Spectre and Eldo simulation not matched

[AdvaRes]

eldo to spectre

Hi all,

After having simulated the VCO Vtune of a PLL with Eldo I decided to do this same simulation with Spectre. By surprise the two results looked compleately different.
In fact Eldo curve starts from 0.08V to stabilizes at 0.8 V after 3µs however the Spectre curve of the same signal starts from 1.5 V and become stable at 0.8V after 16 µs.
What confused me is that the power supply used is 1.2 V, so how could the initial Spectre signal simulation start at 1.5 V ?
Why the simulation does not match ?
Do you have an idea ?

 

[leehying]

spectre ou eldo

If the initial value is not set, it is guassed by the simulator, which mean it may be any voltage.

 

[AdvaRes]

If the initial value is not set, it is guassed by the simulator, which mean it may be any voltage.

I set the VCO Vtune initial condition to 0.08 V and I simulated. The results still compleately differents.