JPS6042947B2 - Brightness modulation signal generator for liquid crystal display devices - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device that generates signals for displaying halftones in a device that displays images with halftones using a matrix panel.

Display devices using liquid crystals have the advantage of low power consumption and can be viewed even in bright places, so they are used in calculators, watch display panels, etc., and research is also being conducted to use them as TV display devices. .

When a voltage is applied to a liquid crystal, the light transmittance or scattered light intensity changes.

BACKGROUND ART Liquid crystal matrix panels in which pixels are formed in a matrix using transparent electrodes are usually used in alphanumeric display devices, television image display devices, and the like that use liquid crystals. 1st
The figure shows an example of the structure of a liquid crystal matrix panel.
is a front view, and B is a sectional view taken along line A(7)B, -B in the figure.

Band-shaped transparent electrodes 3 and 4 are formed on the surfaces of two glass plates 1 and 2 having a thickness of -. The two glass plates are bonded together via a spacer 5 with a thickness of 10 to several tens of microns, and the gap 6 is filled with liquid crystal.

Polarizing plates 7 and 8 are closely attached so that the planes of polarization are perpendicular or parallel. Among the strip electrodes, 3 are scanning electrodes (hereinafter referred to as Y
4 is a signal electrode (hereinafter referred to as an X electrode). As shown in FIG. 2, the liquid crystal matrix panel has Y electrodes Y1, Y2,
Y. , Y4, and the X electrode is scanned sequentially as X electrode drive circuit 1.
A signal for displaying letters and numbers by 0 or, in the case of a television, a video signal converted into a digital signal is applied. When a voltage is applied to the Yi electrode and the XJ electrode, the liquid crystal at the intersection changes the amount of light transmitted, so the brightness changes.

That is, in FIG. 1B, when the polarization planes of the two polarizing plates 7 and 8 are perpendicular to each other, the light is bright when no voltage is applied, and becomes dark when a voltage is applied because the amount of light transmitted decreases.
When the polarization planes of the two polarizing plates 7 and 8 are parallel, it is dark when no voltage is applied, and becomes bright when a voltage is applied because the amount of light transmitted increases.

In either case, alphanumeric characters or television images can be displayed. The above is an explanation for the field effect mode (FEM) of liquid crystals, but the brightness can also be changed by changing the voltage in the dynamic scattering mode (DSM), which is transparent when no voltage is applied and becomes cloudy and opaque when a voltage is applied. can be controlled. FIG. 3 shows a known drive waveform for a liquid crystal matrix. CP is a clock pulse for AC driving the liquid crystal. are luminance modulation signals Yl, y2... for displaying an image with halftones on a liquid crystal matrix panel.
... is the output signal of the shift register that performs scanning, Vy
is the voltage waveform applied to the Y electrode (Y1 electrode in this case),
(2) X is a voltage waveform applied to the Xj electrode. Vy-Vx
is a voltage waveform applied to the liquid crystal at the intersection of the Y1 electrode and the Xj electrode. It is known that when the number of scanning lines is N, in order to obtain the optimum driving condition, a needs to be set to a value given by the following formula in the formula giving y-Vx.
At this time, the effective voltage S applied to the liquid crystal is given by the following equation.

m is the modulation rate.

Since 0≦τ≦T, 0≦m≦1.

Since m can be changed by changing τ, V
s can be changed. Therefore, it is possible to display an image with halftones. In order to display halftones, m can be changed, and for that purpose, τ can be changed.

FIG. 4 shows a brightness modulation signal (hereinafter referred to as basic pulse width signal) for displaying halftones, and the pulse width ratio is 1:21:22:...2k-1. Using this basic pulse width signal, the pulse width τ is changed by performing the logical operation expressed by equation (4) to obtain a brightness modulation signal τ. This shows the principle of the present invention that can obtain .tau.7. FIG. 4 and equation (4) show the case where k=3, and 8-gradation (generally 2k gradation) display is possible.

The object of the present invention is to achieve a pulse width ratio of 1:21:7:
...An object of the present invention is to provide a device for providing a basic pulse width signal in a method of performing brightness modulation using a 2k-1 basic pulse width signal.

The configuration of the present invention includes a 2k-bit shift register that is cleared by a display start signal of information content for one scanning period, a clock pulse generator that generates a clock pulse for operating the shift register, and a 2k-bit shift register of the shift register. an inverter that inverts the output of the shift register and supplies it as an input signal to the shift register; outputs of the first bit and second bit of the shift register; outputs of the second bit and the seventh bit; An exclusive OR operation is performed on each of the two outputs of the 1st bit and the 2nd k-bit output, and each output has k basic pulse widths with a pulse width ratio of 1:21:S>':...2k-1. k exclusive OR gates that generate the same waveform twice within one scanning period, and the output signal of the inverter are input, reset by the display start signal, and the output drives a liquid crystal matrix panel. It consists of a flip-flop that generates a clock pulse.

