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How to Determine Correct Signal Amplitude and VECP?
Petar Pepeljugoski, IBMJeremy Schaub, IBM
John Ewen, JDS Uniphase
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Why is This a Problem
• Scopes have various settings for determining signal amplitude (mode, mean, min/max)
• Signals measured are complex signals accompanied by ISI, noise, sinusoidal interference– Degradations and data patterns change signal histograms,
may confuse scope algorithms• 802.3ae Draft does not adequately specify how
measurement should be done
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How do we measure amplitude
• Usually histograms for eyes based on OFSTP4A, mode for signal wavefms.
-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0 .4 0 .6 0.8 1-60
-40
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Time [Bit Intervals]
Am
plitu
de
Eye-diagram ISI Penalty=2.5238 [dB]
-0.9 -0.8 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0-20
0
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Test Setup
+26dBamp
Synth2.0GHz
PG LD1
OpticalAtten
ED
Tek scope w80C02 optical head
RX
LD2
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Measured Eye Diagrams, Ideal, No AM, No VECP
Ideal, no AM, EYE (OFSTP4A) Ideal, no AM, Pulse (mode of hist.)
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Measured Eyes With 2.2 dB VECP, No AM
2.2 dB VECP, no AM, EYE method
2.2 dB VECP, no AM, Pulse method
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Measured Eyes, Ideal With AM
Ideal, with AM, Eye method Ideal, with AM, Pulse method
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Measured Eyes, VECP With AM
VECP, AM, EYE method VECP, AM, Pulse method
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Summary of Results
700YesPulseYes
743YesEyeYes
739NoPulseYes
859NoEYEYes
840YesPulseNo
743YesEyeNo
875NoPulseNo
865NoEYENo
AmplitudeISI?MethodAm stress?
Variability – up to 0.9 dB
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How Do We Resolve This?
• The standard does not adequately specify how to measure the signal amplitude– Affects also the stressed signal VECP
determination
• We need to specify the settings, in order to avoid variability in measurements at different sites