RE: [SI-LIST] : Return path for stripline, two ground planes or o ne power and one ground?

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From: Harris, George ([email protected])
Date: Fri Mar 31 2000 - 07:08:08 PST

It depends on the driver type you are using. For a push-pull driver it is
best to surround the signal with a ground plane and a power plane connected
to the same Vdd supply the driver is using. This produces the lowest return
loop inductance by not forcing the return current to flow through the bypass
caps, which would make it follow a longer path.
For open-drain (or open-collector) drivers two ground planes are best.
It is easy to get confused in this case.

George Harris
Tel: 508-467-8893
[email protected]
COMPAQ Computer Corporation


-----Original Message-----
From: [email protected] [mailto:[email protected]]
Sent: Thursday, March 30, 2000 8:00 PM
To: [email protected]
Cc: 'Kai, Francis'
Subject: [SI-LIST] : Return path for stripline, two ground planes or one
power and one ground?

Dear All SI experts,

One question regarding to return path for signals.

If we have stripline configuration, a signal trace between power plane and
ground plane.
When the signal is transient from high to low or low to high, the return
path will be the power or ground plane to a driver's power pins or ground

However, if we change the power plane to ground plane, then the return path
will be the ground planes, above and below the signal trace. It ,then,
passes through the ground planes to the power pins via bypass

cap. or a chip internal path (ground to power).

My question is which configuration is the best for the return path --
1. One power and one ground plane, or
2. Two ground planes with plenty of bypass cap. or
3. Two ground planes with a few bypass, heavily depend on the internal
path. ( I am afraid of noise coupling internally).

Best Regards,
John Lin
SI Engineer
Quanta Computer Inc.,Taiwan, R.O.C.
Email: [email protected]
Tel: 886+3+3979000 ext. 5183

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