一、设计要求：1• 截止频率fH3d=1kHz

2• 带外衰减速率小于-30dB/10倍频

二、总体方案讨论：二阶RC有源滤波器的功能是让一定的频率范围内的信号通过，抑制或急剧衰减此范围内的信号，常用电路有电压控制电压源(VCVS)电路和无限增益多路反馈(MFB)电路，本设计采用电压控制(VCVS)电路，其中运放是通向输入，输入阻抗很高，输入阻抗很低，其优点是电路性能稳定，增益容易调节

-First, the design requirements: 1 •　cutoff frequency fH3d = 1kHz

2 • -of-band octave attenuation rate of less than-30dB/10

Second, the overall program discussion: Second-order RC active filter function is so that a certain frequency range of signals, inhibit or rapid attenuation of signal within this range, common circuit voltage-controlled voltage source (VCVS) circuit and an infinite gain Multiple feedback (MFB) circuit, this design uses a voltage-controlled (VCVS) circuit, which op amp is the path input, input impedance, high input impedance is very low, its advantage is that the circuit performance is stable, easy to adjust the gain