A Front-End Amplifier With Current Compensation Feedback Input Impedance Booster for Neural Signal Applications

Zhijun Zhou

doi:10.1109/access.2020.3026178

Abstract

In integrated circuit form, the front-end amplifier (FEA) determines the fidelity of the biosignal detection, signal-to-noise ratio, power consumption and detector size for the future multi-channel neural signal recording systems and applications. Especially for the high-density implantable applications, a higher input impedance reduces the signal attenuation (with respect to the high-impedance miniature electrodes), and lowers the current into the tissue (to avoid the overheating damage). In this paper, an input impedance booster with current compensation feedback technique is proposed, it neutralizes any currents generated at input of FEA without affecting the gain. It substantially yields a high input impedance across process and device mismatches. The proposed front-end circuit is implemented on a $0.18\mu \text{m}$ CMOS process, it achieves an input impedance of approximately 60 $\text{G}\Omega $ , and CMRR of 61 dB with 57 dB PSRR. The input-referred noise is approximately $5.6~\mu \text{v}/\surd $ Hz while consuming $7.6~\mu \text{W}$ in 0. 025mm2chip area.

Highlights

Growing research interests in biomedical applications demand neural interfacing systems which are capable of simultaneously monitoring the activity of large numbers of neurons [1]–[4]
In IC platform, the proposed current compensation feedback (CCF) booster is less susceptible to the process and device mismatches
In this paper, a new input impedance booster with current compensation feedback technique is proposed for neural signal recording front-end amplifier (FEA)

Summary

INTRODUCTION

Growing research interests in biomedical applications demand neural interfacing systems which are capable of simultaneously monitoring the activity of large numbers of neurons [1]–[4]. A smaller form factor allows more highdensity recording channels [5], [6] Neural signals, such as electroencephalogram (EEG), electrocardiogram (ECG) and electromyogram (EMG) shown in Fig., are low in both amplitude and frequency [7]. To monitor and record such signals, a front-end amplifier (FEA) with relatively wide percentage bandwidth, low noise, high input impedance and low power consumption is required. Capacitive feedback (CF) technique is widely used in neural signal recording FEAs. As shown in Fig.2(a), the gain is configured by the ratio of capacitors, and the tissue/electrode DC offset is simultaneously rejected by input coupling capacitor [1]. A new current compensation feedback input impedance booster for FEA is proposed, it neutralizes any current generated by the input capacitor, without affecting the gain

FEA WITH CURRENT COMPENSATION

RESULTS

CONCLUSION