双线性变换法及脉冲相应不变法设计IIR数字滤波器,观察双线性变换及脉冲响应不变法设计的滤波器的频域特性，了解双线性变换法及脉冲响应不变法的特点。-Bilinear transform and impulse response invariant design method of IIR digital filter, and observed the frequency domain characteristics of the bilinear transformation and impul