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MAS Architecture
What's required to actually do MAS
- Multi-level transmitter
- Multiple receiver thresholds
To make it work in the practical world you will also need...
While you're doing that, you might as well add...
- Adaptive equalization - to fix problems with channel pulse response
- Scrambled line coding - to fix problems with EMI
I'm not suggesting that multilevel signaling (or multi-amplitude signaling, MAS) is easy.
Far from it. This is the sort of thing you do when you need to go faster and don't have
any other alternative.
But, given the incredible resources made available to us by improvements in chip technology,
I can't think of a better use for all those hundreds of millions of transistors.
And think about some of the benefits -- especially from adaptive equalization. It can
cure problems with bad connectors, trace stubs, and other artifacts. Maybe we are headed towards a
day when we can spend less time worrying about the impedance of the channel, and minor reflections,
and more time worrying about important issues like backplane protocols and system throughput.
What about EMI? It's better. Scrambling the channel, a provision often incorporated to insure
the rapid convergence of adaptive-equalization algorithms, will spread the emissions spectrum of
the data lines, providing huge benefits in EMI compliance.
And what about clocks? Don't need 'em. Every serial receiver comes with it's own built-it
clock-recovery subsystem. The clock is coded in the data. There's aren't any separate clocks.
Scrambled, serial links are an EMI dream-come-true.
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