Light-emitting diode backlighting systems
First Claim
1. A lighting system to energize strings of light-emitting diodes, comprising:
- current sources each configured to provide to a respective one of said strings a current having an amplitude responsive to a control voltage and to provide a monitor voltage representative of said amplitude;
control voltage sources each configured to provide the control voltage of a respective one of said current sources;
a comparator to compare a voltage at an input port of said comparator to a reference voltage; and
a multiplexer arranged to couple the monitor voltage of any selected one of said current sources to said input port;
an output signal of said comparator thereby indicating a calibration state of each of said current sources in response to its respective control voltage.
1 Assignment
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Accused Products
Abstract
Lighting system embodiments are provided to energize and calibrate strings of light-emitting diodes. These embodiments are particularly useful for calibration of strings of light-emitting diodes that are arranged to provide backlighting of liquid crystal displays. The systems are structured around the use of a single comparator that is multiplexed to facilitate calibration of a plurality of current sources. The systems can be adapted for use in displays in which different techniques (e.g., “analog dimming” and “pulse-width modulation”) are used to vary the brightness of the display. The systems remove the need for special structures (e.g., fuse arrays, special test equipment, and interfaces).
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Citations
15 Claims
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1. A lighting system to energize strings of light-emitting diodes, comprising:
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current sources each configured to provide to a respective one of said strings a current having an amplitude responsive to a control voltage and to provide a monitor voltage representative of said amplitude; control voltage sources each configured to provide the control voltage of a respective one of said current sources; a comparator to compare a voltage at an input port of said comparator to a reference voltage; and a multiplexer arranged to couple the monitor voltage of any selected one of said current sources to said input port; an output signal of said comparator thereby indicating a calibration state of each of said current sources in response to its respective control voltage. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A lighting system to energize strings of light-emitting diodes, comprising:
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current sources each configured to include; a transistor having a control terminal and first and second current terminals responsive to said control terminal wherein said second current terminal is available for coupling to a respective one of said strings; a resistor coupled to said first current terminal; and a differential amplifier arranged to drive said control terminal and having positive and negative input terminals with said negative input terminal coupled to said first current terminal; control voltage sources each configured to provide a selectable control voltage to the positive terminal of the differential amplifier of a respective one of said current sources; a comparator having a first input terminal and having a second input terminal for reception of a reference voltage; and a multiplexer arranged to couple the first current terminal of any selected one of said current sources to said first input terminal; an output signal of said comparator thereby indicating a calibration state of each of said current sources in response to its respective trim voltages. - View Dependent Claims (9, 10, 11, 12, 13)
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14. A method to energize strings of light-emitting diodes, comprising the steps of:
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providing to each of said strings a current having an amplitude responsive to a control voltage and further providing a monitor voltage representative of said amplitude; varying the control voltage corresponding to a respective one of said strings; comparing a voltage at a comparison port to a reference voltage; and multiplexing the monitor voltage corresponding to any selected one of said currents to said comparison port; the comparing step thereby indicating a calibration state of the current of each strings in response to its respective control voltage. - View Dependent Claims (15)
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Specification