JPH10261936A - Surface acoustic wave filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a surface acoustic wave filter with a wide band and a large attenuation outside a band whose characteristic is less affected by manufacture tolerance. SOLUTION: Two of 2-port surface acoustic wave resonators 7a, 8a which arranges an input interdigital transducer(IDT) 2 and an output IDT 3 on a piezoelectric substrate 1 opposite to each other and is provided with a grating reflector 6 to the both sides of the IDTs 2, 3 are formed so as to be connected electrically in parallel. Then two of the 2-port surface acoustic wave resonators 7a, 8a are arranged and formed so that one of a highest frequency band resonance point coincides with another of a lowest frequency band resonance point.

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 utilizing the propagation characteristics of surface acoustic waves used in, for example, a high-frequency circuit of a mobile communication device.

[0002]

2. Description of the Related Art FIG. 8 shows a configuration of a conventional surface acoustic wave filter disclosed in, for example, Japanese Patent Application Laid-Open No. 7-58585. In FIG. 8, 1 is a piezoelectric substrate, and 2 is an input interdigital transducer electrode (hereinafter referred to as I) disposed on the piezoelectric substrate along the propagation direction of the surface acoustic wave.
DT), 3 is the output IDT, 4 is the input I
An input terminal to which DT2 is connected, 5 is an output terminal to which output IDT3 is connected, and 6 is a grating reflector provided outside the input and output IDT2,3.

[0003] Reference numerals 7 and 8 denote two-port surface acoustic wave resonators comprising the input and output IDTs 2 and 3 and grating reflectors 6 on both sides thereof. Therefore 1
A pair of two-port surface acoustic wave resonators 7 and 8 are arranged on the piezoelectric substrate 1 and are electrically connected in parallel.

FIG. 9 is a diagram showing the frequency characteristics of the two-port surface acoustic wave resonator and the entire surface acoustic wave filter.
(a) shows the frequency characteristics of the surface acoustic wave resonator 7, (b) shows the frequency characteristics of the surface acoustic wave resonator 8, and (c) shows the frequency characteristics of the entire surface acoustic wave filter.

Next, the operation will be described. As shown in FIGS. 9 (a) and (b), three different longitudinal modes, multiple reflections a and d between input and output IDTs 2, 3; input and output IDTs 2, 3 own internal reflections b and e; And a pair of surface acoustic wave resonators 7 and 8 in which multiple reflections c and f between two grating reflectors 6 occur on the frequency axis,
The resonance points a and e and the resonance points b and f
Are combined, a filter characteristic as shown in FIG. 9C can be obtained as the whole surface acoustic wave filter.

[0006]

In the above-described conventional surface acoustic wave filter, resonance points must be synthesized at two points at the same time, and it is necessary to synthesize resonance points with high accuracy. There has been a problem that it is very susceptible to manufacturing variations.

Further, if one of the two resonance points is shifted, there is a problem that ripple occurs due to frequency characteristics. Furthermore, since the resonance points are combined at two places, it has been difficult to obtain a wide band.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and can reduce the effects of manufacturing variations, minimize the occurrence of ripples in frequency characteristics, and provide a wide-band elastic surface. The aim is to obtain a wave filter.

[0009]

SUMMARY OF THE INVENTION In view of the above objects, a first aspect of the present invention is to provide an input interdigital transducer electrode connected to an input terminal, comprising a piezoelectric substrate and a comb-shaped electrode finger. At least one two-port surface acoustic wave resonator comprising an output interdigital transducer electrode disposed opposite to the input interdigital transducer electrode connected to a terminal, and grating reflectors provided on both sides of the output interdigital transducer electrode.
A first resonator region including the first resonator region and a second resonator region including the same number of the two-port surface acoustic wave resonators as the first resonator region are electrically connected in parallel to each other on the piezoelectric substrate;
And a two-port surface acoustic wave resonator portion formed such that one of the highest frequency resonance points coincides with the other lowest frequency resonance point. is there.

