VCO(ring oscillator) phase noise/flicker noise analysis question!

Discussion in 'Cadence' started by like, May 2, 2007.

  1. like

    like Guest

    HI, I am doing some analysis of ring oscillator,expecially the phase
    noise analysis.

    I am using st120nm(0.13um) digital process to do the simulation.

    As lots of papers[1][2] have pointed out that the flicker noise in the
    tail current are one of the main contribution to the total phase
    noise. Therefore, I want to find a some way to build a practical low-
    pass filter within the tail current part.

    However, I can not find any effect when I build a low-pass filter
    together with the ring oscillator.

    As a simple examle, I build almost same circuit which has discussed in
    the paper [1][2], and add a very big capacitor between the bias point
    and ground. and then run the PSS --PNOISE analysis, however , there is
    almost no difference between the phase noise results by adding/
    excluding the capacitors. The capacitor may big as 100uf.

    I can find the phase noise performance decrease at 30dB/Decade in the
    normal PNOISE analysis, and by remove the sideband (-1), the phase
    noise performance decrease at 20dB/Decade which assumes that the
    flicker noise has been removed within the simulation environment. In
    theory, I assume that add the filters, the phase noise performance
    should be located between these two lines.

    However, now, the difficulty for me is that I can not find any effect
    in the simulation. Therefore, I think maybe the problems happens at
    simulation environment setup of the device model.

    can anyone give me some suggestion or ideas?

    The oscillator working almost at 4-5GHz,

    the relative harmonic: 1
    start stop range at 1K ----10M
    sweep type for nNO.steps 300-500
    sideband: 7/10 (exclude -1 for the purpose of removing flicker noise
    analysis as mentioned above)

    [1] Analysis and design of low-phase-noise ring oscillators
    Dai, L.; Harjani, R.;
    Low Power Electronics and Design, 2000. ISLPED '00. Proceedings of the
    2000 International Symposium on

    [2] Phase Noise and Jitter in CMOS Ring Oscillators
    Abidi, A.A.;
    Solid-State Circuits, IEEE Journal of
    Volume 41, Issue 8, Aug. 2006 Page(s):1803 - 1816
    like, May 2, 2007
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