WO1995010794B1

WO1995010794B1 - Frame response compensated, video rate addressable matrix display system

Info

Publication number: WO1995010794B1
Application number: PCT/US1994/011149
Authority: WO
Filing date: 1994-09-30
Publication date: 1995-05-04

Abstract

A display system (10) uses an electrically driven compensator cell (16) not only to improve the color quality of the display system but also to solve viewability problems stemming from the frame response effect. The display system includes a liquid crystal cell (14) patterned as a matrix display device and the compensator cell patterned in a row-only fashion. Corresponding row electrodes (26, 32) of the matrix display cell and the compensator cell areconcurrently driven from the same row driver circuit (40). The cells are constructed and oriented relative to each other so as to cancel unwanted polarization state changes resulting from the frame response effect. The resulting light transmission through the display system in the OFF optical state is substantially at a minimum at all times during a frame period.

Claims

AMENDED CLAIMS[received by the International Bureau on 31 March 1995 (31.03.95); original claims 1 and 8 amended; remaining claims unchanged (4 pages)]

1. In a passive matrix display system including a display device of an optically retarding type having an optic axis and overlapping first and second electrodes positioned on opposite sides of an electro-optic material to define an array of display elements, the first electrodes receiving corresponding first drive signals during a frame period to cause sequential selections of the first electrodes during the frame period, the second electrodes receiving corresponding second drive signals during the selections of the first electrodes to provide a desired information pattern on the display elements, and the electro-optic material responding to the selections caused by the first drive signals and having a switching response time that causes the display elements to respond within the frame period and as a consequence not to true rms values of the first signals, a method of providing a display system whose display elements are addressed at video rates in the absence of a substantial decrease in contrast ratio caused by the nonresponse of the display- elements to the true rms values of the first signals, comprising: providing a compensator device of an optically retarding type having first electrodes and a reference electrode structure positioned on opposite sides of an electro-optic material, the compensator device having an optic axis and the reference electrode structure receiving a reference signal; positioning the compensator device in optical association with the display device so that the first electrodes of the display device and the first electrodes of the compensator device spatially overlap and are parallel to one another and so that the optic axis of the display device and the optic axis of the compensator device intersect at an angle; applying the first drive signals concurrently to the first electrodes of the display device and to the first electrodes of the compensator device, the compensator device and display device producing changing amounts of retardation during the frame period in response to the selections by the first drive signals, and the angle being set to a value that offsets the changing amounts of retardation to counteract the nonresponse of the display elements to the true rms values of the first drive signals causing the selections and thereby prevent a significant decrease in contrast ratio; and applying the second drive signals to the second electrodes of the display device to provide the desired information pattern on the display elements.

2. The method of claim 1 in which the display device and the compensator device are of a liquid crystal type.

3. The method of claim 2 in which the display device and the compensator device are of a supertwisted nematic (STN) type.

4. The method of claim 1 in which the optic axes of the display device and the compensator device intersect at an angle of 90 degrees.

5. The method of claim 1 in which each of the display and compensator devices includes a liquid crystal material having directors and a thickness dimension, the directors in the direction of the thickness dimension of the display device being of opposite rotational sense to that of the directors in the direction of the thickness dimension of the compensating device.

6. The method of claim 1 in which the first drive signals are of an Alt and Pleshko sequential waveform type.

7. The method of claim 1 in which the number of first electrodes of the display device is equal to the number of first electrodes of the compensator device.

8. A frame response-compensated passive matrix display system, comprising: a matrix display cell of an optically retarding type having an optic axis and overlapping first and second electrodes positioned on opposites of a liquid crystal material to define an array of display elements, the liquid crystal material having a thickness dimension and directors to which a twist angle is imparted along the thickness dimension; a compensating cell of an optically retarding type having an optic axis and first electrodes positioned adjacent a liquid crystal material, the optic axes of the matrix display and compensating cells being set at an angle, the first electrodes being spatially associated with and oriented parallel to the first electrodes of the matrix display cell, and the liquid crystal material having a thickness dimension and directors to which a twist angle is imparted along the thickness dimension, the twist angle of the liquid crystal material of the compensator cell being of opposite rotational sense to that of the liquid crystal material of the matrix display cell; a first drive circuit applying first signals concurrently to select the first electrodes of the matrix display cell and the spatially associated first electrodes of the compensator cell, the liquid crystal materials of the matrix display and compensating cells responding within the frame period to the selections and therefore not to true rms values of the first signals, the nonresponse to true rms values producing for the matrix display and compensating cells changing amounts of retardation during the frame period, and the angle being set to a value that offsets the changing amounts of retardation to prevent a significant decrease in display system contrast ratio; and a second drive circuit applying second signals to corresponding second electrodes of the matrix display cell during the selections of the first electrodes to provide a desired information pattern on the display elements.

9. The system of claim 8 in which the optic axes of the matrix display and compensator cells are set at 90 degrees relative to each other.

10. The system of claim 8 in which the matrix display and compensator cells are of a supertwisted (STN) type.

11. The system of claim 10 in which the liquid crystal material in the display matrix and compensator cells have the same helical pitch.

12. The system of claim 8 in which the first signals are of an Alt and Pleshko sequential waveform type.

13. The system of claim 8 in which the number of first electrodes of the display matrix cell is equal to the number of first electrodes of the compensator cell.