Method for driving a ferroelectric liquid crystal panel

• US 5,477,235 A
• Filed: 10/06/1993
• Issued: 12/19/1995
• Est. Priority Date: 10/08/1992
• Status: Expired due to Fees

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Numao, Takaji
• Primary Examiner(s): Kuntz, Curtis
• Assistant Examiner(s): CHIN, VIVIAN C
• Application Number:
  US08/132,693
• Time in Patent Office: 804 Days
• Field of Search: 345/94, 345/95, 345/97, 345/87, 348/409
• US Class Current: 345/97
• CPC Class Codes: G09G 2310/04 Partial updating of the display screen
• CPC Class Codes: G09G 2310/06 Details of flat display driving waveforms
• CPC Class Codes: G09G 3/3629 using liquid crystals having memory effects, e.g. ferroelectric liquid crystals

Abstract

A method for driving a ferroelectric liquid crystal panel in which a ferroelectric liquid crystal is disposed between a plurality of scanning and signal electrodes, and a select or a non-select voltage is applied to the scanning electrode whereas a rewriting or a holding voltage is applied to the signal electrode to change the display of each pixel, the method including: dividing all the scanning electrodes into a plurality of groups composed of a plurality of scanning electrodes; selecting a group whose display is to be changed; applying the select voltage to the scanning electrodes of the selected group at once; applying the rewriting voltage to the signal electrodes corresponding to the pixels whose displays are to be changed; applying the select voltage to each scanning electrode of the selected group successively; and applying the rewriting voltage to the signal electrodes corresponding to the pixels whose liquid crystal is to be placed in a second stable state.

Claims

1. A method for driving a ferroelectric liquid crystal panel in which a ferroelectric liquid crystal is disposed between a plurality of scanning electrodes formed on a substrate and a plurality of signal electrodes formed on a opposite substrate and arranged in a direction of running crosswise relative to each other, and either a select voltage or a non-select voltage is selectively applied to the scanning electrodes whereas either a rewriting voltage or a holding voltage is selectively applied to the signal electrodes to change the display of each pixel defined where each scanning electrode and each signal electrode run cross-wise relative to each other, which comprises:

dividing all the scanning electrodes into a plurality of groups comprising a plurality of scanning electrodes;

selecting a group of the scanning electrodes to be changed on display from the divided groups, based on a first display data currently displayed and a second display data to be subsequently displayed; and

performing a first and a second scanning processes with respect to the selected group to rewrite the display by the second display data whereas applying the non-select voltage to the other groups to maintain the current display;

the first scanning process comprising;

applying the select voltage to all the scanning electrodes of selected group substantially at once; and

applying-the rewriting voltage to the signal electrodes corresponding to the pixels whose displays are to be changed to place in a first stable state the liquid crystal of the pixels whereas applying the holding voltage to the other signal electrodes to place in the current stable state the liquid crystal of the pixels;

the second scanning process comprising;

applying the select voltage to each scanning electrode successively with respect to the group in which the first scanning process is completed; and

applying the rewriting voltage to the signal electrodes corresponding to the pixels whose liquid crystal is to be placed in a second stable state whereas applying the holding voltage to the other signal electrodes to place in the current stable state the liquid crystal of the corresponding pixels.

2. A method according to claim 1 wherein the pixel defined between the scanning electrode to which the select voltage is applied and the signal electrode to which the holding voltage is applied is approximately equal to the pixel defined between the scanning electrode to which the non-select voltage is applied and the signal electrode to which either the holding voltage or the rewriting voltage is applied, in transmitted light intensity.

3. A method according to claim 2 wherein the ferroelectric liquid crystal comprises a liquid crystal whose voltage to response rate properties asses the minimum value at a specific voltage;

and

a positive voltage having an absolute value smaller than the minimum value and a negative voltage having an absolute value larger than the minimum value, or a negative voltage having an absolute value smaller than the minimum value and a positive voltage having an absolute value larger than the minimum value are applied, respectively to the pixel defined between the scanning electrode to which the select voltage is applied and the signal electrode to which the holding voltage is applied.

4. A method according to claim 1, 2 or 3 further comprising the step of periodically applying a voltage to the pixels to maintain the display state of the pixels.