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LMX2572: Sweep from 30Mhz to 3GHz

Matti Limingoja
Prodigy 100 points
Part Number: LMX2572

Hi,

Our customer needs wideband frequency sweep from 30MHz to 3GHz. Is LMX2572 capable of doing that? And about those VCO calibration cycles, how many calibration cycles there are when sweeping that band?

And are calibration cycles always needed if temperature remains same?

Regards Matti

  • 0
    TI__Mastermind 28001 points
    Yes, you can sweep this whole frequeny band. But realize that there will be some manual programming as you do have to change the divider.

    The calibration cycles are always needed unless your frequency ramp is really small, say <5-10 MHz.
    As for the calibration cycles, the way it works is that you tell the VCO how often it has to re-calibrate and how much time you allow. If you don't calibrate soon enough, the VCO will on its own. The idea is that there will definitely be breaks where the VCO has to re-calibrate, but at least they can be made to occur at uniform intervals of time of known length. The amount the VCO can go without calibration depends on a few factors. Going up, maybe it can go 20 MHz and going down, more like 10. But we don't test this in production, so you would want calibrate more often to be safe.

    Dean
  • 0 in reply to Dean Banerjee
    Prodigy 20 points
    I tested and found that I can go 30MHz without VCO calibration. Longer than that, the VCO will calibrate every 30MHz. The problem I have is that in the data sheet it says VCO cal time is less than 20us, but from my test it looks like close to 100us. I am missing something here but I don't know what. Any suggestions/advice? Thanks.
  • 0 in reply to qzn_1234
    TI__Guru** 107830 points
    Hi Matti,

    VCO calibration is not a constant, it depends on several variables such as OSCin frequency and register configuration. VCO calibration time can vary from <10us (with full assist) to >100us (without any assist).
    During automatic frequency ramp, "close frequency assist" is used for VCO calibration. Typical calibration time is about 30 to 40us.
    So I would suggest a 100us (VCO calibration time + closed-loop lock time + margin) pause time for automatic frequency ramping.