LMX2592: how to calculate single side band noise

Noriyuki Takahashi

Part Number: LMX2592

Hi team,

Customer wants to calculate the single side band noise.

Could you tell how to calculate it?

They guess that equations as below can be used for the calculation, but not sure. And they also want understand the equation can be used for both Fractional-N PLL and Integer-N PLL. Could you also confirm this?

They also have a question about the app note as below. On P.6 in the app note, we can see multiplication factor. Could you tell the definition of it?

https://www.ti.com/lit/an/swra029/swra029.pdf?ts=1637327553034&ref_url=https%253A%252F%252Fwww.google.com%252F

Regards,

Noriyuki Takahashi

over 3 years ago

0 Noel Fung over 3 years ago

TI__Guru** 108410 points

Hi Takahashi-san,

We can calculate the total PLL noise due to 1/f noise and noise floor (FOM) using the equations as shown in table note (6). Side band noise is usually refer to the total PLL noise which is the sum of the reference noise, PLL noise and VCO noise. Please read my blog for details.

https://e2e.ti.com/blogs_/b/analogwire/posts/timing-is-everything-understanding-pll-loop-filter-response?keyMatch=TIMING%20IS%20EVERYTHING

PLL N-divider will add noise to the PLL, and the amount is 20log(N). This is one of the reasons why we usually use a higher phase detector frequency because this will make the N smaller.

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LMX2592: how to calculate single side band noise