This paper presents a novel bulk acoustic wave stacked crystal filter (SCF) configuration that improves the inherent narrow bandwidth of this kind of devices and increases their selectivity by means of the allocating of transmission zeros. A set of parallel connected SCFs with their resonant frequencies split along the passband achieves the bandwidth improvement. The SCF detuning is carried out by the thickness of its middle metallic electrode. The filter response covers the 60 MHz bandwidth of a W-CDMA RF application working at 2.14 GHz. The use of SCFs considerably simplifies the layer stack configuration in contrast to other acoustically coupled structures as coupled resonator filters.
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doi:10.2528/PIERL09031605
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