JPH1091129A - Driving circuit for display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress degradation of a display and to improve reliability by outputting an AC signal applied to opposed electrodes and a driving signal applied to a scanning electrode in an OFF period of a switching element (TFT) from the same control circuit together. SOLUTION: In addition to that an output of an opposed voltage generation circuit 8 is outputted as opposed voltage, it is made an input of a power source circuit 9 supplying plural operation voltage of a gate driver 3. A line inversion pulse is inputted to a non-inversion input terminal of an amplifier 84 provided in the opposed voltage generation circuit 8 from a control circuit 4 through a resistor 81. A variable DC power source 83 is connected to a non-inversion input terminal of the amplifier 84. Amplitude Vc of desired opposed voltage is obtained by setting appropriately values of resistors 81, 82. That is, the AC signal applied to the opposed electrode and the driving signal applied to a scanning electrode during an OFF period of a TFT are both obtained from the same control signal outputted from the control circuit 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plurality of signal electrodes arranged in parallel, a plurality of scanning electrodes intersecting with the signal electrodes, a picture element electrode provided near each intersection of the signal electrodes and the scanning electrodes, And a driving circuit of a display device for driving a display unit having a counter electrode provided to face the picture element electrode. In the following, a matrix type liquid crystal display device will be described as an example of a display device. However, the present invention can be applied to other types of display devices, for example, a driving circuit such as an EL (electroluminescence) display device or a plasma display.

[0002]

2. Description of the Related Art FIG. 7 schematically shows an example of a conventional matrix type liquid crystal display device. The matrix type liquid crystal display device of FIG. 7 has a TFT (Thin) as a switching element for driving the pixel electrodes 103 arranged in a matrix.
TF using Film Transistor 104
A T liquid crystal panel 100 is provided. TFT liquid crystal panel 1
00 denotes a plurality of scanning electrodes 101 arranged in parallel with each other.
And a plurality of signal electrodes 102 arranged orthogonally to the scanning electrodes 101 and in parallel with each other. Scan electrode 101
The pixel electrode 10 is close to each intersection of the pixel electrode 10 and the signal electrode 102.
3 is provided. A counter electrode 105 is provided to face the pixel electrode 103. The counter electrode 105 is schematically shown in FIG. 7, but is usually one conductive layer commonly provided to all the pixel electrodes 103, and the counter electrode 105 has the signal electrode 1.
02 in order to reduce the signal amplitude
A “counter voltage” is applied.

[0005] The TFT liquid crystal panel 100 is driven by a drive circuit including a source driver 2 and a gate driver 3. Source driver 2 and gate driver 3 are TFT
They are connected to the signal electrodes 102 and the scanning electrodes 101 of the panel 100, respectively. The source driver 2 samples the input analog image signal or video signal, holds it, and supplies it to the signal electrode 102. On the other hand, the gate driver 3 sequentially outputs scan pulses as drive signals to the scan electrodes 101. Control signals such as timing signals input to the gate driver 3 and the source driver 2 are given from the control circuit 4.

FIG. 6 shows a waveform of a scanning pulse applied to each scanning electrode 101 in a conventional matrix type liquid crystal display device.

[0005]

In the matrix type liquid crystal display device in the conventional driving method, a period in which the scanning pulse applied to the scanning electrode 101 is at a LOW level (that is, a period in which the scanning pulse is applied to the scanning electrode 101).
The TFT 104 connected to the scanning electrode 101 is
The counter voltage is applied to the counter electrode also during the FF period (hereinafter, referred to as a “gate OFF period”). Therefore, the TFT 104 is normally in the gate OFF period.
In order to surely turn off the scanning pulse, the LOW level of the scanning pulse is reduced. However, if the LOW level of the scanning pulse is too low, the TFT 104 cannot be reliably turned off. Thus, the gate OF
It is difficult to reliably turn off the TFT 104 in the period F.

This situation will be described in more detail with reference to FIGS. ± Vc, TF
The stray capacitance between the gate G and the drain D of T104 is C
GD, the capacitance between the pixel electrode 103 and the counter electrode 105 is C
Assuming that LC is the voltage applied to the drain of the TFT 104 when the counter voltage is applied, ΔVx = ± Vc / (1 + CGD / C
LC).

As described above, since the voltage fluctuating by ΔVx is applied to the drain, the relationship between the gate applied voltage Vg of the TFT 104 and the drain current ID changes as shown in FIG. As described above, the optimal value of the gate applied voltage for turning off the TFT 104 varies between VL and VH. Therefore, it is difficult to set the level of the scanning pulse during the gate OFF period to the optimum OFF voltage. If the optimum OFF voltage is not applied, the TFT 10
Since the switch 4 is not completely turned off, the liquid crystal element is deteriorated and the reliability of the display device is reduced.

