Oximeter ambient light cancellation
2 Assignments
0 Petitions
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.
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Citations
35 Claims
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1-17. -17. (canceled)
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18. An oximeter apparatus comprising:
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an amplifier configured to amplify an analog sensor signal to provide an amplified analog sensor signal;
a sigma-delta modulator having an input coupled to receive the amplified analog sensor signal;
a multiple bit analog-to-digital converter coupled to an output of the sigma-delta modulator to provide a digital signal;
a decimator configured to receive the digital signal and output a decimated signal;
a digital filter configured to operate on the decimated signal; and
a controller configured to preload the decimator and digital filter with an estimate of a settled output value. - View Dependent Claims (19, 20, 21, 22, 23, 24, 25, 26)
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27. An method of operating an oximeter apparatus comprising:
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amplifying an 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; and
preloading the decimator and digital filter with an estimate of a settled output value. - View Dependent Claims (28, 29, 30, 31, 32, 33, 34, 35)
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Specification