Help me choose the optimum value of charge pump current

[savithru]

hi all,

I need to operate my pll around 200MHz. Lock time is not a criteria..

For me Jitter is the main Criteria.( My VCO is Ring type which has very bad Jitter performance..)

Now Can u pls guide me what is the optimum value of Charge pump current , I can choose.. Is that 25uA is very less?

Does the Icp has any effect on Jitter?

pls reply

Thanks & Ragards
SavithRu

 

[ieropsaltic]

Re: Charge pump current?

I don't think that determining the optimum value of the current isn't staight forward. High current values will lead to higher Kd which helps to decrease the required minimum value for Kv thus decreased noise at the output for different noise sources .However, increasing the current will lead also to higher gm thus more noisy charge pump .This would require iterations at the design .

 

[hi_tech]

Re: Charge pump current?

change the architecture of VCO, becoz VCO contributes more jitter than charge pump

i.e. use differential type ring oscillator