Realization of current-mode integer and fractional-order filter designs for VLF-MF applications

In this thesis, the design and analysis of analog filter circuits intended to meet the requirements of engineering systems operating within the very low frequency (VLF), low frequency (LF), and medium frequency (MF) bands of the electromagnetic spectrum have been carried out. The developed filter structures operate in current mode and are implemented in both integer-order and fractional-order configurations. These circuits are optimized for narrowband and low-frequency applications such as submarine and acoustic communication, aeronautical and maritime navigation systems, biomedical devices, and control systems. The theoretical foundation of this study is based on the discipline of fractional calculus, which asserts that differentiation and integration need not be limited to integer orders. By applying fractional calculus to analog filter design, enhanced flexibility has been achieved through sharper and more precisely controlled transitions between passbands and stopbands. Fractional-order functionality in the proposed filter circuits is realized via capacitors specifically configured to exhibit fractional behavior. These fractional capacitors are modeled using the Oustaloup approximation method, selected for their superior gain response characteristics, and are implemented with Foster type-I RC networks comprising a minimal number of passive components. To support current-mode operation, active building blocks such as the modified current feedback operational amplifier (MCFOA) and multi-output second-generation current-controlled current conveyors (MOCCCIIs) have been employed. The proposed topologies use only grounded passive components and are capable of producing various filter responses including low-pass, high-pass, band-pass, band-stop, all-pass, step, and Chebyshev low-pass filters, resulting in compact, low-power, and integration-friendly structures. The performance of the designed filter circuits was evaluated through comprehensive simulations in both MATLAB and PSpice environments. Frequency response, roll-off behavior, and cutoff frequency performance were verified. The simulation results also demonstrated that current-mode operation meets key performance metrics such as low total harmonic distortion (THD), wide dynamic range, and low power consumption. Additionally, Monte Carlo analyses were conducted on the proposed topologies, confirming that the filters maintain the required level of precision under parameter variations and manufacturing tolerances—particularly for sensitive applications within the VLF, LF, and MF bands. To ensure real-world implementation compatibility, all passive components were selected in accordance with the E96 series defined by the IEC 60063 standard. In conclusion, this study combines the theoretical principles of fractional calculus with analog filter design to present highly applicable, innovative, and integrable circuit solutions for low-frequency communication and control systems.