OXIMETER AMBIENT LIGHT CANCELLATION
First Claim
1. A method for operating a pulse oximetry system, comprising:
- alternately generating light with a sensor at two wavelengths using a modulation frequency that is a predetermined distance from a common multiple of 50, 60, 100, and 120, where the predetermined distance is greater than a highest pulse rate of a person and lower than a distance of any harmonic of 50, 60, 100, or 120;
receiving an analog sensor signal from the sensor that corresponds to received light;
amplifying the analog sensor signal to provide an amplified analog sensor signal;
modulating the amplified analog sensor signal with a sigma-delta modulator to provide a modulated signal;
converting the modulated signal into a digital signal with a multiple bit analog-to-digital converter;
decimating the digital signal with a decimator to provide a decimated signal;
filtering the decimated signal with a digital filter to provide a filtered signal; and
preloading the decimator and digital filter with an estimate of a settled output value.
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Accused Products
Abstract
A pulse oximeter method and apparatus which provides (1) a notch filter at a distance between a modulation frequency and a common multiple of commonly used power line frequencies (50, 60, 100 and 120) and also (2) a demodulation frequency greater than a highest pulse rate of a person and lower than any harmonic of 50, 60, 100 or 120 Hz, to filter ambient light interference, while choosing an optimum demodulation frequency that avoids interference from the notch filter or from harmonics of the line interference. Also, ambient light for any low frequency interference, such as power line interference, is measured both before and after each of the light emitter wavelengths and the average of the ambient light is then subtracted from the detected signal.
2 Citations
21 Claims
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1. A method for operating a pulse oximetry system, comprising:
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alternately generating light with a sensor at two wavelengths using a modulation frequency that is a predetermined distance from a common multiple of 50, 60, 100, and 120, where the predetermined distance is greater than a highest pulse rate of a person and lower than a distance of any harmonic of 50, 60, 100, or 120; receiving an analog sensor signal from the sensor that corresponds to received light; amplifying the analog sensor signal to provide an amplified analog sensor signal; modulating the amplified analog sensor signal with a sigma-delta modulator to provide a modulated signal; converting the modulated signal into a digital signal with a multiple bit analog-to-digital converter; decimating the digital signal with a decimator to provide a decimated signal; filtering the decimated signal with a digital filter to provide a filtered signal; and preloading the decimator and digital filter with an estimate of a settled output value. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A pulse oximetry system, comprising:
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a first processor board, the first processor board comprising; an interface for receiving an analog sensor signal; a sigma-delta modulator configured to receive the sensor signal and to provide a modulated signal; an analog-to-digital converter configured to convert the modulated signal into a digital signal; and a processor configured to received the digital signal and provide an output related to a physiological parameter; and a second processor board comprising an interface for receiving the output related to the physiological parameter from the first processor board. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18, 19, 21)
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20. A pulse oximetry system, comprising:
a first processor board, the first processor board comprising; a first interface for receiving an analog sensor signal from a sensor; a second interface for receiving calibration information from the sensor; an analog-to-digital converter configured to convert a modulated signal into a digital signal; and a processor configured to received the digital signal and provide an analog output related to a physiological parameter; and a second processor board comprising a host interface for receiving the analog output related to the physiological parameter from the first processor board.
Specification