JPH0792937A - Liquid crystal driving method and liquid crystal display device - Google Patents

Abstract

(57) [Summary] [Object] To provide a liquid crystal driving method and a liquid crystal display device in which an afterimage phenomenon is prevented while achieving multi-gradation. A gray scale voltage composed of a plurality of positive side and negative side is formed by a resistance voltage dividing circuit, and an average value of the positive side gray scale voltage and the negative side gray scale voltage becomes as the signal amplitude decreases. Each of the gradation voltages is formed so as to increase with respect to the common voltage, and the TFT liquid crystal display panel is driven. [Effect] Since the positive voltage and the negative voltage of each gradation voltage can be made asymmetric with respect to the voltage of the common electrode and the average value can be optimally set, it is possible to prevent the afterimage phenomenon while achieving multiple gradations.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal driving method and a liquid crystal display device, and more particularly to a technique effective for use in a multi-gradation display using a TFT (thin film transistor) liquid crystal display panel.

[0002]

2. Description of the Related Art For example, Nikkei McGraw-Hill Company, "Nikkei Electronics" page 211, September 10, 1984, etc. are known as a color liquid crystal display device having an active matrix structure equipped with TFTs. TFT liquid crystal display device,
It is mainly used as a monitor in a microcomputer system as a small and low power consumption display device, but there is a strong demand for multi-gradation and multi-color display as a display device in office automation equipment. As a driver for such multicolor display,
There is one using a CMOS switch that outputs a gradation voltage. An example of such a driver is "Hitachi LCD Driver Data Book" issued by Hitachi, Ltd. in March 1990.

As shown in FIG. 4, the driving voltage of the conventional liquid crystal for performing multi-gradation display is each gradation voltage Vsig1 to Vsign.
However, the reference voltage VC is averaged and converted into an alternating current. This reference voltage VC is also used as a white signal in the case of normally white. In the pixel electrode equivalently acting as a capacitor, a jump voltage from the gate electrode of the TFT transistor is generated. Since this jump-in voltage causes an afterimage phenomenon, in order to prevent it, the voltage Vcom applied to the common electrode of the TFT liquid crystal display panel is shifted from the reference voltage VC so that a DC voltage VDC is added to cancel the jump-in voltage. It is something to do.

[0004]

The method of canceling the jump voltage is based on the assumption that the jump voltage is the same for each gradation voltage. However, according to the research by the inventor of the present application, as shown in FIG. 3, it has been found that as the gray scale voltage increases, the jump amount decreases and approaches the average value A of the gray scale voltage. That is, it has been found that the optimum Vcom in consideration of the above-mentioned jump amount changes as shown by the curve B in response to the increase of the gradation voltage Vsig.
However, since only one common electrode is provided for the display panel, the gray scale voltages supplied to the pixels are different in terms of time and space, so the gray scale voltage of each pixel is different. It is not possible to adjust the voltage of the common electrode correspondingly.

An object of the present invention is to provide a liquid crystal driving method and a liquid crystal display device in which an afterimage phenomenon is prevented while increasing the number of gradations. The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

[0006]

The outline of a typical one of the inventions disclosed in the present application will be briefly described as follows. That is, a positive and negative gradation voltages are formed by the resistance voltage dividing circuit, and the average value of the positive gradation voltage and the negative gradation voltage becomes the common value as the signal amplitude decreases. Each of the gradation voltages is formed so as to increase with respect to the voltage, and the TFT liquid crystal display panel is driven.

[0007]

According to the above means, the average value can be optimally set by asymmetrically setting the positive voltage and the negative voltage of each gradation voltage with respect to the voltage of the common electrode, so that the afterimage phenomenon can be prevented while increasing the number of gradations. It can be prevented.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic block diagram of an embodiment of a liquid crystal display device according to the present invention. In this example,
A circuit for generating a gradation voltage is mainly shown, and a gate driver (scanning line driving circuit) of the liquid crystal display panel TFT-LCD, a circuit for inputting a display signal, a timing control circuit, and the like are omitted.

The adder circuit 4 has a reference voltage VC and a signal voltage V.
S is added to form a positive maximum voltage + V1 (VC + VS). The subtraction circuit 5 changes the signal voltage V from the reference voltage VC.
Subtract S to form the negative maximum voltage −V1 (VC−VS). These voltages are supplied to both ends of a resistance voltage dividing circuit that forms a gradation voltage via the switches 6 and 7. That is, the switch 6 and the switch 7 are switch-controlled by the timing signal 3, and when the switch 6 outputs the positive maximum voltage + V1 (VC + VS), the switch 7 outputs the negative maximum voltage −V1 (VC−). VS)
Is output. When the timing signal 3 is inverted, the switch 6 outputs the negative maximum voltage −V1 and the switch 7 outputs the positive maximum voltage + V1.

