Control process for a matrix display means displaying grey levels

• US 4,752,774 A
• Filed: 04/04/1986
• Issued: 06/21/1988
• Est. Priority Date: 04/04/1985
• Status: Expired due to Term

• Current Assignee: Commissariat a L'Energie Atomique (AES Corporation)
• Original Assignee: Commissariat a L'Energie Atomique (AES Corporation)
• Inventors: Clerc, Jean-Frederic, Sarrasin, Denis
• Primary Examiner(s): Brigance, Gerald L.
• Application Number:
  US06/848,298
• Time in Patent Office: 809 Days
• Field of Search: 340/784, 340/793, 340/805, 340/811, 350/332, 350/333, 358/241
• US Class Current: 345/89
• CPC Class Codes: H04N 3/127 using liquid crystals

Abstract

A process for the control of a matrix display such as a liquid crystal display displaying grey levels comprising a display material inserted between m electrode rows and p electrode columns which cross the rows, a material zone M_i N_j being excited by the application to row M_i of a first series of pulse signals and to column N_j of a second series of continuous signals, with i,j being integers such that 1≦i≦m and 1≦j≦p, said signals being cyclical of cycle T with polarity reversal at each half-cycle T/2, T/2 being subdivided into n time fractions equal to 2.sup.(k-1) mτ, in which k is an integer such that 1≦k≦n and τ a time interval useful for exciting the material, the signal of the second series having a maximum of 2 n polarity reversals over a cylcle T and for each time fraction being either in phase, or in phase opposition with the signal of the first series.

Claims

1. A control process of an optical characteristic of a material for obtaining a display of 2ⁿ different levels, said material having a plurality of zones distributed in a matrix-like manner and interposed between a first group of m rows and a second group of p columns of parallel electrodes, the rows and the columns being crossed, a zone MiNj of said material being defined by the rgion of the material covered by row Mi and column Nj, i and j being integers such that 1≦

i≦

m and 1≦

j≦

p, wherein for controlling the zone MiNj of the material the process includes;

applying a first series of signals on row Mi for a half-cycle duration;

applying a second series of signals on column Nk for said half-cycle;

dividing said half-cycle into n different time fractions of different durations;

giving to said first series of signals applied on row Mi, in each of said time fractions, an amplitude of a given first polarity for a duration equal to 1/m of the duration of said time fraction and a null amplitude for the remaining portion of said time fraction;

giving to said second series of signals applied on column Nj a continuous amplitude for the entirety of a time fraction, said amplitude having a given second polarity, said second polarity being the same as or opposite to said first polarity;

allowing change of said second polarity only when passing from one time fraction to the next;

selecting said second series of signals from among a series of 2ⁿ signals corresponding to the 2ⁿ possible combinations of n successive time fractions having a given polarity; and

reversing said first and second polarities after each half-cycle.

2. A control process according to claim 1, wherein the n different time fractions are such that the k^th time fraction is equal to 2^k-1 mτ

, in which τ

is a time interval useful for exciting the material.

3. A control process according to claim 1, wherein the signals applied to the rows and columns of electrodes are square-wave signals.

4. A control process according to claim 1, wherein the material is a liquid crystal film, the exciting signals applied to the rows of electrodes and columns of electrodes being voltages.