A wideband high-CMRR single-ended to differential converter

A novel circuit topology that provides wideband single-ended to differential conversion is presented. The proposed circuit exploits a negative feedback loop to generate a second input signal for a differential pair, thus obtaining 6 dB extra conversion gain and higher CMRR with respect to a simple differential pair driven singleended. A signal and noise model for the circuit is proposed, based on admittance parameters and the use of a novel analysis technique to open the feedback loop while maintaining closed loop loading effects. The model is exploited to derive design guidelines in bipolar and MOS technologies. Measurements on a test chip in STMicroelectronics BiCMOS7 technology are reported to compare the performance of the proposed topology and of a simple differential pair used as single-ended to differential converter.