JPH05100637A - Method for driving liquid crystal display device - Google Patents

Abstract

PURPOSE:To saturate a shift in I/V characteristics of a nonlinear element, to equalize write conditions of charges to a liquid crystal layer as to all picture elements on a screen, and to preclude an after-image phenomenon by applying a large voltage right before a selection period while its polarity is inverted plural times. CONSTITUTION:Column electrodes Xm and row electrodes Yn are formed on opposite substrates and a nonlinear element 116 and a liquid crystal layer 115 are arranged in series at each fulcrum. The shift register start signal DY of a Y driver 102 is shifted as a shift locking signal YSCL falls and a selective signal is transferred exactly according to its width. The DY is as wide as four clocks, so the selective signal also has the clock width (four selection periods) of the YSCL4. In this period, a voltage which is larger than that in a normal selection period is applied. Since FR performs one-line inversion driving which causes inversion at each selection period, so an AC inverted signal has the dummy signal of three selection periods before a signal is actually selected and the polarity is changed three times.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of driving a liquid crystal display device, and more particularly to a method of driving a two-terminal type active matrix liquid crystal display device.

[0002]

2. Description of the Related Art Since an active matrix type liquid crystal display device can obtain a higher contrast than a conventional passive type liquid crystal display device, it is often used in various display application fields. There are two types of active elements used, the two-terminal type and the three-terminal type, and it is considered that the two-terminal type is more economically advantageous.

As a two-terminal type active element, MIM
(Metal-Insulator-Metal), M
IS (Metal-Insulator-Semico)
Ndductor), ring diode, varistor, etc. are adopted.

A two-terminal type active element generally used in an active matrix type liquid crystal display device is shown in FIG.
It has the following IV characteristics. That is, the switching function based on the non-linear current characteristic with respect to the applied voltage is used to effectively charge and discharge the pixel.

FIG. 3 is a drive waveform diagram of a two-terminal type active matrix liquid crystal display device. FR represents an AC inverted signal, Xm and Yn represent output signals of a column side driving circuit and a row side driving circuit (hereinafter referred to as an X driver and a Y driver, respectively) of the liquid crystal panel, and Xm-Yn are m columns. A signal applied to a pixel located at an intersection of n rows is shown. (Fig. 1
See the LCD panel section of. Xm-Yn is actually applied to the two-terminal element 116 and the liquid crystal layer 115. ) Ts indicates a selection period and Th indicates a non-selection period. Xm at FR = [0] is -Va as the OFF level (Voff), O
Va is taken as the N level (Von), and when FR = [1], Va is taken as the OFF level and -V is taken as the ON level.
Take a. Von and Vof depending on the video signal level
The ratio of f changes, and a display including a halftone by PWM (pulse width modulation) becomes possible. Yn takes -Vp when FR = [0] and Vp when FR = [1] in the selection period Ts. In the non-selection period Th, -Va is taken in the period following -Vp, and Va is taken in the period following Vp.
Take As a result, the difference signal Xm-Yn is positive in the non-selection period Th after selection due to the positive polarity and negative in Th after selection due to the negative polarity, so that the charges written in the liquid crystal layer 115 during the selection period Ts are retained. To be done. During the selection period Ts, the voltage Vms applied to the non-linear element 116 is large, so the current flowing into the liquid crystal layer 115 through the non-linear element also becomes large, and the voltage Vls of the liquid crystal layer rises. Vls is X
The ratio of Von and Voff of m can be calculated. In the ratio selection period Th, the voltage Vmh applied to the non-linear element 116 has a relatively small value, so that the electric charge is less discharged through the non-linear element and the liquid crystal layer retains the electric charge better. The driving of the two-terminal active matrix liquid crystal display device will be described based on such operation.

[0006]

However, the two-terminal type non-linear element, especially the MIM or MIS type element, has a characteristic shift as described below. In FIG.
I / V1 is the initial voltage-current characteristic of the two-terminal nonlinear element, but when the voltage is continuously applied to the element, the characteristic shifts like I / V2. (Reference: E. Mizoba
ta, et al. , SID91 DIGEST, p.
226 (1991)) characteristic I / V2 has a larger resistance when the voltage is higher than the characteristic I / V1, which means that writing of charges to the liquid crystal layer at the time of selection is reduced. .. It means that there is not much difference in resistance when the voltage is small, and there is not much difference in charge retention of the liquid crystal layer when not selected. Further, it is known that this I / V characteristic shift is saturated.

