HyperLynx Signal Integrity

Signal integrity is essentially the analog analysis of the switching behavior of high-speed digital signals. What determines whether signal is “high-speed” and should be considered for signal integrity purposes isn't the data rate; it's the output driver's edge rate. Once the electrical length (delay) of a signal exceeds 1/4 of the driver's rise time, the signal becomes prone to problems with reflections and ringing if impedances aren't carefully managed. This is the threshold where signal integrity becomes important. Signals with low data rates can still have problems with ringing and reflections because signal integrity is about edge rate, not data rate.

Against that backdrop, signal data rates continue to increase dramatically, with edge rates decreasing to keep up. Meanwhile, PCB's aren't really getting smaller, so signal integrity issues are becoming pervasive. 250ps is a typical output edge rate for modern devices, at which point traces longer than 0.375 inches should be considered for signal integrity purposes. The need to consider signal integrity is pervasive in modern design!

To keep the designer’s tasks manageable, many component interfaces are based on standards that define how signals are to be connected and what their electrical characteristics should be. DDR memory and serial link protocols like Ethernet are good examples. If the signal traces conform to these specifications and the components also meet or exceed the specification, the interface *should* work. That said, many of the interface standards specify electrical characteristics like impedance, loss, crosstalk, skew and eye openings - that require detailed modeling and simulation to predict. HyperLynx SI is an ideal solution to these issues.