3.6 mW Active-Electrode ECG/ETI Sensor System Using Wideband Low-Noise Instrumentation Amplifier and High Impedance...

Area of Science:

• Biomedical Engineering
• Integrated Circuit Design
• Wearable Health Technology

Background:

• Accurate electrocardiogram (ECG) and electrode-tissue impedance (ETI) monitoring is crucial for diagnosing cardiac conditions and assessing electrode-skin contact.
• Existing systems often face challenges with integration, power consumption, and measurement precision for both ECG and ETI.
• Development of compact, low-power integrated circuits is essential for advanced wearable and implantable biomedical devices.

Purpose of the Study:

• To propose and validate an integrated active electrode (AE) and back-end (BE) system for simultaneous enhanced ECG and ETI measurements.
• To improve the performance of key circuit blocks, including the current driver and preamplifier, for greater accuracy and wider measurement ranges.
• To demonstrate the feasibility of a miniaturized, low-power CMOS implementation for practical biomedical applications.

Main Methods:

• Designed an AE featuring a balanced current driver with negative feedback for high output impedance and a novel source degeneration method for a wide linear input range.
• Implemented a capacitively-coupled instrumentation amplifier (CCIA) with a ripple-reduction loop (RRL) and active frequency feedback compensation (AFFC) for bandwidth extension.
• Developed a BE for sensing ECG, band power (BP) for QRS complex detection, and impedance (IMP) for resistance and reactance measurements.

Main Results:

• The integrated system was fabricated in a 180 nm CMOS process, occupying a small area of 1.26 mm².
• The current driver achieved high output impedance (>1 MΩ at 500 kHz) and the ETI system accurately measured resistance (10 mΩ-3 kΩ) and capacitance (100 nF-100 μF).
• The system demonstrated efficient operation, consuming only 3.6 mW from a single 1.8 V supply.

Conclusions:

• The proposed integrated AE/BE system offers a robust and efficient solution for simultaneous ECG and ETI monitoring.
• The circuit innovations, including AFFC and improved current driver design, contribute to enhanced performance and miniaturization.
• This technology holds promise for next-generation wearable and implantable devices requiring precise physiological signal and impedance measurements.