A Standard-Cell-Based CMFB for Fully Synthesizable OTAs

Abstract

In this paper, we propose a fully standard-cell-based common-mode feedback (CMFB) loop with an explicit voltage reference to improve the CMRR of pseudo-differential standard-cell-based amplifiers and to stabilize the dc output voltage. This latter feature allows robust biasing of operational transconductance amplifiers (OTAs) based on a cascade of such stages. A detailed analysis of the CMFB is reported to both provide insight into circuit behavior and to derive useful design guidelines. The proposed CMFB is then exploited to build a fully standard-cell OTA suitable for automatic place and route. Simulation results referring to the standard-cell library of a commercial 130 nm CMOS process illustrated a differential gain of 28.3 dB with a gain-bandwidth product of 15.4 MHz when driving a 1.5 pF load capacitance. The OTA exhibits good robustness under PVT and mismatch variations and achieves state-of-the-art FOMs also thanks to the limited area footprint.