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raja.cedt Senior Fellow Offline Posts: 1516 Germany	Re: Loop gain Stability analysis Reply #15 - Feb 13^th, 2011, 6:05pm hello all, some told me if open loop is stable then bode can be used to examine closed loop behavior and both phase and magnitude should be monotonic ..) correct me if i am wrong Thanks.
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vp1953 Senior Member Offline Posts: 172	Re: Loop gain Stability analysis Reply #16 - Feb 14^th, 2011, 10:57am Hi Rakesh, Gain crossover happening before phase crossover with some margin for the phase should ensure stability.
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Rakesh Community Member Offline Posts: 60	Re: Loop gain Stability analysis Reply #17 - Feb 14^th, 2011, 1:32pm Hi all, Can some one give some reference material where i can understand these stability properly. Thanks Rakesh
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Lex Senior Member Offline Posts: 201 Eindhoven, Holland	Re: Loop gain Stability analysis Reply #18 - Feb 15^th, 2011, 12:47am In most analog circuit design/control system books you can find something on stability. Please use google instead of cluttering this forum.
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Berti

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Re: Loop gain Stability analysis
Reply #19 - Feb 15^th, 2011, 1:07am

Alexandar,

The simple bode stability does not apply in all cases. Most real system however are simple enough that they can be analyzed using the bode stability criterion. On the other hand, conditionally stable systems for instance (like the amplifiers design by Xignal for their CT Sigma-Delta or maybe the example given in this thread) need to be analyzed using the Nyquist diagram.

I therefore think that �Rakesh's question whether bode stability criterion is enough or the Nyquist plot has to be drawn is not that trivial ... and often ignored in classical text books ... and in my experience often poorly understood by many EE!

Regards

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Lex

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Eindhoven, Holland

Re: Loop gain Stability analysis
Reply #20 - Feb 15^th, 2011, 1:30am

Berti wrote on Feb 15^th, 2011, 1:07am:

Alexandar,

The simple bode stability does not apply in all cases. Most real system however are simple enough that they can be analyzed using the bode stability criterion. On the other hand, conditionally stable systems for instance (like the amplifiers design by Xignal for their CT Sigma-Delta) need to be analyzed using the Nyquist diagram.

I therefore think that �Rakesh's question whether bode stability criterion is enough or the Nyquist plot has to be drawn is not that trivial ... and often ignored in classical text books!

Regards

FYI.. Bode plots and Nyquist plots show exactly the same information. It does not mean that if <insert some layman rule> does not apply, we need to use a Nyquist plot. Imho best to use is the complex plane w/ rootlocus method.

BTW strong nonlinear dynamics can be solved using the phase plane, that is if u are really interested into going the theoretical way. These are NOT Nyquist plots...

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