*Article* **A Standard-Cell-Based CMFB for Fully Synthesizable OTAs**

**Francesco Centurelli, Riccardo Della Sala \* and Giuseppe Scotti**

Department of Information and Communication Technologies, Sapienza University of Rome, 00184 Rome, Italy; francesco.centurelli@uniroma1.it (F.C.); giuseppe.scotti@uniroma1.it (G.S.) **\*** Correspondence: riccardo.dellasala@uniroma1.it; Tel.: +39-06-4458-5679

**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-cellbased 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.

**Keywords:** OTA; CMFB; low voltage; low power; automatic place and route; standard-cell-based analog circuits
