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Loop Filter Coefficients in Timing Recovery loop in Baseband Receiver

Started by avi1987 3 years ago2 replieslatest reply 3 years ago269 views

Hi!

I am trying to design the Symbol timing recovery(#STR) block of #DVBS Receiver.  For reference, I am using the following matlab simulink design  (NDA timing recovery part within Digital Baseband Receiver)

http://www.mathworks.com/matlabcentral/fileexchang...

The design has considered a roll-off factor of 0.5. I need to design for a roll-off factor of 0.2.

All other parameters remaining constant, I believe the only factor that will change in the design would be the loop filter coefficients. But , I am not able to understand how the loop filter coefficients of PI filter are calculated in the design.

The value of the loop filter coefficients are C2 = 1.35e-4, C1 = C2/128.where c2 = proportional filter coefficient, c1 = integral filter coefficient.

C2 depends on k0,kd,zeta(damping ratio), natural frequency (wn),(zeta and wn determine loop bandwidth). 

How to calculate kd? From my  understanding , it should be the slope of S-CURVE of gardner TED when error tends to zero.

Kindly clarify.

Regards avi

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Reply by SlartibartfastMay 18, 2016

Yes, Kd is the slope around the zero-error region.   The units for that slope must be compatible with the units of Ko, the DDS/VCO gain constant, such that the product of KoKd has units of 1/seconds.

This presentation covers the basics and some important details:

http://www.compdsp.com/presentations/Jacobsen/abin...



[ - ]
Reply by avi1987May 19, 2016

Thank you for the reply.

I was referring the book  " Digital Communications- A discrete time approach" by Michael Rice for the loop filter design. A detailed analysis for the loop filter design with some examples are given in the "Appendix C" of the book. In the examples given, the loop filter coefficients values for C2 are given as 0.1479,0.2958 etc. But in the matlab design that I have referred to in my previous post the range is in e-4(1.35e-4) range which is much different. And my own calculations are coming in the range that is given in the book examples. And with my calculations the timing recovery circuit is not working properly.

If one can clarify regarding this, it would be very helpful.

Regards avi