Impedance Discontinuity on a HDMI/DVI signals

[kudjung]

Hi There,

I've this question. We need to make a DVI to HDMI converter box for a DVI source with custom connector.

From a DVI source, it route through custom DVI cable and then to this converter box then to a custom HDMI cable to the HDMI receiver.

DVI Source(custom connector) ------(A: custom DVI Cable)----->Adaptor Box------(B:custom HDMI Cable)---->HDMI Receiver

I understand that it's not good to do this since it will create impedance discontinuity but what is the best way to this if we really need to do this.

What is the best way to do this to upset Signal Integrity as less as possible and cause less EMI problem. PCB trace on the adapter box will be very short and routed with 100 ohm. Length of both cable is adjustable.

Should we make the A side as short as possible?

Thanks in advance for any comments or opinion.

 

[emresel]

If you are able to make some custom cables, why not ask your cable manufacturer design a cable from custom DVI conn to HDMI conn directly. As i know by means of pinning HDMI and DVI has similiar signals.
If not possible then you can design that converter as you explained. Be sure adjust PCB trace imp @100ohm. On converter pcb you can may be insert some series component (1 ohm smd res), then adjsut value according to final results.

 

[marce]

You just can add resistors and hope! Series resistors have to be placed in a very specific places, not just thrown down and hope!
By trace impedance I presume you mean 100Ohm differential impedance between the signal pairs, there is a difference between this value and the value for single ended...
If realy concerned simulate the design to check the signal integrity of the layout...