Optimisation of direct auto-zeroing offset cancellation in low voltage applications using dual level CMFB

A modified CMFB circuit is presented that reinstates the use of direct opamp auto-zeroing offset cancellation techniques in low voltage applications. This approach is particularly useful for high precision sample and hold amplifiers and Nyquist rate ADCs, where the opamp is reset during one of the clock phases. Differential offsets up to 50 mV are effectively reduced as demonstrated by a sample and hold example.