According to a second aspect of the present invention, the first and second resonator regions of the two-port surface acoustic wave resonator section each include two two-port surface acoustic wave resonators, and each two-port surface acoustic wave resonator 2. The surface acoustic wave filter according to claim 1, wherein the resonators are electrically connected in parallel to each other.

According to a third aspect of the present invention, the input interdigital transducer electrode and the output interdigital transducer electrode of each of the two-port surface acoustic wave resonators are each composed of an apodized electrode. The surface acoustic wave filter according to the above.

According to a fourth aspect of the present invention, the input interdigital transducer electrode and the output interdigital transducer electrode of each of the two-port surface acoustic wave resonators are each composed of a thinned-out electrode. The surface acoustic wave filter according to the above.

According to a fifth aspect of the present invention, the input interdigital transducer electrode and the output interdigital transducer electrode of each of the above-described two-port surface acoustic wave resonators are respectively connected to a dummy electrode connected to the ground side. The surface acoustic wave filter according to any one of claims 1 to 4, further comprising an electrode.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. Embodiment 1 FIG. FIG. 1 is a diagram showing a configuration of a surface acoustic wave filter according to one embodiment of the present invention. In FIG. 1, 1 is a piezoelectric substrate, 2 is an input IDT arranged on the piezoelectric substrate along the propagation direction of surface acoustic waves, 3 is an output IDT, 4 is an input terminal to which the input IDT 2 is connected, and 5 is an input terminal.
Is an output terminal to which the output IDT 3 is connected, and 6 is a grating reflector provided outside the input and output IDTs 2 and 3.

Reference numerals 7a and 8a denote two-port surface acoustic wave resonators comprising the input and output IDTs 2 and 3 and the grating reflectors 6 on both sides thereof. Therefore, a pair of two-port surface acoustic wave resonators 7a and 8a are arranged on the piezoelectric substrate 1 and are electrically connected in parallel. The two-port surface acoustic wave resonator 7a forms a first resonator region formed on the piezoelectric substrate 1, and similarly, the two-port surface acoustic wave resonator 8a forms a second resonator region.
a and 8a constitute a two-port surface acoustic wave resonator.

FIG. 2 is a diagram showing the frequency characteristics of the two-port surface acoustic wave resonator and the entire surface acoustic wave filter.
(a) shows the surface acoustic wave resonator 7a, (b) shows the surface acoustic wave resonator 8b, and (c) shows the frequency characteristic of the entire surface acoustic wave filter.

Next, the operation will be described. FIG. 2 (a)
As shown in (b) and (b), three different longitudinal modes are generated in the characteristics of the resonators 7a and 8a. That is, the resonance points a and d due to the multiple reflection between the input and output IDTs 2 and 3, the resonance points b and e due to the internal reflection of the input and output IDTs 2 and 3, and the resonance point c due to the multiple reflection between the grating reflectors 6. f.

In this embodiment, the surface acoustic wave resonators 7a and 8a on the piezoelectric substrate 1 are constructed and arranged such that their resonator characteristics are shifted to a lower side and a higher side on the frequency axis. One resonance point a on the one highest band side and one resonance point f on the other lowest band side are combined so as to coincide with each other.
A filter characteristic as shown in FIG. When this is impedance-matched, as shown in FIG. 3, the influence of manufacturing variations can be reduced as compared with the conventional surface acoustic wave filter.
A broadband surface acoustic wave filter is obtained.

Embodiment 2 FIG. 4 is a diagram showing a configuration of a surface acoustic wave filter according to another embodiment of the present invention. In this embodiment, two 2-port surface acoustic wave resonators 7a and 8a are connected in parallel, respectively, and a total of four surface acoustic wave resonators 7a and 8a are connected in parallel, and as shown in FIG. By combining a and f, the same effect as in the first embodiment is obtained. In addition, 2
Two two-port surface acoustic wave resonators 7a form a first resonator region formed on the piezoelectric substrate 1, and similarly, two two-port surface acoustic wave resonators 8a form a second resonator region.
The two resonators 7a and 8a constitute a two-port surface acoustic wave resonator.

