Analytical Approaches to Load Modulation Power Amplifier Design
Doktorsavhandling, 2019

In future mobile communication networks, there will be a shift toward higher carrier frequencies and highly integrated multiple antenna systems. The system performance will largely depend on the available radio frequency (RF) hardware. As such, RF power amplifiers (PAs) with improved performance, e.g. energy efficiency, are needed. Active load modulation (ALM) is one of the most common PA efficiency enhancement techniques. Unfortunately, different ALM techniques come at the cost of degrading other PA attributes. Through investigation of new ALM design techniques, the overall objective of this thesis is to improve upon different attributes and performance trade-offs in ALM PAs for future wireless systems.
The working principle of ALM PAs is determined by both how the individual transistors are operated and how their outputs are combined. In the first part of the thesis, an analytical approach, where the output combiner is assumed to be an arbitrary black-box, is applied to the Doherty PA. The fundamental interaction between the main and auxiliary transistors is analyzed and generalized. New solutions with improved performance are identified, such as higher gain and an improved efficiency-linearity trade-off. This approach also introduces improved integration possibilities, which are demonstrated by a transmitter where the antenna acts as both the radiator and the Doherty combiner. Additionally, the analytical approach is applied to an isolated two-way power divider. This unlocks many new possibilities, such as improved integration and layout flexibility.
In the second part, one embodiment of the emerging ALM architecture, the load modulated balanced amplifier (LMBA), is proposed: the RF-input Doherty-like LMBA. Design equations are derived and the fundamental operation is studied. This variant presents several advantages over other known architectures, such as higher gain and device periphery scaling of the different transistors.
The third part proposes a new measurement-based ALM PA design procedure, which emulates the full behavior of the transistors in any ALM architecture using active load-pull measurements. This method can predict the intricate behavior in ALM PAs and it gives measurement-based insights into the internal operation of the circuit already at the design stage. This facilitates the design for optimal ALM PA performance.
The thesis contributes with several promising techniques for reducing performance trade-offs and improving the overall performance of ALM PAs. Therefore, the results will contribute to the development of more energy efficient and high capacity wireless services in the future.


load modulated balanced amplifier (LMBA)

Active load-pull

radio frequency (RF)

Wilkinson power divider.

load modulation

energy efficiency


power amplifier (PA)


Kollektorn, MC2, Kemivägen 9
Opponent: Dr. Frederick H. Raab, Green Mountain Radio Research LLC, USA


William Hallberg

Chalmers, Mikroteknologi och nanovetenskap, Mikrovågselektronik

Have you ever wondered about the underlying systems allowing social media and smartphone games on the go? If so, you can probably appreciate that there are loads and loads of technologies enabling these modern delights. Naturally, the modern human needs to be free from annoying wires to experience all the conveniences of the age of communications. Unfortunately, designing wireless communication systems becomes increasingly challenging as users expect better quality streaming, faster data transfers, and better connectivity. The power amplifier is one out of many essential components in a wireless system. The amplifier's job is to amplify a signal – containing information about, e.g., the latest meal your friend has consumed – to a sufficient energy level such that it can reach your phone without any loss of information. It turns out that power amplifiers possess many different attributes that need careful consideration for the wireless system to function correctly and optimally. To make things worse, improving one power amplifier attribute will most likely degrade another. Additionally, power amplifier design is challenging since modern communication signals are transmitted on high frequency waves, so high that high school level electronics theory falls apart.
Energy efficiency of the power amplifier is important for many reasons. Handheld devices should not become too hot, large and heavy cooling should be minimized in transmission towers, and the energy consumption of the wireless system should be kept at minimum level. The latter is of uttermost importance when developing wireless systems sustainably.

In my thesis, I propose many different techniques for highly efficient power amplifiers with improved attributes. I take an analytical approach in the design, where I strive to assume as little as possible about the power amplifier topology. More specifically, I mathematically determine what the topology should be in order to enable the best performance. It turns out that this approach allows for new ways of designing power amplifiers that can be highly efficient without degrading other properties too much. Overall, the techniques I propose in this thesis help in designing better and sustainable wireless systems.




Annan elektroteknik och elektronik



Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4550



Kollektorn, MC2, Kemivägen 9

Opponent: Dr. Frederick H. Raab, Green Mountain Radio Research LLC, USA

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