Wave transmission lines and networks – Coupling networks – Electromechanical filter
Patent
1992-10-09
1995-02-28
Lee, Benny
Wave transmission lines and networks
Coupling networks
Electromechanical filter
333191, 333200, 310348, 310370, H03H 910, H03H 921
Patent
active
053941233
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates generally to ladder type filters, and more particularly, to a ladder type filter in which serial resonators and parallel resonators are provided using tuning fork type piezoelectric resonators.
BACKGROUND OF THE INVENTION
One example of the structure of a conventional ladder type filter is shown in FIG. 2. This conventional ladder type filter is constructed using a plurality of piezoelectric resonators utilizing an extension mode of vibration of a square plate. More specifically, a two-stage ladder type filter containing four elements shown in the circuit diagram of FIG. 3 is constructed using rectangular plate-shaped serial resonators 1 and 2 and rectangular plate-shaped parallel resonators and 4.
In FIG. 2, reference numeral 2a denotes an electrode formed on one major surface of the serial resonator 2. The same electrode is formed on the other major surface of the serial resonator 2. In addition, the same electrodes are formed on both major surfaces of the serial resonator 1. On the other hand, electrodes 3a and 4a are respectively formed on the entire surface of both major surfaces of the parallel resonators 3 and 4.
Furthermore, reference numerals 5 to 11 denote metal terminals, which are used for electrically connecting the serial resonators 1 and 2 and the parallel resonators 3 and 4 to each other, in the manner shown in FIG. 3. The metal terminals 5 to 11, together with the serial resonators 1 and 2 and the parallel resonators 3 and 4, are contained in a case 12 made of an insulating material. In addition, an upper opening 12a of the case 12 is closed by a cover member (not shown), to construct one ladder type filter component. In this case, the metal terminals 9 to 11 extended out of the case 12, and are utilized as connecting terminals to the exterior. As shown in FIG. 3, the metal terminals 9, 11 are used as electrodes for the circuit of the conventional ladder type filter.
Meanwhile, when the above described ladder type filter is driven, the serial resonators 1 and 2 and the parallel resonators 3 and 4, which are contained in the case 12 must be vibrated in a desired manner. More specifically, the vibration of each of the resonators 1 to 4 must not be prevented by the case 12 in which the resonators 1 to 4 are contained. Therefore, a so-.called spring terminal having spring properties is used as the metal terminal 11 positioned at an end of the ladder type filter.
In the ladder type filter shown in FIG. 2, a spring terminal is used as the metal terminal 11 so as not to prevent the vibration of the resonators 1 to 4, when the resonators 1-4 are contained in the case 12. Accordingly, additional space is required in the case 12 thereby significantly increasing the overall size of the ladder type filter. For example, the two-stage ladder type filter containing four elements as shown in FIG. 2 measures approximately 7.0 mm by 8.0 mm by 8.0 mm thick when it is constructed as a final ladder type filter component.
Furthermore, in recent years, there has been a demand for a ladder type filter, which in a manner similar to other electronic components is constructed as a surface mounted type electronic component.
OBJECT OF THE INVENTION
Accordingly, an object of the present invention is to provide a ladder type filter which can be constructed as a surface mounted type electronic component and is small in overall size.
DISCLOSURE OF THE INVENTION
The present invention provides a ladder type filter, which is constructed by connecting at least one serial resonator and at least one parallel resonator, having the following structure.
More specifically, in the present invention, a tuning fork type piezoelectric resonator is used as the serial resonator and the parallel resonator. The tuning fork type piezoelectric resonator is constructed by forming second and third slits extending inward from one edge of a piezoelectric substrate such that a first slit extending inward from the one edge thereof is interposed therebetween so as to form a tuning fork-
REFERENCES:
patent: 2639393 (1953-05-01), Birt et al.
patent: 4564825 (1986-01-01), Takahashi et al.
patent: 5159301 (1992-10-01), Kaida et al.
patent: 5159302 (1992-10-01), Tanaka
Inoue Jiro
Kaida Hiroaki
Lee Benny
Murata Manufacturing Co. Ltd.
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