Eye pattern

The eye diagram is a graphical representation of electrical signal waveforms by means of which the signal quality of a digital data transmission can be assessed. It is produced by the graphic overlay of multiple measurements of the same signal at different times. To the data stream is subdivided into equally long sections which are a multiple of the symbol duration in length. These are above each other using a luminescent oscilloscope or storage oscilloscope. This creates a kind of summation of randomly distributed potential waveforms on the screen. Due to the influences to which the signal is subjected to pass the theoretically infinitely steep transitions from 0 to 1 and vice versa not mathematically rectangular or constant at the same position, but as a more or less broad smeared ramps, whereby in the center is formed, the typical shape of an eye.

The vertical eye opening shows whether a transfer is possible and how sensitive the transmission over interference is. If the eye is closed, so no signal reconstruction is possible by a simple threshold filter. If the transmission faults can be predicted because they are causal and deterministic, the signal can be received by equalization continue.

The horizontal eye opening indicates the time range in which the sampling ( evaluation) of the logical instantaneous state is possible and is limited among others by the symbol crosstalk. Due to jitter, the phase relationships are not clear or change too much, then closes the eye ( second image from right). At even an open eye, the identification will be impossible if the level does not have the necessary amount to control the subsequent step.

Eye diagram of the binary signal

Deteriorating eye diagram of a binary signal by inter-symbol interference

Eye diagram of a signal with four icons ( four states)