Problem in getting jitter from phase noise of pll

kooller

Hi all,
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2 ~. ]) G! ]1 N) }" q$ T% C8 ~I'm recently doing the jitter simulation of PLL, and I first got phase noise of PLL by adding every part of noise of PLL.

% X; G& o- \& H$ j9 v; hThen calculate jitter by the following formula:
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4 M5 l1 q. R* ^/ Mphase jitter = sqrt(integral(fre,2*Lpll))/(2*pi*f);
period jitter = sqrt(8*integral(fre,Lpll.*(sin(pi*fre*T)).^2)/((2*pi*f)^2));
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* _# e* u  |. Q' KFrequency of PLL is 5GHz, and the integral band of phase noise is 100Hz~100MHz, phase noise of PLL is as follows: -85dBc/Hz @100Hz; -64dBc/Hz @100kHz; -80dBc/Hz @1MHz; -102dBc/Hz@10MHz; -125dBc/Hz@100MHz.
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The calculated jitter results is :
, t! [4 r2 P+ w' v. G  cphase jitter: 18.9ps.
period jitter: 0.04ps.
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$ Z" E' g0 ?% L4 f& f  k6 M* j% EThis shows that the period jitter is so small, and only 1/450 times of phase jitter, while our test results shows that the period jitter is about 1.8ps.
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So can somebody tell me where is the problem of my calculation, and how much will phase jitter larger than period jitter?

anita66

看您的PN那麼差,jitter應該不可能不到20ps,其實PN是ㄧ個積分所得到的數值,同樣,jitter換算回來時,也是要累加才對,所以,你的算法有問題,可以再找一下正確的計算公式,3Q~