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MIKON 2024 Workshop

Load-Modulated Balanced Amplifier: From First Invention to Recent Advances

Organized by Professor Anding Zhu, University College Dublin, Ireland

The load-modulated balanced amplifier (LMBA) is a power amplifier architecture, where a control signal is injected into a balanced amplifier via a commonly terminated port of a coupler at the output. The LMBA is capable to modulate the impedance seen by the balanced amplifier by varying the amplitude and phase of the external control signal. By using a wideband coupler as the load modulation network, the LMBA can potentially achieve high efficiency at a different power back-off across a very wide bandwidth. Because of its distinct characters and advantages, LMBA has attracted significant attentions in recent years, and extensive research has been carried out. In this workshop, we will review the recent advances of LMBAs to provide an in-depth look at how this PA architecture has evolved from the first invention to recent advancements. Various configurations and design approaches will be discussed, including new system architectures, continuous-mode operation, novel design strategies and most recent extension of the orthogonal LMBA.


Kenle Chen

University of Central Florida, Orlando, USA

Email: Kenle.Chen@ucf.edu

Talk 1: Load-Modulated Balanced Amplifier (LMBA) for Emerging Wireless Communications

Abstract: Load modulation has been a compelling technology for high-efficiency power amplification of spectrally-efficient modulated signals. However, conventional Doherty power amplifiers (PAs) face limitations including restricted bandwidth, a limited dynamic range, and high sensitivity to load impedance mismatch. In this presentation, we will discuss a new family of load-modulation PAs based on quadrature-balanced topology, namely load-modulated balanced amplifier (LMBA). Together with versatile carrier/peaking biasing schemes, a plethora of different LMBA modes can be formed including 2/3/4-way modulation, which offer unprecedented dynamic range for efficiency enhancement, literally unlimited bandwidth, and intrinsic linearity. Moreover, by leveraging the balanced nature and varactor-less reconfigurability, LMBA is able to maintain both the wideband efficiency and linearity performance against arbitrary antenna impedance variations (e.g., up to 3:1 VSWR), which resemble a common issue in the emerging array-based wireless systems. Furthermore, a novel load-modulated double-balanced amplifier (LMDBA) will be presented, which is endowed with an inherent isolation from the antenna. This innovation holds promise for eliminating the need for magnetic circulators that are widely deployed in current 5G massive MIMO systems.

Speaker’s Bio: Dr. Kenle Chen received the Ph.D. degree in Electrical Engineering from Purdue University, West Lafayette, Indiana, USA, in 2013. He is currently an Assistant Professor with the Department of Electrical and Computer Engineering at the University of Central Florida, Orlando, FL. His research interests include ultra-efficient and wideband power amplifiers, AI-assisted RF circuits and systems, and heterogeneous integration of radio system in package. Prior to his career in academia, he worked as Principle/Lead RFIC engineer with several industry-leading companies, such as Skyworks Solutions Inc., where he focused on the development of advanced RF front-ends for various emerging wireless platforms. Dr. Chen received the NSF CAREER Award in 2023, and his group have won multiple prestigious research-based awards, including First Place Best Paper Award of IEEE MTT-S International Microwave Symposium (IMS) 2020, three Best Paper Awards in IEEE Wireless and Microwave Conference (WAMICON), and four times of First Place Awards in IEEE MTT-S Student Design Competitions from 2018-2021. He has also been serving as Associate Editor of IEEE Transactions on Microwave Theory and Techniques, IEEE MTT-S Adcom Regional Coordinator, TPC Chair and Steering Committee Member of multiple IEEE conferences.

Ruibin Gao

Chongqing University, China

Email: ruibin.gao@stu.cqu.edu.cn

Talk 2: Load Modulated Balanced Amplifier Using Continuous-Mode Technique

Abstract: In recent years, the load modulated balanced amplifier (LMBA) and its derivatives have emerged as promising candidates for achieving both high efficiency and broadband operation in RF power amplification, particularly in contemporary wireless communication systems. Additionally, the continuous-mode technology, renowned for enhancing bandwidth and efficiency in RF power amplifiers, has been proven to be a viable approach for further optimizing the performance of LMBAs, especially in configurations that incorporate output matching networks. This presentation offers a comprehensive analysis and demonstration of the effective integration of continuous-mode operations into the design of LMBAs, spanning from theoretical frameworks to practical implementations. Furthermore, several illustrative design examples will be presented to demonstrate how different continuous modes are applied in RF-input LMBAs and sequential LMBAs, providing valuable insights for the design and optimization of these amplifiers.

Speaker’s Bio: Ruibin Gao received the M.S. degree in school of microelectronics and communication engineering, Chongqing University, Chongqing, China, in 2022. He is currently pursuing the Ph.D. degree at Chongqing University. Mr. Gao has been actively involved in the research and development of numerous RF power amplifiers, leveraging III-V technology for both 5G base-station and terminal applications with China’s premier communication equipment manufacturer. Mr. Gao was awarded the Special Prize in the 2022 Huawei College Student Wireless Base Station Massive MIMO Innovation Competition. His current research interests include broadband high-efficiency power amplifiers, load modulated balanced power amplifiers, multi-way Doherty power amplifiers, load mismatch tolerant power amplifiers and monolithic microwave integrated circuit (MMIC) power amplifier design.

Luis C. Nunes

University of Aveiro, Portugal

Email: cotimos@ua.pt

Talk 3: Wideband Sequential LMBA Design Considering the Balance PA’s OFF-State Impedance

Abstract: This talk starts by addressing the Balance PA’s (BPA) OFF-state impedance impact on the sequential load-modulated balance amplifier (SLMBA), showing how efficiency can be severely affected when proper compensation is not used. This issue has been revealed to be a challenge for high-power and wideband applications, thereby serving as a pivotal constraint in realizing the full potential of SLMBA technology. This talk will then delve into a novel design strategy where the BPA’s matching network is optimized considering its OFF-state impedance to achieve a proper load trajectory to prevent the undesired SLMBA performance degradation. This novel design technique avoids the use of the conventional narrowband compensation offset lines strategy, being able to obtain optimum efficiency and output power performance when the BPAs are turned on across wide bandwidths. The talk concludes by showing a selection of SLMBA implementations driven by this novel design technique.

Speaker’s Bio: Luis C. Nunes received his M.Sc. and Ph.D. degrees in Electrical Engineering from the Universidade de Aveiro, Portugal. From 2016 to 2017, he was an RF design engineer at Huawei Technologies, Sweden. He is currently a Researcher at the Institute of Telecommunications—Aveiro, Portugal. His main research interests include active device modeling, nonlinear distortion analysis, and the design of microwave circuits, especially high-efficiency and linear power amplifiers. Dr. Luis Nunes received the 2022 EuMIC Best Paper Award and the 2024 Microwave Prize.

Jean-Baptiste Urvoy

Cardiff University, UK

Email: urvoyJ@cardiff.ac.uk

Talk 4: LMBA and OLMBA: Achieving Multi-mode PA Operation

Abstract: The discovery of the LMBA architecture has opened a new frontier in the design of power amplifiers as their effective load modulation can be exploited to achieve performance improvement over different domains.  The presentation discusses a few design examples and experimental results where LMBA and OLMBA architectures have demonstrated the advantages of this flexibility in terms of frequency, power and load mismatch configuration.

Speaker’s Bio: Jean-Baptiste is a PhD student at the Centre for High Frequency Engineering at Cardiff University, working on furthering the design of LMBA in multi-mode, multi-standard applications.