An object of the present invention is to ensure that the pixel electrode is in a non-driving state during a period in which the pixel electrode is not driven (in the above-described conventional example, the gate OFF period), and this non-driving state is for a long time. It is an object of the present invention to provide a display device driving circuit which does not cause deterioration of the display device or the like due to the continuity of the display device.

[0009]

A driving circuit for a display device according to the present invention comprises a plurality of signal electrodes arranged in parallel, a plurality of scanning electrodes crossing the signal electrodes, and a vicinity of each intersection of the signal electrodes and the scanning electrodes. And a switching element for driving the pixel electrode, and a driving circuit for a display device having a counter electrode provided to face the pixel electrode and to which an AC signal is applied. The drive circuit includes a source driver and a gate driver connected to the signal electrode and the scan electrode, and a control circuit for inputting a control signal to the source driver and the gate driver, and an AC voltage applied to the counter electrode. Signal and OF of the switching element
The drive signal applied to the scan electrode during the F period is obtained from the same control signal output from the control circuit, thereby achieving the above object.

At this time, the AC signal applied to the counter electrode and the drive signal applied to the scan electrode during the OFF period of the switching element may both be output from the same power supply circuit.

The driving circuit of the display device according to the present invention is provided near a plurality of parallel signal electrodes, a plurality of scanning electrodes crossing the signal electrodes, and respective intersections between the signal electrodes and the scanning electrodes. A driving circuit for a display device, comprising: a pixel electrode; a switching element for driving the pixel electrode; and a counter electrode provided to face the pixel electrode and to which an AC signal is applied; Has a source driver and a gate driver connected to the signal electrode and the scanning electrode, and a control circuit for inputting a control signal to the source driver and the gate driver, and a scanning signal which is a control signal output from the control circuit. The clock pulse and the scan start pulse are characterized in that they are input to the gate driver via respective photocouplers, whereby Serial object is achieved.

[0012]

Embodiments of the present invention will be described below.

FIG. 1 shows a configuration near the gate driver 3 according to the embodiment of the present invention. The configuration of this embodiment is
Except for the configuration shown in FIG. 1, it can be the same as that shown in FIG. In the present embodiment, the output of the opposing voltage generating circuit 8 is output as the opposing voltage as in a normal driving circuit, and in addition, the power supply circuit 9 for supplying a plurality of operating voltages of the gate driver 3 Is also input.

The counter voltage generating circuit 8 has an amplifier 84, and a line inversion pulse is input from the control circuit 4 via a resistor 81 to an inverting input terminal of the amplifier 84. A variable DC power supply 83 is connected to a non-inverting input terminal of the amplifier 84. By appropriately setting the values of the resistors 81 and 82, a desired counter voltage amplitude ± Vc can be obtained.

The power supply circuit 9 has a series circuit including a resistor 91, three Zener diodes 93a to 93c, and a resistor 92. One end on the resistor 91 side of this series circuit is HI
It is connected to a GH level gate voltage source VGH, and one end on the resistor 92 side is connected to a LOW level gate voltage source VGL. The output of the amplifier 84 is a Zener diode 9
3b and 93c. Power supply circuit 9
Also has another series circuit with three capacitors 95a-95c. Each of the capacitors 95a to 95c is connected in parallel with each of the Zener diodes 93a to 93c. That is, one end of the capacitor 95a is connected to a node between the resistor 91 and the capacitor 93a,
The node 5b is connected to the nodes of the Zener diodes 93a and 93b, the nodes of the capacitors 95b and 95c are connected to the nodes of the Zener diodes 93b and 93c, and the other end of the capacitor 95c is connected to the nodes of the resistor 92 and the capacitor 93c. The Zener voltages of the Zener diodes 93a, 93b and 93c are Vz1, Vz2 and Vz3, respectively.

From the power supply circuit 9 having such a configuration, three types of voltage pulses VDD, VCC and VEE (VDD>VCC> VE) are obtained.
E) is output and input to the gate driver 3. The voltage pulse VCC is used for logic control of the gate driver 3. The waveforms of the voltage pulses VDD and VEE are shown in FIGS. 2A and 2C, respectively. FIG. 2B shows the waveform of the common electrode drive voltage VCOM. The pulse VDD is a pulse signal corresponding to a conventional scanning pulse with the AC component ± Vc of the opposite voltage superimposed thereon, and the voltage pulse VEE is the AC component ± Vc
And a pulse signal having the same amplitude as that of the counter voltage and the same phase.

