A fully-differential class-AB OTA with CMRR improved by local feedback

The fully differential class-AB OTA topology by Peluso presents a poor Common-Mode Rejection Ratio (CMRR) and could become unusable for a common-mode gain larger than 1. We propose a local feedback loop that exploits internal nodes and triode-biased transistors to improve the CMRR with a limited power and area penalty. Simulations in 40-nm CMOS technology show a net improvement of the CMRR without affecting the differential-mode behavior; simulations of a sample- and-hold exploiting the proposed OTA topology are also presented.