Ricerc@Sapienza

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- A nd-hold exploiting the proposed OTA topology are also presented.

An improvement of a standard fully differential class-AB symmetrical operational transconductance amplifier (OTA) topology is proposed in this brief to enhance the common-mode behavior. Common-mode behavior could be critical in fully differential class-AB OTAs, where the total current is not fixed and differential to common-mode conversion could therefore be present. A signal proportional to the input commonmode component is generated through a simple low-current auxiliary amplifier and used to modulate a bias voltage, achieving cancellation of the output common-mode component.