I think seeing the CFA device(s) ... as being in common base mode is fully misleading.
The CFA input stage is always described as a buffer (a voltage follower in series with a low impedance)...
Sorry, your reasoning is probably right but I do not see its aim.
Chris, it is similar as the analysis of a feedback loop with a Middlebrook probe for instance...
Jan
For long, I thought that the input device of a CFA, and even more of a VFA, worked in an hybrid mode...
...sorry if it came across like that.
Jan
...I saw this sentence repeated many times :
the input devices are in common base, seen from the feedback network.
A very puzzling sight.
The feedback network is the output load of the buffer....
By the way, note that there is also no need to refer to a diamond circuit for the analysis of the CFA concept...
The basic concept of current feedback can be traced all the way back to early vacuum tubes feedback circuitry, which uses negative feedback to the input tube cathode. This use of the cathode for feedback would be analogous to the CFB op-amp's low impedance input.
I don't understand what allow you to say that Z is the product of the differential input impedance by the differential voltage gain.Consider any amplifier that has inverting and non-inverting inputs and a single ended output. There is an impedance rd between the inputs. We could describe the output stage as a voltage source vo in series with ro or equivalently, a current source io in parallel with ro. And we could state that vo is equal to the unitless parameter A times the difference between the input voltages, or alternatively that vo is equal to the product of an impedance Z and the current flowing into an input, where Z = A · rd.
Chris,
I don't understand what allow you to say that Z is the product of the differential input impedance by the differential voltage gain.
Also, your model seems to show that the current is flowing between the 2 inputs, that is not the case in real life.
forr, in the model,
vo = A · (vd) = A · (rd · if) = (A · rd) · if = (Z) · if
So, Z = A · rd
It is true that you cannot generalize that current flows between the inputs. I shouldn't have called rd a differential input impedance.
However, there are generally impedances between the inverting input and ground and between the inverting and non-inverting inputs. In the model I presented, these can be combined into a single impedance, rd.
I discovered them a few days ago and Cyril Mechkow a month ago with this discussionhttps://www.researchgate.net/profile/Cyril_Mechkovhttps://www.researchgate.net/profile/Cyril_Mechkov What is the truth about the exotic current feedback amplifier? Is it something new or just well known old? Is it really a current feedback device?Personally, I did not find the references you provided to be particularly enlightening, but perhaps that's just me.
I don't dispute the calculation, but the model.
So, with the exception of the sign the two inputs are equivalent, I think you have to have to refine your model.
I found interesting to show that similar ideas have come to the mind of very different persons whose education and formation completely differ and who did not know each other at all. Many times when reading Mechkow, I felt consolidated in my thinking.
Whichever group is misunderstanding how the circuit actually works, I don't think it is telling that it is made up of a significant number of people with different backgrounds.
The main notable CFA innovation that I can think of is the diamond differential stage, which probably dates back to the 1980's.