Yes. This is always the case cos like the feedback resistor bypass it doesn't determine the Loop Gain 'directly' like plain Miller, MIC, TPC, TMC, 'pure Cherry' etc .. but tweaks it.
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Gurus JPV & Zan, I'm itching to do some serious work along the lines you have suggested.
My $0.02 is the Excess Phase might be less of a problem if we keep loops to 3 or less active devices in their path ala Cherry.
The aim of the exercise being to understand the 'real life' issues and hopefully develop strategies to deal with them .. rather than to bolster some fancy theory.
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It would be nice if you could post a few examples of what you consider GOOD practice instead of cr*p.michaelkiwanuka said:
The evidence so far suggests .. for all your pontificating, you are incapable of designing power amps with even mildly acceptable stability & THD ... even in SPICE world
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Without taking sides, that's a pretty hefty comment.The evidence so far suggests .. for all your pontificating, you are incapable of designing power amps with even mildly acceptable stability & THD ... even in SPICE world
The evidence so far suggests .. for all your pontificating, you are incapable of designing power amps with even mildly acceptable stability & THD ... even in SPICE world
What a blessed fool you are. By your own account you're a SPICE "newbie". You then, with a straight face, pompously pontificate about my abilities as an amplifier designer on the basis of SPICE which you barely know anything about. How stupid is that?
There is no fool like an old fool.
Care to suggest another interpretation of MikeK's SPICE examples?[*]
I can't claim to have searched them all out but certainly ALL the ones I've been stupid enough to download and try ... have shown appalling stabiltiy & THD.
I note he tends to dismiss 'real life' examples & evidence so his SPICE models are all we have to go on. Could be my lack of facilty with LTspice of course
All I'm asking is that he provides some evidence, preferably 'real life' but SPICE will do for a start, that he is 'capable'. I'm not sure, copious dubious pontificating and quoting loadsa books is 'evidence'.
But he's obviously a true master at semantic pedantry though its hard to see how any of it translates to good amplifier design.
And he's scaled new heights in invective too.
[*] One possibility is that Mike's examples are just to 'prove' everyone else is cerebrally challenged but I'm sure he couldn't possibly take such an offensive view
I know you cherish the emitter bypass capacitor but as far as I can see, it can only put us back to where we started before we added the emitter resistor. *On reconsideration, maybe it can be useful if correctly chosen
Seems the best plan is to keep the VIS (= VAS/TIS = Very Important Section) emitter resistor low and maximise the current in the VIS, which makes sense on first principles. I have the next two weeks on holiday to re-read Cherry and see why he doesn't do this.
Mike also recommends this. Nice to see you two in accord.
Seriously, lets keep it that way, I appreciate both your comments.
What about the proposal a few posts back to use an EF buffer on the VIS and return the Miller capacitor after the buffer rather than before?
I have never considered this, probably because Self and Cordell don't even consider it, as far as I know.
Nor do the op-amps circuits use it, also AFAIK. Does that imply it's a poor choice?
Best wishes
David
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Yes. Finally I understand...probably
. Thank you very much.So, Mr Lee. The VIS emitter resistor bypass capacitor should be used with a Miller capacitor series resistor to force the zero into the LHP.
You need both to have sufficient free parameters.
Kind of chuffed to have worked it out at last, so I may have rushed and made a mistake, but it looks correct. Cherry did not pick up on this AFAIK.
Best wishes
David
ON ANOTHER TOPIC.
Here is the EC buffer that I mentioned previously. I saw others were going in that direction so I decided to post it. Bob, this is a really great example of EC. I think you can imagine how this could be used in many places to improve linearity.
http://www.diyaudio.com/forums/analogue-source/154210-mpp.html#post3554680
Here is the EC buffer that I mentioned previously. I saw others were going in that direction so I decided to post it. Bob, this is a really great example of EC. I think you can imagine how this could be used in many places to improve linearity.
http://www.diyaudio.com/forums/analogue-source/154210-mpp.html#post3554680
I think we now have the most universal naming scheme for the VAS/TIS, I like
I had the same thought. Voltage-Impedance stage. Current in, voltage out. Maybe it's going in the right direction? VYS - Voltage Admittance stage. V in, V out. I think this is close to the right way to do it.
I had an interesting idea on a shorthand way of using math symbols to represent stages, but there is no easy way to insert superscript or subscript.
I had an interesting idea on a shorthand way of using math symbols to represent stages, but there is no easy way to insert superscript or subscript.
Sorry for the long time (a few days) delay on this reply.
I was referring to the input voltage of the OTA/Opamp, which is the “error voltage” in the negative feedback context.
Well, you can for example check the books
K. Laker and W. Sansen, Design of Analog Integrated Circuits and Systems
Willy Sansen, Analog Design Essentials
If you google a bit, you’ll find many papers calling OTA to the 2 stage miller amplifier. For example:
IEEE Xplore - Fast-settling CMOS two-stage operational transconductance amplifiers and their systematic design
IEEE Xplore - A 0.5-V 8-bit 10-Ms/s Pipelined ADC in 90-nm CMOS
http://www.cecs.uci.edu/~papers/compendium94-03/papers/2003/islped03/pdffiles/14_3.pdf
So, as I said, there are many people calling OTA to the two-stage miller amplifier due to its high output impedance (at low/medium frequencies). Again, I understand you argument that the output impedance drops due the effect of the compensation capacitance. But the fact is that with a two-stage miller amplifier you cannot do something you typically do with a “standard” Opamp: apply resistive feedback. Well you can, but resistances in the kohm range would lower significantly the DC gain, which is a behavior you’d (well, I would) find unacceptable in any Opamp. That the reason why Opamps have a low impedance output buffer.