The influence of the I / V characteristic shift on the display will be described. In FIG. 4, the display content is a white window display on a black background. The pixel P1 is located at the intersection of the column electrode Xm1 and the row electrode Yn, and displays black. The pixel P2 is located at the intersection of the column electrode Xm2 and the row electrode Yn and displays white. Next, as shown in FIG. 5, when the entire screen is displayed in halftone, the previous window display contents remain as an afterimage. That is, the pixel P1 becomes brighter than the pixel P2. The reason will be described with reference to FIG. Xm1-
Yn is a signal applied to the pixel P1, and Xm2-Yn is a signal applied to the pixel P2. Select period T in white display period
At s, the voltage Vms applied to the nonlinear element of the pixel P2
W is larger than the voltage VmsB applied to the nonlinear element of the pixel P1 during the black display period. Therefore, the non-linear element of the pixel P2 has a larger I / V characteristic shift amount. (During the non-selection period, the voltage applied to the non-linear element is relatively small for all the pixels.) Therefore, when the half-tone display is performed for all the pixels, the non-linear element of the pixel P2 is the same as that of the pixel P1. In comparison, since the I / V characteristics are shifted so that the resistance becomes high when a large voltage is applied, the charge of the liquid crystal layer far during the selection period is insufficient as compared with P1. The effective voltage to the liquid crystal layer is proportional to the area of the shaded area in the figure, but obviously S1> S2, and as a result, the pixel P2 becomes the pixel P.
It becomes darker than 1 and is recognized as an afterimage.

This can be explained more clearly with reference to FIG. Xm-Yn is a signal applied to the pixel located at the intersection of the Xm column and the Yn row. When the image displayed on the pixel (m, n) is “white”, the I / V in FIG.
Since the characteristic shift is large, the charge of the liquid crystal layer 115 during the selection period Ts is small. On the other hand, when the previous display content is "black", the shift of the I / V characteristic is small, and therefore the charge of the liquid crystal layer 115 during the selection period Ts is larger than that when it is "white". During the non-selection period Th, as described above, the shift of the I / V characteristic is small regardless of the "white" and "black" of the previous display, and there is no significant difference in the charge holding state in the liquid crystal layer 115.
As a whole, the difference in effective voltage is the difference in area between S1 and S2 shown in the figure. S2 is after "white" is displayed, S1 is after "black" is displayed, and it is clear that S1> S2.
The display after "black" is displayed is brighter than that after "white" is displayed, and is recognized as an afterimage. The present invention is intended to solve the problem of the conventional art, that is, the afterimage phenomenon in a two-terminal active matrix liquid crystal display device.

[0009]

According to the method of driving a liquid crystal display device of the present invention, in a two-terminal active matrix liquid crystal display device, a plurality of periods immediately before a selection period of each row are equal to or at the time of selection, or A voltage higher than that is applied between the row and column electrodes with the polarity changed at least twice.

[0010]

By applying the large voltage with the polarity changed a plurality of times immediately before the selection period, the frequency of the time when the large voltage is applied to the non-linear element increases, and the shift of the I / V characteristic of the non-linear element is saturated. Therefore, the conditions for writing charges in the liquid crystal layer are uniform for all pixels in the screen, and the afterimage phenomenon can be prevented.

[0011]

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

FIG. 1 is an example of one configuration diagram of a matrix liquid crystal display device using a two-terminal active element for realizing the present invention. Reference numeral 103 is an active matrix type liquid crystal panel, 101 is a column direction drive circuit (X driver) that drives the column electrodes of the liquid crystal panel 103, and 102 is a row direction drive circuit (Y driver) that drives the row electrodes.

