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WEBENCH® Tools/LMX2595: Various questions

Prodigy 10 points

Replies: 1

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Part Number: LMX2595

Tool/software: WEBENCH® Design Tools

  • Many of these questions refer to the Pllatinum Simulator

    1. When I run the Pllatinum simulator, what is the lock time (frequency settling) for full assisted calibration? I am thinking I have to include VCO cal table and partial assist, is that right?

    2. In lock time in the simulator, how does discrete lock time model differ from Analog lock time?

    3. Is there any documentaton on the simulator that answers the above and other questions?

    4. I need to operate just slightly below 19 GHz but would like to operate slightly above 85C. Is an EP suffix planned for this part?

    5. What degradation could be assumed up to a 100C case temperature?

    6. Would the LMX2820 be a better choice for me?

    7. What does MASH stand for and what does it mean? Appears to mean fractional.

    8. Will a single VCO calibration work over the entire temperature range?

    9. The simulation shows a phase detector spur in the range of -60 to -80 dBc (200 MHz fractional PFD). Analog Devices parts show a much lower spur (e.g. ADF4371). Is there anything that can be done to reduce this spur? Will more loop filtering help or not? Is it really that high? 1

    10. What are S1, S2 and S3 in the simulator?

    11. How do I pick the VCO for the LMX2595 in the simulation? It lets me pick any VCO for any frequency, isn't this wrong? 

    12. The simulator does not seem to account for the internal X2 of the LMX2595, is there a way to include this?

  • Hello Denny,

    1. For full assist there is only analog lock time, as the VCO settings are programmed into the device. I would exclude both VCO Calibration Time and Partial Assist VCO Calibration
    2. The "Discrete Lock Time Model" section has a little "?" button next to it which describes the model
    3. There is not documentation, however  the "?" buttons serve as guidance
    4. I do not believe so, we do have the LMX2694-EP however this is the equivalent of the LMX2594 not the LMX2595.
    5. The device may not perform as specified if used outside the recommended operating conditions.
    6. The LMX2820 has better phase noise and has a dedicated SYSREF output, additionally the outputs can each have their own divider.
    7. MASH_ORDER or Fractional order, distributes the power of spurs over the spectrum to reduce the magnitude of the larger spurs, this may increase the overall phase noise
    8. Yes, the PLL will stay locked across the temperature range after VCO calibration is complete.
    9. You can use a higher order MASH_ORDER
    10. S1, S2 and S3 can be used to find spurs in the vicinity of a frequency you think there will be a spur. For example if you think there will be a spur around 6050 kHz offset you can enter 6050 into S1 and the tool will pull the location of the spur around that offset.
    11. What frequency are you using? In general you would check the box that says "Model as Multicore VCO"
    12. If you type the required output frequency into the Fout box, the channel divider will turn into a x2