Practical considerations for the design of fully differential OTAs with SC-CMFB

Practical considerations for the design of fully differential OTAs and their switched-capacitor common mode feedback (SC-CMFB) network are presented. Different factors affecting the system performance such as OTA gain, bandwidth, common mode open loop gain and bandwidth, and CMFB parameters are discussed. The impact of varying CMFB capacitances and switch sizes are analyzed by means of transistor level simulations. The results showed that larger capacitance ratios produce slower settling times per cycle. However it is better to keep switch widths and capacitances small since clock feedthrough and charge injection can cause significant errors in the steady state CM Voltage.