Tunable Bandpass/Bandstop Digital Filters Basedon 1st-order Allpass Network Instead of Unit Delay

This paper presents a design and realization of tunable bandpass and bandstop digital filters based on using tunable digital lowpass and highpass filters. The frequency response of both digital lowpass and highpass filters which called prototype filters can be changed/tuned by replacing unit delay elements in filter structure with 1st-order allpass network. From the tunable digital lowpass and highpass filters, the cascade connection of them can give tunable bandpass filter, the parallel connection can give tunable bandstop filter. The conditions of using proposed tunable bandpass/bandstop filters will be analyzed and explained in this work. A high flexibility of tuning both center frequency and bandwidth can be achieved from the proposed design and realization. Simulation results also be compared with experimental results from hardware implementation on FPGA using NI-myRIO device to ensure that the obtained frequency responses are correspondence.