资源描述：
《外文翻译--系统芯片》由会员上传分享，免费在线阅读，更多相关内容在教育资源-天天文库。
1、怼羡袼暄蓿前蓝盘潮喈百英文资料：淙慈嵯馀束忿嫉糙绳妨汩1Introduction洋钞碗贸践回夜磺眩涮我Theuseofthesystem-on-chip(SoC)techniqueallowsforanunprecedenteddegreeofminiaturizationofrubidiumatomicfrequencystandards.Acompactdirectdigitalfrequencysynthesizer(DDFS)playsanimportantroleinourminiaturizedrubidiumatomicfrequencystandards
2、formodulated5.3125MHzsinewavegeneration.DDFSsareabletogeneratesingle-phaseorquadraturesinusoidswithexcellentfrequencyresolution,goodspectralpurity,veryfastfrequencyswitching[1],andphasecontinuityonswitching.Generally,aDDFSconsistsofaphaseaccumulator,aphasetosineconverter(sineROM),andaDAC
3、.Ateachclockpulse,thephaseincrementwordinafrequencyregisterisaddedtothephasevaluepreviouslyheldinthephaseaccumulator.Thephasevalueisgeneratedusingthemodulo2joverflowingpropertyofajbitphaseaccumulator[2].Theoutputfrequencyistherateoftheoverflows,辑哥抬透闪饧鼓宠瘙佼岳whereΔpisthephaseincrementword,j
4、isthenumberofphaseaccumulatorbits,fclkisthesystemclockfrequency,andfoutistheoutputfrequency.Thepreviousconstraintisrequiredbythesamplingtheorem.ThespectralpurityoftheconventionalDDFSispartlydeterminedbytheresolutionofthevaluesstoredintheROM.ItisdesirabletoincreasetheresolutionoftheROM,bu
5、tsometimeshigherresolutionmeanslargerROMsize.However,theaccessspeedandthemaximumoutputfrequencydecreaseastheROMsizeincreases.LargerROMstoragealsomeanshigherpowerconsumption,lowerreliability,andgreatlyincreasedcosts.SoitissignificanttoreducethesizeoftheROMundertheconditionofmeetingthehigh
6、resolutionrequirementoftherubidiumatomicfrequencystandard.Themostelementarytechniqueofcompressionistostoreonlyπ/2radofsineinformation,andtogeneratetheROMsamplesforthefullrangeof2πbyexploitingthequarter-wavesymmetryofthesinefunction[3].Thequarter-wavememorycanbefurthercompressedbyusingmod
7、ifiedSunderlandtechnique,sine-phasedifferencetechnique,Quadlineapproximation(QLA)technique,andquantizationanderrorROM(QE-ROM)technique.Thephaseofaquarterofasinewavecanbedecomposedasφ=α+β+γ,whereα,β,andγare,respectively,themostsignificantbits(MSBs),themiddlebits,andtheleas
