Phase Noise In PLL

Discussion in 'General Electronics Chat' started by lkgan, May 24, 2010.

  1. lkgan

    Thread Starter Member

    Dec 18, 2009
    Hi everyone,

    Currently I am studying PLL phase noise and really have difficulty in understanding them. The attached pic shows the PFD-referred noise (low frequency) and VCO-referred noise (high frequency). Here are the few questions that I don't understand about the slide.

    1. How do we calculate noise? Base on the graph, what does the function S(f) mean?

    2. The VCO noise shows -20dB/dec, means that at high freq, the VCO noise is attenuated? But the lower graph shows the it's high pass filtered?

    3. The optimal bandwidth is the meeting point of the PFD and VCO noise which is shown in the upper right graph. What does it mean Higher bandwidth will pass more PFD-referred noise and Lower bandwidth will pass more VCO-referred noise? Isn't higher bandwidth will pass more of both noises?

    I am really having difficulty in studying phase noise, can someone please provide my some material to start from basics to understand them. I tried to search from internet, but seems like the materials are quite tough. Please help. Thanks.