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LMK04828: TIDA-01023 LMK04828 distribution mode input port hardware considerations

Lazba Filipp
Prodigy 30 points

Part Number: LMK04828

Tool/software:

Hi everyone!
In the document High-Channel-Count JESD204B Clock Generation Reference Design for RADAR and 5G Wireless Testers distribution mode is used both for master and slave devices. 

It is said that CLKin0, which is used for SYNC(which resets dividers) input has to be DC coupled, and it is driven with differential signal on 2 coax cables, while distributed 300 MHz CLKin1 uses balun and is, I guess, AC coupled. So CLKin0 requires 2 cables and CLKin1 requires 1 cable.

1) why  SYNC signal has to be DC coupled? Is that because it is low-frequency aperiodic signal which is only pulsed some times at the start and that's all or why?

2) why does CLKin0 use differential signal instead of single-endedas described in Figure 28 of LMK04828 datasheet?

3) why does CLKin1 input use external balun if in LMK04828 there is option of single-ended driving?

4) if CLKin0 uses differential signal due to lower noise and jitter, why then use single-ended signal with balun for CLKin1?

5) how is single-ended output achieved on LMK04828-EVB if all (S)DCLKoutX output of LMK04828 options are differential and there is no any transformer on LMK04828EVB board?

  • +1
    TI__Mastermind 32152 points

    Hello Lazba, 
    1.The SYNC pin should be DC coupled to ensure the pin is low when not in use.The SYNC input should always stay low and accept a positive pulse,so it cannot be AC-coupled.

    2. CLKin0 is a differential input with a different input receiver architecture that allows for differential inputs. 
    In theory CLKinX can also be used SE. 

    3. This question needs to be addressed to the reference design team. I cannot say why they would use a Balun. 

    4. Same as 3^ 

    5. There is no need for a Balun/Transformer - you're correct on the EVM you can just input a single ended signal. 

    Best regards, 

    Vicente