JP2007068211A - Surface acoustic wave filter and communication apparatus employing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface acoustic wave (SAW) filter in which out-of-band attenuation is increased, and which is improved in performance with low loss. <P>SOLUTION: A first multi-electrode SAW filter 2a comprises: a first comb-like electrode configured by a first input electrode 6a and a first output electrode 6b opposite to each other; and first reflectors 5a disposed at both sides of the comb-like electrode, respectively. A second multi-electrode SAW filter 2b comprises: a second comb-like electrode configured by a second input electrode 4a and a second output electrode 4b opposite to each other; and second reflectors 5b disposed at both sides of the comb-like electrode, respectively. In a SAW filter, the first multi-electrode SAW filter 2a and the second multi-electrode SAW filter 2b are provided on the same piezoelectric substrate 1 so that the comb-like electrodes and the reflectors of the multi-electrode SAW filters 2a and 2b are provided along a SAW propagation direction X. In such a SAW filter, the first multi-electrode SAW filter 2a and the second multi-electrode SAW filter are disposed along the SAW propagation direction X. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a surface acoustic wave filter which 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 and a communication device using the same.

  In recent years, communication devices such as mobile phones and cordless phones are rapidly becoming more compact and lighter, and surface acoustic wave filters for processing radio signals are used in such mobile phones. Yes. 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).

  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.

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.
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 output terminals, 5a and 5b are reflectors, 6a and 6b are input electrodes, 7a, 7b is an output electrode, and 8a and 8b are wires.

  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.

  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.

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.
JP-A-6-204781 JP-A-6-104686

  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.

  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.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a surface acoustic wave filter that eliminates the disadvantages of the prior art, has a large out-of-band attenuation, and is excellent in performance with low loss, and a communication device using the same.

In order to achieve the above object, the present invention provides:
A first comb-shaped electrode configured by opposing a first input electrode and a first output electrode, and first reflectors respectively disposed on both sides of the comb-shaped electrode. A multi-electrode surface acoustic wave filter;
A second multi-electrode including a second comb-shaped electrode configured by opposing the second input electrode and the second output electrode, and second reflectors disposed on both sides of the comb-shaped electrode, respectively. An electrode surface acoustic wave filter,
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.

  The first multi-electrode surface acoustic wave filter and the second multi-electrode surface acoustic wave filter are slightly displaced along the surface acoustic wave propagation direction, for example, on a straight line or in a direction perpendicular to the surface acoustic wave propagation direction. It is characterized by being arranged.

  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 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, the insertion loss can be reduced and the out-of-band attenuation can be improved, and a surface acoustic wave filter excellent in performance and a communication device using the same can be provided.

    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.

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.

  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.

  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.

  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.

  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.

  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.

  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).

  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.

  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 inventors that the mutual interference does not change even if it is larger than 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.

  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.

  That is, when 0 <d1 <50λ and 0 <d2 <200λ, excellent characteristics can be exhibited as this type of surface acoustic wave filter.

  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.

  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.

  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.

  In order to solve such a problem, in the first embodiment, as described above, the comb-shaped electrodes are arranged as follows.

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.

  The surface acoustic wave filter according to the present invention is used in communication equipment such as a mobile phone and a cordless phone.

1 is a schematic configuration diagram of a surface acoustic wave filter according to a first embodiment of the present invention. It is a frequency characteristic figure of the surface acoustic wave filter. It is a schematic block diagram of the surface acoustic wave filter which concerns on the 2nd Embodiment of this invention. It is a frequency characteristic figure of the surface acoustic wave filter. It is a schematic block diagram of the conventional surface acoustic wave filter. It is a frequency characteristic figure of the surface acoustic wave filter.

Explanation of symbols

    1: piezoelectric substrate, 2a: first multi-electrode surface acoustic wave filter, 2b: second multi-electrode surface acoustic wave filter, 3a: first input terminal, 3b: second input terminal, 4a: first Output terminal, 4b: second output terminal, 5a: first 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 (3)

A first comb-shaped electrode configured by opposing a first input electrode and a first output electrode, and first reflectors respectively disposed on both sides of the comb-shaped electrode. A multi-electrode surface acoustic wave filter;
A second multi-electrode including a second comb-shaped electrode configured by opposing the second input electrode and the second output electrode, and second reflectors disposed on both sides of the comb-shaped electrode, respectively. An electrode surface acoustic wave filter,
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 surface acoustic wave filter, wherein the first multi-electrode surface acoustic wave filter and the second multi-electrode surface acoustic wave filter are disposed along a surface acoustic wave propagation direction. 2. The elasticity according to claim 1, wherein the first multi-electrode surface acoustic wave filter and the second multi-electrode surface acoustic wave filter are arranged so as to be shifted in a direction orthogonal to the surface acoustic wave propagation direction. Surface wave filter. 3. A communication device using a surface acoustic wave filter, wherein the surface acoustic wave filter is the surface acoustic wave filter according to claim 1 or 2.

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