基于DDS信号发生器的杂散研究与设计

【作者】 郑伦贵；

【导师】 郑宾；

【作者基本信息】 中北大学 ， 测试计量技术及仪器， 2007， 硕士

【摘要】 直接数字式频率合成技术是信号频率合成领域里的一次革命。它在硬件方面具有全数字结构,具有频率转换速度快、频率分辨率高,相位噪声低、频率捷变时相位连续等优点,近十几年来目前,DDS技术已经在雷达、通信和仪器仪表等领域得到广泛应用。受奈奎斯特定理、自身的结构缺陷以及目前数字器件工作速度的限制,DDS的输出频率较低、杂散性能不够理想,这就在一定程度上限制了DDS的应用。本文对直接数字频率合成技术进行了系统研究,介绍了频率合成技术的发展,分析了DDS的输出频谱特性,通过计算机仿真对相位截位条件下和存在幅度量化误差情况下的频谱特性进行了深入的研究。对数模转换器(DAC)的非理性特性对输出频谱的影响进行了定性分析。在深入研究DDS输出频谱特性的基础上对DDS杂散抑制方法进行了研究,这些方法包括随机扰动技术(包含相位扰动和幅度扰动技术)和ROM压缩技术等。这样就避免了DDS的杂散性能受ROM容量的限制。同时为了得到高纯度的信号,设计了七阶椭圆滤波器来减少杂波,通过对7阶椭圆滤波器特性进行仿真和比较,该滤波器很好的滤除掉20MHz以上的杂波,在软件设计过程中设计了新的数据处理方法很好地兼顾了long型变量处理11字节控制字问题同时也保证了输出信号频谱的纯度。最后结合课题研制了DDS信号产生器控制电路。总之,DDS是目前所有频率合成方法中比较先进的方法之一,但是它在合成信号的带宽方面还存在固有的缺陷,这限制了它在频率合成领域中更加广泛的使用。本文的最后给出了下一步工作的建议,以期完善频率合成的性能指标。更多还原

【Abstract】 The invention of Direct Digital Synthesis (DDS) is the revolution of signal frequency synthesis technology. DDS is a wholly digital structure circuit with variousadvantages such as fast frequency switching speed, high frequency resolution, lowphase noise and maintaining constant phase while frequency hopping. In the recent decade, it has been widely used in the fields of radar, communication, apparatus, etc. For the limitation of digital hardware operating speed, Nyquist theorem and DDS structure, the spurious performance of DDS’ output is bad and the output frequency can’ t reach a high level.In this dissertation, a systematic research is made on DDS. The development of the frequency synthesis is introduced. The output spectrum of the DDS on the presence of both phase and amplitude truncation is analyzed by computer simulation. An analysis is also made on the effect of the DAC’s nonlinearity. Based on analyzing the output spectrum of the DDS, some methods to reduce spurs are proposed. They are modified random dithering and Rom compressing techniques. Then a sine/cosine generator is researched. In this structure, the spurious performance is no longer restricted by the capacity of the ROM. A seven-order ellipse Filter Circuit which reduce the noise of the signal above 20MHz is designed to get little spurs, and desin a new process method to lower the DDS’ output spurs which resolve the the problem that process eleven character with the four character variable.Finally, combined with the practical engineering, the controlling circuit of the low spurs and wideband DDS signal.All in a word, DDS is one of the most advanced frequency synthesizing techniques, but there are still some disadvantages in using DDS, for example, the narrow bandwidth, which more or less limits its application. In the last part of the thesis, some suggestion are proposed to further improve the result of frequency synthesis.更多还原