An adaptive active band-pass filter by using tachometer circuit

Abstract

This thesis presented the design and construction of an adaptive active band-pass filter by using a tachometer circuit. The main part was the multi voltage-mode filter circuit based on an operational transconductance amplifier, which could automatically adjust the center frequency to adapt to the input signal frequency by the tachometer circuit. The frequency error value in the center frequency was set to be ≤ 3% of the input signal. Furthermore, the proposed filter could support the input signal in the frequency range of 10 Hz - 10 kHz. From the simulation and experimental results of the proposed prototype filter, it could respond to the frequency according to the theory of the band-pass filter and the error in choosing the center frequency, which was 1.45 % and 2.6 %, respectively (below the set error value of 3 %). Therefore, the proposed filter could be used for real application. The working principles of the proposed prototype filter could also be applied to the noise attenuation circuit of an electrocardiogram machine. Moreover, this research could be used as a guideline study for those who want to develop other types of adaptive active filters for higher efficiency.