JP4454703B2 - Surface acoustic wave filter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a surface acoustic wave filter that is a device using surface acoustic waves, and more particularly to a surface acoustic wave filter in which a plurality of multi-electrode surface acoustic wave filters are arranged on the same piezoelectric substrate.
[0002]
[Prior art]
In recent years, cellular phones, cordless phones, and the like are rapidly becoming more compact and lighter, and surface acoustic wave filters for processing radio signals are used in such cellular phones. This surface acoustic wave filter has a large number of inter-digital transducers (IDTs) arranged along the surface wave propagation direction to reduce the insertion loss from the input to the output, and reflectors on both sides thereof. A formed surface acoustic wave filter is known (see, for example, JP-A-6-204781).
[0003]
Conventionally, one surface acoustic wave filter is usually used in one package. In a so-called dual type surface acoustic wave filter that requires two different functions, a method of putting two piezoelectric substrates having surface acoustic wave filters in one package is also used, but productivity is not good.
[0004]
A method of forming two surface acoustic wave filters on one piezoelectric substrate has been proposed (see, for example, Japanese Patent Laid-Open No. 6-104686). However, since there are many wires, the insertion loss increases due to the influence of electromagnetic coupling, and the out-of-band attenuation becomes small, so there is a problem in the multi-electrode structure with many wires.
FIG. 5 shows an example of a conventional multi-electrode surface acoustic wave filter. In the figure, 1 is a piezoelectric substrate, 2a and 2b are multi-electrode surface acoustic wave filters, 3a and 3b are input terminals, 4a and 4b are input terminals, 5a and 5b are reflectors, 6a and 6b are input electrodes, 7a, 7b is an output electrode, and 8a and 8b are wires.
[0005]
As shown in the figure, in the first multi-electrode surface acoustic wave filter 2a, the input electrode 6a constituting the input IDT and the output electrode 7a constituting the output IDT are opposed to each other to form comb-like electrodes 6a and 7a. Reflectors 5a and 5a are arranged on both sides of the comb-shaped electrodes 6a and 7a. Similarly, in the second multi-electrode surface acoustic wave filter 2b, the input electrode 6b and the output electrode 7b face each other to form comb-shaped electrodes 6b and 7b, and reflectors 5b and 6b are formed on both sides of the comb-shaped electrodes 6b and 7b. 5b is arranged.
[0006]
The reflector 5a-comb-like electrodes 6a, 7a-reflector 5a of the surface acoustic wave filter 2a and the reflector 5b-comb-like electrodes 6b, 7b-reflector 5b of the surface acoustic wave filter 2b are both elastic surfaces. The surface acoustic wave filters 2 a and 2 b are arranged along a straight line along the wave propagation direction X, and are arranged in a direction orthogonal to the surface acoustic wave propagation direction X.
[0007]
All the wires 8a of the surface acoustic wave filter 2a are wired on the input terminal side except those connected to the output terminal 4a, and all the wires 8b of the surface acoustic wave filter 2b are output except for those connected to the input terminal 3b. Wired on the terminal side.
[0008]
[Problems to be solved by the invention]
FIG. 6 shows frequency characteristics of the surface acoustic wave filter configured as described above. As is apparent from the figure, the surface acoustic wave filter having the above-described configuration causes an increase in insertion loss Y and a deterioration in out-of-band attenuation.
[0009]
This is probably because the ground wires of the respective surface acoustic wave filters are concentrated on one side and the direct wave increases. Further, since the lengths of the wires 8a and 8b connected to the input / output terminals 3a, 3b, 4a and 4b are remarkably different, the insertion loss is increased. As described above, the conventional surface acoustic wave filter causes electromagnetic coupling by the wire to each other and interference of the surface acoustic wave, and a surface acoustic wave filter having excellent performance has not been obtained.
