LTspice, a great program, but that UI! - Page 2

Do you have a question? Post it now! No Registration Necessary

Translate This Thread From English to

Threaded View
Re: LTspice, a great program, but that UI!
On 03/16/2017 11:36 AM, John Larkin wrote:
Quoted text here. Click to load it
They have.  The net is that if you have N adjustments that are coupled
at the 10% level, you can do it by hand.  30% requires an expert, and
50% is essentially impossible by hand unless you start out very close to
the optimum.  (And this works in both directions--it doesn't help to put
one axis on a fine thread.)

I remember seeing GPIB-controlled screwdrivers used for adjusting
microwave filters.

Filter tuning is especially exciting when things are very nonlinear,
e.g. one time I had to tune up the RF coupling network in a plasma
etcher that had a solid state PA.  The plasma guys had redesigned the
chuck, and the pi network wouldn't tune--they were way out of
adjustment, and of course the match changes completely when the plasma
strikes.  With the horrible mismatch, they couldn't turn the RF power
high enough to get the plasma to strike before the reverse-power sensor
shut it down to avoid blowing up the final.

Once I got the plasma to strike at lower power, I found that one of the
two caps tuned slowly and the other one very fast.  It was one of those
long narrow canyon problems the numerical analysts talk about, except
that in this case there were rocks falling from the edges. ;)

Tuning by finite differences was the ticket--adjust the slow knob a fair
way, then tweak up the fast knob, noting which slow direction made for
the lower reflected power.

Once that was done, we put a pad capacitor in series with the fast
control, and all was peace and concord.

For ordinary filters, the main pitfall is that it's often easy to tweak
up a beautiful looking passband that's slightly too narrow.  Anyone who
has done that on a filter of 3 sections or more knows that you might as
well start over at that point--the true optimum generally isn't anywhere
nearby.

You want to tune to get the right number of bumps first, spread them out
over the right bandwidth, and then tune for the right return loss shape.

A grid dip meter is helpful for getting the resonant frequencies of the
individual sections right to start with.  Most filter designs I'm
familiar with are more sensitive to that than to the exact L and C.

Cheers

Phil Hobbs

--  
Dr Philip C D Hobbs
Principal Consultant
We've slightly trimmed the long signature. Click to see the full one.
Re: LTspice, a great program, but that UI!
On Thu, 16 Mar 2017 12:51:14 -0400, Phil Hobbs

Quoted text here. Click to load it

Maybe I was lucky. There's nothing wrong with luck.

One advantage that I had was the option to decide, on an irrational
basis, what "good enough" means. It was a tradeoff between pulse shape
and reflection absorption, and "that looks nice to me" was the
optimization goal. Fatigue can alter one's standard of "good enough."


Quoted text here. Click to load it

I once designed a PWM-based DAC that had two trimpots to set gain and
offset. They diverged so agressively that nobody could adjust them. We
wrote down an algorithm to tide us over until I redesigned it.

Quoted text here. Click to load it

Some circuits might be optimum from a cost standpoint or something,
but they are too difficult to optimize. More stages, or a different
topology, or a buffer halfway through, might untangle things.

And some circuits are just not possible to draw in a visually
appealing way. Time to redesign.

Quoted text here. Click to load it

Rob here has optimized filters and other things by cycling through all
reasonable 5% parts, simulating every combination, and picking the
best one. That might run for a few days, generally Python and not
Spice. Again, that works for things with a small number of components.


--  

John Larkin         Highland Technology, Inc
picosecond timing   precision measurement  

We've slightly trimmed the long signature. Click to see the full one.
Re: LTspice, a great program, but that UI!
On 03/16/2017 01:22 PM, John Larkin wrote:
Quoted text here. Click to load it

Well, computing isn't a good substitute for thought, but it sure is
easier. ;)

Cheers

Phil Hobbs


--  
Dr Philip C D Hobbs
Principal Consultant
We've slightly trimmed the long signature. Click to see the full one.
Re: LTspice, a great program, but that UI!
On Thu, 16 Mar 2017 15:45:07 -0400, Phil Hobbs

Quoted text here. Click to load it

Oh. I'm just an engineer.


--  

John Larkin         Highland Technology, Inc
picosecond timing   precision measurement  

We've slightly trimmed the long signature. Click to see the full one.
Re: LTspice, a great program, but that UI!
On Thursday, March 16, 2017 at 3:45:11 PM UTC-4, Phil Hobbs wrote:
Quoted text here. Click to load it
I don't mind f'ing around a bit, to get things to work,  
(and then find the edges where they don't work.)  
But I certainly want to understand (at least in my own  
hand wavy way) why that works.  

