Complex Gain Predistortion in WCDMA Power Amplifiers with Memory Effects

Power amplifiers are essential components in communication systems and are inherently nonlinear. Thenonlinearity creates spectral growth beyond the signal bandwidth, which interferes with adjacent channels. It also causesdistortions within the signal bandwidth, which decreases the bit error rate at the receiver. In digital predistortion system, aninverse characteristic of power amplifier is generated and its amplitude and phase are combined to the signal input. So theinput signal is predistorted and the power amplifier response is corrected. This process has to be controlled at high accuracyto achieve a satisfactory compensation effect. The inverse characteristics are stored in a memory (look-up table) and this dataare updated using an error that is produced by comparing the outputs of power amplifier with the input signals. In this paper anovel technique for compensating such effects is proposed. It is a combination of two techniques, memory polynomialpredistortion and the gain based predistorter method. This method is compared with the other technique, memory polynomialmethod and validated using a 1.9 GHz 60W LDMOS power amplifier and various signals such as 2-carrier WCDMA with 10MHz carrier spacing and 15 MHz bandwidth. Simulations and results show improvement in ACLR reduction and EVM withapplying this method