STN LCD device displaying multiple colors in response to different voltages which includes a retardation plate

• US 5,585,950 A
• Filed: 04/05/1994
• Issued: 12/17/1996
• Est. Priority Date: 04/12/1993
• Status: Expired due to Term

• Current Assignee: Casio Computer Company Limited
• Original Assignee: Casio Computer Company Limited
• Inventors: Mori, Toshihiko, Sato, Hideshi, Arai, Kazuyoshi, Nishino, Toshiharu, Tanaka, Yukikazu, Nishida, Yasushi
• Primary Examiner(s): Gross, Anita Pellman
• Assistant Examiner(s): TON, MINH TOAN T
• Application Number:
  US08/223,219
• Time in Patent Office: 987 Days
• Field of Search: 359/53, 359/73, 359/57, 359/59, 359/93, 345/88, 345/89
• US Class Current: 349/118
• CPC Class Codes: G02F 1/13363 Birefringent elements, e.g. for optical compensation
• CPC Class Codes: G02F 1/1397 the twist being substantially higher than 90°, e.g. STN-, SBE-, OMI-LC cells
• CPC Class Codes: G02F 2203/34 Colour display without the use of colour mosaic filters

Abstract

A pair of polarizing plates are disposed on two sides of an STN type liquid crystal cell constituted by a liquid crystal twist-aligned at a twist angle of 180° to 270°. A retardation plate is disposed between one of the polarizing plates and the liquid crystal cell in such a manner that the optical axis of the retardation plate crosses the transmission axis of the adjacent polarizing plate at 35° to 55°. The pair of polarizing plates are arranged such that their transmission axes are parallel to each other. The liquid crystal cell is arranged such that the optical axis of the retardation plate crosses the aligning direction of the liquid crystal molecules on the substrate side adjacent to the retardation plate at a predetermined angle. A driving circuit is connected to the liquid crystal cell. This circuit serves to apply a voltage to the liquid crystal in accordance with display data having color information to change the polarized state of elliptically polarized light transmitted through the liquid crystal to change the color of emerging light.

Claims

1. A color liquid crystal display apparatus comprising:

a pair of substrates having opposing surfaces, electrodes respectively formed on the opposing surfaces, and aligning films respectively formed to cover said electrodes, said aligning films having undergone aligning treatment in predetermined directions;

a liquid crystal layer formed between said pair of substrates and having liquid crystal molecules aligned to be twisted at a twist angle of 180°

to 270°

from one substrate to the other substrate;

a pair of polarizing plates disposed outside said pair of substrates to sandwich said substrates and respectively having transmission axes for linearly polarizing incident light;

a retardation plate having a maximum refraction index direction which is within a plane parallel to a surface of said retardation plate and having a value of retardation for coloring light transmitted through the liquid crystal display apparatus, in combination with the Δ

n·

d of the liquid crystal layer, said retardation plate being disposed between said pair of polarizing plates such that an angle defined by said maximum refractive index direction, and the transmission axis of an adjacent one of said polarizing plates is 35°

to 55°

; and

driving means, connected to said electrodes, for applying a voltage to said liquid crystal layer to change a polarized state of light transmitted through said liquid crystal layer so as to change a color of light transmitted through said polarizing plate on an exit side into plural colors including at least two chromatic colors.

2. An apparatus according to claim 1, further comprising another retardation plate disposed between said pair of polarizing plates.

3. An apparatus according to claim 2, wherein said another retardation plate is disposed between said retardation plate and one of said pair of polarizing plates which is adjacent thereto.

4. An apparatus according to claim 2, wherein said another retardation plate is disposed to be adjacent to one of said substrates which is on an opposite side to the other substrate to which said retardation plate is adjacent.

5. An apparatus according to claim 1, further comprising a reflection plate disposed outside one of said pair of polarizing plates.

6. An apparatus according to claim 5, further comprising another retardation plate disposed between said pair of polarizing plates.

7. An apparatus according to claim 6, wherein said another retardation plate is disposed between said retardation plate and said polarizing plate adjacent thereto.

8. An apparatus according to claim 6, wherein said another retardation plate is disposed outside one of said pair of substrates which is located on an opposite side to the other substrate to which said retardation plate is adjacent.

9. An apparatus according to claim 1, wherein said retardation plate is a retardation plate which satisfies n_X >

n_Z >

n_Y where n_X, n_y, and n_Z are refractive indexes in an X direction in which the refractive index is the maximum, a Y direction perpendicular to the X direction within a plane parallel to said retardation plate, and a Z direction of thickness, respectively.

10. An apparatus according to claim 1, wherein liquid crystal molecules of said liquid crystal layer are aligned to be twisted from one substrate to the other substrate at a twist angle of 250°

.

11. An apparatus according to claim 1, wherein said pair of substrates include a plurality of electrodes formed on the opposing surfaces thereof to extend in orthogonal directions, and portions where electrodes respectively formed on the opposing surfaces oppose form a plurality of display dots arranged in the form of a matrix.

12. An apparatus according to claim 11, wherein said driving means includes driving voltage generating means for generating a plurality of voltages having different magnitudes, display signal generating means for generating a display signal corresponding to color data to be displayed, and display driving means for selecting a driving voltage in accordance with the display signal and forming a driving waveform.

