AWR1243: LO distribution for cascading two chips

Faiz Ahmed

Part Number: AWR1243

Hello,

I was looking at the released cascade document and it mentions that there are two possible topologies for LO distribution. I am curious to see if this third solution is possible:

Route LO signal from master to slave using pins FMCW_CLKOUT and FMCW_SYNCIN1. Route master FMCW_SYNCOUT back to itself (FMCW_SYNCIN2) and keep the both the LO trace lengths the same.The four chip cascade system seems to do something like this but this solution won't have a LO splitter. Is it alright to do it with two chips?

Thank you,

Faiz

over 7 years ago

0 Akash Gondalia over 7 years ago

TI__Guru 50240 points

Hi Faiz,

You're question has been referred to a TI Specialist on this subject and someone will have an answer for you shortly.

Cheers,
Akash

0 bginzz over 7 years ago

TI__Prodigy 545 points

Hi Faiz,

Yes, that topology is fine. There is no need to have an LO splitter in the path unless you want to support more chips.

Regards,
Brian

0 RJimmy over 7 years ago in reply to bginzz

Intellectual 535 points

Question: The recommended LO combinations from the cascaded system application note always puzzles me. The Master LO output and input pins locate at the opposite side of chip. It is very hard to route them, since the LO either travels a long way to the opposite side or across the TX/RX RF trace.

Can you help me solve this puzzle? I would really appreciate it!

Can

0 Faiz Ahmed over 7 years ago

Intellectual 460 points

Hello,

Too add to what to RJimmy mentioned, is it possible to switch the master LO input to make routing easier? So use, FM_CW_CLKOUT (D15) with FM_CW_SYNCIN2 (D15) or FM_CW_SYNCOUT (D1) with FM_CW_SYNCIN1 (B1)?

Thanks

0 RJimmy over 7 years ago in reply to bginzz

Intellectual 535 points

Any solution on my question?

I am waiting for a long time.

Thanks,

0 bginzz over 7 years ago in reply to Faiz Ahmed

TI__Prodigy 545 points

The recommendation to route FM_CW_CLKOUT to FM_CW_SYNCIN1 was to minimize any unintentional coupling on the PCB between neighboring lines. The chip does allow for FM_CW_CLKOUT (B15) to be routed back to FM_CW_SYNCIN2 (D15) or FM_CW_SYNCOUT to FM_CW_SYNCIN1. It is recommended to route these to try and maintain as high isolation as possible.

One way to handle the routing across the package, as per the original recommendation, is to route on a second layer, such as an additional RF layer underneath the L2 ground plane.

Regards,

Brian

0 RJimmy over 7 years ago in reply to bginzz

Intellectual 535 points

Ok, thanks for your answer.

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AWR1243: LO distribution for cascading two chips