LMX2595: Phase Noise

Adrian Inauen

Part Number: LMX2595

Hello TI experts, Hi Noel

We want to use the LMX2595 with a 200MHz clock to generate chirp patterns at 19GHz.

For now, we want to test phase noise with the LMX2595EVM, and therefore changed the input frequency to 100MHz.
We use the following settings:

The aim is to get at 100kHz offset a level of -102dB or better.
With this set up, I measure -95.5dB at 100kHz.
Is there a way to reach the goal, besides changing Fpd?

Best Regards
Adrian

over 1 year ago

0 vicente flores prado over 1 year ago

TI__Mastermind 29542 points

Hi Adrian,
Please use PLLatinumSim to improve/optimize phase noise.
Please note overall phase noise will be dominated by reference phase noise - thus if you reference is bad so will your output phase noise be.

Regards,

Vicente

0 Adrian Inauen over 1 year ago in reply to vicente flores prado

Prodigy 30 points

Hi Vicente

Thank you for your answer.

We are curious about the following message from TICS Pro:
When Ramping is used, one can not use both the R divider and input multiplier
What is the reason behind this?

Regards,
Adrian

0 Noel Fung over 1 year ago in reply to Adrian Inauen

TI__Guru** 111030 points

Hi Adrian,

Where did you get that message? Could you provide a screen shot?

0 Adrian Inauen over 1 year ago in reply to Noel Fung

Prodigy 30 points

Hi Noel

I got that message on the RAMP Tab, where the Information from the PLL Tab is placed (top right corner). There the Fpd is highlighted with exactly this message.

Best Regards
Adrian

0 Noel Fung over 1 year ago in reply to Adrian Inauen

TI__Guru** 111030 points

Hi Adrian,

I don't think this warning is valid, I will check with the original developer. In fact, I verified this on one board, I don't have any issue using both MULT and R divider.

BTW, your PLL configuration is not correct. Doubler and MULT cannot be used simultaneously. If you want fpd=125MHz, you can configure it as below.

0 Adrian Inauen over 1 year ago in reply to Noel Fung

Prodigy 30 points

Hi Noel

Thank your for your answer. I am curious what the result is regarding the warning.

Best Regards
Adrian

+1 Noel Fung over 1 year ago in reply to Adrian Inauen

TI__Guru** 111030 points

Hi Adrian,

I've checked with the developer, likely this warning is not valid anymore. He might be seeing some issue with this configuration, but most likely this is not the actual reason of failure. He cannot confirm this warning is 100% true.

0 Adrian Inauen over 1 year ago in reply to Noel Fung

Prodigy 30 points

Hi Noel

OK, thank you. We will go ahead with ignoring this warning then.

Best Regards
Adrian

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LMX2595: Phase Noise