LMX2594: 200 MHz Offset Spurs

Dylan Hensley

Part Number: LMX2594
Other Parts Discussed in Thread: PLLATINUMSIM-SW,

On our custom layout on our board, we are seeing 200 MHz sidebands out of the LMX2594 at approximately 55 dBc. We are using 100 MHz reference and using the internal doubler. Our layout is proprietary. We are wondering if others have seen 100 MHz or 200 MHz sidebands caused or exacerbated by the layout.

over 5 years ago

0 Vibhu Vanjari over 5 years ago

TI__Genius 11900 points

Hello Dylan,

Could provide more details on what your VCO frequency, loop bandwidth, etc are?

Note that you can use the PLLATINUMSIM-SW (http://www.ti.com/tool/PLLATINUMSIM-SW) to simulate phase noise and expected spurs based on your PLL settings. We have some layout guidelines in section "10 Layout" of the datasheet, and you can also refer to the LMX2594EVM altium files.

Thanks,

Vibhu

0 Dylan Hensley over 5 years ago in reply to Vibhu Vanjari

Prodigy 20 points

Vibhu,

Below are my simulations from PLLatinum. I am seeing no spurs using the tool which is odd. Let me know what else I can provide. Thank you.

0 Noel Fung over 5 years ago in reply to Dylan Hensley

TI__Guru** 111200 points

Hi Dylan,

Could you set CAL_CLK_DIV = 1, also use a smaller charge pump current if possible.

Another trial is set R2[10]=0, this will stop the clock being used for VCO calibration.

Are you using the same loop filter values as shown in the simulation? It does not seem right. What is your target loop bandwidth?

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LMX2594: 200 MHz Offset Spurs