# US 4,392,718 A · Resistive electrode LCD and voltage supply means

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- Number: US 4,392,718 A
- Document ID: US4392718A
- Status: Granted
- Kind: A
- Application number: 06/221,499
- Filed: 1980-12-30
- Granted: 1983-07-12
- Earliest claimed: 1980-01-12
- Assignees: Ferranti Limited (now Ferranti plc)
- Inventors: John M. Morrison
- Web page: https://patentgrep.com/patent/US4392718A

## CPC

- G01R 13/407: {using a plurality of passive display elements, e.g. liquid crystal or Kerr-effect display elements (G01R13/408 takes precedence)}
- G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12)

## Abstract

A liquid display device comprises two spaced electrodes each having a resistance characteristic such that a potential gradient may be developed across the electrode. A liquid crystal material is located between the two electrodes. Voltage supply means are provided which apply an alternating potential across each electrode, such that the two potentials are of the same frequency, and, preferably, in quadrature with one another.

## Claims

### Claim 1

A display device which includes a pair of spaced electrodes each having a resistance characteristic such that a potential gradient may be developed across the electrode, a pair of terminals on each electrode located such that the potential gradients developed across the two electrodes extend at an angle to one another, a liquid crystal material located between the two electrodes and being of a type which becomes opaque when an electric field is applied across it, voltage supply means operable to apply an alternating potential across each pair of terminals, such that the two potentials are of the same frequency and are out of phase with one another by an angle which determines the form of the display and in which the voltage supply means are arranged to provide, across each electrode, a constant voltage and include means for varying the potential of each terminal with respect to a reference potential.

### Claim 2 (depends on 1)

A display device as claimed in claim 1 in which the electrodes are arranged such that their potential gradients are perpendicular to one another, and in which the alternating potentials applied across the two pairs of terminals are in quadrature with one another.

### Claim 3 (depends on 2)

A display device as claimed in claim 2 in which at least one of the electrodes is transparent and is mounted on a transparent substrate.

### Claim 4 (depends on 1)

A display device as claimed in claim 1 in which the voltage supply includes, for each electrode, multiplying means to which are applied a constant alternating input voltage and a variable control voltage and having its output connected to one terminal of the electrode, a constant gain amplifier to which is applied the said input voltage, and a summing amplifier having as its inputs the outputs of the multiplier and of the constant gain amplifier and having its output connected to the other terminal of the electrode.

### Claim 5 (depends on 4)

A display device as claimed in claim 4 in which the control voltage is variable over the range from zero to a value numerically equal to the gain of the constant gain amplifier.

### Claim 6 (depends on 1)

A display device as claimed in claim 1 in which the alternating potentials are of sinusoidal waveform.