Automatic parameter search for a given output in LTSpice

Question

I am simulating a circuit on LTSpice and was wondering if there is a way to set output parameters for LT to aim for by adjusting values of other components. I have used some software in the past that does this but i cannot remember if it was LTSpice or something else.

Thanks in advance

I do not understand what you are trying to accomplish. – Arsenal Dec 06 '15 at 15:29 — Arsenal, Dec 06 '15 at 15:29

Fizz · Answer 1 · 2015-12-06T20:44:09.380

What Daniel says is correct and applies to all SPICEs unless they are seriously enhanced. However what you can do is to vary some sensible design parameters using .step param and see how the output changes. But it won't design an optimal circuit for you by itself. There are some hacks using SPICE in a feedback loop, i.e. driving it by some other external program to do a guided optimization. Without knowing what you're trying to do, I'm not gonna get into that.

It turns out most [non-free] commercial SPICEs actually do offer some add-on or built-in optimizer. Below I tried to include links to examples with each so you can get some idea; generally these commercial SPICE don't have on-line documentation accessible unless you're paying customer, so precise capabilities are little hard to ascertain beforehand.

Synopsys HSPICE: fairly old examples found on-line.
Silvaco SmartSpice: slides from a training.
Mentor Graphics Eldo: whitepaper that requires registration to read.
and even IsSpice4 or TINA (not the free TI version though) have something.
Keysight's ADS Spice module has some capabilities listed in this blurb, but I could only find on-line examples (that didn't require customer log-in) for their for their Momentum EM optimizer.
Cadence PSpice and Spectre (SPICE-alike) each have their own optimizer. The one for PSpice is included only in the Designer Plus version.
OPUS SPICE is the only free one that seem to have such features, but they are pretty extensive; also paper about them. (OPUS is kinda kludgy to use for other purposes, in my opinion.)

Since the optimization function[s] are not part of Berkeley SPICE, you should expect a fair amount of differences between these, so evaluate before you buy if you can.

As a separate optimizer that runs on top of other SPICEs, ASCO seems pretty capable... and it's also free; It can run with LTspice, ngspice and with some of the non-free commercial ones (Eldo, HSPICE, Spectre). Also, Qucs uses ASCO for optimization.

lol SPICE in a feedback loop. I got to try that sometime. Have you had success or just heard/read about it ? — efox29, Dec 06 '15 at 16:06
@efox29: not with LTspice. Needs something that's command-line based. — Fizz, Dec 06 '15 at 16:11
http://hackaday.com/2012/07/09/on-not-designing-circuits-with-evolutionary-algorithms/ — Daniel, Dec 06 '15 at 16:20
Keysight's ads offers substantial optimization capabilities. I'd guess that HSPICE would also, but I don't use HSPICE. — The Photon, Dec 06 '15 at 17:10

score 1 · Answer 2 · answered Dec 06 '15 at 15:38

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I don't think there is any way to get LTSpice to goal-seek. While you can do some pretty complicated things with directives (like monte-carlo analyses!) it's still just a simulator not an optimizer.

answered Dec 06 '15 at 15:38

Daniel

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Monte-Carlo [is for masochists only](http://electronics.stackexchange.com/questions/137934/parts-tolerance-simulations-in-ltspice) in LTspice... – Fizz Dec 07 '15 at 04:44

Automatic parameter search for a given output in LTSpice

2 Answers2