A Low-Power Photoplethysmogram-Based Heart Rate Sensor Using Heartbeat Locked Loop

Area of Science:

• Biomedical Engineering
• Wearable Technology
• Sensor Design

Background:

• Photoplethysmography (PPG) is widely used for heart rate (HR) monitoring.
• Existing PPG sensors often suffer from high power consumption, limiting their use in long-term wearable applications.
• Reducing power consumption is critical for developing efficient and unobtrusive health monitoring devices.

Purpose of the Study:

• To develop an ultra-low power PPG sensor for accurate heart rate monitoring.
• To investigate the effectiveness of a heartbeat-locked loop (HBLL) for power reduction in PPG sensing.
• To demonstrate a novel CMOS-based PPG sensor with significantly reduced energy consumption.

Main Methods:

• Implementation of a novel heartbeat-locked loop (HBLL) circuit.
• Design and fabrication of a prototype PPG sensor using 0.18 μm CMOS technology.
• Characterization of the sensor's power consumption and heart rate measurement accuracy.

Main Results:

• The developed PPG sensor achieves an ultra-low power consumption of 43.4 μW at 60 beats/min.
• The effective duty-cycle of the sensor is as low as 0.01%.
• The sensor demonstrates a heart rate error of less than 2.1 beats/min for HR below 180 beats/min, outperforming existing state-of-the-art sensors.

Conclusions:

• The proposed HBLL-based PPG sensor offers the lowest power consumption reported to date for PPG sensing.
• This technology enables highly efficient and accurate continuous heart rate monitoring.
• The sensor design holds significant potential for integration into next-generation wearable health devices.