JPH05206778A - Composite filter for surface acoustic wave resonator - Google Patents

Abstract

PURPOSE:To obtain a steep frequency characteristic and to improve the production yield by connecting between one or more surface acoustic wave resonators connected in parallel to each other and a common earth potential electrode with a via hole on a substrate and a conductive material embedding this via hole. CONSTITUTION:Plural surface acoustic wave resonators 2 are connected to each other on a piezoelectric substrate 1 set on a stem 6, and the input and the output of each resonator 2 are connected to the input and output terminals IN and OUT respectively via the metallic thin wires 8. At the same time, the earth side of the one or more resonators 2 connected to a common earth potential electrode connected to the output path of the signal in parallel and the common earth potential electrode is connected. This connection is performed via a conductive paste material put into a via hole 10 formed on the substrate 1. Thus the inductance caused by the connection is minimized. As a result, a steep frequency characteristic is obtained with the least variance of the inductance and improvement of the production yield in comparison with the connection secured by the wires 8.

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, and more particularly to a surface acoustic wave resonator formed by arranging a large number of pairs of thin film interdigital electrodes on a piezoelectric substrate capable of propagating surface acoustic waves. And combining and converting multiple surface acoustic wave resonators,
The present invention relates to a band-pass or band-rejection type surface acoustic wave filter that has a small loss due to reverse conversion and is capable of supplying electric power in watts.

[0002]

2. Description of the Related Art A conventional surface acoustic wave resonator composite type filter is disclosed in Japanese Unexamined Patent Publication (Kokai) No. 63-132515, and it has a single aperture elasticity composed of a plurality of thin film interdigital electrodes formed on a single piezoelectric substrate. It consists of a combination of surface acoustic wave resonators, and the pass characteristics of the filter or the rise and fall characteristics between bands are determined by the electrode structure of the resonator and the material constants of the piezoelectric substrate. In addition, the single-aperture surface acoustic wave resonator described in JP-A-1-260911 is a composite surface acoustic wave resonator in which a plurality of propagation paths each having a wavelength of at least half the wavelength are introduced into a solid type or series type resonator. The characteristics of the shape filter were improved. In these conventional techniques, a thin metal wire is used to electrically connect the surface acoustic wave resonator connected in parallel to the signal path and the common ground potential electrode.

[0003]

In the surface acoustic wave resonator connected in parallel to the signal path, the frequency characteristics of the electrical impedance of the surface acoustic wave resonator are utilized to connect the surface acoustic wave resonator in series. The resonance frequency forms the attenuation band of the filter and the parallel resonance frequency forms the pass band of the filter.
However, the surface acoustic wave resonator connected in parallel to the signal path is useful when the attenuation band of the filter is located at a frequency lower than the pass band. Here, since the ratio of the series resonance frequency to the parallel resonance frequency is proportional to the electromechanical coupling coefficient, which is the material constant of the piezoelectric substrate, when the attenuation band and the pass band of the filter are close to each other, the Generally, a piezoelectric substrate having a small mechanical coupling coefficient is used, and conversely, a piezoelectric substrate having a large electromechanical coupling coefficient is used when the attenuation band and the pass band of the filter are relatively distant from each other.

In the surface acoustic wave resonator connected in parallel to the signal path, in addition to the electromechanical coupling constant, a thin metal wire for making an electrical connection between the surface acoustic wave resonator and the common ground potential electrode. It is known that the inductance component generated by the filter affects the frequency characteristic of the filter. That is,
Even with a piezoelectric substrate having a series resonance frequency fr and a parallel resonance frequency fa, the presence of an inductance component in a surface acoustic wave resonator connected in parallel to the signal path causes
The series resonance frequency apparently decreases to fr-ΔL.
At this time, the parallel resonance frequency is fa and is not affected by the inductance component.

Therefore, when it is desired to bring the series resonance frequency and the parallel resonance frequency close to each other, that is, to design a filter having a close attenuation band and close to the pass band, the electrical connection between the surface acoustic wave resonator and the common ground potential electrode is required. In many cases, the inductance component generated by the thin metal wire for performing the physical connection is unnecessary. Further, since the inductance component of the thin metal wire is influenced by the wiring shape of the thin metal wire, the variation in the wiring shape, which is difficult to control in the mass production process, causes the variation in the frequency characteristic. In the conventional technology, no consideration has been given to the influence of the inductance component generated by the thin metal wire.

