Temperature compensation method and apparatus for spectroscopic devices

• US 5,477,853 A
• Filed: 12/01/1992
• Issued: 12/26/1995
• Est. Priority Date: 12/01/1992
• Status: Expired due to Term

• Current Assignee: Nellcor Puritan Bennett LLC (Medtronic Plc)
• Original Assignee: Somanetics Corporation (Medtronic Plc)
• Inventors: Farkas, Richard A., Lewis, Gary D.
• Primary Examiner(s): Cohen, Lee S.
• Assistant Examiner(s): GILBERT, SAMUEL G
• Application Number:
  US07/983,817
• Time in Patent Office: 1,120 Days
• Field of Search: 356/326, 372/31, 372/32, 128/632, 128/633, 128/664, 128/665, 604/31
• US Class Current: 600/310
• CPC Class Codes: A61B 2560/0252 using ambient temperature
• CPC Class Codes: A61B 5/14553 specially adapted for cerebral tissue
• CPC Class Codes: A61B 5/1495 Calibrating or testing of in-vivo probes
• CPC Class Codes: G01J 3/10 Arrangements of light sources specially adapted for spectrometry or colorimetry
• CPC Class Codes: G01N 21/255 Details, e.g. use of specially adapted sources, lighting or optical systems

Abstract

An apparatus and method which detects temperature variations of an LED used with spectroscopic devices. The apparatus and method uses a source to supply a signal to the LED. A detector coupled to the LED detects a signal at the LED. A controller is coupled to the detector to determine variations in operating characteristics of the LED resulting from changes in temperature.

Claims

1. Apparatus for determining variations in operating characteristics of a spectroscopic device, comprising:

an LED;

a current generator having an output connected to the LED to apply a current thereto;

a voltage detector having at least one input and at least one output, and circuitry connecting said at least one input mid output of said voltage detector across said LED, said voltage detector including means to detect the voltage across said LED when said current is applied to said LED and provide a characteristic signal at said at least one output which has a predetermined relationship to said detected voltage and which characterizes the particular operation of said LED; and

a processor coupled to said at least one output of said detector to receive said characteristic signal provided by said detector, said processor including means to provide an output in response to said characteristic signal which is representative of variations in the operating characteristics of said LED resulting from temperature changes of said LED.

2. The apparatus as defined in claim 1 wherein said current generator includes means for generating intermittent pulses of current and a small trickle current between said intermittent pulses, said pulses being substantially larger in magnitude than said trickle current.

3. The apparatus as defined in claim 2 wherein said processor includes means for determining variations in operating characteristics of said LED responsive to said trickle current when said intermittent pulses of current are not being generated.

4. Apparatus for determining variations in operating characteristics of a spectroscopic device, comprising:

an LED;

a current generator having a current output connected to said LED to apply said current output thereto;

a voltage detector, said voltage detector having at least one input and at least one output, means for connecting said at least one input of said voltage detector to at least one terminal of said LED such that, said voltage detector detects a voltage level at said at least one terminal of said LED when said current output is applied to said LED and provides a characteristic signal at said at least one output which has a predetermined relationship to said detected voltage level;

a processor coupled to said at least one output of said detector to receive said characteristic signal provided by said voltage detector, said processor including means for determining variations in operating characteristics of said LED from said characteristic signal including variations which result from temperature changes of said LED; and

said current generator including a constant current source.

5. Apparatus for determining variations in operating characteristics of a spectroscopic device, comprising:

an LED;

a current generator, said current generator supplying a current at an output thereof, said output connected to said LED to apply said current thereto;

a voltage detector, said voltage detector having at least one input and at least one output, said at least one input of said voltage detector connected to at least one terminal of said LED such that said voltage detector detects a voltage level at said at least one terminal of said LED when said current is applied to said LED and provides a characteristic signal at said at least one output having a predetermined relationship to said detected voltage level;

a processor coupled to said at least one output of said detector to receive said characteristic signal provided by said detector, said processor including means to determine from said characteristic signal variations in operating characteristics of said LED including variations which result from temperature changes of said LED;

said current generator including means for generating intermittent pulses of current and a small trickle current between said intermittent pulses, said pulses being substantially larger in magnitude than said trickle current;

said processor including means for determining variations in operating characteristics of said LED responsive to said trickle current when said intermittent pulses of current are not being generated; and

said detecting means being responsive to said characteristic signal substantially immediately following a downward transition of each said intermittent pulse to detect said variations in operating characteristics of said LED.

