Blocker and image reject low-IF frontend

In this paper we present a design of a low-IF receiver frontend using a selective N-path filter which serves blocker rejection, image rejection, and downconversion. The filter makes use of quadrature impedance upconversion technique using multiphase clocking and can be programmed by baseband capacitance and gm-cell transconductance values to meet the low-IF criterion in various cases. Presented is both a mathematical model of the filter and circuit simulation results including parasitic effects. Image rejection of 14 dB at IF that is provided by the filter mitigates the demands for the ultimate image rejection by the IQ mode. The blocker rejection at IF is larger than 50 dB. Designed in in 65 nm CMOS the low-IF receiver frontend with a modified N-path filter in simulations achieves NF < 6 dB and OOB IIP3 > +8 dBm in 0.5-1 GHz band.