Liquid crystal integrated circuit display including as arrangement for maintaining the liquid crystal at a controlled temperature

• US 5,694,147 A
• Filed: 04/14/1995
• Issued: 12/02/1997
• Est. Priority Date: 04/14/1995
• Status: Expired due to Term

• Current Assignee: Citizen Finetech Miyota Company Limited (Citizen Electronics Company Limited)
• Original Assignee: Displaytech Inc (Micron Technology, Inc.)
• Inventors: Handschy, Mark A., Gaalema, Stephen D.
• Primary Examiner(s): Hjerpe, Richard
• Assistant Examiner(s): CHANG, KENT WU
• Application Number:
  US08/421,899
• Time in Patent Office: 963 Days
• Field of Search: 345/87, 345/101, 359/86, 323/366, 349/42, 349/43, 349/72
• US Class Current: 345/101
• 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
• CPC Class Codes: G09G 2320/041 Temperature compensation
• CPC Class Codes: G09G 3/3648 using an active matrix G09G3/367 - G09G3/3696 take precedence

Abstract

An active matrix liquid crystal display includes an arrangement for maintaining the liquid crystal material of the display at a controlled temperature above ambient temperature. The liquid crystal material of the display is disposed over a substrate containing integrated circuitry. The arrangement for maintaining the temperature of the liquid crystal includes (i) an arrangement for heating the liquid crystal material sufficient to maintain the liquid crystal material at the controlled temperature, (ii) an arrangement for sensing the temperature at a location in close proximity to the liquid crystal material and producing an output signal representative of the temperature, and (iii) a servo-circuit responsive to the output signal for causing the heating arrangement to maintain the liquid crystal material at the controlled temperature. In accordance with the present invention, at least some of the elements making up the arrangement for heating the liquid crystal, the arrangement for sensing the temperature, or the servo-circuitry are formed as part of the integrated circuitry contained within the substrate which the liquid crystal is disposed over. In one preferred embodiment of the present invention, all of the elements making up the arrangement for heating the liquid crystal, the arrangement for sensing the temperature, and the servo-circuitry are formed as part of the integrated circuitry contained within the substrate which the liquid crystal is disposed over.

Claims

1. In an active matrix liquid crystal display including a layer of liquid crystal material disposed adjacent a substrate containing integrated circuitry including specific circuitry for controlling the light modulating state of the liquid crystal material, an arrangement for maintaining the liquid crystal material at a controlled temperature above ambient temperature, said arrangement comprising:

(a) means forming part of said integrated circuitry for heating said liquid crystal material sufficient to maintain the liquid crystal material at said controlled temperature, said means heating including a transistor for regulating the amount of power from a source of electrical power dissipated as heat within a heating element, said transistor also being larger than is otherwise necessary for operating said means for heating from an electrical standpoint whereby to more evenly distribute the heat generated by said transistor within said substrate than would otherwise be the case if the transistor were smaller;

(b) means for sensing the temperature at a location in close proximity to said liquid crystal material and producing an output signal representative of said temperature; and

(c) a servo-circuit responsive to said output signal for causing said heating means to maintain said liquid crystal material at said controlled temperature.

2. An arrangement according to claim 1 wherein said means for sensing the temperature is integrally formed as part of said integrated circuitry.

3. An arrangement according to claim 2 wherein said means for heating said liquid crystal material is integrally formed as part of said integrated circuitry.

4. An arrangement according to claim 1 wherein said means for heating said liquid crystal material is integrally formed as part of said integrated circuitry.

5. An arrangement according to claim 1 wherein said means for heating said liquid crystal material includes a pattern of polysilicon material formed on said substrate serving as said heating element.

6. An arrangement according to claim 5 wherein said means for sensing the temperature includes circuitry forming a Wheatstone bridge including first and second parallel pairs of first and second series connected resistors and means for applying a voltage across said bridge.

7. An arrangement according to claim 2 wherein said first resistor of said first pair of resistors and said second resistor of said second pair of resistors are substantially temperature-independent resistors having substantially equal resistances which remain relatively constant over a range of temperatures.

8. An arrangement according to claim 7 wherein said second resistor of said first pair of resistors and said first resistor of said second pair of resistors are temperature-dependent resistors whose resistance varies with changes in temperature to a much greater extent than said temperature-independent resistors.

9. An arrangement according to claim 8 wherein said temperature-independent resistors are polysilicon resistors.

10. An arrangement according to claim 8 wherein said temperature-dependent resistors are formed as moderately doped regions in said substrate such as would be formed in the making of wells in a typical CMOS process.

