electronics Article Design Trade-Offs in Common-Mode Feedback Implementations for Highly Linear Three-Stage Operational Transconductance Amplifiers Joseph Riad 1,* , Sergio Soto-Aguilar 1 , Johan J. Estrada-López 2,* , Oscar Moreira-Tamayo 1 and Edgar Sánchez-Sinencio 1 1 Electrical and Computer Engineering Department, Texas A&M University, College Station, TX 77843, USA;
[email protected] (S.S.-A.);
[email protected] (O.M.-T.);
[email protected] (E.S.-S.) 2 Faculty of Mathematics, Autonomous University of Yucatán, Mérida 97110, Yucatán, Mexico * Correspondence:
[email protected] (J.R.);
[email protected] (J.J.E.-L.) Abstract: Fully differential amplifiers require the use of common-mode feedback (CMFB) circuits to properly set the amplifier’s operating point. Due to scaling trends in CMOS technology, modern amplifiers increasingly rely on cascading more than two stages to achieve sufficient gain. With multiple gain stages, different topologies for implementing CMFB are possible, whether using a single CMFB loop or multiple ones. However, the impact on performance of each CMFB approach has seldom been studied in the literature. The aim of this work is to guide the choice of the CMFB implementation topology evaluating performance in terms of stability, linearity, noise and common- mode rejection. We present a detailed theoretical analysis, comparing the relative performance of Citation: Riad, J.; Soto-Aguilar, S.; two CMFB configurations for 3-stage OTA topologies in an implementation-agnostic manner. Our Estrada-López, J.J.; Moreira-Tamayo, analysis is then corroborated through a case study with full simulation results comparing the two O.; Sánchez-Sinencio, E.