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LMK04131 / RMS jitter @snlu099A


I received the following question from my customer.

There is Table3 and Table 4 on the snlu099A p15.

My customer think that jitter value is calculated by phase noise.

For example, 515.4dBc/Hz@10Hz is calculated by -76.6rmsfs@10Hz and -108.9rmsfs@100Hz.

Is it correct?

Best Regards,


  • Your customer is correct that jitter value is calculated by phase noise. Specifically jitter in a specific integration bandwidth is calculated by phase noise values in that integration bandwidth. Jitter is the integration of phase noise. So the 515.4 fs rms = integration from 10 Hz to 20 MHz.

    Table 3 is spot phase noise at different offsets and has units dBc/Hz, the different spot offsets are 10 Hz, 100 Hz, etc. Table 4 is the integration of the phase noise from the low offset listed, 10 Hz, 100 Hz, etc. to 20 MHz and has units of rms fs (for jitter).

    Please refer to the" Choosing Loop Bandwidth for PLLs" file in the E2E files section, e2e.ti.com/.../664163
    Take note of slide 7.