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I am looking for explanation of the P Q R parameters for CDCE949.
I can choose N & M parameters and I can calculate the P Q R parameters.
Though not specifically stated, it seems that results with R = 0 may be be desired above R > 0 results.
But I don't UNDERSTAND what R signifies, except that it is a remainder.
I notice that several combinations of N/M produce multipliers that result in R = 0.
1.00,1.0625,1.125,1.1875,1.25,1.3125,1.375,1.4375,1.5,1.5625,1.625,1.6875,1.75,1.8125,1.875,1.9375,2
,2.125,2.25,2.375,2.5,2.625,2.75,2.875,3,3.125,3.25,3.375,3.5,3.625,3.75,3.875,4,4.25,4.5,4.75,5,5.25
,5.5,5.75,6,6.25,6.5,6.75,7,7.25,7.5,7.75,8,8.5,9,9.5,10,10.5,11,11.5,12,12.5,13,13.5,14,14.5,15,15.5
,16,17,18,19,20,21,22,23,24,25,26,27,28 (there are more, I just stopped this list at 28)
I realize that P is inversely proportional to the size of the multiplier, for example:
P = 4 for a multiplier of 1.00, P = 0 for a multiplier of 16 or above.
What is the purpose of multiplying the original numerator "N" by 2^P ?
Q = int( (N * (2^P)) / M) but again what is the significance?
Hi Lee,
More details below:
I'm not sure how this will help with the actual application though. These are just frequency synthesis parameters. The optimization will be to aim at higher N and M, according to the referred thread.
Julian did not contradict himself. The N in the first quote is different than the N in the second quote. We typically use (N + num/den) for the fractional feedback divider between the VCO and PFD. In other words, f_VCO = fPFD * (N + num / den). CDCE9xx, however, is off the standard. Instead of using the (N + num/den) that we typically do, the feedback N divider is translated into Q and R parameters. And again, this "N" in the N divider is not the same "N" in the "N, P, Q, R" parameters.
Regards,
Hao
