Frequency Locked Loop and Phase Locked Loop

[OMEsystem]

Why we need FLL sometimes rahter than PLL?
What's the advantage and disadvantage of FLL?

BTW, what's the relation between FLL and AFC we often see this?

Thanks,

 

[rjshmadala]

Hi,

In a PLL first of all it should try to make VCO frequency equal to that of the reference frequency.after that it decrease phase difference to zero. so that PLL locks. if the difference between ref. frequency VCO frequency higher than certain level PLL fails to lock.in this case we need Frequency Detector(FD) .this FD makes two frequencies equal and after that it losses control on loop and give control to PLL.and PLL try to eleminate Phase Diference. and it locks .mostly clock and data recovery(CDR) circuits use this prnciple.

Regards

 

[OMEsystem]

What's the occasion that the FLL is alone without PLL?