11. An arrangement according to claim 8 wherein said servo-circuit includes a differential amplifier having two input terminals and an output terminal for amplifying said output signal, a first of said input terminals being electrically connected to said first pair of resistors between said first and second resistor making up said first pair of resistors, the second of said input terminals being electrically connected to said second pair of resistors between said first and second resistor making up said second pair of resistors, and the output terminal being electrically connected to said transistor of said means for heating said liquid crystal material.

12. An arrangement according to claim 11 wherein one of said input terminals of said differential amplifier is adapted to be electrically connected to elements external to said servo-circuitry for purposes of controllably adjusting the current applied to said one of said input terminals of said differential amplifier.

13. An arrangement according to claim 12 wherein said output terminal of said differential amplifier is adapted to be electrically connected to elements external to said servo-circuitry for purposes of providing a stabilizing feedback signal to said one of said input terminals of said differential amplifier.

14. An arrangement according to claim 1 further comprising means external of said integrated circuitry for adjusting the value of said controlled temperature.

15. In a liquid crystal display including a layer of liquid crystal material, an arrangement for maintaining the liquid crystal material at a controlled temperature above ambient temperature, said arrangement comprising:

(a) means for heating said liquid crystal material sufficient to maintain the liquid crystal material at said controlled temperature, said heating means including a transistor for regulating the amount of power from a source of electrical power dissipated as heat within a heating element, said transistor also being larger than is otherwise necessary for operating said heating means from an electrical standpoint whereby to more evenly distribute the heat generated by said transistor than would otherwise be the case if the transistor were smaller;

(b) means for sensing the temperature at a location in close proximity to said liquid crystal material and producing an output signal representative of said temperature; and

(c) a servo-circuit responsive to said output signal for causing said heating means to maintain said liquid crystal material at said controlled temperature.

16. An arrangement according to claim 15, wherein said means for heating said liquid crystal material is disposed adjacent a substrate containing integrated circuitry including specific circuitry for controlling the light modulating state of the liquid crystal material and wherein said means for heating includes a pattern of polysilicon material formed on said substrate, said pattern of polysilicon material serving as said heating element.

17. In an active matrix liquid crystal display including a layer of liquid crystal material disposed adjacent a substrate containing integrated circuitry including specific circuitry for controlling the light modulating state of the liquid crystal material, a method for maintaining the liquid crystal material at a controlled temperature above ambient temperature, said method comprising the steps of:

(a) providing an arrangement for maintaining the liquid crystal material at a controlled temperature with at least some of the components making up said arrangement being formed as part of said integrated circuitry, said arrangement including,

(i) means for heating said liquid crystal material sufficient to maintain the liquid crystal material at said controlled temperature, said heating means including a transistor for regulating the amount of power from a source of electrical power dissipated as heat within a heating element, said transistor also being larger than is otherwise necessary for operating said heating means from an electrical standpoint whereby to more evenly distribute the heat generated by said transistor within said substrate than would otherwise be the case if the transistor were smaller

(ii) means for sensing the temperature at a location in close proximity to said liquid crystal material and producing an output signal representative of said temperature, and

(iii) a servo-circuit responsive to said output signal for causing said heating means to maintain said liquid crystal material at said controlled temperature;

(b) using said sensing means to sense the temperature at a location in close proximity to said liquid crystal material and produce an output signal representative of said temperature; and

(c) using said servo-circuit to cause said heating means to maintain said liquid crystal material at said controlled temperature.

18. A method according to claim 17 wherein all of said components making up said arrangement for maintaining the liquid crystal material at a controlled temperature are formed as part of said integrated circuitry.

19. A method according to claim 17 wherein said means for heating said liquid crystal material includes a pattern of polysilicon material formed on said substrate serving as said heating element.

20. A method according to claim 17 wherein said means for sensing the temperature includes circuitry forming a Wheatstone bridge including first and second parallel pairs of first and second series connected resistors and means for applying a voltage across said bridge.

21. An arrangement according to claim 20 wherein said first resistor of said first pair of resistors and said second resistor of said second pair of resistors are substantially temperature-independent resistors having substantially equal resistances which remain relatively constant over a range of temperatures.

22. A method according to claim 21 wherein said temperature-independent resistors are polysilicon resistors.

23. A method according to claim 20 wherein said second resistor of said first pair of resistors and said first resistor of said second pair of resistors are temperature-dependent resistors whose resistance varies with changes in temperature.

24. A method according to claim 23 wherein said temperature-dependent resistors are formed as moderately doped regions in said substrate such as would be formed in the making of wells in a typical CMOS process.

