Thanks Shawn for such an elaborate reply. I do agree with you that initializing the ring-VCO nets to mid-rail is going to be the best strategy for a robust start-up because this ensures that all of the inverters are in high-gain region and a small enough numerical noise in simulation or circuit noise in silicon will reliably start the VCO oscillation. You mentioned something related to having a certain circuitry to ensure this part, can you brief me more on that? What kind of circuit(s) do you use to do that? I have seen one start-up circuit technique where a differential kick is given to the other side of the ac-coupling cap of the VCO buffer which then couples it to the ring and starts it up. As far as the simulation is concerned, initializing ring nets to the mid-rail also did not help. Still having the same issue. O utput log shows that the PSS runs for some time and then it says that the voltage of the ring output is too small to reliably detect the period of the oscillator. Perhaps the nodes with insignificant signal levels were chosen, or perhaps the oscillator was never properly started. Do you have any other suggestions?
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