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altpll "loop filter resistance" parameter: resistance to filtercap or to charge pump?

Altera_Forum
Honored Contributor II
‎07-11-2016 11:46 AM
900 Views

Hi, the altpll reconfiguration interface has a parameter called "loop filter resistance". 

 

Is this the resistance imposed between the charge pump and the VCO control node, or is it the resistance between the VCO control node and the filter capacitor (i.e. the capacitor whose capacitance is one of the other parameters)? 

 

Put another way: is this R1 or R2 in the figure below ("from PLL" means "from charge pump")? 

 

If it matters, this is for a Cyclone III. 

 

Thanks.
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Altera_Forum
Honored Contributor II
‎07-12-2016 03:48 PM
232 Views

It would be R1. See attached .jpg. You would think this would be in the altpll user guide, but alas it is not.

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