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Design of GaN Power Amplifiers (Part 1) by Dr. Edna Hickey

May 30, 2024

Design of GaN Power Amplifiers (Part 1) with Dr. Edna Hickey

Introduction

  • Host: Mike Hamilton (I Triple E Microwave Theory and Technique Society)
  • Speaker: Dr. Edna Hickey
  • Objective: Discuss the design of Gallium Nitride (GaN) power amplifiers

Housekeeping

  • Presentation archived, recording available 24 hours after
  • Questions can be submitted anytime during the talk
  • Interface tips: enlarge slides, full screen mode, adjust volume
  • Slides downloadable via the resource list link

Speaker Background

  • Dr. Edna Hickey: Pioneered RF, microwave, and millimeter wave components development at Westinghouse and Northrop Grumman
  • Holds 9 patents and numerous awards, including the George Westinghouse Innovation Award
  • Over 3,000 professionals lectured since 1983

Presentation Overview

  1. Introduction to power amplifiers
  2. Importance of GaN transistors
  3. Material properties and cooling
  4. High reliability factors
  5. Transistor usage options (actual, mimic, foundry designs)
  6. Reliable operation guidelines
  7. Step-by-step design example for Class A operation

Key Parameters for Power Amplifier Design

  • High power, efficiency, and reliability
  • Good frequency range
  • Non-complex circuitry
  • Wide bandwidth
  • Linear operation for amplitude modulation schemes
  • Cost considerations

GaN Transistor Structure

  • Chip design: Input gate, output drain, ground source
  • Gate fingers: Tailored to frequency of operation
  • Packaging: Various types for different applications (high/low cost packages)

RF Output Power Formula

  • RF output power = function of V_max and I_max
  • Comparison of semiconductor materials (Silicon, GaAs, GaN)

Advantages of GaN Transistors

  • High bandgap (better high-temperature operation)
  • High breakdown field (high voltage)
  • High thermal conductivity when placed on silicon carbide substrate
  • Enhanced electron mobility for higher frequency operations

Reliability Considerations

  • Ability to handle short pulses with high power
  • Manage high VSWR scenarios
  • Maintain low junction temperatures
  • Gate current management to avoid metal migration

Substrate Materials

  • Importance of thermal conductivity and expansion
  • Preferred materials: Copper, copper molybdenum, aluminum diamond
  • Proper layout to avoid overheating

GaN Transistor Types and Foundries

  • Key suppliers: Wolfspeed (Cree), TriQuint (now Qorvo), Sumitomo, Northrop Grumman, HRL
  • Foundries: Raytheon, BAE, HRL, DAU, Fujitsu

Key Device Structures and Enhancements

  • T-gate structure for high electron mobility
  • Field plate implementation to spread depletion region and improve breakdown voltage

Practical Design Example

  • Stability analysis and correction
  • Load line determination
  • Step-by-step matching circuit design
  • Example demonstrated 45 dBm power (30+ watts) with 51% efficiency

Reliability Enhancements in GaN Devices

  • Improved processing to manage traps and dislocations
  • High input IP3 for improved linearity
  • Structural enhancements for electron confinement

Turn-on/Turn-off Sequence for GaN Transistors

  • Proper sequence to avoid damaging the transistor
  • Use of regulators to facilitate proper sequencing

Summary and Next Steps

  • Part Two teaser: Class B operation, F-1 class, Doherty amplifier, and more

Q&A Highlights

  • Reliability extrapolation based on specific operating conditions
  • Efficiency management when combining transistors
  • Differences between GaN HEMT vs GaAs HBT or CMOS in terms of design methodology
  • Effects of traps and memory on low frequency and noise

Full transcript