A Scalable Many-Stage CMOS OTA for Closed-Loop Applications

In this work, a new scalable CMOS OTA design that systematically enables cascading many identical OTA stages is proposed. This scalable design of the many-stage OTA ensures stability, when configurated in closed loop, by means of a new scalable frequency compensation technique. The presented design realizes a CMOS OTA with scalable-gain that increases in 25 dB increments per stage, achieving a total gain from 50 dB to 150 dB for a 2-stage to a 6-stage OTA, respectively. Stability of the many-stage OTA is ensured by re-positioning the poles and zeros of all gain stages in a systematic scalable pattern whenever a new gain-stage is added. The presented design was based on a TSMC 65 nm CMOS process.