Driving method for liquid crystal device

• US 6,323,850 B1
• Filed: 04/28/1999
• Issued: 11/27/2001
• Est. Priority Date: 04/30/1998
• Status: Expired due to Fees

• Current Assignee: Canon Ayutthaya Limited (Canon Inc.)
• Original Assignee: Canon Ayutthaya Limited (Canon Inc.)
• Inventors: Enomoto, Takashi, Miura, Seishi, Takiguchi, Takao, Iba, Jun, Katakura, Kazunori
• Primary Examiner(s): Shalwala, Bipin
• Assistant Examiner(s): Kovalick, Vincent E.
• Application Number:
  US09/300,473
• Time in Patent Office: 944 Days
• Field of Search: 345/87, 345/95, 345/97, 345/204, 345/206, 345/210, 349/37, 349/172, 349/174
• US Class Current: 345/204
• CPC Class Codes: G09G 2310/06 Details of flat display driving waveforms
• CPC Class Codes: G09G 2310/061 for resetting or blanking
• CPC Class Codes: G09G 3/2011 by amplitude modulation
• CPC Class Codes: G09G 3/3614 Control of polarity reversal in general
• CPC Class Codes: G09G 3/3651 using multistable liquid crystals, e.g. ferroelectric liquid crystals

Abstract

A liquid crystal device of the active matrix-type having two-dimensionally arranged pixels along rows and columns is driven frame by frame. In each frame operation, a scanning selection period (T_G) for each selected row is divided into a first period (t₁) and a second period (t₂). In t₁ of a current frame (T_F2), a reset pulse is applied to a pixel concerned, and the reset pulse is set to have an absolute value of voltage identical to and a polarity opposite to those of a writing pulse voltage applied to the pixel in the previous frame (T_F1). Then, in t₂ of the current frame (T_F2), the pixel is supplied with a writing pulse depending on a prescribed display state of the pixel for the current frame. As a result, the reset period is shortened to favor a high-speed display and a higher resolution display.

Claims

1. A driving method for a liquid crystal device of the active matrix-type comprising a pair of substrates, a layer of liquid crystal having a spontaneous polarization disposed between the substrates so as to form two-dimensionally arranged pixels disposed along a plurality of rows and a plurality of columns, and a switching device disposed at each pixel so as to control a voltage applied to the liquid crystal at the pixel;

said driving method comprising a frame operation including;

dividing a scanning selection period for each selected row into a first period and a second period in a current frame,

in the first period, applying a reset pulse having an amplitude V_R and a pulse width t_R to the liquid crystal at each pixel on the selected row, said reset pulse having a polarity opposite to that of a writing pulse voltage having an amplitude V_W and a pulse width t_W applied to the liquid crystal at the pixel in a previous frame, thereby resetting the pixels on the selected row to a first transmittance, and

in the second period, applying a writing pulse having a prescribed amplitude and a prescribed pulse width to the liquid crystal at each pixel to establish a prescribed transmittance for current frame display at the pixel,

wherein the reset pulse in the current frame has an absolute value of a product of the amplitude V_R and the pulse width t_R equal to an absolute value of a product of the amplitude V_W and the pulse width t_W of the writing pulse in the previous frame, at each pixel on the selected row.

2. A driving method according to claim 1, wherein the liquid crystal has alignment characteristic and voltage-transmittance characteristic such that the liquid crystal assumes a first alignment state exhibiting a first transmittance under no electric field, is tilted from the first alignment state to a second alignment state in one direction when supplied with a voltage of a first polarity to exhibit a second transmittance at prescribed voltage V₀, and is tilted from the first alignment state to a third alignment state in the other direction when supplied with a voltage of a second polarity opposite to the second polarity to exhibit a second transmittance at a prescribed voltage −

V₀, and the liquid crystal changes its transmittance continuously between the first transmittance and the second transmittance depending on a voltage applied thereto.

3. A driving method according to claim 1, wherein the liquid crystal has alignment characteristic and voltage-transmittance characteristic such that the liquid crystal assumes a monostable first alignment state exhibiting a first transmittance under no electric field, is tilted from the monostable first alignment state in one direction when supplied with a voltage of a first polarity at a tilt angle which varies depending on magnitude of the supplied voltage thereby providing a second transmittance which also varies continuously depending on magnitude of the supplied voltage, and retains the monostable first alignment state exhibiting the first transmittance when supplied with a voltage of a second polarity opposite to the first polarity.

4. A driving method according to claim 1, wherein the liquid crystal has alignment characteristic and voltage-transmittance characteristic such that the liquid crystal assumes a monostable first alignment state exhibiting a first transmittance under no electric field, is tilted from the monostable first alignment state in one direction when supplied with a voltage of a first polarity at a tilt angle which varies depending on magnitude of the supplied voltage thereby providing a second transmittance which also varies continuously depending on magnitude of the supplied voltage, and is tilted from the monostable first alignment state in the other direction when supplied with a voltage of a second polarity opposite to the first polarity at a tilt angle which varies depending on magnitude of the voltage of the second polarity but provides only a maximum value that is smaller than a maximum tilt angle formed under application of the voltage of the first polarity.

5. A driving method according to claim 1, wherein the polarity of the writing pulse is inverted for each frame.

6. A driving method according to claim 1, wherein the reset pulse for each pixel in the current frame has a voltage value determined based on a display state at the pixel in the previous frame.

7. A driving method according to claim 1, wherein a non-selection period is disposed between the first and second periods for each selected row.

8. A driving method according to claim 1, wherein the reset pulse for each pixel in the current frame has a voltage value determined based on a display state in the previous frame and a display state in the current frame, respectively at the pixel.

9. A driving method according to any of claims 1 and 2-8, wherein the liquid crystal is an anti-ferroelectric liquid crystal.