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First post! n00b questions about PLL

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tony ennis

New Member
Hello! Yes, I am a neophyte. :D

I am contemplating a PLL that would need to multiply the frequency of a low Hz pulse by 200. Is this possible/practical, or do I need multiple PLL stages.

Or are there better ways to proceed?

Also, how does one know if a part is obsolete? I saw on one forum (this one?) a guy mentioning an old EPROM he was going to use. People laughed at him (nicely) about raiding the Smithsonian for parts.

But how does a beginner know if a component is out of date?
 

MikeMl

Well-Known Member
Most Helpful Member
Hi Tony,

If the reference clock for your PLL is very periodic (i.e. stable frequency), then a 200:1 frequency divider in the feedback loop is doable. If the ref. freq is only tens of Hz, then it will take a long time (up to several seconds) for the PLL to establish lock at start-up. If there is a lot of phase/frequency jitter in your reference, you can steer your vco to the "average" phase/freq, but there will be a slow time-constant in the response of the VCO if the ref suddenly changes.

I did something like this once using the now dated (maybe obsolete) LM565.

As to making sure parts are still available, go to Mouser.com or Digi-Key.com, and look up the parts. Sometimes the OEM will publish "LAST ORDER" dates on their web site for parts that are about to be obsoleted.
 
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unclejed613

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Most Helpful Member
back in the 80's there was a circuit in either Popular Electronics or Radio Electronics magazine for a PLL that was used for measuring sub 1hz signals by multiplying the frequency by 100 and feeding the VCO output into a frequency counter. once the lock indicator lit, then the VCO was locked to the input signal, and the frequency counter reading was accurate
 

Tesla23

Member
back in the 80's there was a circuit in either Popular Electronics or Radio Electronics magazine for a PLL that was used for measuring sub 1hz signals by multiplying the frequency by 100 and feeding the VCO output into a frequency counter. once the lock indicator lit, then the VCO was locked to the input signal, and the frequency counter reading was accurate
This it? X100 Frequency Multiplier
 

unclejed613

Well-Known Member
Most Helpful Member
that was probably it, but i'm not absolutely sure since i couldn't read the page. i got some kind of notice that i had gone over some limit on viewing the page.
 
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