JPS6165222A - Liquid-crystal driving method - Google Patents

Abstract

PURPOSE:To equalize the modulation speed of a pulse width modulator to the period T of liquid-crystal driving by applying one driving electrode with a rectangular wave voltage having a period T/A, where A is display gradations, and the other electrode with a pulse which has a period T and also it is applied with pulse width modulation with an input gradation signal. CONSTITUTION:A pulse 11 from a rectangular wave generator 11a which has a period equal to the gradation display period T is multiplied by a frequency multiplier 32a into a pulse 32 which has a period T/A, where A is display gradations; and the pulse 32 is applied to a liquid-crystal driving electrode 3. A pulse width modulator 31a is modulated with a gradation signal 21 and a pulse 31 whose pulse width is an integral multiple of T/A is outputted. The other electrode 1 of liquid crystal 2 is applied with the exclusive OR output 33 between inputs 31 and 32. The applied voltage 32-33 between electrodes is 0V when the pulse 31 is at a level L and becomes a rectangular wave alternating current which has a mean value O, + or -V volt peaks, and period T/A, thereby driving the liquid crystal according to the gradation signal 21. Consequently, the memory readout speed and arithmetic speed of the pulse width modulator are reduced to a half as fast as before.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention utilizes a liquid crystal as an electric shutter, and is used in a liquid crystal device that displays an image in combination with a backlight, etc., and allows gradation display by controlling the transmittance. This invention relates to a liquid crystal driving method.

Conventional Structure and Problems If a DC voltage is applied to a liquid crystal device for a long time, the liquid crystal will be destroyed due to electrochemical changes, so normally an AC voltage is applied to control the light transmittance. Normally, to display halftones (1)
Two methods have been used: (2) a method of controlling the applied AC voltage; and (2) a method of controlling the application time of the applied AC voltage.

Figure 1 (fL), (blt/'i) shows the cross-sectional structure of a liquid crystal device and the driving voltage waveform of the electrodes in the conventional liquid crystal driving method. Powered by voltage.

In FIG. 1 (2L), 1.2.3 is a schematic diagram of a liquid crystal device, 1.3 is a liquid crystal drive electrode, 2 is a liquid crystal, and drive electrode 1.2.3 is a schematic diagram of a liquid crystal device.
It shows the liquid crystal sealed between 3. Furthermore, in FIG. 1 (bl), 11 is a square wave with a period T, duty 50%, and voltage that oscillates between +V volts and 0 volts, which is applied to the liquid crystal drive electrode 2, and when this voltage is applied to the electrode 3, When the same voltage is applied to electrode 1 facing gold for 11 times as shown in 12, the voltage between the liquid crystal electrodes is 11-12=
0, no driving voltage is applied to the liquid crystal, the light transmittance is small, and a black display is produced (the display is determined by the arrangement of the polarizing plates combined with the liquid crystal, but here the polarizing plates are arranged in this way). Next, when a voltage such as 13, which differs in phase from 11 by 180, is applied to electrode 1, the voltage applied to the liquid crystal is 1
l-13 = (±V, resulting in a white display. When applying a voltage 14, which differs only in phase from 11 by a certain angle α (○ α < 180) to the electrode 1, the voltage applied to the liquid crystal is 11-14 =
Since a period of 1.5 occurs, the liquid crystal is not driven sufficiently compared to case 13, resulting in a half-tone display.

FIGS. 2(a) and 2(b) show circuit blocks and waveforms for driving as shown in FIG. 1. In FIG. 2(a), 21 is a gradation signal input, 112Lld is a square wave generator that generates a square wave with a period T and a duty of 50%, and 11 is its output waveform. 11 and is added to the liquid crystal electrode 3. 22SL is a pulse width modulator in which the rising and falling edges of the square wave 11 generated by the square wave generator 11& are used as rising edges, and the pulse width thereof changes depending on the gradation signal, and 22 is its output waveform. 23 is an exclusive OR circuit that performs an exclusive OR operation, and obtains an output 24 from the input of 22.11, which is applied to the liquid crystal electrode 1. Second
As shown in the figure (bl), the output 22 of the pulse width modulator 22& starts at 10, 12, 14, . . . , and the pulse width changes depending on the input grayscale signal 21 (tl.

t3... is a pulse width modulated pulse whose period is T. At this time, the period is equal to the exclusive OR output 24i11 of inputs 22 and 11, and the phase is input 2.
1, that is, a signal obtained by phase modulating the signal 11, which is the same signal as 14 in FIG. 1(b).

