An active balun for high-CMRR IC design

A circuit topology that provides large bandwidth single-ended to differential conversion is presented. The proposed cell is based on a differential pair where feedback on common mode signal provides about 6 dB conversion gain increase, together with attenuation of common mode signal. Small-signal characterisation is presented, based on a block decomposition of the cell. Measurements on a SiGe test IC show more than 5 dB of gain improvement with respect to a simple differential pair.