Interference cancellation for higher harmonics of supply-modulated efficient RF power amplifier systems

Abstract

In building highly efficient transmitters of today, one is forced to sacrifice linearity for efficiency. Some of the highest power amplifier efficiency figures are reported by envelope tracking (ET) amplifiers. These amplifiers can generate strong higher-order harmonics, which can lead to interference with receivers operating at the harmonic frequencies. Using non-linear interference cancellation, we can help to remove the interference being caused in those receivers. This paper looks at the problem of modeling the third and second-order harmonic emission from an ET amplifier. It derives the non-linear kernel for estimating such interference. This kernel has been rigorously expanded to show its correlation with the various harmonics and its effectiveness in predicting the harmonic content. We then set up an envelope amplifier test-bench to capture harmonic signal content and cancel it using the derived kernel model. The experiment yields excellent agreement with theory and provides a validation of the system and concept.