Synthesis and Design of Enhanced N-Path Filters With 60-dB/decade RF Selectivity

A "third-order" passive mixer-first receiver is presented to improve channel selectivity and resilience to close-in blockers, by building an N-path filter which drives an impedance with 60-dB/decade roll-off. A step-by-step derivation is provided for the synthesis of the first ever driving point impedance with 60-dB/decade roll-off. An integrated circuit prototype was fabricated in 28-nm bulk CMOS as proof-of-concept and characterized. The receiver front-end is capable of broadband operation from 0.2 to 4.5 GHz, demonstrates third-order filtering of close-in blockers, and achieves an out-of-band IIP3 of +21 dBm and B1dB of greater than 6 dBm for blockers at the alternate channel. Additionally, it achieves a noise figure of 6.8 dB in the presence of a 0-dBm blocker.