OTA-based tunable fractional-order devices for biomedical engineering

Abstract

This research realizes fractional-order devices or constant phase element (CPE) using continued fraction expansion (CFE) and rational function approximation methods. An RC ladder network prototype was realized using CFE based on the Cauer network principle. The RC ladder network and signal flow graph (SFG) were employed to realize the proposed CPE. Voltage gain circuits and voltage-mode integrators were realized by using operational transconductance amplifiers (OTA) and grounded capacitors. The proposed CPE was subsequently synthesized using voltage gain circuits and voltage-mode integrators based on SFG. The proposed CPE could function as fractional-order capacitor and fractional-order inductor. Besides, the CPE could be constructed in arbitrary fractional-orders. The impedance and operation frequency are independently tunable by manipulating OTA bias current. To validate, the proposed fractional-order device was applied to six types of electrical Cole models of skull tissues, and simulation results were compared with the approximation function and theory. The electrical characteristics of the Cole models based on the proposed CPE are comparable to the theoretical characteristics of the Cole model.