Realization of Low-Loss Fully Passive Harmonic Rejection N-Path Filters

This work presents a low-loss fully passive harmonic rejection (HR) N-path filter that performs finite impulse response (FIR) filtering within its core by sequentially charging the baseband capacitors and exploiting combined charge sharing and capacitor stacking techniques. The proposed HR N-path filter achieves an in-band (IB) gain of −2 to +0.5 dB across the 0.25-2 GHz frequency range while consuming 2.3–15.7 mW of power. It achieves an HR ratio (HRR) of $>$ 46/48 dB with $>$ +8/+11 dBm third/ fifth-order harmonic blocker P1dB.

I. Introduction

Highly tunable integrated bandpass filters (BPFs) are required for various wireless applications such as wideband sub-6-GHz receivers and spectrum scanners [1], [2]. Aside from tunability, such applications demand high signal rejection at close-in and far-off frequencies. Traditional microwave filters have limited tunability and occupy a large footprint to implement inductors/transmission lines. Furthermore, many of these filters are transparent at odd harmonics of the center frequency and are far from being true BPFs [3].