration occurs, it becomes difficult to set the current flowing through the organic EL element to a target current value within a predetermined pixel selection time, so that each pixel 21 emits light with the luminance specified by the image signal. It becomes difficult to make.

  The cause of such a vibration phenomenon is that the slew rate of the output voltage of the general comparison amplifier circuit 2 is large, so that the voltage change per unit time of the output voltage of the comparison amplifier circuit 2 is the unit of the feedback voltage described above. It is that it is larger than the voltage change per hour.

  The present invention has been made in consideration of such points, and provides an organic EL display device capable of efficiently and quickly bringing a current flowing through an organic EL element in each pixel close to a target current. For the purpose.

  The present invention is an organic EL display device in which a plurality of pixels are arranged in a matrix, a pixel is selected from the plurality of pixels according to a scanning signal, and the selected pixel is caused to emit light according to an image signal. A comparison amplifier circuit that is connected to the pixel and applies a voltage to each pixel, and a feedback circuit that is connected to the comparison amplifier circuit and each pixel and feeds back a voltage proportional to the current flowing through the organic EL element in each pixel to the comparison amplifier circuit And a slew rate switching circuit that is connected to the feedback circuit and the comparison amplification circuit, and the comparison amplification circuit switches the slew rate of the voltage applied to each pixel, and each pixel includes an organic EL element that is a light emitting element, and the organic A current control thin film transistor for controlling the current flowing through the EL element, and application / non-application of the output voltage of the comparison amplifier circuit according to the scanning signal A first pixel selecting thin film transistor that switches between, a second pixel selecting thin film transistor that switches transmission / non-transmission of a current flowing from a feedback circuit to the organic EL element according to the scanning signal, and a power source according to an inverted signal of the scanning signal A third pixel selecting thin film transistor for switching transmission / non-transmission of a current flowing to the organic EL element, and a voltage holding capacitor for holding the output voltage of the comparison amplifier circuit applied via the first pixel selecting thin film transistor The comparison amplifier circuit is connected to the gate electrode of the current control thin film transistor in each pixel based on the target voltage and the voltage proportional to the current flowing through the organic EL element in each pixel fed back from the feedback circuit. The voltage is applied and the slew rate switching circuit An organic EL display device, wherein the comparison amplifier circuit switches a slew rate of a voltage applied to each pixel based on a voltage proportional to a current flowing through an organic EL element in each pixel fed back from a back circuit. is there.

  With such a configuration, the current flowing through the organic EL element in each pixel can be brought close to the target current efficiently and quickly.

  In the present invention, when the slew rate switching circuit has a difference between a voltage value proportional to a current flowing through the organic EL element in each pixel fed back from the feedback circuit and a target voltage value within a predetermined value, An organic EL display device characterized in that a slew rate of a voltage applied to each pixel is lowered by a comparison amplifier circuit.

  With such a configuration, the current flowing through the organic EL element in each pixel can be brought close to the target current efficiently and quickly.

  The present invention is an organic EL display device in which a slew rate switching circuit switches a slew rate of a voltage applied to each pixel by changing an output current of the comparison amplifier circuit.

  In the present invention, when the difference between the voltage value proportional to the current flowing through the organic EL element in each pixel fed back from the feedback circuit and the target voltage value is within a predetermined value, An organic EL display device having an auxiliary constant current source for stopping the supply of.

  The present invention is an organic EL display device in which a slew rate switching circuit switches a slew rate of a voltage applied to each pixel by changing a phase compensation capacitance of the comparison amplifier circuit.

  In the present invention, the comparison amplifier circuit performs comparison when the difference between the voltage value proportional to the current flowing through the organic EL element in each pixel fed back from the feedback circuit and the target voltage value is within a predetermined value. An organic EL display device having an auxiliary capacitor for increasing a phase compensation capacity of an amplifier circuit.

  The present invention is the organic EL display device in which the feedback circuit includes a current mirror circuit and a resistor.

  In the present invention, a target voltage input unit for inputting a target voltage is connected to the comparison amplifier circuit and the slew rate switching circuit, and the slew rate switching circuit is connected to the pair of comparators connected to the feedback circuit and the pair of comparators. A first power source having a positive electrode disposed on one comparator side between the target voltage input unit and one comparator, and the target voltage input unit and the other A second power source in which a negative electrode is disposed on the other comparator side is provided between the comparator and the organic EL display device.

