Abstract: A 3-terminal operational filter circuit is presented that can be used to construct various types of active filters. The filter circuit can be used to construct various orders of low pass, band-pass, high pass, and notch filters by simply coupling a few circuit elements (e.g., resistors and capacitors) to the filter circuit terminals. By cascading filter circuits, various types of higher order filters can constructed. The filter circuit can be manufactured with particular internal resistance and capacitance to enable the circuit to operate within a selected range of center frequencies. Users can then select a particular center frequency, notch frequency, quality factor, and gain of the filter circuit by selecting particular values for the circuit elements coupled to the filter circuit terminals.

Abstract: A 3-terminal operational filter circuit is presented that can be used to construct various types of active filters. The filter circuit can be configured to provide 2nd order low pass and band-pass frequency responses by coupling three resistors to the three filter terminals. Similarly, the filter circuit can be configured to provide 2nd order band-pass and high pass frequency responses by coupling two resistors and a capacitor to the three filter terminals. Furthermore, a plurality of filter circuits can be cascaded to construct various types of higher order filters. The filter circuit can be manufactured to operate within a selected range of center frequencies by selecting particular values for the internal filter capacitance and resistance. Users can then select a particular center frequency, quality factor, and gain of the filter circuit by selecting particular values for the circuit elements to be coupled to the three terminals.