Why the equations that were used in the description of the component models by the simulator does not appear in the documentation/help file?


We can see that a model of a component has some parameters, like for example in the case of a mosfet:

WHAT IS MISSING IN THE HELP/DOCUMENTATION of QSPICE (and is the same case for LTspice) is that we can see that only the parameters are described in the documentation/help, but the associated equations does not appear in documentation (they are missing).


For example (in the case of a diode):

In the documentation we will se only something like this:

And the associated equation will not be shown in the help/documentation:

I wonder why, in addition to the description of the parameters used by the model in the help file, the associated equations does not also appear, so that people can know in which equations the respective parameters appear and what equations were used in describing the model by the simulator.

I am sure that someone will say: “look on the internet to find the equations”, “look on these books”, then still the questions will appear whether the equation you found on the internet/book is the correct one used by the respective simulator in the description of the models or not, and so other like questions.

I wonder why all the equations used in the description of the component models are missing in the help/documentation, in order to understand correctly in which equation each parameter appear, beside the fact that each parameter used by the equations are described in the documentation of the simulator?

Any explanation for this?

The best answer should always come from Mike Engelhardt. Here is just my personal opinion. In the Qspice HELP section, under Acknowledgments, it is mentioned that Berkeley SPICE version 3F5 and the BSIM code from bsim.berkeley.edu have been extensively reworked for the Qspice project. Spice has a long history, and its work is built on a vast foundation.

For example, bipolor transistor model Mextram 504, NXP official document is 90 pages, and with few hundred device equation in that document. Possibly for anyone who are not work on device modeling (including me) has very difficult time in understand that even all formula are provided.
Mextram definition document : The Mextram Bipolar Transistor Model (nxp.com)

In this forum, Mike recommended a book multiple times, which is 2nd edition of Semiconductor Device Modeling with SPICE by Paolo Antognetti and Giuseppe Massobrio. This is a great reference and give me a lot of help when I preparing the device guideline in my Github especially the section of Diode, Transistor and MOSFET.
What are the best books on the SPICE simulator? - QSPICE - Qorvo Tech Forum

If Mike works on listing all device equation in help, possibly he won’t have time to work on Qspice coding anymore.

If you are not work in device modeling, possibly you just need to understand several critical parameters which help to slightly adjust the model to better fit the model into datasheet or measurement results. In addition, user likes @bordodynov in this forum has in-depth knowledge of device equation adjustment. So, possibly you can get help from this forum too.

I highly recommend the book recommended by Mike if you want to start your journey of understanding device equation.

I do not know why this should be the case…QSPICE is owned by a company - Qorvo company, right? Therefore I think that they could probably find someone from the company to take care of documenting the equations used by models inside the simulator. Finally the equations were written already on the back in simulator, so they are filtered and adjusted and brought to the final form from the sources/books you said above (and maybe others, I don’t want to guess what equations were used by the models inside the simulator), thus the equations just need to be documented. And Mike can work further on coding, he only needs to supervise the one who will document the equations. And that’s it…

And if only Mike takes care of everything this simulator means…without having others to help him with such tasks and other task then I am not sure what to say about this. But maybe Mike/Qorvo company does not want to reveal these things like what equations were used in describing each models, and this could be a much stronger reason of why those equations are missing from the help menu, beside the fact that all parameters used by these equations are described there.

I highly recommend the book recommended by Mike if you want to start your journey of understanding device equation.

As I said previously, then still the questions will appear whether the equations you found on the internet/books are the one used by the respective simulator or has other forms in the description of the models or not.

It would be good to know more details about what equations they have implemented for their models in the simulator to understand better which parameter influences what equation.

You can continue to whine here and on other sites, but I don’t think you are making any progress with your arguments. At least not with anybody disposed to help you.

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It’s not about progress, it’s about understanding why these equations of the models are missing from the help menu (beside the fact that the parameters involved in these equations are described there, so it’s only half of the things described there, and the other half (the equations) is left away) and why they are not possible to documente somehow. (The argument that these equations cannot be used in understanding the things and that they are useless it’s not an argument as already Kelvin showed in his documents that these equations can be very helpful in better understanding how models are constructed/how the respective component works and how to understand better the simulation results)

Have you ever wondered - who needs you to know what mathematical expressions are used in the program? This may constitute a trade secret. There is a lot of information on the Internet. When it was I who needed to create models of MOS transistors at an enterprise that manufactures CMOS chips, I found the equations. Compiled algorithms for a program (Fortran was used) to extract spice parameters of transistors. He made a proposal for measuring various current characteristics. Special test structures on a chip (with different geometric dimensions) were also developed. Subsequently, they were manufactured and measured using my method. Processed by a written program. But back then I didn’t have the Internet.
It’s easier now. And I had to analyze the text of the Spice2 program (obtained by spies) and study the formulas.

I remember those days! The first time I got a SPICE tape from U.C. Berkeley I had to submit an affidavit that would would not share the code with any of a very long list of countries, including of course the CCCP and all her satellite states.

After Glasnost and later the fall the the CCCP, the list dwindled to just Vietnam and North Korea. And finally there were no restrictions. I actually released LTspice XVII first during a seminar in Vietnam, an irony I enjoyed. I released it there as a trial market to see if there were going to be any problems with the release.


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