Wave transmission lines and networks – Coupling networks – Electromechanical filter
Reexamination Certificate
1999-08-27
2001-05-01
Lee, Benny (Department: 2817)
Wave transmission lines and networks
Coupling networks
Electromechanical filter
C333S190000, C333S192000, C310S348000
Reexamination Certificate
active
06225877
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to piezoelectric filter to be suitably used for a filter circuit of mobile radio telecommunication equipment such as a portable mobile radio transmitter/receiver unit or an automobile telephone set.
2. Related Background Art
A piezoelectric filter of the type under consideration typically comprises a multiple of unit filter circuits, each having one or more than one series resonators and one or more than one parallel resonators connected to form an L-connection and arranged between an input terminal and an output terminal or a grounding terminal. The resonance frequency of the series resonators and the antiresonance frequency of the parallel resonators are made to correspond with each other and the difference between the antiresonance frequency of any of the series resonators and the resonance frequency of any of the parallel resonators is held to a constant value. These and other ideas have been proposed for piezoelectric filters comprising a plurality of resonators in order to improve the performance and reduce the required number of piezoelectric filters. An example of such conventional piezoelectric filters is disclosed in Examined Japanese UM Publication No. 57-12579.
However, in most conventional piezoelectric filters having a configuration as described above, resonators and terminal plates are typically assembled to a multilayer structure within a casing and hence they inevitably comprise a large number of components to entail a cumbersome assembling process. Meanwhile, piezoelectric filters are often required to be as thin as several millimeters to meet the trend of downsizing. Additionally, they are required to be configured in such a way that each of the piezoelectric filters can be electrically connected with relative ease to a predetermined electric path arranged on a plane that carries resonators thereon and the resonators are electrically and mechanically protected.
Still additionally, piezoelectric filters should be easy to manufacture and assemble.
SUMMARY OF THE INVENTION
In view of these circumstances, it is therefore an object of the present invention to provide a multilayer type piezoelectric filter that can solve the above identified problems.
According to the invention, there is provided a multilayer type piezoelectric filter comprising;
a plurality of resonator elements arranged to form a multilayer structure vertically extended, each being surrounded by a frame-like spacer element;
a plurality of intermediary printed circuit board elements each interposed between the adjacent resonator elements, each being provided with predetermined conducting patterns on an upper and lower surfaces thereof;
a top printed circuit board element arranged on the top of the resonator elements and provided with a predetermined conducting pattern on a lower surface thereof; and
a bottom printed circuit board element arranged under the bottom of the resonator elements and provided with a plurality of connection electrodes on a lower surface and predetermined conducting paths on an upper and lower surfaces thereof;
the frame-like spacer elements, the top printed circuit board element and said bottom printed circuit board element being bonded together at the peripheral edges thereof;
each electrode of each of the resonator elements being connected by means of the conducting patterns provided on the respective printed circuit board elements to one of the connection electrodes on the bottom printed circuit board element to form a predetermined filter circuit.
In the multilayer type piezoelectric filter according to the present invention, each frame-like spacer element may be provided with conducting grooves on a front and rear edges thereof which are arranged to form conducting paths vertically extended.
Preferably, coating resists may be provided on an upper and lower surfaces of each of the intermediary printed circuit board members, a lower surface of the top printed circuit board member and an upper surface of the bottom printed circuit board member for substantially covering the conducting patterns on those printed circuit board members to electrically insulate them from each other.
With the above arrangement, the piezoelectric filter shows a simple configuration of a multilayer structure of a number of elements and hence can be down-sized particularly in terms of height. At the same time, the piezoelectric filter can be very robust and is electrically and mechanically protected because each of the resonator elements is protected by a frame-like spacer and the top and bottom printed circuit board members.
Preferably, the piezoelectric filter according to the present invention may comprise three plate-like resonator elements, of which one is either a series resonator or a parallel resonator and the other two are parallel resonators or series resonators, whichever appropriate.
Alternatively, the piezoelectric filter according to the present invention may comprise six plate-like resonator elements, three of which are arranged to form a T-type circuit of a S-P-S structure, the other three are arranged to form a &pgr;-type circuit of a P-S-P structure.
With this arrangement, a filter circuit comprising six element sheets is provided by two filters and each of the filter can be down-sized particularly in terms of height.
Preferably, the components of the piezoelectric filter may be bonded together by means of adhesive sheets held in face contact with the respective frame-like spacers. Each of the adhesive sheets may be frame-like which is substantially similar to that of the frame-like spacer elements.
Then, the piezoelectric filter can be produced simply by laying the components including the adhesive sheets one on the other to a multilayer structure and heating the components. Thus, such piezoelectric filters may be manufactured on a mass production basis in a simple fashion.
REFERENCES:
patent: 4864259 (1989-09-01), Takamoro et al.
patent: 5109176 (1992-04-01), Nguyen et al.
patent: 5717365 (1998-02-01), Kaida et al.
patent: 6002308 (1999-12-01), Gamo
patent: 6160462 (2000-12-01), Sugiyama et al.
patent: 54-12579 (1982-03-01), None
patent: 62-11314 (1987-01-01), None
patent: 3-97314 (1991-04-01), None
patent: 4-4603 (1992-01-01), None
patent: 6-224687 (1994-08-01), None
patent: 9-18285 (1997-01-01), None
Ogawa Tatsuo
Ozeki Eiji
Larson & Taylor PLC
Lee Benny
NGK Spark Plug Co. Ltd.
Summons Barbara
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