Interference-resistant compensation for illumination devices using multiple series of measurement intervals

Abstract

A method and illumination device are provided for interference-resistant compensation in light emitting diode (LED) illumination devices. In one embodiment, the method includes bringing to a level insufficient to produce illumination the respective drive current of all except one of multiple emission LED elements for the duration of a first measurement interval and a later-occurring second measurement interval. The first and second measurement intervals are within respective first and second series of measurement intervals interspersed with periods of illumination, and the first and second series of measurement intervals are separated by respective first and second offsets from a timing reference. An embodiment of an illumination device includes multiple emission LED elements, one or more photodetectors, and a lamp control circuit, where the lamp control circuit is adapted to perform steps of the method.

What is claimed is: 
     
       1. A method for controlling an illumination device comprising multiple emission light emitting diode (LED) elements, the method comprising:
 operating one or more of the multiple emission LED elements to produce illumination substantially continuously by supplying a respective drive current at an operative drive current level to each of the one or more of the multiple emission LED elements; 
 bringing the respective drive current of all except one of the emission LED elements within the illumination device to a non-operative drive current level, which is insufficient to produce illumination, for the a duration of a first measurement interval, wherein the first measurement interval is one of a first series of measurement intervals interspersed with periods of said illumination; and 
 bringing the respective drive current of all except one of the emission LED elements to a non-operative drive current level, which is insufficient to produce illumination, for the a duration of a second measurement interval subsequent to the first measurement interval, wherein the second measurement interval is one of a second series of measurement intervals interspersed with periods of said illumination, and wherein the first series of measurement intervals and second series of measurement intervals are separated by respective first and second offsets from a timing reference. 
 
     
     
       2. The method of  claim 1 , further comprising, at a time subsequent to the end of the first measurement interval, discontinuing use of the first series of measurement intervals. 
     
     
       3. The method of  claim 1 , further comprising:
 during each of said first measurement interval and said second measurement interval, applying a drive current at an operative drive current level, which is sufficient to produce illumination, to the one of the emission LED elements; and 
 monitoring a measurement photocurrent induced in a measurement photodetector during said applying a drive current. 
 
     
     
       4. The method of  claim 3 , further comprising determining whether a result of said monitoring a measurement photocurrent during the first measurement interval is outside of an expected range. 
     
     
       5. The method of  claim 4 , wherein said bringing the respective drive current of all except one of the emission LED elements to a non-operative drive current level which is insufficient to produce illumination, for the duration of a second measurement interval is in response to a determination that the result of said monitoring a measurement photocurrent is outside of the expected range. 
     
     
       6. The method of  claim 4 , further comprising, in response to a determination that the result of said monitoring a measurement photocurrent during the first measurement interval is outside of the expected range:
 repeating, during an additional one of the first series of measurement intervals, said applying a drive current at an operative drive current level, which is sufficient to produce illumination, to the one of the emission LED elements and said monitoring a measurement photocurrent induced in the measurement photodetector; and 
 determining whether a predetermined number of out-of-range measurements using the first series of measurement intervals has occurred. 
 
     
     
       7. The method of  claim 6 , wherein said bringing the respective drive current of all except one of the emission LED elements to a non-operative drive current level, which is insufficient to produce illumination, for the duration of a second measurement interval is in response to a determination that the predetermined number of out-of-range measurements using the first series of measurement intervals has occurred. 
     
     
       8. The method of  claim 4 , further comprising, for each of the first and second measurement intervals:
 bringing the drive current applied to the one of the emission LED elements to a non-operative drive current level, which is insufficient to produce illumination, for a portion of the measurement interval, such that the respective drive currents of all of the emission LED elements within the illumination device are at a non-operative drive current level for the portion of the measurement interval; 
 monitoring a background photocurrent induced in the measurement photodetector during the portion of the measurement interval; and 
 subtracting the background photocurrent from the measurement photocurrent. 
 
     
     
       9. The method of  claim 8 , wherein the result of said monitoring a measurement photocurrent during the first measurement interval comprises a result of said subtracting the background photocurrent from the measurement photocurrent for the first measurement interval. 
     
     
       10. The method of  claim 4 , wherein said determining that a result of said monitoring a measurement photocurrent during the first measurement interval is outside of an expected range comprises comparing the result to a previously stored result. 
     
     
       11. An illumination device, comprising:
 multiple emission light emitting diode (LED) elements; 
 one or more photodetectors; and 
 a control circuit operably coupled to the multiple emission LED elements and the one or more photodetectors, wherein the control circuit is adapted to:
 operate one or more of the multiple emission LED elements to produce illumination substantially continuously by supplying a respective drive current at an operative drive current level to each of the one or more of the multiple emission LED elements; 
 bring the respective drive currents of all except one of the emission LED elements within the illumination device to a non-operative drive current level, which is insufficient to produce illumination for the a duration of a first measurement interval, wherein the first measurement interval is one of a first series of measurement intervals interspersed with periods of said illumination; and 
 
 bring the respective drive currents of all except one of the emission LED elements to a non-operative drive current level, which is insufficient to produce illumination, for the a duration of a second measurement interval subsequent to the first measurement interval, wherein the second measurement interval is one of a second series of measurement intervals interspersed with periods of said illumination, and wherein the first series of measurement intervals and second series of measurement intervals are separated by respective first and second offsets from a timing reference. 
 
