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LMX2594: Manual ramping and automatic ramping issue.

Ricardo Li
Intellectual 1045 points
Part Number: LMX2594

Dears,

The customer is using LMX2594, now he have some problems. 

When using the manual ramping example (Datasheet Page 27) . The signal will suddenly lose lock in the process of manual ramping. The start frequency is 10GHz, and the step forward is 10MHz, at about 10.130GHz the loss of lock will occur, after about 30s the signal jump to 10.450GHz, then the signal will return to normal. 

 RAMP_TRIG_CAL=0, RAMP_THRESH=300MHz, because the customer said when set RAMP_TRIG_CAL=1,  the ramping do not work.

I want to know how to  solve this problem.

Regards,

Ricardo

  • 0
    TI__Mastermind 27581 points
    Ricardo,
    I think the issue is related to RAMP_THESH=300 MHz. If you lock the device at 10 GHz, you can likly tune the VCO on the order of 130 MHz before it has to recalibrate. If you set the threshold to 300 MHz, then you are not allowing the VCO to recalibrate. If you set RAMP_THRESH=5MHz, then you trigger every step. Or you can set RAMP_THRESH=50MHz, then you cna re-calibrate. But you have to let the VCO recalibrate and 300 MHz is too large.
    Regards,
    Dean
  • 0 in reply to Dean Banerjee
    TI__Intellectual 1045 points

    Hi Dean,

    Thanks a lot for prompt response. I will confirm with the customer.

    Regards,

    Ricardo

  • 0 in reply to Dean Banerjee
    Prodigy 30 points
    Bean,
    thanks for response, I have set RAMP_THRESH=50MHz , but auto ramping do not work ,so I set RAMP_THRESH = 300MHz ,it works .but frequency bandwidth less than 125MHz , when I set bandwidth more than 125MHz ,the part larger than 125MHz ,would not work , I do not known where is the problem. And you said 'tune the VCO on the order of 130 MHz before it has to recalibrate',means VCO could only recalibrate 130MHz ? I do not read it on the datasheet . I am not good at English ,If there is anything wrong, please understand. Thanks~
    Regards,
    Peng Cao
  • 0 in reply to peng cao1
    Prodigy 30 points
    Bean ,
    If I do not use the VCO recalibrate , the bandwidth is less than 130MHz ? (I set the bandwidth in the ONE VCO core).
  • 0 in reply to peng cao1
    TI__Mastermind 27581 points

    Ricardo,

    The LMX2594 has 7x 183 = 1281 frequency bands.  Each VCO core is further divided into 183 frequency bands.  There is a substantial amount of overlap between these bands to account for frequency drift, but none of these bands is 300 MHz wide, or even close.  130 MHz is about the width of these bands.  The 183 corresponds to the 183 different values of VCO_CAPCTRL.

    Regards,
    Dean

  • 0 in reply to Dean Banerjee
    Prodigy 30 points

    If I want to achieve sweep function, how do I set the register? Which registers should I set ? How to set it? Can you give me a detailed plan?

    Thanks~

    Regards，

    Peng Cao

  • 0 in reply to peng cao1
    TI__Mastermind 27581 points

    Peng,

    I am not sure of all the specifics of your ramping, but would recommend first using the TICSPro software with the specifics you want and then use this to translate to get the register values.  The raming tab on TICSPro should hopefully prove to be  very useful.  For the calibration threshold, I would set something about 50 Mhz.

    In general.
    1.Set ramp thresholds far away from where you need the ramp frequency to be

    2. Set the ramp threshold value.  Default is 30 MHz.  As we don't test this in production or guarantee this, this number is very conservative.

    3.  Set RAMP_MANUAL to checked

    4.  For the trigger, I typically set the Trigger A to the RAMPCLK rising edge and then set RAMP0_NEXT_TRIG and RAMP1_NEXT_TRIG to trigger A.

    Regards,
    Dean