Oximeter cross-talk reduction

• US 20050187452A1
• Filed: 02/25/2004
• Published: 08/25/2005
• Est. Priority Date: 02/25/2004
• Status: Active Grant

• Current Assignee: Covidien LP (Medtronic Plc)
• Original Assignee: Nellcor Puritan Bennett Incorporated (Medtronic Plc)
• Inventors: Petersen, Ethan, Chew, Bradford B., Shea, William
• Granted Patent: US 7,215,985 B2
• Time in Patent Office: Days
• US Class Current: 600/336
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• CPC Class Codes: A61B 5/725 using specific filters therefor, e.g. Kalman or adaptive filters A61B5/316 take precedence

Abstract

A method and apparatus for reducing cross-talk in an oximeter. The oximeter includes a band pass filter. The amount of cross-talk through the band pass filter is estimated. Based on this estimate, the corner frequencies of the band pass filter are adjusted when it is designed to minimize the cross-talk. In one embodiment, a calibration mode is performed when a sensor is attached to the oximeter. In the calibration mode, the signals are measured with first only the red LED on and then with only the IR LED on. Any signal measured in the off channel is assumed to be a result of cross-talk from the other channel. The magnitude of the cross-talk is determined as a percentage, and subsequently the percentage is multiplied by the actual signal and subtracted from the other LED signal as cross-talk compensation.

Claims

1. A method for reducing cross-talk in an oximeter, comprising:

providing a signal corresponding to an oximeter sensor signal;

applying said signal to a band pass filter;

estimating an amount of cross-talk of a signal through said band pass filter; and

adjusting the corner frequencies of said band pass filter to minimize said cross-talk.

2. The method of claim 1 wherein said band pass filter is a hardware filter.

3. The method of claim 2 wherein said hardware band pass filter is coupled to the output of a current to voltage converter in said oximeter.

4. The method of claim 2 further comprising:

measuring an amount of remaining cross-talk through said hardware band pass filter after said adjusting; and

minimizing said remaining cross-talk by compensation in software of a digitized signal from said hardware band pass filter.

5. The method of claim 2 wherein said measuring comprises:

measuring a current from a red LED with no current provided to an IR LED; and

measuring a current from said IR LED with no current provided to said red LED.

6. The method of claim 5 further comprising:

in a calibration mode, measuring an IR cross-talk signal obtained during an IR LED period, said signal corresponding to cross-talk from a signal from said red LED;

comparing said IR cross-talk signal to said current from said IR LED to determine an IR cross-talk percentage;

measuring a red cross-talk signal obtained during an red LED period, said signal corresponding to cross-talk from a signal from said IR LED;

comparing said red cross-talk signal to said current from said red LED to determine a red cross-talk percentage;

during normal operation of said oximeter, multiplying said IR cross-talk percentage in software by a detected IR signal to give an IR cross-talk signal, and subtracting said IR cross-talk signal from a detected red signal; and

during normal operation of said oximeter, multiplying said red cross-talk percentage in software by a detected red signal to give a red cross-talk signal, and subtracting said red cross-talk signal from said detected IR signal.

7. A method for compensating for cross-talk in an oximeter, comprising:

providing a signal corresponding to an oximeter sensor signal;

applying said signal to a hardware band pass filter, wherein said hardware band pass filter is coupled to the output of a current to voltage converter in said oximeter;

estimating an amount of cross-talk of a signal through said band pass filter;

adjusting the corner frequencies of said band pass filter to minimize said cross-talk;

in a calibration mode, measuring an IR cross-talk signal obtained during an IR LED period, said signal corresponding to cross-talk from a signal from said red LED;

comparing said IR cross-talk signal to said current from said IR LED to determine an IR cross-talk percentage;

measuring a red cross-talk signal obtained during an red LED period, said signal corresponding to cross-talk from a signal from said IR LED;

comparing said red cross-talk signal to said current from said red LED to determine a red cross-talk percentage;

during normal operation of said oximeter, multiplying said IR cross-talk percentage in software by a detected IR signal to give an IR cross-talk signal, and subtracting said IR cross-talk signal from a detected red signal; and

during normal operation of said oximeter, multiplying said red cross-talk percentage in software by a detected red signal to give a red cross-talk signal, and subtracting said red cross-talk signal from said detected IR signal.

8. An oximeter with reduced cross-talk comprising:

an oximeter sensor input;

a current to voltage converted coupled to said oximeter sensor input;

a band pass filter coupled to said current to voltage converter, said band pass filter having corner frequencies adjusted to minimize cross-talk;

an analog-to-digital converter coupled to said band pass filter for converting a detected signal into a digitized detector signal; and

a processor coupled to said analog-to-digital converter for manipulating a said digitized detector signal and calculating oxygen saturation.

9. The oximeter of claim 8 further comprising:

a test circuit for providing a test signal to said band pass filter;

a memory storing a program for operating said test circuit to estimate an amount of remaining cross-talk and determining red and IR cross-talk compensation factors to be used in software during normal operation of said oximeter.

10. The oximeter of claim 9 wherein said test circuit comprises:

a resistor;

a switching circuit for alternately coupling said resistor to red and IR LEDs; and

a switch for coupling said resistor to said band pass filter.