Further, in this embodiment, since four surface acoustic wave resonators are connected in parallel, the terminal impedance is lower than that of the surface acoustic wave filter of the first embodiment comprising two surface acoustic wave resonators. The surface acoustic wave filter can be reduced to about half, and the influence on the frequency characteristics due to the variation of the matching element is small when performing the impedance matching.

Embodiment 3 FIG. 5 is a diagram showing a configuration of a surface acoustic wave filter according to still another embodiment of the present invention. In this embodiment, the surface acoustic wave resonator 7
The input IDT 2a and output IDT 3a of a and 8a are apodized electrodes, and the resonance points a and f of FIGS. 2A and 2B are combined to obtain the same effect as in the first embodiment. .

In this embodiment, the input I
Since the DT2a and the output IDT3a are apodized electrodes, it is possible to suppress the spurious generated due to the influence of the transverse mode of the resonator on the high frequency side near the pass band.
A highly steep surface acoustic wave filter is obtained.

Embodiment 4 FIG. 6 is a diagram showing a configuration of a surface acoustic wave filter according to still another embodiment of the present invention. In this embodiment, the surface acoustic wave resonator 7
By using the input IDT 2b and output IDT 3b of a and 8a as thinning-out electrodes and combining the resonance points a and f of FIGS. 2A and 2B, the same effect as in the first embodiment is obtained. .

In this embodiment, the input I
By using the DT2b and the output IDT3b as thinned-out electrodes, a surface acoustic wave filter having a larger attenuation outside the band than the characteristics of the surface acoustic wave filter of the first embodiment can be obtained.

Embodiment 5 FIG. FIG. 7 is a diagram showing a configuration of a surface acoustic wave filter according to still another embodiment of the present invention. In this embodiment, the surface acoustic wave resonator 7
a, a dummy electrode 9 is provided between the input IDT 2 c and the output IDT 3 c of the output IDT 3 c, respectively.
The ground is connected to the ground side of the output IDT 3c.
By combining the resonance points a and f of (a) and (b), the same effect as in the first embodiment is obtained.

In this embodiment, the input I
Dummy electrodes 9 are provided between the DT2c and the output IDT3c, respectively, and these are connected to the input IDT2c and the output IDT.
Since each is grounded to the ground side of T3c, the input ID
The direct wave that passes through the output IDT 3c directly from T2c as an electric signal can be grounded by the dummy electrode 9, and the out-of-band attenuation due to the leakage of the direct wave can be prevented from deteriorating. Is obtained.

[0027]

As described above, according to the first aspect of the present invention, the input interdigital transducer electrode connected to the input terminal and the output terminal connected to the input terminal are formed by combining the piezoelectric substrate and the comb-shaped electrode fingers. A first resonator region including at least one two-port surface acoustic wave resonator including an output interdigital transducer electrode disposed opposite to the input interdigital transducer electrode, and grating reflectors provided on both sides thereof; A second resonator region including the same number of the two-port surface acoustic wave resonators as one resonator region is electrically connected in parallel to each other on the piezoelectric substrate, and one of the highest-band resonance points and the other is connected to the other. A surface acoustic wave filter having a two-port surface acoustic wave resonator formed so as to coincide with a low-frequency resonance point Since the, possible to reduce the influence of manufacturing variations, the frequency characteristics, the effect of such that can provide broadband surface acoustic wave filter is obtained with the occurrence of ripples can be minimized.

In the second aspect of the present invention, the first and second resonator regions of the two-port surface acoustic wave resonator section each include two two-port surface acoustic wave resonators, and each two-port surface acoustic wave resonator Since the resonators are electrically connected in parallel with each other, the terminal impedance can be reduced to about half that of the surface acoustic wave filter of the first invention, and the variation of the matching element when performing impedance matching. Thus, an effect such as providing a surface acoustic wave filter having a small influence on the frequency characteristics due to the above can be obtained.

According to the third aspect of the present invention, the input interdigital transducer electrode and the output interdigital transducer electrode of each two-port surface acoustic wave resonator are formed as apodized electrodes, so that they are located on the high frequency side near the pass band. The spurious generated due to the influence of the transverse mode of the resonator can be suppressed, and effects such as providing a steep surface acoustic wave filter can be obtained.

