A Hybrid Complex-Filtering Scheme with High Image Rejection and Efficient Channel Selection for Low-IF Receivers

In this paper, a new hybrid filtering scheme is proposed for low-intermediate frequency (IF) receivers, implemented in a 0.18-μm CMOS process. The design adopts a compact two-stage architecture: the first stage integrates a polyphase filter (PPF) with a biquad complex band-pass filter (CBPF) to improve image rejection ratio (IRR) with reduced power overhead, while the second stage enhances aliasing rejection by combining a PPF with a biquad low-pass filter (LPF). Unlike conventional approaches, the PPF functions as the input transconductance stage, eliminating redundant OTAs, which reduces power and area. Besides, the current-mode signal path allows direct I/Q summation, while good anti-aliasing is achieved by the cascading biquad LPF. Simulation results demonstrate that the hybrid filter achieves over 60 dB IRR from 3 MHz to 5 MHz, with an aliasing rejection ratio (ARR) of 30 dB at 10 MHz and a total power consumption of 0.75mW.