Feedback Low Sampling Rate For Digital Predistortion Of Broadband RF Power Amplifier

To improve the business data rate, it is clearly presented that the transmissionbandwidth needs to be extended to100MHz in IMT-Advanced wireless mobilebroadband communication system. The broadband radio frequency (RF) poweramplifier (PA) are inherently nonlinear and memory effect, as the indispensable keycomponent in the communication system.However,100MHz signal will be extended to more than500MHz caused by PA’snonlinear spectral regrowth, which bring new problems to broadband digitalpredistortion (DPD) technology, for example,(1) Increased the contradiction between the PA efficiency and the PAlinearization, followed the increase of the bandwidth requirements.(2) Lead to the PA feedback path ADC conversion’s high sampling rate problem,followed the increase of the PA output signal bandwidth. And novelbroadband signal DPD solutions need to be presented for wideband signals.To cure the above problems，this paper study the existing DPD technology basedon the characteristics and behavioral modeling of PA. And two kinds of low samplingrate DPD solutions are proposed to lower the feedback signal sampling rate.First, the band-limited DPD method is proposed for the case of PA linearizationrequirement in a certain bandwidth range. In this method, the band pass filter (BPF) isused in the feedback loop to form band-limited feedback signal. Then, the band-limitedfunction is inserted behind the traditional pre-distorter to construct band-limitedpredistortion model. The analysis and simulation results show that, when the PA inputand feedback signals are respectively100MHz and300MHz, the ACPR can improveby25.62dB.The ADC sampling rate is reduced more than40%.Second, the deconvolution DPD method is presented for the narrow feedbackbandwidth. In this method, a BPF is added in the feedback path before ADC, and thedeconvolution is performed to recover the PA output signal. The analysis andsimulation results indicate that, when the PA input signal is100MHz, and the feedbacksignal sampling rate merely needs368.64MHz, is able to improve the ACPR by23.00dB. The ADC sampling rate can be reduced by about60%.The research in this thesis, the proposed DPD methods can realize the PAlinearization in a low sampling rate, which solve the problem of high sampling rate ofPA feedback signal. The research can be applied to efficient broadband RF PA system,and has important theoretical and practical value.