Formulations and a Computer-Aided Test Method for the Estimation of IMD Levels in an Envelope Feedback RFIC Power Amplifier

This paper presents new formulations, together with an efficient computer-aided test approach intended for radio frequency integrated circuit power amplifiers (PAs), allowing the estimation of linearity requirements for the circuit blocks typically found in the error signal path of an envelope feedback amplifier. The formulations are based on a three-tone excitation, allowing analysis of intermodulation distortion (IMD) within the feedback system using parameterized peak-to-average envelope voltage. They are also based on a fifth-degree representation, and may be extended to higher degrees of nonlinearities in the RF PA block, enabling IMD analysis of envelope feedback amplifiers at low power. The approach proposed in this paper circumvents the difficulty of measuring error signals during closed-loop operation for troubleshooting purposes. This approach is also very useful for computer-aided test setups intended for development work independent of the often idealized circuit simulation environment.