According to the fourth aspect of the present invention, the input interdigital transducer electrode and the output interdigital transducer electrode of each of the two-port surface acoustic wave resonators are thinned-out electrodes, so that the surface acoustic wave having a large out-of-band attenuation is provided. The effect of providing a wave filter can be obtained.

According to the fifth aspect of the present invention, the input interdigital transducer electrode and the output interdigital transducer electrode of each of the two-port surface acoustic wave resonators are provided between the dummy electrode and the dummy electrode connected to the ground. Is provided, it is possible to prevent the deterioration of the out-of-band attenuation due to the influence of the leakage of the direct wave, and to obtain an effect such as providing a surface acoustic wave filter having a large out-of-band attenuation.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a surface acoustic wave filter according to an embodiment of the present invention.

FIG. 2 is a diagram showing frequency characteristics of a two-port surface acoustic wave resonator of the surface acoustic wave filter of the present invention and the entire surface acoustic wave filter.

FIG. 3 is a diagram showing the frequency characteristics of the impedance-matched surface acoustic wave filter of the present invention.

FIG. 4 is a diagram showing a configuration of a surface acoustic wave filter according to another embodiment of the present invention.

FIG. 5 is a diagram showing a configuration of a surface acoustic wave filter according to still another embodiment of the present invention.

FIG. 6 is a diagram showing a configuration of a surface acoustic wave filter according to still another embodiment of the present invention.

FIG. 7 is a diagram showing a configuration of a surface acoustic wave filter according to still another embodiment of the present invention.

FIG. 8 is a diagram showing a configuration of a conventional surface acoustic wave filter.

FIG. 9 is a diagram illustrating frequency characteristics of a two-port surface acoustic wave resonator of a conventional surface acoustic wave filter and the entire surface acoustic wave filter.

[Explanation of symbols]

Reference Signs List 1 piezoelectric substrate, 2, 2c input interdigital transducer electrode (input IDT), 2a apodized input IDT, 2b thinned input IDT, 3, 3c
Output interdigital transducer electrode (output I
DT), 3a apodized output IDT, 3b thinned output IDT, 4 input terminals, 5 output terminals, 6 grating reflectors, 7a, 8a 2-port surface acoustic wave resonator, 9 dummy electrodes.

Claims (5)

[Claims] 1. An interdigital transducer electrode comprising a combination of a piezoelectric substrate and a comb-shaped electrode finger. The interdigital transducer electrode connected to an input terminal and the output interdigital transducer arranged opposite to the input interdigital transducer electrode connected to an output terminal. A first resonator region including at least one two-port surface acoustic wave resonator including a transducer electrode and grating reflectors provided on both sides thereof; and the same number of the two-port surface acoustic waves as the first resonator region A second resonator region including the resonator,
A two-port surface acoustic wave resonator portion electrically connected in parallel with each other on the piezoelectric substrate, and formed such that one of the highest resonance points coincides with the other of the lowest resonance points; A surface acoustic wave filter comprising: 2. A first part of the two-port surface acoustic wave resonator.
2. The device according to claim 1, wherein each of the first and second resonator regions includes two two-port surface acoustic wave resonators, and each of the two-port surface acoustic wave resonators is electrically connected to each other in parallel. Surface acoustic wave filter. 3. The surface acoustic wave filter according to claim 1, wherein the input interdigital transducer electrode and the output interdigital transducer electrode of each of the two-port surface acoustic wave resonators are each composed of an apodized electrode. . 4. The surface acoustic wave filter according to claim 1, wherein the input interdigital transducer electrode and the output interdigital transducer electrode of each of the two-port surface acoustic wave resonators are thinned electrodes. . 5. The method according to claim 1, wherein the input interdigital transducer electrode and the output interdigital transducer electrode of each of the two-port surface acoustic wave resonators are provided with a dummy electrode connected to the ground side between them. The surface acoustic wave filter according to any one of claims 1 to 4, wherein: