Re: usefullness of V/T curves

Chris Rokusek wrote:

> Betty,
>
> Can't comment specifically on the HSPICE implementation

V/T tables work quite well in HSPICE. They correlate to the
original spice as well as other behavorial simulators, limited
only by the number of waveform points.

regards,

scott

--
Scott McMorrow
Principal Engineer
SiQual, Signal Quality Engineering
18735 SW Boones Ferry Road
Tualatin, OR  97062-3090
(503) 885-1231
http://www.siqual.com
>
>
> > -----Original Message-----
> > From: Betty Luk [mailto:Betty@genesis-microchip.com]
> > Sent: Tuesday, September 19, 2000 2:28 PM
> > To: ibis-users@eda.org
> > Subject: usefullness of V/T curves
> >
> >
> > Hello IBIS users,
> >
> > I just started trying to create an IBIS model for a CMOS 3-State
> > output pad.  I am not an expert on modelling or signal integrity,
> > so I would greatly appreciate any help and feedback.
> >
> > I have a question regarding the usefullness of an IBIS model:
> >
> > In the IBIS Cookbook, it recommends that 4 V/T curves be
> > generated for a standard CMOS buffer, using a 50 Ohm load
> > connected to GND or Vcc.  When using the IBIS model in HSPICE,
> > there is an optional parameter that can be specified (ramp_rwf)
> > to indicate that the [Rising waveform] and/or [Falling waveform]
> > data is to be used instead of the [Ramp] ratio.
> >
> > Specifying the [Rising waveform] and [Falling waveform] should
> > provide better accuracy for the IBIS model because in reality the
> > output switching of the device is not a linear ramp.
> >
> > My confusion is, how is this data useful for the customer, when
> > the load is not a 50 Ohm resistor, but, say capacitive?  How can
> > the data provided by the [Rising waveform] and [Falling waveform]
> > in the IBIS model give accurate simulation results, when the
> > loading on the device has been changed?
> >
> > Thank you very much,
> >
> > Betty Luk
> >
> > IC Technology
> > Genesis Microchip Inc.
> > 165 Commerce Valley Dr. W.
> > Thornhill, Ont. L3T 7V8
> > (905) 889-5400 x2256
> >
> >