A SiGe differential active filter using a Sallen and Key cell

Abstract

In this paper, a 1.3 GHz band pass filter, based on a Sallen and Key cell, is presented. A new amplifier topology of the S-K cell is proposed, with input and output differential amplifiers optimized to have high performances in terms of CMMR, IP3 and noise figure. All the filter stages were realized with a SiGe BiCMOS technology. Comparison showed a good agreement between simulation and measurements. In particular, the S-K amplifier gain and the filter selectivity can be tuned. Q factors of up to 60 were measured. The measured even-mode rejection is close to 30 dB at the center frequency.