Ultra-Low-Power VDD-Scalable Self-Body Biased Inverter-Based Fully-Differential OTA Topologies Enhanced by Composite Transistors Arrays

This work presents a family of fully-differential inverter-based OTAs operating in the sub-threshold regime and enhanced through composite transistor arrays, namely Rectangular Transistor Arrays (RTA) and Improved Composite Transistors (ICT), combined with a reference-less self-body-biasing (RLSBB) technique. These structures simultaneously boost intrinsic gain, improve PVT robustness, and maintain nanowatt-level power consumption in standard 180-nm CMOS technology. Three representative OTA topologies, namely Nauta, output-common-mode-feedback (OCMFB), and bulk-common-mode-feedback (BCMFB), are analyzed, designed, and experimentally validated across 0.3 V–0.5 V supply voltages. Experimental results confirm that BCMFB-RTA achieves the highest measured GBW, reaching 9.5 kHz at VDD= 0.5 V and the highest slew rate, while OCMFB-ICT reaches more than 55 dB DC gain at VDD= 0.3 V. Depending on topology and supply voltage, the proposed OTAs achieve PSRR values from 30 to 53 dB and output swings up to 87%, while remaining operational down to 0.3 V. The proposed circuits target ultra-low-power low-frequency sensor-conditioning and analog-processing applications.