Firstly, this paper analyzes the key technologies of GSM communication system, introduces the system composition and working principle of GSM mobile phone baseband and radio frequency in detail, and further analyzes and studies the platform MTK6225 provided by MediaTek, as well as the hardware design and basic debugging of GSM mobile phone on this platform. For this, the main research work is as follows:
1. The circuit and principle of two parts on MTK6225 platform are introduced in detail. First of all, it is the radio frequency part, the main chip of which is MT6139, and the adopted radio frequency structure is a very low intermediate frequency structure. From the signal direction, RF can be divided into two parts: receiving and transmitting. The basic modules include antenna, RF connector, acoustic surface filter, antenna matching circuit, transceiver MT6139, power amplifier, crystal oscillator and RF power supply circuit. This paper draws the basic schematic diagram and peripheral matching circuit of each module through the overall understanding of RF. As for baseband, its basic modules include audio module, charging module, memory module, camera module, main screen LCD module, multimedia card interface module, SIM card module, USB module, keyboard and key lamp module, motor drive and Hall switch module, etc. This paper also draws the schematic diagram of each module of baseband in detail.
2. After the realization of the schematic diagram, this paper has further completed the manufacture of six-layer PCB. By skillfully using the EDA tool PADS, the layout of RF and baseband parts has been rationalized to ensure that important signal lines (RF and audio lines, etc.) do not interfere with each other. On this basis, under the constraints of various detailed rules, the optimized and reasonable wiring is carried out to ensure the complete realization of various protection treatments of some important signal lines such as power supply, radio frequency and audio frequency, so as to ensure the function and performance of PCB development board and prepare for the later test.
3. Finally, a complete radio frequency test and baseband function test of the mobile phone development board are carried out, and the radio frequency reports of the mobile phone are given, including the receiving sensitivity test report, the frequency error test report, the phase error test report, the output power test report, the transmission carrier envelope test report, the modulation spectrum and the switching spectrum test report. According to the test report, some data which do not conform to the GSM communication protocol are improved by modifying and debugging the schematic diagram or PCB. In the aspect of baseband, some hardware problems encountered in the test are given, and the work done to solve these problems is explained.
GSM mobile phone is a typical complex embedded system, and its development includes microwave radio frequency technology, digital signal processing and coding technology, smart card, real-time operating system, communication protocol and many other hardware and software technologies. At the same time, the development of GSM mobile phone can have different modes, including peripheral technology development, core technology development and basic technology development. The core technology of mobile phone is radio frequency unit design, baseband unit design and protocol software design. The peripheral design technology of mobile phone is modeling design and man-machine interface software design, while the basic technology development is mainly the development of baseband dedicated chip and physical layer software design (including voice signal compression coding, decoding, channel coding, encryption and so on). From the hardware point of view, the design of RF chip and baseband chip is one of the core technologies of mobile terminal system.
In recent years, GSM mobile phones are the main ones that we have come into contact with. This paper introduces the hardware implementation principle and manufacturing process of GSM mobile phones. The hardware module of mobile phone introduced in this paper is based on the GSM module of MTK, which includes the baseband processing of GSM system and the receiving and transmitting of RF signals. Firstly, the content will introduce the GSM communication system, the basic principle of GSM mobile phone, and the schematic diagram of each module. At the same time, according to the customer’s requirements, on the basis of the existing platform, we will expand the functions and optimize the performance.
In addition, PCB wiring is an important part of the overall design of mobile phones. Mastering this technology will master a part of the sovereignty of localization of mobile phones. In the process of PCB design, electromagnetic compatibility is a very difficult problem. On dozens or dozens of square centimeters of circuit boards, the frequency changes greatly, and the level signals range from small signals of microvolts to large signals of several watts of power. It is a difficult and challenging thing to avoid their interference. In addition, it is also a difficult problem to eliminate the distortion during signal transmission. For high-frequency signals