利用双线性变换设计IIR滤波器（只介绍巴特沃斯数字低通滤波器的设计），首先要设计出满足指标要求的模拟滤波器的传递函数 ，然后由 通过双线性变换可得所要设计的IIR滤波器的系统函数 。-IIR filter design using bilinear transform (only introduced the Butterworth digital low-pass filter design), first designed to meet the index requirements of analog filter transfer function, then available via the bilinear transformation to design of the IIR filter system function.