Acoustical Imaging Using Capacitive Micromachined Ultrasonic ...

Acoustical Imaging Using Capacitive Micromachined Ultrasonic ...

A bit about analog, and a bit about bits Prof. Tom Lee Stanford University Matrix Semiconductor [email protected] 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.

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. 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. 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.

Source: Hans Moravec, CMU 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 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. Man is the only computer that can be mass-produced by unskilled labor.

-Wernher von Braun, rocket scientist

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