Tutorial: Role of Current-Mode Passive Mixers and N-Path Filters in RF Receivers

Modern multimode sub-6GHz receivers heavily employ current-mode passive mixers and N-path filters to simultaneously satisfy the noise requirements and deal with large in-band and out-of-band interferences. After a brief description of a typical receiver structure and its performance matrix, the operation of current-mode receivers and N-path filters will be explained in detail. In particular, this tutorial will focus on the impedance transformation property and reciprocal mixing of those structures. The tutorial will then cover architectures and applications exploiting N-path filters, such as high-order programmable bandpass filters, magnetic-free circulators, mixer-first, and low-noise trans-impedance amplifier (LNTA)-based receivers.