Electronic Design
First Commercially Available Atomic Clock: Smaller, Lighter, And More Efficient

First Commercially Available Atomic Clock: Smaller, Lighter, And More Efficient

Timing is everything. Until now, however, traditional quartz-based timing options have forced users to make tradeoffs among size, accuracy, and power consumption. This is especially problematic in communications equipment used for sophisticated and critical (such as military) applications.

Oven-controlled crystal oscillators (OCXOs) still enable many products, but their specs are insufficient for newer, high-end equipment needs. The accuracy and stability of an atomic clock is ideal, but the widely used GPS-based clocks are impractical due to size, weight, and efficiency considerations. Symmetricom has solved this problem with its SA.45s chip-scale atomic clock (CSAC).

An atomic clock is a precise and stable oscillator whose frequency is based on the oscillation of the atoms in a specific material. Most atomic clocks use the gaseous atoms of cesium 133 or rubidium. Standards organizations around the world use the oscillation of cesium 133 (9,192,631,770 cycles, to be exact) as the definition of one second.

All government and commercial timing equipment, including the precise timing signals from GPS satellites, is based on such atomic clocks. These GPS signals are commonly received and decoded to recover exact timing signals for use in a variety of high-precision equipment, such as cellular basestations.

Symmetricom has applied microelectromechanical-systems (MEMS) and other sophisticated packaging that generates this frequency to control the output of a standard oscillator with an amazing accuracy and stability, reducing the size and power consumption of the physics package.

The SA.45s (see the figure) CSAC provides the accuracy and stability of an atomic clock while delivering dramatic improvements in size, weight, and power. It is only 16 cc in volume, weighs only 35 g, requires only 115 mW, and provides time accuracy two orders of magnitude better than the higher-power quartz-based solutions it replaces, such as OCXOs and temperature compensated crystal oscillators (TCXOs).

The device operates from 3.3 V dc, and the output is a 10-MHz square wave. Frequency accuracy is ±5 x 10-11 with a stability of less than 2 x 10-10 over one second. Furthermore, the SA.45s CSAC features a 1-pps output with an accuracy of ±50 ns. A CMOS-compatible RS-2332 interface facilitates internal monitoring and external control and tuning. A 1-pps synchronization input is also available to sync to an external source.

Thanks to its ultra-high-precision and low power consumption, the SA.45s CSAC enables a whole new range of portable and other applications, such as dismounted (backpack) improvised explosive device (IED) jammers, unmanned aerial vehicles (UAVs), next-generation man-pack radios, and military handheld GPS units, as well as geophysical sensors including underwater exploration gorphones/hydrophones. The SA.45s CSAC will be particularly useful in hold-over clocks that maintain timing and frequency control even if another timing source (such as a GPS signal) is lost.

In fact, early adopters have already validated the advanced technology benefits of the SA.45s CSAC. Makers of underwater sensors have used the CSAC’s low power consumption and increased stability to prolong mission duration. Users who rely on military GPS systems have found that the CSAC has the stability to maintain synchronization even during long GPS outages and that it also enables rapid signal reacquisition. Its small size and extremely low power consumption provide these benefits even in man-pack systems.

The SA.45s CSAC is a member of Symmetricom’s Quantum family of atomic oscillators. It is available in two versions. Option 001 operates from –10°C to 70°C for commercial applications, and Option 002 operates from –40°C to 85°C for military applications. The SA.45s CSAC is available now at a U.S. list price starting at $1500 in small quantities.

Symmetricom Inc.

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