[0010]
An object of the present invention is to provide a surface acoustic wave filter that eliminates the drawbacks of the prior art, has a large out-of-band attenuation, and is excellent in performance with low loss.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides:
A first comb-shaped electrode configured such that the first input electrode and the first output electrode are opposed to each other; a first substrate end side reflector disposed on both sides of the first comb-shaped electrode ; A first multi-electrode surface acoustic wave filter comprising a first substrate center side reflector ;
A second comb-shaped electrode configured such that the second input electrode and the second output electrode are opposed to each other; a second substrate end side reflector disposed on both sides of the second comb-shaped electrode ; A second multi-electrode surface acoustic wave filter provided with a second substrate center side reflector ,
The object is a surface acoustic wave filter in which comb-shaped electrodes and reflectors of each multi-electrode surface acoustic wave filter are provided along the surface acoustic wave propagation direction on the same piezoelectric substrate.
[0012]
The first multi-electrode surface acoustic wave filter and the second multi-electrode surface acoustic wave filter are arranged along the surface acoustic wave propagation direction at a substantially central portion in a direction orthogonal to the surface acoustic wave propagation direction on the piezoelectric substrate. By arranging them side by side, the first substrate center-side reflector of the first multi-electrode surface acoustic wave filter and the second substrate center-side reflector of the second multi-electrode surface acoustic wave filter are adjacent to each other. Lined up like
When the gap between the first substrate center side reflector and the second substrate center side reflector in the direction orthogonal to the surface acoustic wave propagation direction is d1, and the repetition period of the comb-shaped electrode is 1 / 2λ Have the following relationship :
0 <d1 <50λ (where λ is the wavelength of the frequency band to be used)
And from the end surface facing the first substrate end side reflector of the first comb-shaped electrode to the end surface facing the second substrate end side reflector of the second comb-shaped electrode The arrangement interval is d2, and has the following relationship:
0 <d2 <200λ
The ground conductor wire extending from the input / output electrode of the first multi-electrode surface acoustic wave filter and the ground conductor wire extending from the input / output electrode of the second multi-electrode surface acoustic wave filter are dispersed to each end of the piezoelectric substrate. It is characterized by extending to the side .
[0013]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, as described above, by arranging the first multi-electrode surface acoustic wave filter and the second multi-electrode surface acoustic wave filter along the surface acoustic wave propagation direction, interference with each other's characteristics is suppressed. The lengths of the input / output wires of each surface acoustic wave filter are substantially uniform, and optimum impedance matching can be achieved. Therefore, it is possible to reduce the insertion loss and improve the out-of-band attenuation, and provide a surface acoustic wave filter excellent in performance.
[0014]
Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of a surface acoustic wave filter according to the first embodiment, and FIG. 2 is a frequency characteristic diagram thereof.
[0015]
As shown in FIG. 1, a first multi-electrode surface acoustic wave filter 2 a and a second multi-electrode surface acoustic wave filter 2 b having a function of using two different frequency bands are arranged on one piezoelectric substrate 1. ing.
As the piezoelectric substrate 1, a piezoelectric substrate made of lithium niobate with 64 ° rotation Y-axis cut X-axis propagation was used. The center frequency of the first surface acoustic wave filter 2a is 818 MHz, the center frequency of the second surface acoustic wave filter 2b is 872.5 MHz, and the wavelength λ of the surface acoustic wave filter 2a is 5.5 μm.
[0016]
In this embodiment, the lower center frequency is 818 MHz and the higher center frequency is 872.5 MHz, but the lower frequency can be appropriately selected from the band of 810 to 826 MHz and the higher frequency is 870 to 885 MHz. It is.
[0017]
As shown in the figure, the first surface acoustic wave filter 2a and the second surface acoustic wave filter 2b are arranged along the surface acoustic wave propagation direction X unlike the conventional example shown in FIG. It is slightly shifted in the direction orthogonal to X. A specific deviation amount will be described later.
