I am using simPLL to simulate the loop filter, and no matter how to change the parameter of the loop, the frequency always appears jumps in a range of hundreds Hz.
Do you know how to handle it.
Not sure what you mean by "the frequency always jumps...". When simulating a loop filter with known component values set the "specify" drop down to "Components". Now the tool calculates a loop BW and phase margin for the given component values at the frequency specified under "design freq".
To go the other way select "phase margin" instead of "components". Now the tool calculates loop filter component values for the specified loop BW and phase margin.
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