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Dissertation/Thesis Abstract

Efficient Power Amplifiers for Millimeter-Wave Beamformers
by Sarkar, Anirban, Ph.D., North Carolina State University, 2016, 162; 10583288
Abstract (Summary)

Wireless communication systems in the millimeter-wave frequency bands have shown the capability to meet higher capacity desired in the future generation of communication systems. One of the challenges in realizing commercial millimeter-wave communication systems is the availability of compact and power-efficient phased-array transceiver integrated circuits in low-cost silicon-based technologies. To enable low-power and compact phased arrays, this work investigates circuit design techniques for high efficiency and high output power millimeter-wave Power Amplifiers (PAs) in low-cost SiGe BiCMOS processes. Further, the efficiency and output power enhancement techniques presented in this work are suitable for high peak-to-average ratio modulation schemes.

Harmonic-tuned continuous class-AB mode PAs are investigated for high peak and back-off power added efficiency (PAE) while eliminating the necessity of short and open resonators. A novel harmonic output matching network architecture consisting of a bandpass filter cascaded with or surrounded by a low pass matching network is proposed for integrated continuous class-AB mode millimeter-wave PAs. A parasitic-aware design technique is introduced to realize compact and low-loss harmonic matching networks with lumped components. This technique demonstrates a method of manipulating the second-harmonic phase of a Chebyshev band-pass filter while maintaining a suitable impedance match at the fundamental. The harmonic-tuned PA shows 4–5% point improvement in peak PAE compared to a traditional LC-tuned PA at 28 GHz. The technique is applied to a 28-GHz PA in SiGe BiCMOS which achieves 15.3-dB gain, 18.6-dBm saturated output power, 15.5-dBm output 1-dB compression point (oP1dB), 35.3% peak PAE, and 11.5% PAE at 6-dB output power back-off (PAE-6dBo).

Efficacy of second-harmonic tuning versus frequency is studied to establish a break-even frequency above which harmonic tuning no longer offers any performance benefit. Harmonic generation capability of the device is studied through constrained load-pull simulations. A second type of harmonic matching network is presented which can be realized with microstrip transmission lines and is suitable for higher millimeter-wave frequencies. Simulation results with finite-Q elements show that harmonic tuning improves PAE by 3–5% points from 28 to 43 GHz and about 2–3% points from 43 to 66 GHz and the break-even frequency is established as 68 GHz. Two-stage PAs operating at 28 and 60 GHz were fabricated to demonstrate the effect of harmonic tuning and validate our predictions. A broadband inter-stage match network design technique is also presented for the 60 GHz PA. The 28(60)-GHz PA achieves 30(19)-dB gain, 16.2(13.3)-dBm oP 1dB, 35.5(25)% peak PAE and 14(9)% PAE-6dBo.

After investigating techniques for high peak efficiency single-path millimeter-wave PAs, we explore multi-path PA architectures that can improve the output power or back-off PAE of the PA. Design methodologies for a Doherty PA suitable for a millimeter-wave Doherty beamformer are presented. In particular, choice of multi-stage Doherty architectures, necessity of harmonic matching networks, output combiner choice are investigated for optimum Doherty operation. Bandwidth versus PAE trade-off of harmonic tuning in Doherty PA is demonstrated. Trade-offs in design of the peaking PA and impact on overall Doherty performance are presented. With these design considerations, a 60-GHz Doherty PA is fabricated and characterized. Measurement results demonstrate at least 3–4% point improvement in PAE-6dBo over state-of-the-art 60-GHz PAs.

Transformer-based compact and low-loss combiners are investigated for realizing efficient and high output power millimeter-wave PAs. A simplified and generalized co-design technique for the transformer and the adjoining matching network is presented to minimize the power loss of a series-parallel combiner using an accurate lumped transformer model. Efficacy of this technique is demonstrated with a two-way series two-way parallel power-combined PA which shows greater than 5-dB improvement in output power with only 3–4% point reduction in efficiency compared to the unit PA.

Indexing (document details)
Advisor: Floyd, Brian
School: North Carolina State University
School Location: United States -- North Carolina
Source: DAI-B 78/08(E), Dissertation Abstracts International
Subjects: Electrical engineering
Keywords: 28 GHz, 5G, Harmonic toning, Millimeter wave, Phased array, Power amplifier
Publication Number: 10583288
ISBN: 978-1-369-61983-6
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