JP3088801B2 - Surface acoustic wave filter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave filter used for communication equipment.

[0002]

2. Description of the Related Art FIG. 2 is a diagram showing an example of a conventional filter configuration using a bulk wave oscillator such as a quartz oscillator. FIG. 2 (A)
Has a discrete configuration, in which two oscillators 1 such as independent quartz oscillators are cascaded, and a coupling capacitor 2 is provided at an intermediate connection point 10 to form a filter. FIG. 2B shows a monolithic structure, in which electrodes for forming two bulk wave vibrators in one piezoelectric material such as a piezoelectric ceramic are arranged close to each other, and a monolithic filter 11 using acoustic coupling is used. is there.

[0003]

However, the discrete filter shown in FIG. 2A is assembled after sealing the individual vibrators in independent packages, or separately fixing the two vibrators. In general, the entire structure is sealed. This is a major obstacle in reducing the size of the filter. Further, the frequency depends on the thickness of the vibrator, and the higher the frequency, the thinner the thickness and the processing accuracy becomes a problem.

Further, the monolithic filter shown in FIG. 2 (B) can cope with miniaturization to some extent because two vibrators are formed in one chip. However, as with the discrete type filter, there is a limit in increasing the frequency. In addition, discrete and monolithic filters use both sides of the piezoelectric plate,
At the time of packaging, it is necessary to provide a gap between the front and back surfaces and the case, and there is a disadvantage that the fixing method is limited. SUMMARY OF THE INVENTION An object of the present invention is to provide a surface acoustic wave filter that solves the problems of the prior art with respect to miniaturization and higher frequency and that eliminates restrictions on the mounting surface.

[0005]

A surface acoustic wave filter according to the present invention comprises a piezoelectric substrate 1 having two one-terminal-pair surface acoustic wave resonator interdigital transducers and electrodes of a grating reflector. The two resonators are arranged in parallel along the direction, the two resonators are electrically connected in cascade, and the connection point is further connected to the interdigital transducer (IDT) of the two resonators.
The filter is formed by connecting interdigital electrodes for coupling capacitors arranged at right angles to the nsducer. Hereinafter, the present invention will be described in detail with reference to the drawings.

[0006]

FIG. 1 is a block diagram showing an embodiment of a surface acoustic wave filter according to the present invention. In the figure, two energy confining surface acoustic wave resonators each having an interdigital transducer 3 and grating reflectors 4 on both sides of the interdigital transducer 3 are provided on the surface of a piezoelectric substrate 7 in the propagation direction of the surface wave. And the two one-port resonators I
DT3 is electrically connected in series to form an input terminal 8, an output terminal 9, and a connection point 10. Furthermore, the interdigital electrode 5 for the coupling capacitor is connected to the connection point 10 and the terminals 8 ', 9'.
And the two surface acoustic wave resonators are arranged in a right angle with the interdigital transducer 3. Then, the terminals 8, 8 'become an input terminal pair,
The terminals 9, 9 'are output terminal pairs.

When comparing the configuration of the present invention shown in FIG. 1 with the conventional configuration shown in FIG. 2A, the vibrator 1 and the capacitor 2 in the circuit configuration shown in FIG. , And the surface acoustic wave resonator comprising the grating reflector 4 and the IDT 5 for the capacitor, respectively, so that the filter theory of the configuration of the present invention can apply the theory of the conventional configuration as it is.

However, a feature of the present invention is that the size of the chip can be greatly reduced because there is an advantage that the two resonators and the coupling capacitor can be configured as one chip only on one side of the piezoelectric substrate 7. Since only one side is used, there is a degree of freedom in packaging. The two surface acoustic wave resonators and the interdigital transducer electrode 5 can be simultaneously formed in the same process by photolithography technology, and their dimensions can be applied to the submicron range, so that they can be put to practical use up to the high frequency range. Can be.

The IDT 5 shown in FIG. 1 is used as a capacitor. The IDT 5 also excites a surface wave due to its nature. However, in the electrode arrangement of FIG. 1, the direction of surface wave propagation (opening direction) of the interdigital transducer 5 is set to the direction of surface acoustic wave propagation of the surface acoustic wave resonator, that is, the direction in which the piezoelectric substrate 7 most efficiently excites surface waves. The surface wave is hardly excited because it is at right angles to the direction. Also,
Even if a weak surface wave is excited, it is not electrically coupled to the surface acoustic wave resonator because it is disposed outside the grating reflector 4. If there is a possibility that the interdigital transducer 5 may excite a surface wave, a sound absorbing material 6 such as an insulating epoxy resin may be provided on the surface thereof.
Can be completely handled only as a capacitor. Further, since the interdigital electrodes 5 are used as capacitors, the electrode pitch can be set arbitrarily.

[0010]

As described above in detail, by implementing the present invention, the size can be significantly reduced, and the degree of freedom in packaging can be increased. In addition, it is possible to significantly increase the frequency.

[Brief description of the drawings]

FIG. 1 is a structural diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing an example of a conventional filter configuration.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Piezoelectric vibrator 2 Capacitor 3 IDT 4 Grating reflector 5 IDT for capacitor 6 Insulating resin 7 Piezoelectric substrate 8, 8 'Input terminal pair 9, 9' Output terminal pair 10 Connection point 11 Monolithic Piezo filter

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H03H 9/64 H03H 9/25

Claims (1)

(57) [Claims] 1. A piezoelectric substrate comprising: a piezoelectric substrate; and, on the piezoelectric substrate, an interdigital transducer and grating reflectors on both sides of the interdigital transducer. Two surface acoustic wave resonators connected in series, and one terminal connected to an intermediate connection point between the two surface acoustic wave resonators and a surface outside one of the grating reflectors of the two surface acoustic wave resonators An IDT for a coupling capacitor arranged so that a wave propagation direction is perpendicular to the SAW propagation direction of the two surface acoustic wave resonators, and the other of the IDTs for the coupling capacitor. Terminal and 2
A surface acoustic wave filter configured such that each of an input terminal and an output terminal of one surface acoustic wave resonator forms an input terminal pair and an output terminal pair.