RE: [SI-LIST] : Clean sheet of paper

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From: Chris Cheng (hycheng@3pardata.com)
Date: Wed Dec 22 1999 - 18:02:22 PST


with the growing trend of source sync or clock forwarding buses.
symmetry of the drivers/terminators is going to be important too.
neither GTL nor PECL is ideal in this area.

-----Original Message-----
From: owner-si-list@silab.eng.sun.com
[mailto:owner-si-list@silab.eng.sun.com]On Behalf Of D. C. Sessions
Sent: Tuesday, December 21, 1999 3:04 PM
To: SI-List
Subject: [SI-LIST] : Clean sheet of paper

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
  voltage-stress-tolerant semiconductors.

* 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
dc.sessions@vlsi.com

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