PURPOSE: To increase input/output impedance and at the same time to improve filter characteristics, by decreasing properly the length of an electrode finger on the split interface of the split interdigital transducer electrode.
CONSTITUTION: A multipair of interdigital transducer electrodes which are arranged in series on a single piezoelectric substrate 1 and along the propagating direction of a surface acoustic wave are divided into two parts. These divided electrodes are connected electrically and in series with the single side of the electrodes 5 and 6 respectively used as a bus bar. In such way, a surface acoustic wave filter is formed. The high frequency voltage V is applied to the bus bars of the divided electrodes 5 and 6, and the V/2 voltage is applied between the fingers of the divided electrodes. The lengths of the electrode fingers 10 and 11 which are opposite to each other on a split interface of the electrodes 5 and 6 are decreased. At the same time, the cross width w2 of the fingers 10 and 11 is set 2/3 cross width w1 of the electrode fingers at other areas. Thus the exciting intensity F of the surface acoustic on the split interface varies slowly to the nearby intensity, and the effect is minimized to the prescribed filter characteristics. Furthermore the input/output impedance can be increased.
MORITA TAKAO
KUROSAKI TAKEFUMI
| JPS53131737A | 1978-11-16 |