Realization of open‐input type second‐order active RC filters using two operational amplifiers

Abstract

AbstractOne of the active RC circuit realization methods is the inductance simulation method. Conventionally, the modeling of the floating inductance is aimed at the bi‐directional inductance L. In this paper, the authors consider the case where realization of the “unilateral” inductance is simpler than the bidirectional inductance and perform the realization using two operational amplifiers. It is shown also that the unilateral FDNR can be realized by the same procedures. These unilateral L and FDNR are applied in the realization of the open‐input type (∞‐0 type) second‐order filters which are new circuit types. Moreover, it is shown that the ∞‐0 type second‐order filters can also be derived from the ∞‐0 type for the realization of the open‐input/voltage source‐output circuits. In either circuit type, all the second‐order transfer functions are realized in the ∞‐0 type filters by using the L and FDNR circuits. The second‐order filter groups proposed in this paper have advantages in that the number of elements is less and the sensitivity is lower than in the ∞‐0 type filters. As an experimental example, the measured and calculated values are shown for the frequency characteristics of the ∞‐0 type second‐order low‐pass filters. Their operations are then verified.