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LMX2594EVM: No Output

user3764392
Prodigy 60 points
Part Number: LMX2594EVM


Hallo,

I´ve got this EVM and hooked it up as told in the instructions, but I don´t get anything out of it. After uploading the default configuration the LED indicates that PLL has locked, but wether OUTA or OUTB got any signal. 

And if I want to use this modul at 100MHz output - will I have to modify the loopfilter?

Regards,

Alex

  • 0
    TI__Expert 5370 points
    Hello Alex,

    sorry to hear you are having an issue.

    It sounds you are doing the right thing. What equipment do you use to look at the output? The default is 7 GHz so you would typically use a spectrum analyzer to look at it. Is that what you have?

    You may also reduce the output frequency to 100 MHz with the output divider and no changes to the loop filter would be required.

    I hope this helps,

    Regards, Simon.
  • 0
    Prodigy 60 points
    Hey Simon,

    I monitored the output with 24 GHz oszilloscope, so the outputsignal should be visible. As you told I switched to a spectrum analyzer and got a really weak signal, but its there. It´s just about -25 dBm, and the noisefloor around the carrier is about -55 dBm, so SNR is not really good. I tried to increase output level by editing the field OUTB_PWR, but that didn´t change anything. It´s the same with decreasing.

    Now I´ve tried to divide the output frequency a little more, but it´s impossible to get more then a fraction of 6. If I choose more I got no signal and in TICS Pro the input field CHDIV becomes red.

    What am I doing wrong?
  • 0 in reply to user3764392
    Prodigy 60 points
    Ok, thanks to the datasheet, with F_vco at 11.5 GHz fractions greater than 6 are possible. But as I lower the frequency, the amplitude of the carrier decreases and at around 1GHz it´s lost within the noise floor. Any idea what´s the reason for this?
  • 0 in reply to user3764392
    Prodigy 60 points
    OK, most things are done. But still there ist a problem with the channel divider. For SEG3 greater one I got no output. But for Frequencies around 100MHz it is nessesary to to set it to 2.
  • 0 in reply to user3764392
    TI__Expert 5370 points
    Dear user,

    We have had a problem in manufacturing. The output connector may be not well soldered onto the PCB. The issue was with the center pin where small stress cause a fracture or there is not enough soldering. You may have this problem as you describe. You will need to reflow the center pin on the output connector.

    Let me know if this fix the problem.

    Regards, Simon.