The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Design >> Analog Design >> how to determine loop bandwidth for PI with digital filter?
https://designers-guide.org/forum/YaBB.pl?num=1302621351

Message started by casual on Apr 12^th, 2011, 8:15am

Title: how to determine loop bandwidth for PI with digital filter?
Post by casual on Apr 12^th, 2011, 8:15am

how to determine loop bandwidth for PI with digital filter?

Title: Re: how to determine loop bandwidth for PI with digital filter?
Post by raja.cedt on Apr 12^th, 2011, 9:01am

what do you mean by PI loop BW..its an open loop system

Title: Re: how to determine loop bandwidth for PI with digital filter?
Post by casual on Apr 12^th, 2011, 5:12pm

PI output go to a CDR loop

Title: Re: how to determine loop bandwidth for PI with digital filter?
Post by raja.cedt on Apr 12^th, 2011, 9:35pm

yes,
so should ask CDR bandwidth riteee....
so this is a different question now. Tell me weather your CDR is 1st order or 2nd order from there we can decide.

Title: Re: how to determine loop bandwidth for PI with digital filter?
Post by casual on Apr 13^th, 2011, 1:12am

since PI replacing the vco, there is no 1/s integral part. Then it should be 1st order.
digital loop filter is used.

Title: Re: how to determine loop bandwidth for PI with digital filter?
Post by raja.cedt on Apr 13^th, 2011, 5:02am

correct but what about loop filter. General rule is if you need only phase tracking use first order, but if any frequency tracking required (like systems which are having ppm between TX and RX) then 2nd order imp.

Thanks.

Title: Re: how to determine loop bandwidth for PI with digital filter?
Post by casual on Apr 13^th, 2011, 5:55am

how to determine the loop filter?
input does not have ssc.
could you point me some of the good papers?

Title: Re: how to determine loop bandwidth for PI with digital filter?
Post by raja.cedt on Apr 14^th, 2011, 10:12pm

hi,

http://www.ece.tamu.edu/~spalermo/ecen689/cdr_hlee_stanford_2006.pdf

http://www.ece.tamu.edu/~spalermo/ecen689/dig_cdr_bb_pll_sonntag_jssc_2006.pdf
Thanks.

Title: Re: how to determine loop bandwidth for PI with digital filter?
Post by casual on Apr 14^th, 2011, 11:25pm

thank you :)

Title: Re: how to determine loop bandwidth for PI with digital filter?
Post by casual on Apr 24^th, 2011, 7:28am

how could the PI has 2nd order loop??
2nd order loop implies that the PI can adjust its clock frequency. The PI has only fixed frequency but the phase can be adjusted.

Title: Re: how to determine loop bandwidth for PI with digital filter?
Post by raja.cedt on Apr 24^th, 2011, 12:36pm

good question, i also understand little bit. So please refer the above thesis. What i feel is rate of change of phase is frequency. If you know any answer for this let me know

Thanks.

Title: Re: how to determine loop bandwidth for PI with digital filter?
Post by casual on May 12^th, 2011, 6:09am

got it.

freq=d(phi)/dt (1st order)
ramping freq = d(phi)^2/dt^2 (2nd order)