JP2000278075A - Surface acoustic wave filter device and unidirectional converter used therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To satisfy various characteristics while practically using a unidirectional characteristic by connecting a first electrode finger to a first electrode, connecting second and fourth electrode fingers, constituting a shorting-type floating electrode and connecting a third electrode finger to a second electrode so as to form a couple. SOLUTION: A first electrode (positive electrode) 2 and a second electrode (negative electrode) 3 are installed. In a part of a couple A, first to fourth electrode fingers 4-7 whose width of the transmitting direction of a surface acoustic wave is λ/12 are connected to the positive electrode 2. The center-to-center distance of the first and second electrode fingers 4 and 5 is set to be λ/6, the intermediate distance of the first and third electrode fingers 4 and 6 to be λ/2 and the center-to-center distance of the first and forth electrode fingers 4 and 7 to be 2λ/3. In the other couple B, a first electrode finger 8 is connected to the positive electrode 2, a second electrode finger 9 and a fourth electrode finger 10 are mutually connected, a short-circuiting type floating electrode 11 is constituted and a third electrode 12 is connected to the negative electrode 3. The center-to-center distance of the first and second electrode fingers 8 and 9 is set to be λ/6, the center-to-center distance of the first and third electrode fingers 8 and 12 to be λ/2 and the center-to-center distance of the first and fourth electrode fingers 8 and 10 to be 2λ/3.

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 device having a one-way converter having a thinned-out electrode structure, and a one-way converter suitable for the device.

[0002]

2. Description of the Related Art Conventionally, each electrode finger of a short-circuit type floating electrode is moved from an intermediate position between an electrode finger of an adjacent positive electrode and an electrode finger of a negative electrode in a propagation direction of a surface acoustic wave or in a direction opposite thereto. A surface acoustic wave filter device having a one-way transducer positioned with a λ / 12 deviation is disclosed in, for example, Japanese Patent Application Laid-Open No.
No. 6,009,045.

In a surface acoustic wave filter device having such a unidirectional converter, the insertion loss is enhanced by appropriately utilizing the excitation effect and the reflection effect of the electrode finger by enhancing the unidirectionality based on the asymmetry of the electrode. It can be greatly reduced.

[0004]

In recent years, there has been a demand for a surface acoustic wave filter device that satisfies various characteristics (for example, sets a large out-of-band attenuation characteristic) while making use of the unidirectional characteristics.

An object of the present invention is to provide a surface acoustic wave filter device which satisfies various characteristics while making full use of the one-way characteristics.

Another object of the present invention is to provide a unidirectional converter used in a surface acoustic wave filter device to satisfy various characteristics while making full use of the unidirectional characteristics.

[0007]

According to a first aspect of the present invention, there is provided a unidirectional transducer for a surface acoustic wave filter device, wherein the electromechanical coupling coefficient is 0.1 to 0.1.
A 1.5% piezoelectric substrate, a first electrode formed on the piezoelectric substrate, and a second electrode formed on the piezoelectric substrate so as to face the first electrode; Is the propagation wavelength of the basic surface acoustic wave, the width of the surface acoustic wave in the propagation direction is approximately λ / 12 between the first electrode and the second electrode.
And the center-to-center distance between the first electrode finger and the first electrode finger is λ /
6 is approximately λ / 12 in the propagation direction of the surface acoustic wave.
The center distance between the second electrode finger and the first electrode finger is λ /
2 has a width of approximately λ / 12 in the propagation direction of the surface acoustic wave.
And the fourth electrode having a distance of 2λ / 3 between the third electrode finger and the first electrode and having a width of approximately λ / 12 in the propagation direction of the surface acoustic wave.
The electrode fingers are periodically formed at a pitch of λ, and some pairs are
Each of the first to fourth electrode fingers is a pair connected to the first electrode, and the other pair is a pair where the first electrode finger is connected to the first electrode and the second electrode finger and the fourth electrode finger are connected. Are connected to each other to form a short-circuit type floating electrode, and the third electrode finger is connected to the second electrode to form a pair.

