LMX2820: PLL Phase noise issue

Hi Vigneshwar,

Your configuration is good. 

According to your configuration, there should be no multiples of 250kHz spurs. Are you using DC/DC supply?

The phase noise of your 100Mhz TCXO is not good, so you are actually measuring the TCXO noise at 4.442GHz.

I do not know your loop filter design, from the plot, looks to me that the loop bandwidth is around 30kHz. Below is the simulation result, you can see the overall phase noise is dominated by the reference clock.

Hello Noel,

Thanks for your immediate response.

1. We have isolated that TCXO and and OSCin 100MHz clock was given from ultra low phase noise oscillator O-CDFE028EW-P-R-10MHz/100MHz.At this time also I have seen the same poor phase noise performance. Please refer the attached spectrum images.

The marked spurious are degrading phase noise performance. They are unstable and their frequency & power is changing at every time of capturing.

2. Please provide the LMX2820 Evaluation board Spectrum results with

OSCin Frequency = 100MHz (from Signal Generator or any other Low phase noise TCXO/OCXO)

Output Frequency =4.442GHz

I need the following results for analysis.

a) Spectrum images of 4.442GHz Output with RBW:10Hz and Span:2KHz

b) Phase Noise of Output Clock 4.442GHz and Input Clock 100MHz (Start Offset: 10Hz to Stop Offset:10MHz)

c) Register Configuration file used for measurement.

d) Loop Filter Settings

Thanks in advance,

Vigneshwar Raj

Hi Vigneshwar,

Those are very low frequency "signal" coming from external source such as power supply, the chip will not and cannot generate these signal.

I have a 9GHz plot in my pocket. This plot was taken with the default TICS Pro configuration.

Hello Noel,

Thanks for the shared phase noise plot. But I need the phase Noise plot with Start offset 10Hz.

I measured my module power Supplies. I have not observed any noise or ther signals.

Please provide the LMX2820 Evaluation board Spectrum results with

OSCin Frequency = 100MHz (from Signal Generator or any other Low phase noise TCXO/OCXO)

Output Frequency =4.442GHz

I need the following results for analysis.

a) Spectrum images of 4.442GHz Output with RBW:10Hz and Span:2KHz

b) Phase Noise of Output Clock 4.442GHz and Input Clock 100MHz (Start Offset: 10Hz to Stop Offset:10MHz)

c) Register Configuration file used for measurement.

Thanks,
Vigneshwar Raj

Hi Vigneshwar,

Please allow us some time, I'll get the test done on EVM and will share the results on your required setup. Stay tuned.

Regards,

Ajeet Pal