We use S parameters to analyze a PCB channel. Once the S parameters are extracted, what I have seen is SI engineers will check the S parameters obtained are passive and casual.

I have some questions about it.

  1. A PCB channel consists of copper traces. The trace has some resistance, capacitance and inductance. May I know in any case will this trace become an active element.

  2. Will this channel become non-causal at any time.


1 Answer 1


Such a channel will always be passive and causal (not casual).

What they are checking for is not that the channel is passive/causal, they know that, it's that the measurements of the channel show it to be passive/causal.

A measurement showing it to be otherwise would demonstrate that the measurement was wrong.

  • \$\begingroup\$ ,thank you. "it's that the measurements of the channel show it to be passive/causal.".You mean they are checking that the tool extracted S parameters properly or not \$\endgroup\$
    – HARI T O
    Dec 2, 2021 at 6:07
  • \$\begingroup\$ @HARITO yes. It's like checking a police speed radar camera reading. If the reported speed of a car over 300 km/hr, it's quite clearly the measurement that's wrong. \$\endgroup\$
    – Neil_UK
    Dec 2, 2021 at 7:44

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