I find that perhaps it's effect is like open loop- f6 X9 p+ Y) f
modulation. I mean that the average vco input voltage is fixed by another negative feed back loop , K1 X, E i! D$ P& vbut add some small ac voltage into the vco input node to get like Frequency modulation2 [& G9 O' h0 W6 e5 @8 s
(spread spectrum effect) the above is my concept 2 O* J( R5 |! }" I. Kjust provide you to think about it