How does spur change after frequency divider?

I have a question:

How does spur change after frequency divider? I know that offset frequency won't change, but how about spur power level? Also unchange?

Thanks,

How do you say that offset frequency is unchanged after frequency division?
let say I have frequency 1MHz and is divided by 100 then I have 10KHz.
Also let say the spur is at 900KHz then spur is located after division at what frequency?
it has few cases to understand in case of digital division.

Yes, you are right. In the case you mentioned, the spur will fold back. When I talked about un-changed spur offset frequency, I meant that like multi-GHz clock divided down to multi-GHz clock and spurs are at MHz offset. Sorry, I didn make it clear.

Can you tell me, in this case, how does spur level change? Like phase noise, reduce by 6dB by every divide-by-2? Or stay un-changed?

Do you have any papers discuss this topic?

Thanks,

Well, imagine a carrier with some sort of small frequency modulation going on. If there is a single tone at frequency Fm modulating the carrier, the spectrum can be approximated by:

sideband power in dbc = 20 Log (Δf/(2* Fm))

where Δf is the frequency deviation, and Fm is the modulating rate.

If you were to pass this thru a divide by 2 circuit, the Δf frequency deviation would half, but the Fm would stay the same. So after the divide by 2, the sidebands would still be at the same +/- Fm distance from the carrier, but their level would be 6 dB lower.