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LMX2581: Supressing REF multiplication wave on the Output

Part Number: LMX2581

Hi team,

My customer would like to find a synth IC which doesn't have less REF multiplication wave on output.
If you have any such specifications or measurement results which may help, could you please recommend?
(It means the harmonics of REF itself, not the reference leak or the difference frequency component of PFD that comes out on both sides of the synth output.)
In addition, if you have any knowledge that emits less REF multiplication wave to the synth output, please let me know.

He doesn't want to output REF x N - LO signals at the mixer output.
He assumes that the above signal will be generated when the synth output is multiplied by REF and the signal is input to the mixer.

If you have any insights, please let me know.
In addition, if there is a synth IC that features that less REF multiplication wave go out, please recommend it.
Thank you very much.

Itoh

  • Hi Itoh-san,

    I think you are talking about reference spurs.

    Usually a small amplitude and high slew rate reference clock will produce less reference spurs.

    For LMX2581, OSCin requires 0.4Vpp - 1.7Vpp signal. A single-ended LVDS signal (400mVpp) may be possible, otherwise a LVPECL signal (usually greater than 600mVpp) is a good reference clock.

  • Hi Noel-san,

    OK.

    Could you please recommend VCO integrated synthesizer which is able to suppress REF spur as much as possible?

    My customer assumes that REF supur depends on frequency multiplication inside IC, so the REF spur level depends on IC.

    Is this correct?

    Regards,

    Itoh

  • Hi Itoh-san,

    Since VCO and PLL are all integrated into one small chip, signal crosstalk within the chip is unavoidable. Crosstalk mechanism is very complex and hard to predict, so nobody know the ref spurs level until we have the part and measure it. 

    What is your customer's specification on ref spurs? can they share their reference clock freq and desired output frequency?