LMX2572: Output power and Phase offset

Alberto Burani

Part Number: LMX2572

Hello Support team,

we are debugging a new application using 8 LMX2572 and we noticed that changing the output power register introduce a phase offset. Is this normal?

The pll is set to produce 2400MHz.

Second question

In my undertanding writing the Mash seed register introduce a phase offset in the output of the PLL that can be used to create 2 or more coherent outputs. When I need to change the frequency i.e. from 2400 to 2463 i have to:

Set the PLL regiters
Recalibrate the VCO (Writing R0)
trigger the sync signal (Cat3 sync)

Do I also need to reset the mash seed by writing the register to start the new frequency with a predefined phase of the signal? In my case all sources shall be maintaned coherent.

Thank you

5 months ago

0 Noel Fung 5 months ago

TI__Guru** 120040 points

Hi There,

I don't think changing the output power setting would affect the phase, I need to verify this in the lab.

A VCO calibration will reset the MASH, so after sync, you need to program Mashseed again to change the phase.

0 Alberto Burani 5 months ago in reply to Noel Fung

Prodigy 90 points

Thanks for your quick answer, I was thinking the same, I'll wait for your test at the lab. Please test it at 2.4GHz so you can take in to account also parasitic effect in your ttest.

Thanks for your support

+1 Noel Fung 5 months ago in reply to Alberto Burani

TI__Guru** 120040 points

Hi There,

I tried this in the lab, I tried 2400MHz and 2463MHz, the phase remains unchanged when changing the output power setting. I tried both sync and non-sync mode.

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LMX2572: Output power and Phase offset