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Message started by henrytqy on Apr 8th, 2012, 7:52pm

Title: peaking in frequency V.S. overshoot in time domain?
Post by henrytqy on Apr 8th, 2012, 7:52pm

Hi, guys

I'am very confused with the concept of peaking and overshoot.

Dose they descripe the same thing just in the different domain?

If not, is there any relationship between them?

Thanks a lot~~~

Title: Re: peaking in frequency V.S. overshoot in time domain?
Post by aaron_do on Apr 9th, 2012, 1:23am

They are related through the circuit Q, or damping ratio.

regards,
Aaron

Title: Re: peaking in frequency V.S. overshoot in time domain?
Post by henrytqy on Apr 9th, 2012, 3:29am


aaron_do wrote on Apr 9th, 2012, 1:23am:
They are related through the circuit Q, or damping ratio.

regards,
Aaron

I know that in a 2nd order system, there is a standard description about Q or damping ratio. How about higher order?

Recently, I have desgned a cascade AMP which is used in the open-loop condition. In the bode diagram, the plot(Mag V.S. Freq) is flat without peaking, while in the trans digram, the overshoot(ring) is series. Do you know how I can solve this problem?

Thank you so much~~~

Title: Re: peaking in frequency V.S. overshoot in time domain?
Post by raja.cedt on Apr 9th, 2012, 4:28am

post the schematic and plots...

Title: Re: peaking in frequency V.S. overshoot in time domain?
Post by loose-electron on Apr 9th, 2012, 1:49pm


aaron_do wrote on Apr 9th, 2012, 1:23am:
They are related through the circuit Q, or damping ratio.

regards,
Aaron

Sometime yes and sometimes no.

So - Not necessarily

Peaking can refer to just the spectral response and at a particular frequency

Ringing and damping can refer to either reactive ringing or control systems and their
zeta (phase margin ) response.

(Both have Q, but a feedback system is generally looked at differently than a RL inductive ringing.)

Math types will say that that one is the same, and I will 50% agree with that.

Title: Re: peaking in frequency V.S. overshoot in time domain?
Post by henrytqy on Apr 10th, 2012, 4:25am


raja.cedt wrote on Apr 9th, 2012, 4:28am:
post the schematic and plots...


This architecture is from one of papers I have read before,adding the interleaving active feedback make the whole system behaves equally as another topology in the next pic.

Title: Re: peaking in frequency V.S. overshoot in time domain?
Post by henrytqy on Apr 10th, 2012, 4:30am

Assuming that, every G(s) has the form of A/(1+sRC), and Gf(s)=B/(1+sRC); So the whole poles,totally 6 with 2 real and 2 pair of compex, is splitting.

Title: Re: peaking in frequency V.S. overshoot in time domain?
Post by henrytqy on Apr 10th, 2012, 4:36am

The splitting bring a more flatten AC gain response.

I also find that one pair of the complex pole will have a high reactive part due to the splitting.  So I guess maybe this is the reason why it has a high overshoot.

Is this right?

Title: Re: peaking in frequency V.S. overshoot in time domain?
Post by aaron_do on Apr 10th, 2012, 5:24pm

You should be able to tell based on the Q of the complex poles.


Aaron

Title: Re: peaking in frequency V.S. overshoot in time domain?
Post by henrytqy on Apr 11th, 2012, 6:32am


aaron_do wrote on Apr 10th, 2012, 5:24pm:
You should be able to tell based on the Q of the complex poles.


Aaron


Sorry, I don't understand your meaning. Do you mean that I should give out the Q of the pole?

Title: Re: peaking in frequency V.S. overshoot in time domain?
Post by aaron_do on Apr 11th, 2012, 5:38pm

Hi,


Actually I haven't really read up on this in a long time, but just browsing through my book, "Feedback Control of Dynamic Systems", if you have a transfer function which can be written as,

H(s) = (s-a)(s-b)
        -----------
      (s-c)(s-d)(s-e)

you can do a partial fraction expansion to see the effect of each pole. Real poles result in no overshoot, but for complex poles, the amount of overshoot depends on the Q factor, or damping factor of the poles. It seems that you have the transfer function, so you should be able to tell if the overshoot is due to the complex poles just by looking at their Q factor...


regards,
Aaron


BTW, if you are injecting a large signal and looking at the overshoot, then the above explanation doesn't really apply since it is for a linear system.

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