[IBIS-Users] Problem in developin NMOS Open Drain type IBIS

Hello all,


I am generating IBIS model(ver 4.2) for a circuit which is working in 
Open drain mode.
I have included in the IBIS file one pulldown curve and 2 V-T waveforms 
(both with high fixture, one falling and one rising).
Simulations show that the operating point for high input is different in 
case of original circuit and IBIS file.
For low input it is the same.
So when i give some Falling input at the input of model both the IBIS 
waveform and original waveform fall to the same voltage but
at the start they are at different voltage.
Infact i get operating point for high input half of the voltage which i 
should actually get..


Is their something tricky in modelling of Open Drain model ??
I have modelled a few IBIS models of output type and I/O type but never 
did i get such a problem.

Thanks for your support
Amit Kumar
Design Engineer
ST Microelectronics India


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