TP2 Waveform Capture

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TP2 Waveform Capture

• Pavel Zivny with input from Greg LeCheminant

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TOC

• Proposal for the TP2 CR and Trigger method
• Issues for jitter/noise analysis
• TP2 uncorrelated jitter/noise measurements

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TP2 - CR and Trigger methodProposal

• Record the single valued data pattern waveform
  (rather than the eye diagram) using a
  synchronizing timing reference obtained with a
  clock recovery unit having a characteristic as
  described in 802.3ae 52.9.7 Transmitter optical
  waveform. If a sampling oscilloscope is used,
  the pattern waveform is acquired by means of
  triggering on divided recovered clock (the
  recovered clock is divided by the pattern length
  to produce a trigger edge occurring once per
  pattern repetition).
• Only bits ltxgt through ltygt of pattern ltzgt are
  analyzed. The bits are recognized by their
  position relative to the longest transition-less
  sequence in the pattern. In particular the bits
  are located ltkgt UIs after the sequence lt?gt.

See next page
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TP2 - CR and Trigger methodSupplementary info
CRU per 802.3ae
From 802.3ae 52.9.7 Transmitter optical
waveform A clock recovery unit (CRU) should be
used to trigger the scope for mask measurements
as shown in Figure 52-9. It should have a
high-frequency corner bandwidth of less than or
equal to 4 MHz and a slope of -20 dB/decade."
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Issues for jitter/noise analysis

• Measured uncorrelated jitter and noise are
  assumed Gaussian or other high probability
  jitter. Low probability, high PkPk value
  jitter/noise escapes detection through RMS test.
  Mask test captures this, if thered be no mask
  test this would need addressing in another way.
• Pj, Pn are both bundled into R(andom) component
• Thats a pessimism. Comment from Xmitter
  designers desireable is P ever a problem?
• Always measure with the ORR on. Is there a
  consensus on this?

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Background InformationThree methods of
Jitter/Noise Analysis

• Analyze an LF square-wave
• Simplest Measurement equipment setup
• - Signal far from natural
• - Dedicated pattern not useful for other
  measurements
• Analyze Dedicated bit(s) within a Multi-use
  348-bit Stress Pattern
• Useful, near-natural pattern
• Rj and Rn measurements simple easily
  verifiable
• - Needs Trigger on Pattern (with e.g. a bit
  countdown trigger)
• - Needs a bit search (not implemented today)
• Perform complete Jitter/Noise analysis (Rj and
  Rn, DDj and DDn) on the whole Pattern (e.g. the
  Multi-use 348-bit Stress Pattern)
• Useful, near-natural pattern
• Complete Jitter/Noise measured (rather than just
  one, possibly special, bit)
• - Needs Trigger on Pattern (with e.g. a bit
  countdown trigger)
• - Needs complete jitter/noise analysis package
  (single source, marginal availability today)

Current choice