IIR数字滤波器的特点是h(n)为无限长序列。设计的基本思想是：模拟系统与离散系统存在着互相模仿的理论基础，所以可以让数字滤波器的特性去模仿一个模拟滤波器的特性，得到数字滤波器的H(z)，H( )之间的变换关系。设计时，先设计一个模拟滤波器的传递函数 ，然后通过s变量与z变量之间的变换关系求出数字滤波器的系统函数H(z)。-IIR digital filter is characterized by h (n) for infinitely long sequence. The basic idea of the design are: analog systems and discrete systems there is the theoretical basis of mutual imitation, so you can make the characteristics of a digital filter to imitate the characteristics of an analog filters, digital filters are H (z), H () of the the relationship between the transformation. Design, first to design a simulation of the filter transfer function, s variables and z and then transform the relationship between variables derived digital filter system function H (z).