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Design >> Analog Design >> Ringing Frequency
https://designers-guide.org/forum/YaBB.pl?num=1251454141

Message started by raja.cedt on Aug 28^th, 2009, 3:08am

Title: Ringing Frequency
Post by raja.cedt on Aug 28^th, 2009, 3:08am

hi,
i have a system with some phase margin and i am getting some ringing in the step response, now if i increase system PM, then i know that no of rings will decrease..but how about frequency of ringing?

thanks,
Rajasekhar.

Title: Re: Ringing Frequency
Post by buddypoor on Aug 28^th, 2009, 3:46am

raja.cedt wrote on Aug 28^th, 2009, 3:08am:

1.) Why do you expect no decrease in ringing ? Normally, ringing becomes smaller with increased PM.
2.) Frequency of ringing is app. identical to the unity gain frequency of the loop gain. Thus, it depends on the method of PM increase which you are going to apply.

Title: Re: Ringing Frequency
Post by bharat on Aug 31^st, 2009, 1:41am

Rajasekhar,
I am reading your question as "but how about frequency at the ringing"?

1) You sweep the AC freq at the input and (where you are giving step response) and see the output in freq domain. The freq at which max O/P is seen is the freq of trouble where you are seeing the ringing. Let's say that freq is 250MHz. Mind it, it won't be regular AC sims of breaking the loop rather colsed loop simulation.
To verify the same in time domain run the transient simulation
and sweep the freq in the neighborhood of 240Mhz-260Mhz ( what you got in the freq response) of sinusoidal input for small amplitude of say 100mV, you may see that O/P is ringing with larger amplitude than the I/P is given.

Alternatively; If you can sweep the freq of sinusoidal input for small amplitude of say 100mV, you may see that O/P is ringing with larger amplitude that the I/P is given. Though this is tedious and you have to sweep the frequency of much larger range.

Regards,
-Bharat

Title: Re: Ringing Frequency
Post by raja.cedt on Aug 31^st, 2009, 4:22am

hi all,
tx for your inputs

Title: Re: Ringing Frequency
Post by vamshikrishna on Aug 31^st, 2009, 9:50pm

hi raja,

If we consider a second order sys the damping freq is given by Wd = Wn*sqrt(1-zeta^2)

so the ringing freq reduces with increase in zeta. As one can observe that zeta prop. to PM the ringing freq also decreases with increase of PM.

Thanks
vamshi

Title: Re: Ringing Frequency
Post by raja.cedt on Sep 1^st, 2009, 8:12pm

hi vamsi,
i am asking for any general system...first there is damping factor for above 2nd order....and as buddy poor said ringing frequency depends on the ugb..so strongly it depends on how did you compensate....for example in case of dominate pole compensation ugb will decrease so ringing frequency also decreases
thanks,
Rajasekhar.