Design Trade-Offs in Common-Mode Feedback Implementations for Highly Linear Three-Stage Operational Transconductance Amplifiers

• DOI: 10.3390/electronics10090991
• Publication Date: 2021-04-21T16:47:07Z
• Authors: Joseph Riad; Sergio Soto-Aguilar; Johan J. Estrada-...; Oscar Moreira-Tamayo; Edgar Sánchez-Sin...
• Keywords: Transconductance; Operational transconductance amplifier; Linearity; Open-loop gain

Fully differential amplifiers require the use of common-mode feedback (CMFB) circuits to properly set amplifier’s operating point. Due scaling trends in CMOS technology, modern increasingly rely on cascading more than two stages achieve sufficient gain. With multiple gain stages, different topologies for implementing CMFB are possible, whether using a single loop or ones. However, impact performance each approach has seldom been studied literature. The aim this work is guide choice implementation topology evaluating terms stability, linearity, noise and rejection. We present detailed theoretical analysis, comparing relative configurations 3-stage OTA an implementation-agnostic manner. Our analysis then corroborated through case study with full simulation results at transistor level confirming intuition. An active-RC filter used as example high-linearity application, highlighting 6 dB improvement P1dB multi-loop respect single-loop case.