But we have no difference of opinion I believe. And even if we had, so what
Ha ha. The collective camaraderie around here is going to turn that into the forum motto for sure!
Laugh if you will Gentlefolk, but it has now been more than 24 hours since one of the denizens of this thread turned to another and muttered the equivalent of “Jane, you ignorant slut!” Watch Weekend Update: Jane, You Ignorant Slut From Saturday Night Live - NBC.com
Of course, I grant you that it is the weekend, and perhaps some of us, including the members of the Loyal Opposition, are taking a holiday.
Let’s see what Monday brings.
Of course, I grant you that it is the weekend, and perhaps some of us, including the members of the Loyal Opposition, are taking a holiday.
Let’s see what Monday brings.
I found two texts from Hanspeter Schmid which have been mentionned in DiyAudio posts only a very few time. They introduce a bit of philospophy in the debate on the meaning of current and voltage feedback amplifiers :
Why the terms `current mode' and `voltage mode' neither divide nor qualify circuits ?
http://www.schmid-werren.ch/hanspeter/publications/2002iscas1.pdf
Why 'Current Mode' Does Not Guarantee Good Performance ?
http://www.schmid-werren.ch/hanspeter/publications/2003aicsp.pdf
Why the terms `current mode' and `voltage mode' neither divide nor qualify circuits ?
http://www.schmid-werren.ch/hanspeter/publications/2002iscas1.pdf
Why 'Current Mode' Does Not Guarantee Good Performance ?
http://www.schmid-werren.ch/hanspeter/publications/2003aicsp.pdf
Yes, just what the discussion needs now. We might as well be discussing the Trinity. I notice with some relief that the second paper you linked to doesn't have "(C) 20XX IEEE" stamped anywhere.
We are discussing a trinity : voltage, current and the law determining their relations. The main problem relies more in the words than in the equations (hence the file title), and is above all, a case of diverging interpretations... just like it happens for religions.
Thanks to bring it to my attention. Currently, the link I gave does not work. As a replacement :
https://www.google.fr/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&ved=0ahUKEwjQ9JDxq73WAhWCPRoKHVRxCNUQFggqMAE&url=https%3A%2F%2Fwww.researchgate.net%2Ffile.PostFileLoader.html%3Fid%3D5190a40bcf57d79056000015%26assetKey%3DAS%253A272115490590720%25401441888796534&usg=AFQjCNFmcUmflLg4vMI3XOhJD9Qrs8qO5A
The link worked fine for me. Perhaps I wasn't clear; if the IEEE started accepting papers like that it wouldn't reflect positively on their vetting processes nor the seriousness of their engineering journals.
Insider tells all
Thanks for posting those Hanspeter Schmid papers.
BTW If you have limited time, the second paper (2003) is an amplification of the first (2002), so read the second one first.
P85 (2003 paper) "...it is a major problem for the current-mode approach that its main dogma, 'current-mode is better than voltage-mode' . . is not true."
So how can this be true if the higher speed of 'current mode' circuits is real??? Hanspeter explains; it is not due to any fundamental principle, it is just the use of a simpler internal circuit with less internal nodes (2002 p31, 2003 p87).
A secondary factor is a time lag in 'process technology' (2003 p88) between most voltage-mode and current-mode opamps which appeared to give a superior performance, at least for a few years, until higher speed VFA IC's were also made using the same faster process technology eg http://www.analog.com/media/en/analog-dialogue/volume-28/number-3/articles/volume28-number3.pdf#page=6 .
So ... audio power amplifier designer's beware. Don't accept the "propaganda" (Hanspeter's term) of the early CFA designers that CFA's are inherently better than VFA's.
It's a strange world we live in when such "propaganda" is apparently necessary for commercial reasons; quoting Hanspeter 2003 p86,
When we discard the "propaganda" we are left with just a simpler internal circuit with less internal nodes (less stages) as the 'magic' of CFA's. This is a useful lesson we can apply to audio power amplifier designing. See Post #82 for more.
As for IC's using the CFA and VFA architecture's, the differences are both the reduced internal nodes AND the use of very fast BJT transistors in CFA's (but only a few VFA's, hence the apparent disparity).
Thanks 'forr' – for starting this thread to distill truth from "propaganda". Thanks also Hanspeter (if you read this).
Thanks for posting those Hanspeter Schmid papers.
BTW If you have limited time, the second paper (2003) is an amplification of the first (2002), so read the second one first.
P85 (2003 paper) "...it is a major problem for the current-mode approach that its main dogma, 'current-mode is better than voltage-mode' . . is not true."
So how can this be true if the higher speed of 'current mode' circuits is real??? Hanspeter explains; it is not due to any fundamental principle, it is just the use of a simpler internal circuit with less internal nodes (2002 p31, 2003 p87).
A secondary factor is a time lag in 'process technology' (2003 p88) between most voltage-mode and current-mode opamps which appeared to give a superior performance, at least for a few years, until higher speed VFA IC's were also made using the same faster process technology eg http://www.analog.com/media/en/analog-dialogue/volume-28/number-3/articles/volume28-number3.pdf#page=6 .
So ... audio power amplifier designer's beware. Don't accept the "propaganda" (Hanspeter's term) of the early CFA designers that CFA's are inherently better than VFA's.
It's a strange world we live in when such "propaganda" is apparently necessary for commercial reasons; quoting Hanspeter 2003 p86,
"Without some tenacity and propaganda at the beginning, no idea can ripen because people could not be convinced to invest time and money."
When we discard the "propaganda" we are left with just a simpler internal circuit with less internal nodes (less stages) as the 'magic' of CFA's. This is a useful lesson we can apply to audio power amplifier designing. See Post #82 for more.
