Out-of-band compensation for non-linear device

A method, for reducing nonlinear distortion in a nonlinear device which has a nominal operating point above which it reaches saturation for increased levels of power in an input signal, comprising the steps of:

• (a) combining an out-of-band signal with an input signal to produce a combined signal having a power substantially equal to a nominal linear operating point for a nonlinear device;
• (b) maintaining the power of said combined signal at a level substantially equal to said nominal operating point;
• (c) processing said combined signal in said nonlinear device to produce an output;
• and
• (d) filtering said output to remove said out-of-band signal.

Apparatus for reducing nonlinear distortion introduced when a signal is processed by a nonlinear device which has a nominal operating point above which it reaches saturation for increased levels of power in an input signal, comprising:

• a nonlinear device input;
• a signal source generating a variable magnitude out-of-band signal, with respect to said input signal;
• a combiner connected in series with said nonlinear device input and to said signal source to receive and combine said out-of-band signal with said input signal to produce a combined signal for input to said nonlinear device;
• an automatic gain control (AGC) circuit coupled to said combiner to maintain the power of said combined signal within a predetermined substantially constant power magnitude envelope which is less than or equal to said nominal operating point for said nonlinear device, comprising:
• a detector coupled to said combiner to detect the power of said combined signal and produce a detected power signal;
• an adder coupled to an output of said detector to add the negative of said detected power signal with a signal having a value substantially equal to said nominal operating point to produce a power difference signal;
• a second filter coupled to an output of said adder to filter said power difference signal to generate a gain update signal;
• and
• a variable gain amplifier coupled to an output of said second filter to amplify said out-of-band signal according to said gain update signal to cause said combined signal to have a power substantially equal to said nominal operating point;
• and
• a filter coupled to an output of said nonlinear device to remove said out-of-band signal from said output of said nonlinear device.