Since the X driver 101 digitally inputs the gradation signal, the video signal is input to the A / D converter 10
At step 4, it is converted into a digital signal. This function may be built in the X driver 101. In the X driver 101, the shift register 105 performs a shift operation in synchronization with the shift clock signal XSCL to sample the input digital signal. A latch circuit 106 latches and holds the data sampled by the shift register 105. An Xm drive circuit 107 drives the column electrode Xm by outputting either the potential Va or -Va based on the AC inversion signal FR and the data held in the latch circuit 106.

In the Y driver 102, reference numeral 108 denotes a liquid crystal power supply generation circuit, which is Vr, Vp, Va, -Va, -V.
Six types of voltage, p and -Vr, are input and the AC inversion signal F
Liquid crystal power supplies Vs, V multiplexed in synchronism with R
n and Vr are generated. Here, Vr ≧ Vp ≧ Va ≧ −Va
The potential is ≧ −Vp ≧ −Va. A shift register 109 is activated by a shift start signal DY, performs a shift operation in synchronization with the shift clock signal YSCL, and generates a selection signal Cn. In addition, the selection signal that is one time before the selection signal Cn (for one YSCL cycle) is Cn−1. Reference numerals 112, 113, and 114 denote analog switches, each source input of which is a power supply Vs, Vn, Vr, and each gate input of which is a logical product 11 of selection signals Cn, Cn and Cn-1.
0, Cn and the logical product 111 of the inverted signal of Cn−1 are connected, each drain output is commonly connected, and drives the row electrode Yn. That is, when Cn = "0", the non-selection potential Vn is irrespective of Cn-1, Cn = "1", and when Cn-1 = "1", the selection potential Vr is Cn = "1", Cn-1 = "". At "0", the selection potential Vs is output to the row electrode Yn. That is, the output potential is Yn = “+ Vr”, FR = when the selection signal Cn = “1”, Cn = “1”, the AC inversion signal FR = “1”.
When "0", Yn = "-Vr" is selected and the selection signal C
When n = “1” and Cn−1 = “0”, the AC inversion signal F
When R = “1”, Yn = “+ Vp” is selected, and when FR = “0”, Yn = “− Vp” is selected.

Reference numeral 103 denotes an active matrix type liquid crystal panel, in which the column electrodes Xm and the row electrodes Yn are formed on opposite substrates, and the non-linear element 113 is located at the intersection.
And the liquid crystal layer 112 are arranged in series. Here, the voltages applied to the liquid crystal layer 112 and the non-linear element 113 with reference to the row electrode potential are Vl and Vm, respectively.

The characteristics of the non-linear element are as described above.

FIGS. 7, 8 and 9 are time charts based on the present invention, and the operation of the liquid crystal display device of FIG. 1 will be described with reference to these figures.

In FIG. 7, DY is a Y driver 102.
Of the shift register start signal, the shift operation is performed at the falling edge of the shift clock signal YSCL, and the selection signal is transferred according to its width. now,
One cycle of YSCL is set as one selection period (normally, one selection period corresponds to one horizontal scanning period, and one horizontal scanning period is abbreviated as 1H hereinafter). Since the width of DY is 4 clocks of YSCL in FIG. 7, the selection signal also has a width of 4 clocks of YSCL (for 4 selection periods), and this width is shifted and transferred at the falling edge of YSCL.

When the Y driver 102 of FIG. 1 is operated in this manner, the selection signal has four selection periods and the phase is inverted every one selection period, so that the signal applied to the pixel of the liquid crystal panel 103 is as shown in FIG. Become. Select signals Cn and Cn-
Since 1 is shifted by 1H, Cn = “1”, Cn−1
The period of "1" is 3H. In this period, a voltage longer than the normal selection period (Cn = "1", Cn-1 = "0") is applied. Here, the AC inversion signal FR is set to one line inversion drive in which it is inverted every one selection period. Therefore, there is a dummy signal for three selection periods before the signal to be actually selected, and the polarity changes three times.

