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LMX2595: LMX2595, LMX2594

Alex Cohen
Prodigy 30 points
Part Number: LMX2595


Hi,
I'm planing to use LMX2595 as a wideband synthesizer and I want to implement Harmonics Filter Bank to reduce harmonics content.
In order to reduce the number of RF switches I want to use both lines on each channel, RFoutAP and RFoutAM to drive separate filters.
Can I use both lines while one line will always see "open" and the other "load", I haven't seen any reference of terminating (50 ohm) one of the lines when using in Single End mode.
Thanks
Alex

  • 0
    Prodigy 30 points
    Sorry, found it.

    8.1.4 RF Output Buffer Pullup
    The choice of output buffer components is very important and can have a profound impact on the output power.
    Table 39 shows how to treat each pin. If using single-ended, the pullup is still needed, and user puts a 50-Ω
    resistor after the capacitor.

    How ever If I maintain 50ohm Layout can I use separate loads on each line?
  • 0 in reply to Alex Cohen
    TI__Guru** 111060 points
    Hi Alex,

    Pull up is always required because the buffer output is an open-drain structure. Since it is a differential buffer, it is recommended to keep both output pins balance. That is, they should see similar load impedance. It is not a good idea to have one pin seeing a 50 Ω load while the other pin seeing an open.
    LMX2595 has two output buffers, may be you can implement different filter on each buffer.
  • 0 in reply to Noel Fung
    Prodigy 30 points
    Thanks Noel, I figured it out too.
    I know puling up is mandatory but I wasn't sure about the balance issue.
    I'm using both LMX2595 output buffers so I will simply use an extra RF switch for my design.
    Thanks for the help.
    Alex