Based On The Vector Signal Processing Of Rf Power Amplifier Predistortion Technology Research

As a kind of linearization techniques, predistortion has become the main technique used in base stations because of its easy realization, low cost, good performance. Compared with digital predistortion and radio frequency (RF) predistortion, the hybrid digital/RF predistortion integrates the advantages of the digital predistortion and RF predistortion. On the one hand, it overcomes the debugging difficulties of RF predistortion, on the other hand, it conquers the inconvenience of collecting the base data in digital predistortion. This article adopts the method of vector signal processing to realize the hybrid digital/RF predistortion and the main content of this article is the simulation and validation test of the hybrid digital/RF predistortion.The problems analyzed and solved in this dissertation are listed as follows,1. The vector signals (I/Q) are adopted to realize the adjustmet of the signal’s amplitude and phase rather than the tranditional method of using the cascade of the attenuator and phase shifter.2. The hybrid digital/RF predistortion validation system is bulit. The results of the simulation and experiment show that this structure of the hybrid digital/RF predistortion can improve the linearity of the power amplifiers (PAs). In the experiment, the detected input signal’s envelope is used as the index of the look up table (LUT), the output as the control signal of the vector signal element to adjust the variation of gain and phase to achieve the predistortion.3. The impacts of the delay mismatches of the two paths, quadrature imperferction of the vector modulator and the filters on the performance of the predistortion system are analysed. In order to make up the delay mismatches of the two paths, the method of adding large delay element in the RF path and adding fractional delay filter in the small signal processing path is adopted. Besides, compensation algorithms in the LUT make up the non-idealities of the vector modulator and the filters.This data is based on the measurements of the PA on a Vector Signal Generator and Vector Spectrum Analyzer (VSG-VSA) test bed, model on the data above and save the predistortion parameters in the LUT to achieve digital control. The test is done by using a Freescale’s PA working at2.14GHz. Under the condition of without lowering the output power, the results show that this method can achieve over26dB of the IM3correction, over a1MHz bandwidth, and over21dB for a2MHz bandwidth. The results of the experiments above show that the scheme of the hybird RF/digital predistortion can reduce out-of-band spectral emissions.