Broadband Synthetic Transmission-Line N-Path Filter Design

A synthetic transmission-line N-path bandpass filter technique that lowers the in-band insertion loss and increases the out-of-band rejection of the traditional N-path filter is analyzed. The performance limitations of the traditional N-path filter in terms of in-band insertion loss and limited rejection are reviewed. Measurement results from 0.1 to 1.6 GHz of a single-ended, four-stage synthetic transmission-line N-path filter fabricated in a 65-nm CMOS technology that achieves less than 5-dB insertion loss across the tuning range, 30-50-dB out-of-band rejection, in-band third-order distortion input-referred intercept point (IIP3) of +29 dBm, and a +11-dBm input-referred 1-dB compression point (P1dB_Jam) out-of-band jammer tolerance are presented.