LMX2694-EP: LMX2694-EP：questions about spurs

jiao he

Part Number: LMX2694-EP

Hello All,

1、I am looking for the evaluation board design files. An Altium board package or gerbers would be of great help。my email address：hejiao@yinhe.ht。

2、I have designed a new product useing LMX2694-ep。Could you help to review the designe?My PCB pictures is as follows.

the schematic

top layer

the second layer

the third layer

the last layer

3、my question is “How to eliminate the 100MHz-spurs”。when I test my product in “2、”,The spectrum diagram is as follows(The spectrum diagram have 100MHz-spurs):

I test The LMX2694-EPEVM,The spectrum diagram is as follows(The spectrum diagram have not 100MHz-spurs)。

thank you very much!

over 4 years ago

0 Noel Fung over 4 years ago

TI__Guru** 121110 points

Hi Jiao,

Looks like you have an amplifier in front of OSCin, would that be the reason for the 100MHz spurs?

You have a few traces underneath the synthesizer, this is not ideal, a solid ground plane is preferred.

Here is the gerber file.

LMX2694EVM_gerber.zip

0 jiao he over 4 years ago in reply to Noel Fung

Prodigy 40 points

I have jumped the amplifier,but the spurs still remains.

0 jiao he over 4 years ago in reply to Noel Fung

Prodigy 40 points

I have jumped the traces in second layer,but no help to 100MHz-spurs

0 Noel Fung over 4 years ago in reply to jiao he

TI__Guru** 121110 points

Hi Jiao,

I don't know how you could "jump" the traces in the second inner layer. One of the critical traces, Vtune-Z1, has crosstalk between multiple traces on top layer and a trace (I guess it is power supply) on the third layer. I think a new layout is needed in order to eliminate the spurs due to input reference clock.

Clock & timing

Clock & timing forum

LMX2694-EP: LMX2694-EP：questions about spurs