i.MX8M Mini Ethernet signals

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i.MX8M Mini Ethernet signals

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nija_mankodi
Contributor II

Hi NXP team,,

We are designing a product on i.MX8M Mini processor and Ethernet signals are used for VoIP calling.

However, because of mechanical constraint, we have to route Ethernet signals via B2B connector and its flex cable. The total Ethernet differential signals length from RJ45 to processor (including flex cable) goes about 7 inches. I understand that such huge length is not recommended for high speed signals but we have no other option.

So, if there any possibility of using Ethernet differential buffers to maintain signal integrity and avoid losses due to more length? Do you recommend any part for buffers?

Is there any possibility to increase drive strength of these signals to achieve signal integrity or any other option that you can suggest?

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nija_mankodi
Contributor II

Hi NXP team,

Please update on this ASAP.

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nxf54947
NXP Employee
NXP Employee

Dear Nija Mankodi,

My apologies for the delay in my response.

To answer your first question, you can use buffers for impedance matching across the transmission line. I would suggest you to start looking at the dual buffers that are included in the Ethernet section of the schematics contained in the i.MX 8M Mini EVK Design Files:

i.MX 8M Mini Evaluation Kit DDR4 Design Files

i.MX 8M Mini Evaluation Kit LPDDR4 Design Files

Regarding the drive strength  alternative, you can try to change that muxing characteristic of the processor's pads. However, please keep in mind that there are channels that commonly act like a low-pass filter that introduces distortion to the high speed signals. Hence, increasing the power transmitted might not solve the issue at frequency domain. So, you should characterize the 7 inches channel in order to study how the Ethernet signals are going to be affected.

 

Signal equalization is a common technique to compensate channel's distortion. Basically, it uses a high-pass filter that increases the magnitude of the high frequency components of a signal. That would be a good starting point to try achieving a more opened eye diagram and signal integrity.

Also, you should validate if the Ethernet PHY that you select contains any module that would be helpful to accomplish your goal.

I hope that the information was helpful.

Best regards,

Ruben

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nija_mankodi
Contributor II

Hi Charles,

Thanks for your valuable comments.

However, EVM kits has driver/buffers for signals between SoC and PHY. However, we are in need of buffers/drivers for Ethernet differential signals as its length goes above 7 inches. So could you please suggest, buffers/drivers for these 100ohm differential signals.

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nxf54947
NXP Employee
NXP Employee

Hi Nija,

Unfortunately, NXP does not provide that kind of buffers. I understand that there are other third parties that provide this devices. However, I cannot suggest you any of them since we do not use it in our designs.

I apologize for the inconvenience that this may cause to you.

Best regards,

Ruben

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