13. An apparatus according to claim 1, wherein said driving means comprises means for generating a plurality of signal voltages corresponding to a plurality of predetermined different display colors, and applied voltage control means for selecting one of the plurality of signal voltages for each frame in accordance with color to be displayed in one period constituted by a predetermined number of frames, and applying a voltage corresponding to a display color to said liquid crystal layer.

14. An apparatus according to claim 1, further comprising pixel electrodes regularly arranged on one of said pair of substrates, and thin-film transistors arranged in correspondence with said respective pixel electrodes, each of said thin-film transistors having a source electrode connected to a corresponding one of said pixel electrodes, a drain electrode connected to a signal line for supplying a display signal, and a gate electrode connected to a scanning line for supplying a scanning signal.

15. A color liquid crystal display apparatus comprising:

;

a pair of substrates having opposing surfaces, electrodes respectively formed on the opposing surfaces, and aligning films respectively formed to cover said electrodes, said aligning films having undergone aligning treatment in predetermined directions;

a liquid crystal layer formed between said pair of substrates and having liquid crystal molecules aligned to be twisted at a twist angle of 180°

to 270°

from one substrate to the other substrate;

a polarizing plate disposed outside one of said pair of substrates and having a transmission axis for linearly polarizing incident light;

a reflection plate disposed on an opposite side to said polarizing plate with respect to said pair of substrates;

a retardation plate having a maximum refractive index direction which is within a plane parallel to a surface of said retardation plate and having a value of retardation for coloring light transmitted through the liquid crystal display apparatus, in combination with the Δ

n·

d of the liquid crystal layer, said retardation plate being disposed between said polarizing plate and said reflection plate such that an angle defined by said maximum refractive index direction, and the transmission axis of said polarizing plate is 35°

to 55°

; and

driving means, connected to said electrodes, for applying a voltage to said liquid crystal layer to change a polarized state of light transmitted through said polarizing plate on an exit side into plural colors including at least two chromatic colors.

16. An apparatus according to claim 15, further comprising another retardation plate disposed between said polarizing plate and said reflection plate.

17. An apparatus according to claim 16, wherein said another retardation plate is disposed between said retardation plate and said polarizing plate.

18. An apparatus according to claim 16, wherein said another retardation plate is disposed to be adjacent to one of said substrates which is on an opposite side to the other substrate to which said retardation plate is adjacent.

19. An apparatus according to claim 15, wherein said retardation plate is a retardation plate which satisfies n_X >

n_Z >

n_Y where n_X, n_Y, and n_Z are refractive indexes in an X direction in which the refractive index is the maximum, a Y direction perpendicular to the X direction within a plane parallel to said retardation plate, and a Z direction of thickness, respectively.

20. An apparatus according to claim 15, wherein said liquid crystal layer has liquid crystal molecules aligned to be twisted from one substrate to the other substrate at a twist angle of 250°

.

21. An apparatus according to claim 15, wherein said pair of substrates include a plurality of electrodes formed on the opposing surfaces thereof to extend in orthogonal directions, and portions where electrodes respectively formed on the opposing surfaces oppose form a plurality of display dots arranged in the form of a matrix.

22. An apparatus according to claim 21, wherein said driving means includes driving voltage generating means for generating a plurality of voltages having different magnitudes, display signal generating means for generating a display signal corresponding to color data to be displayed, and display driving means for selecting a driving voltage in accordance with the display signal and forming a driving waveform.

23. An apparatus according to claim 15, wherein said driving means comprises means for generating a plurality of signal voltages corresponding to a plurality of predetermined different display colors, and applied voltage control means for selecting one of the plurality of signal voltages for each frame in accordance with color to be displayed in one period constituted by a predetermined number of frames, and applying a voltage corresponding to a display color to said liquid crystal layer.

24. An apparatus according to claim 15, further comprising pixel electrodes regularly arranged on one of said pair of substrates, and thin-film transistors arranged in correspondence with said respective pixel electrodes, each of said thin-film transistors having a source electrode connected to a corresponding one of said pixel electrodes, a drain electrode connected to a signal line for supplying a display signal, and a gate electrode connected to a scanning line for supplying a scanning signal.

25. A color liquid crystal display apparatus for changing a display color in accordance with an applied voltage, comprising:

a pair of substrates having opposing surfaces, electrodes respectively formed on the opposing surfaces, and aligning films respectively formed to cover said electrodes, said aligning films having undergone aligning treatment in predetermined directions;

a liquid crystal layer formed between said pair of substrates and having liquid crystal molecules aligned to be twisted at a twist angle of 180°

to 270°

from one substrate to the other substrate;

a pair of polarizing plates disposed outside said pair of substrates to sandwich said substrates and respectively having transmission axes for linearly polarizing incident light;

a retardation plate having a maximum refractive index direction which is within a plane parallel to a surface of said retardation plate and having a value of retardation for coloring light transmitted through the liquid crystal display apparatus, in combination with the Δ

n·

d of the liquid crystal layer, said retardation plate being disposed to be adjacent to one of said pair of polarizing plates which is located on an incident side, for elliptically polarizing linearly polarized light transmitted through said one of said pair of polarizing plates; and

driving means, connected to said electrodes, for applying at least three different voltages to said liquid crystal layer to change a polarized state of light transmitted through said liquid crystal layer so as to change a display color to at least three colors including at least two chromatic colors.