Why should I communicate with those who don't contribute? S/N increase is a good thing!
Originally Posted by forr
I have not seen any argument to support that it has nothing to do with the discussion. Feedback relies on an amplified difference of two voltages. The amplifier circuit needs an active device to sense it. In its most basic form, this device is a single valve or a singe transistor where the voltage difference is between the input of the device and its voltage following electrode.
A push pull inverting input on which most people here seems to concentrate is nothing more than an improvement of the basic architecture
By the way, what is the date of the first negative feedback applied to a cathode ?
Your analysis is not exactly right, but maybe we should call a CFA IPS a Floating Common Base IPS and everybody would be happy?
At the time, a single transistor input stage was considered as being in common emitter with emitter degeneration.
When the input signal of such a circuit arrives to its base, the single transistor can be in CE or CC, but certainly not in Common Base.
It is the signal at the base of the input transistor and this transistor itself which dictate the behavior of the remaing part of the circuit, and not the feedback signal (in form of a current !) which is supposed by many here to enter the emitter of a common base transistor, cascoded we even have read.
Please let this lie, a circuit it an entity of sometimes many sometimes few interconnected devices whose behavior can be predicted/analysed by some hard work and analysis guided by a lot of knowledge. These simplified analogies of what is going on are difficult to bear without being impolite.
Wavebourn is right a bipolar transistor's Vbe vs Ic relationship is essentially all that matters. A transistor is NOT a current controlled device, the base current is incidental determined by poorly controlled parameters like base width and recombination. The Vbe equation is fundamental physics.
Many are really missing what CMA is all about and how they work internally. Like I have said many times.... there are many books now on the subject. FB to a low Z port isn't IT in its entirety.
Yes, lets drop this one. Let any one curious read a scholarly book on the subject. Then go argue with its authors, not here.
Bonsai has the best description that isn't full of higher mathematics.
THx-RNMarsh
Yes, lets drop this one. Let any one curious read a scholarly book on the subject. Then go argue with its authors, not here.
Bonsai has the best description that isn't full of higher mathematics.
THx-RNMarsh
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The problem is, as soon as voltage is enough to cause carriers jumping over a potential barrier, it causes base-emitter current!
"I ordered a chicken and an egg on Amazon; let's see what comes first!"
What do you consider is missed by the "FB to a low Z port" definition?
Best wishes
David
It was my favourite topology since mid-70'Th. Second transistor loaded on a resistive FB divider, where emitter of the 1'St transistor is connected. For the 1'St device I used also JFETs and MOSFETs. I used it everywhere! Sometimes with additional emitter follower at the output.
Since the feedback goes into a low impedance node, for me it belongs to this family.
There are also CFP's with voltage gain, wasn't a Elektor Output stage such a thing btw.?
D.Self in his book uses Sziklai extensively. I did a comparison between it and a simple follower as the OPS for my headphone amp...... with the values I used, the thd of the HPA was 20dB lower than just a follower.
THx-RNMarsh
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Yes. The entire topic is a mess of different definitions and nomenclature, not to even mention opinions, let alone claims presented with very little evidence.
You made a statement, I would like to know what you mean.
Best wishes
David
Is an emitter follower a CFA ?
Mona
http://www.guitarscience.net/papers/feedback.pdf Section 6. It's shunt (output)-series (input) feedback, so yes, it could be considered as a "CFA" with 100% (unity gain) feedback.
The Sziklay pair is an emitter follower with much improved open loop gain
Activity 11. The Emitter follower (BJT) [Analog Devices Wiki]
However, the two transistor connection itself is 100% voltage feedback.
So yes, the Sziklay pair, viewed as a gain block, is as much an CFA as an emitter follower. It though uses a local voltage feedback loop to increase the global open loop gain.