Moreover, note that nowadays OTAs are mostly used in switched capacitor circuits (inside filters, data converters, etc.), which process sampled signals. In these applications the error in the output voltage of the amplifier is set by the DC gain alone (well, ignoring settling errors). So the argument that the output impedance drops due the effect of the compensation capacitance for higher frequencies is quite irrelevant - in this context it is really behaving as transconductor. Maybe most of the people calling it and OTA are designers working in this area.
However, after having check a few books I have on microelectronics I must say that some,
A. Sedra and K. Smith, Microelectronic Circuits
P. Gray, P. Hurst, S. Lewis and R. Meyer, Analysis and Design of Analog Integrated Circuits
B. Razavi, Design of Analog CMOS Integrated Circuits
do not make any differentiation between an OTA and an Opamp: they simply call everything - amplifiers with one stage, two stage, with and without a low impedance output stage - “Opamp”. Note they are not arguing “Opamp” is the right terminology, they simply make no distinction..
The book
D. Johns and K. Martin, Analog Integrated Circuit Design
also calls everything “Opamp”, but they have a paragraph saying that “some designers use the term OTA”.
In my “professional life” I keep it simple and call everything “amplifier”
Regards
I was referring to the input voltage of the OTA/Opamp, which is the “error voltage” in the negative feedback context.
Well, you can for example check the books
K. Laker and W. Sansen, Design of Analog Integrated Circuits and Systems
Willy Sansen, Analog Design Essentials
If you google a bit, you’ll find many papers calling OTA to the 2 stage miller amplifier. For example:
IEEE Xplore - Fast-settling CMOS two-stage operational transconductance amplifiers and their systematic design
IEEE Xplore - A 0.5-V 8-bit 10-Ms/s Pipelined ADC in 90-nm CMOS
http://www.cecs.uci.edu/~papers/compendium94-03/papers/2003/islped03/pdffiles/14_3.pdf
So, as I said, there are many people calling OTA to the two-stage miller amplifier due to its high output impedance (at low/medium frequencies). Again, I understand you argument that the output impedance drops due the effect of the compensation capacitance. But the fact is that with a two-stage miller amplifier you cannot do something you typically do with a “standard” Opamp: apply resistive feedback. Well you can, but resistances in the kohm range would lower significantly the DC gain, which is a behavior you’d (well, I would) find unacceptable in any Opamp. That the reason why Opamps have a low impedance output buffer.
Moreover, note that nowadays OTAs are mostly used in switched capacitor circuits (inside filters, data converters, etc.), which process sampled signals. In these applications the error in the output voltage of the amplifier is set by the DC gain alone (well, ignoring settling errors). So the argument that the output impedance drops due the effect of the compensation capacitance for higher frequencies is quite irrelevant - in this context it is really behaving as transconductor. Maybe most of the people calling it and OTA are designers working in this area.
However, after having check a few books I have on microelectronics I must say that some,
A. Sedra and K. Smith, Microelectronic Circuits
P. Gray, P. Hurst, S. Lewis and R. Meyer, Analysis and Design of Analog Integrated Circuits
B. Razavi, Design of Analog CMOS Integrated Circuits
do not make any differentiation between an OTA and an Opamp: they simply call everything - amplifiers with one stage, two stage, with and without a low impedance output stage - “Opamp”. Note they are not arguing “Opamp” is the right terminology, they simply make no distinction..
The book
D. Johns and K. Martin, Analog Integrated Circuit Design
also calls everything “Opamp”, but they have a paragraph saying that “some designers use the term OTA”.
In my “professional life” I keep it simple and call everything “amplifier”
Regards
To add information to this last post, let me give some additional nice references from the web so easy to consult;
First, Laker and Sansen are explaining why to use the concept of OTA for 2stage Miller ( and others) and when to name it opamp in feedback connection; As I said, scientific littérature is in continuous evolution towards more and more structure and concepts when things becomes well studied Structured hw design do not escape to this tendency.
Two stage miller ota is NOT a way to call it, there is a reason behind
A pity that this top book is out of print.
From Berkley ( Mike the same as Gray Hurst so as I said no chapel)
From Texas A&M
Sansen analog essentials chapter 5, 6, 7 can be downloaded by googling Sansen OTA Miller
Good reading
First, Laker and Sansen are explaining why to use the concept of OTA for 2stage Miller ( and others) and when to name it opamp in feedback connection; As I said, scientific littérature is in continuous evolution towards more and more structure and concepts when things becomes well studied Structured hw design do not escape to this tendency.
Two stage miller ota is NOT a way to call it, there is a reason behind
A pity that this top book is out of print.
From Berkley ( Mike the same as Gray Hurst so as I said no chapel
)From Texas A&M
Sansen analog essentials chapter 5, 6, 7 can be downloaded by googling Sansen OTA Miller
Good reading
As I said I've got the whole book, and I am still not persuaded that a two-stage Miller compensated amplifier is an OTA. See below:
http://www.diyaudio.com/forums/soli...lls-power-amplifier-book-392.html#post3553200
Can we all come to an agreement that different authors and people will use differing terms to describe the same thing? This is very common in many industries and professions. Unless we are going to use Latin for a base word definition such as botany or biology or such this happens all the time.
Some may say toe-mate-o while another says toe-mot-o and some may say soda in one part of the US while another will call it pop! They are all correct as long as we all agree that we are talking about the same things.
Some may say toe-mate-o while another says toe-mot-o and some may say soda in one part of the US while another will call it pop! They are all correct as long as we all agree that we are talking about the same things.
Amen, thank you kindhorman. Life is too short to waste it on details of semantics and how many angles reside on the tip of a pin
.Cheers,
Bob