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Does the noise density function increase if an OpAmp goes into slew rate limit?

Started by RobertMacy May 28, 2014
On Thu, 29 May 2014 09:46:19 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>On 05/29/2014 09:37 AM, RobertMacy wrote: >> On Wed, 28 May 2014 18:39:11 -0700, Phil Hobbs >> <hobbs@electrooptical.net> wrote:
[snip]
>> >> Again, the energy in the output does not matter, but the noise floor >> 'around' that signal does. > >But in slew limiting, it isn't a linear system, so your linear systems >approximation goes out the window. Worrying about the noise floor in >that situation, when you've got maybe a volt of input error, is just >cracked.
Absolutely... there is no longer "communication" from the input stage to the output... any noise is due only to that hung current mirror.
>
[snip]
> >If you believe SPICE down to that accuracy level. It's asking a lot of >a crappy macromodel, for sure. Unless I'm very much mistaken, it would >be a lot faster and cheaper to make a couple of boards and have a look. > >Cheers > >Phil Hobbs
MACROMODEL... is only a curve-fit to noise reality (usually done by some kid PhD just out of school :-)... in the LINEAR region... AND as have many posted here, limiting/slewing behavior is generally a joke. What is bugging me... recent exposure to a company of young bucks... ALL functions need an OpAmp... they can't really think device-level. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
On Thu, 29 May 2014 08:00:50 -0700, RobertMacy
<robert.a.macy@gmail.com> wrote:

>On Thu, 29 May 2014 07:48:08 -0700, Jim Thompson ><To-Email-Use-The-Envelope-Icon@on-my-web-site.com> wrote: > >>> ...snip.... >> I just checked... the model call for an LT1115 _symbol_ is also >> LT1028... open the symbols (.asy) with a text editor, and see for >> yourself. > >oops, forgot that! > >>> ...snip.... >> The LT1028 model is 100% behavioral, so I suspect your results are >> totally meaningless... sorry. >> >> I'll try to find you an all-device-level OpAmp model to play with. >> >> ...Jim Thompson > >do I only need small input section and small output section? But if you >find the whole thing is ok.
Good OpAmp designs only have two gain stages, compensated by pole-splitting, then a follower output stage. Three stage OpAmps are only created by PhD's :-] ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
On Wed, 28 May 2014 17:29:05 -0700, RobertMacy
<robert.a.macy@gmail.com> wrote:

[snip]
> >Do you own Matlab, or install octave? Or what do you use for math analyses? >
I failed to mention that I have PSpice _A/D_ which has Performance Analysis built-in... it can do most everything that other simulators require script-writing or external data-processing to do, and can produce that analysis as a nice display in Probe. That's what I was trying to do for the Power Bandwidth situation, but the wandering bias was ruining my efforts. (OpAmp under test was a +/100V, +/-100A (Yes AMPS) monster with some wild biasing to keep it alive under fault conditions :-) ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
On Thu, 29 May 2014 09:10:08 -0700, Jim Thompson  
<To-Email-Use-The-Envelope-Icon@on-my-web-site.com> wrote:

> On Wed, 28 May 2014 17:29:05 -0700, RobertMacy > <robert.a.macy@gmail.com> wrote: > > [snip] >> >> Do you own Matlab, or install octave? Or what do you use for math >> analyses? >> > > I failed to mention that I have PSpice _A/D_ which has Performance > Analysis built-in... it can do most everything that other simulators > require script-writing or external data-processing to do, and can > produce that analysis as a nice display in Probe. > > That's what I was trying to do for the Power Bandwidth situation, but > the wandering bias was ruining my efforts. > > (OpAmp under test was a +/100V, +/-100A (Yes AMPS) monster with some > wild biasing to keep it alive under fault conditions :-) > > ...Jim Thompson
Didn't going to super small max steps help? like trying to put 100kHz through the amp, so max step size is 5nS With the 'macromodels' they were stable whether I used 1 or 2nS
On Thu, 29 May 2014 14:03:29 -0700, RobertMacy
<robert.a.macy@gmail.com> wrote:

