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LMX2595: Schematic review for LMX2595

Part Number: LMX2595

Hi team

We are using LMX2595 in our design to generate 16GHz output. May I request you to review the below attached schematics


I also request you to verify the loop filter calculation to generate 16GHz output with 10MHz input.

Few queries on LMX2595:

1. While using RFOUTA as single ended output how to terminate the RFOUTAM pin 

2. If RFOUTB is not required can it be left floating

3. Can the Sysrefreq, Rampclk, Ramdir be left floating if unused




  • Hello Keerthana,

    1. RFOUTA_M should be terminated similarly to how you have terminated OSCINM, with a 50Ω resistor to GND instead of directly coupling the output capacitor to GND. R308 should still be populated as drawn, because it is required to bias the CML output stage.
    2. RFOUTB can be left floating. The output buffer can be powered down in software.
    3. SYSREFREQ, RAMPCLK, and RAMPDIR should be shorted to GND if unused.

    For the loop filter, I have assumed 15mA charge pump gain and a relatively high quality 10MHz OCXO source. I find that the loop is stable with around 30kHz loop bandwidth, 70° phase margin, and mostly reference and VCO-dominated jitter. I have attached a PLLatinum Sim file with the simulation results.



    Derek Payne

  • Thanks Derek we will update the schematics as per your feedback