RF Power Amplifier


Introduction to RF Power Amplifiers

An RF power amplifier(PA) is the last stage which handles maximum amount of power in a transmit chain. In order to deliver large amount of power to load or antenna, it has to handle large signal swings which introduces distortion in the power output due to non-linear characteristics of the transistors. The amount of the distortion a PA can tolerate depends on the modulating signal (wireless standard or modulation technique) to be amplified. The power efficiency of power amplifier influences the overall efficiency of a radio.

 

Performance Metrics

Metrics defined in standard

  • Output Power
  • Spectral Mask
  • ACPR (Adjacent Channel Power Ratio)
  • Signal Modulation

Metrics not defined in standards, but still important from the design perspective are

  • PAE (Power Added Efficiency)
  • Drain Efficiency
  • Power Gain
  • P_{o,1dB} : It is the output signal power at which the small signal gain is compressed by 1-dB. It quantifies the linear power handling capability of an amplifier

 

Modes of Operation

  • Class-A
  • Class-B
  • Class-AB
  • Class-C
  • Class-D
  • Class-E
  • Class-F
  • Class-G
  • Class-H

 

Design Example

 

Power Amplifier Topologies

RF Power Amplifier Manufacturers

 

References