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Method and apparatus for demodulating signals in a pulse oximetry system

  • US 5,919,134 A
  • Filed: 01/12/1998
  • Issued: 07/06/1999
  • Est. Priority Date: 04/14/1997
  • Status: Expired due to Term
First Claim
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1. An apparatus for measuring blood oxygenation in a subject, said apparatus comprising:

  • a first signal source which applies a first input signal during a first time interval;

    a second signal source which applies a second input signal during a second time interval;

    a detector which detects a first parametric signal responsive to said first input signal passing through a portion of said subject having blood therein and which detects a second parametric signal responsive to said second input signal passing through said portion of said subject, said detector generating a detector output signal responsive to said first and second parametric signals; and

    a signal processor which receives said detector output signal, said signal processor demodulating said detector output signal by applying a first demodulation signal to a signal responsive to said detector output signal to generate a first output signal responsive to said first parametric signal and applying a second demodulation signal to said signal responsive to said detector output signal to generate a second output signal responsive to said second parametric signal, each of said first demodulation signal and said second demodulation signal comprising at least a first component having a first frequency and a first amplitude and a second component having a second frequency and a second amplitude, said second frequency being a harmonic of said first frequency, said second amplitude selected to be related to said first amplitude to minimize crosstalk from said first parametric signal to said second output signal and to minimize crosstalk from said second parametric signal to said first output signal.

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