I am trying to keep out of the flame war.
The problem in this thread is semantics.
Running an error amplifier with current input instead of voltage is perfectly valid. National used to make the LM3900, a strange opamp with a Norton current mirror input.
I would still say that the feedback is voltage from the output but if you want to call it cfb that is up to you.
I used to work on high voltage line output transistor drivers and there the drive circuit was essentially current.
The problem in this thread is semantics.
Running an error amplifier with current input instead of voltage is perfectly valid. National used to make the LM3900, a strange opamp with a Norton current mirror input.
I would still say that the feedback is voltage from the output but if you want to call it cfb that is up to you.
I used to work on high voltage line output transistor drivers and there the drive circuit was essentially current.
davidsrsb -
This thread brings back memories of the Wireless World letters pages 30 years ago.
Is a transistor a voltage or current amplifier was a hot topic back then as was the Quad 405 current dumper feedforward/back debate.
Nothing changes.
By the way, notice that the LM3886 chip amp has emitter follower inputs to buffer the inputs from the Miller capacitance of the LTP.
-------------------------------------------------------------------------
transistor is current and voltage amp so is all other devices
kind regards
ps=am i correct?
This thread brings back memories of the Wireless World letters pages 30 years ago.
Is a transistor a voltage or current amplifier was a hot topic back then as was the Quad 405 current dumper feedforward/back debate.
Nothing changes.
By the way, notice that the LM3886 chip amp has emitter follower inputs to buffer the inputs from the Miller capacitance of the LTP.
-------------------------------------------------------------------------
transistor is current and voltage amp so is all other devices
kind regards
ps=am i correct?
mikeks -
Offline
Registered: Jun 2004
Location: Essex, uk
Post #402
quote:
Originally posted by davidsrsb
Too me the so called cfb is actually vfb. You are still sampling the output voltage.
100% correct!!!!
-------------------------------------------
mikeks youre not making yourself understood here i want you to
know that i wasnt born to view posts that say nothing
if you are a scientific person coming from england and knowing
the diffrence of the topic of this thread you should give us the
low down as to why you say what you say by 100% correct
i know english have a nut for explaining things now are you
going to explain to me why you are 100% sure
please correct me if iam wrong but i also agree with you
cheers mate thanks
Offline
Registered: Jun 2004
Location: Essex, uk
Post #402
quote:
Originally posted by davidsrsb
Too me the so called cfb is actually vfb. You are still sampling the output voltage.
100% correct!!!!
-------------------------------------------
mikeks youre not making yourself understood here i want you to
know that i wasnt born to view posts that say nothing
if you are a scientific person coming from england and knowing
the diffrence of the topic of this thread you should give us the
low down as to why you say what you say by 100% correct
i know english have a nut for explaining things now are you
going to explain to me why you are 100% sure
please correct me if iam wrong but i also agree with you
cheers mate thanks
mikeks said:
http://www.diyaudio.com/forums/showthread.php?postid=857979#post857979
Again- will you argue it is 'voltage conveyor' ?
I was unaware of this thread until two days ago and would like to add some personal comments and express my agreement with the ideas that feedback and bipolar control both belong to the voltage world.
When I first saw the expression "current feedback amps" in a magainze, I asked my-self : what's hell that ? The inverting input of the picture shown was a push-pull of two emitters. For long, I thought that, with so much emphasis on currents, I was unable to understand how the whole circuit was working. Till the day, years later, I saw, in the same magazine, that it was nothing else than a push-pull version of the classical feedback scheme used by the amps of the pre-differential days. Would I have read that "this 'current-feedback' stuff is one of the most unfortunate misnomers in linear electronics...", I would have soon been out of my state of doubt about myself.
However a possible trouble in understanding the voltage feedback using a simple device is that the current passing through it is also passing through the lower arm of the feedback network (reference to amplifiers using a positive power supply and a tube, or a single NPN input, with a resistor connected to ground in series with the following electrode).
As stated in another thread, any amplifying device is differential by nature : it is the potential difference, which means the difference between two voltages, the one at the input electrode and the one at the following electrode, which governs its behaviour.
Using a reverse-history trick, a way to see things would be to consider the basic amplifying device (tube or transistor) as a differential circuit where the follower device of the inverting input has been supressed, so this inverting input is at low impedance. This argument has been developped by Mikeks.
I am not aware of analysis of open and closed loop conditions for audio amplifiers using other things than voltages.
