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
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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
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Strained lattice
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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
55
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
1010
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
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