     
     
       12. The illumination device of  claim 11 , further comprising a timing reference generator operatively coupled to the control circuit and adapted to generate a periodic timing reference, and wherein the control circuit is further adapted to:
 generate the first series of measurement intervals synchronized to the timing reference with a first offset from the timing reference; and 
 generate the second series of measurement intervals synchronized to the timing reference with a second offset from the timing reference. 
 
     
     
       13. The illumination device of  claim 11 , wherein the control circuit is further adapted to discontinue use of the first series of measurement intervals at a time subsequent to the end of the first measurement interval. 
     
     
       14. The illumination device of  claim 11 , further comprising an LED driver and receiver circuit operably coupled to the multiple emission LED elements, the one or more photodetectors, and the control circuit, and wherein the control circuit is adapted to use the LED driver and receiver circuit to adjust the respective drive currents of the emission LED elements. 
     
     
       15. The illumination device of  claim 14 , wherein, during each of said first measurement interval and said second measurement interval, the control circuit is further adapted to use the LED driver and receiver circuit to:
 bring the respective drive currents of all except one of the emission LED elements to a non-operative drive current level, which is insufficient to produce illumination; 
 apply a drive current to an operative drive current level, which is sufficient to produce illumination, to the one of the emission LED elements; and 
 monitor a measurement photocurrent induced in the measurement photodetector during said applying a drive current. 
 
     
     
       16. The illumination device of  claim 15 , wherein the control circuit is further adapted to determine whether a result of monitoring the measurement photocurrent during the first measurement interval is outside of an expected range. 
     
     
       17. The illumination device of  claim 16 , further comprising a storage medium operably coupled to the control circuit, and wherein the control circuit is adapted to compare the result of monitoring the measurement photocurrent during the first measurement interval with a result previously stored in the storage medium. 
     
     
       18. The illumination device of  claim 16 , wherein the control circuit is further adapted to bring the respective drive currents of all except one of the emission LED elements to a non-operative drive current level, which is insufficient to produce illumination, for the duration of the second measurement interval in response to a determination that the result is outside of the expected range. 
     
     
       19. The illumination device of  claim 16 , wherein the control circuit is further adapted to determine whether a predetermined number of out-of-range measurements using the first series of measurement intervals has occurred. 
     
     
       20. The illumination device of  claim 16 , wherein, for each of the first and second measurement intervals, the control circuit is further adapted to:
 bring the drive current applied to the one of the emission LED elements to a non-operative drive current level, which is insufficient to produce illumination, for a portion of the measurement interval, such that the respective drive currents of all of the emission LED elements within the illumination device are at a non-operative drive current level for the portion of the measurement interval; 
 monitor a background photocurrent induced in the measurement photodetector during the portion of the measurement interval; and 
 subtract the background photocurrent from the measurement photocurrent. 
 
     
     
       21. The illumination device of  claim 20 , wherein the control circuit is further adapted to determine whether a result of subtracting the background photocurrent from the measurement photocurrent during the first measurement interval is outside of an expected range. 
     
     
       22. A method for controlling an illumination device comprising a first light emitting diode (LED) element and a second LED element, the method comprising:
 supplying a respective operative drive current to each of the first LED element and the second LED element to produce illumination;   performing a first measurement that comprises measuring a first photocurrent induced in at least one photodetector while supplying a respective non-operative drive current to each of the first LED element and the second LED element;   at an end of the first measurement, supplying a respective operative drive current to each of the first LED element and the second LED element to produce illumination;   based at least in part on the first photocurrent, determining that a non-constant illumination is detected;   based at least in part on determining that a non-constant illumination is detected:
 waiting a delay time; and 
 at an end of the delay time, performing a second measurement that comprises measuring a second photocurrent induced in the least one photodetector while supplying a respective non-operative drive current to each of the first LED element and the second LED element; 
   at an end of the second measurement, supplying a respective operative drive current to each of the first LED element and the second LED element to produce illumination;   based at least in part on the second photocurrent, determining that no non-constant illumination is detected;   based at least in part on determining that no non-constant illumination is detected, performing a subsequent measurement that comprises:
 measuring a first photocurrent induced in the at least one photodetector while supplying an operative drive current to the first LED element to produce illumination and supplying a non-operative drive current to the second LED element; and 
 measuring a second photocurrent induced in the at least one photodetector while supplying a respective non-operative drive current to each of the first LED element and the second LED element; 
   based at least in part on the subsequent measurement of the first photocurrent and the second photocurrent,   obtaining a corrected photocurrent; and   at an end of the subsequent measurement, supplying to the first LED element an operative drive current that is determined based at least in part on the corrected photocurrent.   
     
