Anyone know what Circut Bob Pease was going on about?

I think Pease has gone senile. Did everyone see his _religion_ rant in the last issue?

I went to one of his "seminars", didn't learn a thing, saw a lot of application notes and data books on National's products.

As for "...Spice said couldn't work...", what does that mean... Spice couldn't converge on an initial solution? Happens all the time, doesn't mean that the circuit can't work.

Show me the circuit schematic and I assure you I can Spice it.

...Jim Thompson

He usually says that about the LM331.

Cheers,

Phil Hobbs

Anyone have a complete schematic?

...Jim Thompson

Pease has the problem common to columists, out of ideas but deadlines keep coming. He's become an embarassment, but Electronic Design has, too.

HoJo seems to be straining, too.

John

Inadequate and incomplete models, of course. And unknown or unaccounted-for parasitic elements in the circuit. Happens all the time out there in the real world (i.e., the world that's not IC design). :-)

The solution is a painful process to characterize the part, etc., and create a spice model or subcircuit that matches over the range of interest. I also find myself making test PCBs, and taking inductance, capacitance etc. measurements on that. Lots of bench work, serious bench equipment, lots of computer work, plenty of knowledge and experience about what to look for. Given the commonplace absence of this approach, it's rather easy to throw stones at "spice".

But given the careful, time-consuming approach, I find spice extremely useful in my push-the-envelope projects.

Spice is a reasonable general-purpose program for solving systems of nonlinear ordinary differential equations. There are some systems that no program is going to be able to solve, but they're quite rare in applications. Thus just about anything that can be modelled accurately with a set of coupled ODEs can be simulated accurately with Spice.

On the other hand, not everything can be modelled with ODEs, not even every circuit. Some better known non-ODE things, e.g. transmission lines, have been put into Spice by hand. (A transmission line's circuit properties aren't given by an ODE because they're nonlocal, i.e. the output undergoes a true time delay.)

Other classes of problem that can't be modelled as systems of ODES are transport equations--e.g. the Boltzmann equation for electron transport, or any problem that involves convective motion, such as the air in a heat sink.

It isn't great at multiple scale analysis, either, so for instance it would be very poor at modelling the turn-on behaviour of a laser diode, in which time scales from sub-femtosecond (the E & H fields) to hundreds of milliseconds (the thermal transient) all contribute very significantly and nonlinearly. There are codes for this kind of problem, but Spice isn't one of them--it has to follow each cycle laboriously, because a linearized AC analysis won't get the right answer.

And anyway, Pease's main complaint is that people use (generally poor) computer analyses as a substitute for thought--and have tried to beat him up with the results over the years. Most of the rest of his posturing is for fun, I think. You can't really make a serious critique of computer simulation by throwing a computer off the roof of the NSC parking garage. Widlar envy, perhaps.

Cheers,

Phil Hobbs

Thanks.

As Win said, "inadequate Models...", could cover a multitude of sins.

I wonder how well something like a Flash device's charge storage is modeled in Spice.

Robert H.