ADMV4420 Kvco

Question

On the ADMV4420 datasheet, p. 5 it shows the typical VCO tuning sensitivity, Kvco, to be 50 MHz/V. 
 But on p. 39 in the Loop Filter section it says that the loop filter on the eval board was designed with Kvco of 80 MHz/V. 
 Which Kvco value should I use when designing the loop filter for my application? 
 Related question - when I do the math for phase margin using the values in the Loop Filter discussion on p. 39, I get phase margin of 61 degrees. The datasheet says this circuit gives phase margin of 45 degrees. Please verify the 45 degree phase margin calculation and let me know if it is correct. 
 Thanks.

dmailloux · Accepted Answer

The Kvco changes based upon the selected VCO core, band, and the Vtune required for lock. 
 Generally it will be in the range of 45 to 85MHz/V with a Vtune of 1.8 to 2.2V. 
 Please see plot below; the end bands are where you may find more variation. 
 Here&rsquo;s the numbers we use for loop simulations:
 
 VCO = 8.175GHz, Vtune = 1.9V, Kvco = 40MHz/V 
 VCO = 8.375GHz, Vtune = 1.85V, Kvco = 50MHz/V 
 VCO = 9.475GHz, Vtune = 2.1V, Kvco = 85MHz/V 
 VCO = 10.575GHz, Vtune = 2V, Kvco = 70MHz/V

You can consider VCO input capacitance to be < 10pF, so generally try to keep the last capacitor in the loop filter > 100pF; even higher would be better.)

dmailloux · Answer

Also, please see the attached ADIsimPLL models. ADMV4420_ADIsimPLL.zip

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ADMV4420 Kvco