LMX2572EVM: Issue generating a generate a 100 MHz signal

Connor Connaughton

Part Number: LMX2572EVM

Hi Team,

My end goal is to generate a 100 MHz signal at +2.5 dBm with the TICS Pro software.

I can manually click USB communications > Write All Registers.

I know I can edit the number next to the output frequency to adjust the gain but my spectrum analyzer is showing the output is not a clean 100 MHz. Any thoughts? My setup is below.

Thanks!

Connor

over 1 year ago

0 Noel Fung over 1 year ago

TI__Guru* 87690 points

Hi Connor,

If you are referring to the harmonics, this is normal as the divider output is a square wave signal, as a result, it is harmonic rich.

0 Connor Connaughton over 1 year ago in reply to Noel Fung

TI__Expert 4470 points

Hi Noel,

Thanks for the help here.

The big issue is the center frequency is very off the mark.

When my customer programs the device for a 100 MHz output, the first peak is more than 13 MHz off.

Is there a reason for this?

Thanks!

Connor

0 Connor Connaughton over 1 year ago in reply to Connor Connaughton

TI__Expert 4470 points

Hi Noel,

One other question: I am still digging through the datasheet, but does the chip have any kind of memory to auto load a configuration on power up?

Or do the registers have to be written every time power is applied?

Reading through I think it has to be done every power up but please confirm.

Thanks!

Connor

+1 Noel Fung over 1 year ago in reply to Connor Connaughton

TI__Guru* 87690 points

Hi Connor,

Are you working on the EVM or your board?

There is no memory in the chip, every time it is Vcc power down, all the written register values will lost, we need to program all registers again after a Vcc power up.

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LMX2572EVM: Issue generating a generate a 100 MHz signal