  The present invention is the organic EL display device characterized in that the voltage of the first power source input to one comparator is equal to the voltage of the second power source input to the other comparator.

  In the organic EL driving method for driving the organic EL display device described above, the voltage applying step of applying a voltage to the gate electrode of the current control thin film transistor in each pixel by the comparison amplifier circuit connected to the pixel; A feedback step of feeding back a voltage proportional to a current flowing through the organic EL element in each pixel via a feedback circuit to a comparison amplification circuit connected to the pixel, and a slew rate switching circuit connected to the comparison amplification circuit; Slew rate switching that switches the slew rate of the voltage that the comparison amplifier circuit applies to the pixel by the slew rate switching circuit based on the voltage proportional to the current flowing through the organic EL element in each pixel fed back by the process and the target voltage The voltage applied to the pixel at the switched slew rate by the process and the comparison amplifier circuit An organic EL driving method characterized by comprising a, a switching voltage applying step of applying.

  With such a configuration, the current flowing through the organic EL element in each pixel can be brought close to the target current efficiently and quickly.

  According to the present invention, the voltage applied to each pixel by the comparison amplification circuit based on the target voltage (image signal voltage) and the voltage proportional to the current flowing through the organic EL element in each pixel fed back from the feedback circuit. By using a slew rate switching circuit for switching the slew rate, the current flowing through the organic EL element in each pixel can be brought close to the target current efficiently and quickly.

First Embodiment Hereinafter, a first embodiment of an organic EL display device according to the present invention will be described with reference to the drawings. Here, FIG. 1 to FIG. 9 are diagrams showing a first embodiment of the present invention.

  As shown in FIG. 1, the present invention is an organic EL display device that performs display by arranging a plurality of pixels 21 in a matrix.

  Each of such pixels 21 is connected to a scanning signal generation circuit 22 as shown in FIGS. 1 to 3, and a specific pixel 21 is selected from the plurality of pixels 21 in accordance with the scanning signal from the scanning signal generation circuit 22. Is selected, and the selected pixel 21 is caused to emit light according to the image signal.

  As shown in FIG. 10, each pixel 21 includes an organic EL element OLED that is a light emitting element, a current control thin film transistor T that controls a current flowing through the organic EL element OLED, and a scanning signal from the scanning signal generation circuit 22. In accordance with the first pixel selection thin film transistor T1 for switching application / non-application of the output voltage of the comparison amplifier circuit 2 described later and the scanning signal from the scanning signal generating circuit 22, the feedback circuit 5 described later flows from the feedback circuit 5 to the organic EL element. A second pixel selection thin-film transistor T2 that switches between transmission and non-transmission of current, and a third that switches transmission / non-transmission of current flowing from the power supply VDD to the organic EL element OLED according to the inverted signal of the scanning signal from the scanning signal generation circuit 22 Through the pixel selecting thin film transistor T3 and the first pixel selecting thin film transistor T1. It consists a voltage holding capacitor CS which holds the applied output voltage of the comparator amplifier circuit 2.

  As shown in FIG. 1, the organic EL display device is connected to a target voltage input unit 9 for inputting a target voltage (image signal voltage), each pixel 21, and the target voltage input unit 9. A comparison amplifier circuit 2 that applies a voltage to the gate electrode of the current control thin film transistor T, and a comparison amplifier circuit that is connected to the comparison amplifier circuit 2 and each pixel 21 and that is proportional to the current flowing through the organic EL element in each pixel 21. 2 is connected to a feedback circuit 5 having a current mirror circuit 6 using a PNP transistor 6p that feeds back to 2, a target voltage input unit 9, a current mirror circuit 6 and a comparison amplification circuit 2, and the comparison amplification circuit 2 is applied to each pixel 21. And a slew rate switching circuit 1 for switching the slew rate of the voltage to be transmitted. The feedback circuit 5 includes a current mirror circuit 6 and a resistor 6r. In such a configuration, a current flows from the current mirror circuit 6 toward the pixel 21.

  Among these, the comparison amplifier circuit 2 includes a target voltage (image signal voltage) and a voltage (feedback voltage) proportional to the current flowing through the organic EL element in each pixel 21 fed back from the current mirror circuit 6 in FIG. Based on the above, a voltage is applied to the gate electrode of the current controlling thin film transistor T in each pixel 21 so that the current flowing through the organic EL element in each pixel 21 approaches the target current (see FIG. 10).

