LCD compensation for non-optimum voltage conditions

• US 4,834,504 A
• Filed: 10/09/1987
• Issued: 05/30/1989
• Est. Priority Date: 10/09/1987
• Status: Expired due to Term

• Current Assignee: Hewlett-Packard Company (HP Inc.)
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Garner, Grant K.
• Primary Examiner(s): Miller, Stanley D.
• Assistant Examiner(s): Duong, Tai V.
• Application Number:
  US07/107,061
• Time in Patent Office: 599 Days
• Field of Search: 350/331 T, 350/332, 350/333, 350/331 R, 307/227, 307/529, 307/264, 307/268, 307/260, 307/359, 340/784, 340/805, 340/812, 340/813, 340/767, 340/811, 340/765
• US Class Current: 345/87
• CPC Class Codes: G05F 1/625 wherein it is irrelevant whether the variable actually regulated is ac or dc
• CPC Class Codes: G09G 3/18 using liquid crystals
• CPC Class Codes: G09G 3/36 using liquid crystals

Abstract

A liquid crystal display (LCD) compensation circuit, operating within a peak voltage limitation, serves to maximize the on/off voltage ratio applied to the LCD while at the same time meeting the LCD threshold voltage specification to thereby optimize the appearance of the liquid crystal display at all times.

Claims

1. A passive matrix liquid crystal display compensation circuit, the circuit comprising:

reference voltage source means for supplying a desired reference voltage to be applied to the passive matrix liquid crystal display;

summer means having a first summing input for receiving the reference voltage, having a second summing input, and having an output providing a step voltage;

peak voltage function generator means having an input for receiving the step voltage and having an output that provides a source of peak voltage; and

feedback function generator means having an input for receiving the peak voltage and having an output connected to the second summing input of the summer means, the summer means being thereby operative for subtracting the output of the feedback function generator means from the reference voltage to produce a continuously updated value of step voltage.

2. A liquid crystal display compensation circuit as in claim 1 wherein the peak voltage function generator means comprises a constant voltage source.

3. A liquid crystal display compensation circuit as in claim 1 wherein the peak voltage function generator means comprises a voltage multiplier.

4. A liquid crystal display compensation circuit as in claim 1 wherein the output of the feedback function generator means is a defined fractional function of its input.

5. A liquid crystal display compensation circuit as in claim 4 wherein the defined fractional function is equal to 0.28.

6. A liquid crystal display compensation circuit as in claim 1 wherein the output of the feedback function generator means is a defined square root function of its input.

7. A liquid crystal display compensation circuit as in claim 1 wherein the output of the feedback function generator means is related to its input by a multiple of 0.28.

8. A liquid crystal display compensation circuit as in claim 1 wherein the summer means and the feedback function generator means comprise a resistor summing amplifier.