Transflective liquid crystal display with integral heating unit and temperature sensor

• US 4,634,225 A
• Filed: 12/24/1984
• Issued: 01/06/1987
• Est. Priority Date: 12/24/1984
• Status: Expired due to Fees

• Current Assignee: Amespace Incorporated
• Original Assignee: General Electric Company
• Inventors: Suminsby, John E., Haim, Elias S.
• Primary Examiner(s): Corbin, John K.
• Assistant Examiner(s): Lewis, David
• Application Number:
  US06/686,065
• Time in Patent Office: 743 Days
• Field of Search: 350/331 T, 350/588, 350/346, 350/349, 350/338
• US Class Current: 349/161
• CPC Class Codes: G02F 1/132 Thermal activation of liquid crystals exhibiting a thermo-optic effect
• 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

A heated transflective liquid crystal display device has the heating element positioned behind the transflector to keep the heater out of the reflective light path. This construction significantly improves brightness of the display in the reflective mode.

The heating element is positioned between the cell transflector and a temperature sensing thermistor. The thermal gradient of the path between the heating element and the thermistor matches that of the path between the heating element and the liquid crystal cell. As a result, the trip point of the heating element can be set much closer to the minimum cell operating temperature than hitherto possible thereby reducing the power consumption of the display.

This invention relates to liquid crystal display devices, and more particularly to liquid crystal displays incorporating a heating unit.

While the instant invention will be described in the context of a cell of the guest-host variety, the invention is by no means limited thereto. The invention is equally applicable and useful in a liquid crystal display utilizing a liquid crystal solution of the twisted nematic type.

Claims

1. In a heated liquid crystal display, the combination comprising:

(a) a liquid crystal cell containing a liquid crystal solution,

(b) reflector means positioned behind said cell to reflect light entering the front of the cell back through the cell,

(c) heating means located outside of the reflective light path including a heating element and a support element in heat exchanging relationship with said cell for maintaining the temperature of the solution above the minimal operating temperature of the solution,

(d) temperature responsive sensing means positioned adjacent to said heating element and in heat exchange relationship therewith to to generate an electrical signal as a function of temperature, said temperature responsive sensing means is a separate element from said liquid crystal solution and is a separate element from said heating means,

(e) said heating and support elements being constructed so that the temperature gradients between the heater element and the cell solution and the heater element and said sensing means respectively are substantially equal whereby the temperature at the sensing means essentially tracks the cell temperature.

2. The heated liquid crystal display according to claim 1 wherein said heating means is positioned behind and adjacent to said reflector means.

3. The heated liquid crystal display according to claim 2 wherein the heater element on said substrate contacts said reflector and said temperature sensing means is located adjacent said support element on the side away from said heater element to establish a thermal path through said support means to said sensing means.

4. The liquid crystal according to claim 3 wherein said heater element is located on one side of said support element and said temperature sensing means is on the other side of said support element.

5. The heated liquid crystal display according to claim 4 including a transflective element behind said cell and a light source positioned behind said heating means for selectively operating said display in the transmissive mode.

6. The heated liquid crystal display according to claim 5 including a light diffusive element between said light source and the rear of said heating means.

7. The heated liquid crystal display according to claim 6 wherein said temperature sensing means is supported on said diffusing means.

8. The heated liquid crystal display according to claim 7 wherein the rear of said heating means is attached to said light diffusing means.

9. The heated liquid crystal display according to claim 1 wherein said liquid crystal solution is a guest-host solution including an optically active material.

10. The heated liquid crystal display according to claim 8 wherein the said liquid crystal solution includes at least one dichroic dye dissolved in a liquid crystal host and including an optically active chiral material.