On Sat, 1 Feb 2014 05:39:18 +0000 (UTC), Don Kuenz
wrote:

Jim Thompson wrote:
For sometime now I have been trying to build a behavioral model of
logic gates that was consistent with real-world behavior when mixed
into an Analog environment.

(Existing logic models, such as those in PSpice and LTspice are state
machines and do not behave properly when used for Analog applications,
such as when you build a crystal oscillator around a 74HCU04.)

So I now invite you to visit the Device Models & Subcircuits page of
my website...

http://www.analog-innovations.com/

and take a look at FauxMOSFET.pdf, where I have finally created a
purely mathematical behavioral model of a MOSFET... using, of course,
my favorite math function TANH :-)

With all derivatives continuous, it is suitable for modeling logic
elements that can be run in an Analog simulator environment.

Watch this space for further announcements as I develop inverters,
gates and complex functions that will run on any old analog simulator.

At first I was all "Hyperbolic tangent, WTF does that have to do with
SPICE?" Then I saw a TANH plot and the light came on. FWIW this guy
has an intro to Analog Behavioral Modeling.

http://www.ecircuitcenter.com/Circuits/ABM1/ABM1.htm

Thanks, Don, that's a nice intro and a nice composite listing of the
different functions available. I've been at this long enough that I
know that list by heart ;-)

If your simulator supports VALUE, I'd avoid the POLY form
altogether... it's not only obtuse, but difficult to keep your head
and the coefficient order on straight for any order above 2 ;-)

I settled on TANH while pursuing how to handle (simulation device)
current sources which would pull voltages to infinity if unrestrained.
My devices...

http://www.analog-innovations.com/CompliantParts.zip

will not pull below zero volts, thus not only behave "real world", but
have no convergence problems (limiting implemented with a TANH
function).

...Jim Thompson
--
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