TUTORIAL:Oscillators

Ullas Kumar (Rakon)

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Outline

Oscillators

• Oscillators in Synchronization

• Oscillator technologies

• Types of Oscillators

• Selection of Oscillators

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Oscillators in Synchronization

• Local Reference in systems

• Synchronization is hierarchical

I

II II

III III III III

ITU-T G.811

ETSI 300 011Customer Premises

Equipment

ITU-T G.812

ITU-T G.813

Stratum 1

Stratum 4/ 4E

Stratum 3/3E

Stratum 2

Primary Clock

PLL/ Servo Oscillator

+ X ppm- X ppm 0 ppm

ppm – parts per million

- y ppm

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Oscillator Technologies

Various Technologies

Quartz based Oscillators

MEMS Oscillators

Piezo Electric Effect

Undeformed lattice

X+

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Strained lattice

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X• •- +

YY

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A. Ballato, “Doubly rotated thickness mode plate vibrators,” in Physical Acoustics, Vol. XIII, pp. 115-181, Academic Press, 1977.John R. Vig Quartz Crystal Resonators and Oscillators For Frequency Control and Timing Applications - A Tutorial April 2012

TuningVoltage

Crystalresonator

Amplifier

OutputFrequency

Crystal CL

C1 L1 R1

C0

CL

SiTime MEMS Oscillators are Inherently Robust Against Shock & Vibration

Proprietary Design

• Our Resonators are Designed Specifically for Low Sensitivity to Any External Mechanical Acceleration

• Single-Point, Center Anchored MEMS Resonator Virtually Eliminates Stress Error Sources

8

5 MHz Resonator

48 MHz Resonator

524 kHz Resonator

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Quartz Fundamentals

Cuts of the crystal

Making of the oscillator

John R. Vig Quartz Crystal Resonators and Oscillators For Frequency Control and Timing Applications - A Tutorial April 2012

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Types of Oscillators

XOs TCXOs – Temperature compensation OCXOs- Oven control

Output

-450C

+10 ppm

250C

T+1000C

ffD

TemperatureSensor

CompensationNetwork

XO

-450C ffD

+0.1 – 0.05 ppm

+1000C

T

Ovencontrol

XO

TemperatureSensor

Oven

-450CffD

+1 x 10-10

+1000CT

Compensated frequency of TCXO

Compensation

Freq

uenc

y

Uncompensated frequency

T

-40˚C 85˚C

-40˚C 85˚COven temperature variation Due

to external temperature change

Oven Set Point

TemperatureLowerTurnoverPoint (LTP)

UpperTurnoverPoint (UTP)

f (UTP)

f (LTP)

Frequency

Freq

uenc

y

Oscillators are susceptible to temperature variations

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Influences on Oscillators

Aging effect

Temperature Effect

Hysteresis effect

Retrace effect

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Servo Model Impact of Oscillators

Oscillators present a high pass effect to the output

As the loop bandwidths become narrower, output corrections are more infrequent

Variations on the reference oscillator reflect at the output

Oscillator Selection for Clocks

Phase Comparator& Monitors

Loop Filter DCO Output

Synthesizers

Oscillator

Recovered Clocks

Output stability depends on Oscillator performance & Loop bandwidth of the

PLL

Loop Bandwidth 10-100Hz 1-10Hz 0.1Hz – 1Hz 10mHz – 100mHz 1mHz <1mHz

Recommended Oscillator Temperature Stability

500ppb-1ppm 100-300ppb 50-100ppb 20-50ppb 5-10ppb 1-5ppb

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Oscillator requirements are based on • Free Run -> Overall oscillator stability for 10/15/20 years, all causes included • Loop bandwidth -> Support for loop bandwidth at required output error, at constant

temperature and at variable temperature• Frequency Vs Temperature performance -> This forms part of the wander generation and

holdover requirement of the standards • Ageing performance -> This forms part of the wander generation and holdover requirement

specifications • Phase noise, Temperature sensitivity, Allan deviation, shock & vibration performance ->

Other oscillator effects depending on the application.

Oscillator selection

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Summary

Oscillators are fundamental building blocks of clocks

Quartz based oscillators produce clean and stable clocks, other technologies like MEMS are also used

Temperature compensation and oven control and methods used to improve stability of clocks

As the loop bandwidth of the systems decrease, higher stability oscillators to be used to have a certain level of output stability

Wander generation and holdover and key aspects of oscillator selection in systems