EFCC 2015

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Oscillator design guidelines for

implantable medical device applications

FlavienHeu+erSales&Applica+onsEngineer

Agenda

o  Introduc/on

o  Keyparametersinspecifyingquartzcrystals

o  Suggestedscreeningsforquartzcrystals

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INTRODUCTION

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Evolu/onofthequartzcrystalsformedicalimplantabledevice

applica/ons

4

1973

CX1 (8.0 x 3.5mm)

1983-86

First Lithium powered And Non invasive Programmable (Telemetry) pacemaker

CX3 (6.6 x 2.4mm)

1998

CX4 (5.0 x 1.5mm)

3 chamber pacing implemented

Pacemaker with Temperature and Motional sensors

Evolu/onofthequartzcrystalsformedicalimplantabledevice

applica/ons

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2005

CX9 (4.1x1.5mm)

2009

Medical Implantable Communication Service (MICS) devices

2010 - 2013

CX11 (3.2x1.5mm) CX16 (2.0 x 1.2 mm) CX18 (1.55 x 0.95 mm)

BlueTooth Low Energy (BLE) and new generation of MICS. 1st Leadless pacemaker

Retinal Implants

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QuartzCrystaltheory:ModesofMo/on

Flexure Mode Extensional Mode Face Shear Mode

Thickness Shear Mode

Fundamental Mode Thickness Shear

Third Overtone Thickness Shear

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•  TuningForkCrystal–Flexuremode

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•  AT-cutcrystal–Thicknessshearmode

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•  QuartzCrystalConstruc/on

Agenda

o  Introduc/on

o  Keyparametersinspecifyingquartzcrystals

o  Suggestedscreeningsofquartzcrystals

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KEYPARAMETERSINSPECIFYINGQUARTZCRYSTALS

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Keyparametersinspecifyingquartzcrystals

o  Loadcapacitanceo  Gaino  Drivelevel

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Keyparametersinspecifyingquartzcrystals

o  Loadcapacitanceo  Gaino  Drivelevel

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CrystalModelandCL

Symbol for crystal unit CL

C1 L1 R1

C0

CL

Static Arm

Motional Arm

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Total Reactance = X + XCL= 0

LoadCapacitance–FLatCL

TS is the TrimSensi/vity

0

+

- R

eact

ance

0fC21π

Area of usual operation in an oscillator

Antiresonance, fa

Frequency

Resonance, fr

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⎟⎟⎠

⎞⎜⎜⎝

⎛

++=

)(21

0

1

LsL CC

CFF

TS = − 1FdFLdCL

=C1

2(C0 +CL )2

HowtomeasureCL?

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1)  Measure the crystal parameters C1, C0, and Fs with a network or impedance analyzer.

2) Install the measured crystal in the oscillator circuit and measure the oscillation frequency f 3) Then calculate the load capacitance CL. For example with

Fs = 32.7644 kHz C1 = 2.3 fF C0 = 1.5 pF f = 32.768 kHz

we find CL = 9.0 pF.

CL =C12

Fsf −Fs

⎛

⎝⎜

⎞

⎠⎟−C0

ImpactofincorrectCLConsidering a 32.768 kHz CX11 crystal : C0= 1.0 pF , C1 = 3.5 fF,

calibrated for CL1 = 9 pF.

Customer circuit at CL2 = 11 pF, what is the change in frequency ?

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ppm 29

112 0102

112

−=

⎟⎟⎠

⎞⎜⎜⎝

⎛

+−

+=

−

CCCCC

FFF

LL

LL

ImportanceofCL•  Right choice of CL for proper operating frequency

•  Crystal with small load capacitance starts faster

•  Large load capacitors increase the power consumption

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Keyparametersinspecifyingquartzcrystals

o  Loadcapacitanceo  Gaino  Drivelevel

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•  PierceOscillator

Cd Crystal resonator

Amplifier

CG CD

RA

Rf

Fout

Gain–Formula

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gm ≥ 4π2 f 2CG CD +Cd( )Re+ (Cd +

Re

ROCD )RA

⎡

⎣⎢

⎤

⎦⎥

+CG

CD (1+RA

RO)+Cd

1RO

− 4π 2 f 2CdCDRA

⎛

⎝⎜

⎞

⎠⎟ 1+

RA + ReRO

− 4π 2 f 2CdCDRARe⎛

⎝⎜

⎞

⎠⎟

Oscillator AC equivalent

circuit with the crystal

electrical equivalent circuit

XG XD

RO C0’= C0+Cs

L1 C1 R1

ID

Gain–MainpartoftheFormula

2

'

