Hi
I am using an LMX2592EVM to check the phase noise performance. With the default on-board Crystal oscillator, I measured the Phase noise performance, which is pretty good. Now, when I connect a External clock to the EVM (by switching R14p and R14) bypassing the onboard clock, measure the phase noise performance at any output frequency I see lot of spurs in the band 100Hz to 10KHz (which doesn't exist when an onboard crystal is used). I also check the phase noise performance of the External clock before applying as input which is really good. I am not sure, how the spurs are showing up, when they don't exist with onboard crystal. May I know how to get rid of these spurs or atleast why they are occurring on an EVM ? even while using good signal source (better than -135dBc/Hz @ 10KHz offset as specified)
Attached are the phase noise performance curves. Yellow one represents the 100MHz External Clock provided as input, Red One measured with External Clk at 3.9GHz.
Regards
Venu
