Pll and VCO phase noise analysis

kkliaw77

Hi, i am currently running VCO phase noise analysis and plotting the phase noise in the frequency domain. Do i need to know the lPLL oop bandwidth so that i can convert the phase noise to phase jitter? Other than VCO, is there any other source such as reference input, phase detector and loop filter contributing phase noise also? I am constructing the whole PLL so that i can run phase noise analysis on top of whole PLL but i would like to know how related the results between phase noise in VCO and those in PLL? can someone share me his/her experience in designing VCO or PLL to have a low phase noise?

needforspeed

you may use noise transfer function to fit vco noise to total pll phase noise.
you don't have to know loop bandwidth to convert phase noise to phase jitter.

kkliaw77

Could you elaborate more on how can i use noise transfer function to fit my VCO noise into total PLL phase noise?

needforspeed

vco's contribution to pll phase noise could be calculated by using VCO phase transfer function which you could find in many PLL textbooks.
first, you need to simulate vco to get its gain. then, find out your VCO phase transfer function with gain and LPF parameters. finally, pll phase noise due to vco could be obtained by using VCO phase noise and phase transfer function.
good luck!

mmic1978

原帖由 kkliaw77 于 2009-3-29 01:00 发表

                               
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Could you elaborate more on how can i use noise transfer function to fit my VCO noise into total PLL phase noise?

   good~!

kkliaw77

Is the VCO phase transfer function exactly same as high pass filter? For my understanding, we need to find out the -3dB cut-off frequency of this VCO phase transfer function and then applied this cut-off frequency into VCO phase noise plot. All the phase noise more than this cut-off frequency will be propagated into VCO output since VCO will not track the frequency more than this cut-off frequency. With this cut-off frequency and ending frequency (~100Mhz), we can convert the phase noise into phase jitter from the VCO phase noise using spectreRF.

needforspeed

原帖由 kkliaw77 于 2009-3-30 23:17 发表

                               
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Is the VCO phase transfer function exactly same as high pass filter? For my understanding, we need to find out the -3dB cut-off frequency of this VCO phase transfer function and then applied this cut- ...

You don't have to find out what cutoff exactly is. VCO phase transfer function is 1/(1+Hol(s)), where Hol(s) is the open loop transfer function. It's easy to get it by using linear model.

kkliaw77

Sorry..it is not cut-off frequency. Instead, we need to know PLL loop bandwidth. To reduce the VCO phase noise, we need to maximize the loop bandwidth since VCO phase noise transfer function is a high pass filter

kkliaw77

Could you share with me your matlab script to run the whole PLL phase noise?

ralphtwtw

learing !!