A bit about analog, and a bit about bits

1
A bit about analog,and a bit about bits

• Prof. Tom Lee
• Stanford University
• Matrix Semiconductor
• tomlee_at_ee.stanford.edu
• http//www-smirc.stanford.edu

2
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 cant readily convert one analog
  circuit into another one.
• Nature is analog.

3
What, then, is digital?

• Digital signals are discrete in amplitude and in
  time
• 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.

4
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.
• Cant 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.

5
Increasing symbiosis through the ages
6
Increasing symbiosis through the ages
7
Increasing symbiosis through the ages
8
Another 3-D imaging with 2-D CMUTs
9
What you can do with a CMUT
Mechanically scanned transducer Analog processing
2-D electronically scanned array Massive digital
processing
10
So, (why) is analog ascending?

• Purely digital paradigms are limited.
• The Pentium 4 consumes 100W, the human brain but
  25W.

11
Biology has thrown down the gauntlet
Source Hans Moravec, CMU
12
Whither analog?

• One view Analog will serve as merely another
  rationale for Intel to build ever-more powerful
  CPUs. This co-dependency 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.

13
Man is the only computer that can be
mass-produced by unskilled labor.
-Wernher von Braun, rocket scientist