In this way, it is possible to drive the liquid crystal to display gradations by applying voltage signals that differ only in phase depending on the gradation to the two electrodes of the liquid crystal. In order to obtain modulated pulses, a pulse width modulator 222L with a bar period of pulse period T applied to the liquid crystal, that is, twice the modulation speed, is required, and when performing pulse width modulation using a memory, the readout speed is doubled. This causes inconvenience in the circuit configuration.

OBJECTS OF THE INVENTION The present invention eliminates the drawbacks of the prior art example, and aims to make the modulation speed of the pulse width modulator equal to the liquid crystal drive period T.

Structure of the Invention In order to achieve the above object, the present invention applies a high frequency square wave voltage with a period T/mu, assuming the display gradation is mu, to one liquid crystal drive electrode, and applies a high frequency square wave voltage with a period T/mu to the other electrode. The descent coincides with the rise (or fall) of the above high frequency,
This applies a pulse with a period T whose pulse width is modulated by the input gradation signal, and has the advantage of being equal to the modulation period of the pulse width modulator, which is faster than the speed of the conventional example.

DESCRIPTION OF THE EMBODIMENTS Below, the liquid crystal driving method of the present invention will be explained with reference to the drawings. In FIG. vessel, 1
1 is its output waveform, which is the same as in FIGS. 1 and 2. 322L is a frequency multiplier that multiplies the pulse frequency of the signal 11 by the display gradation, 32 is its output waveform diagram, 31fL is a pulse width modulator with a period T that is pulse width modulated by the gradation signal, and 31 is its output waveform diagram. Output, 23 is exclusive OR circuit, 3
The output of 3 ke is shown. 1+ 2+ 3t 112L+
11+ 21+ 23, etc. indicate the same items as those in FIGS. 1 and 2.

In FIG. 3, a pulse 11 whose period is the gradation display period T
r/'i frequency multiplier 32a, if the display gradation is human (mu is a positive integer), the frequency is multiplied by mu, and the period is T.
/m pulse 32 is applied to the liquid crystal drive electrode 3. On the other hand, the pulse width modulator 312L is a pulse width modulator whose output pulse width is width-modulated by the gradation signal 21, and outputs a pulse whose pulse width is an integral multiple of T/mu. The waveform is shown in 31. The exclusive OR output 33 of the inputs 31 and 32 is applied to the other electrode 1 of the liquid crystal.

As a result, as shown in FIG. 3, the voltage applied between the liquid crystal drive electrodes 32-33 is 0 volts during the period when 31 is at L level;
1 is H level period t (changes depending on the gray scale signal 21), a square wave alternating current with an average value of 0 and a heat V volt period T/mu is applied, and the liquid crystal is driven according to the gray scale signal 21. .

When the liquid crystal element consists of a common electrode and a large number of segment electrodes, a high frequency pulse 32 is applied to the common electrode, and a modulation pulse 33 is applied to the segment electrodes during the display period.

Effects of the Invention As described above, according to the present invention, the conventional pulse width modulator only has to output a pulse width modulation output with the same period as the gradation display period T, and the memory read speed of the pulse width modulator can be improved. It has advantages over the conventional example in terms of speed and calculation speed.

[Brief explanation of drawings]

Figures 1(a) and (bl are block diagrams and waveform diagrams explaining the conventional liquid crystal driving method, and Figures 2(a) and (b) are circuit block diagrams and waveform diagrams for realizing the conventional liquid crystal driving method. Figures 3(a) and 3(b) are circuit block diagrams and waveform diagrams for realizing the method of the present invention. 1.3...Liquid crystal drive electrode, 2... Liquid crystal, 11a...Square wave generator, 31a...
・Pulse width modulator, 32aL... Frequency multiplier. Name of agent: Patent attorney Toshio Nakao and 1 other person72
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Claims (1)

[Claims] A high-frequency pulse is applied to a common electrode among the liquid crystal drive electrodes, and the segment electrode is modulated with a pulse width whose frequency is lower than that of the high-frequency pulse applied to the common electrode and whose pulse width period corresponds to an integral multiple of the period of the high-frequency pulse. A liquid crystal driving method characterized by controlling the gradation of a liquid crystal by applying a pulse.