sentences: This paper systematically investigates the design of single transistor second-order active filters out-lining all possible architectures and possible impedance settings using an exhaustive MAPLE search code for all stable cases with the minimum number of passive elements (two resistors and two energy storage elements). The search is performed on six general voltage-input voltage-output transfer functions, derived using a small-signal two-port network transistor model. Selected LC and RC filter designs are verified experimentally. The results presented here fill both a circuit-theoretic gap and an application-oriented gap related to single transistor filter design which, apart from a few examples in the literature, has not been rigorously addressed.