Other Parts Discussed in Thread: LMX2820
Tool/software:
Hi team,
i'm using the evaluation board of the PLL LMX2820 to generate output frequencies up to 4 GHz.
The reference input is a 100 MHz sinewave from a low noise oscillator with output power of about +9 dBm.
The following image shows the LMX2820 configuration:
I tried to measure the phase noise at 4 GHz at the ouput of the PLL with 3 reference clocks with different harmonic levels.
Setup 1
The reference clock is shown in the following image:
The phase noise at 4 GHz at the output of the PLL is shown in the following image:
Phase Noise OK
Setup 2
The reference clock is shown in the following image:
The phase noise at 4 GHz at the output of the PLL is shown in the following image:
Phase Noise NOK
Setup 3
I inserted 2 low pass filter to eliminate the harmonics of the reference clock.
The phase noise at 4 GHz at the output of the PLL is shown in the following image:
Phase Noise OK
So, the slew rate is the same for all 3 setup bu the harmonics levels is not the same.
Why does the spectral content of the reference clock of setup 2 affects the phase noise so negatively?
Thank you in advance.
Best Regards,
Matteo Ricci
