生成一个采样频率2000，由50Hz、120Hz、200Hz正弦信号以及噪声信号组成的数字信号，滤掉150Hz>f>100Hz的频率，计算并显示滤波前后的原始数据波形以及功率谱密度。(A sampling frequency of 2000, a digital signal composed of 50Hz, 120Hz, 200Hz sine and noise signals, is generated to filter out the frequency of 150Hz&