Designing a Low-Power LNA and Filter for Portable EEG Acquisition Applications

Marzieh Moradi,Massoud Dousti,Pooya Torkzadeh

doi:10.1109/access.2021.3076160

Abstract

A circuit with a low-power low-noise amplifier and a Gm-C ultra-low-power filter is proposed in this paper for portable electroencephalogram (EEG) acquisition applications. The proposed circuit contains a two-stage chopper-stabilized fully recycling folded cascode (TSRFC) amplifier and a second-order continuous-time Gm-C low pass filter (LPF) with ultra-low-power consumption. The noise and input offset are reduced using the chopper-stabilized technique. A two-stage amplifier that consists of composite transistors and a recycling structure is proposed for the amplifier. Compared to a typical folded cascode CMOS amplifier, the proposed design has higher DC gain and slew rate as well as lower input-referred noise. This circuit has an adjustable second-order Gm-C LPF with very low power consumption. The amplifier achieves a midband gain of 70 dB and a −3dB bandwidth in the range 0.1–212 Hz. Moreover, the amplifier is designed in 0.18- $\mu \text{m}$ CMOS process and the chip area of the proposed circuit with pads is $450\times 450\,\,\mu \text{m}^{2}$ . The adjustable LPF has a 100 Hz cut-off frequency. The proposed circuit has an input-referred noise of $0.7~\mu $ Vrms, (0.1 ~ 100Hz) and a power consumption of 380 nW at 1 V supply.

Highlights

In recent years, many conventional medical monitoring devices such as electroencephalogram (EEG) devices have become portable and wireless
1: NMOS-based dummy switches are used over their PMOS equivalents for chopper modulator because the transconductance of these switches is higher, and better noise performance is achieved. 2: We introduce an ultra-low-power low-noise design that can be used at the input of EEG data acquisition systems
We use the chopper stabilization technique, which uses NMOS-based dummy switches for minimizing charge injection and dynamic offset noises in two-stage fully recycling folded cascode (TSRFC) amplifiers. These amplifiers operate at low supply voltage and their input-referred noise is decreased by enhancing transconductance while they have a large slew rate, a high DC gain and an improved gain bandwidth

Summary

INTRODUCTION

Many conventional medical monitoring devices such as electroencephalogram (EEG) devices have become portable and wireless. The main transconductance amplifier as EEG instrumentation amplifier (IA) in most of previous works is the folded cascode amplifier [8]–[15] and the more common noise reduction technique in biopotential low-noise amplifiers (LNAs) is chopper stabilization. We use the chopper stabilization technique, which uses NMOS-based dummy switches for minimizing charge injection and dynamic offset noises in two-stage fully recycling folded cascode (TSRFC) amplifiers. These amplifiers operate at low supply voltage and their input-referred noise is decreased by enhancing transconductance while they have a large slew rate, a high DC gain and an improved gain bandwidth.

BLOCK DIAGRAM OF PROPOSED TOPOLOGY

LOW PASS FILTER

St cosh2

NOISE CALCULATION IN LPF

CONCLUSION