JPH04371997A - Liquid crystal driving device - Google Patents

Abstract

PURPOSE:To easily reduce the offset voltage between the input and output of the data-side driving circuit of an active matrix liquid crystal panel without any external control. CONSTITUTION:The common potential of a sampling capacitor 113 is selected by a changeover switch 115 between two voltage values and one potential is an output at the time when the other potential is inputted to a 2nd buffer 116. At this time, the common potential is the output potential of the 2nd buffer at the time of sampling and the input potential of the 2nd buffer at the time of output. Consequently, the offset voltage between the input and output can be reduced by cancellation between the offset voltage of the output buffer 114 and the offset voltage of the 2nd buffer.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly to a drive device for an active matrix liquid crystal panel.

0002

2. Description of the Related Art FIG. 4 shows an example of a conventional liquid crystal driving device. The liquid crystal drive device includes a data side drive circuit 101 and a liquid crystal panel 1.
02, a scanning side drive circuit 103, and a power supply 104. The data side drive circuit 101 is a shift register 11
1, an analog switch 112, a sampling capacitor 113, and an output buffer 114. The liquid crystal panel 102 has a data side electrode 121 and a scanning side electrode 122.
and M, which is a two-terminal nonlinear element placed at the intersection of these
IM (Metal-Insulator-Metal)
It is composed of a pixel 123 composed of an element 124 and a liquid crystal 125.

The operation of the data side drive circuit 101 will be described below. A start signal DX and a shift clock
Sequentially sample. The potentials of the sampled input video signals are stored in sampling capacitors 113, respectively. The counter potential of sampling capacitor 113 is supplied from power supply 104 . After one scan's worth of sampling is completed, the output control signal OE is input, the output buffer 114 operates, and the potential stored in the sampling capacitor 113 is outputted to the data side electrode 121 as a data side drive signal.

The scanning side drive circuit 103 receives a start signal D.
Y and shift clock YSCL are input, and the selected row has a large potential difference with the data side drive signal, and the unselected row has a signal with a small potential difference with the data side drive signal compared to the selected row. is output to the scanning side electrode 122 as a scanning side drive signal.

Incidentally, the data side drive circuit 101 is often implemented as an IC due to the circuit scale, and in this case, it is important that offset voltages do not vary between output terminals and between ICs. As a liquid crystal drive device that has a method of suppressing variations in offset voltage, Japanese Patent Application Laid-Open No.
There is known a horizontal scanning circuit for a liquid crystal television described in Japanese Patent No. 164180, in which the opposing potential of a sampling capacitor is changed by an external input.

[0006]

[Problems to be Solved by the Invention] However, in conventional liquid crystal driving devices, in order to control the opposing potential of the sampling capacitor externally, it is necessary to measure the offset voltage for each IC and then adjust it to the offset voltage of each IC. The amount of change in the opposing potential must be determined. Furthermore, since the amount of change in the counter potential differs for each IC, there is a problem in that the scale of the power supply that supplies the counter potential becomes large.

SUMMARY OF THE INVENTION The present invention is intended to solve these problems, and its purpose is to suppress the offset voltage of the data side drive circuit in a liquid crystal drive device by using a simple power supply. The key is to easily accommodate differences between ICs.

[0008]

[Means for Solving the Problems] The liquid crystal driving device of the present invention includes (1) a liquid crystal panel in which pixels are arranged in a matrix at the intersections of data side electrodes and scanning side electrodes; a data side drive circuit that supplies a drive signal;
a scanning-side drive circuit that supplies a scanning-side drive signal to the scanning-side electrode, and the data-side drive circuit samples and holds an input video signal in a sampling capacitor using a clock signal, and controls the potential of the sampled and held input video signal. In the liquid crystal driving device that outputs a potential corresponding to the data side drive signal via an output buffer as the data side drive signal, means for applying the input video signal to one terminal of the sampling capacitor via a sampling switch;
means for applying a common potential to the other terminal of the sampling capacitor; means for selecting the common potential from a binary potential; and inputting the other potential as one of the binary potentials. and means for supplying the output of the second buffer.

Further, in the liquid crystal driving device (1), the second buffer uses a circuit having the same configuration as the output buffer.

0010

[Embodiments] Examples of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a first embodiment of the present invention. FIG. 2 is a diagram showing waveforms of various parts of the circuit of FIG. 1.

101 is a data side drive circuit, 102 is a liquid crystal panel, 103 is a scanning side drive circuit, and 104 is a power supply circuit. The data side drive circuit 101 is a shift register 111
A driver block 110 includes an analog switch 112, a sampling capacitor 113, and an output buffer 114, a changeover switch 115, and a second buffer 116. LCD panel 10
2 is a data side electrode 121, a scanning side electrode 122, and an MIM (Me) which is a two-terminal nonlinear element placed at the intersection of these electrodes.
tal-Insulator-Metal) element 124
and a pixel 123 composed of a liquid crystal 125 and a liquid crystal 125.

The operation of the data side drive circuit 101 will be described below. A start signal DX and a shift clock XSCL are input to the shift register 111, and its output, a sampling signal Sa, operates an analog switch 112 to sequentially sample the input video signal video. The potential Vin of the sampled input video signal is stored in the sampling capacitor 113, respectively. A common potential Vc is applied to the opposing electrode of the sampling capacitor 113.
is supplied. After one scan of sampling is completed,
The output control signal OE is input, the output buffer 114 operates, and the potential stored in the sampling capacitor 113 is transferred to the data side electrode 12 as the data side drive signal Vout.
1 is output. In this case, the output buffer 114 operates when the output control signal OE is "H", and maintains the data electrode 121 in a high impedance state when the output control signal OE is "L". However, since the data-side electrode and the pixel act as a capacitor, even when the output control signal OE is "L", the data-side drive signal is changed to a different potential through the output buffer 114 when the output control signal OE becomes "H" next. It is kept at the same potential until it is output.