The resistance voltage dividing circuit is composed of series resistors, and has a positive maximum value V1 (+ V1) and a negative maximum value V from both ends thereof.
1 '(-V1) is output. Then, from the interconnection point of the resistors, the gradation voltages V2 ...
n, Vn '... V2' are formed. In this embodiment, as shown in the waveform diagram of FIG. 2, the average value of each of the gradation voltages V2 and V2 ′ to Vn and Vn ′ becomes smaller as the signal amplitude becomes smaller. Positive maximum voltage + to increase with common voltage Vcom
It is made asymmetric with respect to the center value VC of V1 and the negative maximum voltage −V1.

In FIG. 1, the gradation voltage generated by the resistance voltage dividing circuit is a positive gradation voltage V from the upper voltage dividing resistance circuit through a buffer 9 such as a voltage follower circuit.
1 to Vn, the negative gradation voltage V from the lower voltage dividing resistor circuit
It is output as n'-V1 '. In the figure, the polarities of the gradation voltages are shown corresponding to the connection example of the switches 6 and 7. By switching the switches 6 and 7, negative voltage V1 to Vn are output from the upper voltage dividing resistance circuit, and positive voltage Vn 'to V1' are output from the lower voltage dividing resistance circuit.

The gradation voltage formed by the upper resistance voltage dividing circuit is supplied to the upper drain driver 10 of the liquid crystal display panel TFT-LCD, and the gradation voltage formed by the lower resistance voltage dividing circuit is Liquid crystal display panel TFT-LCD
Is supplied to the lower drain driver. The drain line (signal line) of the liquid crystal display panel TFT-LCD is divided into an odd number and an even number and is not particularly limited, but the odd number drain line is driven by the upper drain driver 10 and the even number drain line is lower. Side drain driver 1
Driven by 1. Then, the drain drivers 10 and 11 supply drive signals having mutually opposite polarities to the adjacent drain lines.

In the configuration in which the polarity is switched by the alternating signal on the gradation voltage generating circuit side as described above, the number of switches of the drain driver can be reduced. That is,
This is because both the positive drive voltage and the negative drive voltage can be output corresponding to the display signal by the same switch.

An adjustable midpoint voltage Vasc is supplied to the midpoint of the resistance voltage dividing circuit. This midpoint voltage Vas
c is used as a correction voltage. That is, by adjusting this voltage, all the gradation voltages from the gradation voltages V1 to V1 ′ formed by the resistance voltage dividing circuit can be shifted to the positive or negative side. Then, in the configuration in which the polarity is switched on the side of the gradation voltage generating circuit as in this embodiment, the midpoint voltage Vasc is switched via the switch 8 in order to correspond to the asymmetric drive voltage as shown in FIG. It is supplied to the voltage dividing resistor circuit. The switch 8 is also switched in synchronization with the timing signal 3 like the switches 6 and 7. The switch may be omitted and the midpoint voltage Vasc may be supplied to the fixed point of the voltage dividing resistor circuit.

FIG. 5 is a diagram showing another embodiment of the present invention. The difference from the embodiment shown in FIG. 1 is that this switch is omitted and the midpoint voltage Vsac is supplied to the fixed point of the voltage dividing resistor circuit. FIG. 6 is a diagram for explaining the voltage relationship of each part. Now, in FIG. 5, in order to simplify the explanation, Rn = R
Considering an example where n ′ and n = 8, the result is as shown in FIG.

In FIG. 6 (b), the horizontal axis corresponds to that of FIG. 6 (a), and the vertical axis represents the respective voltages V1 to V1 ', Vasc, VC and Vcom.
3 shows the potential relationship of. However, FIG. 6 shows the time when the switches 6 and 7 are in the state shown in FIG. 5, and at the time when the switches 6 and 7 are switched, the respective voltages V1 to Vn and V
The relationship of 1'-Vn 'is exchanged.

In FIG. 6A, the potential at the end of R8 is V
Since the potentials of the voltages V1 and V1 'are set to + V1 and -V1 respectively, the gradation voltages V1 to V1 are set.
n and V1 ′ to Vn ′ exist on a straight line connecting + V1 and P and on a straight line connecting −V1 and P. Therefore, if the midpoint voltage Vasc is shifted from VC, the pair of V2 and V2 '
The average value A of the pair of Vn and Vn 'changes from Vc to Vasc as n increases.

On the other hand, VC is VD with respect to common voltage Vcom
Since the common voltage Vcom is set to be shifted by C, the average value A shifts from VDC as n increases as shown in FIG. Therefore, by setting the midpoint voltage Vasc to the optimum value, the value of the common voltage Vcom can be equivalently set to the optimum value as shown by the curve B as shown in FIG.

Further, in the above-described embodiment, when the polarity for alternating current is switched for each frame (display period of one screen), the polarity is inverted at a relatively low frequency and the screen accompanying alternating current is changed. Flickering becomes a problem. So 1
The polarity can be switched for each of a plurality of scanning lines in the frame, and the AC conversion frequency can be increased to several hundred Hz to prevent flickering due to the AC conversion. Therefore, also in this embodiment, the polarity of the timing signal is made different between the m-th frame and the next m + 1 frame. In the same figure, the timing signal for one cycle is exemplarily shown, but in reality, it is changed to a plurality of cycles in one frame to increase the alternating frequency to several hundred Hz. is there.

