Design And Implementation Of Low-Cost Frequency Characteristic Tester

Frequency characteristic tester is a kind of measure instrument that is often used in school teaching and scientific research work. The market actuality in our country is that frequency characteristic testers are expensive while the purchasing power of many small-scale schools and middle-scale schools are not enough, so a design project of low-cost frequency characteristic testers is presented in this paper, which suits those schools. In the design of the tester, low-cost elements are adopted on the premise of satisfying the request of system performance. Accordingly, the design cost is availably reduced. In addition, the tester is designed as a multifunctional system. It can be used as not only measure instrument but also common sine signal source and sweep frequency signal source.In the paper, the basic principle and development course of frequency characteristic are summarized firstly. After analyzing the actuality of the tester market in our country, the design project of low-cost frequency characteristic tester is presented. Then the implementation of the project is introduced in detail.The frequency characteristic tester designed in the paper is basically composed of main controller and sweep frequency signal source. The sweep frequency signal source is based on DDS (Direct Digital Frequency Synthesizer), implemented using FPGA, and can get sweep frequency signal with high frequency switch speed and high frequency stability. In the third chapter of the paper, the constituent principle of the DDS signal source and the approach of implementing the design using FPGA is introduced in detail, and the correctness of the approach is proved by software emulate of designed signal source. In the tester system, MSP430F449 MCU acts as the main controller. It controls and manages the whole system. In the fourth chapter of the paper, its hardware circuit design and software design are introduced amply.In order to validate the correctness of the design principle of the frequency characteristic tester, the author designed and made the experiment device and did some validating experiments on the device. In the fifth chapter of the paper, the schematic and PCB diagram of the device, the program lists and the output results of the experiments are shown. By analyzing the results of the experiments,the correctness and feasibility of the design principle is proved.The SOPC project is presented in the sixth chapter of the paper, by which the main parts of the frequency characteristic tester can be integrated. By adopting the project, the frequency measure range of the tester can be enlarged; the performance of the whole system can be improved and the cost-performance ratio of the system can be increased further.