SiRFstarIV Debuts with the Promise of Always On Location Awareness
July 28, 2009Fresh on the heels of completing its merger with CSR, SiRF has unveiled the successor to the SiRFstarIII, the aptly named SiRFstarIV, with hopes that it will do for mobile phones and devices what its predecessors did for GPS handhelds and portable navigation devices (PNDs).
“In the last few years we’ve seen GPS get into more of the non navigation market,” said Kanwar Chadha, a founder of SiRF and now a chief marketing officer at CSR post merger. As far as consumer applications are concerned, GPS has become the foundation for location based services and applications, as opposed to being used solely for navigation, he continued.
But that means the user profile has become very different — unlike the GPS user driving in their car or the hiker with his handheld, a mobile phone user tends to be ducking indoors and out. And unlike the PND or handheld user, who turns on their device in anticipation of using it, a mobile phone user’s handset or other mobile device is always on, and they expect its location applications to be ready on demand, Chadha said. There is typically no pre-planned routing; when it comes to friend-finding, geotagging a camera phone photo, or finding a local pizza place, users just open their phone and do it, or at least want to.
“The challenge you run into is these apps want the device to be location aware all the time,” he added. But as any early adopter already knows, this means increased power consumption, and in a small device, GPS usage can drain the battery quickly, particularly if there are other wireless functions being used at the same time. The trend to ever smaller handsets and other devices presents another problem for GPS: those other radios and the display can interfere with satellite signal reception. And as Chadha noted, GPS often isn’t the center of a small formfactor device and as such, its placement often isn’t advantageous; the formfactor and board design are not optimized for it.
Chadha said that SiRF has actually been thinking about these two problems for some time. “It is tough; it has taken us a few years. If we could have put (SiRFstarIV technology) in III, we would have. We had to rethink how GPS chip should behave,” he said. “We tried to address usage profile of location as an always on element in these new class of consumer devices.”
Parts of the answer are obvious: decrease satellite signal acquisition times and add more gates to the GPS receiver chip. Advances in silicon chip manufacturing technology help, but only go so far. Essentially the challenge for SiRFstarIV was how to keep the GPS chip “alive” with undue power consumption. “If you really start making your system location aware, how do you keep (GPS) alive without consuming too much of the battery?” Chadha asked.
The answer was to adopt what SiRF calls an adaptive micropower controller. More than just a simple standby mode, it keeps certain parts of the receiver fed with minimal amounts of power — 50 to 500 microamps — so that it can maintain hot start capability at all times. In terms of milliwatts (mW) consumed, the SiRFstarIV consumes 37 mW at 1 Hz in continuous tracking mode, 8 mW in SiRF’s TricklePower mode (again at 1 Hz, assuming a 1.8 V power supply), and draws less than 20 microamps of active current when it’s hibernating. By comparison, SiRFstarIII uses 62 mW in continuous operation, and 40 mW in TricklePower mode, and lacks its successor’s hibernation or adaptive micropower mode.
“That is, I think, the fundamental innovation . . . a totally new way of keeping the system alive,” Chadha said. He likened it to the standby mode of a cell phone and long standby times verses actual talk times; it’s not at full-power in standby mode, but can be ready on-demand, at least as far as the user’s perception is concerned.
But SiRFstarIV also offers apparently significant changes in architecture — and apparently firmware as well — in comparison to SiRFstarIII. The package measures 3.4 x 2.7 x 0.68 millimeters, with a typical design footprint taking up 20 mm square, according to SiRF; in comparison its immediate predecessor’s dimensions are 7 x 10 x 1.4 mm with a typical design footprint of 130 square mm. How did SiRF make IV so much smaller than III? Advances in silicon chip fabrication don’t account for all of it, as IV requires no onboard memory; it’s a single die. Navigation and location determination, including support for hybrid location technologies, is done via software on the host side, Chadha explained.
SiRFstarIV also reduces the need to shield its GPS receiver from the more powerful radios and gigahertz CPUs found in mobiles today. It contains an engine that constantly scans for in-band signals of up to 80 dB-Hz that could jam GPS reception and cancels them out, according to SiRF.
Other changes in SiRFstarIV include an interface that can utilize other sensors that may be available in a device, such as an accelerometer. It also utilizes a self-assist mode, opportunistically updating its internal satellite fine time, frequency, and ephemeris data when there is a clear view of satellites in the sky. This latest receiver also boasts 48 channels compared to SiRFstar III’s maximum of 20, and improves its sensitivity over that of its predecessor with tracking of -163dBm, compared to III’s -159 dBm.
Chadha says SiRF already has working SiRFstarIV silicon and software, and is sampling the chip to its lead customers. It anticipates the receiver will be in production by the end of this year with the first consumer products containing the chip hitting store shelves in early 2010.
But What About CSR?
While the announcement of this new SiRF chip follows on heels of its completed merger with Britain’s CSR, the timing was a matter of coincidence. The chip was already in the can, so to speak, before the merger came about; SiRFstarIV achieved first silicon months ago, so there was no impact on the project one way or the other, according to Chadha.
But the merger may have an impact on SiRFstarIV in terms of customer exposure; CSR, which specializes in Bluetooth silicon among other wireless applications, is well-known to makers of handset and other mobile devices. “I think it gets us opened to customers more familiar with CSR than with us,” Chadha said. “It also gets us into more platforms – it lessens the number of suppliers.” Plus there is the fact that SiRF is now part of a larger company and all that implies. “It just opens up many more doors,” he added.
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