Application Report
SNAA296 – January 2017

Vibration and Shock Sensitivity: A Comparative Study ofOscillators
Chao Li, Arvind Sridhar
ABSTRACT
When designing a system that incorporates a clock oscillator, the vibration sensitivity of the oscillator
device is a specification that is easily overlooked. Sensitivity to vibration can have a detrimental impact on
the overall system performance. Since crystal oscillators fundamentally rely on the vibration andmechanical resonance of a piezoelectric material, external disturbances can couple into the device anddegrade its performance. These external disturbances can result in output frequency shifts, elevatedphase noise and spurs. Mechanical shocks of sufficient magnitude can also cause irreversible frequency
shifts at the output of the crystal oscillator.
In the tests outlined in this study, the TI oscillator exhibited an order of magnitude improved resilience tovibration versus two competitor offerings. It also had the least frequency perturbations in response tomechanical shock. Test procedure details and measured results are presented in the following sections.

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Contents
Introduction ................................................................................................................... 2
Test Setup and Procedure .................................................................................................. 2
Data and Results ............................................................................................................ 8
Conclusion .................................................................................................................. 11
References .................................................................................................................. 11
List of Figures

1

Orientation Of The Devices On The Cube With respect To Pin 1. Movement Of The Cube Is Along The Z
Axis. ........................................................................................................................... 3

2

Photo of Vibration Test Equipment ........................................................................................ 4

3

Sinusoidal and Random Vibration Test Setup Diagram ................................................................ 4

4

Vibration Test Setup Showing Cube On Vibration Table With The DUTs Connected To A Power Supply
And Signal Source Analyzer ............................................................................................... 5

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MIL-STD-883H, Method 2026: Random Vibration (1) .................................................................... 6

6

Shock Test Setup Diagram ................................................................................................. 7

7

Shock Test Setup Showing Cube On Shock Table And Guide Rail. Only 1 Dut Is Attached At A Time To
Avoid Causing Damage To The Others. .................................................................................. 88

Sensitivity To X-axis Acceleration Over Frequency Of Vibration. Lower Is Better. ................................. 99Sensitivity To Y-axis Acceleration Over Frequency Of Vibration. Lower Is Better. ................................. 9

10

Sensitivity To Z-axis Acceleration Over Frequency Of Vibration. Lower Is Better. ................................. 911

Phase Jitter Induced by Random Vibration. Lower Is Better. ........................................................ 10

12Frequency Deviation in ppm Under 500-g Shock. Lower Is Better. ................................................. 10
List of Tables(1)

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Typical Acceleration Levels in Various Environments .................................................................. 2

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Devices Tested and Their Specifications ................................................................................. 2“MIL-STD-883H, Test Method Standard, Microcircuits.” Department of Defense. 26 February 2010.

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Introduction

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Introduction
Table 1 below shows typical levels of acceleration that a device might experience in various operating
environments. Sources of vibration are present anywhere from inside a moving vehicle or aircraft, to a
handheld mobile device. Systems are also susceptible to vibrations from sources such as cooling fans in
the equipment chassis. The performance of aircraft radar, for example, is directly related to the reference
oscillator phase noise in the system. Vibration induced elevated phase noise translates to the blurring oftargets and a decrease in accuracy of detection. Medical imaging and ultrasound applications are alsoquite sensitive to vibration. In these systems, the reference oscillator phase noise limits the maximum
achievable resolution, so the system must be resilient to vibration to operate reliably.
Table 1. Typical Acceleration Levels in Various Environments (1)(1)

ENVIRONMENTTYPICAL ACCELERATION (G's)

Buildings, quiescent0.02 rms

Tractor-trailer (3-80 Hz)

0.2 peakArmored personnel carrier

0.5 to 3 rms

Ship - calm seas

0.02 to 0.1 peak

Ship - rough seas

0.8 peakRailroads

0.1 to 1 peak

Propeller aircraft

0.3 to 5 rms

Helicopter

0.1 to 7 rms

Jet aircraft

0.02 to 2 rms

Missile - boost phase

15 peak

John R. Vig, “Quartz Crystal Resonators and Oscillators,” US Army Communications-Electronics Research, Development &Engineering Center. January 2004.

The LMK6xxx family of high-performance fixed and programmable oscillators from Texas Instruments (TI)
is resilient to the effects of vibration and mechanical shock. Integrated circuit (IC) packaging and layout
techniques are optimized to minimize the coupling of external vibrations through the body of the device tothe resonating element.
To test resilience to vibration, three tests were performed on the LMK61E2, the flagship oscillator from TI,
and a similar PLL-based oscillator from another vendor. A surface acoustic wave (SAW) based oscillator
from competition was also added to the test for vibration sensitivity to compare different oscillator
technologies. The units were first subjected to sinusoidal vibration at various frequencies along x, y and z
directions. The test was repeated a second time along each axis with random vibration profiles. The final
test measured the transient frequency deviation of the units during operation in response to mechanicalshock. Phase noise (including spurs) and frequency excursion data was recorded during the tests.

