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LMX2572EVM: start of chirp indicator

ehud zorea
Intellectual 290 points
Part Number: LMX2572EVM
Other Parts Discussed in Thread: LMX2491

Hi TI

I want to use the LMX2572EVM to generate a chirp  (ramp) but I need to sync "the start of ramp" to an external recording device.

is there a pin in the evaluation board that can be configured to indicate that the ramp has started?

thank you.

  • 0
    TI__Expert 8585 points

    Hello Ehud,

    The RAMP_EN indicates that the ramp has started.

    Regards,

    Kia Rahbar

  • 0 in reply to Kia Rahbar
    Intellectual 290 points

    Hi

    i saw that the LMX2572EVM has an issue of VCO calibration in the middle of long chirps:

    can this be overcome with a chirp of BW 500MHz (3.2GHz to 3.7GHz) during a chrip time of ~6ms

    if yes, how can it be configured to do so?

  • 0 in reply to ehud zorea
    TI__Mastermind 27581 points

    Ehud,

    First of all, if your VCO frequency moves this much, there will be calibration breaks in the middle of the ramp.

    This cannot be avoided.

    So if your application cannot tolerate calibration breaks (and there will be on the order of 50 of them), then this chip cannot be used.

    If you do nothing with the setup, the frequency changes before the VCO calibrates (dF) and the time it takes to calibrate (dT)  variable based on frequency and part.

    However, you can specify a value of dF that is shorter than what is needed and a value of dT that is longer than what is needed.  IN this way, you might calibrate slightly more often and it might take slightly more time, but the intervals when it calibrates and time it takes to calibrate will be completely predictable.

    TICSPro has a special ramp GUI for this that is very helpful.

    REgards,
    Dean

  • 0 in reply to Dean Banerjee
    Intellectual 290 points

    Dean,

    i highly appreciate your quick response.

    as I am building a radar device out of eval boards, i need to generate an ongoing chirp of roughly 3GHz to 3.5GHz (or ~3.2 to 3.7Ghz) with a chirp length of roughly 6ms. this will be a continuous cycle of chirp which I will not change often, if at all.

    can you please suggest a TI PLL-VCO synthesizer solution for this chirp generation (based on TI's EVAL)

    much thanks.

  • 0 in reply to ehud zorea
    TI__Guru* 81510 points

    Hi Ehud,

    500MHz linear ramp is not possible with LMX25xx devices as calibration break is required. 

    You can consider LMX2491 + external VCO to achieve linear ramp, if I remember right, you have made related posts in this forms already.