SN65DPHY440SS: loss analysis

Hi David,

should we also include Pre-emphasis 2.5dB?

We don’t know yet, but base on your experience, do you think how long we can support coaxial ?

HI,

2.5dB would pre-compensate for the TX output loss. I assume they are not putting the DPHY440 inside the cable, so I did not include pre-emphasis. 

I honestly don't know if DPHY440 will support this particular cable, how much loss the cable has is the most important factor.

Thanks

David

Hi David

one question , can this retimer be cascade?

just in case.

Hi,

Yes, you can cascade two DPHY440.

Thanks

David

Hi David,

quick question, why does this redriver can cascade but also have pre-emphasis function?

I thought limited redriver can’t cascade 

Hi,

DPHY440 is a re-timer, not a re-driver, and you can cascade them.

Thanks

David

Hi David,

here's their analysis, both signa losses are larger than maximum 4dB EQ,

obvious we need some pre-emphasis support,

does this mean I can't place the retimer too close to CPU, so I can leverage TX driver's pre-emphasis, right?

Hi,

Do you have a block diagram of the overall connection that you can share?

Thanks

David

Not yet it’s very early stage, they will use two of our retimers, one for IR camera the other for RGB.

but what I trying to say is we should leverage TX if we want to compensate 5.68dB,

so we should spare some length between CPU and retimer , right?

Hi,

You could use the TX pre-emphasis to provide compensation. But the DPHY440 RX also provides de-skew function. So any skew on the TX side will not be de-skewed.

Thanks

David

Hi David,

sorry, little confused,

are you saying if we enable TX pre-amphasis,

the de-skew function will not be valid, which mean I can only choose either one?

is it listed in the datasheet?

Hi,

No. Please see the example below 

If I have a 5in input trace, DPHY440 RX will able to provide de-skew function for the 5in input trace. 

But if I have a 3in input trace and 2in output trace, DPHY440 will only able to provide de-skew function for the 3in. The skew for the 2in will not be compensated by DPHY440.

Thanks

David

Hi David,

thanks I got your point now,

but regarding TX pre-emphasis,

Do we still have meaning or point to enable it if we left all 5 inch on the RX side?

that's say 5inch has 5dB loss, and we still missing  1dB at RX,

is there improvement if we enable TX pre-emphasis?

Hi,

For the 5in on the RX side, you will use RX EQ to compensation for the loss. You will only enable TX pre-emphasis to compensation for any trace loss at the DPHY440 output.

Thanks

David

But what if RX EQ gain is not enough,

And we need to leverage TX pre-emphasis?

shouldn’t we consider move redriver closer to TX a bit and enable pre-emphasis?

Hi David,

it’s alright, since it’s not linear redriver, i assume and guess it may not compensate for under-equalizer input signal .

anyway I will recommend them place at CPU as close as possible,

thank you for your support