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 Thu Mar 22 15:22:40 2001