Subject: min and max rising/falling waveforms in s2ibis2

From: Betty Luk <[email-masked]>
Date: Fri, 17 Nov 2000 17:07:23 -0500

Hi,
 
I am using s2ibis2 to generate my IBIS model.  I have set the [Voltage
Range] to be 3.3 3.0 3.6 (typ, min, max).  The IBIS cookbook suggests that a
50 ohm resistive load Vdd be used for the rising and falling waveform VT
data.  In the s2ibis2-generated Spice files, the 50 Ohm load always
connected to 3.3V, even for the min and max case.
 
Is this the correct behaviour?  And if so, why are 3.0 and 3.6V (for min and
max respectively) not used?
 
I would appreciate any feedback.
 
Thanks,
Betty Luk

---

From: Al Davis <[email-masked]>
Date: Sat, 18 Nov 2000 01:31:07 -0800

On Fri, 17 Nov 2000, Betty Luk wrote:
> I am using s2ibis2 to generate my IBIS model.  I have set the
> [Voltage Range] to be 3.3 3.0 3.6 (typ, min, max).  The IBIS
> cookbook suggests that a 50 ohm resistive load Vdd be used for the
> rising and falling waveform VT data.  In the s2ibis2-generated
> Spice files, the 50 Ohm load always connected to 3.3V, even for the
> min and max case.
>
> Is this the correct behaviour?  And if so, why are 3.0 and 3.6V
> (for min and max respectively) not used?

The voltage the test load is connected to in the waveform tables has 
nothing to do with the voltages the device operates on.  You could 
connect it to some middle voltage if you want, which would be a 
better choice when the device is used differentially.

You should supply at least two waveforms of each type.  Normally, one 
would have a pullup load, and the other would have a pulldown load.  
By supplying only one of each, you do not adequately characterize 
both devices.  A load to ground characterizes the pullup device 
fairly well, but does nothing for the pulldown device.  Likewise, a 
load to Vcc characterizes the pulldown device fairly well, and 
supplies almost no information about the pullup device.