N-Path Filters and Mixers Controllable by a Digital Multi-Phase Clock

Eric Klumperink
University of Twente, NL


FDSOI technology offers both power-efficient and high-performance digital, amongst others because SOI-MOSFET switches have lower parasitic capacitances compared to bulk-technologies. These benefits are not only relevant for digital signal processing, but can also benefit analog radio frequency circuits. For “Software Defined Radios”, very selective Radio Frequency bandpass-filters are wanted with a flexibly programmable center frequency to choose the channel. Also, highly linear mixers for frequency down-conversion to baseband before A/D conversion are needed. It turns out that these functions can both be implemented exploiting switches, combined with linear capacitors and resistors, realizing so called “N-path filters” or “Frequency Translated filters”. Moreover, the reception frequency is defined by the frequency of a digital clock, which can be implemented using digital dividers and logic. The resulting N-path filters benefit from CMOS scaling as switch parasitics improve, and increasingly higher digital clock frequencies are feasible. This contribution will review the developments in CMOS N-path filters over the last decade, highlighting promising achieved results, while also discussing some implementation aspects and simulation results in 22nm FDSOI.