PLL active loop filter

[hakihaki]

Hi~:razz:

I've designed a PLL with the 3rd passive RC Loop filter. But, after layout, the size of RC filter was so big and same area with the integrated inductor.

So, instead I thought the active loop filter. And I have question.

Is the active filter helpful for reducing layout size(cap)?

Thanks

 

[Milad-D]

It is possible but the filter will be more nonlinear. The simplest way to reduce the cap size is to use miller idea. if you have an amplifier with gain of a, you can have effective cap of c(1+a).