开关电容滤波器设计与仿真方法的研究

Study on Design and Simulation for Switched Capacitor Filters

为解决开关电容滤波器不能直接应用传统的电路分析程序和仿真方法的设计问题,提出了将开关电容网络的时变拓扑,变换为时不变拓扑,再对时不变网络进行分析的方法。建立了开关电容模拟电阻的z域模型,应用电阻替代方法,设计了二阶开关电容滤波器电路。将二阶开关电容滤波器级联,给出了8阶切比雪夫低通开关电容滤波器的设计与仿真实例,并给出了实现低Q值开关电容滤波器模型的SPICE程序。仿真结果显示,开关电容滤波器与有源低通滤波器的输出特性曲线相一致,满足切比雪夫低通滤波器的设计要求。该滤波器设计方法原理简明,建立模型容易,给出的开关电容模拟电阻的SPICE模型也非常理想,适合于高通、带通、陷波等各种滤波器的设计与仿真。

To solve the problem that switched capacitor filters can't be designed by directly using traditional circuit analysis and simulation technique, the method of analyzing time-invariant network after transforming the switched capacitor network from time-varying topology into time-invariant topology is proposed. z-domain models for equivalent resistance using switched capacitor is derived, and a 2nd-order switched capacitor is designed by utilizing such resistance substitution method. By cascading the 2nd-order switched capacitor filters, the design and simulation of 8th-order switched capacitor for Chebyshev low pass filter,SPICE program of low Q switched capacitor filter model are given. The simulation results show that output characteristics of switched capacitor filter are in good agreement with that of active low pass filter and also satisfied with the design specifications. The proposed method is simple and easy for model building. The ideal and useful SPICE model of equivalent resistance using switched capacitor can be used for designing high pass, band pass, band reject and other filter circuits.