A Low-Power Single-Path Bio-Impedance Measurement System Using an Analog-to-Digital Converter for I/Q Demodulation

Area of Science:

• Biomedical Engineering
• Electrical Engineering
• Cardiology

Background:

• Acute myocardial ischemia detection is crucial for timely intervention.
• Existing bio-impedance systems may face limitations in power consumption and integration.
• The need for efficient, low-power wearable or implantable diagnostic tools is growing.

Purpose of the Study:

• To present a low-power, single-path bio-impedance (Bio-Z) measurement system for early detection of acute myocardial ischemia.
• To demonstrate the system's capability to measure tissue impedance using in-phase and quadrature (I/Q) components.
• To achieve significant power and silicon area reduction through integrated analog-to-digital converter (ADC) functionality.

Main Methods:

• Developed a fully integrated system including a current source, amplifier, and ADC.
• Utilized the ADC to separate I/Q components for real and imaginary impedance parts.
• Employed a capacitively-coupled instrumentation amplifier for low power, low noise, and high linearity.
• Implemented the circuit in 0.18 µm CMOS technology with a 1 V power supply.

Main Results:

• The system measures input impedance in the range of 0.03-7.5 kΩ with a resolution of 0.766 Ωrms.
• Achieved ultra-low power consumption of 2 µW.
• Demonstrated successful recording of impedance variations related to respiration and heartbeat.

Conclusions:

• The proposed low-power Bio-Z system is effective for early detection of acute myocardial ischemia.
• The integrated design offers reduced power and area, suitable for portable or implantable applications.
• The system's ability to capture physiological impedance changes highlights its potential in continuous health monitoring.