# 4046 pll Filter Design Help

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#### sebosfato

##### New Member
Hello i'm designing a Phase locked loop circuit and i need help with the filter calculations for Phase comparator 2 for being able to choose the best components for it. My vco goes from 8809Hz to 96899Hz R1 = 10k R2 = 100kvr + 10k C1 = 1n And i have 3 divide by 10 counters in line to have other ranges of frequencies like from 8hz to 96 - 88 to 968hz - 880hz to 9689hz and 8809hz to 96899hz. The filter will be subjected to frequencies from 8 hz and 96khz. I calculated 100k for R3 and R4 10% of R3 so R4 10K and the capacitor C2 1uf to have a 1,5hz cutt off. I don't know if it is right, any help would be appreciated.

I would like to know also the voltage range of the vco. And if it change if the vco have an off set.

This links are very good information on 4046 pll
https://www.electro-tech-online.com/custompdfs/2009/06/phase-ll-scha003b.pdf
https://www.electro-tech-online.com/custompdfs/2009/06/scha002a.pdf

The pdf here is the calculations i made for the vco, filter and frequency ranges.
Thank you.

#### Attachments

• pll final.pdf
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#### schmitt trigger

##### Well-Known Member
if your minimum oscillator frequency is 8809 Hz, you don't need a low pass filter with a cutoff frequency of 1.59 Hz. The settling time would take forever.... The PLL would not be able to track any frequency changes.

As a starting point, make it 1/10 of your lowest VCO frequency, or 880 Hz.

#### sebosfato

##### New Member
Ok i'm going to try that
Thank you very much

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