The one-way converter according to the first aspect of the present invention is used as an input converter or an output converter of a surface acoustic wave filter device. Here, when such a one-way converter is used for the input-side converter, that is, the first converter is used.
Consider a case where the four to four electrode fingers are sequentially formed in the propagation direction of the surface acoustic wave. One of the first electrode and the second electrode is a positive electrode, and the other is a negative electrode. For each of the other pairs, since the short-circuit type floating electrode is arranged to force the potential at that position to zero, the potential distribution is forcibly changed, and the excitation center is changed. As a result, considering the case where the excitation wave excites in the direction of the output converter,
The direction of the vector sum of the reflected waves of each electrode finger matches the direction of the excitation wave. On the other hand, considering the case where the excitation wave excites in the reverse direction of the output-side converter, the direction of the vector sum of the reflected waves of each electrode finger is exactly opposite to the direction of the excitation wave, and these directions cancel each other. Therefore, in the other pairs, the excitation wave and the reflected wave propagate only in the direction of the output-side converter.

On the other hand, no excitation wave is generated in each of some of the pairs because the first to fourth electrode fingers are all connected to the first electrode. In this case, the excitation wave generated in the other pair upstream and the reflected wave generated in the upstream pair propagate to some pairs, and only the reflected waves of the first to fourth electrode fingers are generated. Since the direction of the vector sum of these reflected waves is the same as the direction of the excitation waves generated in the other pairs upstream, the reflected waves propagate only in the direction of the output-side converter even in some pairs. In addition, with a thinning electrode structure in which the first to fourth electrode fingers are connected to only the first electrode for some pairs,
Since the electrode finger width of each pair is the same, the propagation speed of the surface acoustic wave propagating through some of the pairs is the same as the propagation speed of the surface acoustic wave propagating through the other pairs. The properties of are not adversely affected.

As described above, some of the pairs have the first to fourth
By connecting the electrode finger only to the first electrode, it is possible to perform thinning weighting that satisfies various characteristics while making full use of the unidirectional characteristics. Note that the same operation and effect can be obtained even when such a one-way converter is used as the output-side converter.

As the piezoelectric substrate of a surface acoustic wave filter device using such a one-way converter as an input converter or an output converter, a lithium niobate substrate (LiNbO ₃ ), a quartz substrate, Lithium tantalate substrate (LiTaO ₃ ), lithium borate substrate (Li ₂ B ₄ O)
₇ ), a langasite substrate (La ₃ Ga ₅ SiO ₁₄ ) or the like is used. Among these substrates, the lithium niobate substrate has a relatively large electromechanical coupling coefficient (K ² ) of 5.5%, and thus has an advantage that good conversion characteristics can be obtained. However, it has been used only as a filter for a wide band because there is a disadvantage in the temperature characteristic, that is, there is an inconvenience that a change in a bandwidth with respect to a temperature change becomes large. Because of its structure, the resonance-type filter is D. T. However, a major problem was strongly pointed out.
On the other hand, the surface acoustic wave filter device having the floating electrode type converter effectively utilizes the asymmetric structure of the electrodes, so that the insertion loss and the G.I. D. T. (Group De
(Layer Time) can be greatly reduced.
Therefore, if an asymmetric internal reflection electrode structure is applied to a piezoelectric substrate having excellent temperature characteristics, G.I. D. T. In addition, it is possible to realize a surface acoustic wave filter device which is excellent in insertion loss and in which a change in a normal band with respect to a temperature change is extremely small.

In view of such circumstances, according to the surface acoustic wave filter device of the present invention, the temperature characteristic with respect to frequency is extremely small, and the electromechanical coupling coefficient is one third to one digit smaller than that of the lithium niobate substrate. In addition, a piezoelectric substrate having a reflection coefficient by the electrode finger having a positive reflection coefficient with respect to the floating electrode is used. Since the frequency variation of these substrates with respect to a temperature change is very small, if any of these substrates is used as the piezoelectric substrate, the variation of the pass frequency band with respect to the temperature characteristics can be maintained in a minute range. However, if an existing converter is formed as it is on a substrate having a small electromechanical coupling coefficient, a surface acoustic wave filter device having good characteristics cannot be realized from the viewpoint of insertion loss.

As a result of a detailed study of the insertion loss in a substrate having a small electromechanical coupling coefficient,
It was found that the sign of the reflection coefficient of the floating electrode greatly affected the insertion loss. In the case of such a substrate, when a short-circuit type floating electrode is used, the center of excitation of the electrode finger shifts, and the phase of the excitation wave matches the phase of the reflected wave. Further, the short-circuit type floating electrode has a larger reflection coefficient than the open type floating electrode. Therefore, it is preferable to use a short-circuit type floating electrode as a floating electrode for pitches other than the above-mentioned partial pitch. With this configuration,
Even if a substrate having a small electromechanical coupling coefficient is used, the insertion loss can be suppressed to an extremely small range, and as a result, a broadband surface acoustic wave filter device having excellent temperature characteristics and low loss can be realized.

