US 8,283,876 B2Granted

Circuit for driving an infrared transmitter LED with temperature compensation

AssigneeDialog Semiconductor GmbH

InventorCang Ji

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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.

Claims20

Dependent claims

A method for driving an infrared transmitter LED with temperature compensation for a circuit comprising the following steps:

(1) providing 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, wherein the digital-to-analog converter structure comprises a coarse DAC inputting all bits of the output of the coarse DAC to a fine DAC, 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 wherein the driver current is adjusted using the resistive digital-to-analog converter structure.

3 more elements

A circuit for driving one or more infrared transmitter LEDs with temperature compensation comprises:

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 the analog-to-digital converter, comprising
a resistive digital-to-analog converter structure having two inputs, wherein a first input is a reference voltage and a second input is an output of said analog-to digital converter;
an error amplifier having three inputs and an output wherein a first input is an output of said resistive digital-to-analog converter structure, a second input is a control signal and a third input is a feedback indicating a value of drive current of the LEDs, and the output is a voltage controlling a voltage-to-current converter wherein an output of said voltage-to-current converter is the current driving the LEDs;
and
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 voltages, wherein said programmable current sink circuitry comprises an arrangement of matched scaled metal-oxide-semiconductor (MOS) current mirror devices and a correspondent arrangement of switches allowing generating values of currents in multiple steps as required for measuring forward voltage of the LEDs using different values of current;
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;
and
the analog-to-digital converter converting said measurements of the battery voltage and said difference of forward voltages of the LEDs to digital values.

6 more elements

Dependencies are inferred from the claim text.