A Power Amplifier (PA)increases the strength of the incident information-carrying signal to a level suitable for transmission. It differs from a Driver Amplifier only in the output level it is operating at. In this site we are defining PAs as devices capable of producing 100 mW or more.
Power amplifiers have output matches that present the desired load line, i.e. they are set for output power, efficiency, and distortion characteristics rather than for best reflection. The optimum match for a discrete transistor used as a PA is a complex function of bias, desired output power, and desired linearity as well as device parasitics, and typically needs to be characterized for each individual application. Commonly, the output of a power amplifier will not have a low VSWR. Because of the high power levels involved, heatsinking and thermal management are very important considerations for power amplifiers.
Power amplifiers are often chartgorized by type of bias. A class A amplifier has a bias point that does not shift as a function of drive level. Class A ampliifers have the best linearity, and the poorest efficiency (the maximum theoretical power added efficency for a Class A amplifier is 50%). Class C amplifiers have their bias set entirely by the incident RF signal. They are less linear than class A amplifiers, but far more efficient (60% to 70% efficiency is common). Class AB amplifiers have a bias level partially set by DC circuitry, but adjusted by the RF drive. These amplifiers are nearly as efficient as Class C amplifiers, but far more linear.
Agilent Technologies Products for Power Amplifier Applications
- Discrete Devices:
- Bipolar Transistors as Power Amplifiers
- Output Power comparison for Bipolar Transistors
- GaAs FETs as Power Amplifiers
- Output Power comparison for GaAs FETs
- Integrated Circuits:
- ICs for RF/uW Power Amplifiers
- Output Power comparison - RF/uW ICs
- ICs for millimeter wave Receivers, Direct Tansmitters, or Upconverting Transmitters
- Output Power comparison - mmw ICs