Addressing liquid crystal cells

• US 4,909,607 A
• Filed: 03/31/1987
• Issued: 03/20/1990
• Est. Priority Date: 04/01/1986
• Status: Expired due to Term

• Current Assignee: Nortel Networks Limited (Nortel Networks Corporation)
• Original Assignee: STC PLC (f/k/a Standard Telephones and Cables)
• Inventors: Ross, Peter W.
• Primary Examiner(s): Miller, Stanley D.
• Assistant Examiner(s): PHAN, TRONG Q
• Application Number:
  US07/032,759
• Time in Patent Office: 1,085 Days
• Field of Search: 350/350 S, 350/332, 350/333, 350/346, 350/330, 350/356, 340/805, 340/811, 340/784
• US Class Current: 345/94
• CPC Class Codes: G09G 2310/06 Details of flat display driving waveforms
• CPC Class Codes: G09G 2310/065 Waveforms comprising zero voltage phase or pause
• CPC Class Codes: G09G 3/3629 using liquid crystals having memory effects, e.g. ferroelectric liquid crystals

Abstract

A method of addressing a matrix addressed ferroelectric liquid crystal cell is described that uses parallel entry of balanced bipolar data pulses on one set of electrodes to co-operate with serial entry of unipolar strobe pulses on the other set of electrodes. The polarity of the strobe pulses is periodically reversed to maintain charge balance in the long term.

Claims

1. A method of addressing a matrix-array type liquid crystal cell with a ferroelectric liquid crystal layer whose pixels are defined by the areas of overlap between the members of a first set of electrodes on one side of the liquid crystal layer and the members of a second set on the other side of the layer, in which method the pixels are selectively addressed on a line-by-line basis by the application of unipolar strobing pulses serially to the members of the first set of electrodes while charge balanced bipolar data pulses are applied in parallel to the members of the second set, the positive going parts of the bipolar data pulses being synchronised with a strobe pulse for one data significance and the negative going parts being synchronized with the strobe pulse for the other data significance, wherein the pixels of both data significance are set into their correct states by said line-by-line addressing by first setting the pixels of one data significance into their correct state using unipolar strobe pulses of one polarity type and then setting the pixels of the other data significance into their correct state using unipolar strobe pulses of the opposite polarity type.

2. A method as claimed in claim 1, wherein in respect of each member of said first set of electrodes the polarity of each unipolar strobe pulse applied to that member is the opposite of that of the immediately preceding unipolar strobe pulse applied to that member.

3. A method as claimed in claim 1, wherein a gap separates the positive and negative going portions of each balanced bipolar data pulse.

4. A method as claimed in claim 1, wherein a gap always precedes or follows each balanced bipolar data pulse.

5. A method as claimed in claim 1, wherein the positive and negative going portions of each balanced bipolar data pulse are asymmetric, one part

having m times the amplitude of the other and 1/m^th the duration.

6. A method as claimed in claim 5, wherein a gap separates the positive and negative going portions of each balanced bipolar data pulse.

7. A method as claimed in claim 5, wherein a gap always precedes or follows each balanced bipolar data pulse.

8. A method as claimed in claim 7, wherein a gap separates the positive and negative going portions of each balanced bipolar data pulse.

9. A method as claimed in claim 1, wherein a gap separates the positive and negative going portions of each balanced bipolar data pulse and a gap always precedes or follows each such data pulse.