Frame response compensated, video rate addressable liquid crystal passive matrix display system

• US 5,457,551 A
• Filed: 10/08/1993
• Issued: 10/10/1995
• Est. Priority Date: 10/08/1993
• Status: Expired due to Fees

• Current Assignee: Planar Systems Incorporated (Leyard Optoelectronic Co., Ltd.)
• Original Assignee: Planar Systems Incorporated (Leyard Optoelectronic Co., Ltd.)
• Inventors: Culter, Robert G., Kongslie, Keith F.
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): Duong, Tai V.
• Application Number:
  US08/133,700
• Time in Patent Office: 732 Days
• Field of Search: 359/54, 359/53, 359/73, 359/103, 359/55, 359/93, 359/87, 359/85, 345/87, 345/94, 348/761, 348/766
• US Class Current: 349/76
• CPC Class Codes: G02F 1/13471 in which all the liquid crystal cells or layers remain transparent, e.g. FLC, ECB, DAP, HAN, TN, STN, SBE-LC cells G02F1/13475 takes precedence
• CPC Class Codes: G09G 2300/023 Display panel composed of stacked panels
• CPC Class Codes: G09G 2320/041 Temperature compensation
• CPC Class Codes: G09G 3/36 using liquid crystals
• CPC Class Codes: G09G 3/3622 using a passive matrix G09G3/3674 - G09G3/3696 take precedence

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 are concurrently 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

1. A driving method for 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 a supertwisted nematic liquid crystal 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 supertwisted nematic liquid crystal material instantaneously responding to the first drive signals and thereby resulting in a transient change in display element transmittance before returning to a quiescent state corresponding to a lower rms voltage over the remainder of the frame period, the method comprising:

providing a compensator device of an optically retarding type having first electrodes and a reference electrode structure positioned on opposite sides of a supertwisted nematic liquid crystal material, the compensator device having an optic axis;

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 a predetermined 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 offsetting changing amounts of retardation during the frame period to prevent a significant decrease in contrast ratio;

applying the second drive signals to the second electrodes of the display device to provide the desired information pattern on the display elements; and

applying a reference signal to the reference electrode structure.

2. 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.

3. 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.

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

5. 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.

6. 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 opposite sides of a supertwisted nematic 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, a reference electrode, and first electrodes positioned adjacent a supertwisted nematic liquid crystal material, the optic axes of the matrix display and compensating cells being set at a predetermined 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; and

second drive circuits applying a reference signal to the reference electrode and 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, the liquid crystal materials of the matrix and compensating cells instantaneously responding to the first signals and producing offsetting changing amounts of retardation that prevent a resultant transient change in display element transmittance.

7. The system of claim 6 in which the optic axes of the matrix display and compensator cells are set at 90 degrees relative to each other.

8. The system of claim 6 in which the liquid crystal material in the display matrix and compensator cells have the same helical pitch.

9. The system of claim 6 in which the first signals are of an Alt and Pleshko sequential waveform type.

10. The system of claim 6 in which the number of first electrodes of the display matrix cell is equal to the number of first electrodes of the compensator cell.