  As shown in FIG. 2, the slew rate switching circuit 1 includes a pair of comparators 11 and 12 connected to the current mirror circuit 6 and an OR circuit 13 connected to the pair of comparators 11 and 12. ing. Further, as shown in FIG. 2, a first power supply 16 having a positive electrode disposed on one comparator 11 side is provided between the target voltage input unit 9 and one comparator 11, and the target voltage input unit 9 And the other comparator 12 is provided with a second power source 17 in which a negative electrode is disposed on the other comparator 12 side. Note that the voltage α of the first power supply 16 input to one comparator 11 is equal to the voltage α of the second power supply 17 input to the other comparator 12.

  Such a slew rate switching circuit 1 has a target voltage (image signal voltage) and a voltage (feedback voltage) proportional to the current flowing through the organic EL elements in each pixel 21 fed back from the current mirror circuit 6 in FIG. Based on the above, the slew rate of the voltage applied to each pixel 21 by the comparison amplifier circuit 2 is switched. That is, the slew rate switching circuit 1 has a voltage (feedback voltage) value proportional to a current flowing through the organic EL element in each pixel 21 fed back from the current mirror circuit 6 and a target voltage (image signal voltage) value. When the difference is within the predetermined value α (see FIG. 5), the auxiliary constant current source 35 of the comparison amplifier circuit 2 stops supplying current, thereby reducing the slew rate of the voltage applied to each pixel 21. (Slow down).

  Specifically, as shown in FIGS. 3 and 4, the comparison amplifier circuit 2 is a voltage (feedback voltage) value proportional to the current flowing through the organic EL element in each pixel 21 fed back from the current mirror circuit 6. And the target voltage (image signal voltage) value is within a predetermined value α, the switch 44 is turned off to have an auxiliary constant current source 35 that stops the supply of current.

  The slew rate switching circuit 1 turns on the switch 44 of the comparison amplifier circuit 2 to supply current to the auxiliary constant current source 35, or turns off the switch 44 to stop the current from the auxiliary constant current source 35. Thus, the output current of the comparison amplification circuit 2 is changed, and the slew rate of the voltage applied to each pixel 21 by the comparison amplification circuit 2 is switched.

  As shown in FIG. 4, the comparison amplifier circuit 2 is connected to the power supply VCC, connected to the current mirror circuit 36 using the PNP transistor 36p, the current mirror circuit 36, and the + terminal 51 (FIG. 1). The NPN transistor 38n connected to the current mirror circuit 36 and the NPN transistor 37n connected to the negative terminal 52 (see FIGS. 1, 2 and 3) have.

  Also, as shown in FIG. 4, a PNP transistor 41p is connected to the power supply VCC. The PNP transistor 41p includes an NPN transistor 38n connected to the + terminal 51, an output unit 49, a capacitor 42 (capacitance C) connected to the output unit 49, and a second constant connected to the ground VSS. A current source 32 is connected. Note that a capacitor and an output unit 49 are connected to the second constant current source 32. The output unit 49 is connected to each pixel 21 (see FIGS. 1 to 3).

  As shown in FIGS. 1 to 3, the + terminal 51 is connected to the target voltage input unit 9, and the − terminal 52 is connected to the current mirror circuit 6.

  As shown in FIG. 4, the NPN transistor 38n connected to the + terminal 51 and the NPN transistor 37n connected to the-terminal 52 are connected to the first constant current source 31 connected to the ground VSS and the ground VSS. In addition to being connected, the switch 44 is connected to an auxiliary constant current source 35 that can be turned ON / OFF freely.

  Further, as shown in FIGS. 1 to 3, each pixel 21 is connected to a scanning signal generation circuit 22. The scanning signal generation circuit 22 switches the pixel 21 to which a voltage is applied by the comparison amplification circuit 2.

  Next, the operation of the present embodiment having such a configuration will be described.

  First, a method for deriving the slew rate will be described with reference to FIG. 7 showing a general comparison amplifier circuit 2. The comparison amplifier circuit 2 shown in FIG. 7 has substantially the same configuration as the comparison amplifier circuit 2 in the present embodiment shown in FIG. 4 except that the second constant current source 32 is not provided. In the following, the case where the voltage Vbe + input from the + terminal 51 is higher than the voltage Vbe− input from the − terminal 52 will be described with reference to FIG. 7.

