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LMX2594: OUTx_PD=1 output residiual power

Pavel Pershin
Prodigy 40 points
Part Number: LMX2594

Hi team. What is the residual power at Output A and Output B in POWER DOWN mode (R44[7] or R44[6] is set to 0) reference to maximum output level? The most interest for me is the next combination: Output A in active mode and Output B in PD mode (R44[7]=1, R44[6]=0). What is the residual power at Output B in this case? Is it like Xtalk=-50 dBc (table 6.5 of datasheet)? How it will be changed if at the same time power down external Vcc pullup at  Output B?

  • 0
    TI__Guru** 107780 points

    Hi Pavel,

    When the buffer is powerdown, the output signal is around -4x dBm.

    If you only need one output buffer, you can leave the pins of the unused buffer open. The buffer is an open-drain buffer, without the external pull-up, it should not working and I believe the output signal will be less than -4x dBm.

  • 0 in reply to Noel Fung
    Prodigy 40 points

    Noel, thank you for your answer. In my application I need both outputs: Output A is always on and Output B some time turn on and some time turn off. The level of an Output B Power Down state is critical for me. Can you measure a real level of an Output B Power Down state for frequency band 10 - 15 GHz?

  • 0 in reply to Pavel Pershin
    TI__Guru** 107780 points

    Hi Pavel,

    We will take some data tomorrow. Stay tuned.

  • 0 in reply to Noel Fung
    TI__Genius 11900 points

    Hello Pavel,

    I tested this in the lab on the EVM, for 14 GHz VCO, OUTA_MUX = VCO, OUTB_MUX = VCO

    • When OUTA_PD = 1  and OUTB_PD = 1, power at RFOUTBP = -39 dBm (RFOUTBM, RFOUTAP, RFOUTAM terminated to GND with 50-ohm)
    • When OUTA_PD = 1 and OUTB_PD = 1, power at RFOUTBP = -38 dBm (RFOUTAP, RFOUTAM terminated to GND with 50-ohm)
    • When OUTA_PD = 1 and OUTB_PD = 1, power at RFOUTBP = -38 dBm (no outputs terminated to GND with 50-ohm)
    • When OUTA_PD = 0  and OUTB_PD = 1, power at RFOUTBP = -26 dBm (RFOUTBM, RFOUTAP, RFOUTAM terminated to GND with 50-ohm)
    • When OUTA_PD = 0 and OUTB_PD = 1, power at RFOUTBP = -26 dBm (RFOUTAP, RFOUTAM terminated to GND with 50-ohm)
    • When OUTA_PD = 0 and OUTB_PD = 1, power at RFOUTBP = -26 dBm (no outputs terminated to GND with 50-ohm)

    I briefly checked at 12 GHz and 10 GHz and saw that the case where both outputs were turned off resulted in much lower power in the -40 dBm to -50 dBm range. There wasn't a significant difference in the one output powered down case.

    Thanks,

    Vibhu

  • 0 in reply to Vibhu Vanjari
    Prodigy 40 points

    Hello team!

    Noel, Vibhu. Big thanks for your answers.