The effect of shifting the I / V characteristic of the active element (eg, MIM) on the panel when the above driving is performed will be described. The I / V characteristic shift is caused by the voltage applied to the element as described above. FIG. 8 shows a black display in the pixel Xm1Yn and a white display in the pixel Xm2Yn, and shows a signal applied to each pixel when the display is switched to the halftone display at a certain time. Vm
s1 is an effective value added to the MIM when the halftone is selected after the characteristic shift is performed by the black display, Vms2 is an effective value added to the MIM when the halftone is selected after the characteristic shift is performed by the white display, and S1 is the characteristic due to the black display The effective value for the holding period after selecting the halftone after the shift, and S2 is the effective value for the holding period after selecting the halftone after the characteristic shift due to white display. The afterimage is caused by the difference in these effective values. However, in the driving according to the present invention, as is clear from the figure, a voltage Vmr larger than three times is applied to the element before the true selection voltage Vms, and since the polarities are respectively inverted, a substantially larger voltage is generated. (That is, Vmr2> Vmr1) By applying to the MIM element, the I / V characteristic shift of the element described above can be saturated. This means that the characteristic shift of the pixel displaying black is the same as the characteristic shift of the pixel displaying white. This will be described in more detail with reference to FIG. FIG. 9 is an enlarged view of the halftone display period of FIG. In the figure, Ts represents a true selection period, Ts' represents a dummy selection period, and Th represents a holding period. According to the driving according to the present invention, the effective value added to the MIM when selected regardless of the black display and the white display and the effective value holding the same are equal. That is, Vms1 = Vm
s2, S1 = S2. Therefore, it is possible to eliminate the difference in the I / V characteristic shift of the element between the white display and the black display, make the I / V characteristic shift of the entire screen uniform regardless of the display content, and eliminate the afterimage. it can. Also, 2
In the active matrix panel using terminal elements,
Since pixel writing is determined by the data content in the Ts period which is a true selection, the image quality is not affected by the dummy selection period.

[0021]

According to the present invention, the two-terminal active
In a matrix liquid crystal display device, by driving a large voltage by changing its polarity a plurality of times immediately before the selection period and applying the voltage, the frequency of the large voltage applied to the non-linear element increases and the I / V characteristic shifts. Is saturated, the charge write conditions for all pixels in the screen are made uniform, the afterimage phenomenon is prevented, and the image quality is improved.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a liquid crystal display device.

FIG. 2 is a diagram showing IV characteristics of a non-linear element.

FIG. 3 is a drive waveform diagram of a liquid crystal display device (conventional example).

FIG. 4 is a window display diagram on a liquid crystal panel.

FIG. 5 is a halftone display diagram on a liquid crystal panel.

FIG. 6 is a P drive waveform diagram of the liquid crystal display device.

FIG. 7 is a time chart of each part in FIG.

FIG. 8 is a drive waveform diagram of a liquid crystal display device (according to the present invention).

FIG. 9 is a drive waveform diagram of a liquid crystal display device (according to the present invention).

[Explanation of symbols]

 101 column electrode drive circuit (X driver) 102 row electrode drive circuit (Y driver) 103 liquid crystal panel 104 A / D converter 105 shift register 106 latch circuit 107 Xm drive circuit 108 liquid crystal power supply generation circuit 109 shift register 110 AND gate 111 AND gate 112 analog switch 113 analog switch 114 analog switch 115 liquid crystal layer 116 nonlinear element

Claims (3)

[Claims] 1. A) A two-terminal element having a non-linear resistance characteristic and a liquid crystal layer at an intersection of a plurality of row electrodes to which a scanning signal is supplied and a plurality of column electrodes to which a data signal based on a video signal is supplied. B), a relatively large voltage is applied between the row and column electrodes when each row is selected, and a relatively small voltage when not selected. In a driving method of a liquid crystal display device to which a voltage is applied, C) a voltage corresponding to the plurality of rows immediately before the selection period is equal to the selection period, or higher than the selection period,
A method of driving a liquid crystal display device, characterized in that the polarity is changed at least twice or more and the voltage is applied between the row and column electrodes. 2. The method of driving a liquid crystal display device according to claim 1, wherein A) the two-terminal element has a metal-insulator-metal structure. 3. The method of driving a liquid crystal display device according to claim 1, wherein A) the two-terminal element has a structure of metal-insulator-semiconductor.