RE: [sv-dc] 4-state vs 3-D

Z=>is a defined impedance. It is infinite for voltage sources. For current sources it is a zero current with an infinite impedance.

Kindest Regards,
Jim Lear
Cirrus Logic
(512) 851-4612
(512) 293-7248 (mobile)
From: owner-sv-dc@eda.org [mailto:owner-sv-dc@eda.org] On Behalf Of Ian Wilson
Sent: Thursday, December 09, 2010 11:50 AM
To: Scott Cranston
Cc: Kevin Cameron; Arturo Salz; sv-dc@eda.org
Subject: Re: [sv-dc] 4-state vs 3-D

If you look at real values in a mixed signal simulation as representing continuous
electrical quantities, then:
  X => can't compute a solution (voltage sources in parallel, current sources in series, etc)
  Z => no defined impedance associated with this branch (floating (if current-driven) or
           grounded (if voltage-driven))

I think Scott stated the question well - it makes little sense to discuss the representation
until there is a clear idea of what sort of behavior one is trying to model using real values.

It would be interesting to consider what sort of behavior(s) that real-valued variables should
be modeling at mixed-signal interface(s) rather than in one domain or other. It seems to me that
any useful behavior involves more than can be expressed in simple scalars without trickery
involving magic values. (In other words, I agree with the position that 'undriven', for example,
is information that should not be expressed by trying to encode it into the real value of the driver
or other entity).

--ian

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