Nonlinear Behavioral Modeling of W-CDMA InGaP HBT Power Amplifiers for Predicting Spectral Regrowth

초록

Simple and accurate nonlinear behavioral models of power amplifiers (PAs) are required when a total radio-frequency (RF) transceiver is designed, especially on a board, because the simulation time depends on the complexity of the model. The wideband code division multiple access (W-CDMA) RF standard requires the suppression of spectral regrowth, which may interrupt communication on an adjacent channel. Spectral regrowth can possibly be predicted for the total RF system. The spectral regrowth caused by nonlinearity appears differently depending on the materials of the RF transistor or the RF modulations. Therefore, it is important to find a proper InGaP heterojunction bipolar transistor (HBT) power amplifier model for W-CDMA by considering its complexity and accuracy. The polynomial model is chosen to predict the spectral regrowth because InGaP HBT is relatively linear, exhibiting low memory effect for W-CDMA modulation. Various high-order polynomial nonlinear equations from 7th- to 17th-order polynomial functions were established for PA modeling and the results were compared with each other. As a result, a polynomial model of 11th- or more order can predict the adjacent channel power leakage less than about a 0.9-dB error over the whole 10-dB output power range from 15.4 to 25.4 dBm for W-CDMA InGaP HBT power amplifiers.

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