Phased array systems have become paramount to the development of next generation wireless communication networks, with errors on phase shifters contributing to beam pointing error. Oscillation-based built-in self-testing (OBIST) of phase shifters may improve on this accuracy. We propose a singleended oscillation-based test technique for passive RF phase shifters. The method uses a negative resistance oscillator topology, where the phase shifter is used to capacitively load the active negative resistance circuit resulting in a dependency between relative phase shift and output oscillation frequency. Simulation results indicate an average sensitivity of 0.14 MHz/° of phase shift around a nominal 617 MHz output oscillation when testing an Xband reflection-type phase shifter, while the addition of OBT circuitry increases the phase shifter's mid-band insertion loss by 0.93 dB..

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This paper presents a systematic comparison of the relationship between transmission line characteristic impedance and Q-factor of CPW, slow-wave CPW, microstrip, and slow-wave microstrip in the same CMOS back-end-of-line process. It is found that the characteristic impedance for optimal Q-factor depends on the ground-to-ground spacing of the slow-wave transmission line. Although the media are shown to be similar from a mode of propagation point of view, the 60-GHz optimal Q-factor for slow-wave transmission lines is achieved when the characteristic impedance is ≈23 Ω for slow-wave CPWs and ≈43 Ω for slow-wave microstrip lines, with Q-factor increasing for wider ground plane gaps. Moreover, it is shown that slow-wave CPW is found to have a 12% higher optimal Q-factor than slow-wave microstrip for a similar chip area. The data presented here may be used in selecting Z0 values for S-MS and S-CPW passives in CMOS that maximize transmission line Q-factors.

In this paper, an X-band reflection-type phase shifter is presented. It is based on a single layer stub-loaded coupled line coupler loaded by two-varactor tuning circuits. This choice of coupler significantly improves on the phase shifter bandwidth achievable with a branch-line coupler, as it features lower phase imbalance across the band of interest. The proof-ofconcept prototype achieves better than 10-dB return loss across a 20 % fractional bandwidth. The phase shifter further exhibits insertion loss of 2.1 ± 1.3 dB and maximum phase shift of 392° at 10 GHz, leading to a state-of-the-art figure of merit at X-band of 115 °/dB. The occupied area is 0.25 λg 2 .

We investigate the effect of passivation contouring, surface roughness, and sidewall tapering on the FEM modelling accuracy of mm-wave couplers in CMOS BEOL. Of three effects, sidewall tapering leads to the most significant improvement (0.37 dB) in predicting peak coupling magnitude at V-band. Ultimately, it is found that none of these measures substantially improve on modelling accuracy.