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Minimum possible voltage on the loop filter in a charge pump PLL

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amsdesign

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Hi,

I am trying to make my VCO run across all different process corners.
For the slow corner I need a very small control voltage to drive the VCO at the same frequency as required in the fast and typical corners.

But how small can this voltage be? Can it be in micro volts? The Loop filter is as shown below.

loop_filter.png
 

Hi,

the shown components will not be problematic for the low voltage.

It is more likely that other - active - components are more problematic. It surely is specified in the datasheets.

Klaus
 

It surely is specified in the datasheets
Notice that this is an IC design question, there's no datasheet, instead the IC designer (the OP) has to answer the question himself.

I agree that the useful control voltage will be restricted by the linear PFD and VCO linear range.
 

At very low control voltages you may find that ground noise
(like, if you use an external loop filter cap) may be proportionally
more of a problem to phase noise / jitter. Also what happens
when your VCO control offset gets to the wrong side of gound?

If you have an active loop amp producing this near-ground
voltage, realize that all op amps lose gain as they approach
the rails, and your loop compensation may need work to
accommodate that in the corners.
 

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