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LMX2594: ramp generation

FRANCESCO FIUME
Prodigy 170 points
Part Number: LMX2594
Other Parts Discussed in Thread: LMX2492,

Good morning,

I would like to ask you for detailed information on how to create a ramp using the LMX2594EVM board. Putting into practice the instructions provided by the attached pdf, conflicts are generated regarding the setting of

the frequency:

changing the values in the "RAMP" window also change abnormally in the "PLL" window.

You can give me all the detailed information to be able to generate a ramp with the following values: Fstart = 9187.5 MHz, Fend = 9562.5 MHz, duration = 1000 us. Which commands enable in the "PLL" and "RAMP"

windows? Thanks for your cooperation. 

www.ti.com/.../LMX2594EVM

LMX2594 EVM Instructions – 15-GHz Wideband Low Noise PLL With Integrated VCO

  • 0
    TI__Mastermind 27981 points

    Francesco,

    Attached is a file you can load into TICSPro.  A few points.

    1.  To start the ramping, toggle the RAMP_EN bit.  In other words, the action of programming register R0 with RAMP_EN=1 activates ramping.

    2.  Realize that there will be calibration breaks for the VCO to calibrate and these are mandatory.  You can set a time and interval for them, but there is a maximum frequency change and minimum calibration time for these. 

    3.  Understand that these calibration breaks are the way it works.  Only if the frequency change is small can you ramp without the VCO not taking time to calibrate.   For some applications, this is a deal breaker, but that's the way it is.  The other alternative is to use an external VCO part like the LMX2492.  We have no electrical specificaion for how far the ramp can go without calibrating, but the following attached document goes in to more details.

    Regards,

    Dean

    5732.LMX2594 Calibration Free Ramping.pdfLMX2594Ramping.tcs

  • 0 in reply to Dean Banerjee
    Prodigy 170 points

    Thank you for your previous answers. I would like to ask you the reason why by changing the ramp parameters (low and high frequency limits / duration) the out signal is not changing.

    I aspect a variation about shape and frequency of out signal. I tested all the components (mixer,cable,power divider) and they are ok. My questions is: if i generate a ramp signal from 9187.5 to 9562.5 MHz with a duration 1000 us why i cannot see a changing in my out signal? I tested positively also the ramp signal in LMX2594 syntetizer ( pin Vtune_TP) as you can see in the attached files.

    Thank you for your cooperation.

  • 0 in reply to FRANCESCO FIUME
    TI__Mastermind 27981 points
    Francesco,

    WIth your frequency switch, your ramp is not anywhere near to being calibration free. What this means is that the VCO has to calibrate many times during this ramp. This calibration takes a long time and the time that you are seeing is likely dominated by the calibration time of the VCO. The numbers in the TICSPro GUI are for the analog ramping portion; they do not account for the calibration time of the VCO.
    For experimental purposes, you might want to start with something calibration free. Try 9187.5 to 9197.5 MHz to see what the ramp looks like without the VCO calibration.

    Now above I was talking about ramp duration. The desired start and end frequencies should have an impact and the ramp limits should have an impact if they restrict the ramp.

    Regards,
    Dean