I guess I'm speaking of twiddling with solder and not code,
but same sorta idea in my mind....  
poking around is a good first strategy, if you don't
quite know what is going on.

George H.    
Quoted text here. Click to load it


Re: LTspice, a great program, but that UI!
"John Larkin"  wrote in message  

Quoted text here. Click to load it

f>idddling just kept making things worse.

Quoted text here. Click to load it

Yes it has. One is called genetic algorithms (GA), Its based on the  
Darwinian triple axioms of random variation, replication and selection.

They pop up some really novel topologies, that work really well, apparently.


I think the PSpice optimiser does that as well by other methods. Like having  
goal functions and stuff that it twiddles to. I dont use PSpice anymore, so  
Jim will have to answer that one.

-- Kevin Aylward
http://www.anasoft.co.uk - SuperSpice
http://www.kevinaylward.co.uk/ee/index.html


Re: LTspice, a great program, but that UI!
On Thu, 16 Mar 2017 08:36:22 -0700, John Larkin wrote:

Quoted text here. Click to load it
  
I rarely if ever do that - speaker crossovers are about as
close as I've gotten (years ago when hi fi was a thing).
But I really admire the RF folk - things are totally different
up there, where parasitics are as much a part of the circuit
as parts. GHz especially, all those odd-shaped trace squiggles.
That stuff must be a bear to simulate.
  
Quoted text here. Click to load it

Actually, the dynamics of fiddling is very important to me,
especially for those pesky ANR filters... because the headset
is a physical system affected by many unknowns and variable
conditions, the filter specs are also unknown. I don't know
the exact requirements! Even if I did, the optimum response
changes with just about everything.. not looking for optimum,
looking for something that's good enough and is forgiving.

For math types a situation to this problem is often deemed
impossible but the solution is actually very simple - knobs!
Literally. Replace the resistors with trimmers, capacitors
with switches that select likely values, turn the knobs
until it works right. For our stuff we have no problem
manually adjusting around 18 values provided the selections
are fairly restrained and each adjustment does something
fairly specific and can be assigned a sensible label.
Usually the one doing the adjusting doesn't know much
about electronics so I set it up so with the knobs about
half way it should be in the ballpark, go from there.

Terry

Re: LTspice, a great program, but that UI!



Quoted text here. Click to load it



All the difficult problems, pretty much need this twiddle approach. All the  
simple ways to make money, were done a long time ago, like dos 1.0

To explain.

As prior noted, I design ASICS for "high performance" TCXOs and OCXOs.

Every single oscillator is calibrated by running through several temperature  
cycles, say -40 deg to 105 deg. i.e. banks of ovens/coolers.

The TCXOs have many order chebychev polynomial function generators to  
generate the inverse control voltage to a VCXO to counter the xtal temp  
variation. i.e. summing up a number of cheby co-efficients. No secrets here  
so I can give the main details, all the basics in patents 30 years ago.

The chebys are generated from gilbert cells. Ideally, gilberts are  
independent of temp, but in practice, they are, and also not exact  
multiplications due to other 2nd order effects.

However, all these variations don't matter, even the temp co of the band gap  
reference, that drives all the circuits, don't matter. It don't matter  
because, every transfer function over temperature, including the nonlinear  
temperature to voltage temp sensor, are all measured in the calibration  
runs. So, all the dacs controlling all of the co-efficients are set to  
whatever they need to be for the actual final compensating curve to do what  
it needs to be. Typically, you can get a 20ppm down to 50ppb over  
temperature.

All of this calibration, unlike your menial labour, is automated in  
software.


-- Kevin Aylward
http://www.anasoft.co.uk - SuperSpice
http://www.kevinaylward.co.uk/ee/index.html


Re: LTspice, a great program, but that UI!
On 16/03/2017 21:19, Kevin Aylward wrote:
Quoted text here. Click to load it

Pretty much the same thing is done to calibrate downhole tools over  
their operating range (typically 40 to 200+).

Spice doesn't help much in that field.  In fact component datasheets  
aren't of much use either...


Re: LTspice, a great program, but that UI!
On Thu, 16 Mar 2017 21:19:45 +0000, Kevin Aylward wrote:

Quoted text here. Click to load it

That "menial" labor resulted in $millions of sales and it
wasn't menial at all - it can take weeks to find the best
settings because it has to be tested under all conditions
before committing a particular design to production.
It is not simple and it cannot be automated.

Quoted text here. Click to load it

What makes you think we don't automate with software?
Before something can be calibrated there has to be
something decent to calibrate.

