[SI-LIST] : HSPICE Start Up conditions

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From: Kai Keskinen (keskinen@nortelnetworks.com)
Date: Wed Mar 22 2000 - 07:45:53 PST


Hi SI Folk:

I had a lot of problems getting a spice model of a gigabit ethernet chip to
run properly. The differential outputs are tied to ground with 4.5kOhm
resistors and then coupled to the long T-lines (W-element) with ~1nF caps.
They are terminated with 100ohms across the differential pairs just before
the receiver. It turned out that if we did not set the initial charging
conditions on the coupling caps to a very narrow range of values, the
simulation never actually worked. One or both of the differential outputs
did not at all resemble what the chip should transmit even for very long
simulation times.

My questions are: Why did the circuit not charge up the caps and then work
as would happen in reality? Is this a very common effect when running HSPICE
or other sims?

Thanks,

Kai Keskinen
Equipment and Network Interconnect
Nortel Subsystems and Performance Networks (NSPaN)
(613)-765-3506 (ESN 395)
keskinen@nortelnetworks.com <mailto:keskinen@nortelnetworks.com>

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