From: D. C. Sessions (firstname.lastname@example.org)
Date: Tue Dec 21 1999 - 15:04:02 PST
With the year wrapping up and my inbox filling with
"Out of Office Autoresponse" messages, I thought I'd
kick off something more interesting than the joys of LVDS.
In particular, what would we use for signaling if we could
start with a totally clean sheet of paper? Rather than
immediately jump to a solution, I'm looking for some criteria:
* It has to be scalable. Given silicon technology trends, it
should migrate gracefully to lower-voltages and less
* It has to be SI clean. Output impedance should be matched
(stringency variable) to the line across the switching range.
Inputs switchpoints should be symmetrical and well-defined
(ie differential receivers). Power plane proliferation
leads to bad SI and wasted money, so separate termination
supplies are a Bad Thing.
* It has to be versatile. Single-ended, balanced single-ended, or
differential; multidrop or point-to-point; uni- or bidirectional;
all should be minor variations on the same system.
* It should be economical. Wasted power is a Bad Thing, so low
swing is a must. Padrings are some of the most expensive real
estate around, so pincount should be minimized. Line termination
can dominate a PWB so KISS is the rule. Power supplies (esp.
ones that can both sink and source current) are expensive and
nasty to deal with, so do without (both for termination and
funny analog functions in the I/O circuits.)
What can we add to the list? Remove? Priorities? (This is
engineering, we make tradeoffs.) Where does this take us?
-- D. C. Sessions email@example.com
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