Driving method for a ferroelectric liquid crystal displays having no change data pulses

• US 5,488,495 A
• Filed: 05/05/1993
• Issued: 01/30/1996
• Est. Priority Date: 08/31/1987
• Status: Expired due to Term

• Current Assignee: Sharp Electronics Corporation (Hon Hai Precision Industry Co., Ltd.), 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): Sikes, William L.
• Assistant Examiner(s): Duong, Tai V.
• Application Number:
  US08/056,948
• Time in Patent Office: 1,000 Days
• Field of Search: 350/331 R, 350/332, 350/333, 350/350 S, 340/784, 340/805, 340/799, 359/56, 345/97, 345/98, 345/100
• US Class Current: 345/97
• CPC Class Codes: G09G 2310/06 Details of flat display driving waveforms
• CPC Class Codes: G09G 2320/0247 Flicker reduction other than flicker reduction circuits used for single beam cathode-ray tubes
• CPC Class Codes: G09G 3/3629 using liquid crystals having memory effects, e.g. ferroelectric liquid crystals

Abstract

A ferroelectric liquid crystal display system suited for use in a matrix liquid crystal display device includes scanning electrodes Lp (p=1, 2, . . . m, wherein m is a positive integer) and signal electrodes arranged so as to intersect with the scanning electrodes in the form of a matrix of columns and rows. Further, a picture element is disposed at each point of intersection between the scanning and signal electrodes. The ferroelectric liquid crystal display system is characterized in the provision of a device for indicating which one of bright and dark displays each picture element on the selected scanning electrode has previously effected. It is so designed that a voltage to be applied to the picture element in the event that a dark display should be effected while a bright display has previously been effected or a bright display should be effected while a dark display has previously been effected, and a voltage to be applied to the picture element Akj on the non-selected scanning electrodes Lk at particular cases, are so selected as to give a significant difference enough to avoid any possible optical adverse influence which may act on the picture element then held in a bright or dark memory state.

Claims

1. A method of driving a liquid crystal display device including a ferroelectric display material, a plurality of parallel scanning electrodes disposed in a first direction, a plurality of parallel signal electrodes intersecting the plurality of parallel scanning electrodes and disposed in a second direction perpendicular to the first direction, and picture elements formed at each signal and scanning electrode intersection, each picture element being switched to a bright display state, when a voltage difference between a scanning and signal electrodes associated with the picture element exceeds a first threshold voltage (+Va), and being switched to a dark display state, when said voltage difference falls below a second threshold voltage (-Vb), wherein the first threshold voltage is greater than the second threshold voltage, said method comprising the steps of:

(a) storing a previous display state for each picture element;

(b) determining, for each picture element, one of three previous to new display state scenarios, wherein,

(i) a first scenario (X), occurs when the previous and new display states of the picture element are a dark display state and a bright display state, respectively,

(ii) a second scenario (Y), occurs when the previous and new display states of the picture element are a bright display state and dark display state, respectively, and

(iii) a third scenario (Z), occurs when the new display state of the picture element is the same as the previous display state;

(c) applying a first voltage pattern when said first scenario (X) is determined, the first voltage pattern having a peak voltage greater than the first threshold voltage, wherein an integrated value of the first voltage pattern is equal to zero;

(d) applying a second voltage pattern when said second scenario (Y) is determined, the second voltage pattern having a peak voltage smaller than the second threshold voltage, wherein an integrated value of the second voltage pattern is equal to zero; and

(e) applying third voltage patterns when said third scenario (Z) is determined, the third voltage patterns having a peak voltage between the first and second threshold voltages, wherein an integrated value of the third voltage patterns is equal to zero, the third voltage patterns applied to picture elements of a selected scanning electrode and a non-selected scanning electrode respectively having the same waveform and opposite polarities.

2. A method of driving a liquid crystal display device including a ferroelectric display material, a plurality of parallel scanning electrodes disposed in a first direction, a plurality of parallel signal electrodes, intersecting the plurality of parallel signal electrodes, disposed in a second direction perpendicular to the first direction, and picture elements formed at each signal and scanning electrode intersection, said method comprising the steps of:

a) selecting, sequentially, each of the plurality of scanning electrodes to be driven and subsequently applying a first driving voltage thereto and applying a second driving voltage to non-selected scanning electrodes;

b) receiving, in a delay device, an input present display state and outputting a previous display state for each of the plurality of picture elements;

c) receiving, in a driving device, both an input present display state and the previous display state from the delay device for each of the plurality of picture elements;

d) applying a first rewrite voltage to the plurality of signal electrodes from the driving device to change a picture element corresponding to each selected scanning electrode from a first display state to a second display state upon receiving a first display state as the previous display state and a second display state as the input present display state, and maintaining a picture element corresponding to each non-selected scanning electrode in a same display state as that of the previous display state;

e) applying a second rewrite voltage, different from said first rewrite voltage, to the plurality of signal electrodes from the driving device to change a picture element corresponding to each selected scanning electrode from said second display state to said first display state upon receiving a second display state as the previous display state and a first display state as the input present display state, and maintaining a picture element corresponding to each non-selected scanning electrode in a same display state as that of the previous display state; and

f) applying a non-rewrite voltage to the plurality of signal electrodes from the driving device to maintain a picture element corresponding to each selected and non-selected scanning electrode in one of a first and second display state upon receiving the same one of the first and second display state, respectively, as both the previous and the input present display state, a voltage patterns applied to picture elements of a selected scanning electrode and a non-selected scanning electrode respectively having the same waveform and opposite polarities.

3. The method of claim 2, wherein the steps d-f of maintaining a picture element in the same display state are achieved by application of a voltage of a constant absolute value.

4. The method of claim 3, wherein the absolute value of the voltage applied to the picture elements maintained in the same display state in steps d-f is zero.

5. The method of claim 3, wherein the absolute value of the voltage applied to maintain picture elements in the same display state in steps d-f is a bipolar waveform formed of at least one positive voltage waveform and at least one negative voltage waveform.