Eye pattern

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In telecommunication, an eye pattern, also known as an eye diagram, is an oscilloscope display in which a digital data signal from a receiver is repetitively sampled and applied to the vertical input, while the data rate is used to trigger the horizontal sweep. It is so called because, for several types of coding, the pattern looks like a series of eyes between a pair of rails.

Several system performance measures can be derived by analyzing the display. If the signals are too long, too short, poorly synchronized with the system clock, too high, too low, too noisy, or too slow to change, or have too much undershoot or overshoot, this can be observed from the eye diagram. An open eye pattern corresponds to minimal signal distortion. Distortion of the signal waveform due to intersymbol interference and noise appears as closure of the eye pattern. [1][2][3]

Contents

Example

The eye diagram of a binary PSK system

The eye diagram of the same system with multipath interference effects added

Eye diagram of a 4 level ASK signal

Measurements

There are many measurements that can be obtained from an Eye Diagram[4]:

Amplitude Measurements

  • Eye Amplitude
  • Eye Crossing Amplitude
  • Eye Crossing Percentage
  • Eye Height
  • Eye Level
  • Eye SNR
  • Quality Factor
  • Vertical Eye Opening

Time Measurements

  • Deterministic Jitter
  • Eye Crossing Time
  • Eye Delay
  • Eye Fall Time
  • Eye Rise Time
  • Eye Width
  • Horizontal Eye Opening
  • Peak-to-Peak Jitter
  • Random Jitter
  • RMS Jitter
  • Total Jitter

Interpreting Measurements

See also

Notes

References

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