Current feedback - Voltage feedback, how do I see the difference?

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#341
Re: Re: Re: cfb error signal is current

Pjotr said:


For the same you can state:

“But is vastly incorrect because this voltage merely represents an effect, with the causal error signal being the differential current”

But this way of looking does not seem to exist in your world Mike.

It amazes me time after time that a lot of EE’s (not to say the majority) tend to convert everything they encounter into voltages, even when currents are more appropriate.
Cheers 😉
Click to expand...

pjotr....where exactly is this differential current you are refering to??? :whazzat:

http://diyaudio.com/forums/showthread.php?postid=423522#post423522

If you still haven't got it this late in the day, you never will...:smash:
 
#342
Ouroboros said:
People forget that a bipolar transistor is actually a voltage controlled device, with a mathematically precise exponential Ic/Vb transfer function that holds over many decades.

To treat a bipolar transistor as a current controlled Ic/Ib device is a crude approximation.
Click to expand...

I concur...

Ouroboros said:

Not that this affects the analysis of a CFB amp in any way. As Claude has said, the basic error signal in a CFB amp is a current, and now matter how much Mike blusters, his is a lone voice crying out against engineering orthodoxy.
Click to expand...

Having correctly stated that a BJT is a voltage controlled device, i find it hilarious that you should now hold that the primary error signal in a so-called 'CFB' amp. is a current....

...surely it should now be clear to you of all people that this is nonsense......particularly as the input voltage in this lamentable topology is almost always buffered from the usual complementary common-emitter stages, to whose emitters the feedback voltage is returned...

....If the input signal is a voltage, and the feedback network outputs a voltage, then it follows that the primary error signal is a voltage....Period.

...and...No.....what Claude set forth was anything but 'engineering orthodoxy'.....more like engineering perversion....

...as this topology was historically recognized as a voltage feedback scheme before Dr. Eckes (circa 1967) decided to rename the genre in his Phd thesis..... 🙄

see: 'EVOLUTION OF HIGH-SPEED OPERATIONAL AMPLIFIER ARCHITECTURES'
BY
SMITH. D; KOEN. M; & WITULSKI A. F.

IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. 29, #10 OCTOBER 1994


Ouroboros said:

I do agree that the term CFB was perhaps poorly chosen, when it (sometimes and erroneously) had in the past been used to describe feedback where the feedback VOLTAGE was derived by passing the output current through a resistor and measuring the VOLTAGE across the resistor.
Click to expand...

Ahhh...changed you mind then....all in the space of two paragraphs.... 🙂

So....(noting that a BJT is a VCVS), if the feedback signal is a voltage, and the input signal is a voltage also.....then....go figure.... :angel:
 
#345
Re: Re: Re: Re: Re: Re: let us come to the point

mikeks said:

If the amplifier's forward path takes a current as it's input, and delivers a voltage at it's output, (viz: transimpedance gain),.....
Click to expand...


Mike,

Could you please show a schematic(Observe! let's say an inverted amplifier!!) of such a transimpedance amplifier?
Just for clarification we mean a complete schematic, not a single transistor stage, (and forget for a moment the feedback stuff), if you don't find anyone you are wellcome to make a drawing!
Please elaborate according to the signal you feed at the non-inverting input, how such an amplifier works and why it IS really a current signal we feed such an amplifier with, just trying to find out how you see it so I can understand you better! 😎
 
#346
mikeks said:



Ahhh...changed you mind then....all in the space of two paragraphs.... 🙂

So....(noting that a BJT is a VCVS), if the feedback signal is a voltage, and the input signal is a voltage also.....then....go figure.... :angel:
Click to expand...


No I didn't change my mind, I stated that when the CFB op-amps first appeared, perhaps a less-contentious name should have been chosen!

A BJT is a VCVS! What nonsense. A BJT is a VCCS, often erroneously considered to be an CCCS.
 
#347
Anyone wishing to delve into this subject and wants a more academic study than the arguments here are advised to read:

'The Current Conveyor: history, progress and new results.'
IEE procedings, Vol137 partG April 1990.

I believe this paper is on the web, but I can email a .pdf to anyone who wants it.
 
#349
I HAVE NEVER READ SO MUCH INANE PIFFLE IN ALL MY LIFE!

You people keep trying to score points off one another but collectively you are all showing yourselves to be rediculous pedants.

What next? A resistor is a "voltage controlled current sink"? No! No! It's not - it's a "current controlled voltage source" and furthermore your gandmother smells of elderberries!

Come on folks, at least pretend to be engineers and stop wasting disk space. Ok?
🙄
 
#350
Ouroboros said:
A BJT is a VCVS! What nonsense. A BJT is a VCCS, often erroneously considered to be an CCCS.
Click to expand...

You are correct in this respect......a typo on my part....cheers.

However, if you had actually taken the time to read through the thread, you should have found that i was the first to bring this point up in the context of this discussion...here:

http://diyaudio.com/forums/showthread.php?postid=423668#post423668

http://diyaudio.com/forums/showthread.php?postid=423866#post423866

🙄
 
#352
Moreover....

Ouroboros said:
Anyone wishing to delve into this subject and wants a more academic study than the arguments here are advised to read:

'The Current Conveyor: history, progress and new results.'
IEE procedings, Vol137 partG April 1990.
Click to expand...

I am thoroughly conversant with the contents of this paper and fail to see its relevance to this thread.... 🙂

I suggest you read Cherry, and Smith, Koen, Witulski.......these give a broad intellectual and historical perspective.....
 
#356
Re: Re: Re: Re: Re: Re: Re: Re: let us come to the point

mikeks said:
Mike,
UT said:
Mike,
Could you please show a schematic of such a transimpedance amplifier?
Just for clarification we mean a complete schematic, not a single transistor stage, (and forget for a moment the feedback stuff), if you don't find anyone you are wellcome to make a drawing!
Please elaborate according to the signal you feed at the non-inverting input, how such an amplifier works and why it IS really a current signal we feed such an amplifier with, just trying to find out how you see it so I can understand you better!
Click to expand...

A research effort for your good self perhaps?
Click to expand...


No, I'm serious, be so kind and tell what a "current in - voltage out" amplifier is, and preferably a schematic is wellcome to illustrate your answer! 😎
 
#357
I'm sure you knew When he bit off more than he could chew.

I suggest you stop reading Cherry, and Smith, Koen, Witulski....... and learn Ohm's law and some simple basics about how a transistor works.

Or are you planning on making this your lifes work? That would be fine also, since it would keep you out of other people's hair.


"And now, the end is near;
And so I face the final curtain.
My friend, I'll say it clear,
I'll state my case, of which I'm certain."

Oh please let the end be near.......... :bawling:

:smash: V=IxR:smash:
 
#358
The last verse was the best.....................😀
 

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#360
Traderbam:

You forgot the part about "your father was a hamster..........."

Makes about as good a use of bandwidth as that of a lone voice, pining for the fiords.

"It is not pining.....it has passed on......."

Wish this thread would do the same. Somehow, I suspect it will outlive some of us..................

Jocko
 
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