Signal Degradation
Performance metrics for high-speed digital channels describe the reduction in the open area of an oscilloscope display representing the transitions of a random data sequence. When eye closure increases, the margin for error in sampling the high and low voltage states shrinks, making the system more vulnerable to bit errors. This metric quantifies the collective impact of attenuation, inter-symbol interference and crosstalk on the received signal.
It applies to active transmission lines operating at high data rates, but ceases to be useful if the receiver uses equalization to reconstruct the signal before sampling.
Jitter Influence
Noise sources on the circuit board, such as power plane fluctuations and trace-to-trace coupling, directly alter the signal waveforms. As these disturbances accumulate, the horizontal and vertical open dimensions of the signal eye shrink. This contraction indicates that the transmission path has exceeded its design budget.
Receiver Margin
Multi-gigabit designs require that the signal maintain a minimum open area at the receiver pins to ensure a low bit error rate. If the eye is shut beyond the limits of the receiver, the data cannot be recovered. The layout must then be modified to reduce trace lengths or use higher-quality laminate materials.
