LED driver with compensation of thermally induced color drift

1. A circuit arrangement comprising:

a temperature sensing circuit configured to provide a temperature signal representing temperature(s) of a plurality of light emitting diodes emitting light of different colors arranged adjacent to each other for additive color mixing to provide a desired color, wherein the temperature sensing circuit includes a sigma-delta-modulator configured to generate a stream of bits or digital words whose time average represents the sensed temperature(s), the stream of bits or digital words forming the temperature signal;

a current source for each light emitting diode of the plurality of light emitting diodes, current sources configured to provide the light emitting diodes with respective load currents in accordance with corresponding control signals received by the current sources;

a first modulator unit and a second modulator unit configured to generate the control signals which are modulated such that a time average value of each control signal corresponds to the value of a corresponding input signal of the respective modulator unit; and

a calibration circuit configured to provide the input signals dependent on a color signal defining the desired color and dependent on the temperature signal, wherein the calibration circuit includes a lookup table unit including color calibration data for different discrete temperature values, the lookup table unit is configured to provide a set of calibration data selected dependent on the temperature signal, the input signals of the modulator units being responsive to the selected set of calibration data.

2. The circuit arrangement of claim 1 , further comprising the plurality of light emitting diodes.

3. A circuit arrangement comprising:

a temperature sensing circuit configured to provide a temperature signal representing temperature(s) of a plurality of light emitting diodes emitting light of different colors arranged adjacent to each other for additive color mixing to provide a desired color;

a current source for each light emitting diode of the plurality of light emitting diodes, current sources configured to provide the light emitting diodes with respective load currents in accordance with corresponding control signals received by the current sources;

a first modulator unit and a second modulator unit configured to generate the control signals which are modulated such that a time average value of each control signal corresponds to the value of a corresponding input signal of the respective modulator unit; and

a calibration circuit configured to provide the input signals dependent on a color signal defining the desired color and dependent on the temperature signal, wherein the calibration circuit includes a lookup table unit including color calibration data for different discrete temperature values, the lookup table unit is configured to provide a set of calibration data selected dependent on the temperature signal, the input signals of the modulator units being responsive to the selected set of calibration data.

4. The circuit arrangement of claim 3 , wherein the lookup table unit comprises:

a calibration table including selectable calibrated current values for the light emitting diodes associated with a defined color value, the current values being calibrated for a reference temperature and the selection of the calibrated current values being based on the color signal; and

a compensation table including selectable compensation coefficients, each coefficient being associated with one LED and a discrete temperature value, the selection of the compensation coefficients being based on the temperature signal;

wherein the calibrated current values are combined with the respective compensation coefficients to provide, as calibration data, corresponding current values recalibrated for the sensed temperature(s).

5. The circuit arrangement of claim 4 , wherein the calibration circuit further includes:

sigma-delta-modulators configured to generate a bit-stream corresponding to each compensation coefficient, the time average of each bit-stream representing the respective compensation coefficient; and

a multiplier configured to multiply the bit streams representing the compensation coefficients with the calibrated current values obtained from the calibration table, the multiplier providing the calibration data.

6. The circuit arrangement of claim 5 , wherein the multiplier is configured to receive as further multiplying factor a bit stream whose time average represents a brightness value.

7. The circuit arrangement of claim 3 , wherein the lookup table unit comprises a calibration table including selectable calibrated current values for the light emitting diodes associated with a defined color value, the current values being calibrated for a plurality of different temperatures and the selection of the calibrated current values being based on the color signal and on the temperature signal.

8. The circuit arrangement of claim 3 , further comprising the plurality of light emitting diodes.

9. A method for driving a multi-color LED arrangement including a plurality of light emitting diodes emitting light of different colors and arranged adjacent to each other for additive color mixing to provide a desired color, the method comprising:

generating a temperature signal representing temperature(s) of the light emitting diodes, wherein generating the temperature signal comprises

providing a sense signal representing temperature(s) of one or more light emitting diodes, and

sigma-delta modulating the sense signal thus generating a stream of bits or digital words, whose time average represents the sensed temperature(s), to provide the temperature signal;

supplying, to each light emitting diode, load currents regulated in accordance with corresponding control signals;

generating modulated signals as the control signals which are modulated such that a time average value of each control signal corresponds to a value of a corresponding input signal; and

providing the input signals dependent on a color signal defining the desired color and dependent on the temperature signal using a look-up table, wherein the look-up table includes color calibration data for different discrete temperature values, and wherein a set of calibration data is selectable dependent on the temperature signal, the input signals for the sigma-delta modulation being responsive to a selected set of calibration data.

10. The method of claim 9 , wherein the sigma-delta modulating comprises:

low-pass filtering the stream of bits or digital words to provide the temperature signal.

11. The method of claim 9 , wherein the temperature signal is further provided by low-pass filtering the stream of bits or digital words.

12. A method for driving a multi-color LED arrangement including a plurality of light emitting diodes emitting light of different colors and arranged adjacent to each other for additive color mixing to provide a desired color, the method comprising:

generating a temperature signal representing temperature(s) of the light emitting diodes;

supplying, to each light emitting diode, load currents regulated in accordance with corresponding control signals;

generating modulated signals as the control signals which are modulated such that a time average value of each control signal corresponds to a value of a corresponding input signal; and

providing the input signals dependent on a color signal defining the desired color and dependent on the temperature signal using a look-up table, wherein the look-up table includes color calibration data for different discrete temperature values, and wherein a set of calibration data is selectable dependent on the temperature signal, the input signals being responsive to a selected set of calibration data.

13. The method of claim 12 , wherein the look-up table comprises:

a calibration table including selectable calibrated current values for the LEDs associated with a defined color value; the current values being calibrated for a reference temperature and the selection of the calibrated current values being based on the color signal; and

a compensation table including selectable compensation coefficients, each coefficient being associated with one LED and a discrete temperature value, the selection of the compensation coefficients being based on the temperature signal;

wherein the calibrated current values are combined with the respective compensation coefficients to provide, as calibration data, corresponding current values recalibrated for sensed temperature(s).

14. The method of claim 13 , wherein providing the input signals using the look-up table comprises:

generating a bit-stream corresponding to each compensation coefficient using sigma-delta modulation, a time average of each bit-stream representing the respective compensation coefficient; and

using a multiplier to multiply the bit streams representing the compensation coefficients with the calibrated current values obtained from the calibration table, thus providing the calibration data.

15. The method of claim 14 , wherein the multiplier receives as further multiplying factor a bit stream whose time average represents a brightness value.

16. The method of claim 15 , wherein the look-up table comprises a calibration table including selectable calibrated current values for the LEDs associated with a defined color value, the current values being calibrated for a plurality of different temperatures and the selection of the calibrated current values being based on the color signal and on the temperature signal.