A Low-Power Heart Rate Sensor with Adaptive Heartbeat Locked Loop

Abstract

Photoplethysmography (PPG) is one of the widely used noninvasive heart rate (HR) monitoring techniques in wearable devices. Lighting of the LED dominates the power consumption of a PPG sensor. Lowering the LED lighting duration is an effectively approach to save power. This paper proposes an adaptive heartbeat locked loop (AHBLL) technique, which can dynamically adjust the dividing ratio N according to the heart rate derivative (HRD). In this way, the LED pulse duty cycle can be significantly reduced to save power. To improve the robustness of the AHBLL system, the relationship between HRD and the dividing ratio N is theoretically analyzed, which provides an optimal design guideline. To verify the proposed technique, an HR sensing circuit including an HRD detector is designed and simulated. The results show that the LED power consumption is reduced by 2.2∼3.3× compared with the state-of-the-art heartbeat locked loop (HBLL) technique.

Simple low-power demodulator for the measurement of basal and physiological changes of electrical bioimpedance

“…However, PPG sensors need a light source -an LED-hence its power consumption is not as low as desirable. One way to reduce its power consumption is to decrease its duty cycle, and even adapt it to skip some heartbeats whenever the HR is stable and low, increasing it only when the detected HR increases [2]. Nonetheless, PPG provides only HR and sometimes ResR with the appropriate signal processing.…”