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LMX2491: Matching question

Aaron Liao96
Prodigy 60 points
Part Number: LMX2491

1. How can I make sure OSCin/OSCin* has well matching? 

2. In the datahseet, figure 14. it shows there is a T pad attenuator bewteen oscillator and LMX2491, why do we need this T pad? it seems provide 6 dB attenuation, too.

Thanks~

Aaron

  • 0
    TI__Mastermind 28011 points
    Aaron,
    1. For optimal spurious, you want the impedance as seen looking out of the OSCin* pin to be similar to that looking out of the OSCin pin. The impedance is relatively high, but we do not test or guarnatee this, so you want this to be more determined by external components

    2. At higher frequencies, maybe the impedance is not high enough relative to 50 ohms, so a T pad is a more conservative approach.
    Sure, you could remove the 50 ohm and pad entirely and get higher signal swing, but then matching might not e as good.

    Regards,
    Dean