Absolutely... there is no longer "communication" from the input stage to the output... any noise is due only to that hung current mirror.
[snip]
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.
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.
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.
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.
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.
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
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| 1962 | I love to cook with wine. Sometimes I even put it in the food.
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.
Will you know the answer to the question as to what the noise floor WITH and WITHOUT slew rate limiting will be? Example: power from +/-12Vdc, Rinput=Rfdbk=1k, Cfdbk=22pF, Rload=10k, Cload=10pF, compare driving with 7mVpk at 1MHz to driving with 7Vpk sinewave. The first should be easy with .noise; but the other...?
I have no idea... you're supposed to elucidate me >:-} ...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.
OK, but i still have questions about how to separate the distortion products from the noise. I suppose that there may be a way with only moderate to heavy levels of serious analysis. There may be a way to find and account for the distortion products and subtract that from the final waveform and analyze the result for noise. May take some rather fancy tools though.
First, drive the system with a pure sinewave. Next, assume that distortion of a repetitive waveform can ONLY be related to the frequency of that sinewave. For example, drive with 1MHz and without any distortion caused by the slew rate limit you should get 7 Vpk, but what comes out is a really weird 2Vpk signal. Now the ONLY energy you should have in that signal is at 1MHz, 2MHz, 3MHz, 4MHz, 5MHz etc. It is NOT possible to get anything else. [I think] Where would say 349kHz come from? You can't get there from here.
Small note: if by examination the waveform appears to be symmetrical about the axis [top looks like mirror image of bottom]; you will have a dominance of ODD harmonics. The EVEN harmonics will be VERY small.
To get rid of weird startup effects, throw away a little at the start. To simplify [but not necessary] I set up the tran statement like this: .tran 0 1.1m 0.1m 0.01us
Now after making all the steps uniform using ltsputil.exe for a total of
100001 samples of your output waveform remember has a step size of 0.01 uS, the output data is the output from 0.1m to 1.1m, where the new t=0 was at 0.1m and the new t=1m was at 1.1m, and throw away t=0 data point. That leaves you with a sampled packet length of 100000. In 'FFT' signal processing that translates into Nyquist rate of 50MHz with a BW of 1kHz - very adequate for what we're doing. To compare apples to apples, run the .noise from 1kHz to 50MHz.
Now take the FFT of your data and the first harmonic is down, third is close by, and so on.
Since you KNOW each harmonic, simply remove it.
Just as you write a batch file to run ltsputil.exe, write some functions to get rid of ALL harmonics. I purposely have noise in the signals so removing signal harmonics leaves only the noise WITHOUT the signal and I can see how the noise density function has changed.
Try on something and you can convince yourself it is simple.
If interested, I think I could mock up a little OpAmp circuit with some feedback diodes to clip the output, then you can see the effects on the noise caused by the non-linearity and see the 1/f effects, too. There is no real need to remove the signals and all harmonics, because the noise floor looks just like you're using a spectrum analyzer. Do you have octave, free Matlab clone?
--
| 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.
I had hoped somebody had done such a test using a spectrum analyzer for confirmation. However, staying with circuit simulations and using your MC1530 OpAmp containing those 2N3904's thrown in placed into a simple inverting configurations [GND the IN+] using 10K external resistors for GAIN=-1 powered by +/-6Vdc...
To find the noise density function at the output, run .noise which shows
24.1 nVrms/rtHz, as reference value.
As a 'walk before run' ONLY added the noise from R7, 6K, and R11, 30k, and the external Rinput, 10k, and Rfdbk, 10k. and drive the inverter with a
2mVpk 400kHz sine signal. .tran shows very 'clean' signal, but if I run ".tranoise" the output looks more 'realistic' with an approprite noise floor for the FFT. Just these four sources produce a huge level of noise,
16.4nVrm/rtHz, [Remember, that's from just from those four sources, not including any other resistors nor NPN transistor noise!].
Next the input signal was increased to put the OpAmp into slew rate limit using 2Vpk sine wave at 400kHz. Get about 1.2 to 1.5Vpk out and looks very 'sawtooth'. The .tranoise now shows the background noise has indeed increased to more than 50nVrms/rtHz! increasing more than 3 times. from memory the same thing happened with the OpAmp macromodels which increase theirnoise floor around 10dB, also.
Since I'm now comfortable with your text netlist being accurately transferred into LTspice schematic form, matching the style on the Data Sheet, I'll soon send you a copy for your website info.
If you want, to be really complete, tell me which Pins go to which LEAD/LAG compensation internal components, and I'll include a 'complete' module, too.
Didn't see any comment to yesterday's posting, showing preliminary modleing of slew rate limiting effects.
Also, I have the subckt model AND the discrete model all done to send to you. just found your teaching aid .pdf with the mask photo, didn't see the CAP yet, but at least have the pin out now, so can do a 'complete' MC1530 subckt model including the lead/lag terminals.
Do those 'minimum size' NPNs really act like the 3904 model? seems their areas would have to affect the model's terms in some way.
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