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Evaluation of GaAs Power MESFET for Wireless Communication

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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Evaluation of GaAs Power MESFET for Wireless Communication

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  1. Evaluation of GaAs Power MESFET for Wireless Communication Li Xiang

  2. 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

  3. 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

  4. 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

  5. Linearity • Definitions of linearity • 1 dB gain compression point • Third-order intermodulation distortion • Adjacent channel leakage power

  6. 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

  7. Fabrication Flow

  8. Frequency Dispersion of Idss • FETs with setback layer show smaller frequency dispersion • 15-20% improvement at 1 MHz

  9. RF Power Measurement

  10. Power Characteristics at 950 MHz • Test signal: /4 shift QPSK modulation • Operational condition: class AB • Improved linearity: P1dB 34.5 dBm 36 dBm

  11. IM3 Characteristics • Bias point: 10% Idss • Improved IM3: 10 dB smaller

  12. Distortion Characteristics • Channel separation: 50 kHz • Improvements: 11 dB lower at 31.5 dBm output power

  13. 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.

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