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32ndSpaceSymposium,TechnicalTrack,ColoradoSprings,Colorado,UnitedStatesofAmericaPresentedonApril11-12,2016
Copyright©2015byMicrosemiAllrightsreserved. Page1of5
PrecisionCommercialoftheShelf(COTS)OscillatorsforSpaceApplications
PeterCashMicrosemi,[email protected]
MikeSilveira,MattStanczyk
Microsemi,[email protected],[email protected]
ABSTRACT
Spacemissionsareevolvingandnowspanawiderangeoforbitsandmissionlifetimesthatrequiredifferent
methodssofmitigationforradiation.Somemissionsnowleveragecommercialelectronicsthatallowforstateoftheartperformanceatcostsappropriatefortheprograms.Microsemicontinuestoprovidetimingforapplicationssuch as GPS and SBIRS that require stringent performance, reliability and radiation performance. In addition,Microsemihasadaptedseveralproductsfromeithermilitaryheritageorcommercialdesignsthathaveadequateradiationtolerancesforshortduration,CubeSatandlowearthorbit(LEO)orexperimentalmissions.
The presentation will describe Microsemi’s COTS quartz oscillators and atomic clocks, and the results ofradiationtestingto100krads(Si.)Inaddition,backgroundinformationregardingsingleeventeffect(SEE)radiationsusceptibility of quartz oscillators to more severe environments that contain neutrons and heavy ions will bereviewed.ContextforthedecisiontouseofCOTSproductsincomparisontoradiationhardeningbydesignwillbeprovided.
Introduction
Inthepast,frequencysourcesforspacesuchascrystaloscillatorsoratomicclocksweredevelopedalongthe
linesof radiationhardbydesignandtestingofcomponentsandtheclock in itsentirety.Suchapproacheswereneededbecauseof longmissiondurations,beyond15years,andcomplexnaturalandman-madeenvironments.In order tomaximize the radiation hardness of clocks, common parts were leveraged with definitive radiationresponsiveness. Frequently, retestingwasperformedas a greaterunderstandingof themission conditionswasdefined.Radiationanalysiswasthenutilizedtodeterminethechangesincomponentsparametersbytheuseofstatistics,andtheseresultsusedinWorstCaseCircuitAnalysistovalidatethattheclockwouldoperateoverthemission. Finally, radiation testing is performed on hardware as appropriate. Testing included 100% screeningand/orradiationqualificationtesting.
Developinglowercostclockshavetwodistinctpaths.Thefirstpathistosubstitutecommercialpartsintoanestablished radiation hardened design. The second path is to characterize commercial clocks under specificradiationconditions.Thisissimilartoanup-screenapproach.Microsemiisintheprocessofcharacterizingthreedifferentdevicesforapplicationsinspace.Thefirstdeviceisanovenizedcrystalcontrolledoscillator,designatedthemodel9635QT.ThesecondandthirddevicesarecommercialatomicclockstheSA45,referredtoastheCSAC-ChipScaleAtomicClock,andtheSA33,referredtoastheMAC–MiniatureAtomicClock.
9635QTThe 9635QT is based on the heritage designs of the Microsemi 9600 and 9700 ovenized crystal control
oscillators.Thedesignwasdevelopedin1995andupdatedapproximatelytenyearslater.Over500oscillatorsforthis family have been launched into Commercial, Military and Scientific applications. The baseline design is
32ndSpaceSymposium,TechnicalTrack,ColoradoSprings,Colorado,UnitedStatesofAmericaPresentedonApril11-12,2016
Copyright©2016byMicrosemiAllrightsreserved. Page2of5
radiation hardened above 100 krad (Si), along with neutron insensitivity, SEL immunity and SEU acceptablebehavior. As is thecasewithMicrosemi’sspacequalifiedcrystaloscillators,anadaptedColpittsconfiguration isemployedforoscillationandthecrystalofchoiceisa3rdovertoneSC(StressCompensatedDevice.)Theoscillatorrepresentsagoodtrade-offofhighperformanceandSWaP(SizeWeightandPower).
