Signal Flow Graph Realization of Higher-Order CurrentMode All Pole Low-Pass Filters Using Five Current Follower Transconductance Amplifiers (CFTAs)
Objective: Signal flow graph realization of higher-order current-mode all-pole low-pass current transfer functions with five Current Follower Transconductance Amplifiers (CFTAs) is presented. The fifth presented filters with one input and three outputs employ five CFTAs and five capacitors, and it can simultaneously realize third order low pass, fourth-order low pass, and fifth-order low pass current responses, from the proposed circuit topologies. Bipolar and CMOS technologies are used for CFTA implementation. This study aims to provide a literature survey for identifying research gaps and to design and implementation of the Current follower Transconductance Amplifier (CFTA) with constant gm demonstrated. To implement the CFTA active device in the bipolar technology structure depicted in CFTA which has been employed using transistor model parameters PR100N (PNP) and NP100N (NPN) of the bipolar arrays ALA400 and the COMS technology structure using, 0.5 μm CMOS process parameters for nMOS and pMOS transistors.
Methods: The approach had been based on drawing a signal flow graph directly from the given transfer function and then obtaining, from the graph, the Active-C filter involving CFTAs. Third-order Butterworth low-pass circuit requires only three CFTAs and three grounded capacitors, fourth-order Butterworth low-pass circuit requires only four CFTAs and four grounded capacitors and fifth-order Butterworth low-pass circuit require only five CFTAs and five grounded capacitors. One Filter based on input and output is characterized by its transfer function. The transfer function of a filter is the ratio of the output signal to that of the input signal as a function of the complex frequency. The obtained filter characteristics include the natural frequency (ωo) and the quality factor (Q-factor) which are electronically tuned through biasing current of the transconductance gain of the CFTAs. The resulting circuits obtained from the synthesis procedure are resistorless structures and are especially suitable for monolithic implementation. The circuits also have low sensitivity characteristics and exhibit electronic controllability coefficients via transconductance gains (gm) of CFTAs.
Results: To demonstrate the proposed approach, the third-order, fourthorder, and fifth Butterworth all-pole low-pass filters were designed and simulated using MATLAB Simulink. Conclusion: The study of the simulation of the third-order, fourth-order, and fifth-order all-pole low-pass filters has been carried out. The CFTA circuits have been simulated using MATLAB SIMULINK. The simulation results are in agreement with the theory.