JPH0553092A - Driving waveform - Google Patents

Abstract

PURPOSE:To reduce leakage in non-selection, to obtain stable contrast for temperature change, and also, to reduce crosstalk and unnaturalness in gradation display. CONSTITUTION:The driving waveform of a signal applied between the upper and lover substrates of a liquid crystal panel in which a two-terminal element is formed on at least the substrate on one side is provided with a selective period and a non-selective period, and the time means of the potential in the non-selective period shows not always a value other than 0 volt, and a fluctuation rate by the temperature of the maximum potential 11, 12 in the non- selective period is set higher than the fluctuation rate by the temperature of such mean potential. Also, the fluctuation rate by the differential temperature of selective pulses in selective periods when the liquid crystal panel is put on and off is set smaller than the fluctuation rate by the temperature of the maximum potential 11, 12 in the selective period when the mean range between 10-50 deg.C is taken.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to optimization of a drive waveform of a liquid crystal panel using a two-terminal element such as MIM, and particularly to temperature compensation.

[0002]

2. Description of the Related Art In recent years, large-capacity matrix liquid crystal panels have begun to be used for personal computer displays and the like. When these liquid crystal panels are classified by the address system, they are classified into a simple matrix system, an active matrix system, an optical address system and the like. In view of the above, the active matrix system has come into the market as a display with high image quality and large capacity. A typical active matrix liquid crystal panel is a TFT liquid crystal panel using amorphous silicon or polysilicon. In addition, a two-terminal element has been manufactured, which has a simple manufacturing process and is expected to have a high yield and a low cost. Two
A typical terminal element is a MIM liquid crystal panel.
Hereinafter, the MIM panel will be described as an example.

FIG. 2 shows an example of drive waveforms applied between the upper and lower substrates of a conventional liquid crystal panel. The horizontal axis represents time, and the vertical axis represents voltage. (1) shows a drive waveform when the panel is on. (2) is a diagram showing a drive waveform when the panel is off. Reference numeral 21 is a selection period, and 22 is a non-selection period.
Reference numeral 23 is a selection pulse when turned on. The bias potential 24 is the time average of the potentials Va and Vb of the signal when not selected. This bias potential differs between the positive period 26 and the negative period 27, and the bias potential 25 in the negative period is the time average of Vc and Vd. When the panel is off, the voltage 28 of the selection pulse is lower by the data amplitude voltage 211 than when it is on. (3) shows the voltage applied to the liquid crystal of the pixel. The solid line is the voltage waveform 29 when the ON waveform is applied to the panel, and the broken line is the voltage waveform 210 when the OFF waveform is applied to the panel. In this way, the effective voltage applied to the liquid crystal can be drastically changed by changing the voltage level during the selection period, so that display can be performed.

FIG. 3 is a diagram showing changes in the drive waveform of the conventional MIM liquid crystal panel when the temperature is changed. (1) shows a voltage waveform at the time of ON which is applied between the upper and lower substrates at a temperature of 20 ° C. (2)
Shows a voltage waveform at the time of ON, which is applied between the upper and lower substrates at a temperature of 50 ° C. It can be seen that the voltage level of the drive waveform applied to the panel is decreased by increasing the temperature. When the maximum potential at the time of turning on is named the maximum selection potential, the rate of change VS (50) / VS (20) of the maximum selection potentials 31, 32 due to temperature is the rate of change VB (50) / VB (of the bias potentials 33, 34). It was the same as 20). (3) shows the waveform of the data signal when the temperature is 20 ° C. (4) shows a data signal waveform at a temperature of 50 ° C. (5) is the selection signal waveform when the temperature is 20 ° C., and (6) is the temperature 5
It is a selection signal waveform at 0 ° C. The signal waveform of (1) is
The signal waveform of (3) is obtained by subtracting the signal waveform of (5), and the signal waveform of (2) is obtained by subtracting the signal waveform of (6) from the signal waveform of (4). FIG. 4 is a diagram showing an example of a temperature compensation circuit of a conventional MIM liquid crystal panel. The voltage between A and B (the potential at the point A is V0 and the potential at the point B is V7) changes with the temperature change. This voltage is resistance-divided and other voltages V1: 35, V2: 36, V3: 37, V4: 3 are input to the panel.
It produces 8, V5: 39 and V6: 310. Therefore, the rate of change of all voltage changes with temperature is constant. Since the bias potential VB is also represented by (V0-V3) / 2- (V0-V1), it changes at a constant rate of change like other voltages. Since the maximum selection potential is equal to the potential between A and B, it naturally has the same rate of change. Reference numeral 41 is a temperature compensation circuit block.

