Color liquid crystal display device

• US 5,852,430 A
• Filed: 04/09/1996
• Issued: 12/22/1998
• Est. Priority Date: 04/20/1995
• Status: Expired due to Fees

• Current Assignee: Casio Computer Company Limited
• Original Assignee: Casio Computer Company Limited
• Inventors: Endo, Kenzo
• Primary Examiner(s): Bayerl, Raymond J.
• Assistant Examiner(s): Luu, Matthew
• Application Number:
  US08/629,508
• Time in Patent Office: 987 Days
• Field of Search: 345/88, 345/101, 345/106, 345/148, 345/150
• US Class Current: 345/101
• CPC Class Codes: G09G 2320/041 Temperature compensation
• CPC Class Codes: G09G 3/3607 for displaying colours or for displaying grey scales with a specific pixel layout, e.g. using sub-pixels display of colours in flat matrix panels other than liquid crystal displays G09G3/2003; grey scales specific for television H04N3/127

Abstract

A temperature detection circuit and two RAMs are connected to a conversion circuit for converting image data into voltage designation signals and outputting the signals to a signal electrode driver. The temperature detection circuit detects the temperature of a liquid crystal display element as one of conditions which influence the behavior of liquid crystal molecules. One RAM is used to store a conversion table in which voltage designation signals for designating effective voltage to be applied to a liquid crystal layer are preset for image data for each predetermined temperature range of the liquid crystal display element. The other RAM is used to store input image data. In the conversion table, the number of different voltage designation signals in a high-temperature range is set to be smaller than that of different voltage designation signals in a normal temperature range. The conversion circuit reads out voltage designation signals in accordance with a detection signal from the temperature detection circuit and image data, and outputs the signals to the signal electrode driver. With this operation, effective voltages corresponding to the voltage designation signals are applied to the liquid crystal layer, and a color display with excellent perceptibility can always be obtained regardless of the temperature of the liquid crystal display element.

Claims

1. A color liquid crystal display device comprising:

a liquid crystal display element for controlling a birefringence action of a liquid crystal layer sandwiched between a pair of substrates by applying a voltage to the liquid crystal layer, thereby displaying a plurality of colors;

image data supply means for supplying image data for defining colors to be displayed; and

drive control means for selecting one of a plurality of groups including a first group constituted by n (a positive integer) different effective voltages preset for the image data, and a second group constituted by m (a positive integer different from n) different effective voltages preset for the image data, and applying the effective voltages in the selected group which are related to the image data to the liquid crystal layer.

2. A device according to claim 1, wherein said drive control means comprises means for selecting a group of effective voltages to be applied in accordance with a condition which influences a behavior of liquid crystal molecules of said liquid crystal display element, selecting effective voltages corresponding to the image data from the selected group of effective voltages, and applying the effective voltages to the liquid crystal layer.

3. A device according to claim 1, wherein said drive control means comprises

detection means for detecting a change in the condition which influences the behavior of the liquid crystal molecules of said liquid crystal display element and outputting a correction signal, and

means for receiving the correction signal, selecting a group of effective voltages to be applied in accordance with the correction signal, selecting effective voltages corresponding to the image data from the selected group of effective voltages, and applying the effective voltages to the liquid crystal layer.

4. A device according to claim 1, wherein said drive control means comprises

detection means for detecting a change in the condition which influences the behavior of the liquid crystal molecules of said liquid crystal display element and outputting a correction signal,

voltage generating means for generating n different signal voltages to be applied to one of groups of electrodes respectively formed on opposing surfaces of the substrates of said liquid crystal display element, and

means for selecting the group of effective voltages in accordance with the correction signal from said detection means, selecting signal voltages, from the n signal voltages, which provide at least one effective voltage, in the selected group of effective voltages, which correspond to the image data, and applying the selected signal voltages to said electrodes.

5. A device according to claim 1, wherein said drive control means comprises

detection means for outputting a detection signal by detecting a temperature of said liquid crystal display element, and

selecting means for selecting a group of effective voltages to be applied in accordance with a correction signal from said detection means, selecting at least one effective voltage corresponding to the image data from the selected group, and applying the effective voltages to the liquid crystal layer.

6. A device according to claim 5, wherein said selecting means comprises

storage means for storing effective voltages to be applied to the liquid crystal layer in accordance with the image data for each of a plurality of temperature ranges of said liquid crystal display element, and

voltage applying means for reading out effective voltages from said storage means on the basis of the image data and the detection signal, and applying the effective voltages to the liquid crystal layer.

7. A device according to claim 5, wherein said selecting means comprises

voltage generating means for generating pulse signal voltages to be applied to one of groups of electrodes formed on opposing surfaces of the substrates of said liquid crystal display element,

storage means for storing voltage designation signals for designating effective voltages to be applied to the liquid crystal layer of said liquid crystal display element for each of a plurality of temperature ranges of said liquid crystal display element in correspondence with the image data, and

voltage modulation applying means for reading out the voltage designation signals from said storage means in accordance with the image data and the detection signal, modulating the pulse voltages in accordance with the readout voltage designation signals, and applying the modulated voltages to said electrodes.

8. A device according to claim 7, wherein said voltage modulation applying means comprises pulse width modulation type voltage modulation applying means for changing pulse widths of the pulse voltages in accordance with the voltage designation signals.