Terry

Re: LTspice, a great program, but that UI!

On Thu, 16 Mar 2017 21:19:45 +0000, Kevin Aylward wrote:

Quoted text here. Click to load it


Well, maybe a a bit too harsh a word

Quoted text here. Click to load it

Well, usually that amounts to "mundane" work. One of the best jobs I ever  
had was mundane. It was during summer break from uni. Job was to put round  
metal disks onto a plate, and stamp a serial number on it. Bestobell Steam  
products. Quite relaxing.

Quoted text here. Click to load it


Don't really see where was that conclusion was implied?

-- Kevin Aylward
http://www.anasoft.co.uk - SuperSpice
http://www.kevinaylward.co.uk/ee/index.html


Re: LTspice, a great program, but that UI!
On 03/16/2017 01:50 AM, Terry Newton wrote:
Quoted text here. Click to load it
Don't mind Kevin, he's just throwing rocks because somebody said his
baby picture was ugly. ;)

Cheers

Phil "Not much of a SPICE fan anyway"  Hobbs

--  
Dr Philip C D Hobbs
Principal Consultant
We've slightly trimmed the long signature. Click to see the full one.
Re: LTspice, a great program, but that UI!
On Thu, 16 Mar 2017 12:38:00 -0400, Phil Hobbs wrote:

Quoted text here. Click to load it

It's kinda fun and I learned some things... and nobody found my
accidental easter egg yet - hint never do head math at 1am when
trying to lob the rocks back.... they tend to miss.

Terry

Re: LTspice, a great program, but that UI!

Quoted text here. Click to load it


I really wouldn't assume too much about my design approach. None of "not up  
on available SC spice models are available" really translates to  
requirements for a lecture on board level design.

As I noted, over 15 years designed, medical imaging front ends, audio power  
amps, pro audio mixing desks, telecom boards....

Got my first electronics kit aged around 11. Built quite a lot of stuff from  
14 to 18, whence I went to uni.

Just curious, when did you build your first crystal set with high impedance  
headphones...?

Quoted text here. Click to load it



Sure, having a good model is really useful. The however though is, if  
LTSpice did not exist, one would think that they would be providing a model  
for the existing spices.

To analyse the worth of LTSpice to LT, one needs to do an A B comparison.  
With and without existence. What would happen? So, if LTSpice didn't exist,  
it does not mean that you would not have been able to discover the effect  
you needed to discover. The models are independent of spice

Quoted text here. Click to load it


No idea how my comment, translates to what you say here.

Quoted text here. Click to load it

More plugging here.... I implemented a fair bit of filter design in SS, if  
you ever get around to trying it. It will design various passive and active  
low and high pass filters, and place the design on the schematic.

Butterworth, Bessel, Chebychev and Gaussian

Second from bottom screen shoot.

http://www.anasoft.co.uk/screenshots.htm

Quoted text here. Click to load it

Yeah, component variation. Its a big issue, even for board level design, not  
just ic design.

That's why I said LTSpice is useless for me. Sure, a lot of board level  
design can get around modelling that in spice as board design can have  
access to 1% components, but still, having inbuilt Worst Case and Monte  
Carlo is really useful for all designs.

Quoted text here. Click to load it

Sure. Again, you *assume* much about my approach to design. Sure, I am up on  
math a tad, e.g.

http://www.kevinaylward.co.uk/gr/index.html

but I hardly use any math whatsoever when designing a chip. Its all spice.  
That's what it does well. The math.

If you get the standard academic books, they will produce whacking big  
equations. The proffs that wrote them say, this is how you design. They are  
wrong. They are completely useless for design, and NO ONE does it that way.  
To many variables and approximations to rationally deal with. .

The idea is that you have to understand the principles, like what changes in  
L and W do to speed, matching, accuracy, gain, what different topologies do,  
like cascode, folded cascode, Millar compensation, etc..what ways there are  
to put poles and zeros in say, an opamp feedback loop, how they effect  
things such as PSRR.

You then do systematic parameter runs, and "intelligently" twiddle with the  
values, until you converge to the spec you find acceptable.

For example, for an LDO, maybe 2 comp caps, two comp resistors, and be  
stable over a range of load caps from 0 to 10uf, and loads from 100 to 1M  
ohms., over all process corners and temperatures and power supply voltages.  
As I noted, maybe 100,000 total simulations.

And again, when one does Worst Case modelling in spice that supports it, one  
includes the variations that might be present on say, the board. I might not  
know if the parasitic board capacitance is 5pf or 10pf, but I can but the  
min and max estimates into the models and just press the button and get a  
suite of results that will enable a descent, first pass design to be done.



