## Diagnosis using the eye diagram

#### From the eye diagram it is possible to make an engineering judgement on the likely performance and sources of degradation in a data communications link. Shown here are examples of eye diagrams for various types of distortion – each having a unique identifiable effect on the appearance of the 'eye opening'.

#### The effect of timing error is seen as a skewing of the eye diagram and a closing of the eye due to the received symbol stream no longer being sampled at the point of zero ISI. The addition of noise affects the timing recovery circuitry and also causes a general closing of the eye until eventually the noise occasionally causes full 'eye-closure' and errors occur.

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