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LMX2820EVM: Phase Synchronize Multiple LMX2820 Devices by generating the sync signal with the distributor clock LMX1204

Ferdinando Catania
Prodigy 10 points

Part Number: LMX2820EVM
Other Parts Discussed in Thread: LMX1204EVM, LMX1204, LMX2820

Hi,

I’m trying to synchronize two PLLs LMX2820EVM as shown in the figure below:

image.png

  • The PLLs will operate in SYNC category 2.
  • The idea is to use the SYSREF outputs of the LMX1204EVM as synchronization signals for the PLLs. The SYNC/SYSREF output will be genereted internally to the LMX1204EVM.
  • After the PLLs are synchronized,  the SYNC signals generated by the LMX1204 will be programmed as SYSREF inputs (maybe changing the frequency) to the PLL2820EVM, which will then be used in repeater mode.

I would like to know whether this architecture is feasible, what the main challenges might be, and how I should configure the PSYNC pin of the PLLs (and the related resistors) to make this work.

Thank you in advance for your support.

Best,
Ferdinando

 

  • 0
    TI__Guru** 120300 points

    Hi Ferdinado,

    Since you have the RF clock buffer, you can use it to fanout RF clock from a single synthesizer, no need to use two synthesizers.

    If you want to stick on your architecture, you can simply use a logic device to generate the sync pulse for the synthesizers. This is possible because the timing of the sync pulse is not important for a Cat.2 sync.

  • 0
    Prodigy 10 points

    Hi Noel,
    thank you for your reply.

    When you say “logic device,” are you referring to the LMX1204 clock distributor, or to another component?
    Unfortunately, I cannot modify the architecture I showed you earlier, I cannot add devices or change the number of channels being used.

    My goal is to use two SYSREF outputs from the clock distributor to synchronize the two PLLs. Do you think this is feasible?

    I also noticed that the SYSREF outputs of the LMX1204 use CML levels, while on the LMX2820EVM GUI the PSYNC input can be configured as CMOS or LVDS.
    Could you suggest how to properly adapt the signals between these standards?

  • +1 in reply to Ferdinando Catania
    TI__Guru** 120300 points

    Hi Ferdinando,

    Logic device means MCU or FPGA. 

    You can use a GPIO from the MCU to provide the sync pulse to both LMX2820. 

  • 0 in reply to Noel Fung
    Prodigy 10 points

    Hi Noel,
    I get it, thank you.