CP的mismatch对phase noise的影响，求解

flyawayfc

本人流片了一个PLL，测试发现CP的mismatch对相位噪声有非常大的影响，原来以为mismatch仅仅会造成reference spur，但是测试发现还会大大影响phase noise，请问流过PLL的大神们，这是为啥原因？因为使用的是简单地CP。比如CP的vcontrol偏离中心点时，CP的mismatch严重，锁住的phase noise 就极差。

niklas

First, I want to correct a concept misunderstanding here, spur is one type of phase noise, which results in phase error and in another word, jitter.

Ok, before we walk through your case, may I know how do you test the PLL and the reason you make the conclusion that cp dominate your phase noise measurement.
Couple of things to try, increase cp current, move output freq to another channel, for example

Bottom line is, CP mismatch only create spur, and even with 20% mismatch, it should not dominate your phase noise performance. So, I doubt about your test flow and how you draw the conclusion

flyawayfc

回复 2# niklas


    测试的确发现CP mismatch时，spur会上来，并且phase noise 会急剧下降，我做的是40GHZ 的PLL,尤其是CPmismatch较严重的时候。以前对PLL的理解是CP的mismatch仅仅会造成reference spur的上升，不会造成phasenoise的下降，测试了才知道不是那么一回事，测试应该不会有问题吧

ralphtwtw

who is correct?