通用二阶滤波器的高频特性研究

Research on High Frequency Characteristics of Universal Second Order Filter on OP

为了获得高频率、高精度通用二阶滤波器,以运放的单极点模型为基础,分析了基本电路模块的开环频率特性及其一级近似,给出了TT滤波器、KHN滤波器的特征方程,在一级近似条件下求出了2种滤波器极点频率和品质因素的计算式.结果表明:在高频场合,2种滤波器均会出现"Q移位"和"ω0移位"现象,即TT滤波器只会出现Q增强和ω0减弱现象,而KHN滤波器不仅会出现Q增强和ω0减弱现象,而且也会出现Q减弱和ω0增强现象.最后以KHN滤波器为例,取Q=0.612,通过频率预失真技术,消除了"Q移位"和"ω0移位"现象,给出了foa=100 kH z,Qa=0.612的KHN滤波器.计算机仿真表明理论分析正确无误.

In order to obtain universal second-order filter with high frequency and high accuracy, the frequency response of circuit modules using actual OP was analyzed based on the open-Sloop frequency response of actual OP. The characteristics equations of ＂IT and KHN filter on OP＇ s and the first order approximate equations of the Qa and to ω0a of the filter were given. The Q and too shifts in the filter were analyzed. The Q enhancement and too reducing effects were only found in TT filter. The effect of Q enhancement and too reducing and the effect of Q reducing and too enhancement were all found in KHN filter. Finally, for Q = 0.612, the shifts in the Q and ω0 of the filter can be eliminated by frequency pre-distortion. The KHN filter with foa = 100 kHz, Qa = 0.612 was given. The results of computer simulation show that the analysis method is valid and effective.