Effects of even-order terms on behavior model of envelope tracking transmitters

In the envelope tracking (ET) transmitters, the supply voltage is modulated according to the power levels for high efficiency. Such an operation generates quite different nonlinear characteristic in comparison with the conventional standalone power amplifiers (PAs). The effects of even-order nonlinear terms on ET transmitters are explored for the behavior model and digital predistortion technique. By including the even-order terms, the modeling accuracy of ET PA are significantly improved, especially for memory effect. To demonstrate the improved accuracy for the nonlinear prediction of the ET transmitter, the indirect learning based Enhanced Hammerstein predistorter is employed to compensate the transmitter. For the long term evolution signal with 10-MHz bandwidth and 6.5-dB peak-to-average power ratio, the predistorter including the even-order terms delivers a significantly better linearization result than the predistorter without the even-order terms.