Subject: Spice to IBIS conversion - 25 ohmns vs. 50 ohms

From: [email-masked]
Date: Thu, 22 Mar 2001 13:25:39 -0600

What is the ramifications of creating an IBIS model from a SPICE deck 
setup into a 25 ohm load vs. a 50 ohm load.
My contractor that is doing the work claims that the Waveform doesn't look 
right going into 50 ohms (which is what the IC manufacture claim is the 
test load) but looks better going into 25 ohms.
What does this mean to me?
Possible incorrect AC parameters?
What?

Thanks in advance,
Stacy

---

From: "Peters, Stephen" <[email-masked]>
Date: Fri, 23 Mar 2001 12:24:51 -0800

Hi Stacy:
 
  I'm not sure what your contractor means by 'don't look right', but in
general a 25 ohm load means a reduced output voltage swing.  This may be a
problem if your are trying to capture a detailed VT curve and the transition
is so small you have to make the time step very small to get any detail.
Also, (and this may be more important) assuming the device your modeling is
intended to work into a 40-60 ohm load (i.e. a typical PCB trace), then VT
curves taken with a 50 ohms load will reflect device operation better than
ones taken at 25 ohms.  If I were you I'd enquire further about what doesn't
look right with the waveforms into 50 ohms.
 
  Regards,
  Stephen Peters
  Intel Corp.

-----Original Message-----
From: [email-masked] [mailto:[email-masked]]
Sent: Thursday, March 22, 2001 11:26 AM
To: [email-masked]
Subject: Spice to IBIS conversion - 25 ohmns vs. 50 ohms

What is the ramifications of creating an IBIS model from a SPICE deck setup
into a 25 ohm load vs. a 50 ohm load. 
My contractor that is doing the work claims that the Waveform doesn't look
right going into 50 ohms (which is what the IC manufacture claim is the test
load) but looks better going into 25 ohms. 
What does this mean to me? 
Possible incorrect AC parameters? 
What? 

Thanks in advance, 
Stacy