A method for estimating the IMD performance requirements of circuit blocks in the error signal path of an envelope feedback amplifier

This paper presents an equations based approach for estimating the linearity requirements for the RF envelope detectors and the other circuit blocks typically found in the error signal path of an envelope feedback amplifier. The proposed equations are based on a three-tone excitation and a 5th degree power series representation of the nonlinearities in the RF power amplifier block, which allows estimating inter-modulation distortion within the feedback system using peak-to-average envelope voltage ratios that may be parameterized. The proposed approach for validating and optimizing the linearity performances of the envelope detectors in open loop conditions, as a function of feedback parameters and closed loop IMD goals, can be used to analyze envelope feedback systems during the design phase, and may be particularly helpful for circuit characterization independently of the simulation environment.