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frequency synthesizer

Discussion in 'Electronic Design' started by Lost'n Found, Aug 8, 2006.

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  1. Lost'n Found

    Lost'n Found Guest

    Hello,

    I was reading about frequency synthesizers and it seems I am missing some
    concept.

    These synthesizers can generate higher frequency. On the specification
    sheets, I read that we can divide the reference frequency by certain
    factors. My question is: If we are dividing the frequency, why are we
    getting much higher frequencies at the output?
     
  2. Tim Wescott

    Tim Wescott Guest

    A:

    You can find out amazing amounts of stuff doing web searches, like on
    "frequency synthesizer theory".

    B:

    You can only get frequencies out that are multiples of the reference
    frequency going to the phase detector (unless you're using a fractional
    N synthesizer -- You can find out amazing amounts of stuff doing web
    searches). It's easier to make a good clock source from a crystal, so
    if you want to have a synthesizer work in 5kHz steps you'll want to
    generate a clock at (say) 5MHz, divide it by 1000, then synthesize a
    frequency from that in 5kHz steps.

    --

    Tim Wescott
    Wescott Design Services
    http://www.wescottdesign.com

    Posting from Google? See http://cfaj.freeshell.org/google/

    "Applied Control Theory for Embedded Systems" came out in April.
    See details at http://www.wescottdesign.com/actfes/actfes.html
     
  3. Rich Grise

    Rich Grise Guest

    This might be helpful:
    http://en.wikipedia.org/wiki/Frequency_synthesiser
    That's just one of "about 381,000 for 'frequency synthesizer'" at
    http://www.google.com/search?q="frequency+synthesizer"

    Have Fun!
    Rich
     
  4. Andrew Holme

    Andrew Holme Guest

    Because we divide down and then multiply up. A common reason for doing so
    is to reduce the step size / comparison frequency.
     
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