Vibra&oncompensatedTCXOsandOCXOsenableimprovedsystem

performanceinvibratoryenvironments

FlavienHeur&erSales&Applica&onsEngineer

Presenta&onoutline

•  Accelera&onsensi&vityofthequartz•  Characterizingtheaccelera&onsensi&vity•  Improvingtheaccelera&onperformance•  Conclusion

ACCELERATIONSENSITIVITYOFTHEQUARTZCRYSTAL

Accelera&onSensi&vityofthequartzcrystal

•  Accelera&onsensi&vitycommonlyreferredas“g-sensi&vity”•  AlsoGreekgamma,Γ

•  Accelera&onforcescauseschangeinresonantfrequencyduetomoun&ngstructure•  Non-uniformstressonac&veareaofthequartzcrystal•  SmallfrequencyshiMs(oMenno-no&cedinmanyapps)

•  Linearlypropor&onaltoappliedforce•  Upto50g’s(dependingonmount)

•  Γisavectorquan&ty•  FrequencyshiMishighlydependedonappliedforce

Accelera&onSensi&vityofthequartzcrystal

f (!a) = f0 (1+!Γ⋅!a)

FrequencyshiMisdirec&onallydependent:

•  Maximallyposi&vewhenisparallelto•  Maximallynega&vewhenisan&-parallelto•  Zerowhenisperpendicularto

!a!a!a

!Γ !

Γ!Γ

Accelera&onSensi&vityversusdirec&onalappliedforce

Γd =!Γ ⋅!a ⋅cosα

Accelera&onSensi&vityversusdirec&onofappliedforcein3D

CHARACTERIZINGTHEACCELERATIONSENSITIVITY

MeasurementSystems

•  ForMeasurementofrela&vesidebandslevelswithsinusoidalvibra&on•  ForMeasurementofphasenoiseduringrandomvibra&on

AxisDefini&onforSC-cutCrystal

AxisDefini&onforStripCrystal

ATStripCrystal

•  Miniaturesize–assmallas1.5x1.0mm•  CanprovideprecisionperformanceforTCXOs•  Surfacemountpackage

•  Consistentaccelera&onsensi&vity•  Somedesignsachieve<1.10-10/g

•  Statekisalignedwiththesameaxis•  Facilitatesmoun&ngandalignment

Γ

Γ

MiniatureATStripCrystal

SphericalCoordinateSystemforDefiningCrystalg-sensi&vityVector

!Γ = Γx

2 +Γy2 +Γz

2

Θ = sin−1 Γz!Γ

⎛

⎝

⎜⎜

⎞

⎠

⎟⎟

Φ= cos−1 ΓxΓ2x +Γ

2y

⎛

⎝

⎜⎜

⎞

⎠

⎟⎟

SidebandsgeneratedbySingleFrequencyVibra&on

•  For20MHzTCXOVib=10gpeak90Hz=>=1.56ppb/g

Γ

SBLevel(dBc) = 20 log!a×!Γ× fnom2 fv

⎛

⎝⎜

⎞

⎠⎟

!Γ=

2 fv!a× fnom⎛

⎝⎜

⎞

⎠⎟×10

SBLevel (dBc)20

PhaseNoisePlot–RandomVibra&on

£( fv ) = 20 log!Γ× fnom× 2×PSD

2 fv

⎛

⎝⎜

⎞

⎠⎟

PhaseNoisePlot–RandomVibra&on

1.3x10E-9/g

£( fv ) = 20 log!Γ× fnom× 2×PSD

2 fv

⎛

⎝⎜

⎞

⎠⎟

PhaseNoisePlot–RandomVibra&on

£( fv ) = 20 log!Γ× fnom× 2×PSD

2 fv

⎛

⎝⎜

⎞

⎠⎟

Phasenoiseundervibra&onandaccelera&onsensi&vity

•  Phasenoiseundervibra&onisprimarilydeterminedbytheaccelera&onsensi&vity

•  Specifyinganoscillatorwithultra-lowsta&cphasenoisewillnotguaranteetheperformanceundervibra&on.Itwillbedeterminedbytheaccelera&onsensi&vityoftheofthecrystal/oscillator

