LIQUID CRYSTAL VOLTAGE DISPLAY DEVICE HAVING PHOTOCONDUCTIVE MEANS TO ENHANCE THE CONTRAST AT THE INDICATING REGION

• US 3,705,310 A
• Filed: 05/24/1971
• Issued: 12/05/1972
• Est. Priority Date: 05/27/1970
• Status: Expired due to Term

• Current Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Original Assignee: Peter Wild
• Inventors: Wild, Peter
• Primary Examiner(s): Wibert, Ronald L.
• Assistant Examiner(s): Bauer, Edward S.
• Application Number:
  US05/146,196
• Time in Patent Office: 561 Days
• Field of Search: 350/150,16LC 250/229 340/324R 324/92,96,113 315/55,169R
• US Class Current: 250/229
• CPC Class Codes: G01R 13/04 for producing permanent records
• CPC Class Codes: G01R 13/40 using modulation of a light beam otherwise than by mechanical displacement, e.g. by Kerr effect visual indication of correct tuning H03J3/14
• CPC Class Codes: G01R 19/155 Indicating the presence of voltage
• CPC Class Codes: G01R 19/16576 comparing DC or AC voltage with one threshold G01R19/16514, G01R19/16519, G01R19/16528, G01R19/16533 and G01R19/1659 take precedence
• CPC Class Codes: G02F 1/133382 Heating or cooling of liquid crystal cells other than for activation, e.g. circuits or arrangements for temperature control, stabilisation or uniform distribution over the cell

Abstract

In the optical display disclosed, a pair of flat electrodes sandwich a two-dimensionally extending electro-optical medium that exhibits one optical characteristic in an area subjected to a voltage in excess of a threshold voltage and another optical characteristic where subjected to a voltage less than the threshold voltage. A potential gradient is applied along one electrode and segment wise constant voltages applied to the band electrode so that the voltage to which the medium is subjected varies locally from below to above the threshold voltage. The voltage to be displayed is added to the voltage on one electrode so that the threshold level and the boundary between the zones moves along the medium with the voltage to be displayed. The band electrode is formed of discreet bands parallel to the zoneseparating boundary. An additional constant voltage is applied lengthwise across each band. A portion of each band is photoresistive. When this portion senses the one zone that is subject to the higher voltage it increases the voltage applied locally to the medium in the form of a positive feedback. This accentuates the steepness of the threshold. Photosensitive means also change the applied voltages in response to changes of the threshold level. For this purpose circuit means respond to the photosensitive means by changing the applied voltages.

Claims

1. An optical display for displaying an input voltage comprising an electro-optic medium, first and second electrode means sandwiching the medium for applying a potential across said medium, said first electrode means being capable of having a voltage gradient established thereacross in a given direction, said second electrode means being formed by a plurality of conductive bands extending transverse to said given direction, first electric means for applying a voltage across said first electrode means for establishing the voltage gradient in said given direction, second electric means for applying a voltage between said first and second electrode means to cause a first light condition in those portions of said medium in which the voltage exceeds a threshold value while the portions of said medium in which the voltage does not exceed the threshold value exhibit a second light condition, said two light conditions forming a boundary between the two portions, input means for varying the voltage across said medium for causing the boundary between the portions exhibiting the first light condition and the portions exhibiting the second light conditions to move along said given direction, each of said bands having a photoconductive extension disposed in the path of a portion of light passing through said medium, and means for applying a potential across each band and its photoconductive extension so that the potential difference between the portions exhibiting the first light condition and the portions exhibiting the second light condition is increased, thereby enhancing the contrast of said boundary.

2. A display as in claim 1, wherein said bands each have a second extension with a fixed resistance higher than the portion of said bands outside said extensions.

3. A display as in claim 2, wherein each of said extensions extend in opposite directions from the remaining portions of said bands.

4. A display as in claim 2, wherein said electric means form the light conditions to which said medium means is subject on the basis of voltages applied to said electrode, and wherein the resistance of said extensions decreases in response to that optical characteristic which increases the voltage across said medium.

5. A display as in claim 2, wherein said bands are transparent between said extensions and form an indicating zone and wherein said extensions are mounted outside of said indicating zone.

6. A display as in claim 5, wherein said first extensions are bent over to partially mask the indicating zone.

7. A display as in claim 2, wherein said medium includes nematic liquid crystals and said electrode means are solid and sandwich said liquid crystals between them to define the extent of said medium, and further comprising a pair of optical polarizing means arranged optically transverse to each other and located along at least one of said electrode means.

8. A display as in claim 2, wherein the first and second light conditions correspond to respective lower and higher voltage ranges within the voltage gradient, and wherein the potentials to be formed by said second electric means between the ends of said bands is within the lower voltage range.

9. A display as in claim 8, wherein said second electric means intermittently place the other of said electrode means at a potential of zero.

10. A display as in claim 9, wherein said second electrical means places said other electrode means at zero potEntial during intervals of 30 milliseconds and less.

11. A display as in claim 1, wherein said other of said electrode means includes optical partition walls between said bands to decouple said bands optically.

12. A display as in claim 1, wherein said medium includes nematic liquid crystals and said electrode means are solid and sandwich said crystals between them to define the extent of said medium means.

13. A display as in claim 12, further comprising a pair of optical polarizing means arranged optically transverse to each other and located along at least one of said electrode means.

14. A display as in claim 1, wherein said electric means form the light conditions on the basis of voltages applied to said electrode across said medium, and wherein the resistance of said extensions decreases in response to that optical property which increases the voltage across said medium.

15. A display as in claim 1, wherein said electrode means each include secondary electrodes, said electric means forming a voltage gradient along one of said secondary electrodes and a constant voltage across another of said secondary electrodes so as to cause different light conditions in said medium near said secondary electrodes, and further comprising control means including said secondary electrodes and responsive to the light conditions of the medium near said secondary electrodes for varying the voltages of said electric means so as to adjust the voltage gradients and to create one light condition in said medium near one location of said secondary electrodes and another light condition in said medium near another location of said secondary electrodes.

16. A display as in claim 15, wherein said control means includes a pair of photo-detector means each near one of the locations at one of said secondary electrodes and responsive to the light condition of said medium means near said secondary electrodes.

17. A display as in claim 15, wherein said control means includes bands forming one of said secondary electrodes and extending transverse to the voltage gradient formed at said secondary electrodes, and light responsive resistance means on said bands of said secondary electrodes.

18. A display as in claim 1, wherein said medium includes temperature sensitive means and photo-detector means responsive to the condition of said temperature sensitive means, and further comprising temperature control means responsive to said temperature sensitive means for varying the temperature of said medium.

19. A display as in claim 18, wherein said medium includes nematic liquid crystals and wherein said temperature sensitive means includes cholesteric liquid crystals.