Air plans power cut for GPS

The founders of UK start-up Air Semiconductor, David Tester (left in picture) and Steve Graham, reckon their novel approach to decoding the signals from GPS satellites will result in portable devices that use a lot less power to work out where they are

A UK-based startup has developed an approach to dealing with the Global Positioning System (GPS) that it reckons has such a low power demand that it can be kept on all the time in portable electronics devices such as media players and digital cameras.

Set up by chief technology officer David Tester and CEO Steve Graham, Air Semiconductor has attracted series-A funding from Pond Venture Partners to develop a family of chips that are intended to consume far less power than existing GPS receivers. Graham said the average current consumption of the Airwave-1 will be around 1mA. Traditional designs tend to draw around 20mA or more. However, the consumption of the Airwave-1 depends strongly on the accuracy demanded from the positioning system: the key to the lower power consumption, said Graham, lies in the adaptive nature of the algorithm.

Graham said the company has developed a novel approach to decoding the timing signals produced by the GPS satellites. In conventional systems, there is a long delay after the system first powers up. During that time, the receiver downloads vital information on the orbit of each satellite in view and works out how the ionosphere is affecting the weak radio signals they produce. For a cold start, this can take several minutes because the transmission datarate is very low. Air's approach is to have the chip always ticking over to avoid having to download this information before providing a fix. When indoors, and unable to receive any GPS signals, the chip assumes its last fix is valid whereas conventional receivers will 'forget' their position and perform a warm start the next time its picks up a satellite's signal. In the case of the Airwave-1, the chip will progressively update itself without going through the warm-start sequence.

"In a PND [personal navigation device], the assumption is that it is supporting navigation and the device is doing that all the time it is switched on. The power consumption of the GPS is not such an important issue. We flip that around," said Graham. With its approach, the assumption is that determining precise location is only occasionally important. For most of the time, the Airwave-1 determines a coarse location then, when the shutter on the camera is hit, it works harder to get a precise fix from the GPS satellites. "It's enabled by a unique hardware architecture," he claimed, that is able to trade power consumption for precision.

The Airwave-1, which will be the first in a family of devices, will be made by Taiwanese foundry TSMC on a 0.13µm process. "That is about finding the optimum point in terms of cost for the product right now," Graham said. The whole chip design is being performed in-house, he said. "We are doing it in-house through to tape-put. Essentially, we want to keep control of the entire thing. There are some bits of relatively standard IP in there but the design is all about power consumption and that requires a hands-on focus with our core IP blocks."

Image: David Tester (left) and Steve Graham show off a test chip used in the development of the Airwave-1 silicon

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