[SI-LIST] Driver strength and trace capacitance

I was simulating a 2" long net driven by an ASIC and noticed significant 
ringing and non-monotonicity.  This is a bidirectional net and the driver 
at the other end is a 50 ohm driver, which does not require any 
termination.  From the IBIS model I deduced the driver impedance to be 
about 3 ohms, which I thought was quite low.  I was told that the ASIC 
vendor was asked to design the driver to drive a 100 MHz signal in to a 35 
pF load.  The trace capacitance is about 10 pF (including vias), and the 
receiver capacitance is less than 5 pF (package plus die).  To me this 
appears to be a case of over-design.  However, I have one question about 
the trace capacitance.  Can it be considered a lumped load or a 
distributed load.  The Lambda/20 length at 100 MHz is about 3" so I am 
inclined to treat the total trace capacitance as a lumped load.
Regards, Ravinder
Server PCB Development
Hitachi Global Storage Technologies

Email: Ravinder.Ajmani@xxxxxxxxxxxxxx

------------------------------------------------------------------
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:
http://www.freelists.org/webpage/si-list

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

List FAQ wiki page is located at:
                http://si-list.org/wiki/wiki.pl?Si-List_FAQ

List technical documents are available at:
                http://www.si-list.org

List archives are viewable at:     
                http://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

Other related posts: