Nonlinear effects in pseudo differential OTAs with CMFB

A general description of nonlinearities in pseudo differential operational transconductance amplifiers (OTA) with commonmode feedback (CMFB) is introduced. The effects of CMFB nonlinearities on the differential signals are evaluated and design tradeoffs including nonidealities are determined. A practical pseudo differential fully balanced fully symmetric OTA architecture with common-mode feedforward (CMFF) is used as a case study to probe the theory. The OTA has an inherent common-mode detector; hence, the CMFB circuit is efficiently implemented. The OTA is used to implement a 100MHz fourth-order linear-phase OTA-C filter.