• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Answers 1 answer
  • Subscribers 21 subscribers
  • Views 1185 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LMX2595EVM: LMX2595EVM Low Frequency Output Waveforms

Jessie Zhang
Prodigy 30 points

Part Number: LMX2595EVM

Dear TI engineers,

I just bought an LMX2595EVM board, and I tested it at low frequency (100M, 200M, 300M and 400M). The waveform(200MHz) is shown in the figure attached. I don't think the waveforms are correct. I think the waveforms should be square or sine. Besides, with frequency increasing, the peak-peak voltage decreases a lot.

I also attached my circuit setups here. I wonder is there any problems of my board or my setups?

Thanks!

Jessie

  • 0
    TI__Mastermind 28031 points

    Jessie,

    At these lower frequencies, you should get a square wave.   On our board, the default is a 50 ohm pull-up resistor.  The settings on TICSPro seem reasonable and it looks like you are getting the 200 MHz output as expected.

    However, there are two things that I can think of:

    1.  The oscilloscope says  "AC 1 Mohm".  50 ohm should be for better waveform

    2.  We have had a manufacturing issue with the RF SMA connector on some of our boards.  Specifically, the center pin for the RF connector is not always getting soldered down well.  You might want to try a different output (RFoutAM, RFoutBP, RFoutBM) to make sure it is not this.

    Regards,

    Dean

  • 0 in reply to Dean Banerjee
    Prodigy 30 points
    Dean,

    Thanks for your reply. I have another question about the output waveforms. You said at lower frequencies we should get a square wave. Then, I wonder at which frequency I could get the sinewave?

    Jessie
  • 0 in reply to Jessie Zhang
    TI__Mastermind 28031 points
    Jessie,

    At all frequencies, the intention is a square wave. But at higher frequencies, there is higher loss for the higher harmonics, so the output starts looking more like a sine wave than a square wave. At 2 GHz and below, it looks like a square wave, at 8 GHz and above, it looks more like a sine wave. It's not a hard and fast rule, but that's a general guideline.

    Dean
  • 0 in reply to Dean Banerjee
    Prodigy 30 points
    Thanks for your help! I really appreciate that!

    Jessie