[SI-LIST] : Variability of Supply voltages

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From: Bill Cohen (wcohen@taec.toshiba.com)
Date: Tue Oct 10 2000 - 10:31:21 PDT


I am a CMOS integrated circuit designer. I need some board level expertise.

In our I/O circuits we usually have various transistors that run at unique
maximum voltages. So usually we specify three power supplies in our circuits.
The most common are: 3.3V, 2.5V, and 1.8V.
We then try to perform a worst case analysis using the spice simulator.
At the present time we don't assume that the three power supplies track.
So to do a worst case simulation we might run a low 3V supply and a
high 2V supply. The power supplies would supply a single IC and be
resident on the same PC board. My question is as follows:

Can we assume that when one power supply is at a maximum the other two supplies
will be at a maximum? Should we assume that all three supplies can be
independent and we need to perform a maxtrix of 9 combinations to do
a proper worst case analysis?

Bill Cohen
Circuit Design
Technolgoy Development Group Toshiba
Marlborough, MA
wcohen@taec.com

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