Two SC-CMFB networks used in fully differential OTA: measurements and improvements

Two SC common mode feedbacks are separately used to control the output dc level of a fully differential OTA. Both circuits are compared in order to put forward their drawbacks and advantages. Simulations and measurements are presented for both circuits. They show that the design of these SC networks has to be optimized in order to reduce their sensitivity to the layout. Finally the performance of the amplifier is presented, it achieves 70 dB of dc gain, 50 MHz of gain-bandwidth and a phase margin greater than 80 degrees.