US Patent 9826940 Optical tracking of heart rate using PLL optimization

Systems and methods are provided for determining a pulse rate based on a photoplethysmographic measurement of blood in a portion of subsurface vasculature. A plurality of samples of the photoplethysmographic signal are obtained and a plurality of digital phase-locked loops are operated to generate respective oscillating signals based on the plurality of samples. Respective correlations between the plurality of samples and each of the generated oscillating signals are determined and used to select a subset of the plurality of phase-locked loops. The frequencies of the selected oscillating signals generated by the selected phase-locked loops are determined and used to determine a cardiovascular pulse rate. This method can be performed a plurality of times for a respective plurality of overlapping sets of the obtained plurality of samples to determine pulse rates over time.