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ADF4118 S-Parameter Data for RF Input of PLL Circuit

Question asked by Tom_InnoSenT on Aug 30, 2013
Latest reply on Mar 10, 2017 by dancho



I consider using the ADF4418 for a new product.

On page 8 of the datasheet for this RF PLL Cricuit the S-Parameter (mag(S11)) from 0.05 GHz - 1.8 GHz are shown.


I am confused with the printed values (between 0.88 - 0.98). From my understanding a value close to 1 indicates that most of the power is reflected from the RF input back to "prescaler out" of the VCO (when a 50 Ohm line is conected).


I would have expected values lower than 0.3 which would indicate a matching (to 50 Ohms) of -10 dB (= 20*log10(S_11,mag)).


Is there an error in the datasheet or is the definition of S-Parameter different here?


Thanks a lot for your help.