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Heart rate monitor with time varying linear filtering

  • US 9,801,587 B2
  • Filed: 10/18/2016
  • Issued: 10/31/2017
  • Est. Priority Date: 10/19/2015
  • Status: Active Grant
First Claim
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1. A fitness monitor for monitoring a cardiac signal of a user, the device comprising:

  • an emitter configured to transmit light toward skin of the user;

    a receiver configured to receive a reflection of the transmitted light and provide a photoplethysmogram (PPG) signal based on the received reflection of the transmitted light, the PPG signal including a cardiac component and a motion component;

    an inertial sensor configured to provide a motion signal based on sensed movement of the fitness monitor;

    a time-variant filter configured to isolate a component of the PPG signal based on filter coefficients corresponding to a desired component of the PPG signal, anda processor coupled to the emitter, the receiver, the inertial sensor and the time-variant filter, the processor configured to;

    determine one or more frequencies associated with the motion signal;

    transform the PPG signal to the frequency domain;

    identify, in the frequency domain, the cardiac component in the PPG signal based on the determined one or more frequencies of the motion signal and the transformed PPG signal;

    determine filter coefficients based on the identified cardiac component in the PPG signal;

    configure the time-variant filter with the determined filter coefficients;

    filter, in the time domain via the time-variant filter, the motion component from the PPG signal to isolate the identified cardiac component; and

    calculate, in the time domain, the time between successive cycles of the isolated cardiac component of the PPG signal.

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