ibis VT curves

Hi,

I'm working on ibis models and I met the same problem as Betty Luk, it's
to say that in playing around with my IBIS model (changing the ramp data
manually), I didn't see any changes with Sigxplorer (Specctraquest
signal explorer expert). However, in making the same changes in the ibis
model used in pspice I saw differences.
I have done this with an ibis model with and without the VT curves.
I have used "ibis2spice" from Intusoft but this program
doesn't convert the VT curves, it just uses the [Ramp] parameters.
So, I am trying to build a new ibis2spice program using the VT curves.

My questions are:

1) Why doesn't the [Ramp] modifications influence the results (Betty
Luk's question)

2) Why use the VT curves instead of the [Ramp] parameters? Is it "only"
to get a more accurate curve?

3) I am puzzled by the apparent contradiction that might arise if both
the
VT and VI curves are available. For example, a VT curve has been
specified with the following load:
                        

out -----/\/\/\/\/-----|
            50 |
                  + ___|___ 1.25V
                      ---
                       |
                       |
                       |
                      GND

Going from low to high, the VT curve switches from 400mV to 2V.

How can I use this information for other loads?
For example:

- 50 Ohm load only
(i.e. the dc offset has been removed. My simulated output will now want
to be something defined by the VI curve. How do I sensibly use the VT
curve in this case?)

- 100 Ohm load only

4) Do I have to take into account the Rfixture and Vfixture values used
while specifying the VT curves?
  

Thanks for your feedback
Simon Schaeffer
 
Received on Thu Nov 16 05:16:09 2000