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Design >> High-Speed I/O Design >> low BW pll loop filter
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Message started by raja.cedt on Dec 3rd, 2012, 10:25am

Title: low BW pll loop filter
Post by raja.cedt on Dec 3rd, 2012, 10:25am

Hello,
While reading a doc from ee times, i came to know that there are few applications which require PLL bw around 10Hz, i wounder how people manage that kind of filters. The only one idea came to my mind when i read this nA charge pump current  and very low resistance. I would like to hear some implementable solution.

Thanks,
Raj.

Title: Re: low BW pll loop filter
Post by smlogan on Apr 11th, 2013, 9:35am

Hi Raj,

Loop bandwidths of this magnitude are usually bulkwave quartz based. In other words, the Kvco is very low (often much less than 100 ppm/V). They are used for highly stable clocks often referred to as Stratum III or better. In some cases, the frequency varying element is non-crystalline, but also possesses an extremely low Kvco.

I hope this helps!

Shawn

Title: Re: low BW pll loop filter
Post by raja.cedt on Apr 11th, 2013, 12:39pm

hello thanks for the reply. Do you mean filter might be a SAW based and VCO based on crystal oscillator??

Thanks,
raj.

Title: Re: low BW pll loop filter
Post by Lex on Apr 12th, 2013, 2:43am

Go digital?

Title: Re: low BW pll loop filter
Post by smlogan on Apr 17th, 2013, 2:23pm

Hi Raj,

Sorry for the delayed response...

hello thanks for the reply. Do you mean filter might be a SAW based and VCO based on crystal oscillator??

Yes. A bulkwave quartz based oscillator (VCXO) will have a lower Kvco in general than a quartz surface acoustic wave based oscillator (VCSO). Hence, the latter is most often used in low bandwidth PLL.

Shawn

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