25. A method according to claim 20 wherein said servo-circuit includes a differential amplifier having two input terminals and an output terminal for amplifying said output signal, a first of said input terminals being electrically connected to said first pair of resistors between said first and second resistor making up said first pair of resistors, the second of said input terminals being electrically connected to said second pair of resistors between said first and second resistor making up said second pair of resistors, and the output terminal being electrically connected to said means for heating said liquid crystal material.

26. In an active matrix liquid crystal display including a layer of liquid crystal material disposed over a substrate containing integrated circuitry, an arrangement for maintaining the liquid crystal material at a controlled temperature above ambient temperature, said arrangement comprising:

(a) means for heating said liquid crystal material sufficient to maintain the liquid crystal material at said controlled temperature, said means for heating said liquid crystal material being integrally formed as part of said integrated circuitry and said means for heating said liquid crystal material including

(i) a pattern of polysilicon material formed on said substrate serving as a heating element and

(ii) a transistor for regulating the amount of power from a source of electrical power dissipated as heat within said heating element, said transistor being formed entirely within said substrate below said pattern of polysilicon, said transistor also being larger than is otherwise necessary for operating said heating means from an electrical standpoint whereby to more evenly distribute the heat generated by said transistor within the substrate than would otherwise be the case if the transistor were smaller;

(b) means for sensing the temperature at a location in close proximity to said liquid crystal material and producing an output signal representative of said temperature, said means for sensing the temperature being integrally formed as part of said integrated circuitry and said means for sensing the temperature including circuitry forming a Wheatstone bridge having first and second parallel pairs of first and second series connected resistors and means for applying a voltage across said bridge, said first resistor of said first pair of resistors and said second resistor of said second pair of resistors being substantially temperature-independent resistors having substantially equal resistances which remain relatively constant over a range of temperatures, said second resistor of said first pair of resistors and said first resistor of said second pair of resistors being temperature-dependent resistors whose resistance varies with changes in temperature to a much greater extent than said temperature-independent resistors; and

(c) a servo-circuit forming part of said integrated circuitry and responsive to said output signal for causing said heating means to maintain said liquid crystal material at said controlled temperature, said servo-circuit including a differential amplifier having two input terminals and an output terminal for amplifying said output signal, a first of said input terminals being electrically connected to said first pair of resistors between said first and second resistor making up said first pair of resistors, the second of said input terminals being electrically connected to said second pair of resistors between said first and second resistor making up said second pair of resistors, and the output terminal being electrically connected to said transistor of said means for heating said liquid crystal material.

27. An arrangement according to claim 26, wherein one of said input terminals of said differential amplifier is adapted to be electrically connected to elements external to said servo-circuitry for purposes of controllably adjusting the current applied to said one of said input terminals of said differential amplifier.

28. An arrangement according to claim 27 wherein said output terminal of said differential amplifier is adapted to be electrically connected to elements external to said servo-circuitry for purposes of providing a stabilizing feedback signal to said one of said input terminals of said differential amplifier.

29. In an active matrix liquid crystal display including a layer of liquid crystal material disposed over a substrate containing integrated circuitry, a method for maintaining the liquid crystal material at a controlled temperature above ambient temperature, said method comprising the steps of:

(a) providing an arrangement for maintaining the liquid crystal material at a controlled temperature with at least some of the components making up said arrangement being formed as part of said integrated circuitry, said arrangement including,

(i) means for heating said liquid crystal material sufficient to maintain the liquid crystal material at said controlled temperature,

(ii) means for sensing the temperature at a location in close proximity to said liquid crystal material and producing an output signal representative of said temperature, said means for sensing the temperature including circuitry forming a Wheatstone bridge having first and second parallel pairs of first and second series connected resistors and means for applying a voltage across said bridge, and

(iii) a servo-circuit responsive to said output signal for causing said heating means to maintain said liquid crystal material at said controlled temperature, said servo-circuit including a differential amplifier having two input terminals and an output terminal for amplifying said output signal, a first of said input terminals being electrically connected to said first pair of resistors between said first and second resistor making up said first pair of resistors, the second of said input terminals being electrically connected to said second pair of resistors between said first and second resistor making up said second pair of resistors, and the output terminal being electrically connected to said means for heating said liquid crystal material;

(b) using said sensing means to sense the temperature at a location in close proximity to said liquid crystal material and produce an output signal representative of said temperature; and

(c) using said servo-circuit to cause said heating means to maintain said liquid crystal material at said controlled temperature.