[ibis-macro] Re: redriver in spice simulation

  • From: Ambrish Varma <ambrishv@xxxxxxxxxxx>
  • To: Todd Westerhoff <twesterh@xxxxxxxxxx>
  • Date: Wed, 13 Mar 2013 08:45:55 -0700

We were discussing how a normal time domain (non-AMI) simulation will work with 
a redriver in the middle of a channel. I suggested that shorting the redriver 
Rx pins with the related Tx should work as the simulator will take care of the 
analog waveforms going out from the Rx and in the Tx – but that will not work 
as we describe below.


From: Todd Westerhoff [mailto:twesterh@xxxxxxxxxx]
Sent: Tuesday, March 12, 2013 9:24 PM
To: Ambrish Varma
Cc: fangyi rao; ibis-macro@xxxxxxxxxxxxx
Subject: Re: [ibis-macro] Re: redriver in spice simulation


I guess I missed part of this conversation.  What problem are you trying to 


Todd Westerhoff
VP, Software Products
Signal Integrity Software Inc. • www.sisoft.com
6 Clock Tower Place • Suite 250 • Maynard, MA 01754
(978) 461-0449<978-461-0449> x24  •  twesterh@xxxxxxxxxx
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                                             -Sidewalk Prophets

From: "Ambrish Varma" <ambrishv@xxxxxxxxxxx>
To: "fangyi rao" <fangyi_rao@xxxxxxxxxxx>, ibis-macro@xxxxxxxxxxxxx
Sent: Tuesday, March 12, 2013 7:34:02 PM
Subject: [ibis-macro] Re: redriver in spice simulation
Actually, if we short the Rx and Tx of the redriver, regular spice simulations 
using IBIS models and analog repeaters will have issues with the Tx trying to 
pullup to power and pulldown to ground.

In that case, redriver simulation within the realm of an IBIS cct, solutions 
can be:

1)      No  spice (non AMI) simulation allowed for redrivers (easier)

2)      Series switch like implementation (harder)


From: fangyi_rao@xxxxxxxxxxx [mailto:fangyi_rao@xxxxxxxxxxx]
Sent: Tuesday, March 12, 2013 4:58 PM
To: Ambrish Varma; ibis-macro@xxxxxxxxxxxxx
Subject: redriver in spice simulation

Hi, Ambrish;

I am not sure if your suggestion of shorting redriver Rx ibis output pin to the 
redriver Tx ibis input pin in spice simulations will work because in spice 

1.       legacy Tx ibis model is driven by input signal threshold crossing 
events. That’s not how a redriver Tx half is driven by input signal.

2.       legacy Rx ibis model output is a digital signal of 1’s and 0’s 
(hopefully I am correct here). That’s not what redriver Rx half outputs.

Due to the uncertainties in redriver model behavior in non-AMI simulations, I 
prefer to keep my redriver BIRD separate from Walter’s repeater BIRD, at least 
for now.


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