When the voltage Vbe + input from the + terminal 51 becomes larger than the voltage Vbe− input from the − terminal 52, the voltage Vbe + in the NPN transistor 38 n connected to the + terminal 51 is changed in the NPN transistor 37 n connected to the − terminal 52. Most of the current I 1 that is greater than the voltage Vbe− and flows by the first constant current source 31 is supplied from the capacitor 42. The current from the capacitor 42 continues to flow until Vbe + = Vbe−. During this time, the charge ΔQ that changes in the capacitor 42 is
ΔQ = C · ΔV = I1 · t (Formula 1)
It is indicated. Here, C indicates the capacitance of the capacitor 42, t indicates the time required until Vbe + = Vbe−, and ΔV indicates the voltage that changes in the capacitor 42 until Vbe + = Vbe−. . From (Equation 1) described above, the slew rate (hereinafter, the value of the slew rate is indicated as SR) is:
SR = ΔQ / (C · t) = ΔV / t = I1 / C (Formula 2)
It is indicated.

Therefore, the slew rate in the comparison amplifier circuit 2 of the present embodiment shown in FIG. 4 is as follows when the switch 44 connected to the auxiliary constant current source 35 is included.
SR = (I1 + I3) / C (Formula 3)
When the switch 44 connected to the auxiliary constant current source 35 is not turned on,
SR = I1 / C (Formula 2)
It becomes.

  Next, the function and effect of the organic EL display device according to this embodiment will be described.

  First, the comparison amplifying circuit 2 connected to the pixel 21 includes the target voltage (image signal voltage) input from the target voltage input unit 9 and the organic in each pixel 21 fed back from the current mirror circuit 6 as described later. Based on the voltage proportional to the current flowing through the EL element, a voltage is applied to the gate electrode of the current control thin film transistor in each pixel 21 (voltage application step 81) (see FIGS. 3 and 8). At this time, the switch 44 connected to the auxiliary constant current source 35 of the comparison amplifier circuit 2 is turned on, and the slew rate value SR in the comparison amplifier circuit 2 is SR = (I1 + I3) / C (Equation 3). (See FIG. 4).

  Next, the voltage value proportional to the current flowing through the organic EL element in each pixel 21 is connected to the comparison amplification circuit 2 connected to the pixel 21 and the comparison amplification circuit 2 via the current mirror circuit 6. Feedback is provided to the slew rate switching circuit 1 (feedback step 82) (see FIGS. 3 and 8).

  Next, the slew rate switching circuit 1 determines that the difference between the value of the voltage (feedback voltage) proportional to the current flowing through the organic EL element in each pixel 21 and the value of the target voltage (image signal voltage) is a predetermined value. It is determined whether or not the value α is within the range (decision step 85) (see FIGS. 3, 5, and 8).

  Specifically, as shown in FIG. 2, a current mirror circuit 6 is connected to one comparator 11, and a positive electrode is disposed between the comparator 11 and the target voltage input unit 9. Since the first power supply 16 having the voltage α (V) is provided, one comparator 11 has a voltage (feedback voltage) value proportional to the current flowing through the organic EL element in the pixel 21 and a target voltage ( A value (target voltage + α) obtained by adding a predetermined value α to (image signal voltage) is input.

  On the other hand, as shown in FIG. 2, a current mirror circuit 6 is connected to the other comparator 12, and a voltage α is arranged between the target voltage input unit 9 and a negative electrode on the other comparator 12 side. Since the second power source 17 of (V) is provided, the other comparator 12 has a voltage (feedback voltage) value proportional to the current flowing through the organic EL element in the pixel 21 and a target voltage (image signal voltage). ) Minus a predetermined value α (target voltage −α) is input.

  As shown in FIG. 2, since the pair of comparators 11 and 12 are connected to the OR circuit 13, the OR circuit 13 is proportional to the current flowing through the organic EL element in the pixel 21 fed back. It can be determined whether or not the difference between the value of the voltage (feedback voltage) and the value of the target voltage (image signal voltage) is within the range of the predetermined value α.

