说明：  设计一个巴特沃斯模拟低通滤波器，要求通带截止频率 ，通带最大衰减 ，阻带截止频率 ，阻带最小衰减 。要求绘出滤波器的幅频特性曲线。
(A Butterworth analog low-pass filter is designed, which requires passband cutoff frequency, maximum passband attenuation, stopband cutoff frequency, and minimum stopband attenuation. It is required to draw the amplitude frequency characteristic curve of the filter.)