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LMX2595: Synchronize LMX2595 and LMK04832

Christian borelli
Prodigy 20 points
Part Number: LMX2595
Other Parts Discussed in Thread: LMK04832,

Hello, 

   i need to synchronize the LMX2595 and the LMK04832.

One option is to share the same reference but this means to use a crystal with a splitter and this will add jitter.

I would like to use the internal option to synchronize the two synthetizers.

Can you please explain how can i do that?

thanks,

christian

  • 0
    TI__Mastermind 18850 points

    Hi Christian,

    Both of these devices have SYNC pins that can be used for phase synchronization from an external signal, more details are in the datasheets (Section 7.3.11 of LMX2595 datasheet and several parts of Section 8 in the LMK04832 datasheet). I assume that's what you mean by "internal option". However, I don't think this would produce the same effect as having the two devices share the same reference, because this synchronization is supposed to ensure a deterministic delay from input to output. If the two inputs are from different crystals to begin with, then a fixed/known delay would not guarantee the alignment of the outputs. I have paged our RF experts for more comments.

    Thanks,

    Evan Su

  • 0 in reply to Evan Su
    TI__Genius 12560 points

    Hi Christian,

    Can you elaborate more, the actual use case, as both operates at different frequencies and you might be interested to have the deterministic phase between them outputs? 

    You can have the external crystal input at OSCin input of LMK04832 and its OSCout (buffered output) fed to LMX2595. Then using the LMK04832 SYSREFout to the LMX2595, which can acts as a SYNC to LMX and aligned the LMX output wrt OSCin input.

    Thanks!

    Regards,

    Ajeet Pal

  • 0 in reply to Ajeet Pal
    Prodigy 20 points

    Hello Ajeet,

     using your suggestion is it ok to use 100MHz as OSCin for the LMK and buffered it to the LMX?

    thanks,

    Christian

  • 0 in reply to Christian borelli
    TI__Mastermind 18850 points

    Hi Christian,

    100 MHz is within the OSCin specifications for both the LMK04832 and LMK2595, so that should be OK.

    Best,

    Evan Su

  • 0 in reply to Evan Su
    Prodigy 20 points

    Do you know the additive jitter from OSCin to OSCout? I cannot fnd it in the spec.

  • 0 in reply to Christian borelli
    TI__Guru** 107300 points

    Hi Christian,

    OSCout and CLKout buffer has the same performance, their noise floor is identical.

    So, the additive jitter is going to be very low. In fact, the additive jitter from OSCout would only affect the phase noise of the 100MHz signal a little bit at the far out offset which is not important to LMX2595. Far out offset phase noise of LMX2595 is determined by the VCO and RFout buffer noise floor.