Effect of envelope amplifier nonlinearities on the output spectrum of Envelope Tracking Power Amplifiers

This paper examines the sources of Receive Band Noise (RxBN) in the Envelope Tracking Power Amplifier (ETPA) system. The Envelope Amplifier (EA) nonlinearity is found to be the dominant cause. The output spectrum of the ETPA is compared for the cases of highly linear class-A EA and nonlinear EA. To improve the out-of-band noise performance of the ETPA, Digital Pre-Distortion (DPD) on the envelope path is proposed. It is shown that the out-of-band noise is reduced by 10 dB at 100 MHz offset if a highly linear envelope amplifier is used.