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Evaluation of GaAs Power MESFET for Wireless Communication - PowerPoint PPT Presentation


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Evaluation of GaAs Power MESFET for Wireless Communication. Li Xiang. Outline. Introduction on power amplifiers for wireless communications Specific requirements for power amplifier design How to evaluate efficiency and linearity Design example of a low-distortion power MESFET Summary.

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Presentation Transcript
outline
Outline
  • Introduction on power amplifiers for wireless communications
  • Specific requirements for power amplifier design
  • How to evaluate efficiency and linearity
  • Design example of a low-distortion power MESFET
  • Summary
introduction on rf power amplifiers
Introduction on RF Power Amplifiers
  • Technologies suitable for RF power amplifiers
    • Si BJT, MOSFET
    • GaAs MESFET, HFET, HBT
    • SiGe HBT
    • InP HFET
    • Wide bandgap materials
  • Specific requirements for power application
    • Thermal conductivity
    • Breakdown voltage
    • Efficiency
    • Linearity
    • Reliability
efficiency
Efficiency
  • Two normally used definitions:
    • Drain efficiency:
    • Power-added efficiency
  • Methods to improve the efficiency
    • Suppress leakage
      • Schottkey gate leakage
      • Substrate leakage
    • Enhancement mode operation
linearity
Linearity
  • Definitions of linearity
    • 1 dB gain compression point
    • Third-order intermodulation distortion
    • Adjacent channel leakage power
design example low distortion power mesfet
Design Example:* Low-distortion Power MESFET
  • Goal:
    • To design a low-distortion GaAs MESFET suitable for digital communication system using /4 shift QPSK modulation
  • Origination of distortion:
    • Frequency dispersion of transconductance/drain current originated from electron trapping at the gate surface
  • New structure to improve the distortion performance:
    • Form semi-insulating setback layer under the gate

* H. Furukawa et. al. IEEE Transactions on Electron Devices, vol. 43, No. 2, 1996

frequency dispersion of i dss
Frequency Dispersion of Idss
  • FETs with setback layer show smaller frequency dispersion
    • 15-20% improvement at 1 MHz
power characteristics at 950 mhz
Power Characteristics at 950 MHz
  • Test signal: /4 shift QPSK modulation
  • Operational condition: class AB
  • Improved linearity: P1dB 34.5 dBm 36 dBm
im3 characteristics
IM3 Characteristics
  • Bias point: 10% Idss
  • Improved IM3: 10 dB smaller
distortion characteristics
Distortion Characteristics
  • Channel separation: 50 kHz
  • Improvements: 11 dB lower at 31.5 dBm output power
summary
Summary
  • A brief introduction has been given on how to evaluate GaAs power FETs.
  • A GaAs MESFET design with a semi-insulating setback layer has been presented, and the distortion characteristics have been evaluated.