Ultima Thule said:Oops, one picture missing!
UT,
I looked at the pictures. On the second one (can't remember exactly how the first one looked) I saw an opamp symbol with an inverting and non-inverting input. I also noted that the input voltage, the voltage difference between the two pins, is Vin - Vout*beta, where beta is the ratio of the two feedback resistors.
So, this appears to be a clear case of voltage feedback.
Since you offer no commentary, I assume that this is the point you were actually intending to make?
Jan Didden
I was reading a national databook and it defines voltage feedback amps as ones whose voltage output is proportional to the voltage differencial between two input terminals. and they define current feedback amps as oens whose voltage output is proportional to the current flowing into the input terminals (thus a transimpedance gain stage).
Those clueless EE engineers. Why cannot they just consult with our amature amp designers first to set their terminology straight? Is that too much to ask?
Those clueless EE engineers. Why cannot they just consult with our amature amp designers first to set their terminology straight? Is that too much to ask?
janneman said:
Jan,
well I don't know what to call it but I copied the picture from the Intersil PDF Christer posted here. and that paper talk about CFB.
My very first post in this thread in an answer to Mikeks I claimed allready then that a CB stage is current in and voltage out, so I modified the second picture hope you and everybody else noticed that.
The discussion about CFB was in the beginning in this thread about an low impedance feedback input node, not the transfer function, but I mentioned also there is also another type of "CFB" where the current is meassured over a shunt resistor in series with the load but that's another thing that was brought up later in this thread.
This was neither Charles Hansen issue in the beginning I guess...
Cheers
My country experience
The old Doctors, Medicine Doctors, started to be afraid that their knowledge was beeing less respected related the ones prepare drugs.... people gonne to the drugs mixture's people and do not call Medicine Doctors anymore
Today, the fell drugs man that exists, have to go to University and have a degree to sale drugs in nature or mixed, and needed the doctors small paper, with no comprehensive letters.... my people uses to do jokes with them, telling they do not know how to write.
They write fast, and cutt letters, cannot be readable, some technical names in Latim language Aminoacids Sinthesis Cathalizers as example, but in latim.... and people could not anymore as others how to buy, where to buy, and the name to but....this way, we return to Medicine Doctors hands, because no reading, ... 6 hours interval between pill?..... but this is not a 6, can be 8?.... and the drug, is this the one?
This old use, 300 years old crap!.... today is used by Doctors already, but they do not know anymore the reasons.... they think is elegant, that this give class to the society "Doctors", the only one receive this title here, ao PHD, or Universitary extensions degrees are not known as Doctor, ....people do not recognize.... Doctor is the one using white uniforms, the medicine one, those that do not know how to write.... new ones are doing same style, they do not know exactly why....but the go on without reflections about that....beeing "doctors"
I imagine, but have poor knowledge to discuss, i just entered here for some seconds, and fast i will run away from this thread because too much confused to me..... i imagine, same thing happening again..... the matter may be simple as resistance low or high....and the names is Cathaléptics, organeptics, subutherine, dampned disease.
by
Carlos
The old Doctors, Medicine Doctors, started to be afraid that their knowledge was beeing less respected related the ones prepare drugs.... people gonne to the drugs mixture's people and do not call Medicine Doctors anymore
Today, the fell drugs man that exists, have to go to University and have a degree to sale drugs in nature or mixed, and needed the doctors small paper, with no comprehensive letters.... my people uses to do jokes with them, telling they do not know how to write.
They write fast, and cutt letters, cannot be readable, some technical names in Latim language Aminoacids Sinthesis Cathalizers as example, but in latim.... and people could not anymore as others how to buy, where to buy, and the name to but....this way, we return to Medicine Doctors hands, because no reading, ... 6 hours interval between pill?..... but this is not a 6, can be 8?.... and the drug, is this the one?
This old use, 300 years old crap!.... today is used by Doctors already, but they do not know anymore the reasons.... they think is elegant, that this give class to the society "Doctors", the only one receive this title here, ao PHD, or Universitary extensions degrees are not known as Doctor, ....people do not recognize.... Doctor is the one using white uniforms, the medicine one, those that do not know how to write.... new ones are doing same style, they do not know exactly why....but the go on without reflections about that....beeing "doctors"
I imagine, but have poor knowledge to discuss, i just entered here for some seconds, and fast i will run away from this thread because too much confused to me..... i imagine, same thing happening again..... the matter may be simple as resistance low or high....and the names is Cathaléptics, organeptics, subutherine, dampned disease.
by
Carlos
And more, those tricks,... if a trick., are so efficient
That a "good will doctor", can enter and say:
Hey you!, do not make this noise!.... when resistance is low, you will have big current, this way current ueristeingsfarenhouser.... but if resistance (impedance) is high, current beeing low, voltage, or Potencial Difference, will be big... this way they call voltage ueristêingsfarenhouser.
