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Design >> Analog Design >> Multiloop feedback system Stability
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Message started by raja.cedt on May 10^th, 2013, 1:58pm

Title: Multiloop feedback system Stability
Post by raja.cedt on May 10^th, 2013, 1:58pm

Dear all,
I have been reading Analog Circuit Design: High-Speed Clock and Data Recovery, High-Performance . I found very interesting topic on assessment of multiloop feedback stability through step response Fourier transform. Mainly he explained how to find Dumping factor from the step response (i don't know weather it is same as 2nd order system damping factor). Page number 355,356 explains clearly how to implement, even at the end of chapter he described how Texas instrument people use this method to test their ldo under variable load conditions. Can any one explain how this method works.

One important thing, Many people say's for a multiloop system to be stable every loop has to stable individually, But this author says stability in every loop not necessary but sufficient. If any one can't read through Google books let me know i will post these two pages

Thanks,
Raj.

Title: Re: Multiloop feedback system Stability
Post by nrk1 on May 12^th, 2013, 7:48am

raja.cedt wrote on May 10^th, 2013, 1:58pm:

One important thing, Many people say's for a multiloop system to be stable every loop has to stable individually,

This is clearly not the case. You could have an "inner" unstable loop and an outer loop to stabilize it. A simple example is an integrator with positive feedback and another loop which provides a (larger) negative feedback. The overall system will be stable. Alternatively, you can think of many resistors (transconductors in feedback if you want to think of feedback) in parallel, some of which have a negative value. As long as the net conductance is positive the circuit is stable, even though there are some unstable components there.

Title: Re: Multiloop feedback system Stability
Post by Vladislav D on May 14^th, 2013, 2:20am

raja.cedt wrote on May 10^th, 2013, 1:58pm:

But this author says stability in every loop not necessary but sufficient. If any one can't read through Google books let me know i will post these two pages

Thanks,
Raj.

Hi Raj,
Where does he say so? From my memory, the author your mention always claims that every loop should be stable and has to be stabilize individually.

Title: Re: Multiloop feedback system Stability
Post by Vladislav D on May 14^th, 2013, 2:24am

Vladislav D wrote on May 14^th, 2013, 2:20am:

raja.cedt wrote on May 10^th, 2013, 1:58pm:

But this author says stability in every loop not necessary but sufficient. If any one can't read through Google books let me know i will post these two pages

Thanks,
Raj.

Hi Raj,
Where does he say so? From my memory, the author your mention always claims that every loop should be stable and has to be stabilize individually.

OK. Sorry. Found it =)