[SI-LIST] : Cable skew

Muzahid Huda (huda@siimage.com)
Mon, 23 Mar 1998 18:39:55 -0800

I have just finished measuring the intra-pair skew in seven samples of a
6-foot twin-ax cable. This cable consists of 4 twisted pairs (ie. 8
lines) and an individual shield for each pair (ie. 4 shields). The entire
bundle is enclosed by an outer shield.

In all seven samples, the measured intra-pair skew in three of the pairs
was within 50ps. The fourth pair consistently exhibits at least
150ps-200ps of skew. In these samples, it is always the <underline>same
pair</underline> that consistently measures this variation.

I have checked my measurement technique and equipment to eliminate any
systematic errors. I have also cut open a cable to check for physical
length differences, etc. The cable assembly has a molded ferrite choke
on one end; I have even removed this choke and remeasured the skew.
Nothing seems to make a difference.

Any suggestions/ideas/theories will be greatly appreciated.

Muzahid Huda

Staff Engineer

Silicon Image, Inc.

Tel: (408)873-3111 X132