JPH11265166A - Driving circuit for electroluminescent display device - Google Patents

Abstract

(57) [Problem] To provide a driving circuit of an EL display device capable of displaying a high-contrast image and displaying an image with a clear outline of the image. SOLUTION: A video signal supplied from a video signal line D is inputted to a power supply potential modulation circuit 60, and a modulated power supply potential generated by the video signal is supplied to a video signal line D and a scanning signal line G.
Is supplied to the drain electrode 22 of the second thin film transistor 20 in which the gate electrode 21 is connected to the source electrode 13 of the first thin film transistor 10 connected to the organic EL element 30 connected to the drain electrode 22. The light is supplied to the organic EL element 30 to cause the organic EL element 30 to emit light.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electroluminescence (hereinafter referred to as "EL") element and a thin film transistor.
sistor: Hereinafter, referred to as “TFT”. ), A driving circuit for an EL display device.

[0002]

2. Description of the Related Art In recent years, display devices using EL elements have been
T (Cathode Ray Tube) and LCD (Liquid Crystal Dis
Play) has attracted attention as a display device that can replace it. Also,
TF as a switching element for driving the EL element
An EL display device equipped with T has also been researched and developed.

FIG. 5 shows a circuit diagram of an organic EL display device provided with an organic EL element and a TFT. The figure shows the first TF
T110, second TFT 120, and organic EL element 130
It is a circuit diagram of an organic EL display device comprising: The scanning signal line G for supplying the scanning signal and the video signal line D for supplying the video signal are orthogonal to each other, and the organic EL element 130 and the driving of the organic EL element 130 are provided near the intersection of the two signal lines G and D. TFTs 110 and 120 are provided.

First, a first TFT 110 is connected to a scanning signal line G and supplied with a gate electrode 1 to which a scanning signal is supplied.
11, a drain electrode 112 connected to the video signal line D and supplied with a video signal, and a source electrode 113 connected to the gate electrode 121 of the second TFT 120. Next, the second TFT 120 is connected to the first TFT 1
Gate electrode 1 connected to ten source electrodes 113
21, a source electrode 123 connected to the anode 131 of the organic EL element 130, and a drain electrode 122 connected to a driving power supply 140 for supplying a current to the organic EL element 130.

The organic EL element 130 is provided with a second TF
An anode 131 connected to the source electrode 121 of T120,
Cathode 132 and anode 13 connected to pixel electrode 150
1 and a light emitting element layer 133 sandwiched between the cathode 132. When a scanning signal is supplied from the scanning signal line G to the gate electrode 111, the first TFT 110 is turned on, the potential supplied from the video signal line D is supplied to the gate electrode 121, and the second TFT 120 is turned on. Become. Therefore, a current flows from the driving power supply 140 to the organic EL element 130, and the organic EL element 130 emits light.

[0006]

However, the conventional EL
As shown in FIG. 6, the potential supplied from the drive power supply to the element is a constant potential (DC voltage) VC.
Even when the video signal VD (> VC) is input, for example, in the case of a video signal indicated by a dotted line in the drawing that has a potential higher than the voltage VC, a current equal to or higher than the current value corresponding to the potential can be supplied to the EL element. Can not.

Therefore, in the conventional driving circuit, when a video signal with a high potential is supplied, no current can flow according to the video signal with a high potential, so that a high-contrast image or contour is emphasized. Images could not be obtained. In order to solve this problem, it is conceivable to always set a constant high voltage in order to obtain a high-contrast image or an image with emphasized outlines, but this disadvantage increases power consumption. was there.

The present invention has been made in view of the above-mentioned conventional disadvantages, and has as its object to provide a driving circuit of an EL display device capable of obtaining a high-contrast image and an image with an enhanced outline. And

[0009]

According to the present invention, there is provided a driving circuit for an EL display device, comprising: an electroluminescent element comprising an anode, a cathode and a light emitting element layer sandwiched between the two electrodes; and a drain electrode supplying a video signal. A first thin film transistor having a gate electrode connected to a scanning signal line for supplying a scanning signal; a source electrode connected to the anode; a drain electrode connected to a power supply; and a gate electrode connected to a source of the first thin film transistor. A second thin film transistor connected to the electrode, and a power supply potential modulation circuit for modulating the potential of the power supply following a video signal.

