Special requirements and precautions for vehicle GPS system design

To solve these problems, we must first understand the implementation environment of the vehicle GPS navigation system. TriQuint Semiconductor ’s GPS product marketing manager Josh Raha said: "For RF engineers, when designing vehicle GPS navigation systems, relative to personal navigation Equipment, they must consider three key differences. First is the relative position of the receiving antenna and GPS receiver, second is the size, and finally the operating environment is also very important. "

He further explained: "In a personal navigation device, all the components are grouped together. But in a car, the antenna may be three or four meters away from the GPS receiver, which will be affected by additional line losses and possible interference, Therefore, the roof antenna must be "active", which means that it needs to have built-in filtering and gain functions. Therefore, the entire RF receiving link (first SAW filter, low noise amplifier, second SAW Filter) must be designed into the roof antenna box. The other end of the line (under the seat or dashboard) also needs another surface acoustic wave filter, and possibly another low noise amplifier to ensure transmission to the GPS receiver chip The signals of the group are clear and reliable.

In addition to ensuring that the chipset receives high-quality signals, it is also important to improve the sensitivity of the receiver. On the one hand, it can further improve the positioning effect, on the other hand, it can also appropriately reduce the difficulty of designers to design the receiving link. The device is a good example. O2Micro's OZE167 is also a good choice. In addition, for the special features of the automotive environment, SiGe's latest RFIC devices (such as SE4150L, ​​etc.) integrate a high-performance low-noise amplifier, as well as the antenna switching function for dual-antenna systems. When the non-heat-generating heat-reflecting windshield or windshield heater impairs the performance of GPS reception, the dual-antenna system will connect an external GPS antenna to maintain navigation performance. In addition to the sensitivity, the speed of the first time to fix (TIme to First Fix, TTFF) is a technical indicator that all types of GPS applications need to pay attention to. Some programs have a TTFF of more than 30 seconds under cold start conditions, which seriously affects the user ’s Use experience. O2Micro's James Wang said: "Some users will even restart the system frequently because of the long waiting time, which results in the positioning time being further extended, resulting in complaints about GPS devices." Using O2Micro's GPS chip, the test at -135dBm Under the environment, TTFF can be shortened to 13.5 seconds, which is a time that the average user is willing to accept.

Another important design factor to consider is the environment in which the system operates. Components must work in a wider temperature range. The automotive industry's eligibility requirements for electronics suppliers are very complex. Mr. Josh Raha explained: "There are two kinds of requirements: factory qualification and equipment qualification. Automobile manufacturers require that semiconductor suppliers’ factories pass TS-16969 certification. TS-16969 is an ISO technical specification that stipulates the design, development and The quality system requirements for production. However, even if the factory passes the certification, each piece of equipment must be qualified. The Automotive Electronics Association (AutomoTIve Electronics Council, AEC) has formulated the AEC-Qxxx series qualification specifications, including moisture resistance, temperature cycling and vibration / Impact testing. "Automotive designers should select electronic components that meet the AEC-Q100 specifications (active components) or AEC-Q200 specifications (passive components). Car GPS systems have higher requirements for reliability. In addition to selecting components that meet automotive standards, chip integration and soldering technology are also important. James Wang said: "Welding IC pins to the circuit board The above technology is one of the keys to affect the reliability of production, because each solder joint is a potential failure factor. O2Micro GPS chip OZE167 has a total of 124 pins. After the IC is integrated into a single chip, the IC on the circuit board The reduced number means that the number of pins is reduced, thereby reducing the possibility of failure, that is, improving the reliability of the circuit. "

In addition to the traditional navigation functions, it is also very practical to use the GPS system for car theft prevention. Mr. Stefan Fulga said: "By combining GPS with Wi-Fi, GPRS or WiMAX technology to build a communication link to track a stolen vehicle; or to disable certain functions when the vehicle is not in a designated area, it can be prevented Theft function. SiGe, with its extensive experience in GPS, Wi-Fi and WiMAX, can provide a solution that combines the above technologies in a single front-end module, thereby minimizing costs and facilitating integration in the automotive environment. Josh Raha Said: "The best way to integrate more functions for GPS applications is to develop a single GPS receiving link, which then transmits the location information to various applications. In other words, the GPS satellite signal is transmitted to the chipset through the antenna and the radio frequency receiving link for azimuth calculation. After the current position is known, the chipset can transfer this information to any desired application, whether it is stolen vehicle position detection, road navigation, or escort service. "