Analysis of Transmission-Line-Based Quasi-All-Pass Network for Phase-Shifter Design

All-passnetworks (APNs) have long been used in the design of phase shifters. A transmission-line-based quasi-all-pass network (TL-based QAPN) is a series-$C$-configured second-order common-mode APN with its two inductors respectively replaced by two transmission lines. In this work, the TL-based QAPN is, for the first time, analyzed in the context of phase-shifter design. Through the analysis, the conditions for the TL-based QAPN to exhibit zero reflection and the design equations are derived. Two generic switched-network phase-shifter topologies incorporating the TL-based QAPNs are investigated. For experimental verification, a Ka/Q-band 5-bit phase shifter is designed and realized in a 90-nm CMOS technology. The design procedure for using the TL-based QAPN as a phase-shifting bit is described. The measured RMS phase and amplitude errors of the 5-bit phase shifter are less than 4$^{\circ }$ and 0.3 dB, respectively, from 29.0 to 45.1 GHz, which translates into a bandwidth of 43.5%. The performance is among the best results in the literature, demonstrating the usefulness of the proposed TL-based QAPN in phase-shifter design.