What is this topology ?
You can always find transimpedance, in a bipolar VFA you can establish a relation between input base current and the output voltage
I disagree, the test doesn't make the difference between a transimpedance behaviour and a low open loop differential impedance.
All that can be done with a CFA can be done with a VFA, with one advantage for VFA : the impedance feedback network can be increased.
This has be shown by Hierfi with his thevenin equivalent schematics.
So what was this animal, an elephant?
Hans
Not sure. Elephants are not dinosaurs.
As can be seen on this example, the negative input closed loop impedance is more than 20 times the impedance of the feedback network.
Attachments
Back to total serious nonsense, unbelievable. This thread is destined to be some kind of shrine of the absurd.
As mentioned before, it appears you are slowly discovering how feedback really works! One more hint: the difference in signal between +Vin and the -Vin input is exactly Vout/Aol.
And let me take this opportunity again to bring up an earlier accepted distinction between a VFA and a CFA: in a CFA, the current in the feedback node -Vin is the output (collector) current of the input device. In a VFA, the input device (collector) output current comes from the standing tail current.
Have a great Sunday!
Jan
In these replies it has now become more than obvious that both of you are turning the world upside down.
Some manufacturer came to the market with a topology they called CFA.
You are denying this by saying it is not a CFA.
So the whole discussion seems to boil down to the point that you have made your own definition of a CFA that does not correspond to what the industrie has done.
That's like saying: its not a Ferrari but a car and cars where there long before Ferrari.
The first step you both have to make is to accept that this name has been given as a fact of life to a specific topology, whether you like it or not.
And then like Reodor has suggested concentrate on one circuit representative to this group and not on some self created vehicle.
And please don't make unsubstantiated silly remarks about low open loop circuits or tube amplifiers belonging to the CFA category, etc, etc.
As long as you do not accept that this CFA name has been given to a specific topology, this whole discussion is moot.
Hans
Shrine is a good metaphor.
I suppose we should expect a feedback debate to consist of circular arguments.
My post was nearly a 1000 posts ago Scott. Since then we have gone through the great depression. On a side note though... I always wanted to be a Shriner.
To switch the world back to its initial state.
Just read below, there are numerous posts like that, recalling the history behind modern CFA's.
https://www.diyaudio.com/forums/solid-state/81669-current-feedback-suitable-audio-post954201.html
4th July 2006, 10:24 Jan Didden
I can see your point(s), but I also think that the term CFB coming from the
semi corporations is not necessarily the result of their conviction that
indeed it is a different class. I am convinced that an important reason behind it was for marketing purposes. It is difficult to convince customers that your umpteenth opamp is really different, unless you give it a different name.
Hence CFB. And possibly the guy who coined the term wasn't aware of the
previous use of the term current feedback in another context.
These are historical things, and the best we can do is to make clear what we
mean whenever we use the terms.
They do not invented it.
The operation of feedback is based on differential voltage.
The aim of the whole discussion is, or was :
- to establish if the word "current" as used for modern CFA's can be justified
- to observe the mechanism of amplifiers having low impedance inverting input which characterize CFA's what ever their circuits. We could also define them as Unbalanced Input Impedances Amplifiers.
The basic analasys does not change whatever the topology.
Diamond circuits are nothing else than a stacking sophistications of the primary old CFA circuit then (circa 1935) considered as a VFA.
Concentrating on the voltage following electrode(s) of the input stage is valid in any case.
Why do not suggest a naming for the topology of these old circuits to differentiate them from the symetrical eighties circuits ?
This thread is not to the glory of diamond input stages and there is not the slightest reason why they should appropriate this naming.
The industry has been able to impose an expression. If some people find it fallacious, not agreeing with what it pretends to describe, they have all the rights to express their opinion, and they do that with arguments which are strangely not really contested.
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And so you just repeat ad infinitum ‘it’s voltage feedback’ as if that will somehow make it true.
We have also clearly defined current output and current feedback (two totally different things) so you cannot use that as an excuse or claim the semiconductor industry confused the two things. They did not.
We have also clearly defined current output and current feedback (two totally different things) so you cannot use that as an excuse or claim the semiconductor industry confused the two things. They did not.
The Government in Germany has spent a huge 500 Billion Euro's to reduce CO2 production.
No differences in CO2 concentration before/after are recently being measured as a dramatic result of these enormous investments.
Instead of trying to find better ways to come to an effective reduction, the green climate fraction doesn't want to hear this and pushes to go on the same way, throwing money in a black hole without the willingness to listening to anybody at all.
Now and then this CFA discussion has some parallels.
Hans
No differences in CO2 concentration before/after are recently being measured as a dramatic result of these enormous investments.
Instead of trying to find better ways to come to an effective reduction, the green climate fraction doesn't want to hear this and pushes to go on the same way, throwing money in a black hole without the willingness to listening to anybody at all.
Now and then this CFA discussion has some parallels.
Hans
We ?
They did and they were perfectly aware of it. Refer to those who hightlighted the problem since then.
There are more people who prefer to spend huge amounts of money for their wonderful, ultra-powerful and awfully poluting car (see who currently violently manifests in France and why) than people, conscient of the effects of gigantic CO2 production, wondering what to do to diminish them. Even in country where I lived since years because I found the air in town unbreathable, I see the C02 consequences every day.
Your comparisons are weird. This one will lead to political considerations so I won't go further in that direction as speaking of politics is not allowed here, I think.
I don't understand your question. Maybe I was not clear. The Electric Universe is mainly focused in Astronomy and Astro-physics. The predictions I talked about are in that domain.
Audio and RF are electric phenomena, aren't they? We can keep the accepted knowledge for now in that domain.
Dear Scott, as N101N was trying (I think) to warn us, I believe that the abuse of maths and models in an hyper-logic way (left hemisphere) can let us to predict stuff that bears no parallel to reality. What is wrong with good old retro-ductive thinking and empiricism IF it serves to create a working model that can be bombarded with heavy artillery and still function?
I am talking here of method.
As Forr said, in other ways, can there be "current" without a dielectric field being "there" first?
Maybe to solve this "CFA problem", we have to define current, define feedback and define amplifier to start with, hehe.
I forgot to add: do not confound pollution with CO2. Experts say that CO2 has little effect on GW.
Probably the thing goes something like this: increased Solar activity--> increased GW--> increase bio-mass--> increased CO2.
Pollution is bad. That is why I walk and do not use a car...I leave my carbon print on the bathroom...
Cheers everybody,
M.
PS: I am only a dilettante, so please continue with your interesting talk.
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Hi Max,
I'm afraid nobody want to listen to these experts because we have probably past a point of no return.
The climate is permanently changing with a rate of some 100.000 years between Ice Ages and so do sea levels for as long as our planet exists
Be we humans are convinced that we can stop this cycle.
Wouldn't it be nice of we could travel in time and see what's going on 50 years from now?
Hans
Do you remember the Krill thread?
The ArchBishop of nonsense cheering from the sideline.
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Yes, CFA and VFA are Constant Voltage Amplifiers, Constant Current Amplifier is a way of saying Output Current Feedback (ie load current sensing) amplifier.
Dan.
No Max they are not and and long as those who thrive on obfuscation, arguments and plain bovine excrement repeat this nonsense, we have no chance of resolving this.
Please read up on the cononical feedback forms and then current output amplifiers and then tell me the current output = current feedback. It does not.