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Old 3rd October 2013, 11:29 AM   #21
gootee is offline gootee  United States
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First post: define your freaking acronyms!
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Old 3rd October 2013, 12:14 PM   #22
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TIS: Transimpedance stage; also erroneously called the "VAS".

TAS: Transadmittance stage; also known as the input stage.

Anything else?
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Old 3rd October 2013, 01:23 PM   #23
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Quote:
Originally Posted by mcd99uk View Post
The thoughts below may be completely wrong...

It does look like (to me) TPC loads the VAS output more but could this be negated by moving the TPC connection to the next stage (eg. drivers or pre drivers). But this may well require extra compensation as TPC compensation now encloses more transistors? And then the advantage of moving the TPC "take off point" may be reduced?
I still need to think more about some of the content but you may want to look at THIS SITE where similar ideas are discussed.

Best wishes
David

Last edited by Dave Zan; 3rd October 2013 at 01:43 PM. Reason: rewrite more casually
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Old 3rd October 2013, 01:35 PM   #24
sreten is online now sreten  United Kingdom
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Quote:
Originally Posted by mcd99uk View Post
The thoughts below may be completely wrong...

It does look like (to me) TPC loads the VAS output more but could this be negated by moving the TPC connection to the next stage (eg. drivers or pre drivers). But this may well require extra compensation as TPC compensation now encloses more transistors? And then the advantage of moving the TPC "take off point" may be reduced?
Hi,

Moving the take off point of TPC (two pole compensation)
is TMC (transitional miller compensation). An advantage
of TMC is it reduces the loading of the VAS of TPC by
effectively "bootstrapping" the compensation resistor.

By an order of magnitude according to DZ's link.

If your going to move it you may as well enclose
the whole output stage. Note that both arrangements
revert to single pole on the VAS only at higher frequencies.

rgds, sreten.
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Last edited by sreten; 3rd October 2013 at 01:39 PM.
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Old 4th October 2013, 12:32 AM   #25
gootee is offline gootee  United States
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Quote:
Originally Posted by michaelkiwanuka View Post
TIS: Transimpedance stage; also erroneously called the "VAS".

TAS: Transadmittance stage; also known as the input stage.

Anything else?
Thanks but those two were defined in post #1.

How about TPC and TMC?

I guess you're lucky that most people probably already know what "VAS" (Voltage Amplification Stage) stands for.

Acronyms should ALWAYS be defined, the first time they are used, in each document in which they appear.
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Old 4th October 2013, 02:24 AM   #26
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Originally Posted by gootee View Post
How about TPC and TMC?
TPC = Two Pole Compensation
TMC = Transitional Miller Compensation

Both acronyms commonly used in DIY Audio.

Best wishes
David

Last edited by Dave Zan; 4th October 2013 at 02:28 AM.
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Old 4th October 2013, 03:18 AM   #27
gootee is offline gootee  United States
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Quote:
Originally Posted by Dave Zan View Post
TPC = Two Pole Compensation
TMC = Transitional Miller Compensation

Both acronyms commonly used in DIY Audio.

Best wishes
David
"Commonly used" by everyone who already knows what they mean, leaving everyone else clueless, if they are not defined.
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Old 4th October 2013, 07:03 AM   #28
Bonsai is offline Bonsai  Taiwan
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Michael, you have chosen your ULGF wisely, as have you the model used in your expose. It supports your argument. ULGF's for modern bipolar output transistors are typically 1-1.5 MHz so that loop gains can be maximized, and distortion reduced as far as possible.

My rule of thumb is:-
EF2 - upper ULGF using modern bips 3MHz
EF3 - upper ULGF 1.5MHz

(In both cases, use of a Zobel and output inductor mandatory for high loop gain designs).

In your demonstration using real world parts, I would expect the the ULGF differences between TPC and TMC to be significant. So, its not the performance difference between the two comp methods below the loop gain -3 dB bandwidth, but what's happening at HF and the ULGF where stability may be a concern, that is of interest.

Discuss.
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Old 4th October 2013, 08:29 AM   #29
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Originally Posted by gootee View Post
... by everyone who already knows what they mean, leaving everyone else clueless...
"Thank you" to you too

Quote:
Originally Posted by Bonsai View Post
Michael, you have chosen your ULGF wisely, as have you the model used in your expose. It supports your argument. ULGF's for modern bipolar output transistors are typically 1-1.5 MHz so that loop gains can be maximized, and distortion reduced as far as possible.

My rule of thumb is:-
EF2 - upper ULGF using modern bips 3MHz
EF3 - upper ULGF 1.5MHz

(In both cases, use of a Zobel and output inductor mandatory for high loop gain designs).

In your demonstration using real world parts, I would expect the the ULGF differences between TPC and TMC to be significant. So, its not the performance difference between the two comp methods below the loop gain -3 dB bandwidth, but what's happening at HF and the ULGF where stability may be a concern, that is of interest.

Discuss.
OK! First point is one that I have wondered about for a while.
Why can't we push the ULGF up?
Requires precise control of stray capacitance, trace inductance and the like, Zobel for sure.
But should be possible
Some of Ric Lee's early Output Inclusive Compensation (OIC) simulations used slow output transistors and had the ULGF much closer as a fraction of the Ft.
What is the limit on the cancellation of the output transistor pole with a zero inside the loop?
Dennis Feucht writes about this but I still haven't modelled it.

Not much of a discussion but I concur with your last point.

Best wishes
David
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Old 4th October 2013, 09:08 AM   #30
mcd99uk is offline mcd99uk  United Kingdom
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Originally Posted by sreten View Post
Hi,

Moving the take off point of TPC (two pole compensation)
is TMC (transitional miller compensation).

rgds, sreten.
I'm struggling with this point. I can see that moving the TPC take off from the VAS output to the driver/pre-driver would include a proportion of the output stage and that moving the take off point all the way to the output would include the whole output stage. Is this not "two pole OIC (Output Inclusive Compensation"? I'm finding relating (the equivalence of) this form of TPC to TMC a challenge.

Dave Z - Have read the page you posted a link to and followed most of it.

More studying required I think...

Last edited by mcd99uk; 4th October 2013 at 09:17 AM.
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