  In such a determination step 85, the OR circuit 13 of the slew rate switching circuit 1 is fed back with a voltage (feedback voltage) value proportional to the current flowing through the organic EL element in the pixel 21 and a target voltage (image signal voltage). The voltage application step 81, the feedback step 82, and the determination step 85 are sequentially performed until it is determined that the difference from the value is within the range of the predetermined value α (see FIGS. 5 and 8).

  In the determination step 85, the OR circuit 13 of the slew rate switching circuit 1 sets the value of the voltage (feedback voltage) and the target voltage (image signal voltage) proportional to the current flowing back through the organic EL element in the pixel 21. If it is determined that the difference from the value is within the range of the predetermined value α, the comparison amplifier circuit 2 switches the slew rate of the voltage applied to the pixel 21 based on the signal from the OR circuit 13 (slew rate switching step). 90) (See FIGS. 2 and 8).

  Specifically, the switch 44 connected to the auxiliary constant current source 35 of the comparison amplifier circuit 2 is turned off and the supply of current from the auxiliary constant current source 35 is stopped, so that SR = (I1 + I3) / C (Equation 3 The slew rate was changed to SR = I1 / C (formula 2) and slowed down (see FIGS. 3, 4, 6 and 8).

  Next, the comparison amplifier circuit 2 feeds back the target voltage input from the target voltage input unit 9 and the current mirror circuit 6 as described later at the slew rate (SR = I1 / C) thus slowed down. Based on the voltage proportional to the current flowing through the organic EL element in each pixel 21, a voltage is applied to each pixel 21 so that the current flowing through the organic EL element in each pixel 21 approaches the target current value (low speed). Voltage application step (switching voltage application step) 91) (see FIGS. 3, 6 and 8).

  Next, a voltage value proportional to the current flowing through the organic EL element in the pixel 21 due to the slowed slew rate (SR = I1 / C) is compared with the pixel 21 via the current mirror circuit 6. Feedback is provided to the circuit 2 and the slew rate switching circuit 1 connected to the comparison amplifier circuit 2 (low-speed feedback step (switching feedback step) 92) (see FIGS. 3, 6, and 8).

  Thereafter, the above-described low-speed voltage application step 91 and low-speed feedback step 92 are repeated until the current flowing through the organic EL elements in each pixel 21 reaches the target current value (see FIGS. 3 and 8).

  Thus, the comparison amplifier circuit 2 is fed back from the target voltage (image signal voltage) input from the target voltage input unit 9 and the current mirror circuit 6 at a slow slew rate (SR = I1 / C). Based on a voltage (feedback voltage) proportional to the current flowing through the organic EL element in each pixel 21, a voltage is applied to each pixel 21 so that the current flowing through the organic EL element in each pixel 21 approaches the target current value. To do. For this reason, the current flowing through the organic EL element in each pixel 21 can be brought close to the target current efficiently and quickly.

  In the above-described embodiment, the current mirror circuit 6 having the PNP transistor 6p is used for the feedback circuit 5. However, the present invention is not limited to this, and as shown in FIG. A current mirror circuit 6a having a transistor 6n may be used. At this time, the current flows in the opposite direction to the case where the current mirror circuit 6 having the PNP transistor 6p is used, that is, from the pixel 21 side toward the current mirror circuit 6a.

Second Embodiment Next, a second embodiment of the present invention will be described with reference to FIGS. In the second embodiment shown in FIG. 11 and FIG. 12, instead of changing the output current of the comparison amplifier circuit 2, the comparison amplifier circuit 2 changes the phase compensation capacitance of the comparison amplifier circuit 2, so that the comparison amplifier circuit 2 changes the pixel 21. The slew rate of the voltage applied to is switched.

  That is, the difference between the value of the voltage (feedback voltage) proportional to the current flowing through the organic EL element in each pixel 21 fed back from the current mirror circuit 6 and the value of the target voltage (image signal voltage) is within a predetermined value α. In this case, instead of using the comparison amplifier circuit 2 having the auxiliary constant current source 35 for stopping the supply of current (see FIG. 3), each pixel 21 fed back from the current mirror circuit 6 as shown in FIG. Auxiliary capacitor that increases the phase compensation capacity when the difference between the value of the voltage (feedback voltage) proportional to the current flowing through the organic EL element and the value of the target voltage (image signal voltage) is within a predetermined value α. The comparison amplifier circuit 2 having 45 is used.

