LMX2592: Lowest Possible Phase Noise at 9GHz 10KHz Offset

Randy4TIics

Part Number: LMX2592

With our implementation of a transceiver the lowest phase noise we could achieve is -96dBc/Hz at 10KHz offset of a 9GHz carrier. The amplifiers on the chains have phase noise better than -130dBc/Hz. The LMX2592 reference is an OCXO with phase noise of -170dBc/Hz at 10 KHz offset. The power supply used is an "ultra low noise" one. Is this the best the LMX2592 could do?

Thanks for your usual excellent support.

Regards,

Randy

over 4 years ago

0 Noel Fung over 3 years ago

TI__Guru** 107280 points

Hi Randy,

What is your OCXO frequency?

0 Randy4TIics over 3 years ago

Prodigy 165 points

Hi Noel,

100MHz. NEL

Thanks,

Randy

0 Noel Fung over 3 years ago in reply to Randy4TIics

TI__Guru** 107280 points

Hi Randy,

Your OCXO phase noise is good at 9GHz.

If you have an infinite loop bandwidth, the closed-loop phase noise at 10kHz offset should be around -102dBc/Hz when the charge pump current is at its minimal setting.

What is your loop filter configuration and fpd? You can use PLL Sim (www.ti.com/tool/pllatinumsim-sw) to do an estimation.

0 Randy4TIics over 3 years ago in reply to Noel Fung

Prodigy 165 points

Hi Noel,

Thanks for your latest feedback. Attached is the 4th order filter I'm using.

Thanks,

Randy

+1 Noel Fung over 3 years ago in reply to Randy4TIics

TI__Guru** 107280 points

Hi Randy,

Without knowing your fpd and Icp, I made a guess using the max. values and got the following result. The 10kHz offset phase noise is not optimized because the loop bandwidth is not high enough to suppress the VCO noise. If you want a better phase noise at 10kHz offset, you need to make the loop bandwidth wider so that the 10kHz offset phase noise will be dominated by the PLL.

0 Randy4TIics over 3 years ago in reply to Noel Fung

Prodigy 165 points

Thanks again for your assistance. Sorry, I forgot to specify my fpd but it's clear that I just have to widen my loop bandwidth to squeeze in a little more phase noise improvement, with due regard of course to the tolerable amount of spurs.

Best regards,

Randy

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LMX2592: Lowest Possible Phase Noise at 9GHz 10KHz Offset