JPH05346571A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To prolong the life of liquid crystal, reduce the power consumption, and to improve the display quality by supplying a selection voltage which is constant in the quantity of variation to a nonselection voltage to a row electrode in a write period. CONSTITUTION:The row electrode is applied with the selection voltage Vg,on2 in a frame scanning period TF and a transistor(TR) turns on to write a video signal VX in a pixel electrode. At the moment when the row electrode is applied with the nonselection voltage Vg,off1, the potential VP of the pixel electrode holds its potential after varying by DELTAV. Then when a counter electrode voltage VC and the video signal VX are inverted, the nonselection voltage becomes a voltage Vg,off2 varied by nearly the same amplitude in synchronism with VC. Then the row electrode is applied with a selection voltage Vg,on2 varied by VC from the selection voltage Vg,on1 and the inverted video signal is written in the pixel electrode. At the moment when the row electrode is applied with the nonselection voltage Vg,off2 again, the pixel electrode potential VP is held after varying by DELTAV.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a matrix type liquid crystal display device, and more particularly to an active matrix type liquid crystal display device in which a switch composed of a transistor is added to each pixel electrode.

[0002]

2. Description of the Related Art In recent years, an active matrix type liquid crystal display device having more pixels and a higher density has been actively developed as a display for a personal computer or a TV. The conventional liquid crystal display device will be described below.

The basic structure of an active matrix type liquid crystal display device comprises a liquid crystal layer sandwiched between an array substrate and a counter substrate. Pixel electrodes are formed in a matrix on the array substrate, and individual video signals are given by the switching elements connected to the pixel electrodes. On the other hand, the counter electrode is formed on the entire surface of the counter substrate, and the transmittance of the liquid crystal is changed according to the potential difference between the counter potential applied to the counter electrode and the video signal to perform display.

FIG. 5 shows an equivalent circuit of one pixel of such a liquid crystal display device. That is, a switch including the transistor 1 is formed at each intersection of the row electrodes 2 and the column electrodes 3 formed in a matrix. The gate electrode of the transistor 1 is connected to the row electrode 2, and the drain electrode is connected to the column electrode 3. The source electrode is connected to the pixel electrode 5. Then, the pixel electrode 5 and the counter electrode 6
The liquid crystal layer sandwiched therebetween forms a liquid crystal capacitance C _LC 4.

Next, a conventional driving method will be described with reference to FIG. The scanning line voltage V _Y is supplied to the row electrode 2, and the selection voltage V _{g, on} is applied every frame scanning period T _F. On the other hand, a video signal V _X is supplied to the column electrode 3,
During the period in which V _{g, on} is applied to the row electrode 2, the transistor 1 is in the conductive state, and V _X is written in the pixel electrode. This period is usually called a writing period. Next, when the non-selection voltage V _{g, off} is applied to the row electrode, the pixel electrode holds the written voltage until the next selection.
This period is usually called the retention period.

By the way, it is known that the characteristics are deteriorated when the liquid crystal is driven by direct current. Therefore, by making the driving voltage alternating, the life of the liquid crystal substance is extended. Generally, the video signal V _X is inverted at a predetermined cycle, for example, the frame scanning cycle T _F , and at the same time, the counter electrode voltage V _X is reversed.
_By inverting _C at the same cycle as V _X , a method of driving the liquid crystal in an alternating current and reducing the cost of a circuit for driving the column electrodes is used.

However, in such a driving method, the source potential changes during the holding period due to the inversion of the counter electrode voltage V _C , and the switching characteristics become unstable. As a result, the voltage applied to the liquid crystal changes,
There is a drawback that it causes image quality deterioration such as flicker and crosstalk.

In order to solve such a problem, as shown in FIG. 7, there has been proposed a method of applying a bias voltage of the same amplitude and the same phase as the counter electrode voltage to the non-selection voltage applied to the transistor. ..

[0009]

However, even if the above-mentioned driving method is used, a sufficient image quality cannot be obtained, and flicker, crosstalk, and an afterimage are generated, which is a major factor in improving the display quality of the liquid crystal display device. It was an obstacle.

In view of such technical background, the present invention has been made.
An object of the present invention is to provide a liquid crystal display device which realizes a long life of liquid crystal and a reduction in power consumption, and further has an extremely good display quality.

[0011]

In order to solve the above problems, the present invention provides a pixel electrode connected via a transistor to each intersection of a row electrode and a column electrode arranged in a matrix, and this pixel In a liquid crystal display device including a counter electrode facing the electrode through a liquid crystal layer, a means for applying an AC signal having a predetermined phase to the counter electrode and a counter electrode applied to the counter electrode during a holding period of the row electrode. A liquid crystal display device having a means for supplying a non-selection voltage having the same cycle as the voltage applied to the row electrode and supplying a selection voltage having a constant change amount to the non-selection voltage to the row electrode during the writing period. ..

