Wideband Switchable-Capacitor Loaded Differential Phase Shifter with Lattice Structures
This paper presents a differential K/Ka-band switchable-capacitor loaded phase shifter with lattice structures using 28-nm CMOS technology. The lattice structure, which has a wideband characteristic, is loaded with switchable-capacitors and provides 22.5° phase shift. Seven of the lattice phase shifters are cascaded with a switched line 180° phase shifter, resulting in a full 360° phase shifter. The measured bandwidth for a root mean square (rms) phase error of < 5° is from 22.5 to 33.5 GHz, where the rms amplitude error is < 0.53 dB. The measured insertion loss is 11.6±0.8 dB at 28 GHz, and the input and output return losses are both > 10 dB from 22.5 to 33.5 GHz. Over the 5G NR bands at 28 GHz (24.25 to 29.5 GHz), rms phase error is < 2.4° and rms amplitude error is < 0.49 dB. The fabricated phase shifter has a size of 0.45 mm² excluding pads. The proposed K/Ka-band phase shifter based on lattice structures has a wide bandwidth while maintaining low rms phase and amplitude errors.