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Method and apparatus for demodulating signals in a pulse oximetry system

  • US 6,643,530 B2
  • Filed: 12/13/2000
  • Issued: 11/04/2003
  • Est. Priority Date: 04/14/1997
  • Status: Expired due to Term
First Claim
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1. A method of minimizing crosstalk between two signals generated by applying a first pulse and a second pulse to measure a parameter, wherein said first pulse and said second pulse are applied periodically at a first repetition rate defining a period, and wherein said first pulse is generated during a first interval in each period and said second pulse is generated during a second interval in each period, said second interval spaced apart from said first interval, said first and second pulses producing first and second parametric signals responsive to said parameter, said first and second parametric signals being received by a single detector which outputs a composite signal responsive to said first and second parametric signals, said method comprising the steps of:

  • providing said composite signal to an analog to digital converter to produce a sequence of digital values;

    decimating said sequence of digital values to produce a decimated sequence of digital values according to a decimation rate that produces relatively little shaping of said first and second parametric signals and that produces a relatively larger shaping of a noise component of said composite signal according to a decimation rate that produces relatively little shaping of said first and second parametric signals and that produces a relatively larger shaping of a noise component of said composite signal, said decimation rate adjusted according to noise in said first or second parametric signals;

    applying a first sequence of demodulation coefficients to said decimated sequence of digital values to generate a first demodulated output signal;

    applying a second sequence of demodulation coefficients to said decimated sequence of digital values to generate a second demodulated output signal;

    lowpass filtering said first demodulated output signal to generate a first recovered output signal responsive to said first parametric signal; and

    lowpass filtering said second demodulated output signal to generate a second recovered output signal responsive to said second parametric signal.

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