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Old 31st December 2010, 12:04 PM   #11
Elvee is offline Elvee  Belgium
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Very interesting topic. Deserves much more attention than it has received so far.
Please continue your good work, Jcx: now you know at least some folks are following you (I'm pretty sure Steph tsf is also interested).
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Old 14th September 2012, 05:35 PM   #12
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Quote:
One previously known composite op amp with power supply bootstrapping showing loop gain enhancement from the bootstrapping of the internal voltage gain stage is from Mohapatra and Sandman 1980 GB patent.
JCX, can you give more details on this patent? I wasn't able to finde it. Thanks!

Samuel
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Old 14th September 2012, 05:48 PM   #13
jcx is offline jcx  United States
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Default the Search is weak in this one master..

"interface circuits" on 1st page of google search Google Mohapatra and Sandman’ 1980 GB patent

clik: Full Text at United Kingdom Intellectual Property Office (IPO)

Espacenet - Bibliographic data
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Old 14th September 2012, 06:41 PM   #14
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Don't know why I missed this--I did hit Espacenet with the authors. Anyway, thanks!

Samuel
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Old 14th September 2012, 07:18 PM   #15
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2 poles, 2 zeros, lots of gain... yawn
jcx, have you ever possibly tried a rhp pole plus 2 (or even 3) lhp poles plus 1 lhp zero controller? Now this one is tricky!
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Old 14th September 2012, 10:12 PM   #16
jcx is offline jcx  United States
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you mean something with a loop gain curve as complicated as this?

the "upper bode step" comes from the 2-pole T network feedforward around a slower level shift stage interaction with the combining network to drive the output Q

the point-to-point prototype built with slower parts shows good agreement with its sim, but isn't as tightly "tuned" as the sim the plot below comes from - time to start re-learning Eagle...

rh poles, zeros, aren't usually "desired" parts of a design - but may be consequences of other choices with desired benefits – sometimes you just have to work with them for the other benefits - think of designing around them as "learning opportunities"
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Last edited by jcx; 14th September 2012 at 10:30 PM.
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Old 15th September 2012, 06:31 AM   #17
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I found rh pole useful to add intensionally in some cases (unlike rh zero), which most texbooks either omit or say one doesn't want it, because it's bad without thorough analysis. OK, they mension Nyquist plot going twice around the point of interest...
For the global loop it is all you dream about , -6db/dec rolloff with positive 90deg phase shift, which sound like a cigarette that cures cancer, but the rest of loop must also have enough gain to push the rh pole to lh in closed loop. This is very tricky and hard to stabilize under any condition, but can do wonders once working...
Enough said, still under my work, for 5 years now, first implemented without analysis, sort of 'everybody knows something can't be done, until ...' story.
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Old 15th September 2012, 11:00 AM   #18
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Two sim plots, 1st using ideal models, 2nd using real circuit down-to-transistors model
(2poles, 2 zeros, 1 unstable pole). Note that adding some more gain theoretically doesn't affect phase margin
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File Type: png 2.png (36.5 KB, 350 views)
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Old 16th September 2012, 12:28 AM   #19
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I have never been a fan of huge gain in amplifiers.
In my design experience you just end up having to slow things down to stop oscillation.
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Old 1st February 2013, 08:05 AM   #20
Bonsai is offline Bonsai  Taiwan
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I am posting the link up to something I have played with recently

Augmented Feedback Error Correction (AFEC)

I like your clamp circuit jcx - I will need to try it in the next few days.
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