As for IC's using the CFA and VFA architecture's, the differences are both the reduced internal nodes AND the use of very fast BJT transistors in CFA's (but only a few VFA's, hence the apparent disparity).
Thanks 'forr' – for starting this thread to distill truth from "propaganda". Thanks also Hanspeter (if you read this).
The classic CF architecture is perhaps the most practically simple topology with a push-pull class-AB input stage. It's little surprise that it was so dominantly associated with integrated amplifier designs and process technologies pushing the SOTA in bandwidth.
Permitting the wide power bandwidths without having to resort to an impractically large quiescent current for a class A input stage or a more complex "current on demand" VFA architecture instead is an obvious advantage. Also at very high bandwidths (Comlinear were doing 1 GHz+ with their CLCXXX series a long time ago now) external frequency compensation is impractical due to package parasitics, so the degree of gain-bandwidth independence offered by the topology was an other obvious benefit in practical application.
These are sound technical advantages, not philosophical ones wholly contingent on "propaganda" or misguided "current mode thinking" (allegedly all originating from the culprit Barry Gilbert, if that paper is to be believed).
But I am obviously writing from the dark side here.
Permitting the wide power bandwidths without having to resort to an impractically large quiescent current for a class A input stage or a more complex "current on demand" VFA architecture instead is an obvious advantage. Also at very high bandwidths (Comlinear were doing 1 GHz+ with their CLCXXX series a long time ago now) external frequency compensation is impractical due to package parasitics, so the degree of gain-bandwidth independence offered by the topology was an other obvious benefit in practical application.
These are sound technical advantages, not philosophical ones wholly contingent on "propaganda" or misguided "current mode thinking" (allegedly all originating from the culprit Barry Gilbert, if that paper is to be believed).
Right. And the practical and technical merits of an idea cannot play any part? Hello? IMO, rather than enthusiastically endorsed, the attempt in that paper to simplistically distil, in the guise of philosophy, an entire historical facet of electronic engineering down to a battle between the enlightened and the propagandist should be called out for what it unfortunately is - dumb.
But I am obviously writing from the dark side here.
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My first brush with 'current mode approach' was when I got hold of Lidgey and Toumazou's book, decades ago.
What attracted me in the thinking then is that with current mode circuits you can use very low voltages and very low voltage swings which would make the parasitic cap issues very much smaller, extending BW and SR.
As to propaganda and philosophy, if the whole world uses voltage mode circuits and you set out to convert them to start using current mode circuits, you have zero chance to accomplish that on engineering arguments alone.
Jan
What attracted me in the thinking then is that with current mode circuits you can use very low voltages and very low voltage swings which would make the parasitic cap issues very much smaller, extending BW and SR.
As to propaganda and philosophy, if the whole world uses voltage mode circuits and you set out to convert them to start using current mode circuits, you have zero chance to accomplish that on engineering arguments alone.
Jan
The whole world doesn't only use voltage mode circuits and never has. There is a black & white fiction being propagated here. My first application for an integrated CF op-amp (almost 20 years ago) required nigh on 1 GHz bandwidth and there wasn't much if anything to choose from aside from CF-topology parts. I don't recall any kind of propaganda being part of the selection process.
And my first discrete audio power amplifier (built from a kitset whilst a teenager) was in fact a "current-feedback" (as per the contemporary nomenclature) amplifier and I didn't even know it at the time. This amplifier had a single-transistor input stage.
The same sentiment applies. Show me any kind of ubiquitous practical complex analogue circuit or system that is not in reality a combination of "current mode" and "voltage mode" techniques; each applied where necessary for their own practical/technical/implementation/aesthetic advantages/values.
Do purely "voltage mode" and purely "current mode" systems actually exist outside of the simplistic building blocks described in theoretical texts? Can any one analogue designer be singled out as an example of an engineer with a purely "current mode" versus a purely "voltage mode" mindset? (the former presumably persuaded by propaganda and a propagandist himself, the latter an enlightened one wise to the folly of the former).
Do purely "voltage mode" and purely "current mode" systems actually exist outside of the simplistic building blocks described in theoretical texts? Can any one analogue designer be singled out as an example of an engineer with a purely "current mode" versus a purely "voltage mode" mindset? (the former presumably persuaded by propaganda and a propagandist himself, the latter an enlightened one wise to the folly of the former).
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There is only the SE input. For my personal purposes, I use XLR connectors even for SE input, for the reason that I hate RCA-CINCH connectors. Two main reasons - dimensions often differ (to tight or too loose connection), and more important, RCA disconnects signal ground earlier than the live conductor, which is completely unacceptable. So, just for my personal purposes, I go non-standard.
A single-transistor input stage it the simplest way to demonstrate that the main controlling variable of the current feedback as per the contemporary nomenclature is a voltage.
Hi Jan
You describe this like it's a "free" improvement, but there is a precise mathematical duality.
So now you have to modulate the current, so the parasitic inductance issues are inversely increased.
Have you done any trade-off analysis?
Best wishes
David
No I haven't, and as I said it just struck me as an interesting idea.
If you search for actual examples you mostly find current mode filters and similar signal processing examples on CMOS developed in/for academic environments.
Never found an actual commercial implementation. Lidgey and Toumazou have been pushing it for many years but I don't think they made any significant headway.
Jan
If you search for actual examples you mostly find current mode filters and similar signal processing examples on CMOS developed in/for academic environments.
Never found an actual commercial implementation. Lidgey and Toumazou have been pushing it for many years but I don't think they made any significant headway.
Jan