V-by-One HS Isolation with ADN4624

Hi Larry,

Thanks for reaching out. By a quick look, we should find a way to make it work.

Can you provide the input and output eye diagrams? It would be interesting to see the eye diagram at the V-by-One to MIPI bridge receiver inputs and the eye diagram at the isolator receiver. 

My suggestion is to play a little bit with the swing and especially the pre-emphasis levels of the transmitter. Start from 0 pre-emphasis and 400mV typ.

Also, select the Common Mode Output to VDDA-VTOD level, that should minimize the deterministic jitter added by the isolator.

In regards to the receiver,

Can you confirm the input resistance is 100 Ohm? that correctly terminates the differential pairs (which needs to be at a controlled impedance of 100 Ohm as well of course..).

You can even try to reduce the length of the SMA cable at the output of the isolator if non of the above works:

Please, let me know how it goes.

Kind Regards,

Riccardo

Hello 

Thanks for the advise.

> Can you provide the input and output eye diagrams? 

Yes. Please see the following images.

-  ADN4624 input captured at 100ohm termination on EVAL-ADN4624EB1Z

Please ignore the mask pattern because the pattern is not for ADN4624. The VID is more than |100|mV which is the spec of ADN4624 LVDS input.

- ADN4624 output captured at the AC coupling capacitor of THCV242A side

> My suggestion is to play a little bit with the swing and especially the pre-emphasis levels of the transmitter. Start from 0 pre-emphasis and 400mV typ.

I am using the setting of 0 pre-emphasis and 400mV VTOD.

> Can you confirm the input resistance is 100 Ohm? that correctly terminates the differential pairs (which needs to be at a controlled impedance of 100 Ohm as well of course..).

Yes. There is 100ohm register between Pch and Nch at the input of V-by-One HS.

> You can even try to reduce the length of the SMA cable at the output of the isolator if non of the above works:

I did not try with the short cable.

I changed the connection as the following, then I could see the streaming images.
Connect DOUT+ of ADN4624 with Nch of V-by-One HS, and connect DOUT- of ADN4624 with Pch of V-by-One HS.

I cannot see the streaming images if I connect Pch with Nch and Nch with Pch of V-by-One HS without ADN4624.

Does ADN4624 on EVAL-ADN4624EB1Z invert the logic input to DIN+ and DIN-?

The P21 of the datasheet says as following.

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When there is a positive differential voltage of ≥100 mV across a termination resistor between any DINx+ pin and a corresponding DINx− pin, the corresponding DOUTx+ pin sources current. This current flows across the connected transmission line and termination at the receiver at the far end of the bus, while DOUTx− sinks the return current. When there is a negative differential voltage of ≤−100 mV across any DINx± pin, the corresponding DOUTx+ pin sinks
current with the DOUTx− pin sourcing the current. Table 21 shows these input and output combinations.

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However, the device behavior is different from my understanding of the datasheet explanation above.

It would be appreciated if you explain and advise about this phenomenon.

Best regards,

Larry

Hi Larry,

The Eye Diagrams look very good, so I doubt it's a signal integrity issue.

The ADN4624 does not invert the logic but keeps it coherent with the input. If the input is inverted also the output will be so my suggestion is to check your connections at the input of the isolator. Is your input connection inverted?

What about if you remove the isolator? do you see streaming images when connecting the + pin of the MIPI bridge transmitter with the + pin of the MIPI bridge receiver or you need to invert them as well?

BTW, for an even better eye diagram, you can have just one AC coupling capacitor in series with the isolator. You don't need to have two.

Kind Regards,

Riccardo

Hi Larry,

I just noticed the silkscreen of our EVAL board is wrong. I will notify the team responsible of it and we will fix it.

This is the right one for channel 1: 

Probably this is your problem. I apologize for the inconvenience.

Just keep in mind that the isolator logic is coherent with the input one.

Please let me know.

Kind Regards,

Riccardo

Hello 

> I just noticed the silkscreen of our EVAL board is wrong. I will notify the team responsible of it and we will fix it.

Oh, that makes sense.
Thanks for your prompt response to my question.

Best regards,

Larry