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What is back off power in amplifier ?

This page describes back off power in amplifier. It also mentions difference between input back off power and output back off power of power amplifier.

Amplifier Back off power

In applications which require linear Power Amplifier PA) due to PAR, it is essential to operate amplifier at certain power back off from peak power point in order to avoid clipping the waveform.

For example if there is PAR of 10 dB than amplifier should be operated at 10 dB low power to avoid clipping.

Power back off

All amplifiers eventually clip, that is output can not be higher than some multiple of power supply. Peak amplifier output can be arbitrarily large, but average output power will limit.

If we back-off sufficiently from peak so that the amplifier never clips, then we compromise the efficiency. To meet EVM specifications, we can generally make a compromise and choose sufficient back-off.

Input back-off power vs Output back-off power

Let us understand two power back-off types viz. input back-off (IPBO) and output back-off (OPBO).
Input Back-off : Power level at RF amplifier input relative to input power which produces maximum output power.
Output Back-off : Power level at RF amplifier outout relative to maximum output level possible.

Example of Input back off power:
Inputs: Pin (nominal) = -25 dBm, Pin at which amplifier generated max. power output = -20 dBm
Input back off power = 5 dB

Example of output back off power:
Output power (Maximum) = +40 dBm , Nominal output level = +34 dBm
Output Back off power = 6 dB



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