DS90UH948-Q1: 284kHz frequency through the FPD-link cable

Roy Chou1

Part Number: DS90UH948-Q1

Hi Team,

We would like to know if there is 284kHz frequency transmission when the SerDes do the communication.

It may be the back channel speed. But for back channel, the lowest speed is 5Mbps. So I'm not sure if there is any low frequency transmission between SerDes. And now we use the 5Mbps speed for BC.

I checked the datasheet and find below parameter and I have no idea what is Rb,BC. May you help let me know the meaning?

And could you let me know your idea that how to indicate the 284kHz source?

PS. We shield our SerDes and only exposed the cable and find there is 284kHz EMC noise. And adding core on cable could improve the result.

We will adjust BC speed next time. If you have any idea to check the root cause, please let me know. Many thanks.

Regards,

Roy

over 4 years ago

0 Logan Cummins over 4 years ago

TI__Guru 66810 points

Hi Roy,

Roy Chou1 said:
checked the datasheet and find below parameter and I have no idea what is Rb,BC. May you help let me know the meaning?

Rb,BC is the effective GPIO toggling speed/frequency through the back-channel communication.

At first glance, I don't see anything that would be operating at that frequency/harmonic of that frequency. Please give me a day or two to look into this further.

Regards,

Logan

0 Logan Cummins over 4 years ago in reply to Logan Cummins

TI__Guru 66810 points

Hi Roy,

After discussing further internally, there could possibly be either harmonics as the cause or could be related to the power supplies coupling into the cable.

In the past, we've gotten improvement in this frequency range by adding a ferrite clamp to the power cables which are supplying the system.

Regards,

Logan

0 Roy Chou1 over 4 years ago in reply to Logan Cummins

TI__Genius 16090 points

Hi Logan,

Our system used two cables between SerDes. One is 12V power cable and the other is FPD-Link cable(STP). Do you mean that we could try to add ferrite bead nearest the power cable connector? (Deserializer side)

Regards,

Roy

0 Logan Cummins over 4 years ago in reply to Roy Chou1

TI__Guru 66810 points

Hi Roy,

Roy Chou1 said:
. Do you mean that we could try to add ferrite bead nearest the power cable connector?

Yes, that is correct.

Regards,

Logan

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DS90UH948-Q1: 284kHz frequency through the FPD-link cable