[0018]
In the first surface acoustic wave filter 2a, the five input electrodes 6a constituting the input IDT and the four output electrodes 7a constituting the output IDT face each other, and the comb-like electrodes 6a having four repetitions are provided. 7a is formed, and reflectors 5a and 5a are arranged on both sides of the comb-shaped electrodes 6a and 7a, respectively.
[0019]
Similarly, in the second multi-electrode surface acoustic wave filter 2b, the five input electrodes 6b constituting the input IDT and the four output electrodes 7b constituting the output IDT are opposed to each other, and the number of repetitions is four. Electrode 6b, 7b is formed, and reflectors 5b, 5b are arranged on both sides of the comb-shaped electrode 6b, 7b, respectively.
[0020]
Reflector 5a-comb-like electrodes 6a, 7a-reflector 5a of the first multi-electrode surface acoustic wave filter 2a and reflector 5b-comb-like electrode 6b of the second multi-electrode surface acoustic wave filter 2b Both 7b-reflectors 5b are arranged on a straight line along the surface acoustic wave propagation direction X.
[0021]
The distance d1 between the comb-shaped electrodes 6a and 7a and the comb-shaped electrodes 6b and 7b is 82.5 μm (15λ), and the first surface acoustic wave filter 2a and the second surface acoustic wave filter 2b The distance d2 between the adjacent reflectors 5a and 5b was 137.5 μm (25λ).
[0022]
With such an arrangement, there is no interference due to reflection by the IDT on the other side, and the lengths of the input / output wires 8a and 8b are substantially equal. Therefore, as shown in FIG. The frequency characteristic of the out-of-band attenuation is obtained.
[0023]
In the present embodiment, the distance d1 is set to 15λ in order to suppress interference between the comb-shaped electrodes of the two surface acoustic wave filters (where λ is a wavelength using the lower frequency band). This interference is suppressed to a sufficiently negligible level when d1 is set to a specific distance or more, and it has been found by experiments of the present inventor that the mutual interference does not change even if it exceeds 50λ. On the other hand, if d1 is too large, there is a problem that impedance matching cannot be achieved because the lengths of the input and output wires are significantly different.
[0024]
On the other hand, the distance d2 between the two surface acoustic wave filters can be reduced as long as the wires do not intersect, and the smaller one has the advantage that the length of the chip can be shortened. When the number of reflectors 5a and 5b is small, d2 can be set to about zero. In this embodiment, since the structure is repeated four times, 31 reflectors 5a and 19 reflectors 5b are provided. When the number of reflectors is reduced and the number of reflectors is about 200, this can be realized by setting d2 to about 200λ.
[0025]
That is, by setting 0 <d1 <50λ and 0 <d2 <200λ, the first multi-electrode surface acoustic wave filter and the second multi-electrode surface acoustic wave filter are aligned along the surface acoustic wave propagation direction. It is possible to exhibit excellent characteristics as a surface acoustic wave filter arranged so as to be shifted in a direction orthogonal to the surface acoustic wave propagation direction .
[0026]
FIG. 3 is a schematic configuration diagram of the surface acoustic wave filter according to the second embodiment of the present invention. The difference from the first embodiment is that the first surface acoustic wave filter 2a and the second elastic wave filter are the same. The surface wave filter 2b is arranged on a substantially straight line along the surface acoustic wave propagation direction X in the substantially central portion of the piezoelectric substrate 1.
[0027]
As shown in FIG. 4, the surface acoustic wave filter has an out-of-band attenuation Y significantly reduced as compared with the conventional one shown in FIG. This is because the direct wave is reduced because the grounding wires are arranged separately on both sides of the input and output. Further, the length of the wires connected to the input / output terminals can be made substantially the same, and the optimum impedance matching can be obtained, so that the insertion loss is reduced.
