PLL question

Discussion in 'General Electronics Chat' started by lkgan, Dec 20, 2009.

  1. lkgan

    Thread Starter Member

    Dec 18, 2009
    117
    0
    Hi,

    Thanks for explaining the usage of LPF in PLL. Currently I have another question on it. As the input frequencies to the PD differs, the output of the PD will have many high frequency pulses and eventually feed to LPF. My question is, why did the output voltage of LPF rise as there are pulses feed through it and slowly reduce when the width of the pulses become smaller? The output of the LPF is like a small transient. Thank you.
     
  2. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    Greetings Ikgan,

    Welcome to AAC.

    We ask that you start your own threads rather than append you question to an existing thread. This helps avoid confusion between your specific solution and that of the pre-existing thread.

    hgmjr
     
  3. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    If you think about it, the LPF is doing exactly what it is intended to do. The wide pulses out of the PD represent a predominance of low frequency components while the signal with very narrow pulses contains a majority of high frequency components.

    hgmjr
     
  4. lkgan

    Thread Starter Member

    Dec 18, 2009
    117
    0
    Hi hgmjr,

    Alright, I will start my own thread for new questions, thanks for reminding as I am new to forums. I got ur point of the high and low frequency of the pulses output from PD. So what you mean is that the output of the LPF is the average voltage of the pulses?
     
  5. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    That is indeed the case.

    hgmjr
     
Loading...