设计一个IIR数字低通滤波器， 逼近一组模拟滤波器的指标参数（通带截止频率Wp=2*pi*2000rad/s,阻带边界频率Ws=2*pi*3000rad/s,通带波纹 Rp=3db, 阻带衰减Rs=15db, 采样频率f=10000Hz）； 分别用脉冲响应不变法和双线性变换法实现设计，列出传递函数并描绘模拟和数字滤波器的幅频和相频响应曲线。用上述设计滤波器完成几组给定信号的滤波，证明滤波器的有效性和滤波范围限制.-Design a IIR digital low-pass filter, approaching a group of analog filters indicator parameters (pass-band cut-off frequency Wp = 2* pi* 2000rad/s, stop-band edge frequency Ws = 2* pi* 3000rad/s, pass-band ripple Rp = 3db, stop-band attenuation Rs = 15db, the sampling frequency f = 10000Hz)　were used to change the impulse response method and bilinear transformation method for design, list and describe the transfer function of analog and digital filter amplitude-frequency and phase-frequency response curve. A filter was designed with the completion of the above-mentioned groups of a given signal filtering, to prove the effectiveness of filters and filter limit