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I have done a LP filter design in MATLAB, and also replicate the same design in PLLATINUMSIM, which I expect to have ~the same result, C, R values, however, the difference is way large than I expect. I reverified the result refering to book from TI:, which doesn't seem to follow this as well.
So long story short, it would be nice if the technical support can elaborate/enlight me how did the LP filter values are designed.
In the software, there is an option: optimize jitter or optimize phase noise, I guess it will also influence the values of C and R, however, I don't know how they are calculated from the software itself.
  • Hi,

    In regards to my book, a more recent version is available at and it is order from print from LULU press.

    Most likely, the reason for the difference is that it is likely not exactly the same design.  If the filter has k components, it needs k constraints.

    This is why just giving phase margin and loop bandwidth is not enough to uniquely specify the components.  PLLatinum Sim uses:

    2nd order filter:

    Loop Bandwidth, Phase Margin, Gamma

    3rd Order Filter

    Loop Bandwidth, Phase Margin, Gamma, T3/T1 pole ratio, Constraint that C3 is maximized

    4th order filter:

    Loop Bandwidth, Phase Margin, Gamma, T3/T1 Pole Ratio, T4/T3 pole ratio, Constraint that C4 is maximized

    Note that for the case of the 4th order filter, there are 6 constraints, but 7 components, so actually it is possible to have more than one solution

    But for 2nd & third order, it is unique.

    The "Minimize Jitter" and other settings impact loop bandwidth, phase margin, Gamma, T3/T1 ratio, T4/T3 ratio, but do not directly impact the loop filter.