Insertion loss and TTE of SAW filter using 3‐transducer configuration

Abstract

AbstractThe use of a 3‐transducer SAW element configuration gives complete suppression of the triple‐transit effect (TTE) at the frequency at which the external circuit is electrically matched to the central transducer. But when designing such an element as a filter it is necessary to deal with TTE at all frequencies within the filter band. This paper discusses the TTE within the filter band for an element with a 3‐transducer configuration, assuming negligible SAW reflection. The significance of the impedances of the external circuit and the interdigital transducer, the electromechanical coupling coefficient of the substrate and the relation between bandwidth and insertion loss in obtaining 40 dB or better TTE suppression in the main signal is demonstrated. In particular, a TV‐VIF filter with the regular 3‐transducer configuration prepared on a thin‐film ZnO substrate gave 40 dB of TTE suppression in the filter band and had 11 dB insertion loss. A device with a proportional band for use in a TV‐VIF filter was prepared in order to test the theoretical calculation. The TTE and main response signals were separated by means of a pulse modulation set‐up. The TTE frequency response within the filter band was observed directly, and the 3‐transducer configuration was found to be capable of producing the low‐loss filters needed for band design without alteration of commonly‐used design methods, and is an effective method of achieving TTE suppression.