Colibri iMX6 Ethernet

Hi community. I want to bind the Colibri iMX6’s ethernet tx_n-p and rx_n-p lines to another eth phy.
I designed the circuit with capacitive coupling technique.
I referenced the desing from the application note

This is my design for binding ethernet

And my external phy chip is TLK111PT then the capacitive coupling technique is adaptive.

I checked the IRIS eval boards hardware design. Then i saw the ETH RX ± pins werent biased with 50 ohm to 3V3. Is there any internal DC bias on Colibri iMX6’s ETH TX and RX pins. Cuz i removed the R116 and R117 on my design the ping is worked. But eth connection is not good enough. Is this design is correct? Could you please share KSZ8041’s bias scheme? Or could you please give me some information about hardware on Colibri iMX6?

Dear @erdemkahraman,

Sorry for the delay in answering you. This post has passed out of our radar.

If you look at our Colibri Carrier Board Design Guide ( you’ll find this reference schematic for Ethernet:

There you can see that the 50 ohm resistances have been placed with a 100nf Capacitance to the ground.

Does it work well with R116 and R117 connected?

Also, can you share more information about your schematic? It’s not really clear to us how you’re connecting the signals to the final device. You can do this by private message or by mail to

Best regards,

Dear @erdemkahraman, how are you? It’s me again :smiley:

Do you have any news on the ethernet topic?

Best regards,

Hi @gclaudino.tx

Thanks for your reply.

I am trying to connect the ETH signals with capacitive coupling. About my last question, yes it worked well with R116 and R117 connected. But…

I produced 2 boards which are the same with my last schematics.

I am connecting my first Colibri iMX6 to my first baseboard and it seems like worked well (I can send UDP packages over ETH from Colibri to my PHY (TLK111PT) ), I can connect the device over SSH etc.).

Then i connected the second Colibri iMX6 to my first baseboard, link is up but i am not able to connect with SSH or any protocol.

I think the main issue is;

I cant send any data to my second Colibri iMX6 module over ETH.
I decided the analyze ETH lines. It looks great on eye diagram. Then I connected the logic analyzer on Colibri’s ETH PHY (KSZ8041)'s RX_DV

and my baseboard’s PHY (TLK111PT)'s TX_EN

and these signals must be equal. Cuz I am transmitting signal with TX_EN and the KSZ8041 gives information about RX packets RX_DV.
The TX_EN and RX_DV must be equal but on my system (which is second Colibri iMX6 and first baseboard), they aren’t.

Then I connected the my first Colibri iMX6 and my first baseboard. (It was seems worked well). TX_EN and RX_DV was better than others.

Why is there a difference between Colibri iMX6 devices?
Cuz test conditions are baseboards same and Colibri iMX6s different.

Hello erdemkahraman,

can you try if both modules work in our carrier boards?
I just want to exclude that there is something wrong with the modules.

Best Regards,
Matthias Gohlke

Hello @matthias.tx

Thanks for your reply.

  • Yes the ethernet connection was great on Iris and Viola Carrier Boards but they do not use capacitive coupling. They use transformer base coupling.

ok so we can exclude the SOM as a problem.
did you follow the ref guide on the capacitive coupling of the PHY manufacture?
Do you have more information on the PCB layout? did you route the signals impedance controlled?

Best Regards,

Matthias Gohlke

Hi @matthias.tx

Thanks for your reply.

I have already followed these guides.

Yes we have already controlled the lines impedences. They all impedenced as 100 ohm.

Have a nice day.


could you send us some pictures of the different PCB layers. so that we can check for other signalin issues like current return paths?

Best Regards,

Matthias Gohlke