Feed forward amplifier system and method using the pilot frequency from a positive feedback pilot generation and detection circuit to improve second loop convergence

A method for controlling alignment of a feed forward amplifier system comprising an input for receiving an input signal, a first carrier cancellation control loop coupled to the input and having a main amplifier, a second error cancellation control loop coupled to the first control loop and having an error amplifier and a gain adjuster and a phase adjuster, and an output coupled to the second control loop and providing an output signal, the method comprising:

• sampling the output signal;
• generating a variable frequency pilot signal from the sampled output signal and injecting it into the first control loop;
• detecting the frequency of the generated pilot signal;
• adjusting the settings of the gain and phase adjusters in said second control loop from a first adjustment setting to a second adjustment setting using an alignment direction;
• detecting the frequency of the generated pilot signal after said adjusting;
• detecting the difference in the frequency of the generated pilot signal between said first and second adjustment settings;
• altering the alignment direction using the frequency difference between said first and second adjustment settings;
• and
• adjusting the settings of the gain and phase adjusters in said second control loop from the second setting to a third setting using the altered alignment direction.

A feed forward amplifier, comprising:

• an RF input for receiving an RF signal;
• a carrier cancellation loop comprising a main amplifier receiving and amplifying said RF signal, a main amplifier output sampling coupler, a first delay coupled to the RF input and providing a delayed RF signal, and a carrier cancellation combiner coupling the delayed RF signal to the sampled output from the main amplifier;
• an error cancellation loop comprising an error amplifier receiving and amplifying the output of the carrier cancellation combiner, a gain adjuster and a phase adjuster coupled between the carrier cancellation combiner and error amplifier and respectively receiving gain and phase adjustment control signals, a second delay coupled to the output of the main amplifier, and an error injection coupler combining the output from the error amplifier and the delayed main amplifier output from the second delay so as to cancel distortion introduced by the main amplifier;
• an RF output coupled to the error injection coupler output and providing an amplified RF signal;
• an output sampling coupler for providing a sampled output of the amplified RF signal;
• a positive feedback pilot generator circuit for generating a pilot signal from the sampled output of the amplified RF signal and providing the pilot signal to the input of the main amplifier, the positive feedback pilot generator circuit including a frequency detector for detecting the frequency of the generated pilot signal and providing a pilot frequency signal;
• and
• a controller programmed with a loop control algorithm, the controller coupled to receive the pilot frequency signal and outputting said gain and phase adjustment control signals to said gain adjuster and phase adjuster, the controller adjusting the direction of change of the gain and phase adjustment control signals provided to said gain adjuster and phase adjuster based on changes in the pilot frequency signal.