Design of an Active N-Path Filter for 5G mm-wave Receivers

Abstract

Receivers for millimeter-wave (mm-wave) 5G, with the ability to detect a low-power desired signal, in the vicinity of large power blockers, require highly linear circuitry with a large power consumption. Suppressing the out-of-band blockers reduces this power consumption. N-path filters (NPFs) have recently been used to reject interferers in adjacent channels, by using a tunable center frequency. The state-of-the-art NPFs at mm-wave, however, only have a limited attenuation or use a large chip area. In this thesis, a fourth-order NPF is designed for 26-30 GHz. The implemented filter combines two frequency-shifted NPFs to create a flat in-band response and a steep roll-off, without the use of a large passive baseband filter. A rejection of 14 dB in the center of the first adjacent channel is obtained. This increases up to 24 dB at far-out-of-band frequencies. The noise figure of 10-12 dB is the lowest of the state-of-the-art, due to the added low-noise amplifier (LNA) in front of the filter. Despite this LNA, the designed filter achieves a comparable power consumption (40 mW) and smaller area (0.2-0.3 µm) than the state-of-the-art. The filter designed in this thesis is the first reported active N-path filter at mm-wave. The bandwidth is among the smallest reported, while the estimated area is lower than the state-of-the-art.