Tunable Radio-Frequency Filters Using Acoustic Wave Resonators and Variable Capacitors

摘要

In this paper, we describe possible configurations for tunable filters based on RF surface or bulk acoustic wave (SAW/BAW) technologies. The frequency tuning is made possible by variable capacitors (VCs) connected to SAW/BAW resonators in the ladder-type filter configuration. First, it is shown that the passband edges can be controlled by one VC connected to each resonator. Second, it is discussed that the width and location of a passband can be controlled flexibly by two VCs connected to each resonator both in parallel and in series. Finally, the SAW filters with the proposed configuration are fabricated on a Cu-grating/15°YX-LiNbO_3 substrate structure, and the tuning capability is demonstrated.