Can i use Cadence's tools simulate Bandwidth and Phase Margin of a PLL?How can I do it?
chenliy said:Can i use Cadence's tools simulate Bandwidth and Phase Margin of a PLL?How can I do it?
very good!Btrend said:the loop formed by PLL and OPamp are different in nature,
first of all, loop in OPamp (commonly is negative feedback) is continuous time, that is the loop is "always" there.
secondly, the loop in PLL is not "always" exist, it only exist in part of PFD cycle.
so the loop is not continuous, it was said as "sample-data loop" and is not continuous loop. If you want to know the exact behavior of the loop , you need to do Z-domain analysis.
finally, from the above 2 point of view, the usual loop concept using in OPamp is only a approximated version of the actual sample-data loop, this should be keep in mind . Otherwise, you will find a weird thing, why the loop gain > 0 and the phase is -180° which should be oscillated at a usual Opamp negative feedback loop.
option318 said:Thanks, khouly offer work_116 model.
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