A Low-Power High Input Range PPG Readout Amplifier with a Current Buffer Input.

Area of Science:

• Biomedical Engineering
• Electrical Engineering
• Integrated Circuit Design

Background:

• Vital sign monitoring is crucial for managing respiratory diseases and assessing drug safety.
• Existing photoplethysmography (PPG) circuits often suffer from high power consumption.
• There is a need for efficient readout circuits for continuous and remote health monitoring.

Purpose of the Study:

• To develop ultra-low power photoplethysmography (PPG) readout circuits.
• To improve the power efficiency of PPG systems for vital sign monitoring.
• To enable effective monitoring of blood pressure, heart rate, and respiratory rate.

Main Methods:

• Implemented a system architecture with a current buffer between the photodiode (PD) and transimpedance amplifier (TIA).
• Utilized a Class AB amplifier topology for enhanced drive capability.
• Employed pulse wave modulation (PWM) in the LED driver circuit to control ON/OFF times.
• Manufactured the circuits using a 130 nm TSMC CMOS process.

Main Results:

• Achieved ultra-low power consumption of 3.28 µW at a 1% duty cycle and 1.2V supply voltage.
• The current buffer effectively isolates the PD's parasitic capacitance, improving TIA power efficiency.
• The Class AB amplifier and optimized LED driver contribute to reduced overall power usage.
• The TIA demonstrated a maximum input current range of 160 µA, preventing saturation from large DC currents.

Conclusions:

• The developed ultra-low power PPG readout circuits offer a significant advancement in wearable health monitoring technology.
• These circuits are suitable for continuous monitoring of vital signs, aiding in the study of respiratory diseases and drug efficacy.
• The design provides a foundation for next-generation, power-efficient biomedical sensing devices.