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Original question:

LMX2594: ramping function does not work

LMX2594: I'm looking for maximum ramp without calibration

Vinayak Chabbi
Expert 1100 points
Part Number: LMX2594

Hello,

I'm looking for maximum frequency of Ramp without calibration.

E.g, If my start frequency is 8GHz and I want Ramp function and my Fpd is 500MHz and what is the maximum output frequency I can get without calibration?

Regards,

Vinayak

  • 0
    Expert 1100 points

    Hi,

    I have few doubts which I couldn't get details in datasheet of LMX2594.

    Please refer the below question with attached waveform image.

    1. How to calculate the timing of ramp 0  and ramp1 (t1 to t2 in the image).

    2. What is the max and min frequency of f1 and f2 .

    3. What is the rise time and calibration time (τ1 and τ2), and how do we calculate ?

    4. What is max and min of Δf? and how to calculate it?

    5. In ramping configuration, while calibration what will be the output of VCO?

    6. What is the min and max frequency for Δf, without calibration.(i.e, I want to calibrate start of the ramp and then it should ramp without calibrating)

    If any example other than datasheet examples which explains the above questions in detail, will be more helpful.

    Regards,

    Vinayak

  • 0 in reply to Vinayak Chabbi
    TI__Mastermind 18070 points
    Hi Vinayak,

    I'm not very familiar with ramping function. Our expert on this is out of office today. I will get you the answer on Friday.

    Regards,
    Hao
  • 0 in reply to Vinayak Chabbi
    TI__Mastermind 27851 points

    Vinayak,

    OK, for starters, lets talk address question #6, or the "Calibration Free Range".  We don't give any spec for this in the datasheet, but the attached document goes into good detail.  It depends on frequency and temperature, but something realistic is on the order of 25 MHz the VCO can go without calibrating.  Understand that although there are 7 cores, there are actually 183 different bands per core. 

    So first question back to you is is this acceptable?  If not, then no need to go on.

    Assuming it is, here's answers to your other questions.

    1.  For the ramp, you can force a minimum calibration time for the VCO.  If the VCO calibration time actually takes shorter than this, it will wait.  This allows even step intervals.  The minimum VCO calibration setting varieswith conditions and setop, but maybe assome 20-25 MHz.  our TICSPro software actually does a good time of calcuating this.

    2.f1 min is 7500 MHz f2 max is 15000 MHz.  But if you set the output divide by 2, these values are both divided by 2.

    3.  Take the step length by the number of steps.   I really encourage you to try our TICSPro software that has a ramping GUI to address these issues.  Our datasheet explains alsok but the TICSPro GUI is less tieto interpret.

    4.  The rise time can be calculated.  if you take RAMPx_LEN times the phase detector period, you ge the length of the ramp without calibration breaks.  So you can find the slope.  The length of the calibration breaks and how long they take are specified by the user (but can't say calibration break is 0 us or they never happen, uness your frequency chang eis small.

    6.  During ramping, user has a choise.  If OUT_FORCE=0, it's muted, otherwise it's active.

    Regards,
    Dean5621.LMX2594 Calibration Free Ramping.pdf