A Differential Difference Amplifier Employing Pseudo-Differential CMFB for Neural Signal Recording Applications

Abstract

This brief presents a differential difference amplifier (DDA) with a pseudo-differential (PD) common-mode feedback (CMFB) for neural signal recording. One of the input transconductors within the proposed DDA is connected to target neural signal, to ensure a high input impedance. Another input transconductor employs a self-stabilized topology to stabilize the dc quiescent point and to determine the cut-off frequency. The CMFB is applied via the proposed PD terminal. Benefiting from the parallel connection of PD, the common mode rejection ratio (CMRR) is approximately increased by a factor of differential-mode gain, without damaging the voltage headroom and dynamic range. Moreover, the proposed PD CMFB is suitable for multi-channel neural signal acquisition, the more the channels, the higher the CMRR. The circuits are targeted at IC realization, designed in a 0.18- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\boldsymbol {\mu }\text{m}$ </tex-math></inline-formula> CMOS technology. It achieves an input impedance of circa 51 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{G}\boldsymbol{\Omega }$ </tex-math></inline-formula> at 100 Hz, a CMRR of 103 dB, and a power consumption of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.8~\boldsymbol {\mu }\text{W}$ </tex-math></inline-formula> . The proposed DDA (two channels) with a system PD CMFB consumes a die area of 0.24 mm2.