Envelope tracking mechanism for improving efficiency of PA.

Envelope tracking circuit consits of a two ways circuit, a low frequency path driving PA drain according to envelop modulation BW, and a main path with input RF signal.
The PA efficiency is directly improved because the PA bias point moves with input signal, then you can reduce waste of power.

Envelope tracking means that, a envelope detector to adjust the bias of a linear PA, in order to prevent the PA from working in the shallow class A which is inefficient.........The key is always keeping the linearity param (IMR, ACPR...etc.) satisfied within your spec.

An alike way is named "Envelope Elimination & Restoration" (EER or Kahn method), the difference is the PA in EER is a nonlinear PA(switching PA)...driven by a phase-only signal and modulated by a envelope driver......


If the envelope and phase signal is already apart in baseband, another name of "polar method" is more usual. In recent years, many papers on GSM PA --> EDGE PA adopted this method.