[0006]

The problem of the above-mentioned prior art is that the electrical connection between the surface acoustic wave resonator and the common ground potential electrode is buried in the via hole formed on the piezoelectric substrate and the via hole. It is solved by performing it through a conductive material.

Further, the above-mentioned problems of the prior art are similarly solved by electrically connecting the surface acoustic wave resonator and the common ground potential electrode via a conductive material in the form of a conductive paste. It

[0008]

When the electrical connection is made through the via hole formed on the piezoelectric substrate and the conductive material in which the via hole is buried, the generated inductance can be made smaller than that of the conventional electrical connection by the thin metal wire. Furthermore,
It is possible to reduce manufacturing variations as compared with the conventional technique. Similar effects can be obtained when a paste-like conductive material is used. Therefore, according to the present invention, when designing a filter in which the attenuation band and the pass band are close to each other, it is possible to minimize the influence of the inductance and realize a steep frequency characteristic. Further, it is possible to minimize the variation in the frequency characteristic due to the influence of the variation in the inductance generated in the manufacturing process.

[0009]

EXAMPLES In the above-mentioned conventional surface acoustic wave resonator, the electrical connection between the surface acoustic wave resonator and the common ground potential electrode is
Since the thin metal wire is used, the inductance generated therefrom may not realize the original steep frequency characteristic of the surface acoustic wave resonator. Here, first, an equivalent circuit expression of the surface acoustic wave resonator will be described, and based on this, the relationship between the inductance of the thin metal wire and the characteristics of the surface acoustic wave resonator will be described.

FIG. 1 shows a perspective view of a set of surface acoustic wave resonators. A surface acoustic wave resonator composed of a set of thin film comb-shaped interdigital electrodes 2 formed on a piezoelectric substrate 1 is
When a high-frequency electric field is applied between the interdigital electrodes, surface acoustic waves are generated due to the piezoelectricity of the substrate, and a resonance state is realized by multiple reflection between the electrodes.

This surface acoustic wave resonator is often expressed by the equivalent circuit shown in FIG. In FIG. 2, the surface acoustic wave resonator is represented by an inter-electrode electrostatic capacitance 3, an equivalent capacitance 4, and an equivalent inductance 5.

As shown in FIG. 1, the length of the intersection of the electrodes is W, the basic repetition period of the electrodes is p, and the number of times the electrodes are repeated is N. At this time, the inter-electrode capacitance 3 can be obtained by the equation 1, the equivalent capacitance 4 by the equation 2, and the equivalent inductance 5 by the equation 3.

[0013]

[Equation 1]

[0014]

[Equation 2]

[0015]

[Equation 3]

Here, fr and fa are a series resonance frequency and a parallel resonance frequency, respectively, and the series resonance frequency fr is a frequency obtained from the equation 4.

[0017]

[Equation 4]

From the equation 2, the ratio of fa to fr [fa / f
r] satisfies the relationship of Expression 5, and has a value determined by the material constant of the piezoelectric substrate.

[0019]

[Equation 5]

The length W of the intersection of the electrodes of the surface acoustic wave resonator, the basic repetition period p of the electrodes, the number N of times of repetition of the electrodes, and the capacitance coefficient Cs and [fa /
fr], the characteristics of the surface acoustic wave resonator can be simulated by using the relationships of Equations 1 to 5.

FIG. 3 shows the frequency characteristics of the impedance of the surface acoustic wave resonator calculated using the relations of the equations 1 to 5. The impedance is 0 at fr and infinite at fa.
FIG. 5 shows the frequency characteristics of the pass loss when the surface acoustic wave resonator having such frequency characteristics is connected in parallel to the signal input / output circuit as shown in FIG. An attenuation band is formed at a frequency fr at which the impedance of the parallel circuit is 0, and a pass band is formed at a frequency fa at which the impedance of the parallel circuit is infinite. However, in an actual device, the generation of inductance due to mounting cannot be ignored.

