JP3328944B2 - Driving method of liquid crystal display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art An active matrix type liquid crystal display device has a high contrast as compared with a conventional passive type liquid crystal display device, and is therefore widely used in various display application fields. There are two types of active elements, a two-terminal type and a three-terminal type, and the two-terminal type is considered to have an economic advantage.

As a two-terminal type active element, MIM is used.
(Metal-Insulator-Metal), M
IS (Metal-Insulator-Semico)
, a diode, a varistor, and the like.

A two-terminal type active element generally employed in an active matrix type liquid crystal display device is shown in FIG.
It has the following IV characteristics. In other words, the pixel is charged and discharged with effective charge using a switching function based on a non-linear current characteristic with respect to an applied voltage.

FIG. 3 is a driving waveform diagram of a two-terminal type active matrix liquid crystal display device. FR indicates an AC inversion signal, Xm and Yn indicate output signals of a column-side drive circuit and a row-side drive circuit (hereinafter, referred to as an X driver and a Y driver, respectively) of the liquid crystal panel, and Xm-Yn indicates m columns. 5 shows a signal applied to a pixel located at an intersection of n rows. (Figure 1
Refer to the liquid crystal panel section. 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 OFF level (Voff),
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 according to the level of the video signal
The ratio of f changes, and display including a halftone by PWM (pulse width modulation) becomes possible. In the selection period Ts, Yn takes -Vp when FR = [0] and Vp when FR = [1]. In the non-selection period Th, -Va is taken in a period following -Vp, and Va is taken in a period following Vp.
Take. Thereby, in the difference signal Xm-Yn, the positive polarity is positive during the non-selection period Th after selection, and the negative polarity is negative during Th after selection, so that the charge written to the liquid crystal layer 115 during the selection period Ts is retained. Is done. In the selection period Ts, since the voltage Vms applied to the nonlinear element 116 is large, the current flowing into the liquid crystal layer 115 through the nonlinear element becomes large, and the voltage Vls of the liquid crystal layer increases. Vls is X
The ratio between Von and Voff of m can be determined. In the ratio selection period Th, the voltage Vmh applied to the non-linear element 116 has a relatively small value, so that the discharge of the electric charge through the non-linear element is small and the electric charge in the liquid crystal layer is good. The driving of the two-terminal type active matrix liquid crystal display device based on such an operation will be described.

[0006]

However, a two-terminal nonlinear element, particularly an MIM or MIS element, has a characteristic shift as described below. In FIG.
I / V1 is the initial voltage-current characteristic of the two-terminal nonlinear element. If 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)) In the characteristic I / V2, the resistance when the voltage is large is higher than that in the characteristic I / V1, which means that the charge writing to the liquid crystal layer at the time of selection is reduced. . There is little difference in resistance when the voltage is small, which means that there is not much difference in charge retention of the liquid crystal layer when not selected. It is also known that this I / V characteristic shift is saturated.

[0007] The effect of this I / V characteristic shift on 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 as shown in FIG. 5, the content of the window display before that remains as an afterimage. That is, the pixel P1 is 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. Selection period T with white display period
s, the voltage Vms applied to the nonlinear element of the pixel P2
W is higher than the voltage VmsB applied to the nonlinear element of the pixel P1 during the black display period. Therefore, the nonlinear element of the pixel P2 has a larger shift amount of the I / V characteristic. (During the non-selection period, the voltage applied to the non-linear element is relatively small for any pixel.) Therefore, when halftone display is performed for any pixel, 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 writing of the electric charge of the liquid crystal layer during the selection period is insufficient compared to P1. The effective voltage to the liquid crystal layer is proportional to the area of the hatched portion in the figure, but clearly S1> S2, and as a result, the pixel P2
It becomes darker than 1 and is recognized as an afterimage.

This can be more clearly explained 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.
The characteristic shift is large, and thus the charge of the liquid crystal layer 115 during the selection period Ts is relatively small. On the other hand, when the previous display content is “black”, the shift of the I / V characteristic is small, and thus the charge of the liquid crystal layer 115 during the selection period Ts is larger than that in the case where the display content is “white”. In the non-selection period Th, as described above, the shift of the I / V characteristic is small regardless of the previous display of “white” and “black”, and there is no significant difference in the charge holding state in the liquid crystal layer 115.
As a whole, the difference between the effective voltages is the difference between the areas of S1 and S2 shown in the figure. S2 is after “white” display, S1 is after “black” display, and obviously S1> S2, and although it should be the same image display content,
The display after "black" display is brighter than that after "white" display, and is recognized as an afterimage. An object of the present invention is to solve such a problem of the prior art, that is, an afterimage phenomenon in a two-terminal type active matrix liquid crystal display device.

[0009]

The present invention solves the above-mentioned problems by the following constitution. The driving method of the liquid crystal display device of the present invention, a plurality of row electrodes, a plurality of column electrodes, provided at the intersection of the row electrode and the column electrode, a two-terminal element having a nonlinear resistance characteristic, A method for driving a liquid crystal display device having a voltage having an absolute value equal to or greater than an absolute value of a voltage applied to the two-terminal element by the selection pulse before the selection pulse is applied,
A voltage whose polarity changes at least twice or more is applied to the two-terminal element to saturate the I / V characteristic of the two-terminal element having the non-linear resistance characteristic, thereby obtaining a stable I / V characteristic. A method for driving a liquid crystal display device.

