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1、Lecture010–IntroductiontoFrequencySynthesizers(5/5/03)Page010-1LECTURE010–INTRODUCTIONTOFREQUENCYSYNTHESIZERS(References:[1,5,9,10])WhatisaFrequencySynthesizer?Afrequencysynthesizeristhemeansbywhichmanydiscretefrequenciesaregeneratedfromoneormorefixedreferencefrequencies

2、.Controlff1of2Frequencyff3SynthesizerofNFig010-01•Thereferencefrequenciesarestableandspectrallypurefrequencytypicallygeneratedfromapiezoelectriccrystal.•Modernfrequencysynthesizersmustprovidemanydiscreteoutputfrequencysothatitisimpracticaltogeneratethefrequenciesbyhaving

3、areferencefrequencyforeachdesiredoutputfrequency.•Thecontrolinputdeterminesthevalueofthefrequencysynthesizeroutputfrequency,foECE6440FrequencySynthesizers©P.E.Allen-2003Lecture010–IntroductiontoFrequencySynthesizers(5/5/03)Page010-2CharacterizationofaFrequencySynthesizer

4、•Outputfrequencyrange-fmin≤fo≤fmax•Frequencyaccuracy-fo±∆f(typicallyin%orpartspermillion,ppm)•Frequencyswitchingtime–FrequencyTolerancef2Switching•Frequencyresolution(channelspacing)f1TimeTimeFig010-02Magnitude•Spectralpurity(noise)–SpectralimpurityfoFrequencyFig010-03•F

5、requencystabilityasafunctionoftime,temperatureandpowersupplyExpressedaspartspermillionperinfluence(time,temperatureorpowersupply)Shortterm(drift)DesiredLongterm(aging)MagnitudeFrequency•Spuriousoutputs–SpursSpursFig010-04FrequencyECE6440FrequencySynthesizers©P.E.Allen-20

6、03Lecture010–IntroductiontoFrequencySynthesizers(5/5/03)Page010-3ReferenceFrequenciesIdeally,thereferencefrequencyshouldbeasinglefrequencyindependentofallpossibleinfluences.Itisverydifficulttoachieveanoutputfrequencywithbettercharacteristicsthanthereferencefrequency.Reso

7、natorsThereferencefrequencycanbegeneratedusingresonators.Resonatortechnologiesinclude:•Quarter-waveresonators–lossless1/4wavetransmissionline(at3GHzλ/4=1inch)BariumtitanategivesQ=20,000•Quartzresonators–althoughthepiezoelectriceffectissmaller,quartzhasexceptionalmechanic

8、alandelectricalstability.Q≈104to106.5x108CmRS≈foroLm1670Cotf≈t5x108RSRS≈fN2oIllustrationofBulkShearMode