Editing Eye pattern (section)

{{Short description|Oscilloscope display of a digital data signal}}
{{Distinguish|Optical illusion}}

[[File:On-off keying eye diagram.svg|thumb|300px|right|Graphical eye pattern showing an example of two power levels in an [[On-off keying|OOK]] modulation scheme. Constant binary 1 and 0 levels are shown, as well as transitions from 0 to 1, 1 to 0, 0 to 1 to 0, and 1 to 0 to 1. ]]

In [[telecommunications]], an '''eye pattern''', also known as an '''eye diagram''', is an [[oscilloscope]] display in which a [[Digital signal (electronics)|digital signal]] from a receiver is repetitively sampled and applied to the vertical input (''y-axis''), while the data rate is used to trigger the horizontal sweep (''x-axis''). It is so called because, for several types of coding, the pattern looks like a series of eyes between a pair of rails. It is a tool for the evaluation of the combined effects of channel noise, dispersion and [[intersymbol interference]] on the performance of a baseband pulse-transmission system. The technique was first used with the [[World War II|WWII]] [[SIGSALY]] secure speech transmission system.

From a mathematical perspective, an eye pattern is a visualization of the [[probability density function]] (PDF) of the signal, [[Modular_arithmetic|modulo]] the [[Unit_interval_(data_transmission)|unit interval]] (UI). In other words, it shows the probability of the signal being at each possible voltage across the duration of the UI. Typically a [[False_color#Pseudocolor|color ramp]] is applied to the PDF in order to make small brightness differences easier to visualize.

Several [[system]] performance measurements 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 [[Noise (electronics)|noisy]], or too slow to change, or have too much undershoot or [[overshoot (signal)|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.<ref>Christopher M. Miller "High-Speed Digital Transmitter Characterization Using Eye Diagram Analysis". [http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1994-08.pdf 1266 Hewlett-Packard Journal 45(1994) Aug., No,4] {{Webarchive|url=https://web.archive.org/web/20210126091059/http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1994-08.pdf |date=2021-01-26 }}, pp. 29-37.</ref><ref>{{FS1037C MS188}}</ref><ref>John G Proakis, Digital Communications 3rd ed, 2001</ref>