[SI-LIST] rapid io tracking/termination impedance
- From: "WALKER, Mark" <mark.walker@xxxxxxxxxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Wed, 2 Jul 2003 14:42:38 +0100
Dear all, I hope someone can enlighten me about the impedance regime used
for serial rapidio transmission.
I intend to construct a demonstration board (in polyimide) for
characterising the various pre-emphasis and amplitude settings of
transceiver pairs, with a selection of trace lengths and geometries. The
board will have many SMA connectors for interfacing to transceiver specific
boards - some bought, some made, to offer flexibility & future
upgradability.
I had assumed the standard would specify a 100R differential regime, but
when I came to search the rapidio standard, found only the following:
The electrical interface section, on P15 of the tech white paper, states
that "serial Rapidio technology uses differential current steering drivers
based on those defined in the 802.3 XAUI specifications." The standard (page
VI-117) notes that some of the eye diagram relative timing is taken from the
output of a XAUI transmitter in 802.3.
The AC electrical specifications (Chapter 8, part IV of the Rapidio
standard) defines the differential signalling voltage levels and timing for
the short/long run transmitters/receivers at the 1.25, 2.5 & 3.125Gbit/s. It
is noted below each table of specifications that AC coupling may be required
to ensure compatibility between vendors, yet termination and tracking
impedance don't get a mention.
If this is all the standard specifies, I will be forced to refer to specific
device vendor's app notes. The danger is that if characteristic
impedance/termination requirements vary between vendors I may end up with
some specific tracking implementation targeted at my current preferred
vendor that may not work with future transceivers. This then fails to be the
generic board I desire.
I hesitate to ask what seems like such a fundamental question. Hopefully
I've not missed anything obvious and someone seasoned in rapidio
implementation will be able to pass on their expertise. In the mean time I
look forward to your advice. - Mark.
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