Re: Anybody know the fractional spur leakage to in-band spur
Hi RFsystem I have to bother you again. I donot get any reply from the post listed below.
I have a setup in ADS to simulate the folding effect as we discussed.
For the fractional PLL:
Fref=1.728 MHz
divider N=1023+501/(2^10)=1023.48925
loop bandwidth=20kHz
3rd order loop filter and sigma delta modulator
In PLL output phase noise spectrum,a fixed fractional spur is just outstanding there at 37.14KHz offset. I tried around that how to relate this 37.14KHz to Fref and fraction part of the divider N, but cannot see any relationship among them. It is obviously located out of band. But why?
This spur is bigger but locate in the same frequency if I increase the deadzone of the PFD. Unfortranately if I change the fraction of the divider my SDM output screw up.