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Original question:

LMX2581: PLL doesn't lock if ref clock is lost then re-input the reference clock

LMX2581: Does fractional dithering work for improving phase noise performance?

Toshihiro Watanabe
Genius 10235 points

Part Number: LMX2581

Hello,

This is the relating question as below. In the below configuration which is fractional mode, we changed FRAC_DITHER setting from STRONG to WEAK then the phase noise performance seems better. Is fractional dithering for only improving spur performance? Or does it work for phase noise improvement?

Best regards,

Toshihiro Watanabe

  • 0
    TI__Guru** 122180 points
    Hi Watanabe-san,

    Dithering is useful when you have spurs issues. If there is no spurs, for example, with an integer channel, enable dithering may actually make the phase noise worst.
    When you have spurs, dithering can help reducing the spurs level by randomizing the fractional engine. The drawback is, phase noise will be higher.
    in this case, you don't have spurs. So you can actually disable dithering.