A 20.3μW 1.9GΩ Input Impedance Capacitively-Coupled Chopper-Stabilized Amplifier for Bio-Potential Readout
Y. N. Zhou, Shuang Song, Yu Zheng, Tian Yang, Mengyu Li, Yipeng Cao, Feijun Zheng, Kai Huang, Zhichao Tan, Menglian Zhao
Abstract
This paper presents a low-power chopper-stabilized capacitively-coupled frontend amplifier with auxiliary-path-based input impedance ( Z <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathbf{in}}$</tex-math> </inline-formula> ) boosting. In order to achieve a high Z <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathbf{in}}$</tex-math> </inline-formula> , 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathbf{in}}$</tex-math> </inline-formula> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$=$</tex-math> </inline-formula> 0.5 pF, C <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathbf{fb}}$</tex-math> </inline-formula> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$=$</tex-math> </inline-formula> 25 fF) are used with a biased pseudo-resistor ( R <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$=$</tex-math> </inline-formula> 2.5 G <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega $</tex-math> </inline-formula> ) fed back to an amplifier internal node. As a result, a high achievable Z <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathbf{in}}$</tex-math> </inline-formula> and low high-pass corner frequency are achieved. On the circuit level, an input capacitance shielded current feedback (CSCF) topology achieving effective 10 fF C <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathbf{amp}}$</tex-math> </inline-formula> is proposed as the core of the capacitive feedback amplifier in order not to increase the input noise. Moreover, the design space of auxiliary-path-based boosting is explored to obtain the optimal value of buffer bandwidth and auxiliary capacitor size to save power. The amplifier and its Z <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathbf{in}}$</tex-math> </inline-formula> boosting circuit are implemented in a standard 55 nm CMOS process and characterized experimentally. Measurement results show that the proposed amplifier provides an input noise density of 50 nV/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\surd$</tex-math> </inline-formula> Hz, and an integrated noise of 0.85 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu$</tex-math> </inline-formula> V <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathbf{rms}}$</tex-math> </inline-formula> in 200 Hz band. The Z <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathbf{in}}$</tex-math> </inline-formula> is boosted to 1.92 G <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega $</tex-math> </inline-formula> at DC and 1.02 G <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega $</tex-math> </inline-formula> at 50 Hz with only 1.0 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu$</tex-math> </inline-formula> A in each auxiliary path buffer. The amplifier also archives 77 dB CMRR and 76 dB PSRR while consuming 20.3 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu$</tex-math> </inline-formula> W in total.