[0012]

In the driving method shown in FIG. 7, V _P represents the pixel electrode potential. As shown in the figure, the potential applied to the pixel electrode during the writing period is changed by ΔV. This variation ΔV depends on the parasitic capacitance C _gs 8 between the gate and source of the transistor and between the pixel electrode and the row electrode shown in FIG.
It is expressed by the following equation.

ΔV = C _gs · dV _Y / (C _gs + C _LC ) dV _Y = V _{g, on} −V _{g, off} (change amount from selected voltage to non-selected voltage)

In the conventional method, since the dV _Y has two kinds of values dV _Y1 and dV _Y2 , pixels having different fluctuation amounts ΔV are mixed. Therefore, it is very difficult to compensate the fluctuation of the pixel electrode potential. For this reason, a DC component is generated in the voltage applied to the liquid crystal, which causes deterioration of the characteristics of the liquid crystal, a so-called image sticking phenomenon, and image quality deterioration such as flicker and crosstalk.

In the present invention, dV _Y has a constant magnitude, and ΔV has an equal value over the entire display screen. For this reason,
For example, by applying a bias of ΔV to the counter electrode potential, it is possible to compensate for variations in the pixel electrode potential.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows drive waveforms of the liquid crystal display device in this embodiment. V _Y1 and V _Y2 represent scan line voltages applied to the adjacent row electrodes, respectively. V _X represents a video signal applied to the column electrode, and V _C represents a counter electrode voltage applied to the counter electrode.

As shown, V _X and V _C are inverted at the frame scanning period T _F. The selection voltage V _{g, on1} is applied to the row electrodes at the frame scanning period T _F , at which time the transistors are turned on and the video signal V _X is written to the pixel electrodes. Then, at the moment when the non-selection voltage V _{g, off1} is applied to the row electrode, the potential V _{P of the} pixel electrode is ΔV.
This potential is held only after undergoing fluctuations.

Next, the counter electrode voltage V _{C and the} video signal V _X
Is inverted, the non-selection voltage becomes a voltage V _{g, off2} which changes in substantially the same amplitude in synchronization with V _C. Next, the selection voltage V _{g, on2 which} is changed by V _C from the previous selection voltage V _{g, on1} is applied to the row electrode, and the inverted video signal is written in the pixel electrode. Then, at the moment when the non-selection voltage V _{g, off2} is applied to the row electrode again, the pixel electrode potential V _P is changed by ΔV and then held at this potential.

FIG. 2 shows a part of a drive circuit of the liquid crystal display device of this embodiment. That is, a DC signal serving as a reference of the counter electrode voltage is input to the input terminal a102, and a DC signal for controlling the amplitude of the counter electrode voltage is input to the input terminal b103. These signals are input to the adder circuit 104 and the subtractor circuit 105, respectively, and generate a two-level counter electrode voltage. The analog switch 106 alternately selects the two-level voltage in the frame scanning cycle based on the positive / negative polarity logic signal input from the control circuit 101, and outputs it to the counter electrode. On the other hand, a positive / negative logic signal is also input to the video signal drive circuit 119,
The video signals are inverted so as to have opposite polarities in synchronization with the counter electrode voltage.

A DC signal serving as a reference for the selection voltage is input to the input terminal c, and the adding circuit 108 and the subtracting circuit 109 are input.
Outputs two-level selection voltages V _{g, on1} and V _{g, on2} having a potential difference equivalent to the amplitude of the common electrode voltage, based on this signal and the signal sent from the input terminal b. Based on the logic signal sent from the inverter 111, the analog switch 110 selects the output from the subtraction circuit 109 when the analog switch 106 selects the output from the addition circuit 104, and the analog switch 106 selects the output from the subtraction circuit 105. When selected, the output of the adder circuit 108 is selected and output to the gate driver 116.

On the other hand, a DC signal serving as a reference for the non-selected voltage is input to the input terminal d112, and the adder circuit 113 and the subtractor circuit 114 receive the counter electrode voltage based on this signal and the signal sent from the input terminal b. _-Level non-selection voltages V _{g, off1} and V _{g, off2} having a potential difference equivalent to the amplitude of
Is output. In the analog switch 115, based on the logic signal, the analog switch 106 has the addition circuit 104.
When the analog switch 106 selects the output of the subtraction circuit 105, the output of the subtraction circuit 114 is selected and output to the gate driver 116.

The gate driver 116 selects the selection voltage V _{g, on} sent from the analog switch 110 and the non-selection voltage V _{g, off} sent from the analog switch 115 based on the signal sent from the shift register 117, and each row is selected. Output to the electrode.

FIG. 3 shows a concrete circuit configuration of each of the above-mentioned addition circuits and subtraction circuits. For example, in the addition circuit 108 and the subtraction circuit 109, when the resistance values of all the resistors are equal, the selection voltage V that is the output of the analog switch 110
_{g, on} is converted into alternating current with an amplitude equal to the amplitude of the counter electrode voltage.