The 9600/9700 family of oscillators has been analyzed and testednumerousoccasionswithperformdemonstrated in radiation testinglaboratories and on missions. The space version of the oscillatorincludes established reliability and class S equivalent or higherreliabilitycomponents.Thecrystalitselfismanufacturedusingsweptquartz and often radiation preconditioned to further reducesensitivity.The9635QTisa10MHzversionoftheoscillator;howeverCOTs components are used for cost reduction. The crystal is notmanufactured using swept quartz. Testing was performed tounderstandthetotaldosesensitivityoftheoscillator.Thetestingwasperformed on two oscillators at the University of MassachusettsLowelltoatotalaccumulateddoseof100krad(Si.)Theresultswereverysatisfactorywithatypicalchangeoflessthan35ppb,equivalenttoaperradof3.5e-12,verysimilartofullyspacequalifiedversionsofthesameoscillator.
Figure1–9600/9700FamilyofOscillatorsAfter exposing the oscillators to the
radiation, the proper operation was verified bycharacterization testingat theMicrosemi facilityin Beverly, Massachusetts. Although furthertesting for additional radiation environments,may be required, the 9635QT is an excellentcandidate for CubeSat or LEO missions thatrequire excellent performance at a moderateprice.Thisisaresultofthedirectheritagetothespacequalifieddesign.
ChipScaleAtomicClockMicrosemi’s Chip Scale Atomic Clock or CSACwas developed for ultra-low power applications requiring an
atomic clock. The key features are excellent SWaPwith performance exceeding that of conventional ovenizedcrystalcontrolledoscillators.ThepowerconsumptionofCSACislessthan120mW.Thisissignificantlylessthanatomicclocksthathavetypicalpowerofgreaterthan10Watts.TheCSACprovidesa10MHzoutputaswellas1Pulseper Second (PPS) andhas theability tobe steered toa1PPS input. Another interesting capability is theCSACstimeofdayfunctionality.Microsemihasperformedradiationtestingontheclockinthe2013to2014time
Figure2–9635QTFrequencyvs.TotalDose
32ndSpaceSymposium,TechnicalTrack,ColoradoSprings,Colorado,UnitedStatesofAmericaPresentedonApril11-12,2016
Copyright©2016byMicrosemiAllrightsreserved. Page3of5
periodandrealizedthatperformance inenvironmentsofupto50krad(Si)wasreasonablebyreplacementofaradiation susceptible TCXOwith a radiation tolerant device and increasing the shielding thickness . The paperpresentedontheSpaceCSACisreferencedattheendofthispaperandprovidesacomprehensivesummaryoftheoscillator.
Figure3–SpaceCSACSA33–MACMiniatureAtomicClockAlthough the CSAC provides significantly improved accuracy and stability compared to crystal oscillators,
design aspects required to achieve the very low power consumption have reduced performance compared toconventional Rubidium atomic clocks. Conventional Rubidium atomic clocks have been typically large andconsumedsignificantpower,andasaresulthaveonlybeenusedinrareexceptionsonSatellitessuchastheGNSSsystemslikeGPSandGalileo.ThesametechnologythatallowedforthecreationoftheCSAC,CoherentPopulationTrapping, resulted in thedevelopmentofa lowpowerRubidiumoscillator. In thiscase, theSA33provideshighperformanceconsistentwithconventionalclocksandrequiringonly5Wattsofpowerat25degreesCentigrade.Inaddition, thesizeof theoscillator is2”x2”x0.7”. Theendof thispaper referencesacompletepaperon thedesignandperformanceattributesoftheSA33.
Totaldose radiation testingwasperformedon twoSA33oscillatorsandoperationwasdemonstrated to10
krads (Si.) The oscillators lost lock at approximately 12 krads (Si). Analysis of the failure mode indicated thecommercialTCXOinsideoftheclock.ThiswasthesamefailuremodeforsimilartestingoftheCSAC.ThisTCXOcouldbereplacedwitharadiationtolerantversionandthepossibilityofradiationshieldingevaluated.
