When I simulated PLL in hspice , I need to add initial value for VCO and VCO will be oscillated.
But, Do I need to add the other circuit for VCO in order to give it initial value on layout ?
In hspice, when we add an initial value in VCO, that will help HSPICE to oscillate the VCO. That's hspice algorithm. In real circuit, it will be oscillated if your VCO is correct because it always have noise in VCO. So you don't add any circuit in your VCO.
Maybe you can try to add some conditions into the run file.
For example, add the power ramp (from 0 to vdd) or add the interference in the
power rail to model the real environment.
If your circuit can't osc with above conditions, maybe it have some unknow side effect.