频率合成器的设计与实现

直接数字频率合成(DDS)是一种以固定的精确时钟源为基准,利用数字处理模块产生频率和相位均可调的输出信号的技术.为实现直接数字频率的合成,以美国Intel公司的DDS芯片8254和ATEML公司的芯片AT89C51为核心部件,给出一款频率合成器的设计方案.用户通过拨码开关输入所需频率信号的数据,利用单片机寻址相应的频率控制字,输入DDS芯片内核,通过改变调用ROM表中频率控制字的地址,来实现输出频率跳变的目的,同时在DDS输出端增加一个低通滤波器和放大器,可达到抑制杂散同时对输出信号进行放大,最终得到所要求的输出波形.

Design and Implementation of Frequency Synthesizer

Direct digital synthesis(DDS) is a technology of using digital processing modules to generate output signals whose frequency and phase can be adjusted,which takes a fixed-frequency precision clock source as the reference.To realize DDS,a design scheme of frequency synthesizer is presented taking DDS chip 8254 of American Intel Corporations and AT89C51 of ATEML Corporations as the core components.Users can input the frequency data through a dial switch,and the microcontroller reads the relevant value of the frequency tuning word(FTW) and inputs it into the DDS chip.Then the output frequency hopping will be achieved by changing the FTW address in the ROM table.At the same time,a low pass filter and an amplifier are added on the output end of DDS,which can suppress the spurious noise but enlarge the output signal simultaneously.Finally,the required output waveform is obtained.