（1）对选定二阶电路图进行仿真，得到仿真的输入、输出数据；

（2）建立二阶系统函数，用模拟的方法求解其响应，并用matlab平台求出响应波形；

（3）对数据进行拟合；

（4）对拟合的结果进行误差分析

-(1) on the selected second order circuit diagram of the simulation to obtain a simulation of the input and output data　(2) the establishment of the second order system function, solving the response by the simulation method, and was determined using matlab platform response waveform　data (3) be fitted　(4) the results of the fitting error analysis