9. A device according to claim 7, wherein said voltage modulation applying means comprises pulse height modulation type voltage modulation applying means for changing pulse heights of the pulse voltages in accordance with the voltage designation signals.

10. A device according to claim 7, wherein said storage means stores n voltage designation signals for designating n effective voltages in a range not exceeding a predetermined temperature, and one of two voltage designation signals for designating lowest and highest voltages of the n effective voltages in a range exceeding the predetermined temperature in correspondence with the image data.

11. A device according to claim 1, wherein said drive control means comprises

detection means for detecting a voltage of a power supply for generating a voltage to be applied to said liquid crystal display element, and

means for selecting a group of effective voltages to be applied in accordance with a detection signal from said detection means, selecting at least one effective voltage corresponding to the image data from the selected group of effective voltages, and applying the effective voltages to the liquid crystal layer.

12. A device according to claim 1, wherein said liquid crystal display element comprises a liquid crystal cell having the liquid crystal layer set in an aligned state to twist liquid crystal molecules between the substrates, a pair of polarizing plates arranged to sandwich the liquid crystal cell, a retardation plate arranged between one of the polarizing plates and the liquid crystal cell, and a reflecting plate for reflecting light emerging from the polarizing plate on a rear surface side opposite to a display surface to cause the light to be incident on the polarizing plate on the rear surface side.

13. A device according to claim 12, wherein a twist angle of liquid crystal molecules of the liquid crystal cell is an angle within a range of 230°

to 270°

, a value of a product Δ

n·

d of a refractive index anisotropy Δ

n of a liquid crystal and a liquid crystal layer thickness d is a value within a range of 1,300 nm to 1,500 nm, and a value of a retardation of the retardation plate is a value within a range of 1,450 nm to 1,750 nm.

14. A color liquid crystal display device comprising:

a liquid crystal display element for controlling a birefringence action of a liquid crystal layer by applying voltages to the liquid crystal layer sandwiched between a pair of substrates, thereby displaying a color image constituted by a plurality of display colors;

image data supply means for supplying image data for designating a color, of n colors, which is to be displayed; and

drive control means for driving said liquid crystal display element such that at least two types of images expressed by different combinations of colors, one type of image being expressed by a combination of n colors, and the other type of image being expressed by a combination of m colors smaller in number than n colors, are switched in accordance with a condition which influences a behavior of liquid crystal molecules.

15. A device according to claim 14, wherein said drive control means comprises

detection means for detecting a temperature of said liquid crystal display element and outputting a detection signal, and

means for switching the combinations of the colors of images in accordance with the detection signal from said detection means.

16. A device according to claim 14, wherein said drive control means comprises

detection means for detecting a voltage of a power supply for generating a voltage to be applied to said liquid crystal display element and outputting a detection signal, and

means for switching the combinations of the colors of images in accordance with the detection signal from said detection means.

17. A method of driving a color liquid crystal display device, comprising:

a step of controlling a birefringence action of a liquid crystal layer sandwiched between a pair of substrates by applying voltages corresponding to image data to the liquid crystal layer, thereby displaying a plurality of colors;

a step of supplying the image data for defining colors to be displayed;

a step of defining a first group of n (a positive integer) effective voltages preset for the image data;

a step of defining a group, other than the first group, which is constituted by m (a positive integer different from n) different effective voltages preset for the image data; and

a voltage application step of selecting one of the first group and the group other than the first group, and applying effective voltages, of the effective voltages of the selected group, which are preset for the image data to the liquid crystal layer.

18. A method according to claim 17, wherein the voltage application step comprises a sub-step of outputting a correction signal in accordance with a condition which influences a behavior of liquid crystal molecules of said liquid crystal display element, and

a sub-step of selecting a group of effective voltages to be applied to the liquid crystal in accordance with the correction signal, and applying effective voltages, of the selected group of effective voltages, which correspond to the image data to the liquid crystal layer.

19. A method according to claim 17, wherein each of the steps of defining the groups of effective voltages includes a sub-step of storing effective voltages to be applied to the liquid crystal layer for each temperature range of said liquid crystal display element in accordance with the image data, and

the voltage application step comprises

a sub-step of detecting a temperature of said liquid crystal display element and outputting a detection signal,

a sub-step of reading out effective voltages from said storage means in accordance with the image data and the detection signal, and

a sub-step of applying the readout effective voltages to the liquid crystal layer.

20. A method according to claim 17, wherein each of the steps of defining the groups of effective voltages includes a sub-step of storing voltage designation signals for designating effective voltages to be applied to the liquid crystal layer for each of a plurality of temperature ranges of said liquid crystal display element in correspondence with the image data, and

the voltage application step comprises

a sub-step of generating pulse signal voltages to be applied to one of groups of electrodes formed on opposing surfaces of the substrates of said liquid crystal display element,

a sub-step of detecting a temperature of said liquid crystal display element and outputting a detection signal,

a sub-step of reading out the voltage designation signals from said storage means in accordance with the detection signal and the image data, and

a sub-step of modulating the pulse signal voltages in accordance with the readout voltage designation signals and applying the modulated voltages to the liquid crystal layer.

21. A method according to claim 20, wherein the sub-step of storing the voltage designation signals is a sub-step of storing, in said storage means, n voltage designation signals for designating n effective voltages in a range not exceeding a predetermined temperature of said liquid crystal display element, and one of two voltage designation signals for designating lowest and highest voltages of the n effective voltages in a range exceeding the predetermined temperature in correspondence with the image data.