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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
QT88 SERIES
HIGH-RELIABILITY MINIATURE CLOCK OSCILLATORS
1.8 to 5.0Vdc
-
15kHz to 160MHz
QT88 (RevisionD,July2008)(ECO#9381)
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/PhasejitterofaQT88L,3.3Vdc,20MHzclockatoffsetfrequencies10Hzto5MHz,and
phasejitterintegratedoverthebandwidthof12kHzto1MHz.
PhaseNoiseandPhaseJitterIntegration
PeriodJitter
Asdataratesincrease,effectsofjitterbecomecriticalwith
itsbudgetstighter. Jitteristhedeviationofatimingevent
of a signal from its ideal position. Jitter is complex and
is composed of both random and deterministic jitter
components. Random jitter (RJ) is theoretically un-
boundedandGaussianindistribution. Deterministicjitter
(DJ) is bounded and does not follow any predictable
distribution. DJisalsoreferredtoassystematicjitter. A
technique to measure period jitter (RMS) one standard
deviation(1σ)andpeak-to-peakjitterintimedomainisto
use a high sampling rate (>8G samples/s) digitizing
oscilloscope. Figure shows an example of peak-to-peak
jitterandRMSjitter(1σ)ofaQT88L-60MHz,at3.3Vdc.
RMSjitter(1σ):6.46ps
Peak-to-peakjitter:80ps
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.