I do not feel alone.Originally Posted by forr
But it is the exact role given to the current to justify the name of CFA which is under scrutiny. And this, whatever has been said or written remains unclear not to say incoherent
No it does not, except to you..
You would be kind to give it or to indicate a link to read it.
In the context of the discussion of a CFA circuit, the idea I support is that the input transistor acting as an emitter-follower loaded by a resistance remains an emitter follower when this resistance becomes the bottom part of the feedback network. Its status does not change to common-base as I read more than once.
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so you do not know nor want to know what Current-Mode circuitry is all about. Fine. There are others.
-RM
OK, let's get this over with.
First. Stop whining (not you personally) about current feedback having historically another meaning. You are right, we agree, the 'CFA' term is another use of a long standing term defining the way the feedback signal is sampled, not how it is applied. Tough luck.
Second. It is easy to see that the current from the feedback network flows into the inverting input, reflected by the current mirror, into the comp cap. Current feedback, clear and unambiguous.
Third. A VFA input is at a the base of a common emitter stage. The fact that the emitter is also driven independently does not change that; it is common emitter from the signal view point. Google 'superposition'. A CFA input is at the emitter of a common base stage. The fact that the base is also driven independently does not change that; it is common base from the signal view point. Google 'superposition'.
Looking at these two circuits with the name 'VFA' and 'CFA' is a clear, unambiguous and correct naming convention that prevents confusion and promotes communication. Be thankful for that.
We're done here. Saddle up, ride into the sunset and find new dragons to slay, new mademoiselles to rescue. Onward!
Jan
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But can we ignore the feedback provided by the influence on Vbe caused by the current flowing through the two resistors commonly used to define the feedback factor?
To me it seems like the current entering or leaving the emitter would cause positive feedback in a non-inverting amplifier and to make a stable amplifier we must therefore have a bigger negative feedback coming from Vbe.
If you say VFB the V comes before F , the (output)voltage is feed back.
If you say CFB the C comes before F , the (output)current is feed back.
It doesn't say back to what.
To compare with the input voltage or to "superimpose" on a (from the input voltage derived) current.
If CFB is ment to be output voltage derived current superimposed on an input current, name it VCFB , voltage to current feedback.
Otherwise how to name the real CFB ? CxFB , output current feed back to whatever 🙁
Mona
If you say CFB the C comes before F , the (output)current is feed back.
It doesn't say back to what.
To compare with the input voltage or to "superimpose" on a (from the input voltage derived) current.
If CFB is ment to be output voltage derived current superimposed on an input current, name it VCFB , voltage to current feedback.
Otherwise how to name the real CFB ? CxFB , output current feed back to whatever 🙁
Mona
It's not unusual for terms in electronics to get different meanings; for example, a century ago, typing on a computer would have been very impolite, because a computer was a human being who did calculations for a living.
Still, the impression I get from browsing through this thread is that even those who use the term "current feedback" in its modern sense don't agree on what it means: just feedback to one or more emitters, sources or cathodes or feedback to emitters or sources using a diamond-type input stage that operates in a class AB-like mode? Besides, as current feedback in its original meaning is still a very useful technique, we also need a term for that.
All of this is no problem whatsoever as long as anyone who uses the term defines whatever he or she means by it.
OK if we talk about 230V first explain what you mean by V 😀
Sometimes very usefull 😛
Mona
Do you think there is any chance of misinterpretation of 230 V? If so, indeed define what you mean.
You are all wrong 🙂 CFA is a poor name for a topology that uses both positive, current feedback, and negative voltage feedback.
Ketje
IMHO both feedback loops operate in current mode , since both loops controls input pair source current flow which also represent relative low Z node.
IMHO both feedback loops operate in current mode , since both loops controls input pair source current flow which also represent relative low Z node.
TBH it confuses me that there is so much argument, I conclude that it is a matter of semantics and the desire to label a circuit action as one thing or another is not helpful when there are so many complex interactions even in what appears to be a simple circuit. There is a lot of time being wasted here IMO