PCB Currents: How They Flow, How They React

B. Eye Diagrams

An “eye diagram” is a visual, empirical way of looking at a circuit to try to assess the noise margins that may exist in the circuit. It involves letting a circuit run through all possible bit transitions and superimposing all the different signal patterns that emerge. We can do this by simply letting the circuit “free run” for a while, or by programming a specific set of signals that will accomplish the same thing more efficiently. As we will see, the transitions ideally form an eye that is wide open.

An eye diagram is a point concept. That is, it describes what is happening at one specific point in the circuit. A clean eye at one point in a circuit does not imply a clean eye at another point in the circuit. Start by looking ...