[0010]

By applying a large voltage to the nonlinear element a plurality of times with its polarity changed immediately before the selection period, the frequency of application of the large voltage to the nonlinear element increases, and the shift of the I / V characteristics of the nonlinear element is saturated. Thus, the conditions for writing electric charges to the liquid crystal layer for all the pixels in the screen become uniform, and the afterimage phenomenon can be prevented.

[0011]

An embodiment of the present invention will be described below with reference to the drawings.

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

An X driver 101 converts a video signal into an A / D converter 10 for digitally inputting a gradation signal.
At step 4, the signal 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 an input digital signal. A latch circuit 106 latches and holds data sampled by the shift register 105. An Xm driving 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 includes Vr, Vp, Va, -Va, -V
p, -Vr are input, and an AC inversion signal F
Liquid crystal power supplies Vs, V multiplexed in synchronization with R
n and Vr are generated. Here, Vr ≧ Vp ≧ Va ≧ −Va
Which is the potential of ≧ -Vp ≧ V r. A shift register 109 is activated by a shift start signal DY, performs a shift operation in synchronization with a shift clock signal YSCL, and generates a selection signal Cn. Further, the selection signal one time earlier (by one cycle of YSCL) than the selection signal Cn is defined as Cn-1. 112, 113 and 114 are analog switches, each of which has a power source Vs, Vn, Vr at its source input, and a logical product 11 of selection signals Cn, Cn and Cn-1 at each gate input.
0, the logical product 111 of the inverted signal of Cn and the inverted signal of Cn-1 is connected, and the drain outputs are commonly connected to drive the row electrode Yn. That is, when Cn = "0", the non-selection potential Vn is irrespective of Cn-1, and when Cn = "1" and Cn-1 = "1", the selection potential Vr is Cn = "1" and Cn-1 = " At "0", the selection potential Vs is output to the row electrode Yn. That is, when the selection signal Cn = “1”, Cn = “1”, the output potential is Yn = “+ Vr” when the AC inversion signal FR = “1”, and FR =
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”, and when FR = “0”, Yn = “− Vp”.

[0015] 103 is an active matrix type liquid crystal panel, and the column electrode Xm and the row electrodes Yn are formed on a substrate facing each to its intersection nonlinear element 11 6
The liquid crystal layer 11 5 is disposed in series with the. Here the row electrode potential voltage application pressure of <br/> be in the liquid crystal layer 11 5 and the nonlinear element 11 6 based on, Vl respectively, and Vm.

The characteristics of the nonlinear 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 shown in FIG. 1 will be described from these figures.

In FIG. 7, DY represents a Y driver 102.
The shift register start signal is shifted by the falling edge of the shift clock signal YSCL, and the selection signal is transferred according to the width. now,
One cycle of YSCL is defined as one selection period (normally, one selection period corresponds to one horizontal scanning period, and one horizontal scanning period is hereinafter abbreviated as 1H). In FIG. 7, since the width of DY is four clocks of YSCL, the selection signal also has the width of four clocks of YSCL (corresponding to four selection periods) and is shifted and transferred at the falling edge of YSCL.

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

A description will be given of how the above-described driving is effective in shifting the I / V characteristic of the active element (for example, MIM) on the panel. The I / V characteristic shift is caused by the voltage applied to the element as described above. FIG. 8 shows a signal applied to each pixel when black display is performed on the pixel Xm1Yn and white display is performed on the pixel Xm2Yn at the time of switching to the halftone display at a certain time. Vm
s1 is the effective value added to the MIM when the halftone is selected after the characteristic shift by the black display, Vms2 is the effective value added to the MIM when the halftone is selected after the characteristic shift by the white display, and S1 is the characteristic by the black display. S2 is the effective value for selecting the halftone after the shift and the holding period thereof, and S2 is the effective value for selecting the halftone after the characteristic shift by white display and the holding period. An afterimage is caused by the difference between these effective values. However, in the driving according to the present invention, as apparent from the drawing, a voltage Vmr larger than three times is applied to the element before the true selection voltage Vms, and a substantially larger voltage is applied because the polarity is inverted. (That is, Vmr2> Vmr1) By applying to the MIM element, it is possible to saturate the I / V characteristic shift of the element described above. This means that the characteristic shift of the pixel performing black display and the characteristic shift of the pixel performing white display become the same. 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, the Ts period 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 the image is selected irrespective 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, to make the I / V characteristic shift of the whole screen uniform regardless of the display content, and to eliminate the afterimage. it can. Also, 2
In an 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, a two-terminal active
In the matrix liquid crystal display device, the shift of the I / V characteristic of the non-linear two-terminal element can be saturated, and the image quality can be improved.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing an IV characteristic of a nonlinear element.

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

FIG. 4 is a view showing a window 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 unit in FIG. 1;

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

FIG. 9 is a driving waveform diagram of the 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 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

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-3-73924 (JP, A) JP-A-2-181724 (JP, A) JP-A-3-174513 (JP, A) JP-A-5-174 93898 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G09G 3/36 G02F 1/133

Claims (1)

(57) [Claims] A plurality of row electrodes, a plurality of column electrodes, and a plurality of column electrodes provided corresponding to intersections of the row electrodes and the column electrodes;
A two-terminal element having a non-linear resistance characteristic, comprising: a driving method for a liquid crystal display device, comprising: Applying a voltage having an absolute value, the polarity of which changes at least twice or more, to the two-terminal element to saturate the I / V characteristic of the two-terminal element having the non-linear resistance characteristic;
A method for driving a liquid crystal display device, wherein stable I / V characteristics are obtained.