: Yes your point is general and has nothing to do with what I said.
: Two passive components, a resistor and a cap, left in a netlist connected : to ground WITH the other end disconnected causes a circuit to converge when : without them it does not. [. . . .]
You are dead wrong. Here's what I wrote above:
:> When a circuit doesn't converge, besides looking for floating :> nodes . . . . More often than not, I find that I have :> committed some kind of error.
A cap connected to GND with the other end open is a floating node. Avoiding floating nodes is SPICE 101 knowledge.
In any line of work, if you want to use a tool, then you need to have some idea about how it works. Or do you use a hammer to pound screws?
: That does not have anything to do with the type of errors you mentioned. And : the existence of such a problem points to deeper problems with Spice than : you mention.
My point is that SPICE is only as good as the models you use. The models used for IC design are pretty good, whereas those used for board design are useful but limited.
Your arguments about the problems with SPICE are vague, general, and aren't based on any detailed knowledge of SPICE's methods and limitations that I can see. They seem to be more of an objection to computer simulation, and your only evidence is the opinion of Bob Pease (whose job it is to make outre claims as part of National's marketing effort). If you do have something specific and knowledgable about SPICE's limitations to say, I'd be interested in hearing it. Otherwise, I'll bid this thread adieu.
Anyway, you are welcome to not use SPICE in your design work -- if you do design at all. Personally, I would like to see you explain to a job interviewer that you are an electronics engineer who refuses to use SPICE! *snort*
Might it be that he liked the exercise (an unusual thing for a toolie to to be sure)? I generally take stairs over elevators, or escalators, and park in the distant spots in parking lots... Does that make me kooky?.. or perhaps just someone who searches for exercise where he can find it?
Now, if he sings marching songs, at the top of his lungs, as he mounts the stairs, that would be kooky!
Hmmm? Sounds thematically similar to some of your postings about your colon, and stuff ;-)
That's a major pisser! I have a cousin who went most of her life with a brace on one knee, but otherwise ok, who entered Post Polio Syndrome, and found that she could no longer do any kind of repetitive work with her hands, or back... not even computer work... Her doctor told her that basically, she has a certain number of movement cycles left in her hands and back. When they are spent, she will be in full pain, full time.
As I understood things, the sheaths that surround the nerves in her body are deteriorating. Those that are in areas with a lot of motion are going faster. When the sheaths are gone, parts of the nerves that are never supposed to be exposed are going to be fully exposed, and firing at will.
Ok, now that is kooky! Lederhosen? Does anybody actually think that lederhosen are in style for any occasion? ... well, other than during Octoberfest, that is.
The circuit converged with the floating nodes. Or now that you've forced me to go get the book and find his original comments they weren't floating nodes.
They *were* a resistor and capacitor. And both were connected to one point and from there tied to ground. Nothing else was connected to that one point so they had no effect on the circuit action when they were left in.
Bob left them in, the circuit converged. Took them out and the circuit didn't converge. He said they were originally in the circuit then commented out. He accidentally removed the asterisk that commented them out. Pg 204 in the Appendix G "More on Spice", Troubleshooting Analog Circuits, Copyright
1991.
That kind of non-physical behavior from Spice is what he was bitching about. As well as a whole lot of other stuff that was less useful.
And yes, he was probably using an early version done by the company he worked for.
[snip]
No. The example that I'm referring to from Bob has nothing to do with models. Perhaps it has something to do with the early Spice Algorithms. Don't know. And unlike you, I don't assume I know.
No. His reported experience with a circuit that has noting to do with your comments. He may have been wrong. Don't know. Don't think it's that likely but it's certainly possible.
And no. I don't share his opinion of Spice or other Computer Simulation tools. Wrong again. I am interested in what went wrong in his sim and what that says about the algorithms of Spice. If it isn't completely different from what he was working with.
Bye.
Enjoy! You seem just as funny from this end.
Harmonic Balance simulators tend to be used more where I worked but the company originally got PSpice to work on our RF circuits by doing our own modeling. Spent many years with PSpice and Linear Simulators such as Touchstone before moving into ADS.
Doesn't surprise me. Reminds me of people that took a life long aversion to electronic calculators because slide rules were so much better.
Haven't been to any seminars. Did enjoy some of his technical articles on Bandgaps and such on the National Web site. But they were mixed in with a lot more non-technical stuff.
I think a great many (most ?) problems with SPICE and other simulation programs in general are actually due to problems of the "Floating Point" data type. AFAIK the total reason for being of the floating point data type was to get a reasonable range and precision using as little memory as possible. Today memory is not a problem anymore, and one can use a fixed point number format with the desired range and precision necessary for any simulation. A typical construct in many simulations are:
(x0-x1)/k where x0 and x1 are almost equal. This causes problems in floating point. If x0 an x1 are say 1.0 and 1.0001 then it is not a problem. If it is 1000000000.0 and 1000000000.0001, then it bombs out.
