Introduction of the world's mainstream GPS chip

GPS (Global Positioning System) is the abbreviation of Global Positioning System, which provides all-weather positioning, timing and speed measurement functions. GPS has been widely used in aerospace, aviation, navigation, transportation, measurement, exploration and many other fields. With the development of digital LSI and the positioning function requirements, GPS has begun to be more embedded in mobile handheld devices and consumer electronics. The E911 (Enhanced 911) security clause established by the US Federal Communications Commission stipulates that all new mobile phones must be equipped with a simple positioning function before the end of 2005 to facilitate the rescue unit to find the location of the caller in time. The Japanese government announced in 2004 that it will list the GPS receiving function as the basic specification of 3G mobile phones, and said that mobile phones listed after April 2007 will be equipped with GPS receiving functions. Although the mobile phone with integrated GPS function has not yet entered the mainstream market, in the future, the high-end models of 3G mobile phones will generally integrate GPS functions.

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The core chip is one of the key parts of the GPS system. The advantages and disadvantages of the core chip largely determine the performance difference of different GPS products. The chip technology is directly related to the technical indicators and future development of GPS products. The huge attractiveness of GPS's future market capacity has enabled the chip industry to develop rapidly. At present, more than ten manufacturers have launched GPS chips. In July 2005, Xi'an Huaxun Company launched the first GPS chip in China. In 2006, the Institute of Microelectronics of the Chinese Academy of Sciences also successfully developed two GPS baseband SoC chips. However, the GPS chips of domestic enterprises and research institutes are far from the foreign products in terms of performance. The existing chip market is basically occupied by several foreign manufacturers, among which SiRF, Garmin, u-blox and Motorola are the most influential. , Sony, Fujitsu, NXP, Nemerix, uNav and other manufacturers, SiRF, u-blox is particularly eye-catching. This article will detail the SiRF and u-blox chips, and explain the development trend of GPS chip design.

Founded in February 1995, SiRF offers GPS chipsets and corresponding software products, which account for 70% of global GPS chip shipments. SiRF's chips consist of a radio frequency integrated circuit, a digital signal processing circuit and standard embedded GPS software. The radio frequency integrated circuit is used for detecting and processing GPS radio frequency signals, the digital signal processing circuit is used for processing intermediate frequency signals, the standard embedded GPS software is used for searching and tracking GPS satellite signals, and the user coordinates and speed are solved according to these signals, and the main market is Wireless handheld devices, automobiles, portable computing devices, and some GPS professional users. In 1996, SiRF developed the first generation GPS chip structure, called SiRFstarI architecture. In 1999, SiRF developed the second generation chip structure SiRFstarII; in 2004, SiRF introduced the third generation chip structure SiRFstarIII. The common features of these three generations of systems are shown in Table 1.

At the end of 1997, SiRF introduced a low-power SiRFstarI/LX chipset based on the SiRFstarI architecture (LX means low power extension), which is mainly used for car navigation. The SiRFstarI/LX chipset's fast recapture time is only 0.1s, which is important for car navigation, because in the city, satellite signals are temporarily lost as cars travel through tunnels or on high-rise roads. According to statistics, when the car is driving in a high-rise street, the satellite signal is likely to be lost after about 4 to 5 seconds, so the shorter the recapture time, the more positioning data is given in a limited time. . The SiRFstar I/LX chipset can track satellite signals down to -180dBw, so it can be used in areas where the satellite signals are obscured by trees.

In 1999, SiRF developed the second-generation chip structure SiRFstarII, which launched the first chip product SiRFstarIIe. In 2002, it launched SiRFstarIIe/LP and SiRFstarIIt chip products. SiRFstarIIe/LP is a low-power version of SiRFstarIIe. The maximum current of SiRFstarIIe/LP is only 60mA, and the current is only 20mA in TricklePower mode. SiRFstarIIt provides an embedded solution for integrating GPS functions on some processors with systems. SiRFstarIIt needs to share the system's processor and memory before it can be used. The system's processor runs SiRFNav software. SiRFstarII has 1920 parallel correlators, which improves capture sensitivity, shortens the first positioning time (TTFF), and has a cold start sensitivity of -142dBm.