Ueristêingsfarenhouser is nothing, no comprehensive word, means nothing in no language...houser, maybe, têings as a fonetic portuguese word for "things" pronounciation...but no meaning att all.
The problem is, the influence of this trick, is so big, that if one came and explain that this is easy!...no one will believe him.
That's the reason, earth was squared 500 years ago, no one said is rounded.... no!, are you crazy?....no!, it is not!!!!
Carlos
That a "good will doctor", can enter and say:
Hey you!, do not make this noise!.... when resistance is low, you will have big current, this way current ueristeingsfarenhouser.... but if resistance (impedance) is high, current beeing low, voltage, or Potencial Difference, will be big... this way they call voltage ueristêingsfarenhouser.
Ueristêingsfarenhouser is nothing, no comprehensive word, means nothing in no language...houser, maybe, têings as a fonetic portuguese word for "things" pronounciation...but no meaning att all.
The problem is, the influence of this trick, is so big, that if one came and explain that this is easy!...no one will believe him.
That's the reason, earth was squared 500 years ago, no one said is rounded.... no!, are you crazy?....no!, it is not!!!!
Carlos
Ultima Thule said:
right on.
Ultima Thule said:
I have used that notion as well.
foundamentally, the problem is that the world doesn't revolve around diyaudio and us amature amp designers. they use a terminology mistakenly used by us to mean something else, and some of us insist that everybody else is wrong and refuses to accept the reality.
Isn't that sad?
Ultima Thule said:
Jan,
well I don't know what to call it but I copied the picture from the Intersil PDF Christer posted here. and that paper talk about CFB.
My very first post in this thread in an answer to Mikeks I claimed allready then that a CB stage is current in and voltage out, so I modified the second picture hope you and everybody else noticed that.
The discussion about CFB was in the beginning in this thread about an low impedance feedback input node, not the transfer function, but I mentioned also there is also another type of "CFB" where the current is meassured over a shunt resistor in series with the load but that's another thing that was brought up later in this thread.
This was neither Charles Hansen issue in the beginning I guess...
Cheers
Well, I was actually chuckling seeing the diagram. You see, the classical definition of VF (before the marketeers and beancounters hijacked a system of working definitions) was: a topology where the actual amp input voltage was created by subtracting from the source input voltage a feedback voltage.
If I consider the diagram in your drawing as a black box, the actual input voltage for the amp is V+ - V-. Looking at the external connections, with the source voltage at V+ and the feedback voltage at V-, it neatly fits that definition.
Now, you chose to draw that black box "transparantly" and we see actually an asymetrical input stage (low and high input impedance ports).
The question really is: now that you had a peek inside the black box, does it change your view of the external stuff? I would say no. Why should it? I based my observation on comparing the external stuff with a known definition, and that has not changed.
Jan Didden
Hi all,
Ok, so if I do understand you right you insist with me in this case...
For clarification, as I already mentioned earlier, my thought of a CFB amp (or with "low input impedance" at the feedback input node as somebody would say(which is not really the same IMO!)) is an amp with an CB stage, observe, as seen from the feedback input node as the picture of a Hiraga amp in this earlier post or this link:
http://www.bonavolta.ch/hobby/en/audio/hir20.htm
Also I would like to separate the discussion around wheter an amplifier is a CFB from respect to what type of transfer function they are working in, eg. transimpedance, transconductanse etc.
The issue for me is, what is seen from the feedback input node, a VFB amp needs a resistor divider to ground to give it a gain, my point if I now make right conclusions is that a (at least one type of "CFB" as discussed in this post)CFB amplifier would actually not need the dividing resistor going to ground since the current or voltage if you want(make your choice), will be divided by the input impedance in the feedback input node and still have gain which is a clear distinction, did I think right know...!?
As discussed earlier the so called "CFB" Op-Amp as in the picture I attached earlier it's clear that the positive input is high impedance and that the negative input is low impedance,
now we would call an amplifiers transfer function seen from the positive input to output a voltage-voltage, from the negative input to output it would be called a current-voltage (transimpedance) amplifier.
Take a simple circuit as a CCS, it's a CB stage as propably most of us can agree, base has a fixed voltage, it's input at the emitter is current (programmed by a resistor) and a amplified voltage signal over the defined collector resistor but with unit current gain.
Ok, one more example, a cascode transistor is a CB stage, right... meaning the current going in at the emitter has unit current gain seen on the collector side (minus Ib of course but which is negligible!) but voltage gain, eg. transimpedance.
...if these are clear cases then why is an amplifier with a, seen from the feedback negative input node which has an emitter as input as in the Hiraga amplifier not a current input, eg. CFB?
Myself am a bit confused since I still don't feel convinced from either camps, so come on, hate it or love it but up with more intellectual and intelligent comments!
