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Phase locked loop question

Discussion in 'Electronic Design' started by George, Jun 28, 2007.

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  1. George

    George Guest

    Just looking for a very quick ballpark indication, nothing accurate needed.

    Is it easy and cheap to build a PLL with one degree resolution of a 30 kHz
    sinusoidal signal input asuming low pre-detection noise (S/N > 50 dB) and
    100 millisecond acquisition time?

    Thanks, George
  2. Phil Hobbs

    Phil Hobbs Guest

    50 dB SNR means an instantaneous phase uncertainty of
    1/(sqrt(2)*10**2.5) radians, or about 0.13 degree, which is fine. If
    you know that your signal is always near 30 kHz, you can make a VCO with
    a restricted range, so that it will pull in very rapidly. (Simple PLLs
    pull in nice and fast if the frequency offset is less than a few times
    the loop BW.)

    So something like a NE565 or MC14046 can do this, no problems. You'll
    want to use an op amp in the feedback loop if you use a 565 or the XOR
    phase detector of the '4046. If the sinusoid is nice and big, you can
    use the frequency-phase detector in the 4046, which is even easier--no
    op amp required, no limitation on pull-in range.


    Phil Hobbs

    (Do they even make 565s any more?)
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