6. Apparatus for determining variations in operating characteristics of a spectroscopic device, comprising:

an LED;

a current generator having a current output connected to said LED to apply said current output thereto;

a voltage detector, said voltage detector having at least one input and at least one output, means connecting said at least one input of said voltage detector to at least one terminal of said LED, said voltage detector including means to detect a voltage level at said at least one terminal of said LED when said current output is applied to said LED and to provide a characteristic signal at said at least one output which has a predetermined relationship to said detected voltage level;

a processor coupled to said at least one output of said detector to receive said characteristic signal provided by said detector, said processor including means to determine from said characteristic signal variations in operating characteristics of said LED including variations which result from temperature changes of said LED; and

said LED having an associated reference voltage parameter, said processor including memory, and said reference voltage parameter being stored in said processor memory.

7. The apparatus as defined in claim 6 wherein said processor includes means for determining said variations in operating characteristics of said LED from said reference voltage parameter and said characteristic signal.

8. The apparatus as defined in claim 7, where said processor includes means to determine a wavelength variation in the light emitted from said LED on the basis of said reference voltage parameter and said characteristic signal.

9. The apparatus as defined in claim 7, wherein said processor includes means to determine a variation in intensity of the light emitted from said LED on the basis of said reference voltage parameter and said characteristic signal.

10. A spectroscope, comprising:

and LED having first and second terminals;

a photodetector positioned to receive light emitted by said LED, said photodetector having outputs providing output signals corresponding to said received light;

at least one current source having an output connected to at least one of said LED terminals, said at least one current source supplying current to said LED through said output;

a detector connected to at least one terminal of said LED, said detector including means to sense a signal level present on the said at least one terminal of said LED to which it is connected in response to current being supplied to said LED, and said detector further including means to generate an output signal responsive to said sensed signal level; and

a processor coupled to receive said output signal from said detector, said processor including means for responding to said output signal by determining variations in operating characteristics of said LED resulting from changes in the temperature of said LED and compensating for said determined variations in operating characteristics by producing signals representative of correspondingly modified output signals from said photodetector to thereby substantially eliminate the effects of said temperature changes.

11. The spectroscope as defined in claim 10 wherein said at least one current source includes a trickle current source for generating a trickle current at said current source output.

12. The spectroscope as defined in claim 11, wherein said at least one current source further includes a pulse current source generating an intermittent current pulse at said current source output.

13. The spectroscope as defined in claim 12 wherein said processor includes means for determining variations in the operating characteristics of said LED responsive to said trickle current.

14. The apparatus as defined in claim 10, where said processor includes a memory whose content includes at least one stored reference parameter which characterizes the operation of said LED.

15. The apparatus as defined in claim 14, wherein said processor includes means to determine variations in the operating characteristics of said LED based upon said at least one stored reference parameter and said detector output signal.

16. The apparatus as defined in claim 14, wherein said processor includes means to determine variations in a wavelength of light emitted from said LED as a function of said reference parameter and said detector output.

17. The apparatus as defined in claim 14, wherein said processor includes means to determine variations in the intensity of light emitted from said LED as a function of said reference parameter and said detector output.

18. A method of compensating for temperature variations of an LED used in a spectroscope, comprising the steps of:

applying a reference current to the LED;

detecting a resultant voltage at one terminal of the LED responsive to the reference current being applied to the LED and outputting a detection signal responsive thereto;

determining a variation in operating characteristics of the LED resulting from temperature variations from the detection signal ,and a stored parameter signal;

detecting a sensed spectroscopic signal using a photodetector optically coupled to the LED; and

adjusting a sensed spectroscopic signal detected by the photodetector responsive to a light pulse being output by the LED based on the determined variation in operating characteristics.

19. The method as defined in claim 18 wherein the step of applying a reference signal includes applying a low level constant current.

20. The method as defined in claim 19, wherein said step of applying further includes superimposing current pulses on the low level constant current.

21. The method as defined in claim 20, wherein said step of determining a variation is performed when pulses of current are not applied to the LED.