Abstract
At the beginning of this paper, the historical background, present situation and development trend of filters are introduced, and follow on these, the practical significance is gviven. Then we briefly describe the concept and design scheme of program-controled filters. We describe the design process from hardware and software in detail. The hardware part have five parts that include amplification module, filtration module, DDS module, SCM system and button-display module.(外语学习 http://www.hebjjw.com) The software part have four parts that include system initialization, key-scanning, the generation of DDS clock signal and LCD display. Switched Capacitor Filter LMF100 and 51 SCM AT89C51 are the key parts of this system. The cut-off frequency of the filter is adjustable in 1 kHz to 20 kHz range through the button and the step frequency is 1 kHz. Protel 99SE is used to draw the schematic diagram and C language is used to write program.
Key Words: Program-controled filter; LMF100; AT89C51; DDS