>On Thu, 29 May 2014 09:10:08 -0700, Jim Thompson ><To-Email-Use-The-Envelope-Icon@on-my-web-site.com> wrote: > >> On Wed, 28 May 2014 17:29:05 -0700, RobertMacy >> <robert.a.macy@gmail.com> wrote: >> >> [snip] >>> >>> Do you own Matlab, or install octave? Or what do you use for math >>> analyses? >>> >> >> I failed to mention that I have PSpice _A/D_ which has Performance >> Analysis built-in... it can do most everything that other simulators >> require script-writing or external data-processing to do, and can >> produce that analysis as a nice display in Probe. >> >> That's what I was trying to do for the Power Bandwidth situation, but >> the wandering bias was ruining my efforts. >> >> (OpAmp under test was a +/100V, +/-100A (Yes AMPS) monster with some >> wild biasing to keep it alive under fault conditions :-) >> >> ...Jim Thompson > > >Didn't going to super small max steps help? > >like trying to put 100kHz through the amp, so max step size is 5nS > >With the 'macromodels' they were stable whether I used 1 or 2nS
Device-level... "monster" has an excess-phase curve that defies anything but a MULTI-section all-pass. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
On Thu, 29 May 2014 14:06:43 -0700, Jim Thompson  
<To-Email-Use-The-Envelope-Icon@on-my-web-site.com> wrote:

>> ...snip.... > > Device-level... "monster" has an excess-phase curve that defies > anything but a MULTI-section all-pass. > > ...Jim Thompson
I don't quite understand that. Except I kind of envision you have 1500 components in your model and so many things are shifting the phase slightly so by the time the signal gets through, it's been 'rotated' a couple hundred times? did you try ??'s suggestion [was that Tim Williams?]of changing some of those options? .options method=gear because default is trapezoid, which by his description causes the 'happy with this answer being close enough' to bounce back and forth. or gear2 if you have it For what I was doing, I did not see much difference in stability, or speed, but it is interesting to find a few 'handles' to play with. Especilly the pivrel and pivtol
On Thu, 29 May 2014 07:48:08 -0700, Jim Thompson  
<To-Email-Use-The-Envelope-Icon@on-my-web-site.com> wrote:

>> ...snip... > > I'll try to find you an all-device-level OpAmp model to play with. > > ...Jim Thompson
Did you find one?
On Fri, 30 May 2014 12:09:29 -0700, RobertMacy
<robert.a.macy@gmail.com> wrote:

>On Thu, 29 May 2014 07:48:08 -0700, Jim Thompson ><To-Email-Use-The-Envelope-Icon@on-my-web-site.com> wrote: > >>> ...snip... >> >> I'll try to find you an all-device-level OpAmp model to play with. >> >> ...Jim Thompson > >Did you find one?
I'll design you an all-device-level OpAmp over the weekend. How's that for service with a smile ?:-} ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
On Fri, 30 May 2014 12:34:25 -0700, Jim Thompson  
<To-Email-Use-The-Envelope-Icon@on-my-web-site.com> wrote:

> On Fri, 30 May 2014 12:09:29 -0700, RobertMacy > <robert.a.macy@gmail.com> wrote: >>> ....snip... >> Did you find one? > > I'll design you an all-device-level OpAmp over the weekend. How's > that for service with a smile ?:-} > > ...Jim Thompson
Look forward to that! and the design ;) Don't forget, netlist in the pure form I don't have an 'easy' way to implement. I have a copy of OrCAD Capture v 9.62 if that's any help.
On Fri, 30 May 2014 12:58:23 -0700, RobertMacy
<robert.a.macy@gmail.com> wrote:

>On Fri, 30 May 2014 12:34:25 -0700, Jim Thompson ><To-Email-Use-The-Envelope-Icon@on-my-web-site.com> wrote: > >> On Fri, 30 May 2014 12:09:29 -0700, RobertMacy >> <robert.a.macy@gmail.com> wrote: >>>> ....snip... >>> Did you find one? >> >> I'll design you an all-device-level OpAmp over the weekend. How's >> that for service with a smile ?:-} >> >> ...Jim Thompson > > >Look forward to that! and the design ;) > >Don't forget, netlist in the pure form I don't have an 'easy' way to >implement. > >I have a copy of OrCAD Capture v 9.62 if that's any help.
It'll be a subcircuit library... what you do with it from there is up to you... LTspice, OrCAD, what-have-you. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.