Kishori Sharan Mathur

Research Scholar, JJT University,

Jhunjhunu – 333001, Rajasthan, India

kishorimathur@hotmail.com

WHAT IS THE EYE DIAGRAM?

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THE EYE DIAGRAM IS A STATISTICAL REPRESENTATION

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The following aspects of the eye are important: 1. The vertical eye opening indicates the amount of difference in signal level that is present to indicate the difference between one-bits and zero-bits. The bigger the difference the easier it is to discriminate between one and zero. Of course this is affected significantly by noise in the system. 2. The horizontal eye opening indicates the amount of jitter present in the signal. The wider the eye opening is on this axis the less problem we are likely to have with jitter. 3. The thickness of the band of signals at the zero-crossing point is also a good measure of jitter in the signal. However, you need to be careful here as the sweep is usually triggered from the receiver PLL and variations here are as much an indicator of the quality of the PLL as they are of the signal itself! 4. The best indication of signal “goodness” is just the size of the eye opening itself. The larger it is the easier it will be to detect the signal and the lower will be the error rate. When the eye is nearly closed it will be very difficult or impossible to derive meaningful data from the signal.

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JITTER

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THE UNFILTERED EYE

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THE FILTERED EYE

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THE EYE PATTERN

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The analog representation of the digital signal waveform

Overlays both “0” and “1” values

Time

Power

Logic “0”

Logic “1”

Rise/Fall Hold

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EYE-DIAGRAM TEST SETUP

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