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LLRFwithdirectsampling
JesusA.VasquezStanescuUSPAS2017Low
USPAS2017- IntroductiontoLow-LevelRadioFrequencySystems,TechnologyandApplicationstoParticleAccelerators1/20/17 1
1/20/17 USPAS2017- IntroductiontoLow-LevelRadioFrequencySystems,TechnologyandApplicationstoParticleAccelerators 2
Description
• QuarterWaveResonator(QWR)cavities,withresonancefrequenciesof80MHzand160MHz• RFControllercancontrol8cavities• TheRFsignalspicked- upfromthecavitiesaresampledbyRFADCs• ControlloopisimplementedonaFPGA• Themainperturbationsarecausebymicrophonics [HztokHz](pressurevariationsinhelium,temperature,mechanicalvibrations,changeincavityresonancebycurrents/charges).
1/20/17 USPAS2017- IntroductiontoLow-LevelRadioFrequencySystems,TechnologyandApplicationstoParticleAccelerators 3
Systemblockdiagram
1/20/17 USPAS2017- IntroductiontoLow-LevelRadioFrequencySystems,TechnologyandApplicationstoParticleAccelerators 4
Measurereflectedand
forwardpowers
AdaptamplitudelevelsofRFsignals
Algorithmblockdiagram
1/20/17 USPAS2017- IntroductiontoLow-LevelRadioFrequencySystems,TechnologyandApplicationstoParticleAccelerators 5
RFADCs
• ADS42JB69,16bit,250MSPS• Undersampling at121.9MHz
• Noiseisdominatedbyclockjitter
1/20/17 USPAS2017- IntroductiontoLow-LevelRadioFrequencySystems,TechnologyandApplicationstoParticleAccelerators 6
16bitADCSNRmax =98dBtjmin ~0.016ps10bit->62dB->~1.04ps
1/20/17 USPAS2017- IntroductiontoLow-LevelRadioFrequencySystems,TechnologyandApplicationstoParticleAccelerators 7
Systemblockdiagram
1/20/17 USPAS2017- IntroductiontoLow-LevelRadioFrequencySystems,TechnologyandApplicationstoParticleAccelerators 8
RFDACs
• 200MHzsignal• DirectDigitalSynthetizer (FPGA)generates40MHz• NumericalControlledOscillator(DAC)generates160MHz• DACactsasDigitalUpConvertermixingthe40MHzand160MHztoproducethe200MHz
1/20/17 USPAS2017- IntroductiontoLow-LevelRadioFrequencySystems,TechnologyandApplicationstoParticleAccelerators 9
Algorithmblockdiagram
1/20/17 USPAS2017- IntroductiontoLow-LevelRadioFrequencySystems,TechnologyandApplicationstoParticleAccelerators 10
Non-IQsampling
• Thesamplingfrequencyis• NsamplesinMIFperiods
• ExampleM=3,N=25
• errorsfromDCoffsets,clockjitter,ADCquantization,noisereduced• butmorelatencyduetosamplingMIFperiods
1/20/17 USPAS2017- IntroductiontoLow-LevelRadioFrequencySystems,TechnologyandApplicationstoParticleAccelerators 11
