EyeDiagramme

EyeDiagramme, commonly called an eye diagram, is a visualization technique used in digital electronics to assess signal integrity in high-speed interconnects. It shows the superposition of many symbol periods of a digital waveform, overlaid to form an eye-shaped pattern. The diagram is typically generated by a sampling oscilloscope or a digital oscilloscope in eye-diagram mode, by repeatedly sampling the signal around the same reference point in each bit period and accumulating the traces.

Interpretation of the diagram centers on the eye opening. The width of the eye opening corresponds to timing margin, while the height relates to voltage margin. A wide, clear eye indicates low jitter and low noise, and good signal integrity, whereas a closed or narrowed eye suggests jitter, noise, distortion, or inter-symbol interference. The overall shape can reveal timing skew, duty cycle distortion, baseline wander, and other degradations in the transmitted signal.

Applications and measurement considerations: Eye diagrams are used to characterize high-speed serial interfaces such as PCIe, USB, Ethernet, and memory channels, as well as PCB traces and channels in general. They assist in assessing achievable data rates, the effectiveness of equalization, and the requirements for receiver sensitivity. The interpretation depends on the measurement setup’s bandwidth, sampling rate, triggering accuracy, and the coding scheme employed in the signal.

See also: digital signal integrity; jitter; eye pattern; oscilloscope; inter-symbol interference.