Driving circuit for a matrix-addressed liquid crystal display device

• US 4,082,430 A
• Filed: 01/21/1977
• Issued: 04/04/1978
• Est. Priority Date: 03/30/1971
• Status: Expired due to Term

• Current Assignee: BBC AG Brown Boveri & CIE
• Original Assignee: BBC AG Brown Boveri & CIE
• Inventors: Wild, Peter J., Schulthess, Peter U.
• Primary Examiner(s): Bauer, Edward S.
• Application Number:
  US05/760,944
• Time in Patent Office: 438 Days
• Field of Search: 350/160 LC, 340/324 M
• US Class Current: 345/87
• CPC Class Codes: G02F 1/135 Liquid crystal cells structurally associated with a photoconducting or a ferro-electric layer, the properties of which can be optically or electrically varied G02F1/133348 takes precedence
• CPC Class Codes: G02F 1/1357 Electrode structure
• CPC Class Codes: G09G 3/2011 by amplitude modulation
• CPC Class Codes: G09G 3/3622 using a passive matrix G09G3/3674 - G09G3/3696 take precedence

Abstract

In a driving circuit for a liquid crystal display matrix, a source of a direct or low-frequency voltage is connected to drive the selected row and column electrodes, and a high frequency voltage is connected to the driving circuit so that the high frequency potential is effective in combination with the low frequency or direct voltage at non-frequency voltage is effective at the selected crossovers. The high frequency voltage suppresses changes in the optical properties of the liquid crystal at the non-selected crossovers.

Claims

1. A driving circuit for a matrix addressed liquid crystal display device comprising a plurality of row and column electrodes forming a matrix, a liquid crystal disposed between said row and column electrodes, resistor means including a plurality of resistors, circuit means connecting one end of each row and column electrode to one end of a respective one of said resistors, further circuit means connecting the other ends of each resistor to a common point, said liquid crystal having a threshold such that low frequency voltages with a magnitude above said threshold cause dynamic scattering of light in said liquid crystal, said driving circuit further comprising first source means for providing a first electric voltage of a frequency less than a given low frequency and having a magnitude greater than the threshold voltage above which said dynamic scattering is caused, said given low frequency being in a frequency range in which the threshold of said liquid crystal means is substantially frequency independent, first means for applying said first electric voltage between selected row and selected column electrodes for causing dynamic scattering at the matrix crossings defined by said selected row and selected column electrodes, and second means including second source means for simultaneously applying a second voltage having a frequency higher than said given low frequency between said selected column and selected row electrodes and said common point so that said first and second voltage components are both present simultaneously at the crossings of non-selected electrodes with selected electrodes, said second voltage of a frequency higher than said given low frequency having a magnitude and frequency at which in combination with said first voltage the dynamic scattering is substantially completely suppressed, and the dynamic scattering due to said first electric voltage alone is not suppressed at the crossing of said selected row and selected column electrodes, whereby cross-talk is avoided.

2. The driving circuit of claim 1, wherein said first electric voltage having a frequency less than said given frequency is a time constant voltage.

3. The driving circuit of claim 1, wherein said first electric voltage having a frequency less than said given frequency is an alternating voltage.

4. The driving circuit of claim 1, wherein said second source means having a frequency higher than said given frequency is connected between said common point of said resistors and a point of reference potential.

5. The driving circuit of claim 1, wherein said common point of said resistors is connected to a point of reference potential, such as ground.

6. The driving circuit of claim 1, wherein said second source means having a frequency higher than said given frequency is connected between a point of reference potential and one terminal of said first source means for providing a first electric voltage, selector means for connecting the other terminal of said first source means to provide a first electric voltage to said selected row and column electrodes, and wherein said resistors connect said electrodes to said point of reference potential.

7. The driving circuit of claim 1, wherein said second source means having a frequency higher than said given frequency has one terminal connected to a point of reference potential, said circuit further including a pair of diode resistor networks connected to the other terminal of said second source means for producing a pair of opposite phase half wave voltages, said second source means further comprising selecting means for applying one of said half wave voltages to a row electrode and the other of said half wave voltages to a column electrode, said resistor means connecting said electrodes to said point of reference potential.

8. The driving circuit of claim 1, wherein said first source means comprises first and second voltage sources having a frequency less than said given frequency, said second source means further comprising a third voltage source of a frequency higher than said given frequency, and a change-over switch means connected between said first and second voltage sources and said selected row and column electrodes for changing the phase or polarity of the voltage applied between said selected row and column electrodes.

9. The driving circuit of claim 1, wherein said first source means comprise voltage divider means connected to separately control voltages applied to said electrodes, whereby the contrast of the cross-overs of said display device may be adjusted.