PAM Outer Extinction Ratio

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The PAM Outer Extinction Ratio measurement is the ratio the PAM waveform's average level 3 value to the average level 0 value over a defined run of PAM4 symbols on a SSPRQ or a PRBS13Q test pattern. You can select the unit-of-measure to be ratio, decibels, or percent.

The PAM4 ER measurement is constructed from distinct and separate sections of the test pattern and not the eye diagram. Even if the PAM4 eye diagram is displayed, the DCA will construct the measurement on the specific symbols required. This is typically the central 2 symbols from seven consecutive 3’s and six consecutive 0’s. In the absence of those specific symbols, the DCA will find the longest sequences available and annotate the result with a ‘?’. It is impractical to display the construction of the PAM4 ER measurement. When measurement annotation is enabled, the 3 and 0 amplitude levels derived from the appropriate symbols will be displayed, positioned in the center of the PAM4 eye diagram. This should not be interpreted as the signal levels being derived from the aggregate eye diagram.

Example power levels P0 and P3 from PRBS13Q test pattern (Reference from IEEE 802.3 clause 121)
Settings That Affect This Measurement
Setting Description
Pattern lock Required. How to turn on pattern locking.
Waveform wrapping Required. How to turn on waveform wrapping.

The accuracy of the Outer Extinction Ratio measurement can be affected by offsets, including the dark level, generated within the instrument electronics, typically following the photo diode. Offsets add to the incoming signal changing the values of the one and zero levels. This may decrease or increase the measurement result. To minimize Outer Extinction Ratio measurement errors due to offsets, first perform a dark calibration.

Perform a Dark Level calibration if there is no current calibration. If you have previously performed an Dark Level calibration and a change to the environment of the instrument occurs, you may want to perform a new Dark Level calibration to ensure the accuracy of the earlier calibration. These environment changes are as follows:· vertical scale is modified, vertical offset is modified, module is installed/removed, ± 1°C temperature change from calibration temperature, approximately 8 of hours of continuous operation is exceeded, or power is cycled.

The vertical scale setting affects the magnitude of the dark level offset. For best accuracy, perform the Dark Level calibration at the vertical scale at which you will make your measurement.

This measurement applies to PAM4 waveforms and cannot be applied to NRZ waveforms. For NRZ waveforms, use the Extinction Ratio measurement.

Measurement Algorithm

  1. The user should initiate an autoscale. This causes the instrument to detect if the signal is formatted as PAM4 or NRZ.
  2. Determine the approximate signal-level amplitudes.
  3. Locate the crossing (transition) regions on both sides of the eyes.
  4. Determine the symbol period.
  5. Find runs of 6 consecutive 0's and 7 consecutive 1's.
  6. For the central 2 UI of the run, determine the window for measuring the level's RMS value.
  7. The level 0 and level 3 run measurements are made over the central 2 UI of the run. The average amplitude for level 0 and for level 3 are calculated.
  8. The measurement is the ratio of the average level 3 value to the average level 0 value.

To measure

  1. Select Eye/Mask Mode.
  2. Turn on pattern lock.
  3. Turn on waveform wrapping (Wrap Waveform) in the Acquisition Setup dialog.
  4. Click Auto Scale in the menu toolbar.
  5. Click Eye/Mask mode's PAM toolbar.
  6. On the toolbar, locate and click the Outer Extinction Ratio button.

SCPI Command