What known accurate spice models are around?

[jez]

Although spice is a useful tool to all involved in electronics, I have often found (as widely reported by others also) that the spice models available to us are often wildly inaccurate, sometimes by an order of magnitude, when compared with real life measured results. I breadboarded a basic common emitter amplifier stage a few years ago and compared measured results such as
amplification, bandwidth and distortion with simulated results of the same parameters for just half a dozen or so common BJT's I had to hand. The correlation was tenuous in most cases and scarily wide of the mark in others!
To get to the point, I am curious as to if anyone on here has done a more comprehensive and scientific study of this (or just good old practical experience) and can recommend some models for some BJT's/MOSFETS/FET's that can be trusted to simulate somewhere near reality??
It's all very well having thousands of models available for high Ft or low Cob or high gain linearity super modern devices but if they are not accurate then what's the point? Especially if in practice the difference between lets say a real 2N3055 and a simulated one is greater than the actual difference between a real 2N3055 and a real MJL3281
And no I haven't made that test..... Those part numbers are just random but I do seem to vaguely recall a real TIP41C in a CE amp measuring about 30 KHz -3dB and a simulation giving about 10 MHz -3dB so this is the sort of discrepancy we can be up against!

[Eugene Dvoskin]

Check Bob Cordell site. He has a couple of models for BJT's that are the most accurate models, possible to find.
Also, you have to know, how your spice software is treating this model.
For example, LTSPICE is switching from Gummel and Poon model to the Ebers-Moll model when certain parameters are not specified.

[lineup]

Andy_c has done some improved models that are accurate.
Most known are the MJL3281A MJL1302A:
Improved SPICE Models for MJL3281A and MJL1302A - Section 1

[Nico Ras]

Normally purchased product are pretty good such as that from MicroCap. When simulating and testing results are exactly the same. but as Eugene mentioned you have to know what you are simulating.

Stuff available that are for free are exactly that, free and you cannot blame anyone for the accuracy or applicability.

I have downloaded many manufacturers spice files and have not found any inaccuracies their models as these are based on actual measurement and not hearsay.

Maybe it is the quality of the software and calculations, making use of some parameters and ignoring others. I cannot see why manufacturers of components will provide false models, as their livelihood depends on capable engineers designing those components into products that is sold and pays salaries. I cannot imagine any reason for providing lies.

I have experienced some differences in results between free spice simulators with limited capabilities and professional purchased products.

[jez]

Originally Posted by Eugene Dvoskin

Check Bob Cordell site. He has a couple of models for BJT's that are the most accurate models, possible to find.
Also, you have to know, how your spice software is treating this model.
For example, LTSPICE is switching from Gummel and Poon model to the Ebers-Moll model when certain parameters are not specified.

Well this could certainly explain some of the results I've had with LT spice
I'll certainly check out those models on Bob Cordells site! Thanks!

Originally Posted by lineup

Andy_c has done some improved models that are accurate.
Most known are the MJL3281A MJL1302A:
Improved SPICE Models for MJL3281A and MJL1302A - Section 1

These are about the only improved models I was aware of and already have.
This is surely a prime example of how the original models from manufacturers are not always trustworthy....

Originally Posted by Nico Ras

Normally purchased product are pretty good such as that from MicroCap. When simulating and testing results are exactly the same. but as Eugene mentioned you have to know what you are simulating.

Stuff available that are for free are exactly that, free and you cannot blame anyone for the accuracy or applicability.

I have downloaded many manufacturers spice files and have not found any inaccuracies their models as these are based on actual measurement and not hearsay.

Maybe it is the quality of the software and calculations, making use of some parameters and ignoring others. I cannot see why manufacturers of components will provide false models, as their livelihood depends on capable engineers designing those components into products that is sold and pays salaries. I cannot imagine any reason for providing lies.

I have experienced some differences in results between free spice simulators with limited capabilities and professional purchased products.

I have most of the available simulation programs but must admit that when I had rogue results with a particular model on LT spice I didn't do the same test using another programme... Surely a model should generally be interpreted the same by various spice engines??? Or maybe not according to Eugene
The results with the TIP41C were using a manufacturers model!

Basically I'm thinking that a few known accurate models for "general purpose" small signal transistors, plus a few commonly used drivers and a few outputs, would be much more useful than a vast range of possibly totally erroneous ones...

[Nico Ras]

Hi Jez,

I have found significant differences while evaluating different simulators using the exact same models. I am only assuming that the complexity of the computation is relevant. You can perform a limited transfer function with as few as three parameters.

[Conrad Hoffman]

One problem is that BJTs vary widely within a given part number. That's one reason why Harold Black's clever circuit technique is so valuable

I'd love to have a cookbook procedure (follow step 1, follow step 2...) for measuring various BJT and FET parameters and creating a model; some of the model parameters are a bit mystifying- can any of the smart people help me?

[Eugene Dvoskin]

Originally Posted by Nico Ras

Normally purchased product are pretty good such as that from MicroCap. When simulating and testing results are exactly the same. but as Eugene mentioned you have to know what you are simulating.

Stuff available that are for free are exactly that, free and you cannot blame anyone for the accuracy or applicability.

I have downloaded many manufacturers spice files and have not found any inaccuracies their models as these are based on actual measurement and not hearsay.

Maybe it is the quality of the software and calculations, making use of some parameters and ignoring others. I cannot see why manufacturers of components will provide false models, as their livelihood depends on capable engineers designing those components into products that is sold and pays salaries. I cannot imagine any reason for providing lies.

I have experienced some differences in results between free spice simulators with limited capabilities and professional purchased products.

MicroCap has some models, that are hard to find. And I like their user interface. But overall quality of the models, supplied with MicroCap is pretty much similar to the others. Never seen anything interesting within PSPICE library. In any event, I will never use model as a black box - this makes simulation useless. As an example, Linear technology provides encrypted models for their components. It you look at performance of their LT1128, it shows unrealistic performance.

[jez]

Originally Posted by Conrad Hoffman

One problem is that BJTs vary widely within a given part number. That's one reason why Harold Black's clever circuit technique is so valuable

I'd love to have a cookbook procedure (follow step 1, follow step 2...) for measuring various BJT and FET parameters and creating a model; some of the model parameters are a bit mystifying- can any of the smart people help me?

That was one important doodle whilst on a ferry journey
Yes of course there are wide variations as you point out but it would be nice to at least have some accurate models for a "typical" example of a particular device... Rather than be guessing if it is an order of magnitude out or not!

Haven't got any further with that Genrad Digibridge as yet...

[Blackjack8635]

Originally Posted by jez

It's all very well having thousands of models available for high Ft or low Cob or high gain linearity super modern devices but if they are not accurate then what's the point? Especially if in practice the difference between lets say a real 2N3055 and a simulated one is greater than the actual difference between a real 2N3055 and a real MJL3281
!

And I can tell you that quite a few years ago I found gross errors in the MJL3281 and 1302 spice models ( can't just remember which of the pair had the glaring fault at the moment ). The manufacturer and model provider not interested in fixing the errors!