Simultaneously Broadband and Back-Off Efficient mm-Wave PAs: A Multi-Port Network Synthesis Approach

• Published in: IEEE journal of solid-state circuits Vol. 53; no. 9; pp. 2543 - 2559
• Main Authors: Chappidi, Chandrakanth Reddy, Wu, Xue, Sengupta, Kaushik
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.09.2018; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: backoff; Bandwidth; Broadband; Broadband communication; digital power amplifier (PA); Digital to analog converters; Doherty; Efficiency; Frequency synthesizers; Impedance; loadpull; Millimeter waves; millimeter-wave (mm-wave); Network synthesis; OFDM; outphasing; Power amplifiers; power combining; Power efficiency; Power generation; Reconfiguration; Transmitters; Wave power; Wave spectra
• ISSN: 0018-9200; 1558-173X
• DOI: 10.1109/JSSC.2018.2841977

Spectrally efficient operation with high power and high efficiency at deep backoff will be critical for the next generation of millimeter-wave (mm-wave) transmitters for 5G and beyond. In addition, as larger non-contiguous chunks of the mm-wave spectrum open up, dynamic frequency reconfiguration while ensuring high spectral and energy efficiency can become a key toward optimal utilization of spectral resources. In this paper, we present a generalized network synthesis approach that enables simultaneous frequency and back-off reconfigurability in an mm-wave power amplifier (PA) architecture to maintain high-efficiency operation with spectrally efficient codes across a wide frequency range. We show that frequency reconfigurability and back-off enhancement can be treated in a similar fashion with dynamic impedance synthesis. The method is based on the synthesis of a multi-port combiner network that exploits the interaction of mm-wave DAC cells switched asymmetrically to synthesize the optimal impedances across the 2-D space of reconfiguration: frequency and backoff. As a proof of concept, a PA is presented in <inline-formula> <tex-math notation="LaTeX">0.13-\mu \text{m} </tex-math></inline-formula> SiGe BiCMOS process, which operates across 30-55 GHz with peak <inline-formula> <tex-math notation="LaTeX">P_{\mathrm{ sat}} </tex-math></inline-formula> of 23.7 dBm at 40 GHz, output collector efficiency <inline-formula> <tex-math notation="LaTeX">\eta _{\text {out}} </tex-math></inline-formula> of 34.5% and 22% at the 0- and −6-dB backoff, respectively. The PA maintains <inline-formula> <tex-math notation="LaTeX">\eta _{\text {out}} > 16\% </tex-math></inline-formula> at −6-dB backoff across the range. Non-constant modulation is demonstrated with data rates up to 4 Gb/s across the frequencies from 30 to 50 GHz.