FIG. 5 shows an embodiment according to the present invention.

11 is an 8-bit shift register, 12, 13, and 14 are 2
Input exclusive OR gate (Exclusively-0
15 is an inverter, 16 is a flip-flop, 17 is a clock pulse generator, and 18 is a reset pulse generator for resetting the shift register 11 and the flip-flop 16.

FIG. 6 is a timing chart showing waveforms at various parts in FIG. The explanation will be given below using FIGS. 5 and 6. First, the shift register 11 and flip-flop 16 are reset by the output PT of the reset pulse generator 18.

17 generates a clock pulse only when PT=1.

At this time, the outputs a1 to A8 of the shift register 11 are all O, and the output CP of the flip-flop 16 is also zero. The output of A8 is inverted by an inverter 15 and applied to the input 1n of the shift register 11. At one point, when the clock pulse CK is applied, Al, a2, .
, A8 become 1 in sequence. When A8 becomes 1, A8 is inverted by inverter 15 and applied to flip-flop 16, so the output CP of 16 becomes 1. At the same time, the input of the shift register 11 becomes 0. Therefore, a1 becomes O by the 8th clock pulse CK, and thereafter, each time the clock pulse CK is applied, A2, a3, etc.
, A8 become 0 one after another. After the first clock pulse,
After Δ2, the reset pulse level is applied again to the shift register and the flip-flop, so a1 to A8 all become 0 and CP also becomes 0 at the same time.

Pl, P2, and P4 can be obtained by performing the calculation of equation (5). However, 1 means exclusive OR. In FIG. 6, a1 becomes 1 after Δ1 after PT becomes 0, and the b-th clock pulse CK
After Δ2, A8=0 and cp=o.

Δ1 and Δ2 can be made sufficiently small by adjusting the oscillation frequency and pulse width of the clock pulse CK. Above, h=3, that is, 8 on the liquid crystal matrix panel.
We have explained an example of displaying an image with halftones of 2k gradations (when k = 3 in 2k gradations), but in general, to display an image with 2k gradations of halftones, Just A.

The present invention is not limited to an image display device using a liquid crystal matrix panel, but can also be applied to a matrix display device in which brightness can be controlled using the device according to the present invention, for example, a display device in which light emission time can be controlled by an applied signal voltage. It is clear that the same can also be applied. The PT in FIG. 6 uses a horizontal synchronizing pulse or a frequency-divided horizontal synchronizing pulse (for example, Mu frequency division, A frequency division, etc.) when displaying a television image.

Further, in FIG. 5, the explanation has been made using the reference numeral 16 as a J1K flip-flop, but the same operation can be performed using an R-S flip-flop or a T flip-flop. As described above, the present invention has the following effects. (1) Since a shift register that operates with clock pulses having a constant period is used, the ratio of pulse widths can be determined accurately.

(2) The circuit configuration is extremely simple and can be easily integrated into an LSI.

[Brief explanation of drawings]

Figure 1 is a front view and cross-sectional view showing an example of the configuration of a liquid crystal matrix panel, Figure 2 is a diagram showing the driving principle of the liquid crystal matrix panel, Figure 3 is a diagram showing the driving waveform of the liquid crystal matrix panel, and Figure 4 is a diagram showing the driving principle of the liquid crystal matrix panel. FIG. 5 is a diagram illustrating an embodiment of a basic pulse width signal generator according to the present invention; FIG. 6 is a diagram illustrating waveforms of various parts of FIG. 5. . 11: 2k bit shift register, 12, 13, 14
: exclusive OR circuit, 15: inverter, 16: flip-flop, 17: clock pulse generator, 18: reset pulse generator.

Claims (1)

[Claims] 1. In a device that displays an image with 2^k gray scales (k is a positive integer) using a liquid crystal matrix panel,
a 2^k-bit shift register that is cleared by a display start signal of information content for one scanning period; a clock pulse generator that generates a clock pulse for operating the shift register; one inverter that inverts an output signal and supplies it as an input signal to the shift register; outputs of the first and second bits of the shift register; outputs of the second bit and the second^2 bit; ..., the second ^k^-^1 bit and the second
Exclusive OR operation is performed on each of the two k-bit outputs, and each output has a pulse width ratio of 1:2^1:2^2:...2
k exclusive OR gates that generate the same waveform twice in one scanning period from k basic pulse width signals of ^k^-^1, and the output signal of the inverter as input, and the display start signal 1. A brightness modulation signal generating device for a liquid crystal display device, comprising: one flip-flop that is reset by a flip-flop and generates a clock pulse for driving a liquid crystal matrix panel at its output.