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What Are Eye Diagram Fundamentals?
April 06,2016 22:15:33

In telecommunication, an eye pattern, also known as an eye diagram.Eye diagram is a series of digital signal accumulate on the oscilloscope and form a graph,it’s shape is similar to the eye,so called eye diagram.


An eye diagram is a common indicator of the quality of signals in high-speed digital transmissions. Eye diagrams usually include voltage and time samples of the data acquired at some sample rate below the data rate.A perfect eye diagram contains an immense amount of parametric information about a signal, like the effects deriving from physics, irrespective of how infrequently these effects occur.


Eye diagrams provide instant visual data that engineers can use to check the signal integrity of a design and uncover problems early in the design process.Used in conjunction with other measurements such as bit-error rate, an eye diagram can help a designer predict performance and identify possible sources of problems. 


In the testing, it is close relationship between "eye pattern" and "quality". if the eye pattern is good and stable, that is mean the module's quality is good.


There are various shapes of the eye,the eye diagram also.We can quickly judge the signal quality by the shape characteristics of the eye diagram.


1.The below eye diagram of "double eyelid",can judge that the signal may crosstalk or pre (go) aggravation.



2.The below eye diagram "bloodshot eyes",this indicates poor signal quality,test methods may be wrong, also may be PCB layout has an obvious error.



3.A complete eye diagram should contain from "000" to "111" in all state group, 8 states formed an eye diagram,picture as below:

The effect of termination is clearly visible in the eye diagrams generated.


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Related reading: Finisar Active optical cable  Gigabit Ethernet media converter

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