Thanks Yawei and raja!
ywguo wrote on Dec 10th, 2012, 9:47pm:Sure you can estimate transition density if you have recovered clock and data in the receiver. Do you want to measure the transition density on the fly?
Yes, if both recovered clock and data are available, we can do transition density estimation by counting.
What I really want to know whether there is a possible a way to estimate the transition density to help with frequency acquisition in referenceless CDR, meaning before the CDR locks; thus recovered clock and data are not available. That's what I mean by "no reference"
The reason why I am asking this is there is a interesting paper in which a frequency acquisition is presented but its inaccuracy is limited by transition density. If you guys are interested, here is the paper.
[1] R. Inti, S. Member, W. Yin, and A. Elshazly, “CDR With Unlimited Frequency Acquisition Range and Improved Input Duty-Cycle Error Tolerance,” Solid-State Circuits, IEEE Journal of, vol. 46, no. 12, pp. 3150–3162, 2011.
If transition density can be estimated without a reference clock, or even with a clock which has unknown relationship with the data rate, the error can be compensated.