Power‑efficient low‑noise high linear single-stage 140 dB DC gain OTA for biomedical signal acquisition

Abstract

An efficient operational transconductance amplifier (OTA) with high gain, high bandwidth, low noise, high CMRR, and low power is crucial for optimal performance of analog-mixed-signal (AMS) systems. This article presents a low-power, single-stage high-gain adaptive recycling folded cascode (HGARFC) OTA. The design leverages pseudo-resistors (PRs) in a local common-mode feedback (LCMFB) circuit. A compensation technique is also proposed to enhance stability at high gains. The PRs and compensation technique significantly enhance the OTA’s performance. The robustness of the designed OTA has been ensured by process-voltage-temperature (PVT) variations and Monte Carlo analysis. The proposed OTA’s performance is compared with existing high-gain OTAs, all designed for a unity gain frequency (UGF) of 7 MHz with a 500 fF load capacitor. All the designs have been performed using UMC 180 nm technology. The proposed OTA achieves the highest low-frequency gain of 140 dB, the lowest thermal noise of 40 nV/√Hz at 1 MHz, and the lowest flicker noise of 19.7 μV/√Hz at 0.1 Hz among existing high-gain OTA topologies. Furthermore, it achieves the highest slew rate of 13.9 V/μs while consuming only 10 μW of power. Subsequently, the proposed OTA is compared with previously reported designs, demonstrating superior small-signal figure of merit (FOMs) and comparatively high large-signal figure of merit (FOMl) values over most existing OTAs, thereby confirming its power-efficient performance. To validate the proposed HGARFC OTA, a capacitively coupled chopper instrumentation amplifier (CCIA) for biomedical signal acquisition and a switched-capacitor (SC) amplifier are implemented. Discrete fourier transform (DFT) analysis confirms the OTA’s linearity, achieving the highest spurious-free dynamic range (SFDR) (69 dB) among comparable OTAs in the CCIA implementation. Furthermore, the SC amplifier implemented using the proposed OTA demonstrates improved settling behaviour and spectral linearity compared to the folded-cascode counterpart under identical operating conditions. The OTA also successfully amplifies an electrocardiogram (ECG) signal from the MIT–BIH Arrhythmia Database.