Re: gEDA-user: Gnetlist -g PCB

[al davis <ad151@xxxxxxxxxxxxxxxx>]

On Sunday 29 June 2008, John Doty wrote:
> You're assuming voltage interfaces. Current interfaces turn
> that on its head.

No, but....

> And then there's the trick of grounding an 
> opamp "output" and getting output current from the power
> pins: this illustrates that the direction and discipline
> depend on the application, not on the part.

An opamp "output" is really usually an "inout".

I agree that "the direction and discipline depend on the 
application".  An opamp model that claims the output has 
direction "output" is probably not adequate for the application 
you mention.

> I read the book you recommended on Verilog-AMS. It misses the
> critical idea that mixed signal design is applied physics,
> not computer programming. A computer can usually evaluate a
> function that you can logically describe, but circuitry is
> more restricted, especially if speed, noise, and power are
> significant considerations. The top-down design methodology
> the authors advocate is almost guaranteed to demand parts
> made of unobtainium if applied to challenging requirements.
>
> > It looks to me that geda has mixed the concepts of
> > discipline and direction.
>
> Yes, but the real problem is the mixing of such clerical
> concepts into what is really a set of applied physics issues.

Interesting point .. There is nothing keeping you from 
describing things like a one femtoHertz oscillator or a new CPU 
with a 100 TeraHertz clock.  Building it, on the other hand, 
might be a little difficult.


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