In this paper a digital sine signal source based on DDS (Direct Digital frequency Synthesizer) is introduced. It has three kinds of function: outputting sine signal with fixed frequency, outputting sweep signal and testing amplitude-frequency characteristic of electronic elements working together with a common scope. Its main characteristics are as follows: firstly, comparing with conventional analog signal source, its switch speed of signal frequency is quicker and frequency of signal is steadier and it can be controlled more easily. Secondly, it can output sweep signal, but it is cheaper than special sweep signal generator. Thirdly, because it can test amplitude-frequency characteristic of electronic elements working together with a common scope, it can take the place of expensive special sweeper when the user’s precision demand is not very high. For example, it can be used as teaching instrument. The students can learn the amplitude-frequency characteristic of operation amplifier by it. It can satisfy the requirements and the school can save many expense of buying teaching instruments. This kind of signal source is composed of MSP430 MCU (Micro Controller Unit) and FPGA (Field Programmable Gate Array). MSP430 MCU is produced by TI Company. It has ultra-low-power consumption and high performance. Its main function is controlling the whole system, dealing with the data and display them. The FPGA is produced by ALTERA Company. Its main function is outputting waveform data from its own RAM on the basis of control signals from MCU. Certainly, the system also includes D/A converter, commuting circuit, filter and operation amplifier, which are assistant parts. This design method, namely combining MCU with FPGA, not only takes full advantage of control ability of MCU, but also fully incarnates the predominance of FPGA, i.e. high integration, high speed and high reliability. Furthermore, the method makes the design of circuit very easy and decreases difficulty of routing. The hardware structure and software design are given in the paper. The result of experiment shows that the design of the signal source is simple and feasible, convenient and flexible to use, and has high ratio for quality to price.
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