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LMX2820: LMX2820 Phase Synchronization

Vamshi Krishna Singam
Prodigy 60 points

Part Number: LMX2820

Tool/software:

Hi Team. I am currently working with two LMX2820 PLLs in my application, both driven by the same 100 MHz reference clock. One PLL is configured to generate variable frequency ranging from 7 to 14 GHz with 25 MHz steps, while the other is set to a fixed output frequency of 9 GHz. My objective is to achieve phase synchronization between these two PLLs. Could you please provide guidance on utilizing the PSYNC functionality to accomplish this? I have tied two PYNSC signals of PLL1 and PLL2 in this scenario.

Thankyou.

  • 0
    TI__Guru** 121000 points

    Hi Vamshi,

    Please read below appnote on how to sync multiple LMX2820 device.

    https://www.ti.com/lit/pdf/snau273

    Synchronization of multiple devices usually assume all the output frequencies are identical. If their frequencies are different but are integer multiple of each other, this is also fine.

    In your use case, how do you verify two non-integer multiple frequencies are synchronous? For example, when the frequencies are 8975MHz and 9000MHz?

  • 0 in reply to Noel Fung
    Prodigy 60 points

    Thank you for your response. To clarify, does phase synchronization require PLLs to operate at identical output frequencies or at frequencies that are integer multiples of the reference clock?

    Additionally, in a setup where both PLLs share a 100 MHz reference clock and the PSYNC been unsed, what potential phase mismatches could arise?

  • 0 in reply to Vamshi Krishna Singam
    TI__Guru** 121000 points

    Hi Vamshi,

    The LMX device, after performing a phase synchronization, will make the phases between input and output deterministic. There are restrictions on synchronization, please check the datasheet or the appnote again. 

    My question was how to verify two non-integer multiple clocks are synchronized. For example, you have two output clocks, their frequencies are 10Hz and 11Hz. How do we verify they are phase synchronized?