Quoted text here. Click to load it


They wrote marketing blerb to mislead the user. The SMPS models were,  
apparently, just a way to implement the few "digital" bits that would be  
done in any  mixed-mode simulator with a genuine digital engine. A digital  
mode J-K runs way faster than an analog implementation.

Mike did a brilliant job on the engine, but its still an analog engine.

Quoted text here. Click to load it


                                  + sup
                                  |
                                |/c
Quoted text here. Click to load it
                |         _|_     |
                `-----------------*---> out
                                  |     (biased
Quoted text here. Click to load it
                                 _|_    minus a bit)

Quoted text here. Click to load it

Well, I could never be bothered to finish the Filter sets in SS, but it  
still can be useful as is.

There is a wad of freebe filter design stuff on the web, today, anyway.

-- Kevin Aylward
http://www.anasoft.co.uk - SuperSpice
http://www.kevinaylward.co.uk/ee/index.html


Re: LTspice, a great program, but that UI!
On Thu, 16 Mar 2017 18:10:05 +0000, Kevin Aylward wrote:

Quoted text here. Click to load it

I don't assume anything other than what you write.
Actually I like your approach - the TCXO writeup was interesting.
There are many approaches and what works for one thing doesn't
always translate to other things.

Quoted text here. Click to load it

Not lecturing just an observation - available spice models can
make a big difference in what parts I choose to use. Or not..
don't really care about opamp models, for those I go by specs
and pick something with a common pinout so if the one I choose
doesn't work I can use another.  

Quoted text here. Click to load it

I've worked mostly as a service tech but have designed several
tube and solid state guitar amps and related gear like pedals,
intercom systems, mic preamps, testers for various things,
main gig right now is ANR headsets and comm systems. Right
now working on a DSP-like signal processor and it's driving
me batty - 40 years of experience and now it comes down to
soldering a stupid QFN32 without wrecking it.
  
Quoted text here. Click to load it

Well... 9 or so I guess.. if you count a crystal earphone..
wanted hi-z cans but for headphones had to use a transformer.
Sometimes with crappy germanium transistors... ha self biasing...

Terry

Re: LTspice, a great program, but that UI!


Quoted text here. Click to load it


I have yet to find a *really* good analog guy that hasn't started pissing  
about at a young age. Its just the way it seems to be, imo.

I don't recall a really good Ballerina starting at age 20 either....

-- Kevin Aylward
http://www.anasoft.co.uk - SuperSpice
http://www.kevinaylward.co.uk/ee/index.html


Re: LTspice, a great program, but that UI!
Quoted text here. Click to load it

I got a soldering iron when I was 8, does that count? :)


Quoted text here. Click to load it

You have to start early to maintain a physique like that.  Male or female,  
that's HARD work, AND fantastic flexibility!  Gymnasts too, especially like,  
on the rings, free training like that.  The way I heard it described (I long  
since forget what article read this in), you get all the force of lifting  
weights heavier than your body, say -- sheer pumping iron, bench press or  
what have you -- but it's done at such awkward angles that it simultaneously  
builds tremendous muscle strength, while retaining range of motion,  
flexibility.

Tim

--  
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design
We've slightly trimmed the long signature. Click to see the full one.
Re: LTspice, a great program, but that UI!
On Mon, 13 Mar 2017 20:44:27 -0000, "Kevin Aylward"

Quoted text here. Click to load it

Strawman.  It's *never* a 30 minute task to evaluate alternative
parts.  

Re: LTspice, a great program, but that UI!
On Tue, 14 Mar 2017 12:44:50 -0400, snipped-for-privacy@notreal.com wrote:

Quoted text here. Click to load it

Well, it might be for passives and simple discretes. But for a
switcher or something, I generally get an eval board and do some
testing... cap load stability, noise, chip temperature rise, all that.
Might take a day.

I usually test opamps, linear regs, things like that.


--  

John Larkin         Highland Technology, Inc
picosecond timing   precision measurement  

We've slightly trimmed the long signature. Click to see the full one.
Re: LTspice, a great program, but that UI!
On Tue, 14 Mar 2017 10:02:49 -0700, John Larkin

Quoted text here. Click to load it

It takes longer than 30 minutes to search for a simple part[*] and a
*lot* longer to just understand the datasheet.

[*] I play the FAEs off each other for this step but I still have to
talk to them.
Quoted text here. Click to load it

You don't test SMPSs?

Site Timeline