Fully differential operational amplifiers with accurate output balancing

Design considerations are presented for attaining accurate output balancing in fully differential operational amplifiers over the useful operating frequency of the differential signals. Such output balancing is obtained by merging the common-mode feedback and the differential gain paths as close to the front end of the amplifier as possible, ensuring maximum sharing of circuit components. Two circuit designs implemented in a 5-V, 1.75-μm process are presented, one based on a two-stage topology and one based on a folded cascode topology. Experimental results for both designs are given