Patent ID: 7339426
Filing Date: 2008-03-04
Classification: H03F,H03G

Abstract:
1. A power amplifier system, comprising: an input for receiving an RF input signal including a modulated RF carrier having a dynamically varying envelope; a first signal path coupled to the input and including an RF amplifier receiving and amplifying the RF input signal including said carrier and envelope, the RF amplifier having a power supply input; a DC power supply; and a second signal path coupled to the input and comprising an envelope detector and an envelope amplifier responsive to the output of the envelope detector and coupled to the DC power supply and RF amplifier, wherein said envelope amplifier provides a power supply signal to the RF amplifier which varies with the envelope of the input signal to control the back off of the RF amplifier; wherein said envelope amplifier comprises a switching circuit which switches a power supply signal into said RF amplifier power supply input with a frequency related to the envelope of the input signal; wherein said envelope amplifier further comprises a threshold detector; and wherein said envelope amplifier further comprises a preamplifier and a push pull circuit, wherein said preamplifier is coupled to the envelope detector output, said push pull circuit is coupled to the preamplifier output, and said push pull circuit and said switching circuit are coupled to said DC power supply.