LMK01020: Reduce spurious

cafain

Part Number: LMK01020

Hi,

I use LMK01020 as the system clock, but spurious is out.
Please tell me how to reduce it.

We use it under the condition that
Input : 245.76 MHz, LVDS
Output: 245.76 MHz, LVPECL
Events occur that spurious of about -60 dBc (245.76 MHz ± 500 kHz, ± 1 MHz, etc.) is superimposed on the output signal.
A DCDC converter with a switching frequency of 500 kHz or 1 MHz is mounted in another place on the same board.

These DCDC converters are not convinced of spurious sources.
However, I want to challenge to reduce the spurious.

· Reduce spurious level of output frequency
· Improve power switching immunity
I would like to teach you if there is any policy to do so.

best regards

over 6 years ago

0 Tim Chao Li over 6 years ago

TI__Expert 4415 points

Hi,

Yes, it is probable that the DC-DC converter is causing the spurs. To help reduce the spurs make sure that there is adequate power supply filtering on the device supply. See the LMK01000EVM User's Guide for an example schematic (linked below). The filtering capacitors should be placed close to the device supply pins to minimize loop inductance. The capacitors used should also be low ESR. The small 0.1uF capacitors should be placed closest to the supply pins.

www.ti.com/.../snau037a.pdf

This should reduce spurs due to power supply. In general, to reduce other spurs caused by crosstalk, the following measures can be taken:

-Ensure proper input and output termination per the recommendations in the datasheet
-Any unused outputs should be disabled if possible or properly terminated if not

Regards,
-Tim

0 cafain over 6 years ago in reply to Tim Chao Li

Mastermind 6365 points

Hi, Tim-san

Thank you for telling me how to deal with it at once.
Let's challenge attenuation by filtering the effect of DC / DC switching.

best regards
cafain

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LMK01020: Reduce spurious