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Eye pattern

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Graphical eye pattern showing an example of two power levels in an OOK modulation scheme.

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, 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]



[edit] Example

[edit] 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

[edit] Interpreting Measurements

Eye-diagram feature What it measures
Eye opening (height, peak to peak) Additive noise in the signal
Eye overshoot/undershoot Peak distortion due to interruptions in the signal path
Eye width Timing synchronization & jitter effects

[edit] See also

[edit] References

  1. ^ Christopher M. Miller "High-Speed Digital Transmitter Characterization Using Eye Diagram Analysis". 1266 Hewlett-Packard Journal 45(1994) Aug., No,4, pp. 29-37.
  2. ^  This article incorporates public domain material from the General Services Administration document "Federal Standard 1037C" (in support of MIL-STD-188).
  3. ^ John G Proakis, Digital Communications 3rd ed, 2001
  4. ^ [1]Matlab's help file description of how to use the Eye Diagram Functions in the Communications Toolbox

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