LMX2594: Lmx2594 unstable phase noise

shay Barzilay

Prodigy 190 points

Part Number: LMX2594

Hello,

I use lmx2594 in partial assist mode.

LP = 45kHz

Freq test 2410MHz

I perform a calculation by formula to astimate cap , daci and vco .

While working I send the same commands to the component several times and somtimes I get a different phase noise - worse at 10dB

Do you know why the phase noise get worse for the same commands?

Best regards

Shay

over 3 years ago

0 Noel Fung over 3 years ago

TI__Guru* 81580 points

Hi Shay,

Can you read back the VCO parameters to see what are the chosen capctrl, daciset and vco_sel? Can you also do a comparison with auto-calibration? I guess one of the vco parameters are not picked correctly.

0 shay Barzilay over 3 years ago in reply to Noel Fung

Prodigy 190 points

Hello,

I made readback from component for the 2 cases

The readback for cap and dac was almost the same

Dac1 = 129

Cap1=11

Dac2= 128

Cap2=11

The phase noise was different at 8dB

Best regards

Shay

0 Vibhu Vanjari over 3 years ago in reply to shay Barzilay

TI__Genius 11900 points

Hello Shay,

I think what Noel was suggesting is to use auto-calibration and readback registers after auto-calibration to see if your calculated values match the auto-calibration values.

shay Barzilay said:
The phase noise was different at 8dB

Can you explain this to me. Are you checking a particular frequency offset where the difference is 8dB?

Thanks,

Vibhu

0 shay Barzilay over 3 years ago in reply to Vibhu Vanjari

Prodigy 190 points

Hello

Yes, i am checking the same freq in the both cases.

I will test it in auto calibration mode.

Thanks

Shay

0 Vibhu Vanjari over 3 years ago in reply to shay Barzilay

TI__Genius 11900 points

Hello Shay,

Great! Please let me know once you have results.

Thanks,

Vibhu

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LMX2594: Lmx2594 unstable phase noise