ABSTRACT
The N-path filter concept, also known as commutated filter or frequency translated filter, can offer high-Q and high-linearity RF-filtering with acceptable noise. This chapter reviews recent developments in the field of N-path filters and mixers, focusing on ways to improve the selectivity, linearity and blocker tolerance. Then properties of N-path filters will be reviewed (both good and bad ones and other issues you may wonder about). Finally, examples of published circuit implementations will be discussed both exploiting transconductors (Gm) and fully passive solutions which can achieve better linearity. Our goal is to integrate this front-end entirely in CMOS, together with the DSP, without external Surface Acoustic Wave (SAW) filters, but this comes with several challenging listed. The benefits can be explained in different ways, e.g. as exploiting the Miller effect or as a gain-boosted N-path filter. Hence several ideas have been proposed to improve selectivity exploiting passive circuits.
