说明：  matlb编写的IIR滤波器程序，按照给定指标采用模拟低通滤波器（巴特沃思低通或者切比雪夫低通）去逼近理想模拟低通滤波器 ，然后通过双线性变换法对模拟滤波器进行数字化，得到数字滤波器 。
(IIR filter matlb prepared by the procedure, according to set targets and analog low-pass filter (Butterworth low-pass or low-pass Chebyshev) approximation to the ideal analog low-pass filter, and then through the bilinear transformation method for analog filtering device to digitize, the digital filter.)