FIG. 6 shows a perspective view of the conventional mounting. As shown in FIG. 6, since the surface acoustic wave element 7 is mounted on the metallic stem 6, the surface acoustic wave resonator 2 and the stem 6 are arranged.
A thin metal wire 8 is used to connect the upper common electrode. Therefore, when the inductance 9 generated from the thin metal wire 8 is also taken into consideration, the equivalent circuit of the device having the structure shown in FIG. 6 is shown in FIG. 7 in which the inductance 9 of the thin metal wire is added to FIG. Therefore, the frequency characteristic of the impedance of the resonance circuit of FIG. 7 is inductively shifted from the frequency characteristic of the impedance of FIG. 3 due to the influence of the inductance of the thin metal wire 8. In FIG. 8, the frequency characteristic of the original impedance of the surface acoustic wave resonator 2 of FIG. 3 is shown by a broken line for comparison. In FIG. 8, the frequency at which the impedance of the resonance circuit becomes 0 shifts to the lower frequency side by ΔL than the frequency fr originally possessed by the surface acoustic wave resonator 2.

As shown in FIG. 7, even if fr shifts to the low frequency side, fa does not shift. Therefore, when this circuit is connected in parallel with the signal input / output circuit as shown in FIG. The frequency characteristics of are as shown in FIG. In the frequency characteristic of FIG. 10, the frequency in the attenuation range is ΔL more than that of the original surface acoustic wave resonator 2 of FIG. 5 (shown by the dotted line in FIG. 10).
Is only low. As described above, since fa is not affected by the inductance 9 of the thin metal wire, the frequency of the pass band does not change. Therefore, due to the influence of the inductance 9 of the thin metal wire, the steepness of the filter that can be realized is impaired, and the frequency difference between the pass band and the attenuation band becomes large.

Thus, when designing a filter in which the frequencies of the pass band and the attenuation band are close to each other, the inductance 9 of the thin metal wire adversely affects the characteristics. Furthermore, since the inductance 9 of the thin metal wire changes depending on the length and shape of the thin metal wire, a manufacturing deviation will inevitably occur. Since the manufacturing deviation of the inductance appears as a deviation of the frequency characteristic of the filter for the reason already described, it is necessary to suppress the inductance deviation of the thin metal wire to be small in order to improve the manufacturing cost.

Therefore, in the present invention, in order to maximize the steepness that the surface acoustic wave resonator originally has, the connection is not made by a thin metal wire as in the prior art, but as shown in FIG. The via hole 10 is formed in the piezoelectric substrate 1, and the surface acoustic wave resonator 2 and the common ground electrode are connected via the conductive paste embedded in the via hole 10. Therefore, it is possible to minimize the inductance generated due to the connection between the surface acoustic wave resonator 2 and the common ground electrode.

FIG. 12 shows a sectional structure of the device shown in FIG. As shown in FIG. 12, the via hole 1 is used when the device is bonded onto the stem through the conductive paste material 11.
0 is embedded with a conductive paste material 11 to connect the surface acoustic wave resonator 2 and the common ground electrode. Further, since the processing of the via hole is performed by the etching process, the manufacturing deviation such as the diameter of the via hole can be made extremely small, and the deviation of the inductance due to the connection can be minimized.

When the processing of the via hole is difficult, even if the surface acoustic wave resonator and the common ground electrode are connected by a conductive paste material as shown in the perspective view of the embodiment of FIG. The same effect can be obtained. Further, as shown in the perspective view of the embodiment of FIG. 14, the same effect can be obtained by connecting the surface acoustic wave resonator and the common ground electrode by the ribbon-shaped conductor 12 instead of the metal thin wire 8. The embodiments of the present invention have been described above by taking as an example the device in which one surface acoustic wave resonator is introduced in parallel to the signal path.

The utility of the present invention is that the surface acoustic wave resonator composite type filter formed by combining a plurality of surface acoustic wave resonators is connected in parallel to the signal path, as shown by an equivalent circuit in FIG. The performance of the filter can be improved by applying the present invention to the connection of at least one surface acoustic wave resonator connected to the common ground electrode and the common ground electrode.