[0005]

However, the conventional technique has the following problems.

Since the bias potential changes depending on the temperature, even if the bias is adjusted to the optimum bias at normal temperature, the leakage increases at high and low temperatures, the contrast of the panel is significantly lowered, crosstalk increases, and gradation display is unnatural. It became.

FIG. 5 is a graph showing the temperature dependence of the voltage-luminance characteristic of the liquid crystal. From 10 ℃ to 50 ℃,
Only -0.25 volt change occurs. MI at room temperature
It is preferable that the range of voltage used in the M panel is a shaded range and the bias potential VB is approximately in the center of the shaded range. When the bias potential is deviated from the center, the voltage applied to the element increases and the leak at the time of non-selection increases. The magnitude of the change in the bias voltage at present is 10 ° C to 50 ° C.
At about -1.0 volt, which is larger than the ideal. Further, the shaded range may be shifted to the lower voltage side (left side in the figure) when the temperature changes, and the width of the shaded line hardly changes. This means that it is not necessary to change the data amplitude voltage largely depending on the temperature.

An object of the present invention is to reduce leakage when not selected, to obtain stable contrast against temperature changes, and to reduce crosstalk and unnatural gradation display.

[0009]

The above object can be achieved by the following means.

In the drive waveform of the signal applied between the upper and lower substrates of the liquid crystal panel in which the two-terminal element is formed on at least one substrate, the drive waveform has a selection period and a non-selection period. The maximum potential of is referred to as the maximum selection potential, and the time average of the potentials in the non-selection period is referred to as the bias potential. The feature is that it is set larger than the fluctuation rate.

When the difference between the selection pulses in the selection period when the liquid crystal panel is turned on and when it is not turned on is called a data amplitude voltage,
The fluctuation rate of the data amplitude voltage depending on temperature is 10 ° C. to 50 ° C.
It is characterized in that the average of the range of ° C is set to be smaller than the variation rate of the maximum selected potential with temperature.

[0012]

FIG. 6 is a diagram for explaining the reason why the selection pulse of the drive waveform is changed depending on the temperature. The relationship between the voltage and current of the element is shown by the relationship shown in the graph of FIG. 10 ° C
Is shown by a solid line and a graph at 50 ° C. is shown by a broken line. 10
Operating points at ° C are indicated by black circles. If the same current is applied to the element at 50 ° C., the operating point becomes a white circle, and the voltage applied to the element becomes lower than that at 10 ° C. As described above, since the MIM element has a large temperature dependency in the voltage-current characteristic, temperature compensation must be performed by the drive waveform. The structure of the present invention can achieve the object because the compensation of the change in the characteristics of the device due to the temperature and the compensation of the temperature dependence of the liquid crystal can be performed separately.

[0013]

EXAMPLE An example of the present invention will be described below.

FIG. 1 is a diagram showing how the drive waveform of the MIM liquid crystal panel of the present invention changes when the temperature is changed. (1) shows a voltage waveform at the time of ON which is applied between the upper and lower substrates at a temperature of 20 ° C.
(2) shows a voltage waveform at the time of ON which is applied between the upper and lower substrates at a temperature of 50 ° C. The maximum selection potentials 11 and 12 change depending on the temperature, but the bias potentials 13 and 1 change.
4 does not change with temperature. (3) shows the waveform of the data signal when the temperature is 20 ° C. (4) shows a data signal waveform at a temperature of 50 ° C. (5) is a selection signal waveform when the temperature is 20 ° C., and (6) is a selection signal waveform when the temperature is 50 ° C. The signal waveform of (1) is obtained by subtracting the signal waveform of (5) from the signal waveform of (3),
The signal waveform of (2) is obtained by subtracting the signal waveform of (6) from the signal waveform of (4).

