Switched-RC radio frequency N-path filters

In this thesis N-path switched-RC circuits are explored, aiming for RF prefiltering for wireless transceivers. Around the switching frequency, these circuits can be modeled as a resonator and inductor-less high-Q band-pass or band-stop filtering is possible. The filter concept fits well to SDR as the center frequency is programmable by the switching frequency, i.e. via a digital clock. As new CMOS technologies provide higher density capacitors and MOS switches with low onresistance and low parasitic capacitance, N-path filtering benefits from Moore’s law. To demonstrate feasibility, a 4-path differential switched-RC bandpass filter, an 8-path single-ended, as well as an 8-path differential bandstop (notch) filter have been implemented in 65nm CMOS technology. A mathematical analysis is presented to describe the filtering behavior as well as various imperfections for the N-path bandpass and notch filters. The implemented bandpass filter provides an in-band input referred third order intercept point IIP3in-band>+14 dBm with compression point P1dB,in-band>0 dBm at a noise figure NF<6 dB. The filter is tunable from 0.1-1 GHz.