A 20.3μW 1.9GΩ Input Impedance Capacitively-Coupled Chopper-Stabilized Amplifier for Bio-Potential Readout

• Published in: IEEE transactions on circuits and systems. I, Regular papers Regular papers, 2024-04, Vol.71 (4), p.1520-1530
• Main Authors: Zhou, Yizhao, Song, Shuang, Zheng, Yu, Yang, Tian, Li, Mengyu, Cao, Yipeng, Zheng, Feijun, Huang, Kai, Tan, Zhichao, Zhao, Menglian
• Format: Article
• Language: English
• Subjects: Biopotential signal recording; Boosting; Buffers; Capacitors; chopper-stabilization amplifiers; Feedback amplifiers; Impedance; Input impedance; input impedance boosting; Low noise; low power; Resistance; Resistors; Topology; Transistors
• ISSN: 1549-8328; 1558-0806
• DOI: 10.1109/TCSI.2024.3351872

This paper presents a low-power chopper-stabilized capacitively-coupled frontend amplifier with auxiliary-path-based input impedance ( {Z} _{\mathbf {in}} ) boosting. In order to achieve a high {Z} _{\mathbf {in}} , a low noise and a small chip area, techniques on both system level and circuit level are implemented. On the system level, small capacitors ( {C} _{\mathbf {in}} = 0.5 pF, {C} _{\mathbf {fb}} = 25 fF) are used with a biased pseudo-resistor ( {R} = 2.5 \text{G}\Omega ) fed back to an amplifier internal node. As a result, a high achievable {Z} _{\mathbf {in}} and low high-pass corner frequency are achieved. On the circuit level, an input capacitance shielded current feedback (CSCF) topology achieving effective 10 fF {C} _{\mathbf {amp}} is proposed as the core of the capacitive feedback amplifier in order not to increase the input noise. Moreover, the design space of auxiliary-path-based boosting is explored to obtain the optimal value of buffer bandwidth and auxiliary capacitor size to save power. The amplifier and its {Z} _{\mathbf {in}} boosting circuit are implemented in a standard 55 nm CMOS process and characterized experimentally. Measurement results show that the proposed amplifier provides an input noise density of 50 nV/ \surd Hz, and an integrated noise of 0.85~\mu Vrms in 200 Hz band. The {Z} _{\mathbf {in}} is boosted to 1.92 \text{G}\Omega at DC and 1.02 \text{G}\Omega at 50 Hz with only 1.0~\m