FIG. 7 is a diagram showing another example of the change in the drive waveform of the MIM liquid crystal panel of the present invention when the temperature is changed. (1) shows a voltage waveform at the time of ON which is applied between the upper and lower substrates at a temperature of 20 ° C. (2) shows a voltage waveform at the time of ON which is applied between the upper and lower substrates at a temperature of 50 ° C. The rate of change VS (50) / VS (20) of the maximum selection potentials 31, 32 due to temperature is higher than the rate of change VB (50) / VB (20) of the bias potentials 33, 34. (3) shows the waveform of the selection signal when the temperature is 20 ° C. (4) is a data signal waveform when the temperature is 20 ° C., and temperature compensation is performed separately for the data signal and the selection signal.

FIG. 8 is a diagram showing an example of a temperature compensation circuit of the MIM liquid crystal panel of the present invention. The drive waveform corresponds to FIG. The voltage between A and B (the potential at the point A is V0 and the potential at the point B is V7) changes with the temperature change. This voltage is applied to the resistor and Zener diode 8
Another voltage V1 to be input to the panel divided by 1, 82:
35, V2: 36, V3: 37, V4: 38, V5: 39,
V6: 310 is produced. The bias potential VB is constant regardless of the temperature. Since the maximum selection potential is equal to the potential between A and B, it changes with temperature.

FIG. 9 is a diagram showing another example of the temperature compensation circuit of the MIM liquid crystal panel of the present invention. The drive waveform also corresponds to FIG. The voltage between A and B (the potential at the point A is V0 and the potential at the point B is V7) changes with the temperature change. This voltage is applied to the resistance and the heat-sensitive resistance element 9
1 or other voltage divided by a diode or the like and input to the panel V1: 35, V2: 36, V3: 37, V4: 38,
It produces V5: 39 and V6: 310. The bias potential VB varies depending on the temperature, but the rate of change is set smaller than the maximum selection potential, that is, the rate of temperature change of the potential between A and B.

FIG. 10 is a diagram showing another example of the temperature compensation circuit of the MIM liquid crystal panel of the present invention. The drive waveform corresponds to FIG. 7. Selection signal and data signal potentials 71 and 7
2, 73, 74, 75, and 76 are separately temperature-compensated by the temperature compensating circuits 101 and 102, and the bias potential VB changes depending on the temperature, but its change rate is higher than the temperature change rate of the maximum selection potential. It is set small.

[0019]

According to the present invention, even when the temperature changes, the MIM element produces a liquid crystal panel which has little leakage in the non-selected period, stable contrast and little crosstalk, and excellent gradation. You can

[Brief description of drawings]

FIG. 1 is a diagram showing how a drive waveform of an MIM liquid crystal panel of the present invention changes when temperature is changed.

FIG. 2 is an example of a drive waveform applied between the upper and lower substrates of a conventional liquid crystal panel.

FIG. 3 is a diagram showing changes in the drive waveform of the conventional MIM liquid crystal panel when the temperature is changed.

FIG. 4 shows an example of a temperature compensation circuit of a conventional MIM liquid crystal panel.

FIG. 5 is a graph showing temperature dependence of voltage-luminance characteristics of liquid crystal.

FIG. 6 is a diagram for explaining the reason why the selection pulse of the drive waveform is changed according to the temperature.

FIG. 7 is a diagram showing another example of changes in the drive waveform of the MIM liquid crystal panel of the present invention when the temperature is changed.

FIG. 8 shows an example of a temperature compensation circuit of the MIM liquid crystal panel of the present invention.

FIG. 9 shows another example of the temperature compensation circuit of the MIM liquid crystal panel of the present invention.

FIG. 10 shows another example of the temperature compensation circuit of the MIM liquid crystal panel of the present invention.

Claims (2)

[Claims] 1. A drive waveform of a signal applied between upper and lower substrates of a liquid crystal panel in which a two-terminal element is formed on at least one substrate, the drive waveform has a selection period and a non-selection period, The maximum potential in the selection period is referred to as the maximum selection potential, and the time average of the potentials in the non-selection period is called the bias potential. The bias potential is not always 0 volt,
A driving waveform characterized in that the variation rate of the maximum selection potential with temperature is set to be larger than the variation rate of the bias potential with temperature when the range of 10 ° C. to 50 ° C. is averaged. 2. When the difference between the selection pulses in the selection period when the liquid crystal panel is turned on and when the liquid crystal panel is not turned on is referred to as a data amplitude voltage, the rate of variation of the data amplitude voltage with temperature is 10 ° C.
2. The drive waveform according to claim 1, wherein the average of the range of 50 [deg.] C. is set to be smaller than the variation rate of the maximum selection potential with temperature.