Regarding Digital NCO design

>hello all , 
> I am having similar problem as Nusrat. Unable to linkup phase detector
>output with NCO for loop lock condition. 
>Instead of multiplying two signals ( I and Q ) i used atan function to
get
>phase difference.  Upto this point everything seems working good. But i
am
>unable to get this signal to drive NCO . Can anybody tell me how this
>signal can be used to drive NCO. can anybody provide some code on this
part.

See simulink model BPSK phase tracking:

http://electronix.ru/forum/index.php?s=&showtopic=23652&view=findpost&p=459853

and over models... Integrator and complex exp - this is NCO(DDS).

On Oct 15, 12:21&#4294967295;am, Nusrat Nowsheen <nowsheencs...@gmail.com> wrote:
> On Oct 10, 5:35&#4294967295;am, rickman <gnu...@gmail.com> wrote:
>
>
> How can i decide whether the counter is incremented or not and if
> incremented by which value?
> Thanks
> Nusrat

If your signal is leading the NCO output, you need to increment the
phase step size counter so the NCO can catch up.  If the signal is
lagging the NCO output you need to decrement the phase step size
counter to retard the NCO so the signal can catch up.

Rick

On Nov 5, 4:33&#4294967295;am, "pasa" <nwcarv...@yahoo.com> wrote:
> hello all ,
> &#4294967295;I am having similar problem as Nusrat. Unable to linkup phase detector
> output with NCO for loop lock condition.
> Instead of multiplying two signals ( I and Q ) i used atan function to get
> phase difference. &#4294967295;Upto this point everything seems working good. But i am
> unable to get this signal to drive NCO . Can anybody tell me how this
> signal can be used to drive NCO. can anybody provide some code on this part
> .

In a standard 2nd order PLL, the phase difference is applied to a lead-
lag loop filter, a simple system with one pole and one zero, also know
as a Proportional + Integral (PI) loop filter. The loop filter output
is applied as input to the NCO, which integrates it with a wrap at +PI
and -PI. There are two integrators around the loop, hence 2nd order
PLL All of this is richly documented in books and free web sites that
you can locate yourself using a public search engine.

John