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We present in this paper an advanced adaptive baseband/RF predistorter that integrates the concept of the software-defined radio technology into the power-amplifier (PA) linearization area. The linearizer performs an instantaneous characterization of the PA, using two digital receivers, in order to supply its instantaneous AM-AM and AM-PM curves. It then determines an inverse function that represents the best fit to the reciprocal of the PA behavior. Code-division multiple-access and third-generation standard signals applying different stress level on the PA are used to evaluate the performance of the linearizer. The system is validated using digital signal processing/RF co-simulation for a typical 44-dBm class-AB PA. To estimate the performance of the linearizer under realistic condition, experimental results have been carried out in open-loop condition, supported by a software-instruments connectivity, for a 20-W class-AB PA operating at 1.96 GHz. Results for different cases of standards signals reveal a significant reduction, in the order of 5 dB, in effective output power backoff.
Microwave Theory and Techniques, IEEE Transactions on (Volume:52 , Issue: 9 )
Date of Publication: Sept. 2004