Transcript Acoustical Imaging Using Capacitive Micromachined

A bit about analog,
and a bit about bits
Prof. Tom Lee
Stanford University
Matrix Semiconductor
[email protected]
http://www-smirc.stanford.edu
What is analog, anyway?
• Analog quantities – such as voltage, temperature, and
pressure – span a continuum of values.
– Signals can range from, say, WiFi microvolts to power line
megavolts.
– Analog systems typically evince high functionality per unit power
consumed (e.g., the human ear consumes tens of microwatts), but
– Difficult to process and store analog signals faithfully.
– Analog functions are usually highly specialized; typically can’t
readily convert one analog circuit into another one.
• “Nature is analog.”
What, then, is digital?
• Digital signals are discrete in amplitude and in time
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Signals are of uniform amplitude, say.
Digital systems typically consume high power per function, but
Storage and replication may be performed essentially without error.
Digital systems can be quite flexible.
• Paradoxically, this property has killed off circuit design innovation.
• “Digital is unnatural.”
Analog vs. digital: A false dichotomy
• Analog processing of some kind is unavoidable at interfaces
with the physical world.
– No such thing as an “all-digital” radio, for example (despite the
buzz about “software” radios).
• Digital processing is a powerful and flexible way of
transforming, storing, conveying and regenerating
information.
– Can’t expect a 100th-generation photocopy to resemble the original,
but a 100th-generation CD-ROM can be just as good as the master.
• Analog and digital are good at quite different things.
– Explains why the arc of history has traced an increasing synthesis
of these two.
Increasing symbiosis through the ages
Increasing symbiosis through the ages
Increasing symbiosis through the ages
Another: 3-D imaging with 2-D CMUTs
dcell
Oxide passivation
Top electrode
Silicon nitride membrane
tm
Vacuum
tg
Insulating layer
10 m
ti
Bottom electrode (silicon)
100 m
100 m
100 m
20 m
What you can do with a CMUT
Mechanically scanned transducer
Analog processing
2-D electronically scanned array
Massive digital processing
So, (why) is analog ascending?
• Purely digital paradigms are limited.
– The Pentium 4 consumes ~100W, the human brain but 25W.
Biology has thrown down the gauntlet
Whither analog?
• One view: Analog will serve as merely another rationale for
Intel to build ever-more powerful CPUs. This codependency will continue until market forces dictate
otherwise.
• Another view: Insights gained from studying diverse fields
will inform, and drive, a convergent evolution of seemingly
disparate technologies.
– Hard to predict where this will go, but my guess is that ethicists and
social scientists will have plenty to chew on.
Man is the only computer that can be mass-produced
by unskilled labor.
-Wernher von Braun, rocket scientist