A Low-power High-impedance Instrumentation Amplifier with Capacitor-calibration for Bio-sensors
Abstract
The analog front-end (AFE) in biomedical sensors requires high input impedance to suppress interference during bio-potential acquisition. This paper presents a low-power chopping-stabilized AFE with ultra-high input impedance. A self-adjusting variable-capacitor in the positive feedback loop (PFL) dynamically compensates parasitic capacitance, while an oscillation detection loop guides the system from instability to stability, maximizing impedance without over-compensation. A frequency ripple suppression method further mitigates input frequency fluctuations, providing accurate control signals for the variable capacitor. This capacitor decouples control and input signals, ensuring high linearity and wide tuning range. The technique achieves femtofarad-level resolution, overcoming limitations of traditional capacitive arrays in PFL. Fabricated in 0.18 µm CMOS, the AFE attains 46.3 GΩ input impedance at 50 Hz, 83× higher than conventional designs, occupying 0.71 mm2 with 40 dB mid-band gain and only 68 fF input capacitance. It also achieves low noise (0.93 μVrms) and low power consumption (3.48 μW), extending acquisition system operation. Using dry electrodes, the prototype successfully acquired high-quality EEG and ECG signals, validating its applicability to biomedical devices.
Feng Yan
PhD Student
My research interests include circuit design of analog front end for biomedical applications and sensor interfaces.
Bingjun Xiong
PhD Student
My research interests include circuit design of optical receivers and references.
Weijie Ge
PhD Student
My research interests include the design of radio frequency integrated circuits and energy harvesting circuits.
Kangkang Sun
PhD Student
My research interests include circuit design of analog to digital converter for biomedical applications and SAR ADC.
Jingjing Liu
Associate Professor
My research interests include low-power smart micro-sensor integrated circuit design, image sensors, biomedical sensors, and energy harvesting circuits.