Voltage regulator for liquid crystal display
First Claim
1. A voltage regulator for driving a liquid crystal display, said display including display elements having threshold and saturation characteristics which vary with temperature, comprising:
- a voltage source having a positive and a negative terminal;
first resistance means having a resistance varying with temperature;
second resistance means having a first and a second terminal;
a transistor having a gate, and a source-drain path, said first resistance means, second resistance means and source-drain path of the transistor being coupled in series between the positive and the negative terminals of the voltage source; and
an operational amplifier with positive and negative terminals having a stable offset voltage therebetween and an output terminal, the positive and negative terminals of the operational amplifier being coupled to the first and the second terminals of the second resistance means, the output of the operational amplifier being coupled to the gate of the transistor;
whereby the current in the source-drain path of the transistor is equal to the offset voltage divided by the resistance of the second resistance means.
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Abstract
The voltage regulator, entirely of monolithic integrated circuit construction, has an output voltage with a temperature gradient similar to that of the saturation and threshold voltages of liquid crystal elements. Constant current flows through temperature sensitive resistive elements in series with temperature insensitive resistance elements. The output voltage taken across at least a portion of the resistance elements has a voltage/temperature characteristic similar to that of the temperature sensitive elements. Both the level of the output voltage and the temperature gradient of the output voltage are independently controllable and independent of source voltage variations. Buffer circuits may be used between the output of the regulator and load, and sampling techniques are also used to conserve energy by duty cycle operation of higher current circuit elements.
54 Citations
25 Claims
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1. A voltage regulator for driving a liquid crystal display, said display including display elements having threshold and saturation characteristics which vary with temperature, comprising:
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a voltage source having a positive and a negative terminal; first resistance means having a resistance varying with temperature; second resistance means having a first and a second terminal; a transistor having a gate, and a source-drain path, said first resistance means, second resistance means and source-drain path of the transistor being coupled in series between the positive and the negative terminals of the voltage source; and an operational amplifier with positive and negative terminals having a stable offset voltage therebetween and an output terminal, the positive and negative terminals of the operational amplifier being coupled to the first and the second terminals of the second resistance means, the output of the operational amplifier being coupled to the gate of the transistor; whereby the current in the source-drain path of the transistor is equal to the offset voltage divided by the resistance of the second resistance means. - View Dependent Claims (2, 3, 4, 5, 6, 7, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25)
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8. A voltage regulator for driving a liquid crystal display, said display including display elements having threshold saturation characteristics which vary with temperature comprising:
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a voltage source having a positive and a negative terminal; first resistance means having a resistance varying with temperature; second resistance means having a first and a second terminal; a transistor having a gate, and a source-drain path, said first resistance means, second resistance means and source-drain path of the transistor being coupled in series between the positive and the negative terminals of the voltage source; an operational amplifier with positive and negative terminals and an output terminal; and a standard voltage source, the standard voltage source being coupled between one of the positive and negative terminals of the operational amplifier and one of the first and second terminals of the second resistance means, the other terminal of the positive and the negative of the operational amplifier being coupled to the other terminal of the second resistance means, the output of the operational amplifier being coupled to the gate of the transistor;
whereby the current in the source-drain path of the transistor is equal to the voltage of the standard voltage source divided by the resistance of the second resistance means. - View Dependent Claims (9, 10, 11, 12, 13)
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Specification