Go Back   Home > Forums > Member Areas > The Lounge

The Lounge A place to talk about almost anything but politics and religion.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 3rd January 2012, 01:49 AM   #501
diyAudio Member
 
john curl's Avatar
 
Join Date: Jul 2003
Location: berkeley ca
Hi Scott, You still in the area? Why don't you contact Dr. R.G. Meyer at CAL Berkeley, and ask him about it? I attributed it to him, but what do I know? I do know that D.O. Pederson (father of SPICE) and Meyer both taught the same courses, alternately. Pederson put the derivation of the 3'rd from 2'nd harmonic through local feedback in his textbook:
'ANALOG INTEGRATED CIRCUITS FOR COMMUNICATION' pp. 110-111 (no footnote found).

Apparently Pederson took the 'non-linear analog' notes (EE140-240) and published them, and R.G. Meyer used the 'linear analog' notes (EE141-241) to make his textbook: 'Analysis and Design of Analog Integrated Circuits'. I do have an updated copy of the original notes for both courses, but who knows its exact source? I know that Meyer told us how he got into trouble trying to use local feedback to create an attenuator for an RF front end with a mosfet, and this was the source of the problem. So either he independently invented it, or he found out, after his problem with excessive 3'rd became apparent. You know, cross-modulation.

I found this noteworthy and I have always remembered learning it. However, it took years before higher order generation and cancellations were published. I asked RG Meyer about it in 1973, and he thought that this was 'over the top' even thinking about such a thing. It is amazing how things change over the years. '-)

Last edited by john curl; 3rd January 2012 at 02:00 AM.
  Reply With Quote
Old 3rd January 2012, 12:00 PM   #502
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
Quote:
Originally Posted by godfrey
read what Thorsten actually wrote. He did NOT say "degeneration isn't feedback".
He said that they work differently, and degeneration does not increase higher-order products (unlike feedback). As evidence, he claimed support from Boyk et al and also said that feedback lowers output impedance while degeneration raises it.

Someone showed a section from a Boyk paper which says the opposite of what Thorsten claimed: it described degeneration as feedback, and said that it creates higher order distortion. The change in output impedance behaviour arises because voltage feedback reduces output Z while current feedback (such as regeneration) increases output Z. Basically any form of negative feedback acts to stabilise the sampled variable: stabilised voltage means reduced impedance, stabilised current does the opposite. The maths of distortion reduction and extra high-order products does not depend on the sampled variable.

Now of course it could be that for a particular circuit (whether global voltage feedback, or local current feedback) with a particular input signal level the increase in higher order products takes place so far below the noise-and-masking floor that even an audiophile can't hear it.

It could be that an amplifier with an exponential OL gain characteristic works particularly well with feedback because the extra odd-order products tend to be of opposite sign to the intrinsic odd-order products, but that is a separate issue.
  Reply With Quote
Old 3rd January 2012, 12:20 PM   #503
diyAudio Member
 
abraxalito's Avatar
 
Join Date: Sep 2007
Location: Hangzhou - Marco Polo's 'most beautiful city'. 700yrs is a long time though...
Blog Entries: 84
Send a message via MSN to abraxalito Send a message via Yahoo to abraxalito Send a message via Skype™ to abraxalito
Quote:
Originally Posted by godfrey View Post
Notice the difference between the following two sentences:
A) "Carrots taste different to cabbage."
B) "Carrots are not vegetables."
What Thorsten has been claiming is that degeneration is a member of a new category of edible thing. On the surface degeneration looks to the rest of us (yourself and JC excluded perhaps) rather like a vegetable but he claims it does not fit the existing category of vegetable. The onus is firmly on him to provide support for the creation of the new category of edible thing.
__________________
The great audio capacitor myth : 'There's such a thing as too many PSU caps'.

Last edited by abraxalito; 3rd January 2012 at 12:35 PM. Reason: philosophical slip up
  Reply With Quote
Old 3rd January 2012, 01:38 PM   #504
diyAudio Member
 
scott wurcer's Avatar
 
Join Date: Jan 2004
Location: cambridge ma
Quote:
Originally Posted by john curl View Post
Hi Scott, You still in the area?

I know that Meyer told us how he got into trouble trying to use local feedback to create an attenuator for an RF front end with a mosfet, and this was the source of the problem.
No, not till February we still have not found the right place.

How did he factor out the non-linear C's of the FET's (can't be ignored).

In any case take a follower of ANY technology driving an R, Vout = Vin(R/(1/gm+R)). If the gm has any square law component that depends on its inputs the Taylor series has odd powers. This is about as obvious as one can get, the algebra predates electronics and could describe a mechanical system.
__________________
“The earth's rotation will slow within days and stop for several days just prior to the pole shift. This is when you and your loved ones should be situated at your safe location.”

