Advanced load modulated power amplifiers for wireless telecom applications

Kozel, Derek 2024. Advanced load modulated power amplifiers for wireless telecom applications. PhD Thesis, Cardiff University. Item availability restricted.

Preview	PDF - Accepted Post-Print Version Download (17MB) | Preview
	PDF (Cardiff University Electronic Publication Form) Restricted to Repository staff only Download (583kB)

Abstract

This thesis demonstrates a design approach for load modulated RF power amplifiers based on the use of circuit simulation to provide comprehensive visibility into the true behaviors of current and voltage waveforms when they diverge from ideal theory. While RF circuit simulations are standard design tools, identifying and monitoring the numerous interactions of passive and active components as a design transitions from concept to manufacturable circuit remains challenging. This work presents measurement and display techniques to analyze a set of key performance indicators at all design stages of RF power amplifier design. The design approach framework is discussed and demonstrated through the analysis and design of Doherty Power Amplifiers as they make use of active load modulation. The Doherty architecture has been studied extensively since its initial conception in 1936 and is a frequent choice for 5G MIMO applications. The Doherty power amplifier architecture uses one or more auxiliary transistors to generate synthetic load impedances at the output of the amplifiers that help maintain high efficiency even at reduced output power levels. This ability is compelling because it operates without external control circuitry or logic, making it ideal for modern communication signals, which often have high Peak-to-Average Power Ratios due to the need for high data rates within limited bandwidths. iv Transistors exhibit non-linear and complex behaviors when driven by timevarying input signals. The simplifying assumptions of ideal Doherty amplifier design formulas are often invalidated by these non-linearities and the real-world characteristics of other components. Acknowledging these complexities, a pragmatic design process for load-modulated amplifiers has been developed and tested using modern non-linear RF circuit simulators. This process begins by formalizing key Doherty architecture properties, creating systems to measure and evaluate them, and aligning the design process with these metrics. This approach ensures clarity as non-ideal components are integrated and complex behaviors result, providing measurable objectives throughout the design stages. The fabricated 5G mid-band basestation amplifier operating between 3.4 and 3.8GHz achieves a peak power of 46.25 dBm with an efficiency of 62.5% at saturation and 48% at the target average power level of 8.5 dB below peak. When driven with a 10MHz bandwidth OFDM signal it delivers a 38 dBm average power output at 43% efficiency and an ACLR of -51 dBc. Additionally, the design was implemented within a compact 56.1 x 43.5mm total size. These performance results compare favorably with other designs in published literature, validating that the design process results in an effective design.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Schools > Engineering
Uncontrolled Keywords:	Power amplifier Doherty Load modulation efficiency enhancement Gallium nitride Design process
Date of First Compliant Deposit:	7 March 2025
Last Modified:	07 Mar 2025 15:25
URI:	https://orca.cardiff.ac.uk/id/eprint/176696

Actions (repository staff only)

Edit Item