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Discussion in 'Electronic Design' started by RealInfo, Mar 17, 2013.

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  1. RealInfo

    RealInfo Guest

    Hi all

    My question is about the structure of a digitally controlled radio like this

    From the point of view of the micro controller that controls it .

    If I understand well that micro does 3 main things
    1> controls the frequency of the PLL that functions as a local oscillator
    used by the rf mixer
    2> sends the relevant data to the LCD .

    3> respnds ti the buttons .

    I want to concentrate on the first two .

    How the micro controls the PLL so it will produce the exact frequency
    that the LCD displays.

    And how the micro translates the frequency knob to a chosen frequency .

  2. Jasen Betts

    Jasen Betts Guest

    typically the PLL is a VCO which is divided and compared with a fixed
    clock, the microcontroller will program clock divider - it may even
    use an internal counter to do this. this divided clock is compared
    with a reference clock and the difference is fed back to control the VCO
    probably some sort of quadrature encoder and a the micro just counts
    up or down as the knob is turned.
  3. Tauno Voipio

    Tauno Voipio Guest

    Many of the current designs are using Direct Digital Synthesis (DDS)
    instead of a PLL, though also PLL designs are used. The details of
    frequency set-up depend on the frequency generator chip (or chipset)
    chosen and the selected frequency generation scheme.

    For a primer on DDS, see:

    There are also links to chip datasheets and app notes for controlling
  4. RealInfo

    RealInfo Guest

    Many thanks you all
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