Re: [SI-LIST] : Gigabit cable assembly

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From: David Instone ([email protected])
Date: Fri Jul 21 2000 - 02:16:19 PDT

  The Micro-D is the connector used by SSA, the HSSDC is also approved
for use with SSA. At the time the HSSDC was being considered for
approval as an alternative to the Micro-D I did several TDR comparisons
of the two connectors and, at the time, I could see no significant
differences between the two. The HSSDC has improved since then, and
from your decription of a one piece backshell the Micro-D has too, the
backshell was always an EMI problem unless wrapped with copper tape
after assembly.
Intrinsicaly the Micro-D makes a better EMI seal to the panel being
essentialy a tophat shape.

  When it comes to size though the eye can be deceived. Both connectors
require 20mm width of panel space and both can be side stacked at this
pitch, Behind the panel the Micro-D needs a touch under 8mm vertically
and the HSSDC needs 10mm. On PCB 'real estate' the Micro-d takes up
about 20mm x 10mm of board area, the HSSDC varies depending on the style
but 20mm x 17mm is about the norm. The HSSDC is available in a surface
mount style, I believe the Micro-D is only available in through hole.

However, when looking at the plug the Micro-D wins at 20 x 9.5 mm cross
section against the 18 x 16 of the HSSDC, both have about the same
length. When mounted on PCI cards when several cards are stacked side
by side the Micro-D wins because its jack screws can be undone however
many connectors there are, whereas it is impossible to get at the
release latch of the HSSDC. That said, you need a screwdriver to
do/undo the Micro-D whereas the HSSDC requires only your fingers. A
push/pull version of the Micro-D was documented, but I don't know if it
was ever manufactured or used in quantity. The Micro-D plug can be
field assembled and dissasembled, the HSSDC is a moulded assembly. The
close pin spacing of the Micro-D limits the core size of the cable that
can be used, and unless a version with a pcb inside has been developed
an equalized cable assembly is not possible. (probably!)

The later versions of the HSSDC have been shown to be usable at
2.124Gb/s. Unless there has been considerable development of the
Micro-D I would agree that it probably won't work too well.


Dave Instone. Compliance Engineer
 Test Systems, MP24/22
 Xyratex, Langstone Rd., Havant, Hampshire, P09 1SA, UK.
Tel: +44 (0)23-92-496862 (direct line)
Fax: +44 (0)23-92-496014 Tel: +44 (0)23-92-486363


Knighten, Jim L wrote:
> Sunil,
> My company has a 1.0625 Gb/s link from cabinet to cabinet. We chose the
> Micro-D Subminiature by UltiMate along with a one piece backshell can for
> EMI. This choice was made a couple of years ago, prior to the second
> generation HSSDC style. The Micro-D is not impedance matched for either our
> application (150 Ohms) or yours (100 Ohms) in that its differential
> impedance is near 90 Ohms. It is smaller than the original HSSDC. It has
> EMI characteristics which are superior to the HSSDC and we find that we are
> able to operate our links for a few tens of meters without difficulty.
> As we look forward to 2.5 Gb/s and beyond, I don't think our connector will
> be satisfactory for the signal, however.
> Jim

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