Feed-forward linearization without phase shifters

A method of designing an FIR filter for use in a power amplifier, the method comprising:

• choosing a center frequency of operation of the FIR filter;
• choosing a delay difference Δτ between paths of the FIR filter equal to
• Δ
• 
• 
• τ
• =
• 2
• 
• 
• m
• -
• 1
• 2
• 
• 
• f
• c
• ,
• where m is an integer greater than zero, and fc is the center frequency of operation of the FIR filter;
• choose which path of the FIR filter is to have a least time delay, so that the FIR filter has a z-domain impulse response being proportional to one of H(z)=1+α1z−1+α2z−2 and H(z)=α1+1·z−1+α2z−2;
• and
• adjusting scalar multipliers in two of three paths of the FIR filter to adjust roots of the z-domain impulse response to have a selected frequency response.

A power amplification system, comprising:

• a power amplifier having an output;
• an FIR filter, the FIR filter having:
• a main path having a first time delay and a main path output;
• a second path having a second time delay, a first scalar multiplier, and a second path output;
• a third path having a third time delay, a second scalar multiplier and a third path output, the first, second and third time delays being integer multiples of a period of time;
• a first input configured to receive the output of the power amplifier and to channel the output of the power amplifier to the main path of the FIR filter;
• a first adder configured to receive the output of the power amplifier and a reference signal, and to channel a sum of the output of the power amplifier and the reference signal to the second and third path of the FIR filter;
• a second adder configured to sum the main path output with the second path output and the third path output.