The power supply potential modulation circuit comprises a bias generation circuit, a current amplification circuit, and an inversion amplification circuit. Further, the power supply potential modulation circuit further includes a differentiating circuit.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS <First Embodiment> EL of the Present Invention
The case where the drive circuit of the display device is employed in the organic EL display device will be described below. FIG. 1 shows a driving circuit of an EL display device of the present invention.

As shown in FIG. 1, a point different from the conventional driving circuit is that a power supply potential modulating circuit 60 surrounded by a solid frame is added. A power supply voltage modulation circuit 60 surrounded by a solid line frame includes a current amplification circuit 61, an inversion amplification circuit 62,
64, a bias generation circuit 63 and a current amplification circuit 65. After the video signal of the video signal line D is input to the current amplification circuit 61, it is applied to the inverting amplification circuit 62 together with the bias voltage from the bias generation circuit 63. Thereafter, the power supply potential supplied to the organic EL element 30 is generated from the power supply potential modulation circuit 60 by passing through the inverting amplification circuit 64 and the current amplification circuit 65 again.

FIG. 2 (a) shows a signal 1 supplied from a video signal line.
FIG. 4B shows a waveform of a video signal in a horizontal period, and FIG. 4B shows a power supply potential generated by the power supply potential modulation circuit for driving the organic EL element. The waveform shown in FIG. 2A is a waveform when the video signal is a window (window frame) pattern.

As shown in FIG. 2A, the potential during the period from the start time t0 to the time t1 of one horizontal period is VL1, and the potential during the period from the time t1 to the time t2 is VH1.
It is. Then, the potential during the period from time t2 to time t3 becomes VL1 again. On the other hand, as shown in FIG. 2B, the power supply potential is a constant potential VL2 during the period from the start time t0 to the time t1 of one horizontal period and the period after the time t2, but is constant at the time t1. From time t2 to time t2, the potential VH2 corresponds to the waveform of the video signal in FIG.
And That is, when the potential of the video signal supplied from the video signal line D is high, the power supply potential is increased.

Then, the scanning signal is applied from the scanning signal line G to the gate electrode 11 of the first TFT 10 by the circuit shown in FIG. 1 to turn on the first TFT 10 and to be supplied from the video signal line D. The obtained video signal is supplied to the second TFT 20.
Is supplied to the gate electrode 21. Thereby, when the second TFT 20 is turned on, the modulated power supply potential (FIG. 2B) generated by the power supply potential modulation circuit is supplied from the power supply 40. Then, a current flows through the organic EL element 30 and the light emitting layer 32 emits light.

By arranging the display pixels thus configured in a matrix, a display panel of an EL display device is formed. As described above, by supplying the power supply potential modulated according to the video signal supplied from the video signal line D, even when a video signal having a high potential is supplied, the current corresponding to the video signal is supplied to the organic EL. Since it can be supplied to the element, a high-contrast display can be obtained.

Further, since it is not necessary to keep the power supply potential constant at a high level in accordance with a video signal having a high potential, power consumption can be reduced. <Second Embodiment> Hereinafter, a second embodiment of the driving circuit of the EL display device according to the present invention will be described. FIG. 3 shows a video signal supplied from a video signal line and a potential of a power supply supplied to an EL display device.

FIG. 3A shows a waveform of a video signal in one horizontal period, and FIG. 3B shows a power supply potential generated by a power supply potential modulation circuit. The waveform shown in FIG. 3A is a waveform in the case where “b” is displayed in which the center and the periphery are blank. FIG.
As shown in (a), the potential of the video signal is changed from time t2 to time t1 from the start time t0 to the time t1 of one horizontal period.
3 and the period from time t4 to time t5 are VL3, and the potential during the other periods, that is, from time t1 to time t2 and from time t3 to time t4, is VH3.

