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 impulse response filter of the same law designed to understand the bilinear transform and impulse response characteristics of the same method.