'Local Feedback and Nonlinearity of Multistage Feedback Amplifiers' - diyAudio
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Old 15th September 2004, 07:17 PM   #1
mikeks is offline mikeks  United Kingdom
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Default 'Local Feedback and Nonlinearity of Multistage Feedback Amplifiers'

...food for thought...:

http://www.tde.lth.se/home/mlz/paper02c.pdf


....and for dessert...

http://www.tde.lth.se/home/mlz/paper02a.pdf
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Old 15th September 2004, 08:36 PM   #2
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Thanks Mike, it's on my stack and will eventually migrate to the top..

Jan Didden
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Old 16th September 2004, 01:11 AM   #3
jcx is offline jcx  United States
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but first read "Estimates of Nonlinear Distortion in Feedback Amplifiers" E Cherry JAES V48 #4 4/00

then read Cherry again!
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Old 16th September 2004, 02:17 AM   #4
andy_c is offline andy_c  United States
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BTW, jcx, I bought the Wambacq and Sansen book on your recommendation and am in the process of reading it now. It's the most expensive book I've ever bought! But it's excellent. I hadn't studied the Volterra series at all previously. It's a real eye opener, opening up the door to understanding of frequency-dependent nonlinearities. One thing I wish I had access to is the Schetzen text that the authors reference over and over. I tried to buy it at Amazon but it's unfortunately out of print.

I have read the Cherry articles, but there's something about him that gives me the creeps. The tone of his amplifier distortion article is often defensive, and he tends toward hand-waving. Perhaps these two traits go hand in hand? Wambacq and Sansen are anything but hand-waving, so I don't switch into my skeptic mode when reading them.

Books are described here for anyone interested:
http://www.amazon.com/exec/obidos/tg...glance&s=books
http://www.amazon.com/exec/obidos/tg...glance&s=books
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Old 16th September 2004, 04:54 AM   #5
AKSA is offline AKSA  Australia
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Andy,

You raise an interesting point about Cherry.

Years ago I built his NDL amp and it was utterly unstable. I tried everything. A few years later I saw an article on fixing the amplifier. It had so many stabilizing bandaids, many of them inductors, it was unbelievable. He copped a lot of flack for that design.

A fellow I met five years back took out a patent on nested feedback loops, the so-called J-loop amplifier. As he put his patent to rest he went to meet Cherry. The good professor's attitude was duh, why didn't I think of this, then abject resentment towards the fellow who had. He had the impression he was a rather bitter man.

What was that amusing quote about academia? 'And the fighting was bitter, and malicious, and never ending because the stakes were so low'.

Cheers,

Hugh
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Old 16th September 2004, 04:59 PM   #6
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It seems to me that the Halcro patent depended a lot on
nested loops also.
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Old 16th September 2004, 06:17 PM   #7
mikeks is offline mikeks  United Kingdom
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Thumbs up Spot on!!

Quote:
Originally posted by AKSA
Andy,

You raise an interesting point about Cherry.

Years ago I built his NDL amp and it was utterly unstable. I tried everything. A few years later I saw an article on fixing the amplifier. It had so many stabilizing bandaids, many of them inductors, it was unbelievable. He copped a lot of flack for that design.
Cheers,

Hugh
....actually, the design in Cherry's patent is utterly unstable.....

...if you are going to publish a nested feedback amp. (or indeed anything!!), surely one is entitled to expect that the feedback loops in said amp. are each shown to be stable, and that in fact the whole is stable with any transducer.

....at least two of the minor-loops, AND the global feedback loop are demonstrably unstable.....(for sound technical reasons).

...Should have done your homework Prof. Cherry!!
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Old 16th September 2004, 06:21 PM   #8
mikeks is offline mikeks  United Kingdom
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Quote:
Originally posted by andy_c
BTW, jcx, I bought the Wambacq and Sansen book on your recommendation .....
Actually, i prefer Nordholt:

http://www.amazon.com/exec/obidos/tg...glance&s=books
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Old 16th September 2004, 06:23 PM   #9
mikeks is offline mikeks  United Kingdom
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Quote:
Originally posted by jcx
....Nonlinear Distortion........
...an oxymoron methinks.....
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Old 16th September 2004, 06:29 PM   #10
mikeks is offline mikeks  United Kingdom
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Quote:
Originally posted by andy_c

I have read the Cherry articles, but there's something about him that gives me the creeps.
if you are refering to his Electronics World articles on distortion, then you do have a point in some specific areas......

...for instance, despite Cherry's persistent screams to the contrary, output stage inclusive compensation with power BJT's IS unstable...Period.

...Moreover, his 'modification' of Thiel's load stabilizing network invariably results in a grossly unstable global feedback loop...Period.
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