  Other configurations are substantially the same as those of the first embodiment shown in FIGS. Also, in the second embodiment shown in FIGS. 11 and 12, the same parts as those in the first embodiment shown in FIGS. 1 to 8 are denoted by the same reference numerals, and detailed description thereof is omitted.

  Specifically, as shown in FIG. 12, the comparison amplifier circuit 2 is connected to the power supply VCC, connected to the current mirror circuit 36 using the PNP transistor 36p, the current mirror circuit 36, and the + terminal 51. And an NPN transistor 37n connected to the current mirror circuit 36 and connected to the negative terminal 52.

  Also, as shown in FIG. 12, a PNP transistor 41p is connected to the power supply VCC. The PNP transistor 41p is connected to the NPN transistor 38n connected to the + terminal 51, the output unit 49, the first capacitor 48 (capacitance C1) connected to the output unit 49, and the output unit 49. The auxiliary capacitor 45 (capacitance C2) that can be turned on and off by the switch 46 is connected to the second constant current source 32 connected to the ground VSS. The second constant current source 32 is connected to a first capacitor 48 (capacitance C1), an auxiliary capacitor 45 (capacitance C2) that can be turned ON / OFF by a switch 46, and an output unit 49. The output unit 49 is connected to each pixel 21 (see FIG. 11).

  Further, as shown in FIG. 11, the + terminal 51 is connected to the target voltage input unit 9, and the − terminal 52 is connected to the current mirror circuit 6.

  Further, as shown in FIG. 12, the NPN transistor 38n connected to the + terminal 51 and the NPN transistor 37n connected to the − terminal 52 are connected to the first constant current source 31 connected to the ground VSS. .

The slew rate in the comparison amplifier circuit 2 of the present embodiment shown in FIG. 12 is as follows when the switch 46 connected to the auxiliary capacitor 45 is not turned on.
SR = I1 / C1 (Formula 4)
When the switch 46 connected to the auxiliary capacitor 45 is turned on,
SR = I1 / (C1 + C2) (Formula 5)
It becomes.

  Next, the function and effect of the organic EL display device according to this embodiment will be described.

  First, the comparison amplification circuit 2 connected to the pixel 21 includes the target voltage (image signal voltage) input from the target voltage input unit 9 and the organic EL in the pixel 21 fed back from the current mirror circuit 6 as described later. Based on the voltage proportional to the current flowing through the element, a voltage is applied to the gate electrode of the current control thin film transistor in the pixel 21 (voltage application step 81) (see FIGS. 8 and 11). At this time, the switch 46 connected to the auxiliary capacitor 45 of the comparison amplifier circuit 2 is not included, and the slew rate value SR in the comparison amplifier circuit 2 is SR = I1 / C1 (Equation 4). (See FIG. 12).

  Next, a voltage (feedback voltage) value proportional to the current flowing through the organic EL element in the pixel 21 is applied to the comparison amplification circuit 2 connected to the pixel 21 via the current mirror circuit 6 and the comparison amplification circuit 2. Feedback is provided to the connected slew rate switching circuit 1 (feedback step 82) (see FIGS. 8 and 11).

  Next, in the slew rate switching circuit 1, the difference between the value of the voltage (feedback voltage) proportional to the current flowing through the organic EL element in the pixel 21 and the value of the target voltage (image signal voltage) is a predetermined value. It is determined whether it is within the range of α (determination step 85) (see FIGS. 5, 8, and 11).

  In such a determination step 85, the OR circuit 13 of the slew rate switching circuit 1 is fed back with a voltage (feedback voltage) value proportional to the current flowing through the organic EL element in the pixel 21 and a target voltage (image signal voltage). The voltage application step 81, the feedback step 82, and the determination step 85 are sequentially performed until it is determined that the difference from the value is within the range of the predetermined value α (see FIGS. 5 and 8).

  In the determination step 85, the OR circuit 13 of the slew rate switching circuit 1 sets the value of the voltage (feedback voltage) and the target voltage (image signal voltage) proportional to the current flowing back through the organic EL element in the pixel 21. When it is determined that the difference from the value is within the range of the predetermined value α, the slew rate of the voltage applied to the pixel 21 by the comparative amplifier circuit 2 is switched based on the signal from the OR circuit 13 (slew rate switching step 90 (See FIGS. 2, 6, 8, and 11).

