A Higher-Order Highly Linear N-Path Band-Pass Filter

Abstract

This paper proposes a higher-order fully passive N-path filter (HOFPNF) with better pass-band shape and higher out-of-band rejection compared with the conventional N-path filter. Two band-pass filters with slightly different center frequencies are constructed using two frequency mixers and two complex filters which are completely composed of switches and capacitors. The final output of the HOFPNF can be obtained by subtracting the outputs of these two filters. The input–output characteristic of the proposed filter is derived using the Fourier transform. Comparing the theoretical expressions with Spectre RF PSS-PAC simulation results verifies the correctness of the derived transfer function. The system is realized at TSMC 0.18 µm technology. There is no static power consumption, and the proposed filter represents high linearity, thanks to fully passive implementation. Based on post-layout simulations, the following results are obtained: the − 3 dB bandwidth of 20 MHz, center frequency tunability range of 0.2–1.2 GHz, maximum rejection of 61.8 dB (@ fLO = 500 MHz), 4.5–6.7 dB in-band loss, IIP3 > 17.5 dBm, P1dB > 7.9 dBm and the noise figure (NF) is 6.3–7.5 dB. The dynamic power consumption of the system increases from 2.95 to 19.4 mW by tuning the center frequency at the whole frequency band.