RE: [IBIS-Users] problems about extracting IV curves from SPICE model

Yuancheng,

In general it sounds like you are using the right method. I would
recommend performing a simple waveform test into an R load to make sure
that all inputs to your SPICE buffer model are set correctly. Compare
that with the same fixture in IBIS.

A less likely problem is that your SPICE buffer model does not work well
when it's output node is forced to some voltage. If that is the case,
sometimes adding a small value series resistor between the pad and the
forcing voltage supply will help. It is then necessary to use the actual
voltage at the pad instead of the forcing voltage for calculations.

Mike

From: owner-ibis-users@eda.org [mailto:owner-ibis-users@eda.org] On
Behalf Of ji xiao
Sent: Wednesday, May 19, 2010 6:18 AM
To: ibis-users
Subject: [IBIS-Users] problems about extracting IV curves from SPICE
model

Hi, everyone.

For my research purpose, I want to extract IV data (pullup, pulldown,
etc.) from the SPICE model of inverter 74lvc04a, and the result is
supposed to be similar to the IBIS IV table. However, for my case, there
is a large difference (around 10 times smaller than the IV table in IBIS
file) although the whole curve trend looks similar. And it exists for
all IV curves.

For my circuit connection, let's take pulldown curve as an example, I
give corresponding Vdd voltage source to power suply, ground input and
connect the output to a variable voltage source (V1) and use a current
probe to measure the output current(I1) at the output port. I plot the
IV curve I1 vs. V1 and treat it as the pulldown curve. No floating
voltage source in the circuit.

Can anyone tell me what's wrong with my connection?

Thanks and regards,

Yuancheng

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