An Area-Efficient and Highly Linear Reconfigurable Continuous-Time Filter for Biomedical Sensor Applications.

Jinyong Zhang,Lei Wang,Shing-Chow Chan,Hui Li,Nannan Zhang

doi:10.3390/s20072065

Abstract

This paper proposes a compact, high-linearity, and reconfigurable continuous-time filter with a wide frequency-tuning capability for biopotential conditioning. It uses an active filter topology and a new operational-transconductance-amplifier (OTA)-based current-steering (CS) integrator. Consequently, a large time constant , good linearity, and linear bandwidth tuning could be achieved in the presented filter with a small silicon area. The proposed filter has a reconfigurable structure that can be operated as a low-pass filter (LPF) or a notch filter (NF) for different purposes. Based on the novel topology, the filter can be readily implemented monolithically and a prototype circuit was fabricated in the 0.18 μm standard complementary-metal–oxide–semiconductor (CMOS) process. It occupied a small area of 0.068 mm2 and consumed 25 μW from a 1.8 V supply. Measurement results show that the cutoff frequency of the LPF could be linearly tuned from 0.05 Hz to 300 Hz and the total-harmonic-distortion (THD) was less than −76 dB for a 2 Hz, 200 mVpp sine input. The input-referred noises were 5.5 μVrms and 6.4 μVrms for the LPF and NF, respectively. A comparison with conventional designs reveals that the proposed design achieved the lowest harmonic distortion and smallest on-chip capacitor. Moreover, its ultra-low cutoff frequency and relatively linear frequency tuning capability make it an attractive solution as an analog front-end for biopotential acquisitions.

Highlights

Global population aging produces a strong demand for portable and wearable biomedical sensor devices for the continuous monitoring of physiological signals in preventive and personalized healthcare
Analog filters are often preferred over digital filtering in the analog front-end (AFE) for their low power consumption, especially for multi-channel systems
We present an area-efficient, high-linearity, and reconfigurable second-order continuous-time filter architecture by exploiting current-steering (CS) integrators for biopotential recording sensors

Summary

Introduction

Global population aging produces a strong demand for portable and wearable biomedical sensor devices for the continuous monitoring of physiological signals in preventive and personalized healthcare. These devices should possess a high precision, low power consumption, and small size. The performance of such biopotential signal acquisition systems depends critically on the analog front-end (AFE) [1]. Analog filters are often preferred over digital filtering in the AFEs for their low power consumption, especially for multi-channel systems. As most AFEs often support DC offset suppression through the use of chopper stabilization, which requires digital clocks, considerable interference is introduced. Band-limiting analog filters are often utilized to Sensors 2020, 20, 2065; doi:10.3390/s20072065 www.mdpi.com/journal/sensors

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