Inductorless filter design using active elements and piezoelectric resonators

Inductorless active filters using piezoelectric resonators are described. Because of the excellent frequency stability of piezoelectric resonators (quartz crystals in particular), these filters are more suitable for realizing narrow bandwidth responses than are active filters which are restricted to relatively low applications by the limited tracking capability of the components. In addition, because the filters are active, the inductors and transformers which are often required in passive piezoelectric filters are eliminated.