I personally think that with todays systems, the use of floating point should be banned, and in stead large fixed point numbers should be used. The only disadvantage compared to floating point is that it uses more memory. (And the little problem that almost no currently used languages supports them as standard)
I have been told by Mike Engelhardt of LTC that this is simply untrue.
I've use both and it most definitely is not.
Obviously you have never tried it. :) 'Fess up now, how much actual experience with which flavors of SPICE do you really have?
LTspice used properly has little problem with such things (but beware, as always: garbage in - garbage out).
Or maybe they are a bunch of hacks who should swallow their pride and sign up for an LTspice seminar. :)
There recently was an interesting thread about Barrie Gilbert's AD534 on the LTspice Yahoo user's group.
This is more bunk. All you need is a little plain old good engineering judgment. I regularly get very good agreement with my board level designs using just that and LTspice. It is fast and accurate, even for for switching circuit (I rarely use LT models, btw, even though they are excellent). Also, once one gets the knack (a few simple rules of good practice and an occasional "trick" or two), LTspice can be made to converge every time within short order. The methods are based on sound reason, not magic floating components.
(Actually I've never met Barrie, though I've talked to him on the phone a few times; and was a substitute speaker for him in Australia back in 1986.)
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
Wow. What a thread. Well, since I am a pal with both Bob Pease and Marcello, the guy that gets out National's SPICE models I suppose I should toss in my two cents.
First, save any effort in contacting National. We have better things to do then make SPICE models for 30-year-old parts. It is interesting that just tonight I was telling Bill Gross and Tim Regen from LT how the
709 was noisy-- I thought I had heard it from Pease but Bill corrected me--the 741 was noisy, the 709 was actually pretty good. And yeah, that is what Pease said as well, I am geting old.
Next, it looks like a simple Google search would have turned up something but thanks for this little tempest.
Next, there is a huge disconnect with people that use SPICE for board-level and with people that use SPICE for IC design. Yeah, just buy a UNIX workstation ($20k) buy Cadence (150k++) and then run two departments-- one called "Process" and one called "Modeling" ($5-10M) and yup, after 5 years or so you will be able to get good results from SPICE. God bless you.
And, if you buy PSPICE for 10k and still spend the 5 or 10 million those two departments, the modeling and process departments, you can still get good results for transistor-level simulation. Linear Tech uses PSPICE for IC design. I have been told that LT-Cad is just a variant of PSPICE so I am somewhat baffled how people can claim it works "better".
But, PSPICE will still have trouble converging and doing things with fast edges or digital (mixed signal) stuff. That may be why National does not release A to D converter SPICE models. Now with the transistor-level models, Cadence and a weekend to run, an A to D can yield to SPICE, I suspect that Thompson guy gets things to work.
But now I leave you IC designers.. .if you want, I can post the twenty pages of emails I traded with Barrie Gilbert of Analog Devices over this exact subject.
For board-level SPICE you have to be very careful. National's recent models are very good. We even model noise-- just watch the Pease Show (now called "Analog by Design") in a week or two. We just taped it yesterday. We will show how you can check your models to see if the noise shows up like in the real world. We will show National's WEBENCH filter designer SPICE exactly matching Electronics Workbench MultiSim8 SPICE and a real-world board I built, all agreeing within 1/2 dB. At 10kHz. Next I will build a
15MHz filter. That one will not do so well because all my board strays will start effecting the circuit. Stay tuned.
But if you are pushing the edge (and why would you need to do SPICE if you weren't), well, you better be very good to understand all the limitations of board-level SPICE. You have to make sure you have good models and test the models against the real world. Next you have to model the board level stuff. Maybe buy Hyperlynx, the 48 grand 2 1/2 D field-solver to see trace interaction. Maxwell's Equations are always right. But you must build exact
3-D models of your circuit and have a lot of computer power.
And before you accuse Pease of being a hopeless curmudgeon, please separate his "stage persona" from the real guy. I have seen him tell a young guy who asked about SPICE the perfect response-- use it carefully and a little at first and build on your correlations to allow you to SPICE more and more stuff.
And Bob may be a "kook" but he is a truly brilliant man.
So is Barrie Gilbert.
And Jim Thompson.
I just want to get them together in a WWF ring one day.
Now this has been a great thread and it raises some truly great issues for us at National Semiconductor. So when I go in tomorrow I will be sure to get some answers to the question that seems most crucial: "Bob, did you rally wear lederhausen in college?" And if the answer is yes, "Were they lined with silk like the ones in the National Lampoon Mr. Rogers' parody?"
