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The Eye mode PAM Outer OMA measurement measures Optical Modulation Amplitude (OMA) with a PAM4 signal's level 0 and level 3. Amplitude values are not derived from the PAM4 eye diagram but on the central two unit intervals of a run of seven consecutive level 3 UIs and run of six consecutive level 0 UIs. You can select the measurement unit-of-measure to be Watts or dBm for an optical signal and Volts for an electrical signal.

Before making this measurement, observe the following conditions:

  • Select an approximate 13.28125 GHz fourth-order Bssel-Thomson reference filter bandwidth.
  • Use a test pattern that contains at least six consecutive level 0 UIs and seven consecutive level 3 UIs. With a PRBS13Q test pattern, only the longest run of level 3 UIs and the longest run of level 0 UIs are used. For longer patterns several level 3 runs and several level 0 runs may be included.
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.

This measurement applies to PAM4 waveforms and cannot be applied to NRZ waveforms.

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 calculated by subtracting the average level 0 value from the average level 3 value.

To measure

  1. Configure a test pattern that contains at least 6 consecutive level 0 UIs and 7 consecutive level 3 UIs. If the pattern does not contain the correct level runs, FlexDCA displays a status message.
  2. Select Eye/Mask Mode.
  3. Turn on pattern lock.
  4. Turn on waveform wrapping (Wrap Waveform) in the Acquisition Setup dialog.
  5. Click Auto Scale in the menu toolbar.
  6. Click the toolbar's PAM tab.
  7. On the toolbar, locate and click the Outer OMA button.

SCPI Command