In February 2004, SiRF introduced the third generation chip architecture SiRFstarIII. In February 2005, SiRF launched SiRFstarIII-based products GSC3f and GSC3, the former of which contains a flash memory. In November 2006, SiRF introduced the 90nm SiRFstarIII-based products GSC3LT and GSC3Lti, the latter containing a flash memory. SiRFstarIII technology is used to meet the needs of wireless and handheld LBS applications. With the corresponding software, SiRFstarIII can receive auxiliary data from 2G, 2.5G, 3G networks and can be located indoors. The SiRFstar III has a hardware structure equivalent to more than 200 000 correlators, further reducing the initial positioning time.

While developing hardware structures, SiRF has also developed a series of software that makes its products easy to integrate into different systems. These software include SiRFLoc, SiRFXTrac, SiRFDRive and SiRFNav. The functional description of these software is shown in Table 2.

Founded in 1997, Swiss u-blox is a well-known GPS system manufacturer. With its excellent navigation performance and excellent quality, u-blox has the highest market share in the global GPS module market. U-blox itself is a member of the European GPS Committee and the Galileo Development Committee. It is involved in the entire GPS project in Europe and the development of standards and product development for Galileo products. It is currently the largest GPS supplier in Europe. U-blox originally used SiRF's GPS chip to produce modules, using the SiRFstarI/LX and SiRFstarIIe chipsets. Starting with the third generation, u-blox started using its own chips. U-blox's third- and fourth-generation chips are designed by u-blox to design chips, IP cores, and hardware and software architectures. ATMEL Corporation manufactures chipsets. However, from the fifth generation UBX-G5 and later GPS chipsets, it is no longer produced by ATMEL.

U-blox officially announced the development of the UBX-G5 chipset at the GPS industry in the United States on September 25, 2006. The series of chips has adopted a new design architecture, and its performance is close to the limit of GPS theoretical design (GPS The theoretical sensitivity of the chipset design is -162dbm, cold start 27s). The u-blox G5 is different from the previous u-blox GPS series chips, and still uses the same package as the fourth generation, but the hardware and software architecture has completely changed. The u-blox G5 has the following five distinctive features.

(1) There is a parallel channel equivalent to more than 1 000 000 correlators, and the sensitivity is improved from the original -158 dbm to not less than -160 dbm;

(2) The power consumption is not more than 50mw;

(3) Support both GPS and Galileo positioning platforms;

(4) The cold start time is shortened from the original 34s to the cold start 29s, plus AGPS assisted positioning technology, the outdoor cold start can be within 1s;

(5) The number of GPS channels is increased from 16 channels of the fourth generation to 50 channels of the fifth generation;

The UBX-G5 can be used in mobile products such as mobile phones and PDAs, greatly expanding the mobile market.

See Table 3 for a comparison of the performance of several chips from u-blox and SiRF.

Through the development history of the above-mentioned GPS chip manufacturers, it can be seen that the GPS chip is developing with high sensitivity, low power consumption, multi-mode (compatible with Galileo or other navigation systems), and A-GPS.

When developing GPS products, other manufacturers should focus on various IT devices that integrate GPS in the future, such as mobile phones, digital cameras, PDAs, and notebook computers, and do embedded solutions. Do not develop with SiRF and u-blox companies. Competing independent GPS chips. Second, the problem of high sensitivity and low power consumption must be addressed. The most advanced u-blox G5 chip should be aligned to develop algorithms and hardware for weak signal acquisition and tracking.

Before 2010, the Galileo system will be commercially available worldwide, so the development of GPS/Galileo dual-mode receivers has broader prospects. On this basis, if you can make a GPS/Galileo/Beidou three-mode GPS receiver, it will be more competitive. The development of a pure software GPS receiver, through the software to complete the function of the GPS chip, thereby further reducing costs, and enabling more handheld portable devices to adopt GPS functions.