how to define PLL charge pump current value?

[yylei]

pll charge pump current

In 2.4G VCO,what is the current typical value? or how to calculate it from Wc,Kvco etc?
thanks.

 

[qiushidaren]

pll charge pump current value

I am also interested in it...

 

[khouly]

proportion charge pump pll

the current value will depend on the dynamic response of the PLL , settling time , and so on , the loop band width so u should get the optimum current

and also be aware in the new PLL's the current can be varied to get optimum results
also some PLL use dynamic current value which depend on the frequency jump , to speed up the acquisitions

khouly

 

[yylei]

thanks,khouly.
but in some applications,When calc LPF param, it all assume Icp is known,and LPF bandwidth is 1/10 comp frequency, the settling time is variable with the LPF param.Here I can't understand which param should be defined first in Icp and LPF param?

 

[rfsystem]

Because the phase to VCO voltage transfer function does not include any current or impedance the chargepump current is free to choose.

The chargepump current define the impedance of the loop filter components. In practice the chargepump current noise define the current value. Higher current reduce the noise impact on the loop. That is because the RMS of the noise increase by sqrt with the current level but the loop filter impedance scale down linear.

 

[nathanee]

This is a trade-off and depends on the application.

The lower charge pump current, the SNR is worse.
If the charge pump current is large, you have to take care up and down current mismatch.

 

[hackjiang]

Basically, Icp*Kvco proportion to Wc which is the open loop UGB.