Impact of envelope shaping on the linearity of envelope tracking transmitters

A simulator is described for evaluating the impact of timing misalignment between the envelope and RF paths in an envelope tracking (ET) transmitter. Impact is measured by the degradation of the output adjacent channel power ratio (ACPR) when amplifying a 5MHz bandwidth 3GPP Long Term Evolution (LTE) signal. This is modelled with an ideal power amplifier (PA) which has no drain voltage gain dependency. Envelope shaping (ES) is applied and shown to increase the tolerance to timing misalignment, indicating that the nulls of the envelope signal are more susceptible to misalignment than the peaks. Finally measurements from a practical modulator are integrated into the simulator and its impact on ACPR evaluated.