Last edited by scott wurcer; 3rd January 2012 at 01:48 PM.
  Reply With Quote
Old 3rd January 2012, 02:40 PM   #505
diyAudio Member
 
Join Date: Dec 2011
Default non-linearity defines physics of harmonic generation

As noted the key issue is any current dependent capacitance or resistance will create a nonlinearity which allows for two wave mixing in an equivalent circuit. In optics for example:
eScholarship: Equivalent Circuit Analysis of Harmonic Distortions in Photodiode
  Reply With Quote
Old 3rd January 2012, 05:15 PM   #506
diyAudio Member
 
john curl's Avatar
 
Join Date: Jul 2003
Location: berkeley ca
Well, according to my original class notes, a small 3rd harmonic component was added to the square law (prediction) even 40 years ago, because they measured it. However, the 3'rd harmonic got much larger when local feedback was used to make an input attenuator (an obvious choice for the inexperienced). That was the point of the lecture. Please remember, he is slightly younger than me, and I was only 29 years old at the time, then, at that age, we really got enthusiastic about these things. I just have a better memory of such things than most people.
  Reply With Quote
Old 3rd January 2012, 05:57 PM   #507
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
The issue is not that it is feedback, but simply that a signal containing some second-order distortion is allowed to interact again with the original input signal. The result is inevitably some third-order. This is why diode double-balanced mixers need to be properly terminated so that output signals are not reflected back in again - an RF manifestation of the same issue. Pentode screen grid voltage stabilisation is an audio issue - same thing again, second-order gets turned to third-order. Because this crops up in so many different places it is strange that people can still deny it or seem surprised by it.
  Reply With Quote
Old 3rd January 2012, 06:02 PM   #508
diyAudio Member
 
Wavebourn's Avatar
 
Join Date: Sep 2006
Location: Pleasant Hill, CA
Send a message via Skype™ to Wavebourn
Quote:
Originally Posted by john curl View Post
Well, according to my original class notes, a small 3rd harmonic component was added to the square law (prediction) even 40 years ago, because they measured it. However, the 3'rd harmonic got much larger when local feedback was used to make an input attenuator (an obvious choice for the inexperienced). That was the point of the lecture. Please remember, he is slightly younger than me, and I was only 29 years old at the time, then, at that age, we really got enthusiastic about these things. I just have a better memory of such things than most people.
Well, I was excited in the 5'th grade as well, when we learned Algebra.

Transfer function of 2'nd order error only in the common case looks like:

ax^2 +bx +c

where b defines linear gain, a defines distortions, c defines DC shift.


Now, add feedback and see what you get as the result of multiplication...
__________________
If I disappear suddenly, that means I finally created a time machine and pushed wrong button that brought me to Stalin's Russia. In any experiment any result is the result. Even if it is negative.
  Reply With Quote
Old 3rd January 2012, 06:09 PM   #509
diyAudio Member
 
john curl's Avatar
 
Join Date: Jul 2003
Location: berkeley ca
In hindsight, ALMOST EVERYTHING looks easy. That is the problem. First, you have to find a 'departure' from what you expect. Then, you have to try to understand WHY there was a 'departure' from what you may have predicted. Then, you come to understand the mechanism that created the 'departure' and you either use it or avoid it. Later, when you tell someone else about the 'departure', they will at first not believe you. Then, when you show them evidence, they will shrug and say that it is obvious, and finally, they will accept it and claim to others that they invented it, 'perhaps in the 5th grade'. '-)
  Reply With Quote
Old 3rd January 2012, 07:05 PM   #510
diyAudio Member
 
Join Date: Dec 2011
Default feedback harmonics

? my fifth grade never covered complex algebra or talyor series, or matrix cross products, damn 60's set theory new math for elementary grades.

Anyway correct me if I am worng but I think the highest magnitude third order harmonic terms will be the beating of the second order term against the first order e.g. for the complex current harmonics , one set for the signal first order harmonic against the second order feedback(a1*a2f + a1a2f* ) and the feed back first order against the second order device nonlinearity induced third order (-a1f*a2 + -a1fa2*); if the feed back is not exactly Pi out of phase these terms will not cancel and your syrupy transfer function will become bit strident.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Sound Card for Measurements Marik Solid State 2 2nd January 2012 08:59 PM
Sound Card Recommendations (For Audio Measurements) dchisholm Equipment & Tools 5 16th July 2011 09:40 AM
How to protect sound card during amp measurements? okapi Everything Else 13 2nd September 2008 03:06 PM
Quality Control differences = variations in sound quality? KT Class D 0 14th November 2004 06:51 AM
Sound cards - test and measurements jackinnj Everything Else 2 5th July 2003 03:02 PM


New To Site? Need Help?

All times are GMT. The time now is 09:03 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2