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LMX2572LP: Input and Output Impedance

Gordon McKenzie
Intellectual 610 points
Part Number: LMX2572LP

Hello,

is there any data on input impedance on the reference oscillator input and output impedance on the RF outputs?

The datasheet (section 7.3.1) simply says the input is high impedance but I see no value given - can I stick the output of a TCXO straight in with just an AC coupling cap or does it need some kind of matching network here?

Same issue at the RF output. Datasheet (section 7.3.7) just says output impedance is very small (how small?) and can be used to drive a 50R load. Can I take the output of the buffer and drive a 50 Ohm line (via AC coupling cap) or do I need some kind of match here? And does it matter whether I drive it single-ended or differential? I've had problems with inter-stage coupling before, and I really want to make sure I have this set up properly before commiting to using it in a design.

Thanks,

Gordon.

  • 0
    TI__Guru** 107290 points

    Hi Gordon,

    We don't have exact data on the impedance.

    Yes, you can simply AC-couple TCXO output to OSCinP and leave OSCinM floating. There is virtually no performance difference when OSCin is driven single-ended or differential. 

    Similarly, output can drive 50Ω line and load without matching. Unused pin should be AC-couple to ground via a 50Ω resistor. See Figure 158 for details.