LMX2820: Phase noise specification below 1KHz

Slavisa Zigic

Part Number: LMX2820

Tool/software:

Datasheet does not specify phase noise below 1KHz. Assuming that in the range 1Hz-1KHz from carrier I want to know phase noise, what would be the best estimate? With assumption that in that range, phase noise is dominated by reference clock (10MHz) and I want to synthesize 100MHz, can I use rule of thumb "doubling the frequency will add +6dB of phase noise" (synthesizing 100MHz from 10MHz will ad +20db), or there is calculator/simulation tool which will give actual phase noise for this or any configuration using LMX2820?

Note: 10MHz reference is atomic clock. In other words, it is not known if actual clock or LMX2820 is the main contributor to the phase noise in the range 1Hz-1KHz. For atomic clock, phase noise is specified in the range 1Hz and above.

Thanks,

Slavisa

11 days ago

+1 Noel Fung 11 days ago

TI__Guru* 86910 points

Hi Slavisa,

Correct, below 1kHz offset, the phase noise is usually dominated by the reference clock. We can scale the reference phase noise at PLL output by 20log(fout/fin).

If you have the phase noise of the reference clock, you can load it into our simulation tool (https://www.ti.com/tool/PLLATINUMSIM-SW) to check the overall PLL phase noise.

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LMX2820: Phase noise specification below 1KHz