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Always-on GPS location data for 1 mA

When you have location data available all the time, it changes the way you can use GPS”— that is the assertion of startup fabless semiconductor company Air Semiconductor, working towards introducing its first product in mid-2008. Air says that for designers of location-aware systems, it has solved the “TTFF” (time-tofirst- fix) problem: you embed GPS in your product, but when you need GPS data, your system must wait while the GPS function acquires satellite signals and calculates a position. In a battery-powered product in which GPS is a secondary function, the power consumption of GPS is such that you will not have it running all the time. Air says its AirWave chips will solve that problem with a current consumption of 1 mA, and always-on operation: in contrast to previous approaches, you might run this GPS function in a portable product even when all other functions— including the product’s primary one—are turned off.

Air has created an architecture that supports trading off—in dynamic fashion— accuracy against power demand: you can switch from low-power but low-accuracy to high-accuracy—but higher power—modes. On demand, the chip will calculate its current position in a similar manner to any other GPS receiver, to—assuming a clear view of the sky—the usual few metres. At all other times it operates in a low-power mode, in which it always maintains ephemeris and almanac data on visible satellites, but only calculates a coarse fi x on its position. Air co-founder and CEO Stephen Graham says the accuracy of that fi x is variable, but might be in the range of hundreds of metres. The 1-mA fi gure is an average across both modes, with typical usage.

The company intends to produce a series of chips, each optimised for a particular application profi le. The first, AirWave 1, will target makers of digital still cameras, for “geotagging” photographs. In this application, the GPS function will run in its lowpower mode all the time, and the action of taking a photo will be the event that requests an accurate fix—Graham says the by the time a typical camera has carried out the jpeg compression of the image, his chip will return location coordinates to attach to it. In contrast to conventional GPS receivers, when the AirWave loses satellite signals— when you moving indoors, for example— it will continue to return the coordinates of its last known position (as opposed to not outputting any data at all). “Obviously,” Graham says, “that’s a compromise— but for applications such as photo geotagging, a reasonable one.”

AirWave chips comprise the GPS receiver, DSP for GPS computation, and a microcontroller: the fi rst two of these blocks are proprietary, while the µC is bought-in IP. The single-chip will be fixed function, with the µC running from on-chip ROM. Variants in the AirWave series will embody any hardware changes required for different applications, together with an appropriate version of the µC code. External to the chip—which Air will build in standard foundry 1.3-µm CMOS—you will only need an antenna, a SAW filter, and a few passive components. Power management is also on-chip.

Camera makers will likely prefer to add the GPS function in module form, Graham says. Air may build such a module if customers request it; the antenna could be included, but Graham says that antenna positioning is probably going to be so productdesign- dependent that in the most-likely scenario, the company would provide design guidance in that respect. Engineering samples are scheduled for mid-2008: at present, the company will not disclose pricing information.

Air Semiconductor, www.airsemi.com.