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LMX2594: There are many clutter in manual Ramp mode

Amy Luo
Expert 6895 points
Part Number: LMX2594

Hi team,

One of the issues that our customer faced:

As shown in the video, there are interfering peaks in the manual ramp mode, and the frequency of rampclk is 2KHz.

2800M initial, 50Hz step:

5300M initial, 50Hz step:

The following figure is the configuration at the 5300M initial, 50Hz step.

Please give some suggestions to solve the problem. Thanks in advance.

Thanks,

Amy Luo

  • 0
    TI__Guru* 97620 points

    Hi Amy,

    I don't know what was causing this, the VCO frequency is ramping, there should not be a non-moving fixed frequency signal. 

    I don't know if it is relevant, try stop the state machine clock by writing R2[10] = 0 before ramping. 

  • 0 in reply to Noel Fung
    TI__Expert 6895 points

    Hi Noel，

    Thank you.

    At present, this phenomenon still exists. Later, I found that in the non ramping mode, there will be a lot of interfering peaks in the video when directly inputting 2800.001MHZ and 2900.001MHZ fixed frequencies, but there is no such phenomenon when inputting 2800MHz or 2900MHZ. Maybe there is a problem when outputting decimal frequencies?

  • 0 in reply to Amy Luo
    TI__Guru* 97620 points

    Hi Amy,

    at 2800.001MHz, the spurs are known fraction spurs. These spurs exist for any fractional PLL.