Paul
Neil wrote:
semiconductor. I asked intusoft, cause they have a free model service. I bought their entry level software ICAP/4 8.3.3 from a dealer purchased in 2000. For reasons I won't mention, I was denied the request from their sales department.
"Troubleshooting Analog circuits" he doesn't like S.P.I.C.E. and for good reason...........:)
You don't know what you're talking about. First of all, Linear has just about every SPICE simulator available. The opamp people at Linear do tend to use PSPICE(the Microsim/OrCAD/Cadence trademark) but that's because opamps are simple IC's that don't need the best simulation tools and have been done in PSPICE for very many years.
By LT-Cad, I assume you mean LTspice. The only way that could be thought of a PSPICE variant would be because we hired one of the founders of Microsim at the start of the development of that project to find out things like how much time and money it took to develop. LTspice is otherwise a independently developed version of SPICE and is the world's highest performance SPICE with regard to speed, accuracy, and robustness. Just because it runs the PSPICE syntax extension doesn't mean it's a PSPICE variant. It is fantastically more accurate that PSPICE. LTspice is used internally as as upgrade from, e.g., both PSPICE and hspice for internal IC design. My friends Bill Gross and Tim Regen are application engineers and won't know what the IC developers use to design LT IC's besides possible opamps, not that I believe they told you the misinformation you posted here.
What I will say here is that a work college, and myself on and off, have been using LTSpice on some circuits very recently, like currently. Sure, it converges most of the time when XSpice and Tanner spice, and any others don't, however it still has problems on some circuits we have been trying. This is to be compared with TISpice (internal Texas Instruments spice). In a past life of 3+ years, it *never* failed to converge, ever. It seemed to have 100 hundreds of algorithms to try automatically. So, as far as robustness goes, I cant agree. Its good, but not the best, imo. As for speed, I have never compared it to TISpice.
Kevin Aylward snipped-for-privacy@anasoft.co.uk
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SuperSpice, a very affordable Mixed-Mode Windows Simulator with Schematic Capture, Waveform Display, FFT's and Filter Design.
Well, not often I support Mike, but you way off base here. The LTSpice engine is probably the best there is on PCs as far as simulation speed and convergence goes. Its the GUI that leaves a lot to be desired.
Kevin Aylward snipped-for-privacy@anasoft.co.uk
formatting link
SuperSpice, a very affordable Mixed-Mode Windows Simulator with Schematic Capture, Waveform Display, FFT's and Filter Design.
LTspice has improved models for inductors and capacitors that allow realistic parasitics to be entered and computed as an integral part of the element. This prevents the corresponding branch admittances from going to zero or infinity for reduced time steps during a transient analysis, greatly improving run time convergence.
I doubt you or anyone else has a legitimate circuit that would trip up LTspice.
LTspice can without breaking a sweat. Download the program and read the help file topic on L devices.
OK, Maybe it was shorts and long-johns :-)... but definitely very odd in Massachusetts in wintertime... something about Bob's appearance definitely stood out, otherwise I wouldn't have so distinctly remembered just another tech "tool". I didn't even know his name until I saw him at National.
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
Well, it was an LT guy that told me LT-SPICE was a PSPICE variant but I don't have the need to trash people, (even anonymously) that some people do so I will not mention who. I certainly will yield to Mr. Engelhardt on anything about LT SPICE because my LT friends say he is THE MAN for this. After all, we know Swanson would rather work to death one man rather then hire a department. Mike does the work of two departments and I really respect that. LTSPICE is his baby and he has a right to be proud of all that work.
Can he tell me the relationship between SwitcherCAD and LTSPICE? Are they the same thing? And I was once told that LTSPICE does not allow import of models from other vendors like ADI and National. Sounds like bunk but it is a proprietary program after all.
BTW Mike, Bill Gross is a recently retired Vice-president and a former IC designer so I will give him the complement tomorrow that you consider him an apps guy like me. Swanson really must have you chained to a workstation.
Now as to my SPICE experience-- well, Berkeley SPICE and Hollerith cards yeah, a good bit of PSPICE, Intusoft ICAPs, at HP we had this thing I think called DR Deautch or something that was supposed to converge really well and my impression of all of them was they are crap. But this was almost 10 years ago.
I will look for some of the oscillators and stuff that blow up or when I get around to it publish a circuit I was using SPICE on a few months ago and everyone can excoriate me just because I didn't know to set abstol to something and put the .bs command in the deck. Well duh, whenever I have to slow down edges or loosen up accuracies to get a convergence it just seems like a real good time to put down the mouse and pick up a soldering iron. Maybe I am just a scaredy-cat.
I would like to graduate past 7th grade and "you are full of s*1t" comments so let us act like technical people and deal with facts.