'0

1 1 ⎟⎟⎠

⎞⎜⎜⎝

⎛+≈

Le C

CRR

sLL CCC += '

sCCC += 0

'0

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XG XD

RO ID

Xe Re

Pierce Oscillator AC Equivalent Circuit (RA omitted)

gm ≥ 4π2 f 2CGCD Re+

CG

CDRO1+ Re

RO

⎛

⎝⎜

⎞

⎠⎟

CX CG

CD

RA

Rf

Fout

Cd

Compareminimumgaintodrivesealedandunsealed32.768kHzCX11crystal

gm1 gm2 gm gm1 gm2 gm

gm µS (µmho) 0.61 0.54 1.15 5.46 0.82 6.28

f HzCD pFCG pFR1 Ω

Re∪R1(1+C0'/CL

')2 Re ΩRo MΩ

CL=CL'+Cs CL pF

Cs pFC0

'=C0+Cs C0 pF

6.97

1.06

101020

50'000

20

gm = 4π2f2CDCGRe +CG/(CDRo)(1+Re/Ro)

445'000643'992

1

32'768

72'359

Sealed Unsealed

0.31.06

32'768

0.3

17 7

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Keyparametersinspecifyingquartzcrystals

o  Load capacitance

o  Max allowed crystal resistance

o  Drive level

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DriveLevelDefini/onCrystaldrivelevelisameasureofhowhardthecrystalisbeingdriven.Itcanbedefinedasthecurrentpassingthroughtheresonator,butismosto_endefinedasthepowerdissipatedwithintheresonator.Themaximumalloweddrivelevelisgivenbythecrystalmanufacturerandisdependentuponthephysicalsize,geometry,mode,andfrequencyoftheresonator.

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MaxDriveLevelforCX11

TuningForkCX1132.768kHz:0.5μWmax

AT-cutCX1124.0MHz:200μWmax

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Drive-LevelDependency•  Crystaldrive-leveldependency(DLD)referstothedependency

ofthequartzcrystalparameters(frequencyandseries

resistance)tothewithcurrentthroughthecrystal.

•  Highdrivecouldirreversiblydamageaquartzcrystal

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Drive-LevelDependency

10-3 10-2 10-1 1 10 100

Res

ista

nce

R1

IX (mA)

Anomalous starting resistance

Normal operating range

Drive level effects

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Drive-LevelDependency

•  Evenwiththestepswetaketomi/gatethis,therecans/llbesomepartsthatexhibitDLDbehavior.

•  Werecommendcustomersrequiringsomelevelsoftes/ngtoensurereliablestart-upoftheoscillator.

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SUGGESTEDSCREENINGSFORQUARTZCRYSTALS

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SuggestedScreeningsforQuartzCrystals

o  DLD Testing

o  Thermal Shock

o  Hermeticity Testing

o  PIND Testing

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DLDTes/ng

•  Purpose:Toremovecrystalsthatmighthave

start-upissuesintheoscillator.

•  Method:Measurethecrystalfromalowdrive

leveltothenominaldrivelevelandback,looking

formaximumresistanceandchangesinfrequency

andresistance. 35

ThermalShock

•  Purpose:TodetermineResistanceofthecomponentto

exposeatextremetemperature

•  PerMIL-STD-202,Method107

•  Method:Stressthemechanicalstructure(packageand

quartzbonding)andcheckeffectoncrystalparameters.

-55°Cto+125°C/5cycles 36

Herme/cityTes/ng

•  Purpose:Determinetheeffec/venessofsealprocessdetec/ng

poten/alherme/cityissuethroughceramic,preformorsealrim.

•  FineandGrossLeakTes/ng:PerMIL-STD-202,Method112

•  Method:Partsunderhighpressurebeforemeasuringleakage

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PINDTes/ng•  Purpose:Non-destruc/vetesttodetectloosepar/culates,ifany,insidea

componentcavity.

•  Method:Detectloosepar/culatesofsufficientmassacous/callyuponimpact

withthecavity.

•  Par/cleImpactNoiseDetec/onperMil-STD-883,Method2020Condi/onA

•  Needspecialtestenvironmenttoreduceambientandexternalnoises.

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Thankyou

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