JPH027443B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a driving method for line-sequential scanning of a liquid crystal matrix display in which the brightness of the liquid crystal depends on the effective value of an AC voltage applied to the liquid crystal.

[Prior art]

In liquid crystal matrix displays, the first
A liquid crystal panel as shown in the figure is used. In FIG. 1, A and B are a plan view and a sectional view, in which 1 is a front glass plate, 2 is a rear glass plate, 3 is a scanning electrode, 4 is a signal electrode, 5 is a spacer, 6 is a liquid crystal, 7, 8 is a polarizing plate.

In FIGS. 1A and 1B, when a predetermined voltage is applied between the scanning electrode 3 and the signal electrode 4, the liquid crystal 6
The electric field generated changes the liquid crystal structure and changes the polarization characteristics.

If the incident light is irradiated from either side of the polarizing plates 7 and 8, and now the incident light is irradiated from the polarizing plate 8, the incident light becomes linearly polarized light by the polarizing plate 8, and passes through the rear glass plate 2 to the liquid crystal. 6. When the liquid crystal 6 has a polarization characteristic according to the applied electric field, the plane of polarization of the linearly polarized light incident thereon is rotated according to this polarization characteristic. In this way,
The linearly polarized light transmitted through the liquid crystal 6 is incident on the polarizing plate 7 through the front glass plate 1, and from the polarizing plate 7, a straight line of light intensity is generated according to the angular difference between the transmission axis of the polarizing plate 7 and the polarization plane of the linearly polarized light. Polarized light is emitted. Therefore, by sequentially applying a predetermined voltage to each intersection between the scanning electrode 3 and the signal electrode 4, an image with each intersection as a pixel is displayed.

Figure 2 is a characteristic diagram showing the relationship between brightness and the effective value of the voltage applied between the scanning electrode and the signal electrode.Characteristic (a) is bright when no voltage is applied, and dark when voltage is applied. Characteristic (b) is a characteristic in the normally open mode, and is a characteristic in the normally closed mode, which is dark when no voltage is applied and becomes bright when a voltage is applied. These modes are determined by how the transmission axes of the polarizing plates 7 and 8 are set, and images can be displayed in either mode.

FIG. 3 is a diagram showing drive waveforms according to the prior art for displaying an image on the liquid crystal matrix panel of FIG. 1. A scanning voltage Vx is applied to the scanning electrode 3, a signal voltage Vy is applied to the signal electrode 4, and the voltage applied to the intersection of the scanning electrode 3 and the signal electrode 4 is Vx-Vy.

In FIG. 3, A1 indicates a selection period of the scanning electrode 3, and A2 indicates a non-selection period. Gradation display is performed by changing the effective voltage by changing the pulse width of the portion indicated by τ in the figure. By the way, the voltage levels V ₁ to _{V 6} of the waveform shown in FIG.
It is known that the following conditions must be satisfied in order to prevent crosstalk between pixels.

However, if a is the bias ratio and N is the reciprocal of the duty ratio of time-division driving, the maximum contrast ratio can be obtained by setting a=√+1 (2).

Here, the variable range of the effective voltage is from 1/aVo√1+(-1)(-3)...(3) to 1/aVo√1+( ^2-1 )...(4).

Therefore, if the threshold voltage of the liquid crystal is Vth, then Vo>Vth・a/√1+(-1)(-3)
N...(5) From formulas (1) and (5) Therefore, it can be seen that when the reciprocal N of the duty ratio of time-division driving is increased or when the threshold voltage Vth of the liquid crystal is high, the peak value Vo of the applied voltage must be increased.

That is, the withstand voltage of the drive circuit that generates the scanning voltage Vx and the signal voltage Vy shown in FIG. 3 needs to be greater than or equal to the peak value Vo of the applied voltage. However,
In general, circuits that drive liquid crystals use CMOS-LSI to take advantage of the low power consumption of liquid crystals.
is used, so the withstand voltage of the drive circuit is limited to 10-odd volts. Therefore, in the conventional driving method, it was necessary to lower the threshold voltage of the liquid crystal. In addition, the drive circuit that generates the scanning voltage Vx is
Since all the pixels corresponding to one scanning electrode must be driven in common, the output impedance must be lowered, so it has been difficult to make the breakdown voltage higher than that of the circuit that drives the signal electrode.

However, in the conventional driving method, both the scanning and signal electrode driving circuits must have a withstand voltage that is equal to or higher than the liquid crystal applied voltage peak value Vo. For this reason, the breakdown voltage of the scan electrode drive circuit has become one of the limiting conditions for improving image quality.

[Purpose of the invention]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for driving a liquid crystal matrix display, which eliminates the drawbacks of the prior art described above and can increase the voltage that can be applied to the liquid crystal even if the withstand voltage of the circuit that drives the scanning electrodes is low.

[Summary of the Invention] The main point of the present invention is to reduce the peak value of the output voltage of a signal electrode drive circuit, which can easily have a relatively high breakdown voltage.
By setting Vo (1+1/a), the minimum voltage of the output of the circuit that drives the scan electrode, which is difficult to increase the withstand voltage, is 1/aVo, and the maximum voltage is Vo, that is, the amplitude value of the output of the driving circuit. The purpose is to set Vo (1-1/a), which is the difference between the minimum and maximum voltages.

