Introducing the eye diagram method in this app note from ON Semiconductors in determining signal integrity of USB lines. Link here (PDF)
The Universal Serial Bus (USB) has become a popular feature of PCs, cell phones and other electronic devices. USB makes data transfer between electronic devices faster and easier. USB 2.0 transfers data at up to 480 Mbps. At these data rates, any small amount of capacitance added will cause disturbances to the data signals. Designers are left with the challenge of finding ESD protection solutions that can protect these sensitive lines without adding signal degrading capacitance. This document will discuss USB 2.0 and evaluate the importance of low capacitance ESD protection devices with the use of eye diagrams.
Application note from ON Semiconductors about the Data eye diagram methodology to represent and analyze a high speed digital signal. Link here (PDF)
The eye diagram allows key parameters of the electrical quality of the signal to be quickly visualized and determined. The data eye diagram is constructed from a digital waveform by folding the parts of the waveform corresponding to each individual bit into a single graph with signal amplitude on the vertical axis and time on horizontal axis. By repeating this construction over many samples of the waveform, the resultant graph will represent the average statistics of the signal and will resemble an eye. The eye opening corresponds to one bit period and is typically called the Unit Interval (UI) width of the eye diagram. An ideal digital waveform with sharp rise and fall times and constant amplitude will have an eye diagram.