  Specifically, by turning on the switch 46 connected to the auxiliary capacitor 45 of the comparison amplifier circuit 2 and increasing the phase compensation capacity, the slew rate of SR = I1 / C1 (Equation 4) is changed to SR = Switch to I1 / (C1 + C2) (formula 5) and slow down (see FIGS. 6, 8, 11, and 12).

  Next, the comparison amplifier circuit 2 uses the target voltage (image signal voltage) input from the target voltage input unit 9 at the slew rate (SR = I1 / (C1 + C2)) thus slow, as described later. Based on the voltage proportional to the current flowing through the organic EL element in each pixel 21 fed back from the current mirror circuit 6, the current flowing through the organic EL element in each pixel 21 is brought close to the target current value. Is applied (low-speed voltage applying step (switching voltage applying step) 91) (see FIGS. 6, 8, and 11).

  Next, the voltage value proportional to the current flowing through the organic EL element in the pixel 21 is compared with the comparison amplification circuit 2 connected to the pixel 21 and the through voltage connected to the comparison amplification circuit 2 via the current mirror circuit 6. Feedback is made to the rate switching circuit 1 (low speed feedback step (switching feedback step) 92) (see FIGS. 8 and 11).

  Thereafter, the above-described low-speed voltage application step 91 and low-speed feedback step 92 are repeatedly performed until the current flowing through the organic EL elements in each pixel 21 reaches the target current (see FIG. 11).

  In this way, the comparison amplifier circuit 2 is fed back from the feedback circuit 5 with the target voltage (image signal voltage) input from the target voltage input unit 9 at a slow slew rate (SR = I1 / (C1 + C2)). Based on a voltage (feedback voltage) proportional to the current flowing through the organic EL element in each pixel 21, a voltage is applied to each pixel 21 so that the current flowing through the organic EL element in each pixel 21 approaches the target current. To do. For this reason, the current flowing through the organic EL element in each pixel 21 can be brought close to the target current efficiently and quickly.

1 is a configuration diagram showing a first embodiment of an organic EL display device according to the present invention. FIG. The block diagram which shows concretely the slew rate switching circuit in 1st Embodiment of the organic electroluminescent display apparatus by this invention. The block diagram which shows that the output current of a comparison amplifier circuit can change in 1st Embodiment of the organic electroluminescent display apparatus by this invention. 1 is a configuration diagram specifically showing a comparison amplifier circuit in a first embodiment of an organic EL display device according to the present invention. FIG. Schematic which shows the case where a slew rate is switched in 1st Embodiment of the organic electroluminescent display apparatus by this invention using the relationship between a feedback voltage and a target voltage. The graph which showed the relationship between the voltage applied to a pixel, and time in 1st Embodiment of the organic electroluminescent display apparatus by this invention. The block diagram which shows a general comparison amplifier circuit concretely. The flowchart which shows the organic EL drive method in the 1st Embodiment of this invention. The block diagram which shows the modification of 1st Embodiment of the organic electroluminescent display apparatus by this invention. FIG. 3 is a circuit diagram of a pixel in the first embodiment of the present invention. The block diagram which shows that the phase compensation capacity | capacitance of a comparison amplifier circuit can change in 2nd Embodiment of the organic electroluminescent display apparatus by this invention. The block diagram which shows concretely a comparison amplifier circuit in 2nd Embodiment of the organic electroluminescent display apparatus by this invention. The block diagram which shows the conventional organic electroluminescence display. The graph which showed the relationship between the voltage applied to a pixel, and time in the conventional organic EL display apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Slew rate switching circuit 2 Comparison amplification circuit 5 Feedback circuit 6 Current mirror circuit 6r Resistance 9 Target voltage input part 11 One comparator 12 The other comparator 13 OR circuit 16 First power supply 17 Second power supply 21 Pixel 35 Auxiliary constant current source 45 Auxiliary capacitor 81 Voltage application process 82 Feedback process 85 Judgment process 90 Slew rate switching process 91 Low-speed voltage application process (switching voltage application process)
92 Low speed feedback process (switching feedback process)
CS voltage holding capacitor T current control thin film transistor T1 first pixel selection thin film transistor T2 second pixel selection thin film transistor T3 third pixel selection thin film transistor

Claims (10)

