Chip Scale Atomic Clock

Precise timing has many applications in telecommunications. But the precision of commercial systems is typically limited by the precision of a vibrating quartz crystal—a tiny chunk of rock. More precise atomic clocks using the natural frequency of individual atoms have been confined to laboratories and special applications because of their cost, size, and power consumption. But a chip-scale atomic clock (CSAC) that can fit on a PC board has just become commercially available, and this changes everything.

Applications that needed more precise timing than a stand-alone quartz crystal provides can use precision time transmitted by GPS satellites. But the GPS signal can only be used to discipline the quartz clock. That’s like trying to discipline a frisky dog on a leash. Every time it runs to one side of the path, it has to be yanked back. So it can’t run away, but it’s not a very stable reference. An atomic clock is like a trained dog that follows the path without pulling on the leash as much.

There are lots of military applications for a small, low-power atomic clock including unmanned aerial vehicles, and man-carried portable systems. Undersea exploration is a natural fits as well, because GPS is not available under water. It can also be used in telecom applications where getting a GPS signal is costly, like colocation facilities.

One interesting application is performance monitoring in low-latency networks. Measuring round-trip latency from one end of an out-of-service link with a loopback at the far end is relatively easy, because the transmitter and receiver use the same clock. But that only gives a best-case baseline. To test a live system under load, you can tap the signal at various points and time-stamp the packets, then compare the time stamps to continuously measure latency. But the latency measurements are only as good as the time stamps, which are subject to error from variation in the clocks at the measurement points.

High-end live network monitors currently use heated quartz crystals to minimize thermal effects. They can also take in a GPS signal to discipline the clocks. But this only allows precise latency measurements at different places of microsecond order. With cut-through switches now forwarding packets with sub-microsecond latency, there is a gap in the precision of measurement needed. The new CSAC provides time with about two orders of magnitude better stability than the best quartz crystal, and can therefore close this gap.

Not only is the performance of the CSAC two orders of magnitude better than quartz, its size, cost, and power consumption are at least an order of magnitude better than previous low-end atomic clocks. So this is truly a revolutionary, not an evolutionary, breakthrough. There are probably many varied applications for this new technology yet to be discovered as well.

Doug Haluza, C.T.O., Metro|NS

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