Feed forward RF power amplifier with high efficiency main amplifier and highly linear error amplifier

A feed forward amplifier, comprising:

• an RF input for receiving an RF input signal, said RF input signal having an average operating amplitude range and further comprising intermittent signal peaks in a peak range exceeding said average operating range;
• a main amplifier receiving and amplifying said RF input signal, said main amplifier having a first transfer characteristic over its range of operation, said first transfer characteristic having a substantially linear portion corresponding to said average operating amplitude range of said RF input signal and a nonlinear portion corresponding to said RF input signal peak range;
• a main amplifier output signal sampler;
• an error path delay circuit coupled to the RF input and providing a delayed RF input signal;
• a first cancellation combiner coupling the delayed RF input signal to the sampled output from the main amplifier;
• an error amplifier for amplifying the output of the first cancellation combiner, said error amplifier having a second transfer characteristic over its range of operation, said second transfer characteristic having a linear portion corresponding to substantially all of said average and peak operating amplitude range of said RF input;
• a main path delay circuit coupled to the output of the main amplifier;
• a second cancellation combiner combining the output from the error amplifier and the output of the main path delay circuit so as to cancel distortion introduced by the main amplifier;
• and
• an RF output coupled to the second cancellation combiner and providing an amplified RF output.

A method for amplifying a broad bandwidth RF input signal, comprising:

• receiving an RF input signal, said RF input signal having an average operating amplitude range and further comprising intermittent signal peaks in a peak range exceeding said average operating range;
• amplifying said RF input signal employing a main amplifier having a first transfer characteristic over its range of operation, said first transfer characteristic having a substantially linear portion corresponding to said average operating amplitude range of said RF input signal and a nonlinear portion corresponding to said RF input signal peak range;
• sampling the main amplifier output;
• delaying the RF input signal and providing a delayed RF input signal;
• coupling the delayed RF input signal to the sampled output from the main amplifier so as to provide a distortion component of said sampled output from the main amplifier;
• amplifying the distortion component employing an error amplifier having a second transfer characteristic over its range of operation, said second transfer characteristic having a linear portion corresponding to substantially all of said average and peak operating amplitude range of said RF input;
• delaying the output of the main amplifier;
• combining the amplified distortion component and the delayed output of the main amplifier so as to cancel distortion introduced by the main amplifier and providing an amplified RF output.