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

Norbert Herencsar,Jiun-Wei Horng,Martin Venclovsky,Kamil Vrba,Jaroslav Koton

doi:10.5755/j01.eee.21.2.11508

Abstract

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

Highlights

Analog filters have wide area of applications in instrumentation, automatic control, and communication systems
The main aim of this paper is to combine both linear transformation (LT) technique and signal flow graph (SFG) approach such that firstly the active only grounded-C equivalent of third-order VM elliptic low-pass filter (LPF) is designed by LT, i.e. by replacement of passive components by theirs active equivalents and the SFG approach is with advantage used as powerful tool for the LT structure optimization
In order to confirm the theoretical study and to show the performance of the optimized active only grounded-C thirdorder VM elliptic LPF from Fig. 5(b), its behaviour has been verified by experimental measurements

Summary

INTRODUCTION

Analog filters have wide area of applications in instrumentation, automatic control, and communication systems. In the open literature this design technique has been firstly applied using operational amplifiers (OAs) [4], due to smaller dynamic range, narrow bandwidth, and higher power consumption of OAs, on various recently introduced non-conventional high performance ABBs. In open literature various third-order low-pass filter (LPF) realizations exist [6]–[13], this paper is strictly focused on active only grounded-C third-order voltage-mode (VM) elliptic LPF design [10]–[13]. The main aim of this paper is to combine both LT technique and SFG approach such that firstly the active only grounded-C equivalent of third-order VM elliptic LPF is designed by LT, i.e. by replacement of passive components by theirs active equivalents and the SFG approach is with advantage used as powerful tool for the LT structure optimization.

CIRCUIT DESCRIPTION

MEASUREMENT RESULTS

CONCLUSIONS