A predistorter for a power amplifier affected by the even-order distortion [W-CDMA base station applications]

The even-order distortion at baseband perturbs bias conditions of a power amplifier (PA), and creates a new odd-order distortion, which shows a hysteresis effect on AM-AM and AM-PM characteristics. This effect combined with the original odd-order distortion generates imbalanced inter modulation distortion (IMD) outside of the signal bandwidth, which depends on frequency separation. The imbalanced IMD limits the compensation performance of conventional predistorters. We propose a new predistorter for W-CDMA base stations. The predistorter compensates the distortion to less than 60 dBc, even if the PA is affected by even-order distortion. The PA model and the adaptive algorithm are also shown.