LTSpice: Slow on noise sims with foreign opamps

What? You refused to identify yourself with a Username and Password ?>:-}

And there is an E-mailed Digest... quite useful.

Sounds like you don't know how to do a dotAC plus Noise analysis.

Which OpAmp?

...Jim Thompson

I did ID myself. But now they slapped on a stupid "captcha". Which promptly resulted in "Can't identify the machine bla-bla-bla, followed by a challenge question to which they cannot have the answer.

IOW, they are on the path of oversophisticating the Yahoo groups to death.

But can you probably can't ask questions via that.

I don't do noise analyses much, that's usually done on the bench here but in this case it should be sim'd.

OPA4140.

You can try to email to snipped-for-privacy@yahoogroups.com but the email has to come from your yahoo email id or from the id where you get the email digest or individual messages. Or, just create a new account on yahoo and sign up for the ltspice group again.

If all else fails I'll post this for you but you know the first thing they are going to want is an example circuit.

Do we live in the same universe? I've never experienced that.

Sure you can. I participate several times a week. They actually discuss engineering there >:-}

Set-up how? Feedback, bias, supplies, etc. ...Jim Thompson

Tried numerous times, always the captcha. Those things are nasty but after four tries it let me past the virtual bouncer. Wot a pain.

I know they do. But so far I haven't figured out a way inside without that dreaded Yahoo GUI. So where's the back door and how many knocks?

Essentially I've plopped the whole Texas model in there. Right now supplied +/-5V, for the test stripped back to a follower with just 10k OUT to IN-, IN+ to 0V (ground).

With any LTC models it zips right through even with complicated stuff around them, as usual.

I've got the circuit working, it's just that it doesn't seem to like Texas models. No, no, not those :-)

Bwahahahahahaha! The OPA4140 Spice model provided by TI is what gives model-makers a bad name... the sort of model you get when you take a PhD with no hands-on-lab experience and sit them down in front of a simulator.

I don't think I've ever seen such a badly constructed model before. No wonder it takes forever to converge. ...Jim Thompson

Kind of my hunch, but I hadn't thought it was this bad :-(

Burr-Brown used to be a pretty good bunch of engineers, real hands-on guys.

Looking at the bright side it did manage to heat my office by one degree Fahrenheit over lunch.

Hmmmmmm? Maybe cockpit error? In PSpice, Q-point found as fast as you can blink:

• C:\Projects\Expments\OpAmps\OPA4140.sch

**** JOB STATISTICS SUMMARY

Total job time (using Solver 1) = .27

I think I know the problem...

I did this...

.SUBCKT OPA4140 +IN -IN Vout V+ V- ; -IN +IN V- V+ Vout (Rearranged Order to Match PSpice Symbol)

You need to make sure the "pin" order matches the LTspice OpAmp symbol... otherwise you will experience pain and agony.

(The TI pin order is just a wee bit unusual. I do this rearrangement exercise almost daily, so it's second nature to me.) ...Jim Thompson

Then I get this:

Circuit: * E:\Simulations\PGL\PosSense_AC_1.asc

Expanding empty subcircuit: opa4140 WARNING: Less than two connections to node V+. This node is used by V1. WARNING: Less than two connections to node V-. This node is used by V2. Direct Newton iteration for .op point succeeded.

Date: Fri Jan 04 17:14:43 2013 Total elapsed time: 0.047 seconds.

tnom = 27 temp = 27 method = trap totiter = 6 traniter = 0 tranpoints = 0 accept = 0 rejected = 0 matrix size = 17 fillins = 0 solver = Normal Matrix Compiler1: 32 opcodes Matrix Compiler2: 967 bytes object code size

guys.

That is so-o-o-o-o useful. WTF does that mean? Does it work, or not? ...Jim Thompson

No captcha here, either. I'm not a "member" of the LTSpice Yahoo! (can't forget the '!') group but am of a couple of others in the tech.groups.yahoo.com tree. Maybe something with your browser (is javascript on? needed?) or cookie settings?

If not, it may be that somebody (or some algorithm) has decided that your login is being used by a 'bot, since 'bot blocking is the usual reason for putting a captha in-line with the login.

guys.

LTSpice.

Nope. This was the error message LTSpice let off.

Maybe because I leave myself logged in until it throws me off. Usually lasts a few weeks. I really don't like log-in hassles. Why can't they just set a cookie and be done with it?

They can. You probably have it blocked. Mine works.... Firefox v17.0.1 ...Jim Thompson

guys.

LTSpice.

Huh? What does...

"Direct Newton iteration for .op point succeeded."

I always turn cookie on when I look onto the, it's sitchable.