Designer’s Guide Community

‹ Previous topic | Next topic ›

Pages: 1 2

No Peaking with Transient Response with PM of 66 degre (Read 9651 times)

Ricky Chen

Community Member

Offline

Posts: 49

Re: No Peaking with Transient Response with PM of 66 degre
Reply #15 - Apr 30^th, 2012, 7:29am

raja.cedt wrote on Apr 30^th, 2012, 4:17am:

hello ricky,
when you have RHZ step response starts in opposite direction. As you can see in your step response first started in -ve direction and it entered into +ve direction.

Thanks,
raj.

Dear Raj,

Thanks a lot for pointing the very important point.
In the schematic there is a 8pF cap between in and OUT of the OTA.
So this is probably creating a feed-forward path and hence RHZ.
When I removed this cap I didn't get any reverse direction movement in the transient.

Again thanks a lot for pointing this.

Kind Regards,
Ricky

IP Logged

Ricky Chen

Community Member

Offline

Posts: 49

Re: No Peaking with Transient Response with PM of 66 degre
Reply #16 - Apr 30^th, 2012, 7:34am

buddypoor wrote on Apr 29^th, 2012, 11:08pm:

Hi Ricky,

2.) Are you sure that the loop gain was simulated correctly? According to the slope of the magnitude response at unity gain the phase margin should me much lower (perhaps 45-50 deg).

You have mentioned here that the PM shouldn't be much higher from 45 degree. I guess you have thought the 2nd pole is very close to the Unit loop gain.
This actually baffled and scared me about my design and simulation method

IP Logged

raja.cedt Senior Fellow Offline Posts: 1516 Germany	Re: No Peaking with Transient Response with PM of 66 degre Reply #17 - Apr 30^th, 2012, 8:54am hello rycky, i forgot to mention some thing..when you have 67deg phase margin step response slope at t=0 will be lesser than first order and in theory you get 0. But your slope is very, for me it gives first order feeling. Thanks, Raj.
Back to top	IP Logged

Pages: 1 2

‹ Previous topic | Next topic ›