Resonator-type saw filter with independent ground patterns for interdigital transducers and reflectors
AssigneeOki Electric Industry Co., Ltd.
InventorOu Hok Huor
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Abstract
A resonator-type SAW filter has a ladder network of SAW resonators with respective interdigital transducers and reflectors. Individual ground patterns are provided for each interdigital transducer and each reflector in the shunt-arm SAW resonators. These ground patterns are electrically isolated from one another, and are grounded through separate bonding wires or other conductors that couple the ground patterns to a ground lead. This independent grounding scheme is found to improve the attenuation characteristic of the filter on the low side of the passband.
Claims10
A resonator-type. surface-acoustic-wave filter having a plurality of surface-acoustic-wave resonators with respective interdigital transducers and respective reflectors, each interdigital transducer being disposed between a respective pair of said reflectors, separated from the pair of reflectors by a certain distance, the surface-acoustic-wave resonators being coupled in a ladder network having at least one series-arm surface-acoustic-wave resonator and at least one shunt-arm surface-acoustic-wave resonator, the filter also having:
- at least one ground lead;
- a plurality of ground patterns, including a separate ground pattern connected to each said interdigital transducer of each said shunt-arm surface-acoustic-wave resonator and a separate ground pattern connected to each said reflector of each said shunt-arm surface-acoustic-wave resonator, said ground-patterns being electrically isolated from one another;
- and
- a plurality of conductors independently coupling said ground patterns to said at least one ground lead.
A surface-acoustic-wave duplexer including a resonator-type surface-acoustic-wave filter having a lower stopband, a bandpass filter having a passband disposed in said lower stopband, and at least one ground lead, the resonator-type surface-acoustic-wave filter and the bandpass filter both being coupled to an antenna, one of the reasonator-type surface-acoustic-wave filter and the bandpass filter functioning as a transmit filter, another one of the resonator-type surface-acoustic-wave filter and the bandpass filter functioning as a receive filter, the resonator-type surface-acoustic-wave filter comprising:
- a plurality of surface-acoustic-wave resonators with respective interdigital transducers and respective reflectors, each interdigital transducer being disposed between a respective pair of said reflectors, separated from the pair of reflectors by a certain distance, the surface-acoustic-wave resonators being coupled in a ladder network having at least one series-arm surface-acoustic-wave resonator and at least one shunt-arm surface-acoustic-wave resonator;
- a plurality of ground patterns, including a separate ground pattern connected to each said interdigital transducer of each said shunt-arm surface-acoustic-wave resonator and a separate ground pattern connected to each said reflector of each said shunt-arm surface-acoustic-wave resonator, said ground patterns being electrically isolated from one another;
- and
- a plurality of conductors independently coupling said ground patterns to said at least one ground lead;
- the electrical isolation of said plurality of ground patterns providing increased attenuation in said lower stopband.
Dependencies are inferred from the claim text.