Using a 100Ω differential cable for a single ended signal.

[kender]

Folks,

I’ve got a 0.5m cable which consists of eight 100Ω differential pairs. Six pairs are used for high speed differential signals (450MHz). I want to use one of the remaining pairs for sending a 24 MHz reference clock. The clock is single-ended. The receiver of the clock is also single-ended. What are the good ways to accomplish that?

I could use a differential driver and a receiver, course. [Something like MAX9110 and MAX9130, for example.]

I could use baluns.

Are there other [simpler] ways? What do you think?



Any suggestion, insight or reference is really appreciated!

Sincerely,
- Nick

 

[dick_freebird]

I think you would be best off to throw the 24MHz
ref clk as differential, and "throw away the other phase"
at the destination. This, because otherwise you will
push 24MHz common mode toggle onto all the high
speed lines and probably make some contributed DJ.
Whatever comes of the coupling and HF CMRR /
prop delay delta. Might cost you some BER margin
on the lines you care more about.

But with it being twinax the coupling is probably
tiny (other than any longitudinal current). That still
could make an eye picture less pretty, if you bounce
the far end ground with all the displacement current
of the shield driven by the 24MHz single ended.

You might try the differential, then cut & ground
the mate, float the mate, take whatever SI readings
you might be on the hook for later and see if it
matters, if so what's best.

 

[FvM]

Expect a single ended impedance of 60 - 65 ohm with the other line grounded. Common mode crosstalk to differential pairs shouldn't be a problem. EMC could be the major reason to use 50:100 ohms baluns.

 

[BigBoss]

If the other 450MHz carrying Signal Pairs are also Differential, there shouldn't any problem due to Differential structure. I'd use a SE-to-DIFF Amplifier to drive this composite cable.