Istvan Novak, Principal Signal and Power Integrity Engineer, Samtec
“When we have multiple noise sources coming from all sides, . . . mitigation becomes a challenge, and that trend is likely to continue.”
Systems are getting smaller and denser, which creates many power-related challenges. As die shrinking reduces the relative distance between components, coupling coefficients go up. How we manage power distribution becomes critical: When we have so many devices in a small area, through-the-air coupling can sometimes interfere with system functionality. In the “old days,” we had the luxury
of putting distance between noise sources and victims. Now, we can rarely do that. In cases of a single noise source, we may find mitigation relatively easy. When we have multiple noise sources coming from all sides, however, mitigation becomes a challenge, and that trend is likely to continue.
Here is an example. We had a packaged DC-DC converter with a typical pin layout: pins for power input and output, pins for control signals, and a few auxiliary power connections for bias voltages in the few-milliamperes range. We built a circuit using good engineering practices, but it did not function properly. We found out that noise generated by high-current circuitry inside the module was coupling to a low-current supply pin on the DC-DC converter. This finding was surprising because you typically expect problems when noise couples to a sensitive signal, but here it was coupling with a power pin. The resulting strange functionality made the problem difficult to diagnose. The power converter still worked, but it put out the wrong DC voltage by a few millivolts. In some circuits, a couple of millivolts would not matter, but they caused serious problems in our precisely sized circuit. As designs become denser, surprises like this may pop up more frequently.
This is an excerpt from 7 Experts on New Approaches for Power Distribution
Network Design. The eBook was generously sponsored by KEMET Corporation and Mouser Electronics.
