一种类正余弦CIC滤波器

传统CIC滤波器由于其实现不需要乘法器和存储器，因此已在各种变采样率系统中得到了广泛的应用。但是传统CIC滤波器的通带失真较大，阻带衰减较小，而且其积分器工作在高采样率端，这很大程度限制了它在对性能要求较高的变采样率系统中的应用。而后来提出的各种CIC滤波器，如锐化CIC滤波器、ISOP-CIC滤波器和CIC-Cosine滤波器等，或者只改善通带特性，或者只改善阻带特性，或者积分器运行在高采样率端。本文在分析对比了传统的CIC滤波器、锐化CIC滤波器、ISOP-CIC滤波器和CIC-Cosine滤波器的频率特性的基础上，引入一种类余弦预滤波器和一种类正弦预滤波器，再加上多级级联的传统CIC滤波器，构成一种多级结构的类正余弦CIC滤波器。所引入的类正弦预滤波器和类余弦预滤波器分别用于减小CIC滤波器的通带失真和增大其阻带衰减。仿真结果表明，所提出的类正余弦CIC滤波器比传统的CIC滤波器、ISOP-CIC滤波器、CIC-Cosine滤波器都具有更小的通带失真和更大的阻带衰减。同时所引入的两级预滤波器工作在低采样率端，并且通过使用多相分解技术同样可使多级级联的CIC滤波器工作于低采样率端。 

A sine-cosine-like CIC filter

The traditional CIC filter does not require any multiplier or coefficient storages, therefore it’s used widely in various sampling rate conversion system. However, the traditional CIC filter has high pass band distortion and low stop band attenuation, and its integrator is operated at high rate, all of these greatly limit its applications in the sampling rate conversion system that requires higher performance. All kinds of CIC filters, such as sharpened CIC filter, ISOP-CIC filter, the CIC-Cosine filter and so on, were presented later. But they either only improved the pass band characteristics, or only improved the stop band characteristics, or their integrators were operated at high rate. Based on analysis and comparison of the frequency characteristics among the traditional CIC filter, sharpened CIC filter, ISOP-CIC and CIC-Cosine filter, a cosine-sine-like CIC filter which consists of a cosine-like pre-filter, a sine-like pre-filter and multi-stage cascade of the traditional CIC filter is proposed. The sine-like pre-filter presented can reduces the pass band distortion of the whole CIC filter, and the cosine-like pre-filter can increases the stop band attenuation. Simulation results show that the proposed cosine-sine-like CIC filter provides lower pass band distortion and higher stop band attenuation, contrast with the traditional CIC filter, ISOP-CIC filter and CIC-Cosine filter. At the same time, the two pre-filters presented both run at low rate, multistage CIC filter can also be moved to low rate, by the use of polyphase decomposition.