On the other hand, the power supply potential of the power supply 40 is set to a potential that forms a differential waveform of the video signal shown in FIG. 3A (FIG. 3B). That is, the power supply potential at time t1 and time t3 is a potential VH4 modulated corresponding to the positive displacement of the video signal waveform, and the power supply potential at time t2 and time t4 is modulated corresponding to the negative displacement of the video signal waveform. Potential -VH
4, and the power supply potential which becomes the constant potential VL4 in all other periods.

The video signal thus supplied (FIG. 3)
The power supply potential is modulated so as to have a waveform obtained by differentiating (a)) (FIG. 3B). Here, a driving circuit for modulating a power supply potential will be described. FIG. 4 shows a circuit for modulating the power supply potential supplied to the EL element. As shown in the figure,
The power supply potential modulation circuit 60 for modulating the power supply potential includes a differentiation circuit 100, current amplification circuits 101 and 103, an inversion amplification circuit 102, and a bias generation circuit 104.

The power supply potential modulating circuit 60 shown in FIG. 2 differs from that of the first embodiment in that it has a differentiating circuit 100. The video signal on video signal line D is differentiated circuit 1
After being input to 00, it is applied to the inverting amplifier 102 together with the bias voltage from the bias generator 104 via the current amplifier 101. After that, the power supply potential supplied to the organic EL element 30 can be generated by passing through the current amplification circuit 101.

As described above, the power supply potential shown in FIG. 3B can be generated by inputting the video signal of the drain signal line D shown in FIG. 3A to the power supply potential modulation circuit. As shown in FIG. 4, the scanning signal is applied from the scanning signal line G to the gate electrode 11 of the first TFT 10, the first TFT 10 is turned on, and the video signal supplied from the video signal line D is applied to the second TFT 10. Is applied to the gate electrode 21 of the TFT 20, and the second TFT 20 is turned on. Then, the modulated power supply potential shown in FIG. 3B is supplied from the power supply.
Then, a current flows through the organic EL element 30 and the organic EL
The light emitting layer 33 of the element 30 emits light.

As described above, by modulating the power supply potential according to the video signal supplied from the video signal line, even when a video signal having a high potential is supplied, a current corresponding to the video signal is supplied to the organic EL element. Can be supplied to
An image in which the outline of the image is emphasized can be displayed. Further, it is not necessary to supply a constant power supply potential which is always high according to a video signal having a high potential, so that power consumption can be reduced.

[0024]

According to the driving circuit of the EL display device of the present invention, a high-contrast image can be displayed, and an image having a sharp outline can be displayed.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an EL display device according to a first embodiment of the present invention.

FIG. 2 is a waveform diagram of a signal supplied to the EL display device according to the first embodiment of the present invention.

FIG. 3 is a waveform diagram of a signal supplied to an EL display device according to a second embodiment of the present invention.

FIG. 4 is a circuit diagram of an EL display device according to a second embodiment of the present invention.

FIG. 5 is a circuit diagram of a conventional EL display device.

FIG. 6 is a waveform diagram of a signal supplied to a conventional EL display device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 1st TFT 20 2nd TFT 30 Organic EL element 40 Driving power supply terminal 60 Power supply potential modulation circuit 100 Differentiation circuit

Claims (3)

[Claims] 1. An electroluminescent device comprising an anode, a cathode, and a light emitting device layer sandwiched between the two electrodes;
A first thin film transistor having a drain electrode connected to a video signal line for supplying a video signal, a gate electrode connected to a scanning signal line for supplying a scanning signal, a source electrode to the anode, a drain electrode to a power source, and a gate electrode And a second thin film transistor connected to the source electrode of the first thin film transistor, and a power supply potential modulation circuit for modulating the power supply potential following the video signal. A driving circuit for an electroluminescence display device. 2. The driving circuit for an electroluminescent display device according to claim 1, wherein said power supply potential modulation circuit comprises a bias generation circuit, a current amplification circuit, and an inversion amplification circuit. 3. The driving circuit for an electroluminescent display device according to claim 2, wherein said power supply potential modulation circuit further includes a differentiating circuit.