Several years ago EDN magazine did a circuit and gave it to 6 SPICE vendors and Jim Williams at Linear Tech. If I remember about half of the programs failed to converge and the rest gave wrong results, sometimes wildly wrong compared to Jim's real board. Was there a memo I missed? Have models and SPICE engines gotten that much better?
Can anyone really get any kind of mid-range SPICE to deal with non-linear magnetics? Does anyone trust it to design a complex flyback converter?
Are there really A to D models that give the representative data output of the real-world signals? Not just the math and correlations involving the sampled-data theory but the real things going on in the analog and digital sections? (All board-level models of course, not "real" transistor-level models.) Does LT offer models of those new fast converters they make?
OK, the SPICE behind National's WEBENCH uses a later version of the SPICE engine then PSPICE. I have heard one called level or stage two vs a three. So what are the substantive differences? Does PSPICE suck as much as everything else Cadence seems to ruin? Maybe I am complaining about my Model T when everybody else in in a Prius.
I was at Arrowfest tonight where somebody said all SPICE does is solve a matrix. That is what Berkeley SPICE is. What everyone else is doing is writing code to try and get the solution to converge when the math blows up. I had dinner with a guy from PSPICE years ago and he said all of their work is doing code like that, to keep things from blowing up. How comforting. Is this wrong?
When I was at HP we were designing automotive diagnostics. I defy anyone to make a good model of a spark plug gap since most attempts had real trouble converging and then you realize the flame-front and pressure in the cylinder affects the signal. Did I miss that memo as well?
People, people, I am not being combative, I work in the on-line SPICE group at National for crying out loud and really want to use it as much as possible. Please don't jump on me like I am criticizing your religion or politics or wife. It just seems like every time I wade into another type of complex circuit with SPICE I soon feel like I need a CS degree and a month of trial and it is just so much easier to just build the thing. Remember I am talking board-level here, not something that you want to simulate to death since there are 100k of masks at stake. That is why I like our WEBENCH tool. We have a whole department including a couple of apps guys like me to insure that we can give good results when we run a simulation. But we build the circuits with the same exact components and make sure that the SPICE agrees with real-world values so our customers don't have to. Is everybody out there designing things with such similarity to their previous designs they know they can trust the simulations?
Oh, if I have brought Kevin and Mike together then I guess there is redemption in electronics after all.
Now to the important stuff, maybe I can get Pease to sign-up for Google Groups but failing that I can at least post his reply to my lederhausen question today:
**** I do not recall ever wearing or owning Lederhosen, when I was in college. I recall specifically that I did not. But I did wear shorts. In the winter. When bicycling. In the snow. When I went winter-mountaineering, up in New Hampshire, I wore shorts plus long-johns. Red long-johns.
*** I know nothing about silk-lined Lederhosen, and I know nothing about the Lampoon's parody.
*** Since I never had or wore Lederhosen, then I'm sure that some of the ones I didn't wear were silk-lined, and some of the ones I didn't wear were NOT silk-lined. / rap ============================================================
Hey Mike; Tim Regen's birthday tomoroow, come over to Bldg T (The Tastey Subs on Lawrence Expressway by Arques) and I'll buy you a beer.
The name of the program is LTspice/SwitcherCAD III.
More non-sense. Users can import models and since LTspice knows most Pspice and hspice syntax, it can even run the imported models without modification. LTspice's SMPS products are models in a HDL that can't be run in other SPICE programs because the HDL is above their heads.
Opps, I was thinking of Tom Gross, the apps guy, who works in a somewhat closer capacity to Tim Regen, hence I jumped to him instead of the guy that doesn't work here any more. Bill Gross was an op amp designer and then VP of that group that knows little about SPICE and nothing about LTspice. Yes, do pay him my compliments and mention Boeing SPICE. He'll tell you lots of non-sense about SPICE.
You were at an Arrowfest and somebody said something. Wow. Most physical simulators solve a matrix, that doesn't make them varients of each other, it just means it's trying to solve something. I would suggest that you don't dissertate on topics that you aren't familiar instead of posting garbage.
Yes, the people that sell the Webbench thing to National told me that too. I laughed and walked away.
Thanks for posting this. I suspected that the Lederhosen story wasn't true. I find that as my fame, for lack of a better term, evolves, that there's ever increasing strange storys about me that never happened or quotes from me that I never said. The time will come when I'll join Pease and not read Usenet posts anymore.
Very nice..........I will try it this weekend!!, That's great. I tried that approach from the datasheet, like others mentioned to me. I used a macro option inside my SPICE program with the common transistor which I like to use is the 2N4401 and the 2N4403. It's unrealistic, and above par, cause it has way more gain, higher CMRR, so the I scrapped the macro, and started over, and I did, before posting to this group.
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