Hi, all,
I have a question about the design of 4th-order loop filter for charge-pump PLL. Dean give a method to design a loop filter by given pole ratios. In dean's method, the poles of the filter are all on the real axis, but I think it is possible to design a filter with a pair of complex pole, and It may have better attenuation.

Please give me some advise.

Thanks and best Regards.

Hi, BOE,
Thanks for your reply.
I think if the two highest frequency poles are made complex pair, the stability problem may be less grievous. I just want to find a way to design a passive loop filter with a pair of complex pole, and do some experiment. It may be better than we thought.

Leon