SURFACE ACOUSTIC WAVE MULTIPLE MODE FILTER AND ITS PASSING BAND CHARACTERISTIC ADJUSTING METHOD

摘要

PURPOSE:To facilitate the adjustment of passing band width by grounding a conductor pattern for connecting inter-digital electrodes through a variable capacity element such as a variable capacity diode, etc., and adjusting the capacity in accordance with an output of the post-stage. CONSTITUTION:On the same piezoelectric substrates 10, plural surface acoustic wave resonators consisting of inter-digital electrodes 11 - 14 and reflectors 15 - 18 for inserting and holding them are placed adjacently, coupled acoustically, and used between a tuner of a receiver and an intermediate frequency amplification stage. Also, a variable capacity element 21 is connected to a conductor pattern 20 for connecting the inter-digital electrodes 11 - 14 and an earth, and a voltage applied to the variable capacity element 21 is controlled by an output of the intermediate frequency amplification stage. Accordingly, when the capacity connected to the conductor pattern for connecting the inter-digital electrodes 11 - 14 to an earth potential is varied, passing band width and a group delay time are varied. In such a way, since the passing band width can be varied by adjusting the capacity, a passing band characteristic can be aligned easily with a desired characteristic.