[Embodiments of the invention]

Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 4 is a waveform diagram showing an example of driving waveforms for a liquid crystal matrix panel according to the driving method of the present invention. In FIG. 4, Vx is a waveform that drives the scanning electrode, and Vy is a waveform that drives the signal electrode. The voltage applied to the pixel at the intersection of the scanning electrode and the signal electrode is Vx-Vy, and has the same waveform as the conventional example shown in FIG. Below, FIG. 4 will be explained. A waveform Vx with a duty of 50% and having two voltage levels (1/aVo, Vo) with opposite phase relationships in the selection period A1 and the non-selection period A2 is applied to the scanning electrode. A waveform Vy having four voltage levels (0, 2/aVo, (1-1/a)Vo, (1+1/a)Vo) with the same phase relationship as the non-selection period A2 of the scanning electrode is applied to the signal electrode. Apply. Here, the pulse width of the amplitude portion of 0 to 2/aVo, (1-1/a)Vo to (1+1/a)Vo is determined according to the brightness of the liquid crystal pixel. According to this method, the waveform applied to the liquid crystal pixels is the same as the conventional example shown in FIG. 3, so the variable range of the applied voltage is the voltage range given by equations (3) and (4).

FIG. 5 shows an example of the configuration of a driving circuit for a liquid crystal matrix panel according to the driving method of the present invention. In the figure, 9 is a scanning electrode, 10 is a signal electrode, 11 and 12 are electronic switches, and 13 and 14 are control circuits for controlling the respective switches. 1
1 and 13 constitute a circuit for driving the scanning electrode, and 12 and 14 constitute a circuit for driving the signal electrode. 15 is an operational amplifier and constitutes a voltage follower. 17, 18, 19, 20, 21
is a dividing resistor for generating reference voltages of V ₁ , V ₂ , V ₃ , V ₄ , V ₅ , and V ₆ . By setting the respective resistance values to R and (a-3)R, the potential levels V ₁ to V ₆ shown in FIG. 4 can be obtained at the output of the voltage follower. 16 is a power supply terminal of the signal electrode drive circuit, to which a voltage of (1+1/a)Vo is applied. However, it is assumed that Vo satisfies equation (6). Reference numerals 170 and 180 are power supply terminals of the scanning electrode drive circuit, to which voltages of V ₅ and V ₂ are applied.
This potential difference is (1-1/a)Vo.

In the drive circuit of FIG.
alternately selects and outputs the potential levels of V ₂ and V ₅ .
Further, the electronic switch 12 selectively outputs V ₁ , V ₃ , V ₄ , and V ₆ . By doing this,
The liquid crystal matrix panel can be driven by the drive waveform shown in FIG.

〔Effect of the invention〕

According to the present invention, the breakdown voltage of the scan electrode drive circuit can be set to (1-1/a)Vo. Therefore, it is possible to drive a liquid crystal with a high threshold voltage, thereby improving image quality. In addition, since only two potential levels of the output waveform of the scan electrode drive circuit are required, the circuit can be simplified.

[Brief explanation of drawings]

Figure 1A is a plan view of a typical liquid crystal panel, Figure B is a cross-sectional view of the same, and Figure 2 shows the relationship of brightness to the effective value of the voltage applied between the scanning electrode and the signal electrode in the liquid crystal panel. 3 is a waveform diagram showing a conventional driving waveform in a liquid crystal panel, FIG. 4 is a waveform diagram showing an example of a driving waveform when using the driving method of the present invention, and FIG. 5 is a waveform diagram showing an example of the driving waveform when using the driving method according to the present invention FIG. 2 is a circuit diagram showing an example of a configuration of a drive circuit used in the implementation. Description of symbols, 1...Front glass plate, 2...Rear glass plate, 3...Scanning electrode, 4...Signal electrode, 5...Spacer, 6...Liquid crystal, 7, 8...Polarizing plate, 9...Scanning electrode,
10... Signal electrode, 11, 12... Electronic switch, 1
3, 14...control circuit, 15...operational amplifier, 16...
Power supply terminal, 17-21...Division resistor, 170, 18
0...Power terminal.

Claims (1)

[Claims] 1. An intersection of a matrix formed by crossing a signal line and a scanning line is defined as one pixel of a liquid crystal cell,
A method for driving the signal line and scanning line in a liquid crystal matrix display in which the brightness of each pixel is determined depending on the effective value of an AC voltage applied between the signal line electrode and the scanning line electrode at the pixel position, , the reciprocal of the duty ratio of time-division driving is N,
When the peak value of the applied voltage is Vo, the bias ratio a is selected to be a≈√+1, and during the period when no scanning line is selected, an AC voltage consisting of two voltage levels of 1/aVo and Vo is applied to the scanning line. However, during the selected period, an AC voltage having the opposite phase and the same voltage level as the AC voltage is applied to the scanning line, and an AC voltage is applied to the signal line even during the period when the scanning line is not selected. Even in the selected period, the phase relationship is the same, and the first half is 0 and 2/aVo, and the second half is (1+1/a)Vo and (1-1/a)Vo, which is an alternating current with a total of four levels. A voltage is applied, and the ratio of the period when the voltage level is 0 and the period of 2/aVo and the period of (1+1/a)Vo and (1-1/a)Vo is determined according to the brightness of the corresponding liquid crystal pixel. A method for driving a liquid crystal matrix display, characterized in that: