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Current Feedback Amplifiers, not only a semantic problem ?
Current Feedback Amplifiers, not only a semantic problem ?
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Old Today, 07:59 AM   #631
jan.didden is online now jan.didden  Europe
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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
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Old Today, 08:40 AM   #632
PMA is offline PMA  Europe
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Current Feedback Amplifiers, not only a semantic problem ?
My 12 cents - very simple CFA amplifier.

PMA CFA current feedback amplifier
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Old Today, 09:24 AM   #633
poldaaudio is offline poldaaudio
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Quote:
Originally Posted by jan.didden View Post
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

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.
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Old Today, 09:30 AM   #634
jan.didden is online now jan.didden  Europe
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I did not talk about CFA but about 'current mode circuits'. A different subject.

Jan
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Old Today, 09:56 AM   #635
poldaaudio is offline poldaaudio
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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).

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Old Today, 11:28 AM   #636
dadod is offline dadod  Croatia
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Originally Posted by PMA View Post
My 12 cents - very simple CFA amplifier.

PMA CFA current feedback amplifier
This is 1 cent only.
Photo shows balanced inputs, but schematic doesn't.
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Old Today, 12:22 PM   #637
PMA is offline PMA  Europe
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Current Feedback Amplifiers, not only a semantic problem ?
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.
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Old Today, 01:24 PM   #638
forr is offline forr  France
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Quote:
Originally Posted by poldaaudio View Post
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.
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.
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Old Today, 01:50 PM   #639
Dave Zan is offline Dave Zan  Australia
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Quote:
Originally Posted by jan.didden View Post
[W]ith 'current mode approach'...
What attracted me...which would make the parasitic cap issues very much smaller
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
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Old Today, 04:22 PM   #640
jan.didden is online now jan.didden  Europe
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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
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