In the present embodiment, by using such a drive circuit, when the counter electrode is inverted at a predetermined cycle, the variation amount ΔV of the pixel electrode potential V _P becomes a constant value over the entire screen. be able to. Therefore, this variation can be compensated by a simple method, for example, by applying a DC bias corresponding to ΔV to the counter electrode voltage V _C.

Therefore, it is possible to prevent a direct current component from being applied to the liquid crystal layer, suppress deterioration of the liquid crystal substance, and reduce display defects such as so-called image sticking. Further, it is possible to obtain a liquid crystal display device with high display quality by suppressing the occurrence of flicker and crosstalk.

In the above embodiment, the inversion period of the counter electrode voltage and the video signal voltage is set to the frame scanning period T _F.
However, the present invention can also be used in the case of inversion in other cycles, for example, one horizontal scanning period _TH cycle.

FIG. 4 shows an embodiment of the present invention when such a driving method is used. In the driving method shown in FIG. 4, the polarities of the video signals are opposite for each adjacent scanning line. By using such a driving method, it is possible to increase the frequency of luminance unevenness that occurs when the driving signal is inverted, for example, depending on the characteristics of the liquid crystal material, for example, the difference in responsiveness to the positive and negative video signals. You can Therefore, the uneven brightness can be visually reduced, and the display quality can be further improved.

In the liquid crystal display device of each of the above-mentioned embodiments, the fluctuation of the pixel electrode potential can be made a constant value over the entire screen when the counter electrode potential is inverted at a predetermined cycle. Therefore, for example, by applying a DC bias to the counter electrode, this fluctuation can be compensated, the DC potential is prevented from being applied to the liquid crystal, and a burn-in phenomenon, flicker, crosstalk during gradation display, etc. It is possible to significantly reduce the occurrence of the image quality deterioration factor.

Such an effect can be obtained not only by the driving method described above, but it becomes more remarkable especially when the amplitude of the counter electrode potential is equal to or larger than the amplitude of the video signal. Therefore, by using the present invention, it is possible to significantly reduce the load on the video signal drive circuit and reduce the occurrence of image quality deterioration factors, and obtain high image quality.

[0031]

As described above in detail, in the liquid crystal display device of the present invention, when the counter electrode potential is inverted in a predetermined cycle, the variation ΔV of dV _Y and the pixel electrode potential is constant over the entire screen. Can be a value. Therefore, for example, Δ
Fluctuations can be compensated by a simple method of applying a DC bias of V, and a DC component is prevented from being applied to the liquid crystal.
It is possible to prevent the characteristic deterioration of the liquid crystal substance. Further, it is possible to obtain a liquid crystal display device having high display quality by suppressing the occurrence of a burn-in phenomenon, flicker, crosstalk, and the like.

[Brief description of drawings]

FIG. 1 is a waveform diagram showing an example of a driving method of a liquid crystal display device of the present invention.

FIG. 2 is a circuit diagram showing an example of a drive circuit of the liquid crystal display device of the present invention.

FIG. 3 is a circuit diagram showing a part of the circuit of FIG.

FIG. 4 is a waveform diagram showing another example of the driving method of the liquid crystal display device of the present invention.

FIG. 5 is an equivalent circuit diagram showing one pixel of a liquid crystal display device.

FIG. 6 is a waveform diagram showing an example of a driving method of a conventional liquid crystal display device.

FIG. 7 is a waveform diagram showing another example of the driving method of the conventional liquid crystal display device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Transistor 2 ... Row electrode 3 ... Column electrode 4 ... _CLC 5 ... Pixel electrode 6 ... Counter electrode 7 ... Cgs

Claims (3)

[Claims] 1. A liquid crystal display comprising a pixel electrode connected to each intersection of a row electrode and a column electrode arranged in a matrix via a transistor, and a counter electrode facing the pixel electrode via a liquid crystal layer. In the device, means for applying an AC signal having a predetermined phase to the counter electrode, and a non-selection voltage having the same period as the voltage applied to the counter electrode during the holding period to the row electrode, and A liquid crystal display device, comprising means for supplying a selection voltage to the row electrodes, the amount of change to the non-selection voltage being constant during the writing period. 2. A selection voltage supply means for selecting one of a first signal and a second signal having a potential difference equal to the amplitude of the counter electrode at a timing opposite to that of the counter electrode, and an amplitude equal to that of the counter electrode. 2. The liquid crystal display device according to claim 1, further comprising non-selection voltage supply means for selecting one of the third signal and the fourth signal having a potential difference at the same phase as the counter electrode. 3. The liquid crystal display device according to claim 1, wherein the amplitude of the signal applied to the counter electrode is not less than the amplitude of the video signal applied to the column electrode.