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LMK03806 SYNC signal

Nate Wang
Prodigy 170 points

Other Parts Discussed in Thread: LMK03806, LMK04906

Hi ,

In the datasheet of LMK03806, SYNC signal can be used to synchronize the phase of all the clock outputs,

14.4.3 CLOCK OUTPUT SYNCHRONIZATION

Using the SYNC input causes all active clock outputs to share
a rising edge.

If I set all the clock outputs to the same frequency, and all  NO_SYNC_CLKoutX_Y register to 0, does that mean upon the time that SYNC signal goes from low to high, all the clock outputs will start from zero phase(or a fixed phase) at the same time ?

Further question, I have two LMK03806 on two different PCB boards, their clock inputs are of the same frequency but different phase(due to propagation delay through cable), and if I toggle SYNC signal of both LMK03806 at exactly the same timing, will the phase of all the clock outputs of the two LMK03806 exactly the same ?

thanks.

  • 0
    TI__Genius 10320 points

    Hi there,

    Your understanding is correct - since all outputs are configured to be impacted by SYNC, upon release of SYNC, all clock outputs will share a rising edge. Note that alignment is still subject to skew as noted in the "Clock Skew" portion of the DS. Also note the setting for SYNC_POL_INV to set the active state of SYNC accordingly.

    The feature you are discussing is called 0-delay, or some guarantee of edge alignment from clock input to clock output. The LMK03806 does not have this feature - other devices in the family such as the LMK04906 do. This is often used in distributed clock networks as you mentioned for clock alignment throughout the system.

    Gabe

  • 0 in reply to Gabe Ayala
    Prodigy 170 points

    Hi Gabe,

    Thanks for your reply, sorry I did not describe my problem in detail and your answer does not solve my problem, please see below.

    I have two PCBs with LMK03806 on it, each LMK03806 output 8 clocks to 8 ADCs, I need to synchronize all the total 16 clock outputs in order to make sure all the ADCs samples data at exactly the same timing.

    There is an oscillator of 100MHz  on the first PCB, the 100MHz clock is served as the clock input of LMK03806 on the first PCB. And also is transmitted through a RF cable to the second PCB as the clock input of LMK03806. Due to propagation delay of RF cable, the clock inputs of both LMK03806 is of the same frequency but in different phase. Hence the phase of 8 clock outputs of the first LMK03806 is different to the second 8 clock outputs of the second LMK03806.

    I was expecting to synchronize all the 16 clock outputs by asserting SYNC signal to the two LMK03806 at exactly the same timing. But after reading the datasheet of LMK04906, especially refer to "Figure 20. Clock Output synchronization using the SYNC pin (Active Low)", I found clock outputs is synchronized to the input clock(to be precise, the distribution clock), rather than the timing of SYNC signal.

    So, given the phase of clock inputs is different, is there any clock generation chip that is able to synchronize their outputs ?

     

    thanks.

  • 0 in reply to Nate Wang
    TI__Genius 10320 points

    Hi there,


    As I mentioned before, what feature you are looking for is 0-delay functionality. In order to mitigate the effects of propagation time, each device would need to guarantee edge alignment from CLKin to CLKout. This is often done in JESD204B applications for ADCs as you mentioned - devices such as the LMK0482x family have digital delay and analog delay functions as well as 0-delay configurations to fine tune edge alignment at the ADCs.

    Gabe