AnotheradvantageofMicrosemi’sCSACandMACatomicclocksaretheabilitytosurvivehighlevelofshock
and vibration relative to typical commercial devices. The CSAC canwithstand 2000 g’s of shock and theMACoperatinglevelsofvibrationof8grmsandsurvivalabove30grms.
ThefollowingpageshowsaphotographoftheSA33andaplotoftheperformanceunderradiation.
32ndSpaceSymposium,TechnicalTrack,ColoradoSprings,Colorado,UnitedStatesofAmericaPresentedonApril11-12,2016
Copyright©2016byMicrosemiAllrightsreserved. Page4of5
Figure4-SA33RubidiumOscillator
Figure5-RadiationTestingofSA33RadiationEnvironmentsParticularenvironmentsarehighlydependentonthespecificorbitsandinturnthemissionrequirements.
Beyondtheeffectsoftotaldose,thereareneutronresponse,SEEandheavyionimpacts.Ingeneral,thesearelessstringentthanhigherorbitapplications.Thefundamentaldesignofthe9635QT,itssimilaritytothefullyspacequalifiedoscillatorsandsimplerdesignmakesitamenabletomorechallengingenvironments.TheCSAChasbeentestedundermorerigorousenvironmentsandshownstableperformance.Inprincipal,boththeCSACandMACcontainsignificantcommercialcomponentsandarelikelytobesusceptibletoSEEeffects.Areasonableusercasewouldbetouseredundantdevices.Specifictestingwouldberequiredforthesecommercialoscillatorsthatmatchedthemissionconditions.
32ndSpaceSymposium,TechnicalTrack,ColoradoSprings,Colorado,UnitedStatesofAmericaPresentedonApril11-12,2016
Copyright©2016byMicrosemiAllrightsreserved. Page5of5
ComparisonofOscillatorsSelectionoftheoscillatorforanapplicationdependsonthespecificperformancerequirementsandsystem
limitations.Thefollowingtableshowsthekeyperformanceparametersandoptions.
9635QT CSAC MAC CommentOutput 10MHzsinewave 10MHzCMOS
1PPS10MHzCMOS
PowerConsumption 1.3W 120mW 5W Steadystate25degreesC,vacuum
FrequencyAccuracy 2x10-8 5x10-10 5x10-11 Atshipment
TemperatureStability
±2x10-8 ±5x10-10 ±2x10-10 -10to70°C
PhaseNoise ≤-95dBc/Hz≤-125dBc/Hz≤-145dBc/Hz≤-150dBc/Hz
≤-155dBc/Hz
≤-50dBc/Hz≤-70dBc/Hz≤-113dBc/Hz≤-128dBc/Hz
≤-135dBc/Hz
≤-70dBc/Hz≤-87dBc/Hz≤-114dBc/Hz≤-130dBc/Hz
≤-140dBc/Hz
@1Hz@10Hz@100Hz@1kHz@10kHz
Aging(Drift) 9x10-9 9x10-10,typical 1x10-10 PermonthOptions 1PPSSteering,
TimeofDay
ConclusionsSatelliteMissionshaveevolvedoverthepastdecadeinwhichtrade-offshavebeenmadeforduration,
reliability,theabilitytoleveragehighperformancecommercialelectronicstoachieveperformance,pricetargetsandreduceddeploymenttimes.Highperformanceclockscanbeadaptedtosupporttheseobjectiveswithminimalcompromiseforreliability.Microsemi’sprecisionclocksthe9635QT,CSACandMACareuniqueproductsthatarecapableofmeetingthesemissions.
References:1. “SpaceCSAC:Chip-ScaleAtomicClock forLowEarthOrbitApplications”,M.Stanczyk,P.CashandMike
Silveira,2014PTTIMeeting2. “SA.3XmRubidiumOscillator:PerformanceandApplications”,W.Krzewick,P.GerryandJ.Malcolmson,
Microsemi,2016PTTIMeeting