Charge transfer type recursive filter for telecommunications - has SAW propagating surface covering charge transfer delay lines to effect transfer

摘要

The filter is controlled by a double acoustic surface wave and includes a semiconductor substrate having two parallel electrode series defining respective delay lines and having respective injection and collector diodes. A third distribution electrode series couples the two delay lines. The direction of charge transfer in one delay line is the reverse of that of the other and control of charge transfer is effected by a leaf of material for propagating elastic surface waves. Respective transducer at each leaf end are connected to piezoelectric generators, the transducers being offset transversely to apply two elastic surface waves in opposite directions along parallel tracks, the wavelength being equal to the spacing between distribution electrodes. The two transducers are separated by an integral wavelength multiple with the leaf being disposed on the substrate, each surface wave track crossing one of the delay lines to ensure charge transfer.