A topology of fully differential class-AB symmetrical OTA with improved CMRR
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. Simulations
in 40-nm CMOS technology show a net improvement of common mode rejection ratio without affecting differential-mode behavior;
the increase in area and power consumption is minimal,
with a tradeoff between power and settling time. Simulations of
a sample-and-hold exploiting the proposed OTA are presented.