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LMX2594: Calculating Jitter

Ilya Mazurenko
Expert 1300 points
Part Number: LMX2594

Hello Team,

Could you help us please with our customer's question about LMX2594:

Datasheet, Page 12, Figure 8 (Closed Loop Phase Noise at 3.5 GHz):
1) Jitter = 49.4 fs (100 Hz - 100 MHz)
How this Jitter was calculated? (formula)
The customer calculated much higher value.

2) Point 9 on Figure - -127,8 dBc/hz
Where is this point? Why does the graph go to an imaginary point?

BR,
Ilya.

  • 0
    TI__Mastermind 28001 points

    Ilya,

    1)  Attached is a plot from which the jitter was derived.  To calcul;ate jitter, integrate the area and call this A.  Don't forget to multiply by 2 for both sides.   Then the jitter is sqrt(A)/(2*pi*f), where f is the frequency.   This is also discussed in my free online PLL book at ti.com/tool/pll_book.

    2)  The point on the graph is the 100 MHz spur.  Note that this is in dBc/Hz, not dBc.  See it in the attached plot.  You should really ignore this point as this is a spur and also the E5052 sometimes adds a ficticuous spur at the extreme right of the plot.  Instead, pay more attention to the marker at 95 MHz of -151.1 dBc/Hz

    Regards,

    Dean