[0028]
It has been found that the surface acoustic wave filter according to the second embodiment has a new problem that the ripple in the band increases. This is because two surface acoustic wave filters are arranged on the same straight line. In order to reduce leakage loss, reflectors are provided on both sides of the comb-shaped electrode. However, the wave leaking through the reflector has a slight effect on the other surface acoustic wave filter. It is. Furthermore, at the frequency at which one surface acoustic wave filter operates, the comb-shaped electrode of the other surface acoustic wave filter operates as a reflector.
[0029]
In order to solve such a problem, in the first embodiment, as described above, the comb-shaped electrodes are arranged as follows.
[0030]
0 <d1 <50λ and 0 <d2 <200λ
If it is outside this range, the poor isolation such as wire or the wave leaking from one multi-electrode surface acoustic wave filter may be reflected and influenced by the IDT of the other multi-electrode surface acoustic wave filter. is there.
[0031]
【The invention's effect】
The present invention has a configuration as described above, and can provide a surface acoustic wave filter having a large out-of-band attenuation and low loss and excellent performance.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a surface acoustic wave filter according to a first embodiment of the present invention.
FIG. 2 is a frequency characteristic diagram of the surface acoustic wave filter.
FIG. 3 is a schematic configuration diagram of a surface acoustic wave filter according to a second embodiment of the present invention.
FIG. 4 is a frequency characteristic diagram of the surface acoustic wave filter.
FIG. 5 is a schematic configuration diagram of a conventional surface acoustic wave filter.
FIG. 6 is a frequency characteristic diagram of the surface acoustic wave filter.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Piezoelectric substrate 2a 1st multi-electrode surface acoustic wave filter 2b 2nd multi-electrode surface acoustic wave filter 3a 1st input terminal 3b 2nd input terminal 4a 1st output terminal 4b 2nd output terminal 5a 1st Reflector 5b second reflector 6a first input electrode 6b second input electrode 7a first output electrode 7b second output electrode 8a wire 8b wire X surface acoustic wave propagation direction

Claims (1)

A first comb-shaped electrode configured such that the first input electrode and the first output electrode are opposed to each other; a first substrate end side reflector disposed on both sides of the first comb-shaped electrode ; A first multi-electrode surface acoustic wave filter comprising a first substrate center side reflector ;
A second comb-shaped electrode configured such that the second input electrode and the second output electrode are opposed to each other; a second substrate end side reflector disposed on both sides of the second comb-shaped electrode ; A second multi-electrode surface acoustic wave filter provided with a second substrate center side reflector ,
In the surface acoustic wave filter in which the comb-shaped electrode and the reflector of each multi-electrode surface acoustic wave filter are provided along the surface acoustic wave propagation direction on the same piezoelectric substrate,
The first multi-electrode surface acoustic wave filter and the second multi-electrode surface acoustic wave filter are arranged along the surface acoustic wave propagation direction at a substantially central portion in a direction orthogonal to the surface acoustic wave propagation direction on the piezoelectric substrate. The first substrate center side reflector of the first multi-electrode surface acoustic wave filter and the second substrate center side reflector of the second multi-electrode surface acoustic wave filter are adjacent to each other. Lined up like
When the gap between the first substrate center side reflector and the second substrate center side reflector in the direction orthogonal to the surface acoustic wave propagation direction is d1, and the repetition period of the comb-shaped electrode is 1 / 2λ Have the following relationship :
0 <d1 <50λ (where λ is the wavelength of the frequency band to be used)
And from the end surface facing the first substrate end side reflector of the first comb-shaped electrode to the end surface facing the second substrate end side reflector of the second comb-shaped electrode The arrangement interval is d2, and has the following relationship:
0 <d2 <200λ
The ground conductor wire extending from the input / output electrode of the first multi-electrode surface acoustic wave filter and the ground conductor wire extending from the input / output electrode of the second multi-electrode surface acoustic wave filter are dispersed to each end of the piezoelectric substrate. surface acoustic wave filter characterized in that it extends to the side.

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