Envelope tracking describes an approach to RF amplifier design in which the power supply voltage applied to the power amplifier is constantly adjusted to ensure that the amplifier is operating at peak efficiency for the given instantaneous output power requirements.

A conventional RF

Radio frequency

Radio frequency is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals...

 amplifier designed with a fixed supply voltage operates most efficiently only when operating in compression.

Amplifiers operating with a constant supply voltage become less efficient as the crest factor

Crest factor

The crest factor or peak-to-average ratio or peak-to-average power ratio is a measurement of a waveform, calculated from the peak amplitude of the waveform divided by the RMS value of the waveform.C =...

of the signal increases, because the amplifier spends more time operating below peak power and, therefore, spends more time operating below its maximum efficiency.