     
       23. The method of claim 22, wherein the delay time comprises a randomized delay time. 
     
     
       24. The method of claim 22, further comprising:
 performing a plurality of consecutive measurements and determining from the plurality of measurements that no non-constant illumination is detected; and   wherein performing the subsequent measurement comprises performing the subsequent measurement based at least in part on determining from the plurality of measurements that no non-constant illumination is detected.   
     
     
       25. An illumination device comprising:
 a first light emitting diode (LED) element and a second LED element; and   a control circuit operably coupled to the first and the second LED elements, wherein the control circuit is adapted to:
 supply a respective operative drive current to each of the first LED element and the second LED element to produce illumination; 
 perform a first measurement, wherein to perform the first measurement comprises to measure a first photocurrent induced in at least one photodetector while supplying a respective non-operative drive current to each of the first LED element and the second LED element; 
 at an end of the first measurement, supply a respective operative drive current to each of the first LED element and the second LED element to produce illumination; 
 based at least in part on the first photocurrent, determine that a non-constant illumination is detected; 
 based at least in part on determining that a non-constant illumination is detected:
 wait a delay time; and 
 at an end of the delay time, perform a second measurement, wherein to perform the second measurement comprises to measure a second photocurrent induced in the least one photodetector while supplying a respective non-operative drive current to each of the first LED element and the second LED element; 
 
 at an end of the second measurement, supply a respective operative drive current to each of the first LED element and the second LED element to produce illumination; 
 based at least in part on the second photocurrent, determine that no non-constant illumination is detected; 
 based at least in part on determining that no non-constant illumination is detected, perform a subsequent measurement, wherein to perform the subsequent measurement comprises to:
 measure a first photocurrent induced in the at least one photodetector while supplying an operative drive current to the first LED element to produce illumination and supplying a non-operative drive current to the second LED element; and 
 measure a second photocurrent induced in the least one photodetector while supplying a respective non-operative drive current to each of the first LED element and the second LED element; 
 
 based at least in part on the subsequent measurement of the first photocurrent and the second photocurrent, obtain a corrected photocurrent; and 
 at an end of the subsequent measurement, supply to the first LED element an operative drive current that is determined based at least in part on the corrected photocurrent. 
   
     
     
       26. The illumination device of claim 25, wherein the delay time comprises a randomized delay time. 
     
     
       27. The illumination device of claim 25, wherein the control circuit is further adapted to:
 perform a plurality of consecutive measurements and determine from the plurality of measurements that no non-constant illumination is detected: and   wherein to perform the subsequent measuremement comprises to perform the subsequent measurement based at least in part on determining from the plurality of measurements that no non-constant illumination is detected.   
     
     
       28. The method of claim 22,
 wherein the first, second, and subsequent measurements are part of a first series of measurement intervals; and   wherein the method further comprises:
 performing a plurality of measurements and determining from the plurality of measurements that non-constant illumination is detected; and 
 changing to a second series of measurement intervals based on determining that non-constant illumination is detected, wherein the first series of measurement intervals and the second series of measurement intervals are separated from a timing reference by different offset times. 
   
     
     
       29. The method of claim 28, wherein the method further comprises:
 performing, during the second series of measurement intervals, a plurality of measurements to determine whether non-constant illumination is detected.   
     
     
       30. The method of claim 22, further comprising:
 based at least in part on determining that no non-constant illumination is detected,
 measuring a first photocurrent induced in the at least one photodetector while supplying an operative drive current to the second LED element to produce illumination and supplying a non-operative drive current to the first LED element; and
 measuring a second photocurrent induced in the least one photodetector while supplying a respective non-operative drive current to each of the first LED element and the second LED element; 
 
 based at least in part on the first photocurrent and the second photocurrent, measured as a result of determining that no non-constant illumination is detected, obtaining another corrected photocurrent; and 
 supplying to the second LED element an operative drive current that is determined based at least in part on the another corrected photocurrent. 
   
     
     
       31. The illumination device of claim 25,
 wherein the control circuit is adapted to perform the first, second, and subsequent measurements as part of a first series of measurement intervals; and   wherein the control circuit is further adapted to:
 perform a plurality of measurements and determine from the plurality of measurements that non-constant illumination is detected; and 
 change to a second series of measurement intervals based on determining that non-constant illumination is detected, wherein the first series of measurement intervals and the second series of measurement intervals are separated from a timing reference by different offset times. 
   
     
     
       32. The illumination device of claim 31, wherein the control circuit is further adapted to perform, during the second series of measurement intervals, a plurality of measurements to determine whether non-constant illumination is detected. 
     
     
       33. The illumination device of claim 25, wherein the control circuit is further adapted to:
 based at least in part on determining that no non-constant illumination is detected,
 measure a first photocurrent induced in the at least one photodetector while supplying an operative drive current to the second LED element to produce illumination and supplying a non-operative drive current to the first LED element; and 
 measure a second photocurrent induced in the at least one photodetector while supplying a respective non-operative drive current to each of the first LED element and the second LED element; 
   based at least in part on the first photocurrent and the second photocurrent, measured as a result of determining that no non-constant illumination is detected, obtain another corrected photocurrent; and   supply to the second LED element an operative drive current that is determined based at least in part on the another corrected photocurrent.