An organic EL display device in which a plurality of pixels are arranged in a matrix, a pixel is selected according to a scanning signal from the plurality of pixels, and the selected pixel is caused to emit light according to an image signal,
A comparison amplifier circuit connected to each pixel and applying a voltage to each pixel;
A feedback circuit that is connected to the comparison amplification circuit and each pixel and feeds back a voltage proportional to the current flowing through the organic EL element in each pixel to the comparison amplification circuit;
A slew rate switching circuit connected to the feedback circuit and the comparison amplification circuit, the comparison amplification circuit switching a slew rate of a voltage applied to each pixel;
Each pixel includes an organic EL element that is a light emitting element, a current control thin film transistor that controls a current flowing through the organic EL element, and a first pixel that switches application / non-application of the output voltage of the comparison amplifier circuit according to the scanning signal. A thin film transistor for selection, a second thin film transistor for pixel selection for switching transmission / non-transmission of a current flowing from a feedback circuit to the organic EL element according to the scanning signal, and a flow from a power source to the organic EL element according to an inverted signal of the scanning signal A third pixel selecting thin film transistor that switches between transmission and non-transmission of current, and a voltage holding capacitor that holds the output voltage of the comparison amplifier circuit applied through the first pixel selecting thin film transistor,
The comparison amplifier circuit applies a voltage to the gate electrode of the current control thin film transistor in each pixel based on the target voltage and the voltage proportional to the current flowing through the organic EL element in each pixel fed back from the feedback circuit. ,
The slew rate switching circuit switches the slew rate of the voltage applied to each pixel by the comparison amplifier circuit based on the target voltage and the voltage proportional to the current flowing through the organic EL element in each pixel fed back from the feedback circuit. An organic EL display device characterized by that.   When the difference between the voltage value proportional to the current flowing through the organic EL element in each pixel fed back from the feedback circuit and the target voltage value is within a predetermined value, the slew rate switching circuit 2. The organic EL display device according to claim 1, wherein a slew rate of a voltage applied to each pixel is lowered.   2. The organic EL display device according to claim 1, wherein the slew rate switching circuit switches a slew rate of a voltage applied to each pixel by the comparison amplification circuit by changing an output current of the comparison amplification circuit.   The comparison amplifier circuit stops the supply of current when the difference between the voltage value proportional to the current flowing through the organic EL element in each pixel fed back from the feedback circuit and the target voltage value is within a predetermined value. 4. The organic EL display device according to claim 3, further comprising an auxiliary constant current source for performing the operation.   2. The organic EL display device according to claim 1, wherein the slew rate switching circuit switches a slew rate of a voltage applied to each pixel by the comparison amplification circuit by changing a phase compensation capacitance of the comparison amplification circuit.   When the difference between the voltage value proportional to the current flowing through the organic EL element in each pixel fed back from the feedback circuit and the target voltage value is within a predetermined value, the comparison amplifier circuit 6. The organic EL display device according to claim 5, further comprising an auxiliary capacitor for increasing a compensation capacity.   2. The organic EL display device according to claim 1, wherein the feedback circuit includes a current mirror circuit and a resistor. A target voltage input unit for inputting a target voltage is connected to the comparison amplifier circuit and the slew rate switching circuit,
The slew rate switching circuit has a pair of comparators connected to the feedback circuit, and an OR circuit connected to the pair of comparators,
Between the target voltage input unit and one comparator, a first power source in which a positive electrode is disposed on one comparator side is provided,
2. The organic EL display device according to claim 1, wherein a second power source having a negative electrode disposed on the other comparator side is provided between the target voltage input unit and the other comparator.   9. The organic EL display device according to claim 8, wherein the voltage of the first power source input to one comparator is equal to the voltage of the second power source input to the other comparator. An organic EL driving method for driving the organic EL display device according to claim 1,
A voltage application step of applying a voltage to the gate electrode of the current control thin film transistor in the pixel by a comparison amplifier circuit connected to the pixel;
A feedback step of feeding back a voltage proportional to the current flowing through the organic EL element in the pixel via the feedback circuit to the comparison amplification circuit connected to the pixel and the slew rate switching circuit connected to the comparison amplification circuit;
Slew rate switching that switches the slew rate of the voltage that the comparison amplifier circuit applies to the pixel by the slew rate switching circuit based on the voltage proportional to the current flowing through the organic EL element in the pixel fed back by the feedback process and the target voltage Process,
A switching voltage application step of applying a voltage to the pixel at a switched slew rate by a comparison amplifier circuit;
An organic EL driving method comprising:

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