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

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From: Harris, George (George.Harris@compaq.com)
Date: Fri Mar 31 2000 - 07:08:08 PST


John,
 
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
George Harris
Tel: 508-467-8893
george.harris@compaq.com
COMPAQ Computer Corporation

 

-----Original Message-----
From: John@quantatw.com [mailto:John@quantatw.com]
Sent: Thursday, March 30, 2000 8:00 PM
To: si-list@silab.eng.sun.com
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
pins.

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: John@quantatw.com
Tel: 886+3+3979000 ext. 5183

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