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Chip-Scale Atomic Clock

The ultimate in precision--the cesium clock--has been miniaturized

4 min read

The standard by which clocks in the United States are set is a cesium-based atomic clock in Boulder, Colo., that loses less than a nanosecond per day. It’s the size of a small car and draws roughly a kilowatt of power. Less-accurate commercial atomic clocks, which keep time by watching the vibrations of atoms, are typically the size of a suitcase, though not nearly as portable as one. But now, for the first time, atomic clock accuracy is available in a form small enough and power-efficient enough for backpack-size battery-powered devices. Someday an atomic clock might even fit into a smartphone.

Earlier this year, Symmetricom, of San Jose, Calif., introduced the first commercial chip-scale atomic clock, the SA.45s. It measures 4 by 3.5 by 1.1 centimeters, weighs 35 grams, and draws a paltry 115 milliwatts. The tiny clock is accurate to within about less than half a microsecond per day.

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The Transistor at 75

The past, present, and future of the modern world’s most important invention

2 min read
A photo of a birthday cake with 75 written on it.
Lisa Sheehan
LightGreen

Seventy-five years is a long time. It’s so long that most of us don’t remember a time before the transistor, and long enough for many engineers to have devoted entire careers to its use and development. In honor of this most important of technological achievements, this issue’s package of articles explores the transistor’s historical journey and potential future.

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