Thread Links Date Links
Thread Prev Thread Next Thread Index Date Prev Date Next Date Index

Re: [802.3ae] differential skew for 10Gbps serial

Harry Wang wrote:

> Hello,
> What is the spec for differential skew at the electrical 10Gbps serial side?

This parameter is not directly specified. However, differential skew
on the electrical signal is going to contribute to rise/fall time of the
optical signal.

For example, the transmit rise/fall time spec for the optical 10GBase-S
signal is 35ps max. Making the broad assumption that the optics add
no additional rise/fall time penalty, the rise/fall time spec becomes the
differential electrical requirement.

Under the assumption that the 10Gbps driver rise/fall time is 25ps, and
the optics have no contribution, the differential skew is (35-25)=10ps.

If the circuit board propagation delay is 180ps/inch, the differential
signals must be length matched within 0.05".

I have made many assumptions in order to simplify the problem.
I hope I have given you some guidance to help answer your
question. Your mileage may vary.

Tim Warland  P. Eng.
Applications Engineer
Quake Technologies   (613)270-8113 ext 2311

Tough Times don't last, tough people do