Subject: RE: [IBIS-Users] IBIS Info.
From: Ingraham, Andrew (Andrew.Ingraham@compaq.com)
Date: Thu Mar 14 2002 - 06:31:29 PST
> Pullup/Pulldown curves: Does the Pullup VI curve give
> the voltage and current charecteristics when the
> buffer is in logic high state or does it give the VI
> char. when transitioning to the logic high from a
> logic low and vice versa with Pulldown.
The Pulldown curve gives the I/V characteristics when the output is in the low state, but with Clamps subtracted. Pulldown + Clamps = the total output I/V characteristics while in the low state.
Likewise for Pullup.
When switching from one state to the other, the simulator has to figure out how to transition from one I/V curve to the other; i.e., from 100% Pulldown and 0% Pullup, to 0% Pulldown and 100% Pullup. Without V/T data, the exact nature of that transition is a somewhat arbitrary guess, although the speed of transition depends on the Ramp rate. With V/T data, the simulator can adjust the exact transition in accordance with the V/T data.
Regards,
Andy
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