Voltage-Mode CFTA-C Third-Order Elliptic Low-Pass Filter Design and Optimization Using Signal Flow Graph Approach

  • Norbert Herencsar Brno University of Technology
  • Jaroslav Koton Brno University of Technology
  • Jiun-Wei Horng Chung Yuan Christian University
  • Kamil Vrba Brno University of Technology
  • Martin Venclovsky Brno University of Technology
Keywords: Active equivalent, analog filters, current follower transconductance amplifier, CFTA, experiments, Mason-Coastes signal flow graph, LC ladder filter, optimization, passive prototype.


In this work, two active only grounded-C equivalents of third-order voltage-mode (VM) elliptic low-pass (LP) LC ladder prototype are proposed. As active building blocks (ABBs) the recently introduced current follower transconductance amplifier (CFTA) were used. The first active only grounded-C LP filter employing eight CFTAs was proposed by interconnecting CFTA-based active equivalent sub-blocks of passive components, where one of the low-impedance input terminals is not used. Since such feature may cause some noise injection into the proposed circuit, the proposed filter was optimized using Mason-Coates' signal flow graph approach. In several steps the number of ABBs was reduced by two and the unused input terminal was eliminated. The performance of the novel and optimized active only grounded-C third-order VM elliptic LP filter was tested experimentally using the readily available UCC-N1B integrated circuit.

DOI: http://dx.doi.org/10.5755/j01.eee.21.2.11508