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

Mark Randol (ryvw50@email.sps.mot.com)
Wed, 17 Mar 1999 10:05:38 -0700

Nirmal Jain wrote:
>
> Dear Kidong,
>
> I have not heard of adding inductors in series with GND or VCC to reduce the ground bounce or SSN. In fact
> this would increase your power/ground noise.

If you don't add local sources for charge to lower the supply impedance,
that's right. You can't just add some Z to the supply path and call it
"fixed".

> The voltage drop in the VSS and GND planes is given by Leff * di/dt where L is the effective inductance for a particular switching pattern. If you add L in series, your effective L is going to increase and so is the noise.

Again, you're using a shunt C/series L to make a low pass network
onto supply. With the proper C between the L and the part, you've
maintained a local low impedance source while attenuating the high
frequencies getting onto the supply.

-- 
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Mark Randol, RF Systems Engineer        | Motorola SPS, Inc.
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