NSS COTS Oscillators Final - 34th Space Symposium is the case with Microsemi’s space qualified crystal oscillators, an adapted Colpitts configuration is employed for oscillation

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



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



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.



Figure4-SA33RubidiumOscillator

Figure5-RadiationTestingofSA33RadiationEnvironmentsParticularenvironmentsarehighlydependentonthespecificorbitsandinturnthemissionrequirements.

Beyondtheeffectsoftotaldose,thereareneutronresponse,SEEandheavyionimpacts.Ingeneral,thesearelessstringentthanhigherorbitapplications.Thefundamentaldesignofthe9635QT,itssimilaritytothefullyspacequalifiedoscillatorsandsimplerdesignmakesitamenabletomorechallengingenvironments.TheCSAChasbeentestedundermorerigorousenvironmentsandshownstableperformance.Inprincipal,boththeCSACandMACcontainsignificantcommercialcomponentsandarelikelytobesusceptibletoSEEeffects.Areasonableusercasewouldbetouseredundantdevices.Specifictestingwouldberequiredforthesecommercialoscillatorsthatmatchedthemissionconditions.



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

Documents

NSS COTS Oscillators Final - 34th Space Symposium is the case with Microsemi’s space qualified crystal oscillators, an adapted Colpitts configuration is employed for oscillation