[SI-LIST] : Z Odd-mode, edge-coupled, 50ohms?

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From: cadpro2k@dacafe.com
Date: Mon Jan 15 2001 - 14:13:12 PST


Hi all,

I'm in a little need here. I'm a PCB layout person doing a design where
the engineer would like his "pairs" (positive/negative mode) run to give
him 50ohms, edge-coupled, Z-odd mode (what?) coupling which terminate
thorugh 100ohm resistors. What? If someone could put this in more
layman's terms for me I'd really appreciate it. I look at the spec he's
supposedly using and it shows the driver driving the pos/neg signals
thru caps (AC), or not (DC) and with 50 ohm traces to the 100ohm
resistors at the load pins. I've typically done this, but I've never
heard such terminology before.

I'm used to routing 50ohm lines with proper spacings for the pairs as
well as staying "comfortably" away from other pairs or other traces. Is
this really what he's after or am I missing something.

He had first mentioned he wanted the pairs routed as either edge-coupled
100ohm differential or broadside coupled differentials, but when I
questioned him on it he changed the tune.

When is 100ohm differential routing required? Is there some indication
in the device (chip) specs that points to it?

TIA.

Mitch
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