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Test Setup and Procedure

2.1

General Setup
Table 2 lists the 3 devices tested as part of this comparative study. The TI LMK61E2 and Silicon Labs
Si536 utilize a quartz resonator and an internal PLL to synthesize output frequencies (156.25 MHz for thisstudy). The third device selected for the test was an Epson EG-2102CA 125 MHz fixed frequency SAWbased oscillator. The measured data for the Epson device was normalized with respect to frequency togive an accurate representation of relative performance.
Table 2. Devices Tested and Their Specifications
LABEL

MANUFACTURERPART NUMBERTECHNOLOGYFREQUENCY

OUPUT

TI

Texas Instruments

LMK61E2-SIA

XO + PLL

156.25 MHz

LVPECLSL

Silicon Labs

536AB156M250DG

XO + PLL

156.25 MHz

LVPECL

Epson

EG-2102CA
125.0000M-PHPAL3

SAW

125 MHzLVPECLEP

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Vibration and Shock Sensitivity: A Comparative Study of Oscillators
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All devices were installed on identical boards for testing. The board was square shaped with the oscillator
mounted in the center and standoffs at each corner so that when mounted to a test fixture, vibrations
couple into the device uniformly. The board was also designed to minimize extraneous components that
could affect the response of the measurement system to vibration, leading to incorrect conclusions. In
addition to connectors for the output signal and power, the only other components on the boards werepower supply filtering capacitors and LVPECL output passive termination components.
The test fixture for vibration and shock transmitted accelerations along one axis. To test the devices in allaxes with minimum re-configuration, the three boards (one with each device under test, or DUT) were
mounted to a metal plate. A fourth board for which data was not taken was added to each plate to even
the weight distribution on the plate. Three of these plates were then prepared and mounted on different
sides of a metal cube attached to the test fixture. The plates were oriented on the cube such thatmovement of the cube in one axis transmits accelerations in a different axis for each plate and set ofdevices. Figure 1 and Figure 2 depict the finished cube setup.

Figure 1. Orientation Of The Devices On The Cube With respect To Pin 1. Movement Of The Cube Is
Along The Z Axis.

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Test Setup and Procedure

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Figure 2. Photo of Vibration Test Equipment

PC for data
captureAgilent E5052B
Signal source
analyzer

Balun

LVPECL out
Cube

Axis ofacceleration

Agilent E3631A
Power supply
Vibration table

Figure 3. Sinusoidal and Random Vibration Test Setup Diagram
Figure 3 shows the sinusoidal and random vibration test setup. In this test, the cube was mounted on a
vibration table which subjected the units under test to an acceleration of a specific magnitude along one
axis. The DUTs were all powered by a bench power supply. LVPECL differential outputs from the DUTs
were converted to single-ended waveforms before being measured by a signal source analyzer (SSA).
The output clock phase noise and frequency data was then transmitted from the SSA to a PC.

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2.1.1

Test 1: Sinusoidal Vibration
The vibration table was set for a peak acceleration of 4-g. A dwell time of 1 minute was allowed before
taking data to rule out settling effects. The vibration frequencies selected for the test were: 15 Hz, 30 Hz,
60 Hz, 100 Hz, 300 Hz, 600 Hz, 1000 Hz, and 2000 Hz.
Vibrations at a specific frequency manifest as spurs on the output clock phase noise plot that occur at thecorresponding offset from the carrier frequency. The magnitude of these spurs, in dBc, was recorded andconverted into parts per billion (ppb) frequency shifts. Finally, the ppb value was normalized by the peakacceleration of 4-g to obtain a frequency shift per g of acceleration value (ppb/g), which is a measure ofresilience to vibration for an oscillator.

Figure 4. Vibration Test Setup Showing Cube On Vibration Table With The DUTs Connected To A Power
Supply And Signal Source Analyzer

2.1.1.1

Random Vibration

In this test, the cube was subjected to accelerations with random frequency content that mimicked a realworld application. The test setup was similar to the previous one where we measured the impact ofsinusoidal vibration. For the random vibration test, the vibration table was set to generate an acceleration
profile as defined by MIL-STD-883H, Method 2026, Condition B. (1) This profile subjects the DUTs to an
acceleration of 7.5-g rms.
Random vibrations also increase oscillator phase noise. The test hardware generated random vibration
over the specified frequency range, based on the power spectral density level as shown in Figure 5. Since
the vibration was spread over a range of frequencies, there was an overall increase in the phase noise of
the output clock from the DUT rather than just spurs at specific frequency offsets. The integrated RMS
phase jitter values were measured over an integration band from 15 Hz to 10 kHz, which wasapproximately the range of vibration frequency content generated by the vibration table according to MILSTD-883H. Measurements were taken with and without the vibrations present and the RMS jitter
difference between the two cases was calculated to determine the jitter induced by the vibration for each
DUT.

(1)

“MIL-STD-883H, Test Method Standard, Microcircuits.” Department of Defense. 26 February 2010.

