Interference cancellation for odd harmonics of envelope tracking RF power amplifier systems

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