Bob Cordell's Power amplifier book

[Edmond Stuart]

Originally Posted by panomaniac

Rude remarks removed. Please be polite.

Hi Pano,

I wonder whether you have read this post: Mpp
let's hope the same won't happen with this thread.

Cheers,
E.

[Bob Cordell]

Originally Posted by YWN

</p>
Hi Edmond, that is incorrect. Set aside not all second order systems are overshooting and exhibit a phase dip (but only the overdamped systems, or otherwise said in the frequency domain, with close pole/zero pairs), the Bode integrals theory shows clearly that for a constant unity loop gain frequency, and while keeping the closed loop system stable, you can't get more loop gain than what Miller compensation (as a first order system) can provide. Or otherwise said again, for a first order system, the gain times bandwidth product is a constant.

Obviously TMC provides more loop gain than Miller. That extra loop gain has no other way to appear other than from a pole-pole-zero distribution. That is, roll the gain steep and late (in frequency) and bring the roll off to 20dB/decade around the unity loop gain frequency, to keep the closed system stable.

What you can say is that TMC, as a second order system, can provide the same loop gain as TPC (also a second order system) while not requiring the system to be overdamped. This property is indeed an advantage of TMC over TPC, and is one reason why I was looking after an analysis on if and how TMC implements pole splitting.

I would love to further discuss these things, they are indeed fascinating, but it's holydays and I need to get a life

Hi YWN,

There is a bit of a second-order TPC-like nature to TMC if you recognize that the voltage gain of the output stage is less than unity. With TPC, the T resistor is connected to ground and it has no signal on it (and no bootstrapping). With TMC and a nominal output stage gain of unity (but allowing for injection of distortion components into it), the T resistor is completely bypassed and you merely have a largely pure transistion of Miller take-off point from VAS to output.

If you have a nominal output stage gain of 0.9, you have partial bootstrapping of the T resistor, and this probably gives rise to some TPC-like behavior - the resistor has 10% of the signal across it and it looks similar to a resistor of 10X the value connected to ground.

Just thinking out loud here.

Cheers,
Bob

[WuYit]

The transcendental pole-zero cancellation guru says you never stop being amazed by how wishful thinkers make up own rules in order to get theory to match application.

[WuYit]

YWN,
on the other hand, under dynamic conditions each stage effects the Loop, each stage is effected by the Loop and vital parameters, like Loop gain, bandwidth, the poles and zeros of the transfer function constantly vary with the load. The Loop is more or less characterized by the formula z = z² + c
(L)oops!

[wahab]

Originally Posted by YWN

<
Set aside not all second order systems are overshooting and exhibit a phase dip (but only the overdamped systems, or otherwise said in the frequency domain, with close pole/zero pairs),

So overdamped systems are the ones that show overshoots ?...

Yet another completely non sensical sentence..
One has to wonder if it s not pure rethoric...

[Edmond Stuart]

Originally Posted by WuYit

YWN,
.........
The Loop is more or less characterized by the formula z = z² + c
(L)oops!

My Loops are characterized by the formula z = mc²

[Edmond Stuart]

Originally Posted by wahab

So overdamped systems are the ones that show overshoots ?...

Yet another completely non sensical sentence..
One has to wonder if it s not pure rethoric...

Maybe Ophelia told him this (they know each other).

[YWN]

Originally Posted by wahab

So overdamped systems are the ones that show overshoots ?...

Yet another completely non sensical sentence..
One has to wonder if it s not pure rethoric...

Sorry, that would be underdamped. My fault, but then I suspect you understand what I meant. But for you, as for your buddy Edmond, it's just another opportunity to spew some venom.Happy holidays!

[YWN]

Originally Posted by Edmond Stuart

Therefore TMC behaves like a 1st order system. period

Incorrect. TMC behaves as an overdamped (or critically damped) second order system.

[YWN]

Originally Posted by Bob Cordell

Hi YWN,

If you have a nominal output stage gain of 0.9, you have partial bootstrapping of the T resistor, and this probably gives rise to some TPC-like behavior - the resistor has 10% of the signal across it and it looks similar to a resistor of 10X the value connected to ground.

</p>
Yes. Actually by varying the TMC resistor, you can get an over- under- or critically damped second order system.