[SI-LIST] LC filters on power pins
- From: David Kaiser <david.kaiser@xxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Thu, 27 Sep 2001 10:13:53 -0600
I have a question about LC filters on power SERDES and other Gbit devices.
Most SERDES venders provide app notes that suggests using LC filters on the
power pins of these Gbit devices to prevent noise from getting on to the
power planes. But it seems to me that the LC filter components would have no
effect at these Gbit frequencies, and could in fact make matter worse
because the power pins would have no more than maybe a small island of
interplane capacitance for decoupling. It seems that it would be better to
just tie the power pins directly to buired capacitance planes. What do the
SI gurus think?
Also, it seems that at multiple GHz frequencies, the return path for the
noise on the power planes would be so short, that noise would be squelched
to quickly to cause problems on the planes.
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