Design, implementation and verification of a digital predistorter overdrive protection module

by V (Ville) Kivelä

Institution: University of Oulu
Year: 2016
Keywords: Electrical Engineering
Posted: 02/05/2017
Record ID: 2133140
Full text PDF: http://urn.fi/URN:NBN:fi:oulu-201606092483


The goal of this thesis was to design, implement and verify an overdrive protection module to digital predistorter's output path. Former Nokia mobile wireless base-station digital predistorter designs omitted the use of an overdrive protection module, did the overdrive protection in the analog domain or used a simple digital signal clipping approach. This has caused problems with transmission signal quality and even destruction of radio frequency power amplifiers in certain circumstances. Analog limiters might be too slow to react to sudden changes in the signal while hard digital signal clipping causes significant harmonic distortion and intermodulation distortion which is especially harmful for wideband multicarrier modulations. The overdrive protection module described in this thesis tries to solve those issues by applying digital time-domain smoothing filters directly to the output path of the digital predistortion system. The digital predistorer is a submodule of a custom Nokia 2G/3G/4G-LTE base-station digital front end integrated circuit. In this thesis the theoretical background needed to understand the basic functionality of an digital predistorter is first explained and then the overdrive protection's algorithm specification is introduced. The algorithm specification was used as the foundation for overdrive protection module's register transfer level micro-architecture design. The design was implemented entirely with Very High Speed Integrated Circuit Description Language. The overdrive protection module was fully tested and verified using a in-house developed verification flow which is based on the universal verification methodology. The language in which the test bench was written and test cases were developed was SystemVerilog. After comprehensive verification work the overdrive protection module was shown to fully adhere to its specifications passing all required tests. The module also passed hardware emulation testing and was successfully implemented into the digital front end application specific integrated circuit silicon. The overdrive protection module designed in this thesis could be modified to support even higher data rates and wider bandwidths for example to support future applications in a 5G mobile radio system. The module could also be adapted to be used in a field programmable gate array chip with relatively small changes to the designs hardware description. Tämän työn tavoitteena oli suunnitella, toteuttaa ja testata digitaalinen ylikuormituksenestopiiri digitaalisen esisäröttimen lähtöön. Nokian aikaisemmissa matkapuhelinverkon tukiasemissa ei ollut ollenkaan signaalirajoittimia, rajoitus tehtiin analogiaelektroniikalla tai rajoitukseen käytettiin yksinkertaista digitaalista signaalitason rajoitinta. Tämä on aiheuttanut ongelmia lähetyssignaalin laadun kanssa ja joissain tapauksissa radiotaajuustehovahvistimia on jopa tuhoutunut. Analogiset rajoittimet saattavat olla liian hitaita reagoimaan erittäin nopeasti tehotasoaan vaihteleviin digitaalisiin signaaleihin ja jyrkkä…