Channel selection at input of narrowband direct-conversion receiver based on current-driven passive mixer

Some issues when applying a Miller N-path filter to narrowband direct-conversion receiver (DCR) based on current-driven passive mixer and solutions to mitigate those issues are presented. The small impedances of the parallel LC circuit of low noise amplifier (LNA) at high frequencies cause undesirable effects: conversion gain reduction, noise figure increase and non-linear effects of the switches. A commutated network with the addition of resistors RFB1 and RFB2 is proposed to reduce the influence of those undesirable effects. The receiver is designed in the frequency range from 2.4 GHz to 2.6 GHz with 0.18 µm CMOS UMC technology. When applying the Miller N-path filter, although the conversion gain decreased by 3 dB and the noise figure increased by 1 dB, the in-band linearity (P1dB and IIP3) of the DRC increased by 6–9 dB compared to the DRC without the Miller N-path filter.