I designed a PLL, the VCO's control voltage Vtune is in the range of 0.7V~2.5V, the VCO(ring VCO) can oscillate from 10M to 1.2G, the target frequency of VCO is 500M, when the PLL locks, the Vtune is about 1.2V.
The problem is: the VCO gain at Vtune =0.7 or 2.5 (two ends of the tuning range) is very low, especially at Vtune =0.5, the VCO gain is 100M/V, while at Vtune=1.2, the VCO gain is 680M/V, consider about process corner and temperature variations, the VCO gain variation is much bigger.
I designed the loop filter, which can ensure stability when VCO gain is among 300M/V to 1.4G/V, but at low end of the VCO tuning range(Vtune=0.7) , the VCO gain is 100M/V, the pLL is not stable.
At the PLL taget frequency, the VCO tune voltage is between 1~ 1.2V, far away from the low end of the VCO tuning range.
My question is : Will my PLL work properly? when vtune is 0.5V(at this vtune voltage, the PLL loop can be unstble), can it converge to the target voltage of 1.2V?