When younger, I made the current error to consider bipolars as current driven devices and looked beta curves with a lot of attention. Careful reading of Baxandall, Horowitz, Self and many others states the good rule to design with bipolar : "rely on beta as least as possible" (in audio, the location where beta seems to have the greatest importance is in amplifier output stages for delivering currents, but not from a fundamental point of view).
I am sorry to have seen that one of the most popular engineer in the audio field has presented bipolars as current driven devices. I can't see how analysis of bipolar circuits can be done without considering them as voltage controlled devices.
MIKEKS
I knew and appreciated Kevin Aylward's letters in Electronics World and his texts http://www.anasoft.co.uk/EE/index.html long before I discovered the current thread. I think you could have some connexion with this guy.
~~~~~~ Forr
§§§
When I first saw the expression "current feedback amps" in a magainze, I asked my-self : what's hell that ? The inverting input of the picture shown was a push-pull of two emitters. For long, I thought that, with so much emphasis on currents, I was unable to understand how the whole circuit was working. Till the day, years later, I saw, in the same magazine, that it was nothing else than a push-pull version of the classical feedback scheme used by the amps of the pre-differential days. Would I have read that "this 'current-feedback' stuff is one of the most unfortunate misnomers in linear electronics...", I would have soon been out of my state of doubt about myself.
However a possible trouble in understanding the voltage feedback using a simple device is that the current passing through it is also passing through the lower arm of the feedback network (reference to amplifiers using a positive power supply and a tube, or a single NPN input, with a resistor connected to ground in series with the following electrode).
As stated in another thread, any amplifying device is differential by nature : it is the potential difference, which means the difference between two voltages, the one at the input electrode and the one at the following electrode, which governs its behaviour.
Using a reverse-history trick, a way to see things would be to consider the basic amplifying device (tube or transistor) as a differential circuit where the follower device of the inverting input has been supressed, so this inverting input is at low impedance. This argument has been developped by Mikeks.
I am not aware of analysis of open and closed loop conditions for audio amplifiers using other things than voltages.
When younger, I made the current error to consider bipolars as current driven devices and looked beta curves with a lot of attention. Careful reading of Baxandall, Horowitz, Self and many others states the good rule to design with bipolar : "rely on beta as least as possible" (in audio, the location where beta seems to have the greatest importance is in amplifier output stages for delivering currents, but not from a fundamental point of view).
I am sorry to have seen that one of the most popular engineer in the audio field has presented bipolars as current driven devices. I can't see how analysis of bipolar circuits can be done without considering them as voltage controlled devices.
MIKEKS
I knew and appreciated Kevin Aylward's letters in Electronics World and his texts http://www.anasoft.co.uk/EE/index.html long before I discovered the current thread. I think you could have some connexion with this guy.
~~~~~~ Forr
§§§
Guys, I'm amazed that you can fill all these posts over something that you can be described in a page more or less.
Voltage feedback
Current feedback
= 2 different feedback styles
The problem may be to indentify the type which you are dealing with.
Chapter 7 Voltage feedback
Chapter 8 Current feedback
Opamps for everyone, frre book from Texas Instruments.
http://www-s.ti.com/sc/psheets/slod006b/slod006b.pdf
http://focus.ti.com/general/docs/lit/getliterature.tsp?literatureNumber=slod006b&fileType=pdf
Voltage feedback
Current feedback
= 2 different feedback styles
The problem may be to indentify the type which you are dealing with.
Chapter 7 Voltage feedback
Chapter 8 Current feedback
Opamps for everyone, frre book from Texas Instruments.
http://www-s.ti.com/sc/psheets/slod006b/slod006b.pdf
http://focus.ti.com/general/docs/lit/getliterature.tsp?literatureNumber=slod006b&fileType=pdf
there appears to be more technically succinct language(s) for this discussion:
http://people.ee.ethz.ch/~hps/publications/2000cas.pdf
ran across this while adding nordholt to search:
http://www.s2.chalmers.se/graduate/courses/analogVLSI/doc/lecture2.pdf
I don’t think the level of exchange we manage here is really getting at the subject matter
http://people.ee.ethz.ch/~hps/publications/2000cas.pdf
ran across this while adding nordholt to search:
http://www.s2.chalmers.se/graduate/courses/analogVLSI/doc/lecture2.pdf
I don’t think the level of exchange we manage here is really getting at the subject matter
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