[問題] PLL的jitter
大家好,小弟目前做的PLL遇到問題,
VCO的架構是用Ring,使用兩個charge pump去放大電容的架構,
在鎖定於800MHz的時候,除數是16,參考頻率是50MHz,兩個CP電流是56uA以及50.4uA,
大電容是6.5p,小電容是3p,電阻為3.5k.
模擬時,數位一支DVDD,類比一支AVDD,在沒加電感模擬時,整個pll的jitter大概小於1p
,但於AVDD,DVDD,DVSS,AVSS加上5n電感之後,jitter都是幾百p的等級,
有試著調過頻寬等等,好像改善不大,cp的電流不匹配也在1%以下,唯一降低KVCO會改善
較多,但我需要的range很廣,800MHz~3GHz,想請問有什麼辦法可以較明顯的降低jitter
?謝謝!
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