Multisim & PSPICE - using MOSFETs

Hello,

I was wondering if anyone here has experience with modelling MOSFETs on PSPICE and Multisim. As a student, I've been used to using PSPICE 9.1 Schematics to model and simulate circuits. However, I only have the evaluation version, and need more than 10 transistors in my circuit. I also have Multisim available to me, but PSPICE and Multisim seem to be very different in the way the MOSFET models operate. I took a rather uncomplicated N & PMOS from PSPICE and have gotten nowhere in Multisim.

I'm wondering if anyone here has experience with trying to translate between the two programs, especially using transient analyses or the scopes that Multsim provides. Thank you.

Reply to
ER Yost
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What MOS model LEVEL=[a number goes here] is it?

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

So far, in Multisim I've used level 1 virtual enhancement mode MOS as well as two power MOSFETs (P and N-channel) that come with the student version - one by Motorola, one by International Rectifier - I think one is a level 1, the other is a level 3. Power MOS isn't the right application for my research, but it at least it will give me an idea of what is going on for a few periods before giving me a timestep error (right now I have the relative tolerance at 0.01 and ITL4 at 100, which Multisim recommended for timestep errors).

Another thing I'm trying to figure out in general is how to establish the channel resistance in the model since I'm looking into energy dissipation.

Reply to
ER Yost

"ER Yost" schrieb im Newsbeitrag news: snipped-for-privacy@i40g2000cwc.googlegroups.com...

Hello ER Yost,

have you ever heard of LTspice. It's practically free, unlimited and highly compatible to PSPICE on the netlist level. Your MOSFETs will work with LTspice if they work with PSPICE.

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There is also a user group.

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People should be aware that the GUIs of real instruments are mostly compromises because of limitations in the measurement hardware, limitations of the display, knobs and the cursor control. Why want you go with the second choice? I wonder.

It's much more efficient and powerful to work with pure xy-diagrams in the waveform viewer of PSPICE(Probe), LTspice and many other SPICEs.

Best regards, Helmut

Reply to
Helmut Sennewald

Actually, yes, I downloaded LTspice yesterday and it has been very helpful. I've been able to build bigger circuits and get good feedback.

However...

With the research that I am doing this summer, it will be extremely important to be as accurate as possible. You can Google "quantum-dot cellular automata" (QCA) if you'd like - I'm doing research for Notre Dame (1st hit). The circuit that I am building isn't really to help the QCA project itself, but to provide a concrete example of how QCA is going to be more energy efficient than typical circuits today.

I need something more accurate than LTSpice. Sure, PSPICE or Multisim aren't perfect, but they're pretty close. I'd love it if I could get a good enough version of PSPICE to have more than 10 transistors, because I have more experience with that. But, for now, I'd love to be able to use Multisim since it will give me enough computing power to do it.

Nothing against LTSpice. It's definitely saved me time. It just won't be up to par in the end.

Thanks,

ERY

Reply to
ER Yost

I don't think there's actually any issue with LTSpice accuracy as long as you don't use some of its speed-up gimmicks.

But Level=1 and Level=3 models suck the big lemon.

Your issues probably lie there as well as with your inexperience with Spice engines and how to set time-steps.

(I've been using PSpice since it was on DOS ;-)

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

Humbled I am.

Until you mentioned it, I didn't really realize that I could set the MOS models in LTspice. Duh.

Although I still don't get why my basic SPICE model wasn't consistent between programs, I might as well give LTspice my undivided attention and leave it at that.

Thanks,

ERY

Reply to
ER Yost

Hello ERY,

LTspice has normally "data compression" enabled. It's like a lossy data compression of the raw-file. You should switch it off.

.options plotwinsize=0

With this command, LTspice will beat PSPICE and others regarding accuracy by decades! Sorry that this compression setting isn't so obvious for new users.

Best regards, Helmut

Reply to
Helmut Sennewald

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