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LMKDB1108: LMKDB1108 vs LMK1C1108 PLLatinum Sim jitter and phase noise

Paolo Pellati
Prodigy 130 points
Part Number: LMKDB1108
Other Parts Discussed in Thread: LMK1C1108,

Tool/software:

Dear TI,

looking at the jitter specifications reported in the datasheet , the LMK1C1108 has better jitter specification than LMKDB1108 (LMK1C1108: 20fs max/8fs typ @ 156Mhz; LMKDB1108 : 31fs max/21.9fs  typ @ 156Mhz clock).

Anyway when I use the PLLatinum simulator the LMKDB1108 has slightly better phase noise and jitter than LMK1C1108 (LMKDB1108: 171.3 dBc/Hz, 28.66 rms jitter; LMK1C1108: 170 dBc/Hz, 33.29 rms jitter).

Where is the mistake ?

Best regards,

Paolo

  • 0
    TI__Mastermind 29172 points

    Hello Paolo, 
    Here is LMK1C @156.25MHz

    Jitter is ~21fs which matches the DS. 

    When I try the same for LMKDB1108 I get the following: 


    We have a spec in the DS:

    But there is also this PN curve: 

    We say 31fs maximum as reduced slew rates provide worse additive jitter. 

    Unfortunately, we do not have a way to take slew rate into account inside PLLatinumSim. 

    For most accurate measurements, I recommend you use the phase noise profile of the ref clk to estimate the output PN. 
    With this you can also estimate additive jitter for your application. 

    Best regards, 

    Vicente