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Frequency locked loops

Discussion in 'General Electronics Discussion' started by bladesong, Sep 20, 2012.

  1. bladesong

    bladesong

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    Sep 20, 2012
    Hey everyone

    I've been scouring the internet looking for any information on frequency locked loops but it's been dismal at best. I'm not actually sure if a phased locked loop will do the same thing, but essentially I'm looking for something to automatically tune to a given frequency.

    Is there a real difference between FLLs and PLLs? If so, where can I find information on this?

    Additionally, I am trying to avoid use of modern chips like 4046s, instead preferring transistors, or even better, if possible, passive components only. I don't know if this is possible.

    Could anyone help me shed some light on this?

    I'm mostly interested regarding autotuning to a signal within a given bandwidth, such that the circuit would automatically retune itself to the strongest frequency.
     
  2. davenn

    davenn Moderator

    13,244
    1,744
    Sep 5, 2009
    Hi there
    welcome ti electronics point :)

    PLL's are what are used these days, I havent seen a FLL for many years

    and for the complexity of what you want to do you you will have to use PLL chips and other controllers of some sort
    I strongly doubt that you will achieve it with discrete transistors

    Dave
     
  3. bladesong

    bladesong

    3
    0
    Sep 20, 2012
    Hi Davenn, thanks for your input.

    So what are the differences? Where would I be able to find resources, or preferably, schematics on one?

    Given the intended application, chips and controllers are not possible. Basic solid state like transistors and op-amps, maybe, but definitely not microcontrollers and the like. It should be possible as they had this stuff back in the 60s and 70s, and had AFC even back in the days of the tube.

    This has to be a purely analog project which is why I have the constraints I do. Can anyone provide any insight?
     
  4. duke37

    duke37

    5,211
    718
    Jan 9, 2011
    The 4046 data has two comparators. It would be difficult to make one of these in discrete components. Can you make an exclusive or gate?

    If the frequencies are locked, then the phase difference will be constant so I do not see the difference between frequency lock and phase lock.

    FM radios use frequency correction with a Foster-Seely detector but this is not frequency or phase lock, it just brings the frequency somewhere near the correct value.
     
  5. bladesong

    bladesong

    3
    0
    Sep 20, 2012
    Hey duke37,

    Thank you. That makes a lot of sense as I've read and heard that PLLs are important in coherent operations and that that's primarily the only feature lost when using an FLL.

    I'm considering using TTL logic to construct the circuit but if there are any useful alternatives for auto-track frequency following/tuning, I'm all ears. This is kind of just a starting point.

    Thanks
     
  6. davenn

    davenn Moderator

    13,244
    1,744
    Sep 5, 2009
    No I dont have any ccts for discrete device PLL's
    I wouldnt even consider doing it that way, there are just so so many PLL chips available. I wouldnt want to waste my time with discretes

    Dave
     
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