Using fractional delay computations to improve intermodulation performance

Abstract

Enhancing the intermodulation performance of an RF power amplifier by determining a coarse time delay represented by an integer T1; determining a reference point for a transmitted signal waveform of the RF power amplifier; shifting the waveform by a set of offsets comprising a plurality of non-integer fractional steps from (T1−Xd) to (T1+Xd) where T1 is the integer and Xd is a non-integer fractional step size value for defining fractional steps about the integer T1 such that the non-integer fractional steps progress in a positive direction as well as a negative direction; correlating the transmitted signal waveform with a feedback signal waveform to obtain a respective correlation value for each of corresponding fractional steps; obtaining an accurate fractional delay value by selecting a fractional step having a highest respective correlation value; applying the obtained correct fractional delay value to the transmitted signal waveform to provide a compensated transmitted signal waveform, and combining the compensated transmitted signal waveform with the feedback signal waveform to reduce at least one intermodulation product of the RF power amplifier.