Automatic tuning scheme for second order bandstop filters based on phase comparison

Abstract

A new automatic tuning scheme for bandstop filters is proposed. The method is based on tuning the filter parameters such as center frequency, bandwidth and attenuation by using phase comparison, where the phase difference between the input and the output of the bandstop filter is detected by D flip flops. The tuning circuit consists of D flip-flops, counters, switches, DACs, and passive components. The tuning method was verified by simulation and experimental results. Simulation results show the frequency tuning error of $$0.13\%$$ and the bandwidth tuning error of $$0.88\%$$ at 1.5 GHz with a bandwidth of 478 MHz. Experimental results were obtained using discrete components, showing the frequency tuning error of $$0.22\%$$ and the bandwidth tuning error of $$0.66\%$$ at 1 kHz with a bandwidth of 200 Hz.