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Assuming that all the blocks have been simulated and are converging and non-convergence happens only when they are all put together:
I will try the foll:
1.First iteration, relax all the options to low resolutions. Then save the operating point. Start the next simulation with tight resolution...
Metastability is basically when the output is in an undetermined state. If the PFD output is (from the flipflops) metastable that would mean that it is not tracking the input any more. This would cause a dead zone in the PFD response and cause jitter at the PLL output. Hope this helps.
Make sure of enough overdrive (cmos) or degeneration (bjt). degradation starts at overdrive/1.414. any overdrive problems leads to harmonics. slew rate limitation will also cause sine to be distorted, hence each stage should be biased with sufficient current. hope this helps.
Re: settling time of VCO
I would simulate the vco by injection of an current impulse in the range of pico-amps (almost noise) and see how long it takes to reach steady state oscillation amplitude.
Hope that helps.
If there are multiple loops, in addition to above said paper's techniques, I would run a step response transient analysis treating the whole system as a black box. Based on the ringing at the output, damping factor, peaking etc can be determined. Hope this helps.
You can assemble an ideal T/H and run a sinewave through it and the actual design. Compare the ideal and actual design outputs and determine how many bits of accuracy are obtained. If you subtract the actual from ideal, you can get the non-idealities part of it (assuming they are all modelled)...
Re: extend cutoff freq?
adding a cascode isolates the output node from the input node and thereby removing the miller cap from being seen at the output node, hence the improved freq performance. Cascode also provides more gain by increasing effective output impedance. Hope this helps.
The cmfb voltage cnt has to be applied, as per the ckt schematic, such a way that you control the currents in the diff pair load so as to correct any cmfb imbalances.
You can do that by applying the cmfb control voltage to pnt A . Hope that helps.
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