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Q-TECH Corporation - 10150 W. Jefferson Boulevard, Culver City 90232 - Tel: 310-836-7900 - Fax: 310-836-2157 - www.q-tech.com
Q-TECH
CORPORATION
QT90 SERIES
HIGH-RELIABILITY MINIATURE CLOCK OSCILLATORS
1.8 to 5.0Vdc
-
15kHz to 160MHz
QT90 (RevisionC,July2008)(ECO#9383)
Phasenoiseismeasuredinthefrequencydomain,andisexpressedasaratioofsignalpowertonoisepowermeasuredina1Hz
bandwidthatanoffsetfrequencyfromthecarrier,e.g.10Hz,100Hz,1kHz,10kHz,100kHz,etc. Phasenoisemeasurementismade
withanAgilentE5052ASignalSourceAnalyzer(SSA)withbuilt-inoutstandinglow-noiseDCpowersupplysource. TheDCsource
isfloatedfromthegroundandisolatedfromexternalnoisetoensureaccuracyandrepeatability.
Inordertodeterminethetotalnoisepoweroveracertainfrequencyrange(bandwidth),thetimedomainmustbeanalyzedinthe
frequencydomain,andthenreconstructedinthetimedomainintoanrmsvaluewiththeunwantedfrequenciesexcluded. Thismaybe
donebyconvertingL(f)backtoSφ(f)overthebandwidthofinterest,integratingandperformingsomecalculations.
ThevalueofRMSjitteroverthebandwidthofinterest,e.g.10kHzto20MHz,10Hzto20MHz,represents1standarddeviationof
phasejittercontributedbythenoiseinthatdefinedbandwidth.
FigurebelowshowsatypicalPhaseNoise/PhasejitterofaQT90L,3.3Vdc,20MHzclockatoffsetfrequencies10Hzto5MHz,and
phasejitterintegratedoverthebandwidthof12kHzto1MHz.
PhaseNoiseandPhaseJitterIntegration
PeriodJitter
Asdataratesincrease,effectsofjitterbecomecriticalwithits
budgetstighter. Jitteristhedeviationofatimingeventofa
signal from its ideal position. Jitter is complex and is
composed of both random and deterministic jitter
components. Randomjitter(RJ)istheoreticallyunbounded
and Gaussian in distribution. Deterministic jitter (DJ) is
bounded and does not follow any predictable distribution.
DJ is also referred to as systematic jitter. A technique to
measureperiodjitter(RMS)onestandarddeviation(1σ)and
peak-to-peakjitterintimedomainistouseahighsampling
rate(>8Gsamples/s)digitizingoscilloscope. Figureshows
an example of peak-to-peak jitter and RMS jitter (1σ) of a
QT90L-100MHz,at3.3Vdc.
RMSjitter(1σ):7.7ps
Peak-to-peakjitter:56ps
Symbol
Definition
∫L(f)
Integratedsinglesidebandphasenoise(dBc)
Sφ(f)=(180/Π)x
√2∫L(f)df
Spectraldensityofphasemodulation,alsoknownasRMSphaseerror(indegrees)
RMSjitter=Sφ(f)/(fosc.360°)
Jitter(inseconds)duetophasenoise. NoteSφ(f)indegrees.