Re: [SI-LIST] : A Question About Power Noise.

Georg Ramsch (georg.ramsch@po.uni-stuttgart.de)
Fri, 05 Mar 1999 08:56:55 +0100

Hello, Kidong Lee !

The answer to your problem depends on your application.
Lets have a try to explain it (without circuit schematic it is difficult to describe)

1) Does your circuit has any signal connects to other circuitry (supposed to be in a car) ??
If so, it depends where you insert the inductor. Having for example three circuits and for every
circuit an inductor to common GND (GND is reference for all signals!), then the following may happen:
on one circuit is a current transient directed to GND, which causes a GND-bounce.
With active signals at the same time propagating to the other circuitry, you will see this GND-bounce
propagate through low-active signal lines to the other circuitry.
If this GND-bounce peak is near to the switching treshold of logic devices, then you may get sporadic
failures. So it may be not a good idea to insert an inductor.

Also take in regard, that every connector and cable harness puts inductive effects on your circuits !

The best approach for testing this is putting up a Spice model and simulating it.

Besides, a lot of design engineers have the same problem with bussed computer system and plug-in boards.
Every board has a very small inductive path from plug-in board GND to backplane-GND, which is sufficient
to cause a lot of SI-problems.

2) You have one inductor for the whole circuitry. (Here I have no answer ready) Again: simulation with Spice.

Hope, I could help you.

Georg

kidong lee wrote:

> Hello everybody!
>
> In order to reduce power noise, one uses usually a capacitor between VCC
> and GND or(and) adds an inductor to VCC in series.
> Then, how about adding an inductor to GND, too ?
> Does It work well or not ?
> Does Anybody have an answer ?
> Please reply to me.
>
> Thank you!
>
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