Method and apparatus for electronic switching of a reflective color display

A method for controlling the modulation of light by a light modulating material having visually distinguishable first and second optical states wherein the material is switched from the first optical state to the second optical state by means of a voltage pulse having an amplitude no less than a reference voltage V.sub.S and less than a voltage V.sub.S, and reset from the second optical state to the first optical state by eans of a voltage pulse having an amplitude no less than V.sub.R, comprising the steps of:

• a) confining the light modulating material in a space between two planes, one of which planes includes a set of parallel scanning lines and the other of which planes includes a set of parallel segment lines skew to the scanning lines;
• b) supplying a reference voltage V.sub.12 along each scanning line;
• c) superimposing a scanning voltage pulse having an amplitude V.sub.P along one of the scanning lines;
• and
• d) supplying along each segment line a voltage V.sub.21 or V.sub.22 synchronously with the scanning voltage pulse, wherein these voltages and amplitudes satisfy the relationships
• i) .vertline.V.sub.21 -V.sub.12 .vertline.V<V.sub.S ;
• ii) .vertline.V.sub.22 -V.sub.12 .vertline.<V.sub.S ;
• iii) V.sub.S <.vertline.V.sub.21 -V.sub.12 -V.sub.P .vertline.<V.sub.R ;
• and
• iv) .vertline.V.sub.22 -V.sub.12 -V.sub.P .vertline.>V.sub.R.

Light modulating apparatus comprising:

• a) a light modulating material having visually distinguishable stable first and second optical states wherein the material is switched from the first optical state to the second optical state by means of a voltage pulse having an amplitude no less than a reference voltage V.sub.S and less than a voltage V.sub.R, and reset from the second optical state to the first optical state by means of a voltage pulse having an amplitude no less than V.sub.R ;
• b) elongated electrically-conductive scanning line paths supported on one side of the light modulating material;
• c) elongated electrically-conductive segment line paths skewed with respect to the scanning line paths and supported on an opposite side of the light modulating material;
• e) a first gating system in electrical communication with the scanning line paths for enabling a constant voltage V.sub.12 along each of the scanning line paths and sequentially enabling a scanning voltage pulse of amplitude V.sub.P superimposed on the constant voltage V.sub.12 along each scanning line path;
• and
• f) a second gating system in electrical communication with the segment line paths for enabling a voltage V.sub.21 or a voltage V.sub.22 to at least one of the segment line paths synchronously with the scanning pulse;
• g) wherein the amplitudes of the pulses enabled by the first and second gating systems satisfy the relationships
• i) .vertline.V.sub.21 -V.sub.12 .vertline.<V.sub.S ;
• ii) .vertline.V.sub.22 -V.sub.12 .vertline.<V.sub.S ;
• iii) V.sub.S <.vertline.V.sub.21 -V.sub.12 -V.sub.P .vertline.<V.sub.R ;
• and
• iv) .vertline.V.sub.22 -V.sub.12 -V.sub.P .vertline.>V.sub.R.