Re: AW: different rising and falling Ramp dV

Katja,

I searched through the IBIS spec, and at the very end there is indeed
a description of what you have stated. I should have remembered this,
but the issues of IBIS 1.1 seem so far in the past.

Al's comment about simulator differences is no doubt true. So we have
at least 2 areas that simulators possibly handle differently:

1) IBIS models with no waveforms, and different Ramp dV for rise and fall.
2) IBIS models with waveform endpoint that do not match the I/V curves.

Maybe I have missed others, like C_comp de-embedding? Anyway, from now on
I will be more watchful of simulations involving models without waveforms.
Correlating has never been optional, I suppose, for any model. With luck,
all of the models I see from now on will have waveforms and perfectly
matching I/V curves :-)

Mike

Koller Katja wrote:
>
> The ibis models do only have the same value of dV, if the load AND the
> termination voltage have the same value.
> The ibis-ramp termination voltage is defined for
> rising: 0V
> falling: vcc
>
> But you can get the exact dV out of the pullup and pulldown-curves.
>
> Katja
>
> > -----Urspr> üngliche Nachricht-----
> > Von: Mike LaBonte [SMTP:mike@labonte.com]
> > Gesendet am: Freitag, 23. März 2001 00:19
> > An: ibis-users@vhdl.org
> > Betreff: different rising and falling Ramp dV
> >
> > Many IBIS models have different values for dV in the dV/dt_r and dV/dt_f.
> > The clipping below from IBIS spec shows an example. But the usage rules
> > imply that dV must be 60% of the voltage swing. If the voltage swing is
> > measured between the 2 steady-state voltages, then how could you have
> > different values for rise and fall dV? If there is variation in how
> > simulators handle the Ramp dV values, then this may matter.
> >
> > Mike LaBonte
> >
> > |=============================================================================
> > | Keyword: [Ramp]
> > | Required: Yes, except for inputs, terminators, Series and Series_switch
> > | model types.
> > | Description: Defines the rise and fall times of a buffer. The ramp rate
> > | does not include packaging but does include the effects of the
> > | C_comp parameter.
> > | Sub-Params: dV/dt_r, dV/dt_f, R_load
> > | Usage Rules: The rise and fall time is defined as the time it takes the
> > | output to go from 20% to 80% of its final value. The ramp
> > | rate is defined as:
> > |
> > | dV 20% to 80% voltage swing
> > | -- = ----------------------------------------
> > | dt Time it takes to swing the above voltage
> > |
> > | The ramp rate must be specified as an explicit fraction and
> > | must not be reduced. The [Ramp] values can use "NA" for the
> > | min and max values only. The R_load subparameter is optional
> > | if the default 50 ohm load is used. The R_load subparameter
> > | is required if a non-standard load is used.
> > |-----------------------------------------------------------------------------
> > [Ramp]
> > | variable typ min max
> > dV/dt_r 2.20/1.06n 1.92/1.28n 2.49/650p
> > dV/dt_f 2.46/1.21n 2.21/1.54n 2.70/770p
> > R_load = 300ohms
 
Received on Fri Mar 23 05:45:07 2001