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High Speed Signal Integrity

The Internet of Things and Data Science applications are leading to an ever-increasing growth in data requiring ever faster and larger data centers and data interconnect capacity.  5G holds the promise of virtually eliminating data latency.  These factors in turn are leading to new demands for interconnects capable of efficiently handling data at ever greater data rates and over ever greater number of connector pins.  Electrical signals at high bit rates and traveling through different mediums can degrade significantly and to the point where errors occur and the system or device fails. Problems that arise at high speed include the reflections at interconnects caused by mismatched impedances. These can be due to mechanical structure of the interconnect and how they interface to the transmission lines.  Problems such as ringing, reflections, distortion, undershoot, overshoot, and degradation can result. Engineering interconnects to ensure signal integrity is vital to mitigating these effects.

The effects are more pronounced at higher frequencies in digital circuits.  At multi-gigabit/s data rates, designers must consider reflections at impedance changes, noise induced by densely packed neighboring connections (crosstalk), and high-frequency attenuation caused by the skin effect in the metal trace and dielectric loss tangent. For example, impedance mismatches at the pins on each end of the connectors on a PCB cause reflections and significant signal degradation. At high rates, the bit period is shorter than the flight time.  Echoes of previous pulses can lead to eye closure.

Challenges and opportunities exist. New simulation models and instrumentation capable of accurately predicting behavior and measuring such behavior in shorter time need to be developed to allow for faster and more accurate design simulations at these high frequencies.  New interconnect materials may be most helpful with respect to handling impedance mismatch and reducing connector crosstalk.