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LMX1214: Question about LMX1214

Jimmy Huang
Genius 3535 points
Part Number: LMX1214

Hello:

The customer found a lot of clutter when testing LMX1214. May I ask if this is due to the chip itself?

Test situation: Use SMA100B to input 12.8GHz or 6.4GHz, test frequency division 2, 4, and 8 respectively, and output port CLK0. It was found that there is a lot of noise, with a minimum output noise of 50MHz corresponding to an input signal frequency division ratio of over 200 (which will vary proportionally with the input signal).

The test images are as follows:

              

  • 0
    TI__Mastermind 29362 points

    Hi Jimmy, 
    I can look into this further tomorrow. 

    If output is a divider I do expect to see harmonics. For example: for a 3.2 GHz output I am not surprised to see a spur at 1.6 GHz. 
    After switching divider values, if you disable the state machine clock does that help reduce/eliminate spurs? 

    I am curious, what does the reference source look like? Can you see these spurs on the reference? 

    Regards, 

    Vicente 

  • 0 in reply to vicente flores prado
    Genius 3535 points

    Hello  vicente：

    The signal source uses SMA100B, and its signal output has no spurious.
    It is normal to generate 1.6GHz when outputting 3.2GHz, but 800MHz, 1.2GHz, and 2.4GHz all exist (I can understand their existence), which should be caused by repeated frequency division. Then there are many small spurious signals, which are also generated by frequency division. Such small spurious signals should not exist.

  • 0 in reply to Jimmy Huang
    TI__Guru** 108480 points

    Hi Jimmy,

    See below our test data with 6GHz input, div/4 output, there is no spurs.

    Were you using the onboard LDO or not? 

    Could you try, after programming the device, set SMCLK_EN = 0? Also try unplug the usb cable.