11. The oximeter of claim 9 wherein said program includes computer readable code for:

in a calibration mode, measuring an IR cross-talk signal obtained during an IR LED period, said signal corresponding to cross-talk from a signal from said red LED;

comparing said IR cross-talk signal to said current from said IR LED to determine an IR cross-talk percentage;

measuring a red cross-talk signal obtained during an red LED period, said signal corresponding to cross-talk from a signal from said IR LED;

comparing said red cross-talk signal to said current from said red LED to determine a red cross-talk percentage;

during normal operation of said oximeter, multiplying said IR cross-talk percentage in software by a detected IR signal to give an IR cross-talk signal, and subtracting said IR cross-talk signal from a detected red signal; and

during normal operation of said oximeter, multiplying said red cross-talk percentage in software by a detected red signal to give a red cross-talk signal, and subtracting said red cross-talk signal from said detected IR signal.

12. An oximeter with reduced cross-talk comprising:

an oximeter sensor input;

a current to voltage converted coupled to said oximeter sensor input;

a band pass filter coupled to said current to voltage converter, said band pass filter having corner frequencies adjusted to minimize cross-talk;

an analog-to-digital converter coupled to said band pass filter for converting a detected signal into a digitized detector signal;

a processor coupled to said analog-to-digital converter for manipulating a said digitized detector signal and calculating oxygen saturation.

a test circuit for providing a test signal to said band pass filter;

a memory storing a program for operating said test circuit to estimate an amount of remaining cross-talk and determining red and IR cross-talk compensation factors to be used in software during normal operation of said oximeter;

wherein said program includes computer readable code for;

in a calibration mode, measuring an IR cross-talk signal obtained during an IR LED period, said signal corresponding to cross-talk from a red LED signal;

comparing said IR cross-talk signal to said current from an IR LED to determine an IR cross-talk percentage;

measuring a red cross-talk signal obtained during an red LED period, said signal corresponding to cross-talk from an IR LED signal;

comparing said red cross-talk signal to said current from a red LED to determine a red cross-talk percentage;

during normal operation of said oximeter, multiplying said IR cross-talk percentage in software by a detected IR signal to give an IR cross-talk signal, and subtracting said IR cross-talk signal from a detected red signal; and

during normal operation of said oximeter, multiplying said red cross-talk percentage in software by a detected red signal to give a red cross-talk signal, and subtracting said red cross-talk signal from said detected IR signal.

13. A method for compensating for cross-talk in an oximeter using a calibration mode, comprising:

providing detector signals corresponding to first and second light emitter wavelengths;

measuring a first cross-talk signal obtained during an first period corresponding to said first light emitter wavelength, said first cross-talk signal corresponding to cross-talk from a signal from said second light emitter wavelength;

comparing said first cross-talk signal to a current from said detector corresponding to a signal of said first wavelength to determine a first cross-talk percentage;

measuring a second cross-talk signal obtained during a second period corresponding to said second light emitter wavelength, said second cross-talk signal corresponding to cross-talk from a signal from said first light emitter wavelength;

comparing said second cross-talk signal to said current from said detector corresponding to a signal of said first wavelength to determine a second cross-talk percentage;

during normal operation of said oximeter, multiplying said first cross-talk percentage in software by a detected first wavelength signal to give a first cross-talk signal, and subtracting said first cross-talk signal from a detected second wavelength signal; and

during normal operation of said oximeter, multiplying said second cross-talk percentage in software by a detected second wavelength signal to give a second cross-talk signal, and subtracting said second cross-talk signal from a detected first wavelength signal.

14. The method of claim 13 wherein said first wavelength is red and said second wavelength is IR.

15. An oximeter with reduced cross-talk comprising:

an oximeter sensor input for providing a detected signal;

an analog-to-digital converter for converting said detected signal into a digitized detector signal;

a processor coupled to said analog-to-digital converter for manipulating a said digitized detector signal and calculating oxygen saturation.

a test circuit for providing a test signal;

a memory storing a program for operating said test circuit to estimate an amount of remaining cross-talk and determining first and second cross-talk compensation factors to be used in software during normal operation of said oximeter;

wherein said program includes computer readable code for;

providing detector signals corresponding to first and second light emitter wavelengths;

measuring a first cross-talk signal obtained during an first period corresponding to said first light emitter wavelength, said first cross-talk signal corresponding to cross-talk from a signal from said second light emitter wavelength;

comparing said first cross-talk signal to a current from said sensor corresponding to a signal of said first wavelength to determine a first cross-talk percentage;

measuring a second cross-talk signal obtained during a second period corresponding to said second light emitter wavelength, said second cross-talk signal corresponding to cross-talk from a signal from said first light emitter wavelength;

comparing said second cross-talk signal to said current from said sensor corresponding to a signal of said first wavelength to determine a second cross-talk percentage;

during normal operation of said oximeter, multiplying said first cross-talk percentage in software by a detected first wavelength signal to give a first cross-talk signal, and subtracting said first cross-talk signal from a detected second wavelength signal; and

during normal operation of said oximeter, multiplying said second cross-talk percentage in software by a detected second wavelength signal to give a second cross-talk signal, and subtracting said second cross-talk signal from a detected first wavelength signal.

16. The oximeter of claim 15 wherein said first wavelength is red and said second wavelength is IR.