A scanning clock pulse and a scanning start pulse, which are control signals from the control circuit 4 to the gate driver 3, are supplied to the photocoupler 50 as shown in FIG.
1 and 502 respectively.

The gate driver 3 sends the voltage pulses VDD and VEE as scan pulses to each scan electrode 101 at the same timing as in the prior art. That is, when the TFT 104 connected to the scanning electrode 101 is turned on, the voltage pulse VDD is applied.
Is selected, and the voltage pulse VEE is selected during the OFF period. FIG. 2D shows the waveform of the scanning pulse. During the OFF period, the phase of the scanning pulse (solid line) is the same as that of the counter voltage (broken line), and the amplitude of the scanning pulse is the same as the alternating voltage ± Vc of the counter voltage. As is apparent from FIG. 2D, during the gate OFF period, the potential fluctuation of the drain electrode ± Vc / (1) based on the AC component ± Vc of the counter voltage.
+ CGD / CLC) is offset by the scan pulse amplitude,
Since the difference Vgd between the drain voltage and the scanning pulse is always constant, the voltage applied to the gate of the TFT 104 is constant, and the value is determined by the difference Vgd. Since the value of the difference Vgd can be set arbitrarily, an optimal OFF voltage can be applied, and the TFT 104 can be reliably turned off.

The same structure as described above can be applied to a driving circuit of a display device, an OA display device, and the like, in which an auxiliary capacitance is additionally formed near the picture element electrode.

[0020]

According to the driving circuit of the display device of the present invention,
During a period in which the pixel electrode is not driven, the pixel electrode is surely in a non-driving state. Therefore, deterioration of the display device is suppressed, and the reliability of the display device can be improved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram illustrating an embodiment of the present invention.

FIG. 2 is a signal waveform diagram for explaining the operation of the embodiment.

FIG. 3 is a signal waveform diagram in a conventional example.

FIG. 4 is an equivalent circuit diagram near a picture element electrode of the display device.

FIG. 5 is a graph showing a relationship between a gate applied voltage and a drain current of a conventional TFT.

FIG. 6 is a diagram showing scan pulses applied to each scan electrode.

FIG. 7 is a diagram illustrating a configuration of a liquid crystal display device.

[Explanation of symbols]

 2 Source driver 3 Gate driver 4 Control circuit 8 Counter voltage generation circuit 9 Power supply circuit 81 Resistance 82 Resistance 83 Variable DC power supply 84 Amplifier 91 Resistance 92 Resistance 93a Zener diode 93b Zener diode 93c Zener diode 95a Capacitor 95b Capacitor 95c Capacitor 100 TFT liquid crystal panel DESCRIPTION OF SYMBOLS 101 Scan electrode 102 Signal electrode 103 Pixel electrode 104 TFT 105 Counter electrode 501 Photocoupler 502 Photocoupler VGH, VGL Gate voltage source

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hideki Yakushigawa 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka

Claims (3)

[Claims] 1. A plurality of parallel signal electrodes, a plurality of scan electrodes crossing the signal electrodes, a pixel electrode provided near each intersection of the signal electrodes and the scan electrodes, and driving the pixel electrodes And a driving circuit for a display device having a switching element provided to face the pixel electrode and a counter electrode to which an AC signal is applied, wherein the driving circuit is connected to the signal electrode and the scanning electrode. A source driver and a gate driver, and a control circuit for inputting a control signal to the source driver and the gate driver. An AC signal applied to the counter electrode, and an AC signal applied to the scan electrode during an OFF period of the switching element. The drive circuit for a display device, wherein the applied drive signal is obtained from the same control signal output from the control circuit. 2. An AC signal applied to the counter electrode,
2. The drive circuit according to claim 1, wherein the drive signal applied to the scan electrode during an OFF period of the switching element is output from the same power supply circuit. 3. 3. A plurality of signal electrodes in parallel, a plurality of scanning electrodes crossing the signal electrodes, a pixel electrode provided near each intersection of the signal electrodes and the scanning electrodes, and driving the pixel electrodes And a driving circuit for a display device having a switching element provided to face the pixel electrode and a counter electrode to which an AC signal is applied, wherein the driving circuit is connected to the signal electrode and the scanning electrode. A source driver and a gate driver, and a control circuit for inputting a control signal to the source driver and the gate driver. A scan clock pulse and a scan start pulse, which are control signals output from the control circuit, use a photocoupler. A driving circuit for a display device, wherein the driving circuit is inputted to the gate driver through each of the driving circuits.