Electro-optical apparatus having antiferrodielectric liquid crystal panel with normalization to prevent white brightening

• US 6,259,492 B1
• Filed: 10/08/1998
• Issued: 07/10/2001
• Est. Priority Date: 02/12/1997
• Status: Expired due to Fees

• Current Assignee: Citizen Holdings Co., Ltd. (Citizen Electronics Company Limited)
• Original Assignee: Citizen Watch Co Limited (Citizen Electronics Company Limited)
• Inventors: Ebihara, Heihachiro, Imoto, Satoshi
• Primary Examiner(s): Malinowski, Walter J.
• Application Number:
  US09/155,888
• Time in Patent Office: 1,006 Days
• Field of Search: 349/33, 349/72, 349/174, 345/94, 345/101, 345/147
• US Class Current: 349/33
• CPC Class Codes: G09G 2310/06 Details of flat display driving waveforms
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 3/3633 with transmission/voltage characteristic comprising multiple loops, e.g. antiferroelectric liquid crystals

Abstract

An antiferroelectric liquid crystal display apparatus free from burn-in and achieving high display quality is provided by providing means for preventing pixel brightness from varying between pixels continuously held in an ON (bright) state and pixels continuously held in an OFF (dark) state. Aging processing is performed to saturate the brightness level of pixels into a stable state and thereby prevent the occurrence of a white brightening phenomenon. For this purpose, the brightness at a no voltage condition (base brightness) is set to a normalized level for all pixels in the liquid crystal panel that are required to exhibit uniform display performance. Further, temperature variations in the liquid crystal panel are eliminated to stabilize the brightness level and thereby prevent the occurrence of a white darkening phenomenon. Means is also provided for repeatedly performing normalization processes automatically or manually.

Claims

1. An electro-optical apparatus comprising:

an antiferroelectric liquid crystal panel; and

processing means for performing a series of normalization processes as many times as necessary to provide uniform brightness, in a no voltage condition, of all pixels required to exhibit a uniform electro-optical performance in a normalized level that is set not lower than a minimum brightness level and not higher than a level approximately equal to an aging brightness level, wherein said minimum brightness level represents a saturation value of the brightness level, in a no voltage condition, obtained by successively applying to said liquid crystal panel for a period of time, a voltage that causes only liquid crystal molecules in an antiferroelectric state to make a transition to a ferroelectric state, and then terminating the applied voltage, and wherein said aging brightness level represents a saturation value of the brightness level, in a no voltage condition, obtained by applying alternately to said liquid crystal panel, a voltage for a period of time that causes liquid crystal molecules in the antiferroelectric state to make a transition to the ferroelectric state and a voltage for a period of time that causes liquid crystal molecules in the ferroelectric state to make a transition to the antiferroelectric state and then terminating the applied voltage.

2. An electro-optical apparatus as claimed in claim 1, including means for applying to said liquid crystal panel, during said normalization processes, a drive voltage of a voltage value different from that of a drive voltage used to produce a normal display.

3. An electro-optical apparatus as claimed in claim 1, including means for applying to said liquid crystal panel, during said normalization processes, a drive voltage of a waveform different from that of a drive voltage used to produce a normal display.

4. An electro-optical apparatus as claimed in claim 1, wherein, during said normalization processes, a voltage waveform is used that applies alternately to said liquid crystal panel, a voltage that causes the liquid crystal in the antiferroelectric state to make a transition to the ferroelectric state and a voltage that causes the liquid crystal in the ferroelectric state to make a transition back to the antiferroelectric state.

5. An electro-optical apparatus as claimed in claim 1, wherein, during said normalization processes, a voltage waveform is used that has a voltage that causes only the liquid crystal in the antiferroelectric state to make a transition to the ferroelectric state.

6. An electro-optical apparatus as claimed in claim 1, wherein said normalization processes comprise first applying repeatedly a voltage waveform that has only a voltage that causes the liquid crystal in the antiferroelectric state to make a transition to the ferroelectric state, and then applying repeatedly a voltage waveform that has both a voltage that causes the liquid crystal in the antiferroelectric state to make a transition to the ferroelectric state and a voltage that causes the liquid crystal in the ferroelectric state to make a transition back to the antiferroelectric state.

7. An electro-optical apparatus as claimed in claim 1, wherein said normalization processes comprise first repeatedly applying a voltage waveform that has only a voltage that causes the liquid crystal in the antiferroelectric state to make a transition to the ferroelectric state, and then applying a temperature change in such a direction as to reduce the interlayer spacing of said liquid crystal molecules.

8. An electro-optical apparatus as claimed in claim 7, wherein the slope of the change of interlayer spacing relative to the change of temperature of said liquid crystal panel is made substantially zero at or near the center of a targeted operating temperature range.

9. An electro-optical apparatus as claimed in claim 1, including means for performing said normalization processes in interlocking fashion with application of a supply voltage to said apparatus.

10. An electro-optical apparatus as claimed in claim 1, including an external operating member, and means for performing said normalization processes based on an operation of said operating member.

11. An electro-optical apparatus as claimed in claim 1, including temperature detection means for detecting the temperature of said liquid crystal panel, and means for performing said normalization processes based on detection information from said temperature detection means.

12. An electro-optical apparatus as claimed in claim 1, including brightness detection means for detecting the brightness of a specific pixel in said liquid crystal panel in a specific display state, and means for performing said normalization processes based on detection information from said brightness detection means.

13. An electro-optical apparatus as claimed in claim 1, including utilization judging means for determining that the display apparatus has remained in an unoperated condition for a specified period of time, and means for performing said normalization processes based on judgement information from said utilization judging means.

14. An electro-optical apparatus as claimed in claim 1, including an external signal input terminal, and means for performing said normalization processes based on an signal supplied from outside said apparatus.

15. An electro-optical apparatus as claimed in claim 1, including a timer, and means for performing said normalization processes based on an signal supplied from said timer.

16. An electro-optical apparatus as claimed in claim 1, including display data judging means for determining that a pattern of display data is a specific pattern, and means for performing said normalization processes based on a signal supplied from said display data judging means.

17. An electro-optical apparatus as claimed in claim 1, including temperature control means for controlling the temperature of said liquid crystal panel.

18. An electro-optical apparatus as claimed in claim 17, wherein the temperature of said liquid crystal panel is controlled at or near a temperature where the slope of the change of interlayer spacing relative to the change of the temperature is zero.

19. An electro-optical apparatus as claimed in claim 17, wherein the temperature of said liquid crystal panel is controlled to within a temperature range where the amount of change of optical transmittance at said no voltage application condition, due to a change in the temperature, is within 2%.

20. An electro-optical apparatus as claimed in claim 17, wherein the temperature of said liquid crystal panel is controlled to within a temperature range where the amount of change of interlayer spacing of smectic layers in ferroelectric liquid crystal, due to a change in the temperature, is 0.2 Angstroms or less.

21. An electro-optical apparatus as claimed in claim 17, including means for initiating said normalization processes when the temperature of said liquid crystal panel approximately reaches a set temperature after power is turned on.

22. An electro-optical apparatus as claimed in claim 1, wherein said normalized level is set approximately equal to said aging brightness level.

23. An electro-optical apparatus as claimed in claim 1, wherein said normalized level is set approximately equal to said minimum brightness level.