[SI-LIST] Re: Ground, the preferred reference plane

From: "Michael J. Degerstrom" <degers@xxxxxxxxxxxxxxxxxxxx>
To: chris.cheng@xxxxxxxxxxxx,"'si-list@xxxxxxxxxxxxx'" <si-list@xxxxxxxxxxxxx>
Date: Wed, 11 Dec 2002 22:39:52 -0600

Chris,

Once again - if you take the time to read my original post I said that for 
this thread people were using the word 'reference' to mean two very different 
things:

a) In the context of one or more reference planes that set the characteristic 
impedance for the signal. These planes will carry the local return current 
for the signal.

b) In the context of a selected voltage that dictates how circuits interact 
with one another.  For example, consider two ECL chips with external VBB pins 
that are powered from the same VBB on-board supply.  Since these two chips 
have the same switch point voltage reference then they behave very well 
together.  There are cases, where for example, you may want to run these ECL 
chips with a positive voltage in an PECL .   This is often times fine to do 
but if there were grounded metal cases and heat sinks these metal surfaces 
will then be at the positive supply.  I merely mentioned in passing that you 
may not want a design with large areas of bare metal at a non-ground 
potential as the risk of DC shorts during testing, handling, etc., would be 
high.  Please don't read any more into this passing comment - it had no 
relevance to high speed SI issues.

Mike

On Wednesday 11 December 2002 10:17 pm, Chris Cheng wrote:
> I still don't understand what are you talking about. Almost all the high
> performance package I've design or  came across have mulitple planes.
> Sandwiching I/O signal between Gnd and VDDQ is simple to do and common
> practice. Are you telling me there should be no power planes on a package
> because there is potential DC shorting issue ?
>
> -----Original Message-----
> From: Michael J. Degerstrom [mailto:degers@xxxxxxxxxxxxxxxxxxxx]
> Sent: Wednesday, December 11, 2002 6:00 PM
> To: chris.cheng@xxxxxxxxxxxx; 'si-list@xxxxxxxxxxxxx'
> Subject: [SI-LIST] Re: Ground, the preferred reference plane
>
> Also, please note in my original posting my explanations of the two
> different
> meanings of the term 'reference'.  When I spoke about packages, I was
> speaking on the second meaning of 'reference'.  That is, if you are going
> to
>
> change the voltage reference of a part, for example, running ECL as PECL,
> then there are other things to be concerned with beside high-speed issues.
> My example points out that large pieces of metal that were grounded now
> would
> be at the PECL voltage - which could be a potential DC shorting issue.  I
> was
> by no means advocating not using power or ground planes in a high speed
> package.
>
> Mike
> ------------------------------------------------------------------
> To unsubscribe from si-list:
> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
>
> or to administer your membership from a web page, go to:
> //www.freelists.org/webpage/si-list
>
> For help:
> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>
> List archives are viewable at:
>               //www.freelists.org/archives/si-list
> or at our remote archives:
>               http://groups.yahoo.com/group/si-list/messages
> Old (prior to June 6, 2001) list archives are viewable at:
>               http://www.qsl.net/wb6tpu

------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field

or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list

For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field

List archives are viewable at:     
                //www.freelists.org/archives/si-list
or at our remote archives:
                http://groups.yahoo.com/group/si-list/messages 
Old (prior to June 6, 2001) list archives are viewable at:
                http://www.qsl.net/wb6tpu

References:
- [SI-LIST] Re: Ground, the preferred reference plane
  - From: Chris Cheng

[SI-LIST] Re: Ground, the preferred reference plane

Other related posts: