Wideband mm-wave phase shifters based on constant-impedance tunable transmission lines

This paper presents an integrated inverted stripline-like tunable transmission line structure where the propagation velocity can be modified as the characteristic impedance remains constant. As one application of this structure, a mm-wave phase shifter for massive hybrid MIMO applications is implemented in a 45 nm CMOS SOI process. Measurement results at 45 GHz of this phase shifter demonstrate a 79° phase shift tuning range, worst-case insertion loss of 3.3 dB, and effective area of 0.072 mm2. Compared to an on-chip reference phase shifter implemented based on a previously-reported tunable transmission line structure, this work achieves 35% less area occupied and 1.0 dB less insertion loss, while maintaining approximately the same phase shift tuning range.