• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 22 subscribers
  • Views 568 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.

Original question:

LMX2595: LMX2595 PHASE NOISE ISSUE

LMX2595: LMX2595 EVM board sensitive to vibration, low-frequency noise?

gang huang
Prodigy 230 points
Part Number: LMX2595
Other Parts Discussed in Thread: , LMK61E2, LMK61PD0A2, LMX2594, USB2ANYWe recently purchased the LMX2595 EVM. When measuring the phase noise with a Keysight E5052B signal source analyzer, we noticed this board is very sensitive to the vibration of the table. When we place the board on a stable table, the integral from 100Hz to 10MHz is less than 100fs. But if I connect the board to the E5052B directly, the instrument has a fan on it and the vibration is passed to LMX2595EVM, and the integral becomes 300-500fs or even worse. Put it back on the stable table, and tap with a pen, I can see the low-frequency noise goes up a lot. I want to know if this is a problem of the chip or the board, maybe some capacitor or inductor? Can you point to me which capacitor/inductor should be replaced to what to overcome this problem? Thanks
  • 0
    TI__Guru** 107450 points
    Hi Huang,

    This is due the on-board XO, which is sensitive to vibration. You can try using external reference clock (from a signal generator) instead of the on-board XO.
    If you are interested to know some details on the vibration, here is an appsnote. www.ti.com/.../snaa296.pdf
  • 0 in reply to Noel Fung
    Prodigy 230 points
    Hi Noel,
    Thank you and more questions.

    1. For the vibration noise:
    It seems on the REFERENCE PRO board, there is some LMK61E2/LMK61PD0A2, which suppose can resist the vibration a lot according to the document you provided.
    I can try to use the REFERENCE PRO board come with the LMX2595 EVM board to provide reference clock.
    Do you think that can solve this problem?
    Before moving the 0ohm resistors, I also noticed
    " However, the LMX2594 comes with an unboard XO (Vectron VC-708) which is lower noise than the reference Pro. “
    From e2e.ti.com/.../670209
    Will that downgrade the phase noise performance a lot?

    2. For the power:
    And I know can add the LDO to the LMX2595EVM, is that valid if I get the power for the reference board which come from the USB port and provide to the LMX2595EVM?

    3. For the SPI interface
    If I use the reference pro board, can I program it on linux instead of using windows?

    Thanks,
    Gang
  • 0 in reply to gang huang
    TI__Mastermind 18070 points
    Hi Gang,

    For the vibration problem, you can try signal generator first for a quick sanity check and see if it solves the problem. Be sure to rework the board according to the user's guide in order to use external reference.

    If you want to use reference pro, simply connect the output of reference pro to the OSCin of LMX2595 and use the ribbon to connect the header of reference pro to the 10-pin header of LMX2595. By default the power of reference pro is supplied by the USB. Also by default, output of reference pro is 100MHz. The programming with reference pro is the same with that in USB2ANY. They use the same microcontroller.

    LMX2595 needs separate power supply. USB power cannot provide sufficient current.

    Integrated jitter from 100Hz to 100MHz should be around 100fs using reference pro. The datasheet numbers were attained using Wenzel source.

    Regards,
    Hao