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Test Setup and Procedure

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Figure 5. MIL-STD-883H, Method 2026: Random Vibration (2)(2)

6“MIL-STD-883H, Test Method Standard, Microcircuits.” Department of Defense. 26 February 2010.
Vibration and Shock Sensitivity: A Comparative Study of Oscillators
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2.1.2

Test 3: Mechanical ShockPC for data
captureAgilent E5052B
Signal source
analyzer

Balun

LVPECL out
Cube

Direction ofdrop

Agilent E3631A
Power supply

Shock table

Figure 6. Shock Test Setup Diagram
In this test, the cube was subjected to an impulsive acceleration to determine the impact of shock on the
DUT output frequency. Instead of the cube being mounted on a vibration table, it was attached to a guiderail on a shock table which allowed the cube to be lifted and then dropped in a controlled manner,
resulting in mechanical shock when it hit the table. Also, only 1 DUT was attached to the cube at a time, toavoid causing damage to units not being tested. The shock applied is defined by MIL-STD-883H, Method
2002, Condition A. (3) This profile subjects the DUTs to a 1 ms half sine wave shock pulse with anacceleration of 500-g.
A shock impact could result in a momentary output frequency excursion or in extreme cases a permanent
shift in the operating frequency. Data was measured using the transient mode of the signal source
analyzer to record the output frequency every 100 μs for a 10 second duration surrounding the moment of
impact. Three trials were run to account for any inaccuracy that may have resulted from the frequency
excursion falling within the sampling interval. The worst case frequency deviation and any persistentfrequency offset after the impulse was then used to compare the resilience of the DUTs to shock.

(3)“MIL-STD-883H, Test Method Standard, Microcircuits.” Department of Defense. 26 February 2010.

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Data and Results

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Figure 7. Shock Test Setup Showing Cube On Shock Table And Guide Rail. Only 1 Dut Is Attached At A
Time To Avoid Causing Damage To The Others.

3

Data and Results

3.1

Test 1: Sinusoidal Vibration
The two PLL based oscillators showed roughly similar levels of sensitivity to sinusoidal vibration. The
average frequency shift per ‘g’ of acceleration also did not change significantly as the frequency wasvaried for any of the devices. The TI oscillator showed less sensitivity than the other PLL based device at
1 kHz of vibration along the Y-axis, but in general, the devices had comparable performance. The Epson
SAW oscillator was the most sensitive to sinusoidal vibration, exhibiting an order of magnitude more
frequency shift along the X and Z axes.

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Data and Results

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Figure 8. Sensitivity To X-axis Acceleration Over Frequency Of Vibration. Lower Is Better.

Figure 9. Sensitivity To Y-axis Acceleration Over Frequency Of Vibration. Lower Is Better.

Figure 10. Sensitivity To Z-axis Acceleration Over Frequency Of Vibration. Lower Is Better.

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Data and Results

3.2

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Test 2: Random Vibration
The TI oscillator clearly stood out with superior vibration resistance when subjected to random vibration. It
exhibited the lowest average induced phase jitter out of the devices tested. Its performance exceeds thatof the Silicon Labs part along every axis of vibration, with about 25 times less induced jitter along the Z
axis. The Epson SAW oscillator was again the most vibration susceptible device in the test group, with theworst average induced jitter. The fact that the induced jitter can sometimes exceed 100 ps RMS, which issignificantly higher than baseline values, underscores the importance of considering vibration when
designing an oscillator into a system.

Figure 11. Phase Jitter Induced by Random Vibration. Lower Is Better.

3.3

Mechanical ShockThe shock test data was fairly consistent with the results of the random vibration test. The TI oscillator
exhibited significantly less frequency shift compared to the device from Silicon Labs. Neither device
showed a permanent shift in output frequency after the impulse was removed. However, the test was
performed at the lowest acceleration level under the MIL-STD-883H. Increasing the shock to a highenough level could cause permanent damage, so applications wherein high shock impact is plausible,
additional testing is recommended.

Figure 12. Frequency Deviation in ppm Under 500-g Shock. Lower Is Better.

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4

Conclusion
When designing a clock oscillator into a system, the impact of vibration is often overlooked. However, as
demonstrated above, oscillators with similar specifications can exhibit vastly different behaviors whensubject to vibration or shock, possibly resulting in the addition of tens of picoseconds of jitter and violationof design requirements. TI’s LMK61E2 and LMK6xxx family of oscillators are engineered with robustness
in mind and the tests performed in this study demonstrate the effectiveness of their design. The vibrationand shock resilience of TI oscillators complements their ultra-low phase noise, making Texas Instruments
the optimal choice for current and next generation high performance systems

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References
Vig, John R. “Quartz Crystal Resonators and Oscillators.” US Army Communications-Electronics
Research, Development & Engineering Center. January 2004.
“MIL-STD-883H, Test Method Standard, Microcircuits.” Department of Defense. 26 February 2010.

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