想请教一下VCO的噪声特性

intercon

   

原帖由 zwtang 于 2009-3-24 09:46 发表

                               
登录/注册后可看大图

如果CP噪声贡献很小时，in-band就有VCO的噪声贡献。

你的意思是否是 “当CP噪声贡献很小时，带内的VCO噪声影响不可被忽视”

zwtang

如上述附图，如果环路带宽增大为120kHz，带内噪声就是CP的贡献，VCO贡献就只在带外了。

合理的PLL应该是，100Hz以内为参考时钟贡献；100Hz到环路带宽(in-band范围)通常比较平坦，为CP贡献；环路带宽之外为VCO贡献。

环路带宽的最优点为CP噪声贡献与VCO噪声贡献相等。

faithfully

first, VCO's phase noise  is 30dB/dec within corner frequency and then 20dB/dec. The transferfunction for VCO phase noise in pll is -40dB/dec within zero and then -20dB between zero and ubw, and then 0 higher than ubw. so, only between zero and ubw, vco phase noise contribution is flat.
then, the loop parameters in PLL is mainly for attenuating inband VCO phase noise, you never want inband VCO phase noise dominates. From this point of view, the bandwith should be the higher the better, both for attenuating VCO phase noise and fast settling. However, the constrains are 1, stability 2, spur 3, quantiztion noise 4, When the bandwith is wide enough that VCO noise contribution is as small as the lowpass noise sources contribution at ubw frequecy point, if you go on widening the bandwidth, it will not help improving overall phase noise.
finally, all the designs depand on your psec.

[ 本帖最后由 faithfully 于 2009-3-25 08:47 编辑 ]

rainheart

thanks a lot for all

dacaili

eetopeetopeetop

mmic1978

   

原帖由 faithfully 于 2009-3-24 21:31 发表

                               
登录/注册后可看大图

first, VCO's phase noise  is 30dB/dec within corner frequency and then 20dB/dec. The transferfunction for VCO phase noise in pll is -40dB/dec within zero and then -20dB between zero and ubw, and then  ...

:victory: :victory:

mmic1978

   

原帖由 faithfully 于 2009-3-24 21:31 发表

                               
登录/注册后可看大图

first, VCO's phase noise is 30dB/dec within corner frequency and then 20dB/dec. The transferfunction for VCO phase noise in pll is -40dB/dec within zero and then -20dB between zero and ubw, and then ...

牛人，理解很深入啊~~

zzuwy

学习了

karsh

謝謝分享   ， 增廣見聞了

jjchun

thank you for sharing