Rsearch On Synthesis Of Active Filters

Active network synthesis is one of the subjects in the field of circuits and systems.The thchniques of cascade active filter design have been very mature, hundreds ofthousands of second order biqudratic ciucuits are also available, but there is no answerthat how these circuits come out. Research on active RC network synthesis issignificant for riching the theory of circuit design and practical application.Based on a comprehensive summarized active network theory and starting fromthe given symbolic low-pass or high-pass or band-pass or band-stop filter transferfunction, the systematic design method with the nullor model and the expansion ofnodal admittance matrix are studied in this thesis. Since the method is a reversal ofsymbolic circuit ananlysis by Gaussian elimination applied to a circuit nodaladmittance matrix, it can generate all circuits that possess a given symbolic transferfunction using the specified elements. The innovatite points of this dissertationinclude:(1)In the process of second-order lowpass filter synthesis, some new circuits’topologies are derived. Like biquadratic RC lowpass filter circuit, synthesized filercircuit containing ideal operational amplifer and transistor, and the circuit containsdual operational amplifers. The correctness of the circuits is verified by circuitsimulation.(2)By using active network synthesis theory flexibly, some comprehensive filterslike KHN and BH are derived under repeated use of privotal expansions.(3)In the synthesis process of band-stop filer with more than one nullors,Tow-Thomas and kerberg-Mossberg filer are derived with different grouping ofnullators and norators under the same given transfer function. This reflects thesuperiority of the systematic synthesis approach adopted.The synthesized circuit topology in this thesis is derived from symbolic voltage orcurrent transfer functions by admittance matrix transformations without any priorassumption concering circuit architecture or topology. The method is usful forsynthesis of low-order circuits.