A 1.9 nW, Sub-1 V, 542 pA/V Linear Bulk-Driven OTA with 154 dB CMRR for Bio-Sensing Applications

Rafael Sanchotene Silva,Cesar Ramos Rodrigues,Luis Henrique Rodovalho,Orazio Aiello

doi:10.3390/jlpea11040040

Abstract

In this paper, a new technique for improvement on the DC voltage gain, while keeping the high-linearity in symmetrical operational transconductance amplifier (OTA) bulk-driven (BD) topology is proposed. These features are achieved by allying two topological solutions: enhanced forward-body-biasing self-cascode current mirror, and source degeneration. The proposed concept is demonstrated through simulations with typical process parameters and Monte Carlo analysis on nominal transistors of the CMOS TSMC 180 nm node. Results indicate that the proposed OTA can achieve a very small transconductance, only 542 pA/V while keeping a voltage gain higher than 60 dB, 150 dB CMRR, and high linearity of 475 mVpp (1% THD), consuming only 1.9 nW for a supply voltage of 0.6 V. This set of features allows the proposed OTA to be an attractive solution for implementing OTA-C filters for the analog front-ends in wearable devices and bio-sensing.

Highlights

Appl. 2021, 11, 40. https://doi.org/The effort to develop implantable or bio-sensing battery-less biomedical instrumentation systems has been continuously challenging analog designers because of the intensified constraints arising from CMOS scaling [1,2,3]
In order to decrease the size of such filters, operational transconductance amplifier (OTA) must output a very small transconductance in the order of a few nA/V, which is achieved with very low biasing currents [20] at the cost of the OTA linearity
Besides the employed combination of techniques in the OTA topology, we propose an innovative improved self-cascode current mirror (ISCCM) which is based on [35,37]

Summary

Introduction

The effort to develop implantable or bio-sensing battery-less biomedical instrumentation systems has been continuously challenging analog designers because of the intensified constraints arising from CMOS scaling [1,2,3]. Among the typical OTA design techniques to increase linearity is the use of nonunity gain current mirrors [21,22,23] to allow higher biasing currents and maintain a low transconductance. Another well-known technique that is used to improve both OTA linearity and input signal voltage swing is the bulk-driven differential pair [1,24,25,26,27,28,29].

Current Mirrors

Bulk-Driven Symmetrical Operational Transconductance Amplifiers

Simulation Results

Conclusions