An eye diagram is a useful tool for understanding signal impairments in the physical layer of high-speed digital data systems, verifying transmitter output compliance, and revealing the amplitude and time distortion elements that degrade the BER for diagnostic purposes. A Bit Error Rate Tester (BERT) is often used to generate a known, repeatable test pattern, such as a Pseudo-Random Binary Sequence (PRBS), which is essential for constructing a complete eye diagram that includes all possible bit sequences. This parameter indicates the vertical margin between logic “1” and logic “0”, reflecting the noise tolerance of the transmitted optical signal. 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. It then describes different ways that information from an eye diagram can be sliced to gain more insight.
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