The disclosure provides a heart rate monitor (HRM) circuit. The HRM circuit includes an analog front end (AFE). The AFE receives a Photoplethysmographic (PPG) signal, and generates a fine PPG signal. A motion cancellation circuit is coupled to the AFE, and receives the fine PPG signal and an accelerometer signal. The motion cancellation circuit subtracts the accelerometer signal from the fine PPG signal to generate a coarse heart rate. A peak detector is coupled to the motion cancellation circuit and the AFE, and generates an instantaneous heart rate. A filter is coupled to the peak detector, and generates an estimated heart rate from the instantaneous heart rate, the estimated heart rate is provided as a feedback to the peak detector.