US 6,784,968 B1 · Addressing bistable nematic liquid crystal devices

Abstract

A bistable nematic liquid crystal device is addressed by application of a row waveform to successive row electrodes of an x, y matrix of pixels whilst one of two data waveforms are applied to each column electrode. The row waveform has a period of two or more time slots (ts), with two dc pulses of opposite amplitude for causing a switching to a dark state, and two dc pulses of opposite amplitude for causing a switching to a light state. The data waveforms have the same period as the strobe with dc pulses of opposite amplitude and combine with the strobe pulses to switch the device. The device can be addressed in two field periods, one field switching to a dark state, the other field switching to a light state. Alternatively, the device can be blanked to the dark state then selectively switched to the light state. When blanking is used, the row waveform has blanking de pulses placed a short time before selective switching to reduce overall addressing time. Zero voltage pulses may be used within the two or more time slot period of the strobe and data waveforms; these reduce rms. voltages appearing at the pixels and enhance contrast ratio.

Claims28

Dependent claims

A method of addressing a bistable nematic device formed by two cell walls enclosing a layer of nematic or long pitch cholesteric liquid crystal material with electrode structures carried by the walls to form a series of row electrodes on one wall and a series of column electrodes on the other wall to form a matrix of intersecting regions or pixels with a wall surface treatment on at least one wall providing a molecular alignment permitting the molecules at or adjacent the wall to align into two different stable states upon application of appropriate unipolar voltage pulses, the method comprising the steps of:

applying a row waveform to each row in a sequence whilst simultaneously applying one of two data waveforms to each column electrode whereby each pixel can be independently switched between two bistable states;
the row waveform having a period of at least two time slots and at least two unipolar pulses for switching the device to a first state, at least two unipolar pulses for switching the device to a second state;
both data waveforms having a period of at least two time slots with a unipolar pulse in each time slot, with at least one data waveform shaped to combine with the row waveform to cause a switching to one latched state;
whereby each pixel can be addressed to latch into one of said two stable states to collectively provide a desired display, with a substantially net zero dc voltage applied to the device.

1 more element

A bistable nematic device comprising;

two cell walls spaced apart and enclosing a layer of nematic or long pitch cholesteric liquid crystal material;
a first series of electrodes on one wall and a second series of electrodes on the other wall collectively forming a matrix of intersecting regions or pixels;
surface treatments on at least one wall to provide a molecular alignment permitting the molecules at or adjacent the wall to align into two different stable states upon application of appropriate unipolar voltage pulses;
means for distinguishing between the switched states of the liquid crystal material;
means for generating and applying a row waveform to each electrode in the first series of electrodes in a sequence;
means for generating and applying one of two data waveforms to each electrode in the second series of electrodes;
the row waveform having a period of at least two time slots and at least two unipolar pulses for switching the device to a first state, at least two unipolar pulses for switching the device to a second state;
both data waveforms having a period of at least two time slots with a unipolar pulse in each time slot, with at least one data waveform shaped to combine with the row waveform to cause a switching to the first state and the other data waveform shaped to combine with the row waveform to cause a switching to the second state;
whereby each pixel can be independently switched into either stable state to collectively provide a desired display, with a substantially net zero dc voltage applied to the device.

6 more elements

Dependencies are inferred from the claim text.

Addressing bistable nematic liquid crystal devices

Life of this patent

Addressing bistable nematic liquid crystal devices

Life of this patent

Abstract

Claims28