RF Power Amplifier Design Techniques

Course 222

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Summary

Power amplifiers are crucially important in determining a communications system cost, efficiency, size, and weight. Designing high power / high efficiency amplifiers that satisfy the system requirements (bandwidth, linearity, spectral mask, etc.) is challenging. It involves difficult trade-offs, proper understanding of the theory, and careful attention to details. Additionally, designing, building, and testing power amplifiers usually pushes test equipment and lab components to their limits and frequently results in damage to the circuit or lab equipment. This course will examine the different aspects of this challenge with emphasis on hand-on exercises and practical tips to build power amplifiers successfully. This course will give special attention to GaN power amplifiers. Differences between GaN pHEMT, Si LDMOS,GaAs MESFETs, and SiGe will be discussed.

Students are encouraged to bring their laptop computers to class. CAD software will be used to simulate design examples. The design software available for use in this public course is from National Instruments (formerly AWR).

Learning objectives

Upon completing the course you will be able to:

  • Learn the advantages and limitations of various technologies.
  • Gain an understanding of the pros and cons of various classes operations.
  • Learn how to characterize device for power amplifier design.
  • Acquire design know-how of high efficiency amplifiers.
  • Attain practical knowledge on the design of linear amplifiers.
  • Calculate the lifetime of power amplifiers in packaged and unpackaged assemblies.

Target Audience

Microwave engineers who want to design, fabricate, and test power amplifiers, in the 1-50 GHz frequency range, will benefit from this comprehensive design course. Basic knowledge of microwave measurements and transmission line (Smith Chart) theory is assumed.

Outline

Day One

Power amplifier Fundamentals
 • Device technologies: GaAs, LDMOS, GaN, Si, SiGe • Small signal model generation, transistor speed (ft, and fmax) calculation. • Power Amplifier Stability: even mode, odd mode. • Optimum power load estimation, calculation, and simulation. • Load-pull characterization of devices. • Device characteristics and non-idealities. • Dependence of transistor parameters on drive level. • Large signal models. • Power Amplifier biasing. • Exercise: GaN pHEMT small signal model generation.

Day Two

Conventional and High Efficiency Amplifier Design
 • Power amplifier classes A, B, AB, C, and D; concepts, designs, and examples. • Waveform engineering for maximum efficiency. • Class E Switching mode power amplifiers: Concept, Design, Limitations, Maximum Frequency, Exercises, and Examples. • Class F (and F-1) power amplifiers: Concept, Design, Limitations, and Examples. • Comparison of various classes: efficiency, output power, and frequency limitations. • Doherty power amplifiers • Effects of knee voltage, harmonic terminations, and nonlinearities. • GaN pHEMT power amplifiers

Day Three

Linearization Techniques, Power Combing, Packaging, and Reliability
 • Distortions in power amplifiers. • Harmonic balance and time domain simulations. • Linear/Non-linear Memory effects; electrical and thermal memory effects • Measures of Distortion: Third order intermodulation, ACPR, NPR, M-IMR • Linearization techniques: Feed Forward, Predistortion, LINC, Cartesian Feedback, Envelope Elimination and Restoration, Cross Cancellation. • Comparison of Linearization Techniques •  Real world design examples, challenges, and solutions. • Push-pull, Balanced amplifiers, and Traveling Wave Combiners. • Power combining techniques. • Exercise: Design of a power combiner. • Package design • Power Combing, Packaging, and Reliability • Thermal management and reliability calculations. • Biasing and transient considerations. • Exercise: calculating required biasing for 20+ year lifetime.

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