Circuit for driving an infrared transmitter LED with temperature compensation
First Claim
1. A method for a circuit for driving an infrared transmitter LED with temperature compensation comprising the following steps:
- (1) providing of one or more LED diodes, a battery voltage, an analog-to-digital converter, a LED driver comprising a resistive digital-to-analog converter structure controlling a current through the diodes, a circuit to measure a battery voltage and a difference of forward diode voltages, a programmable current sink, a circuit for offset cancellation, and a circuit for resistor load compensation;
(2) calibrating the analog-to-digital converter by canceling an offset between a battery voltage and a forward voltage of said one or more LEDs;
(3) determining if the battery voltage is in an acceptable range;
(4) determining temperature dependency of the forward voltage of said one or more LEDs by comparing the forward voltages when switching a drive current between two constant current values; and
(5) adjusting a driver current of said one or more LEDs according to the temperature dependency determined.
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Abstract
Systems and methods to achieve a circuit for driving one or more infrared transmitter LEDs with temperature compensation have been disclosed. In a preferred embodiment of the invention the circuit has been applied for a rain sensing system. The junction temperature of the LED is measured and compensated by adjusting the driver current of a voltage-to-current converter driving the LED. The LED junction temperature is measured by comparing the difference in the forward diode voltage at different current densities. This voltage difference is extracted when switching the drive currents between different constant values. The measurement results are converted to digital values, which are used by a buffered dual ladder resistive DAC structure to adjust the drive current to temperature variations.
36 Citations
24 Claims
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1. A method for a circuit for driving an infrared transmitter LED with temperature compensation comprising the following steps:
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(1) providing of one or more LED diodes, a battery voltage, an analog-to-digital converter, a LED driver comprising a resistive digital-to-analog converter structure controlling a current through the diodes, a circuit to measure a battery voltage and a difference of forward diode voltages, a programmable current sink, a circuit for offset cancellation, and a circuit for resistor load compensation; (2) calibrating the analog-to-digital converter by canceling an offset between a battery voltage and a forward voltage of said one or more LEDs; (3) determining if the battery voltage is in an acceptable range; (4) determining temperature dependency of the forward voltage of said one or more LEDs by comparing the forward voltages when switching a drive current between two constant current values; and (5) adjusting a driver current of said one or more LEDs according to the temperature dependency determined. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. A circuit for driving one or more infrared transmitter LEDs with temperature compensation comprises:
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a LED transmitter drive circuitry generating a drive current for said one or more LEDs, wherein the drive current is adjusted for temperature variations by an output of an analog-to-digital converter; a programmable current sink circuitry, wherein said programmable current sink provides a drive current for said LEDs having two constant values wherein a difference of forward voltages of the LEDs is used to determine a temperature dependency of said forward voltage; a circuitry for measuring a battery voltage and said difference of forward voltages of the LEDs; a circuitry for compensating a resistor load, wherein the resistor load is caused by resistive voltage dividers used by said circuitry for measuring a battery voltage and said difference of forward voltages of the LEDs; an analog-to-digital converter converting said measurements of the battery voltage and said difference of forward voltages of the LEDs to digital values; and a Digital Signal Processor controlling an operation of the circuit for driving one or more infrared transmitter LEDs with temperature compensation. - View Dependent Claims (16, 17, 18, 19, 20, 21, 22, 23, 24)
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Specification