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LMX2595EVM: LMX2595EVM

Yogender Singh Singh
Prodigy 30 points
Part Number: LMX2595EVM
Other Parts Discussed in Thread: LMX2595

We are testing LMX2595 eval board. We are interesting in automatic ramping mode. Can you please help how to configure it in ramping mode with example. we want to sweep it from 935MHz to 960MHz. Let us also know variable parameters ( sweep time etc)  for sweep mode.

  • 0
    TI__Mastermind 28011 points
    Yogender,

    OK, 935 to 960 MHz, lets set the VCODIV=12 so the VCO ramps 11220 to 11520 MHz.

    Let's take this in steps.
    1. Step 1 is to set the expectations about the VCO calibration breaks. Expect that the VCO will stop 16 times for 25 us to calibrate. So this will cause breaks in your ramp. These breaks should be of a known time and known intervals. If you are wanting to do this without the VCO calibrating, the answer is a flat no.
    2. Step 2 is to get a ramping waveform running. I am attaching an example with TICSPro.
    3. Step 3 is to modify this. Change the threshold to 20 MHz and min calibration time to 25 us to be production worthy.

    In regards to the VCO calibration breaks, be aware that the VCO has 7 cores, but each of these cores has 183 different bands. Around 11 GHz, I am seeing the VCO able to go about 25 MHz upward and about 50 MHz downward without the need to re-calibrate for my worst case over temperature measurements, realize that these are just measurements; they do not imply any sort of guarantee.

    Regards,
    Dean
  • 0 in reply to Dean Banerjee
    Prodigy 30 points
    Ok, Thanks. Need setting in TICSPro for automatic ramping for frequency 935MHz to 960MHz
  • 0 in reply to Yogender Singh Singh
    TI__Mastermind 28011 points

    LMX2594Ramp.tcsOK, So assume the calibration breaks are OK.  Try this file.  I did it and it ramps 935 - 960 MHz.  You can load this in TICSPro.

    Regards,

    Dean

  • 0 in reply to Dean Banerjee
    Prodigy 70 points
    Hi Dean
    Thanks for the file. Now we want to know the total time for one ramp or sweep (935 - 960 MHz) including calibration break. also what will be the frequency step in this ramp ??

    Regards

    Nitesh
  • 0 in reply to Nitesh Kumar50
    TI__Mastermind 28011 points
    OK, if you do the 16 calibration breaks that are 25 us each, that's 400 us. Now I can make the ramp faster, but if I keep the default for each ramp of 100 us, that's an additional 1600 us. So that's 2000 us for the whole ramp. With an infinite loop badnwidth, it would be just the vCO calibration time, which is on the order of 400 us>
  • 0 in reply to Dean Banerjee
    Prodigy 70 points
    Hi Dean

    In our application we want to ramp LMX2595 as fast as possible without degrading its output frequency and amplitude accuracy.

    According to datasheet "For waveforms that are NOT calibration free, the slew rate of the ramp must be kept less than 250 kHz/µs." so it means if we want 300 MHz VCO ramp then it require at least 300x4 us =1200us. is it correct ?? or we can decrease this time with an infinite loop bandwidth.

    Reagard
    Nitesh
  • 0 in reply to Nitesh Kumar50
    TI__Mastermind 28011 points

    1234.LMX2594 Calibration Free Ramping.pdfNitesh,

    This slew rate does not get better for infinite loop bandwidth.

    Your calculation with slew rate of 1200 us is correct except the VCO also has to calibrate and this also takes time.

    I created this document about the VCO needing to calibrate.

    Regards,

    Dean