# US 5,349,367 A · Driving circuit for use in a liquid crystal display device

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- Number: US 5,349,367 A
- Document ID: US5349367A
- Status: Granted
- Kind: A
- Application number: 08/009,850
- Filed: 1993-01-27
- Granted: 1994-09-20
- Earliest claimed: 1992-01-27
- Assignees: Matsushita Electric Industrial Co., Ltd.
- Inventors: Naohide Wakita
- Web page: https://patentgrep.com/patent/US5349367A

## CPC

- G09G 3/3629: {using liquid crystals having memory effects, e.g. ferroelectric liquid crystals}
- G09G 3/2011: {by amplitude modulation}
- G09G 2320/041: Temperature compensation
- G09G: ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION (arrangements for transferring data between digital computers and displays G06F3/14; static indicating arrangements comprising an association of a number of separate sources or light control cells G09F9/00; static indicating arrangements comprising integral associations of a number of light sources H01J, H01K, H10H, H05B33/12; scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission, details thereof H04N1/00)

## Abstract

In a ferroelectric liquid crystal panel, the switching current of spontaneous polarization is detected from the difference between the current supplied to a selected pixel and the constant multiplication of the current supplied to a non-selected reference pixel, and when the amount of switched spontaneous polarization reaches a desired gray scale level, the applied voltage is changed so that even if any nonuniformity is involved within the panel, a uniform analog gray scale display can be realized.

## Claims

### Claim 1

A liquid crystal driving circuit for a liquid crystal panel in which ferroelectric liquid crystals are sandwiched between a plurality of scanning electrodes and a plurality of signal electrodes, which are opposed to each other, said driving circuit comprising:
a switching current detecting section for detecting, from the value of a current supplied from an arbitrary signal electrode a, a switching current value due to switching of spontaneous polarization of the ferroelectric liquid crystals at a selected pixel on the arbitrary signal electrode a;
an integrating section for integrating the switch current value to develop an integral value; and
a comparator for comparing the integrated value with a gray scale indicating voltage which corresponds to gray scale data, wherein the signal voltage value applied to the arbitrary signal electrode a is changed depending on an output of said comparator, so that the gray scale indicating voltage and the integrated value are made coincident with each other.

### Claim 2 (depends on 1)

The liquid crystal driving circuit as claimed in claim 1, wherein the output of the comparator is fed back to an output voltage selecting part of said driving circuit on the side of signal electrodes, whereby when the integrated value is smaller than the gray scale indicating voltage, such a level of signal voltage as to correspond to a select voltage for gray scale data is produced, and when the integrated value exceeds the gray scale signal, the signal voltage is switched to a non-select voltage.

### Claim 3 (depends on 2)

The liquid crystal driving circuit as claimed in claim 2, wherein said switching current detecting section detects said switching current value due to switching of spontaneous polarization, by subtracting a current value resulting from multiplying a current supplied to a reference signal electrode regarded as a non-selected pixel in the vicinity of said selected pixel on the arbitrary signal electrode a by a constant from said current supplied from the arbitrary signal electrode a.

### Claim 4 (depends on 3)

The liquid crystal driving circuit as claimed in claim 3, wherein scanning is effected two times, at a first field scanning one group of signal electrodes, which have been divided into two while the other group is assumed to be said reference signal electrode, and at a second field scanning the other is selected while the one is assumed to be said reference signal electrode.

### Claim 5 (depends on 3)

The liquid crystal driving circuit as claimed in claim 3, wherein the signal voltage is a pulse voltage and the switching current detecting section includes a high frequency cut filter.

### Claim 6 (depends on 1)

A display device, comprising a liquid crystal driving circuit as claimed in claim 1 and a liquid crystal panel in which ferroelectric liquid crystals are sandwiched between scanning electrodes and signal electrodes.

### Claim 7 (depends on 6)

The display device as claimed in claim 6, said liquid crystal panel includes antiferroelectric liquid crystals sandwiched between the scanning electrodes and the signal electrodes.