Cheers
millwood said:
Ok, so if I do understand you right you insist with me in this case...
janneman said:
For clarification, as I already mentioned earlier, my thought of a CFB amp (or with "low input impedance" at the feedback input node as somebody would say(which is not really the same IMO!)) is an amp with an CB stage, observe, as seen from the feedback input node as the picture of a Hiraga amp in this earlier post or this link:
http://www.bonavolta.ch/hobby/en/audio/hir20.htm
Also I would like to separate the discussion around wheter an amplifier is a CFB from respect to what type of transfer function they are working in, eg. transimpedance, transconductanse etc.
The issue for me is, what is seen from the feedback input node, a VFB amp needs a resistor divider to ground to give it a gain, my point if I now make right conclusions is that a (at least one type of "CFB" as discussed in this post)CFB amplifier would actually not need the dividing resistor going to ground since the current or voltage if you want(make your choice), will be divided by the input impedance in the feedback input node and still have gain which is a clear distinction, did I think right know...!?
As discussed earlier the so called "CFB" Op-Amp as in the picture I attached earlier it's clear that the positive input is high impedance and that the negative input is low impedance,
now we would call an amplifiers transfer function seen from the positive input to output a voltage-voltage, from the negative input to output it would be called a current-voltage (transimpedance) amplifier.
Take a simple circuit as a CCS, it's a CB stage as propably most of us can agree, base has a fixed voltage, it's input at the emitter is current (programmed by a resistor) and a amplified voltage signal over the defined collector resistor but with unit current gain.
Ok, one more example, a cascode transistor is a CB stage, right... meaning the current going in at the emitter has unit current gain seen on the collector side (minus Ib of course but which is negligible!) but voltage gain, eg. transimpedance.
...if these are clear cases then why is an amplifier with a, seen from the feedback negative input node which has an emitter as input as in the Hiraga amplifier not a current input, eg. CFB?
Myself am a bit confused since I still don't feel convinced from either camps, so come on, hate it or love it but up with more intellectual and intelligent comments!
Cheers
the issue I guess come from the misunderstanding as to exactly what is fed back to the input terminals. some people interpret the term "current feedback" as a current signal is being fed back to input (thus the shunt resistor sensing amplifier).
the accepted convention out of diyaudio.com appears to be that a voltage signal is being fed back regardless if the amplifier in question is a vfb or cfb amp. so in that regard, you have look at internals of an amp to tell if it is a vfb or cfb: a cfb has to have a transimpedance stage.
Of course, we all know that they are wrong.
the accepted convention out of diyaudio.com appears to be that a voltage signal is being fed back regardless if the amplifier in question is a vfb or cfb amp. so in that regard, you have look at internals of an amp to tell if it is a vfb or cfb: a cfb has to have a transimpedance stage.
Of course, we all know that they are wrong.
Ultima Thule said:
Hi U-T,
Agree with the first statement, this is a way to categorize amplifiers. But do we want to do that? Do you propose to abandon CFB, VFB etc to replace it by NNRTG (Need no Resistor To Ground) or DNRTG amp terms? I am serious; I agree that this thread has probably outlived its usefullness, although I am sure the intense examination of detailed opamp construction has been quite a good learning experience for a lot of people, it has for me.
But my point from the beginning has been that we had a quite sensible definition for VF, and that definition included the so-called CFB opamps, but they are no longer called VFB because some manufacturer(s) needed a catchy term to attract sales.
Your second statement: you are free to call it a current input, although that immediately raises the question: what is the border between current and voltage input. As I said earlier, a heavvy biased CE stage can have a lower input impedance into the base, than a starved CB stage has at it's emitter.
But, even if we can agree on that point, the fact that we agree to call it a "current input" doesn't automagically make the SYSTEM a CFB amplifier! See my comments to your first statement.
It's not the opamp that determines whether it is VFB or CFB. That's the fundamental issue. It is the way the feedback is arranged around an amplifying element that determines whether it is CFB or VFB.
If the system input signal is formed by subtracting a source current from a feedback current, that's CFB, even if the opamp has two high-impedance voltage inputs. And vice versa.
Jan Didden
millwood,millwood said:
i am sorry but this is an ill-informed position....
The term 'voltage feedback' is used to describe the so-called 'current feedback' topology, and has been for ages.....This is recognized by authorities, and other well educated folk in the field.
Just because manufacturers chose to incorrectly redefine this breed of voltage feedback topologies for marketing reasons does not excuse your lamentable inability to grasp elementary first principals.
millwood said:
No...
http://diyaudio.com/forums/showthread.php?postid=422735#post422735
millwood said:
Well, yes, but it IS accepted by others, 1000's of engineers over the last 50 years. Baxandall, Cherry, Pass. The only ones missing are a few 100 from the last few decades and a couple of misguided diyAudio folk
I'm not sure about your last scentence, do you mean "It does sound..."? If that IS what you wanted to write, well, what can I say? This forum bursts at the seams from folk claiming they hear all sorts of sounds nobody else hears
.Have a beer, lighten up!
Jan Didden
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