Subject: RE: [IBIS-Users] Making Pullup curves VCC relative.
From: Ingraham, Andrew (Andrew.Ingraham@hp.com)
Date: Tue Oct 15 2002 - 13:58:08 PDT
"VCC relative" means that 0V in the table, corresponds to Vin or Vout = VCC at the device pin or pad.
In addition, the tables are arranged so that positive table values mean I/O voltages mostly within the normal range between GND and VCC, and negative table values are voltages below GND or above VCC, toward the clamps. (Obviously, if you go far enough in either direction, you will go beyond GND and VCC. Large positive table values correspond to voltages beyond the opposite supply rail.)
Vtable = Vcc - Voutput.
This formula is applied only to the [Pullup] and [Power Clamp] tables. No such adjustment is made to the [Pulldown] and [GND Clamp] tables.
The step of subtracting the clamp currents from the simulated or measured currents, to get the values for the [Pullup] and [Pulldown] tables, is different. It has nothing to do with the fact that the [Pullup] and [Power Clamp] tables are VCC relative. They are two independent steps in the process. Subtracting the clamp currents prevents double counting when they are added back together by the simulator.
Andy
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