[SI-LIST] AC Coupling for SERDES Links across Backplane
- From: "Harjeet Randhawa" <harjeet.randhawa@xxxxxxxxxxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Thu, 28 Oct 2004 12:33:43 +0530
Hi All,
The XAUI spec mandates putting the AC coupling CAPs for the SERDES links
to allow inter-operability among different SERDES technology vendors due
to probable different internal BIAS levels.
But for the scenarios where the SREDES cells are same does it helps in
any way to AC Couple the SERDES links. The scenarios may be where there
is 40" of PCB trace running from a line card to backplane and finally to
a Fabric Card.
The SERDES cells are matched in the sense that they are having same
characteristics and from same vendor. The BIAS voltage is generated on
board with 5% regulation. I do not expect any high current transients on
the BIAS voltage and it is well filtered and decoupled.
Also there is a consistent Ground Plane bridging at backplane connectors
so the GND differential across the TX to RX points should not cause any
significant BIAS reference shifts.
The whole issue is due to fact that the Transmit Pairs of the SERDES are
2-3 rows deep in the package so adding the AC Cap will force to add two
more VIAs on the routes adding to deterioration of the signaling
quality.
Thanking all in advance for their valuable suggestions.
Best Regards,
/---------------------------------------------------------/
Harjeet S Randhawa,
Nevis Networks INC.
/--------------------------------------------------------/
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