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Publication

All-Pass Networks for Millimeter-Wave 5G: Phase-Shifters and Beyond

Book - Dissertation

The fifth generation of wireless cellular technology (5G) arrived with the promise to achieve higher data-rates and higher connectivity, as well as to enable cutting-edge applications such as autonomous driving. To deliver the promised leap-forward, 5G relies on the development of key features, such as millimeter-wave frequencies, Massive multiple-input multiple-output (MIMO), and beamforming. These features require synergy between multiple disciplines, from hardware design, to signal processing and wireless communications. From a hardware perspective, these key technologies translate to the development of integrated antenna phased-arrays. While the use of multiple antennas enables massive MIMO and beamforming, the push for a higher integration between antenna and components arises from the smaller wavelength at millimeter-wave frequencies, which reduces the overall array form-factor. Among the several building blocks integrated into an antenna phased-array, phase-shifters are of crucial importance as the main enablers of analog beamforming and beam-steering. However, although solutions for phase-shifters are present in literature, new requirements on phase-shifter design arise from mm-wave 5G. Two relevant challenges for mm-wave 5G phase-shifters are addressed by this Ph.D. thesis: broadband operation and size reduction. While the frequency spectrum allocated by the standard for mm-wave 5G is quite broad, conventional phase-shifters found in the literature are often narrowband. The broadband operation thus becomes quite interesting for mm-wave 5G, as a single device could address multiple frequency bands. The need for size reduction, on the other hand, arises from the space limitations at mm-wave frequencies. While the available area is bounded by the wavelength, more functionalities are being integrated within the same die. Yet phase-shifters are often bulky components, with multiple instances in a single chip. Reducing the size of phase-shifters leads to a slack on the die area, which could be used to increase product complexity or reduce costs. Within this context, this Ph.D. thesis investigates the use of all-pass networks (APNs) to address the above-mentioned challenges. This effort started by identifying a large gap in the literature regarding APN implementation at mm-wave frequencies, which we attributed to the lack of a suitable synthesis procedure. We then propose a novel APN synthesis procedure that results in feasible networks at mm-wave frequencies. We then proceed by employing the proposed synthesis to the design of ultra-broadband phase-shifters for mm-wave 5G mobile. Using SiGe BiCMOS, we combined the APNs with wideband switches to implement two distinct phase-shifter topologies, both with a 2-bit 45 resolution, sufficient for mobile applications. The resulting devices were manufactured and measured, achieved a bandwidth from 14 to 50 GHz, successfully covered the mm-wave 5G spectrum. The bottlenecks observed from the ultra-broadband phase-shifters for mm-wave 5G mobile applications arise from using APNs and switches separately, which led us to investigate approaches to embed the switch within the APNs. As a solution, we contributed significantly to the development of a dynamic type of APN, which we named variable-phase APN (VP-APN). Firstly, we proposed a topology-independent synthesis procedure for VP-APNs, developing a systematic method to approach VP-APNs. Then, we proceed with the implementation of ultra-broadband phase-shifters for mm-wave 5G base-stations. The stringent resolution requirements for base-stations are almost impossible to be addressed with APNs without the use of VP-APNs. The resulting phase-shifter was manufactured in SiGe BiCMOS and measured on-wafer, achieving a 14 to 54 GHz bandwidth with continuous phase tuning. Additionally to the ultra-broadband phase-shifters, we also used the VP-APNs to implement ultra-compact phase-shifters, both for mm-wave 5G mobile and base-stations. These devices trade-off the bandwidth for a small form-factor, leading to ultra-small areas and addressing the size-reduction challenge. Targeting the 24 to 30 GHz bandwidth, the ultra-compact phase-shifters were designed and manufactured in SiGe BiCMOS, achieving competitive performance with an area below 0.1 mm2 for the base-station design and 0.028 mm2 for the mobile. This Ph.D. thesis also looks beyond phase-shifters, investigating the systems in which they are integrated with two steps. First, the ultra-compact phase-shifter for mm-wave 5G base-station is integrated with a low-noise amplifier (LNA), resulting in an ultra-compact phased-array receiver front-end. Finally, as the ultimate system for phase-shifters, a 28 GHz phased-array demonstrator is implemented. The resulting demonstrator is based on antenna tiles, with an innovative reconfigurability property, targeting mm-wave 5G testbeds. A 5-meter wireless link is demonstrated using the proposed hardware, achieving 4.8 Gbps at 28 GHz.
Publication year:2021
Accessibility:Open