High Input Impedance Chopper-stabilized Analog Front-end Based on Variable-capacitor Calibration for Bio-consumer Electronics
Abstract
Analog front-end (AFE) circuits for bio-consumer electronics require ultra-high input impedance to ensure robust bio-potential acquisition under interference. This paper presents a chopping-stabilized AFE featuring an automatic input-impedance enhancement technique based on a positive feedback loop (PFL) with a continuously tunable variable-capacitor. An oscillation-detection-based calibration loop dynamically adjusts the PFL to compensate front-end parasitic capacitance, driving the system from an unstable condition to an optimal stable boundary with maximized input impedance while avoiding over-compensation. To improve calibration robustness, a frequency ripple suppression scheme is introduced, enabling precise control of the variable-capacitor independent of input frequency variations. The proposed variable-capacitance technique provides femtofarad-level resolution without relying on discrete capacitor arrays, achieving wide tuning range and high linearity. Fabricated in a 0.18 μm CMOS process, the AFE achieves an input impedance of 46.3 GΩ at 50 Hz, representing an 83× improvement over conventional approaches. The prototype occupies 0.71 mm², achieves a mid-band gain of 40 dB, an input-referred noise of 0.93 μVrms, and a power consumption of 3.48 μW. Experimental EEG and ECG measurements using comfortable dry electrodes validate the effectiveness of the proposed AFE for bio-consumer electronic applications.
Feng Yan
PhD Student
My research interests include circuit design of analog front end for biomedical applications and sensor interfaces.
Jingjing Liu
Associate Professor
My research interests include low-power smart micro-sensor integrated circuit design, image sensors, biomedical sensors, and energy harvesting circuits.
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.
Xinying Su
Master’s Student
My research interests include circuit design of CMOS memristor simulators and neuromorphic chips.