The effects obtained from the above embodiment are as follows. That is, (1) a plurality of gradation voltages on the positive side and the negative side are formed by the resistance voltage dividing circuit, and the average value of the positive side gradation voltage and the negative side gradation voltage is reduced as the signal amplitude decreases. However, by driving the TFT liquid crystal display panel by forming each gradation voltage so as to increase with respect to the common voltage, the average value of each gradation voltage can be optimally set with respect to the voltage of the common electrode. The effect that the afterimage phenomenon can be prevented while increasing the number of gradations can be obtained.

(2) The addition voltage and the subtraction voltage of the maximum amplitude voltage and the reference voltage are alternately supplied to the both ends of the resistance voltage dividing circuit that forms a plurality of gradation voltages by the alternating signal, and 2 By supplying an adjustable midpoint voltage to the two midpoints in accordance with the alternating polarity, it is possible to output asymmetrical grayscale voltages of opposite polarity from the same output terminal. If simplification can be achieved, a good effect can be obtained.

Although the invention made by the present inventor has been specifically described based on the embodiments, the invention of the present application is not limited to the embodiments and various modifications can be made without departing from the scope of the invention. Needless to say. For example, when the gradation voltages + V1 to + Vn and -V1 to -Vn are fixedly formed, the addition circuit and the subtraction circuit as described above can be omitted, but the number of switches on the drain driver side increases, but the gradation voltage is generated. The circuit side can be simplified.
Therefore, it is advantageous when the number of gradations is small. In this case, the midpoint voltage Vasc may be omitted and the common voltage Vcom may be varied for adjustment. When color display is performed, three primary color filters may be provided in each pixel of the TFT liquid crystal display panel.

The present invention can be widely used as a liquid crystal driving method and a liquid crystal display device in which gradation display is performed using a TFT liquid crystal display panel.

[0024]

The effects obtained by the typical ones of the inventions disclosed in the present application will be briefly described as follows. That is, a positive and negative gradation voltages are formed by the resistance voltage dividing circuit, and the average value of the positive gradation voltage and the negative gradation voltage becomes the common value as the signal amplitude decreases. By driving the TFT liquid crystal display panel by forming each gradation voltage so as to increase with respect to the voltage, the average value of each gradation voltage with respect to the voltage of the common electrode can be optimally set. It is possible to prevent the afterimage phenomenon while adjusting the tone.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram for explaining an embodiment of a liquid crystal display device according to the present invention.

FIG. 2 is a waveform diagram for explaining each voltage in the liquid crystal driving method and the liquid crystal display device according to the present invention.

FIG. 3 is a characteristic diagram for explaining a relationship between a gradation voltage and an optimum common voltage.

FIG. 4 is a waveform diagram for explaining an example of a conventional multi-gradation drive signal.

FIG. 5 is a schematic configuration diagram for explaining another embodiment of the liquid crystal display device according to the present invention.

FIG. 6 is a diagram for explaining a voltage relationship of each part in another embodiment of the liquid crystal driving method according to the present invention.

FIG. 7 is a diagram for explaining the relationship between the grayscale voltage and the optimum common voltage in the liquid crystal driving method according to the present invention.

[Explanation of symbols]

3 ... Timing signal (AC signal), 4 ... Adder circuit, 5
... subtraction circuit, 6 to 8 ... switch, 9 ... buffer, 10,
11 ... Drain driver, TFT-LCD ... Liquid crystal display panel.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yoshio Owaki, 3681 Hayano, Mobara-shi, Chiba Hitachi Device Engineering Co., Ltd.

Claims (3)

[Claims] 1. A resistance voltage divider circuit is used to form a plurality of positive and negative gradation voltages, and an average value of the positive gradation voltage and the negative gradation voltage as the signal amplitude decreases. However, each gradation voltage is formed so as to increase with respect to the common voltage, and each gradation voltage is set to T in accordance with the display signal.
A liquid crystal driving method comprising supplying to an FT liquid crystal display panel. 2. The resistance ratio is set so that the average value of the positive side grayscale voltage and the negative side grayscale voltage increases with respect to the common voltage as the signal amplitude of the grayscale voltage composed of a plurality decreases. And a resistance voltage dividing circuit for setting each gradation voltage, a buffer circuit for outputting the gradation voltage, and a liquid crystal driver for supplying the gradation voltage according to the display signal to the TFT liquid crystal display panel. Characteristic liquid crystal display device. 3. Both ends of the resistance voltage dividing circuit are alternately supplied with an addition voltage and a subtraction voltage of a maximum amplitude voltage and a reference voltage by an alternating signal, and are adjustable by providing two middle points. 3. The liquid crystal display device according to claim 2, wherein the selected midpoint voltage is supplied according to the polarity of alternating current.