An example of the performance improvement is shown by taking a reception filter of a car phone for the UK as an example. The car phone for the UK has a space of only 12 MHz between the transmission band and the reception band, and the filter is required to have a very steep frequency characteristic. FIG. 16 shows frequency characteristics when the present invention is applied.
Reference numeral 7 shows frequency characteristics when the conventional connection using a thin metal wire is applied. Although the specifications are satisfied in FIG. 16, FIG.
In the transmission band, there is a frequency range that does not satisfy the specifications due to the influence of the inductance of the thin metal wire.

The effectiveness of the present invention has been described above by using the device using the frequency of 900 MHz band as the embodiment. The effectiveness of the present invention is not limited to the frequency of 900 MHz band and is effective regardless of the frequency used. The higher the frequency, the greater the influence of the inductance due to the connection. Therefore, the effect is great especially in the frequency band above the quasi-microwave, where demand will increase in the future.

[0031]

According to the surface acoustic wave resonator composite type filter of the present invention, it is possible to realize a filter specification in which band intervals are narrow and steep rise and fall characteristics are required. Further, the duplexer configured by using the surface acoustic wave resonator composite filter can attenuate a high power transmission signal from the transmission filter through the antenna and a weak power reception signal from the antenna through the reception filter. Can be propagated without. Therefore, it is possible to improve the quality of the transceiver and reduce the power consumption of the device.

Further, by using the duplexer according to the present invention in a mobile radio terminal, or a communication device for consumer use, satellite use, etc., the terminal or device can be made smaller and lighter and the power consumption can be reduced.

[Brief description of drawings]

FIG. 1 is a perspective view of a surface acoustic wave resonator.

FIG. 2 is an equivalent circuit diagram of a surface acoustic wave resonator.

FIG. 3 is a frequency characteristic diagram of impedance of a surface acoustic wave resonator.

FIG. 4 is an evaluation circuit diagram of a surface acoustic wave resonator.

FIG. 5 is a transmission characteristic diagram of the surface acoustic wave resonator.

FIG. 6 is a perspective view of a surface acoustic wave resonator composite filter.

FIG. 7 is an equivalent circuit diagram of a surface acoustic wave resonator.

FIG. 8 is a frequency characteristic diagram of impedance of a surface acoustic wave resonator.

FIG. 9 is an evaluation circuit diagram of a surface acoustic wave resonator.

FIG. 10 is a pass characteristic diagram of the surface acoustic wave resonator composite filter.

FIG. 11 is a perspective view of an embodiment of the present invention.

FIG. 12 is a sectional view of an embodiment of the present invention.

FIG. 13 is a perspective view of a second embodiment of the present invention.

FIG. 14 is a perspective view of a third embodiment of the present invention.

FIG. 15 is an equivalent circuit diagram of an embodiment of the present invention.

FIG. 16 is a pass characteristic diagram of the surface acoustic wave resonator composite filter.

FIG. 17 is a pass characteristic diagram of the surface acoustic wave resonator composite filter.

[Explanation of reference numerals] 1 ... Piezoelectric substrate, 2 ... Surface acoustic wave resonator, 6 ... Stem,
8 ... fine metal wire, 10 ... via hole.

Claims (3)

[Claims] 1. A surface acoustic wave resonator composite type filter comprising a plurality of surface acoustic wave resonators connected on a piezoelectric substrate, wherein the surface acoustic waves are connected in parallel to a signal input / output path. The electrical connection between at least one surface acoustic wave resonator of the resonator and the common ground potential electrode is performed by a via hole formed on the piezoelectric substrate and a conductive material in which the via hole is embedded. Surface acoustic wave resonator composite type filter. 2. A surface acoustic wave resonator composite type filter in which a plurality of surface acoustic wave resonators provided on a piezoelectric substrate are connected, wherein the surface acoustic wave is connected in parallel to a signal input / output path. A surface acoustic wave resonator composite type filter, characterized in that at least one surface acoustic wave resonator among the resonators and a common ground potential electrode are electrically connected by a conductive paste material. 3. A surface acoustic wave resonator composite filter comprising a plurality of surface acoustic wave resonators connected to each other on a piezoelectric substrate, wherein the surface acoustic waves are connected in parallel to a signal input / output path. A composite surface acoustic wave resonator filter, wherein at least one surface acoustic wave resonator among the resonators and a common ground potential electrode are electrically connected by a ribbon-shaped conductor.