Thermal control system for liquid crystal cell

• US 20040164946A1
• Filed: 02/21/2003
• Published: 08/26/2004
• Est. Priority Date: 02/21/2003
• Status: Active Grant

• Current Assignee: II-VI Delaware, Inc. (Coherent Corp.)
• Original Assignee: Xtellus Inc.
• Inventors: Spatz, Neil J., Cavanaugh, Shanti A., Crowley, Mark A.
• Granted Patent: US 6,943,768 B2
• Time in Patent Office: Days
• 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 3/006 Electronic inspection or testing of displays and display drivers, e.g. of LED or LCD displays testing individual LED's G01R31/2635; testing lamps G01R31/44; testing of optical features of LCD displays G02F1/1309

Abstract

A thermal control system for a liquid crystal cell is presented that may utilize a time division scheme to multiplex temperature sensing and heating functions across active thermal elements such that the cell may generally be kept at a constant temperature. A calibration process characterizes the profile of the cell and generates a polynomial regression formula that provides the voltage drive output for a temperature and cell state input. The control system stores the state of the liquid crystal cell, the regression formula, and reads the temperature of the liquid crystal cell to compute end assert the temperature compensated voltage drive.

Claims

1. A method of operating a liquid crystal cell such that the performance of the liquid crystal cell is not effected by temperature, comprising the steps of:

A) performing a calibration process that results in a multi dimensional lookup table that produces an output voltage value for any given temperature and attenuation level,

B) consolidating the lookup table from step a into a calibration formula,

C) providing the temperature of the liquid crystal cell,

D) providing the required state of the liquid crystal cell,

E) computing an output voltage value using the formula of step b given inputs values derived from the steps C and D.

2. The method of claim 1, further including after step E, a step F whereby the liquid crystal cell temperature is maintained about a reference temperature.

3. The method of claim 2, further including after step F, step G whereby steps C through G are repeated.

4. The method of claim 1, wherein the formula that defines the optimal voltage to apply to the liquid crystal cell is provided by:

v=(X+Yθ

+Zθ

²)+(X₁+Y₁θ

+Z₁θ

)T+(X₂+Y₂θ

+Z₂θ

²)T²+(X₃+Y₃θ

+Z₃θ

²)T³+(X₄+Y₄θ

+Z₄θ

²)T⁴

Wherein T may equal temperature of the liquid crystal cell, theta the current cell state or attenuation level, and Xn, Yn, and Zn coefficients derived by the output of five second order regressions.

5. The method of claim 4, wherein the fifteen coefficients generated in step B are stored in control system memory.