[IBIS-Users] IBIS model for differential bipolar current mode logic output

IBIS users, (See schematic below).
           I am a new creator of IBIS models. The circuit that I need to 
model are bipolar.
The first one I did was for s single ended AB driver with 50 ohm output 
impedance.
I have now been chalanged to create/extract a model for a
bipolar differential current mode logic output buffer, similar in 
principle as I have attempted
to draw below. So the differential extraction processed outlined in the 
IBIS cook book seems
rather complex.
1) I know there are no paths for differential currents to flow.
2) The I/V curve should look like a 50 Ohm resistor referenced to VCC.
The problem I had extracting the IV curves is that the IV curve should 
go to zero I
at some point and this is where the VT curves are tested to match. 
However, the actual circuit is
driven into a region it was not intended to operate in and the curves 
don't match. Another way of
saying this is the circuit simply will not operate unless driven into 
the 50 ohm pullup.
Does anyone have an idea how to get around this???

Jon Read


            Inside die/pkg        |       Outside die/pkg
                                  |
                 VCC              |                                      
  VCC                      
                  |               |                                      
   |            
              ____|___            |                                     
____|____        
             /        \           |                                    / 
        \
   50 Ohms   \        / 50 Ohms   |                            50 Ohms \ 
        / 50 Ohms        
             /        \           |                                    / 
        \
             \        /           |                                    
\         /
          QB 
|--------|-----------|-----=========================------|         | 
      
             |        
|-----------|-----=========================----------------|
             |        | Q         |     50 Ohm Transmission lines
          | /          \ |        |
          |/            \|        |
    D ___ |              |____DB  |
          |              |        |
          |<            >|        |
          | \           /|        |
             \         /          |
             |_________|          |
                  |               |
                                |                           |
                     Current Source

-- 
This message has been scanned for viruses and
dangerous content by MailScanner, and is
believed to be clean.

--------------------------------------------------------------------
|For help or to subscribe/unsubscribe, e-mail majordomo@eda-stds.org
|with the appropriate command message(s) in the body:
|
|  help
|  subscribe   ibis       <optional e-mail address, if different>
|  subscribe   ibis-users <optional e-mail address, if different>
|  unsubscribe ibis       <optional e-mail address, if different>
|  unsubscribe ibis-users <optional e-mail address, if different>
|
|or e-mail a request to ibis-request@eda-stds.org.
|
|IBIS reflector archives exist under:
|
|  http://www.eda-stds.org/pub/ibis/email_archive/ Recent
|  http://www.eda-stds.org/pub/ibis/users_archive/ Recent
|  http://www.eda-stds.org/pub/ibis/email/         E-mail since 1993