•  Inmanycases,alowvibra&oncompensatedTCXOcouldprovidelowerphasenoiseundervibra&onthanalownoiseOCXO

PhaseNoisePlot–RandomVibra&on

10MHzOCXO=0.6ppb/g

10MHzTCXOVib.Compens.=0.03ppb/g

Γ

Γ

Accelera&onSensi&vityQuartzCrystalscomparison

IMPROVINGTHEACCELERATIONSENSITIVITYPERFORMANCE

Improvingtheaccelera&onsensi&vityperformance

•  Crystalmanufacturingandmoun&ngtechniques•  Aien&ontomoun&ngstress

•  Oscillatormoun&ngandorienta&on•  Ac&vecompensa&onwithaccelerometer

•  Effec&veatlowfrequency•  Vibra&onisola&on

•  Effec&veabovenaturalfrequencyofisolator•  Addssize,weightandcost

•  Mul&ple-crystalpassivecancella&onmethods•  Aligncrystalswithan&parallel

!Γ

Improvingtheaccelera&onsensi&vityperformance

Y1

Y2

G1

G2

Dual Crystal Acceleration Sensitivity

Cancellation

Gamma Vectors aligned antiparallel

Improvingtheaccelera&onsensi&vityperformance

Finalaccelera&onsensi&vityresults

T1300-1 40MHz

(Crystal Pairs of CT1061-50) Post Seal

Sideband Levels (dBc)* Acceleration Sensitivity (ppb/g)

S/N z y x Γ z Γ y Γ x Γ max 4 -79.1 -88.8 -88.9 0.05 0.02 0.02 0.055 9 -82.9 -86.9 -88.8 0.03 0.02 0.02 0.041

12 -86 -87.3 -88.2 0.02 0.02 0.02 0.035 14 -83.8 -84.2 -85.4 0.03 0.03 0.02 0.047 31 -87.9 -88.1 -87.7 0.02 0.02 0.02 0.031

*(10g's@90Hz)

Varia&onofathighertemperature

Γ

Temp +25C +85C S/N Γ z (ppb/g) Γ z (ppb/g) Delta (ppb/g) 15 0.0218 0.0223 0.0005 21 0.0228 0.0396 0.0168 8 0.0259 0.0196 -0.0063

19 0.0337 0.0362 0.0024 9 0.0379 0.0326 -0.0053

17 0.0379 0.1407 0.1028 7 0.0511 0.0425 -0.0086

16 0.0511 0.0755 0.0245 1 0.0580 0.0425 -0.0155 3 0.0621 0.0908 0.0287

12 0.0713 0.0791 0.0078

PhasenoiseunderRandomVibra&on

A=Standard single crystal Γ≈2.5ppb/g

B=Matched dual crystals Γ≈0.05ppb/g

C=Quiescent phase noise

PhasenoiseunderRandomVibra&on

125MHzTCXOstandard

Γ≈0.95ppb/g

PhasenoiseunderRandomVibra&on

125MHzTCXOdual-mount

Γ≈0.060ppb/g

T1300withdualmoun&ngtechnique

Accelera&onSensi&vityPatent

IntellectualProperty•  Althoughpassive

cancella&ontechniqueshavebeenknownforyears,Greenrayhasbeengrantedapatentforthemethodofimplemen&ngitwithstripcrystals

Conclusion

Althoughitisnotpossibletocompletelyeliminatetheeffectsofaccelera&onontheresonantfrequencyofaquartzcrystal,byunderstandingthevectornatureofthecrystal’sg-sensi&vitycharacteris&c,theimpactinmostapplica&onscanbeminimizedwithcarefuldesignprac&ces.

Thanksalotforyouraien&on.AnyQues&ons?