LMX2572LPEVM: Automatic Ramp Generation - Noise peaks too close to the signal

Amrita Kothari

Part Number: LMX2572LPEVM

Tool/software: TICS PRO

Hi everyone,

We are trying to generate a chirp from 800-900 MHz using LMX2572LPEVM board..the chirp is getting generated but we see a prominent peak at 758 MHz (i.e. very close to the chirp). (screenshot of the signal is attached)

Attached is the TICS PRO file if anyone would like to have a deeper look. Any suggestions on how to eliminate or suppress the noise would be very helpful ?

P_band-800to900_VCO1.tcs

2 months ago

0 Noel Fung 1 month ago

TI__Guru* 97310 points

Hi Amrita,

To support this frequency ramp range, multiple VCO calibrations are required during the ramp. During calibration, the frequency could be completely off from the target frequency, so we will get a wider spectrum than expected.

Please try set OUT_MUTE and OUT_FORCE = 0, this will mute the output during VCO calibration, you should get a better spectrum.

0 Amrita Kothari 1 month ago in reply to Noel Fung

Prodigy 40 points

Hi Noel,

Thanks a lot for the suggestion. We made the above changes and the noise peak did go away but instead of flat response in our band of interest, we get a comb-like response (Attached screenshot). What could be the reason behind this..are we not supposed to see last locked frequency on the RFout while the VCO is calibrating ?

0 Noel Fung 1 month ago in reply to Amrita Kothari

TI__Guru* 97310 points

Hi Amrita,

This is the due to the sweep time of the spectrum analyzer. Make the sweep time smaller will help.

0 Amrita Kothari 1 month ago in reply to Noel Fung

Prodigy 40 points

hi Noel,

I will try it out tomorrow. Just to understand, how does reducing the sweep time help here ?

Thanks,

regards,

Amrita

0 Noel Fung 1 month ago in reply to Amrita Kothari

TI__Guru* 97310 points

Hi Amrita,

Reducing the sweep time with a smaller span and ResBW should give you the details of the sweep.

0 Amrita Kothari 1 month ago in reply to Noel Fung

Prodigy 40 points

Hi Noel,

We tried doing this but still see the drops in power for our frequency range. If possible, can you run the attached TICS PRO file to the post and let us know if there is something that we need to change or something we missed.

Thanks,

regards,

amrita

0 Noel Fung 1 month ago in reply to Amrita Kothari

TI__Guru* 97310 points

Hi Amrita,

I could not download the file, would you please Insert-->Image/video/file here?

0 Amrita Kothari 1 month ago in reply to Noel Fung

Prodigy 40 points

P_band-800to900_VCO1.tcs

let me know if you are able to open it.

0 Noel Fung 1 month ago in reply to Amrita Kothari

TI__Guru* 97310 points

Hi Amrita,

I can download the file and will check tomorrow.

0 Amrita Kothari 1 month ago in reply to Noel Fung

Prodigy 40 points

Hi Noel,

Kindly look at the file and let me know what can be done for these peaks.

+1 Noel Fung 1 month ago in reply to Amrita Kothari

TI__Guru* 97310 points

Hi Amrita,

RAMP_BURST_EN is not required, but it should not make problem.

I will check this configuration in the lab tomorrow.

0 Amrita Kothari 1 month ago in reply to Noel Fung

Prodigy 40 points

Hi Noel,

Were you able to run the file on your set-up ?

0 Noel Fung 1 month ago in reply to Amrita Kothari

TI__Guru* 97310 points

Hi Amrita,

I checked this out and I am afraid I provided wrong suggestion to you. The ramp behavior is out of my expectation when OUT_FORCE = 0. Supposedly, output should be muted only when the RAMP_THRESH counter is hit. From the measurement, it looks like that the output is muted after one ramp, and keep muting until the RAMP_THRESH is over.

For example, given RAMP_THRESH = 50MHz. Output = 800MHz to 900MHz.

Output is unmuted only at 800MHz, 812.5MHz, 825MHz, ....., 900MHz.

My conclusion is OUT_FORCE needs to be set to =1 in automatic ramp mode.

Apologies for giving your wrong direction.

Clock & timing

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LMX2572LPEVM: Automatic Ramp Generation - Noise peaks too close to the signal