The scanning side drive circuit 103 receives a start signal D.
Y and shift clock YSCL are input, and the selected row has a large potential difference with the data side drive signal, and the unselected row has a signal with a small potential difference with the data side drive signal compared to the selected row. is output to the scanning side electrode 122 as a scanning side drive signal.

Here, in the data side drive circuit, the common potential Vc applied to the sampling capacitor 113
is a potential selected from binary potentials Vc1 and Vc2 by the changeover switch 115, Vc1 is a certain DC potential input from the external power supply circuit 104, and Vc
2 is the output obtained when Vc1 is input to the second buffer 116. Output control signal OE is “H” on Vc.
When the voltage is "L", Vc1 is selected, and when the voltage is "L", Vc2 is selected.

By the way, an offset voltage exists in the output buffer 114, and its value is assumed to be ΔVa. That is,
When a certain potential V is input to the output buffer 114, the output becomes V
Suppose that it becomes +ΔVa. Further, the offset voltage of the second buffer is assumed to be ΔVc. That is, Vc2=Vc1+Δ
It becomes Vc.

Then, since the output control signal OE is "L" at the time of sampling, the sampling capacitor 113
The potential difference stored in is Vin-Vc2, and since Vc2 changes to Vc1 when the output control signal OE is "H", Vin is (Vin-Vc2)+Vc1=Vin-Δ
Vc and is input to the output buffer 114. Then, due to the offset voltage ΔVa of the output buffer, the output of the output buffer 114, which should become the data side drive signal, is V
out=Vin-ΔVc+ΔVa.

At this time, if the second buffer 116 is configured so that ΔVc is equal to ΔVa, Vout=
Vin, and the offset voltage between input and output can be eliminated without adjusting the opposing potential of the sampling capacitor 113 from the outside.

Furthermore, if a circuit having the same configuration as the output buffer 114 is used as the second buffer 116, ΔVc and ΔVa will generally have approximately equal values since they are on the same chip. As ΔVc and ΔVa
There is no need to adjust the circuit of the second buffer 116 to make them equal, and offset voltage between input and output can be easily eliminated.

FIG. 3 is a block diagram showing a second embodiment of the present invention. In FIG. 3, only the data side drive circuit 101 and the power supply circuit 104 of the liquid crystal drive device are shown. The liquid crystal panel 102 and the scanning side drive circuit 103 are the same as those shown in FIG. As in the first embodiment, the input video signal video is sampled through the analog switch 112 by the sampling signal Sa from the shift register 111, and the potential Vin of the input video signal is applied to the sampling capacitor 111.
is stored in This potential is output as the data side drive signal Vout through the output buffer 114, but the difference from the first embodiment is that a second analog switch 1 is provided between the analog switch 112 and the output buffer 114.
This is the point where 17 is placed. This second analog switch 117 is turned on and off by the output control signal OE and rewrites the data side drive signal Vout. Output buffer 11
4 is always in operation and supplies a stable potential without being affected by self-discharge in the liquid crystal panel to the data side drive signal Vou.
It can be output as t. In this second embodiment, as in the first embodiment, the offset voltage between input and output can be eliminated by switching the common potential Vc of the sampling capacitor 113 using the changeover switch 115. Note that the waveforms of each part of the circuit at this time can be written in the same manner as in the first embodiment.

[0021]

As described above, according to the present invention, by incorporating a circuit for compensating offset voltage in the IC-based data side drive circuit of a liquid crystal drive device, compensation voltage can be applied to each IC from the outside. This has the advantage that offset voltage can be easily compensated for without inputting voltage, the external power supply can be simplified, and it is easy to deal with differences in offset voltage between ICs.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing a first embodiment of a liquid crystal driving device of the present invention.

FIG. 2 is a diagram showing signal waveforms of each part of the circuit in FIG. 1.

FIG. 3 is a configuration diagram showing a second embodiment of the liquid crystal driving device of the present invention.

FIG. 4 is a configuration diagram showing a conventional liquid crystal driving device.

[Explanation of symbols]

101 Data side drive circuit 102 Liquid crystal panel 103 Scanning side drive circuit 104 Power supply circuit 110 Driver block 111 Shift register 112 Analog switch 113 Sampling capacitor 114 Output buffer 115 Changeover switch 116 Second buffer 117 Second analog switch 121 Data side electrode 122 Scanning side electrode 123 pixels 124 MIM element 125 LCD

Claims (2)

[Claims] 1. a) a liquid crystal panel in which pixels are arranged in a matrix at intersections of data-side electrodes and scanning-side electrodes; a data-side drive circuit that supplies a data-side drive signal to the data-side electrode; a scanning-side drive circuit that supplies a scanning-side drive signal to the side electrodes, and the data-side drive circuit samples and holds an input video signal in a sampling capacitor using a clock signal, and according to the potential of the sampled and held input video signal. a liquid crystal driving device that outputs a potential as the data-side drive signal via an output buffer, b) means for applying the input video signal to one terminal of the sampling capacitor via a sampling switch; and c) means for applying the input video signal to one terminal of the sampling capacitor. means for applying a common potential to the other terminal of the sampling capacitor; d) means for selecting the common potential from binary potentials;
e) A liquid crystal driving device characterized by comprising: means for supplying, as one of the two potentials, the output of a second buffer that receives the other potential as input. 2. The liquid crystal driving device according to claim 1, wherein the second buffer uses a circuit having the same configuration as the output buffer.