标签: 频合

频合常见问题答疑AsktheApplicationsEngineer―30byAdrianFox[adrian.fox@analog.com]PLLSYNTHESIZERSQ.WhatisaPLLSynthesizer?A.Afrequencysynthesizerallowsthedesignertogenerateavarietyofoutputfrequenciesasmultiplesofasinglereferencefrequency.Themainapplicationisingeneratinglocaloscillator(LO)signalsfortheup-anddown-conversionofRFsignals.Thesynthesizerworksinaphase-lockedloop(PLL),whereaphase/frequencydetector(PFD)comparesafedbackfrequencywithadivided-downversionofthereferencefrequency(Figure1).ThePFD’soutputcurrentpulsesarefilteredandintegratedtogenerateavoltage.Thisvoltagedrivesanexternalvoltage-controlledoscillator(VCO)toincreaseordecreasetheoutputfrequencysoastodrivethePFD’saverageoutputtoward……