The Design Of A Digital Tester For Frequency Response Characteristic

The tester for frequency characteristic, which is also called frequency-sweeping instrument, is used to test amplitude frequency characteristic and phase frequency characteristic of the quizzed network. This is one of all basilic test instruments in electronic area. Traditional tester for frequency characteristic cannot give phase frequency characteristic of the quizzed network, cannot save frequency characteristic is tested and cannot connet with PC. These give user a lot of discommodity. In this paper, the construction and principle of the test instrumwent for testing the frequency characteristic are introduced. A design of the tester for frequency response characteristic based on DDS+DSP is presented. The system of the tester is recounted from both hardware construction and software design. The DDS device AD9854 is used to generate frequency up to 400MHz and can be programmed to operate in frequency-sweeping mode and so on. The frequencies can be set by the user between 0.1hz and 400MHz and more than one mode be provided. It uses DSP+CPLD as the key device. Thus, flexibility, adaptability and dependability of the system of tester are advanced. Amplitude and phase frequency characteristic curves are displayed with liquid crystal display (LCD) module, whose volume is smaller than other displayer. The tester can be connected to PC with RS-232 and to printer with interface for printer. Digital and miniaturization be fulfilled in this design of the frequency characteristic instrument. Cost for instrument can be reduced.