Current Feedback Amplifiers, not only a semantic problem?

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Joined 2012
I think the lack of a schematic and the refusal to put one up speaks volumes.

(I had 11 IC designers in my team at one stage. Smart guys, but absolutely incapable of stepping out of their bubble except for one guy who after 5 or 6 very successful years left and went into project management and ended up running a team of 200 design/test/integration engineers on SOIC's. $200 million dev budget at the time. He was smart and related well to people - MSc grad. Get some mentoring - you need it :)

:):cool:


Maybe another explanation into why a C across the FB resistor to a (-) base (VFB circuit) and to an emitter (CFB) does the opposites. Could be another helpful insight or view.


-THx-RNMarsh
 
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The inverting input of a CFA has a low impedance so it is often considered as current input rather than a voltage input.





Well, actually, there is a bit more to it than that. Once you understand the role that the impedance of the feedback network plays in frequency compensating the amplifier it is no longer baffling that the established term "current feedback" has been chosen to purposefully distinguish this topology.


I honestly do no know what any discussion on the merits of the established nomenclature that either skips past or fails to grasp this fundamental aspect brings to the table, aside from circular repetition.
 
Mind you, that's totally atypical and extreme. Input stage uses 4 ultra low noise discrete devices, biased at the optimum (voltage noise wise) collector current of 12mA each. At this collector current, each transistor has a beta of about 600, which pretty much covers the rather low input current noise. Then the negative input impedance is 1 ohm, which makes the emitter current noise contribution small. I suspect this is though the largest component of the input referred noise.

Completely out of reach for any IC in an usual process. Otherwise, it's a typical "because I can" monster implementation, without any advantages over much simpler, jfet based, approaches.


Well, we are not discussing "IC only here"?
"Monster implementation" yes, true, leads to great voltage noise figures.
I agree, an easier way is to use a complementary JFet input, spares a complementary BJT pair because no diamond is needed, and the inverting input would just be at the JFet source (in a similar way as the F5 from Pass). Perfect for MM cartridges, for MC you'll need paralleling.


(Btw, I think a power amp with 80 BJT is also a monster implementation with not much advantages over simpler designs....)
 
Well, actually, there is a bit more to it than that. Once you understand the role that the impedance of the feedback network plays in frequency compensating the amplifier it is no longer baffling that the established term "current feedback" has been chosen to purposefully distinguish this topology.
Whatever the topology, with increasing frequency, a primary effect of the usual compensation is to increase the potential difference between the non-inverting input and inverting input of the sensing device which controls the feedback loop.

I honestly do no know what any discussion on the merits of the established nomenclature that either skips past or fails to grasp this fundamental aspect brings to the table, aside from circular repetition.
Honestly, the "established nomenclature" of Current Feedback as a topology should be revised or at least, students and beginners in electronics should be seriously warned against its incoherence.
 
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Disabled Account
Joined 2012
Well, actually, there is a bit more to it than that. Once you understand the role that the impedance of the feedback network plays in frequency compensating the amplifier it is no longer baffling that the established term "current feedback" has been chosen to purposefully distinguish this topology.


I honestly do no know what any discussion on the merits of the established nomenclature that either skips past or fails to grasp this fundamental aspect brings to the table, aside from circular repetition.


This is what I continue to say over and over...... and there exists literature and books on the subject which explains the differences. Why bother with anyone's opinion here?


View attachment 1A.pdf

View attachment 1B.pdf



:) :cool:


-RNM
 
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