Cholesteric liquid crystal display device and display driver

• US 20030085858A1
• Filed: 10/31/2002
• Published: 05/08/2003
• Est. Priority Date: 11/02/2001
• Status: Active Grant

• Current Assignee: Nanox Corp (Nippon Sheet Glass Company Limited)
• Original Assignee: Nanox Corp (Nippon Sheet Glass Company Limited)
• Inventors: Okafuji, Masaharu, Nimura, Koji, Takami, Manabu
• Granted Patent: US 7,138,973 B2
• Time in Patent Office: Days
• US Class Current: 345/87
• CPC Class Codes: G09G 2300/0486 Cholesteric liquid crystals, including chiral-nematic liquid crystals, with transitions between focal conic, planar, and homeotropic states
• CPC Class Codes: G09G 2310/0224 Details of interlacing
• CPC Class Codes: G09G 2310/06 Details of flat display driving waveforms
• CPC Class Codes: G09G 2320/0223 Compensation for problems related to R-C delay and attenuation in electrodes of matrix panels, e.g. in gate electrodes or on-substrate video signal electrodes
• CPC Class Codes: G09G 3/3629 using liquid crystals having memory effects, e.g. ferroelectric liquid crystals
• CPC Class Codes: G09G 3/3681 suitable for passive matrices only
• CPC Class Codes: G09G 3/3692 suitable for passive matrices only

Abstract

A display driver is provided which is suitable for driving dynamically a cholesteric liquid crystal display panel of a passive matrix drive type. The driver comprises a shift register for shifting a row data or column data inputted to the driver, a data latch circuit for latching the row data or column data from the shift register, and a drive voltage select/output circuit for selecting at least one of a plurality of voltage supplies and outputting a row drive voltage or column drive voltage to form an alternated drive voltage which activates picture elements of the liquid crystal panel.

Claims

1. A display driver for driving a passive matrix liquid crystal display panel using cholesteric liquid crystal material comprising:

a shift register for shifting a row data or column data inputted to the driver;

a data latch circuit for latching the row data or column data from the shift register; and

a drive voltage select/output circuit for selecting at least one of a plurality of voltage supplies and outputting a row drive voltage or column drive voltage to form an alternated drive voltage which activates picture elements of the liquid crystal panel.

2. The display driver of claim 1, wherein the drive voltage select/output circuit comprises;

a select circuit for generating a select signal to select at least one of the plurality of voltage supplies by the row data or column data latched by the data latch circuit, and

a voltage output circuit for outputting the row drive voltage or column drive voltage by the voltage supplies selected by the select signal.

3. The display driver of claim 2, wherein the polarity of the row drive voltage or column drive voltage is unipolar.

4. The display driver of claim 3, wherein the driver is operated in a row mode or column mode which is set by inputting a row/column mode signal to the select circuit.

5. The display driver of claim 4, wherein the select circuit selects by a conventional/dynamic mode signal inputted thereto either of a dynamic drive in which the transition of cholesteric liquid crystal texture is controlled by a series of stages or a conventional drive in which the transition of cholesteric liquid crystal texture is controlled by one stage.

6. The display driver of claim 5, wherein the series of stages include;

a preparation stage for transforming the liquid crystal material to a homeotropic state,

a selection stage for selecting either the maintaining of a homeotroic state or the transformation to a transient twisted planar state, and

an evolution stage for evolving the liquid crystal material selected so as to be transformed to the transient twisted planar state during the selection step to a focal conic state, and holds the homeotropic state of the liquid crystal selected to remain in the homeotropic state during selection stage.

7. The display driver of claim 5, wherein the series of stages include;

a preparation stage for transforming the liquid crystal material to a homeotropic state,

a pre-selection stage for allowing the liquid crystal material to relax to a transient twisted planar state,

a selection stage for selecting either the maintaining of a homeotroic state or the transformation to a transient twisted planar state, and

an evolution stage for evolving the liquid crystal material selected so as to be transformed to the transient twisted planar state during the selection step to a focal conic state, and holds the homeotropic state of the liquid crystal selected to remain in the homeotropic state during selection stage.

8. The display driver of claim 6 or 7, further comprising a mask register for masking the row data latched in the data latch circuit corresponding to the region on the panel where a rewrite is not required, when the driver is used in a row mode.

9. A cholesteric liquid crystal display device, comprising:

a passive matrix liquid crystal display panel using cholesteric liquid crystal material;

a first driver set in a row mode of claim 6 or 7 for supplying row drive voltages to row electrodes of the panel;

a second driver set in a column mode of claim 6 or 7 for supplying column drive voltages to column electrodes of the panel; and

a controller for controlling the first and second drivers.

10. The cholesteric liquid crystal display device of claim 9, wherein the controller controls the first driver such that a high speed rewrite is carried out by an interlaced scanning with the row drive voltage being supplied to separated even-numbered row electrodes and odd-numbered row electrodes.

11. A cholesteric liquid crystal display device, comprising:

a passive matrix liquid crystal display panel using cholesteric liquid crystal material;

a plurality of first drivers each set in a row mode of claim 6 or 7 for supplying row drive voltages to row electrodes of the panel;

a plurality of second drivers each set in a column mode of claim 6 or 7 for supplying column drive voltages to column electrodes of the panel; and

a controller for controlling the plurality of first and second drivers,

wherein the controller supplies row data simultaneously to the plurality of first drivers, and supplies column data simultaneously to the plurality of second drivers.

12. The cholesteric liquid crystal display device of claim 9, wherein when difference in time is caused between the rise or fall of the row drive voltage and that of the column drive voltage, the controller controls the first and second drivers such that the difference is caused to be small by delaying the signal for alternation in one of the first and second drivers with respect to that in the other of the first and second drivers.