GPS isn't the only navigation system around. The European Space Agency (ESA) is developing the Galileo Navigation System for the European Union. Unlike GPS, it will be under civilian control. But the two systems aren't all that different. SiGe Semiconductor's highly integrated SE4120L receiver uses software-defined radio (SDR) techniques to comply with both navigation standards.
The Galileo system uses 30 satellites in three orbits 23,222 km high with a 56° inclination to the equator for full world coverage. The satellites transmit on the same frequencies as GPS, but the signals use a different modulation scheme. The CDMA signals are easily sorted out and distinguished from one another because of their unique codes.
GPS uses binary phase-shift keying (BPSK) modulation while Galileo uses a new form of modulation called binary offset carrier (BOC) 1.1. This difference lets the United States or the ESA block each other's signals whenever necessary. The Galileo system is more accurate than the GPS system. It provides a 1-m margin of error, whereas GPS has a 3-m margin.
Thanks to an agreement between the U.S. and the ESA, GPS and Galileo are complementary, so their coverage of the Earth is far more complete than each system alone. All the major gaps across the globe are filled in, making reception more reliable from almost anywhere—if you have a receiver that covers both systems. That's where the SiGe SE4120L comes in.
This IC targets consumer electronics like laptops, PDAs, cell phones, handheld and automotive navigation systems, digital cameras, and MP3 players. It will receive both Galileo and GPS signals (see the figure). The antenna input is applied to an low-noise amplifier (LNA) with a gain of 18 dB and a noise figure of only 1.6 dB. No power-hungry external active antenna is necessary.
I/Q image reject mixers downconvert the signal to an intermediate frequency of 4.092 MHz, where bandwidth can be adjusted, 2.2 MHz for GPS signals and 4.4 MHz for both the GPS and Galileo signals. A linear automatic gain control (AGC) system is incorporated along with a multibit analog-to-digital converter (ADC). The overall sensitivity is as high as -170 dBm, making it possible to grab weak satellite signals under degenerating environmental conditions.
The output signal is serial applied to the external base-band processing chip, usually an ARM9 or equivalent CPU that handles the navigation computation. The SE4120L is designed to be controlled by the external processor, which is fully software programmed for Galileo and GPS functions. With the SDR nature of the resulting systems, the receiver can be updated as future versions of the Galileo system are finalized.
The SE4120L comes in a 24-pin, 4- by 4-by 0.9-mm quad flat no-lead (QFN) RoHS MSL-1 package. Operating from a 2.7- to 3.3-V supply, the receiver draws a low 10 mA, making it ideal for battery powered products. Sampling now, full production is expected in the first quarter of 2007. Price is expected to be $3 in 100,000-unit lots.
SiGe Semiconductor Inc.
www.sige.com