According to a second aspect of the present invention, in the unidirectional converter, the piezoelectric substrate is a quartz substrate, a lithium tantalate substrate, a lithium borate substrate, or a langasite substrate. .

In the present invention, the electromechanical coupling coefficient is 0.1 to
As a 1.5% piezoelectric substrate, the electromechanical coupling coefficient is 0.1%.
1 to 1.5% quartz substrate (0.14%), lithium tantalate substrate (0.64%), lithium borate substrate (1.0%) or langasite substrate (0.3 to 0.4%)
%).

According to a third aspect of the present invention, there is provided a surface acoustic wave filter device having a piezoelectric substrate having an electromechanical coupling coefficient of 0.1 to 1.5%, and an electric signal formed on the piezoelectric substrate. An input converter that is externally input and converts this electric signal into a surface acoustic wave, and a surface acoustic wave formed on the piezoelectric substrate and excited by the input converter is converted into an electric signal. An output-side converter that outputs an electric signal to the outside, and the input-side converter and the output-side converter, respectively.
A first electrode formed on the piezoelectric substrate and a second electrode formed on the piezoelectric substrate to face the first electrode;
A first electrode finger having a width in the propagation direction of the surface acoustic wave of approximately λ / 12 between the first electrode and the second electrode, where λ is the propagation wavelength of the basic surface acoustic wave. And this first
A second electrode finger having a center-to-center distance of λ / 6 from the electrode finger and having a width in the propagation direction of the surface acoustic wave of approximately λ / 12;
A third electrode finger whose center-to-center distance from the electrode finger is λ / 2 and whose width in the propagation direction of the surface acoustic wave is approximately λ / 12;
A fourth electrode finger having a width of approximately λ / 12 in the propagation direction of the surface acoustic wave located at a distance of 2λ / 3 from the electrode is periodically formed at a pitch of λ, and a part of the pair is formed of the first electrode finger. To the four electrode fingers are connected to the first electrode, the other pairs are connected to the first electrode finger and the first electrode, and the second electrode finger and the fourth electrode finger are connected to each other. And a short-circuit type floating electrode is formed by connecting the third electrode finger to the second electrode.

In such a surface acoustic wave filter device,
The same operation and effect as the surface acoustic wave filter device in which two one-way converters according to claim 1 are combined are provided.

According to a fourth aspect of the present invention, there is provided a surface acoustic wave filter device comprising a piezoelectric substrate having an electromechanical coupling coefficient of 0.1 to 1.5%, and an electric signal formed on the piezoelectric substrate. An input converter that is externally input and converts this electric signal into a surface acoustic wave, and a surface acoustic wave formed on the piezoelectric substrate and excited by the input converter is converted into an electric signal. An output-side converter that outputs an electric signal to the outside, wherein one of the input-side converter and the output-side converter is connected to a first electrode formed on the piezoelectric substrate, and the first electrode is connected to the first electrode. And a second electrode formed on the piezoelectric substrate so as to face each other. When λ is the propagation wavelength of the basic surface acoustic wave, a surface acoustic wave is formed between the first electrode and the second electrode. A first electrode finger whose width in the propagation direction is approximately λ / 12;
The second electrode whose center distance from the first electrode finger is located at λ / 6
The distance between the electrode finger, the third electrode finger whose center distance between the first electrode finger is λ / 2, and the first electrode is 2λ / 3
Are periodically formed at a pitch of [lambda], and a part of the pairs are respectively connected to the first to fourth electrode fingers by the first.
The other pair is connected to the electrode, and the other pair is configured such that the first electrode finger is connected to the first electrode, and the second electrode finger and the fourth electrode finger are connected to each other to form a short-circuit type floating electrode. ,And,
The third electrode finger may be a pair of one-way converters connected to the second electrode, and the other of the input-side converter and the output-side converter may be a bidirectional converter. Things.

As described above, the surface acoustic wave filter device according to the present invention can be constructed by combining the unidirectional converter according to the first aspect with the bidirectional converter, and such a surface acoustic wave filter device. Is particularly suitable for a surface acoustic wave filter device for CDMA.

The frequency characteristic of the electric signal obtained by such a surface acoustic wave filter device is a characteristic obtained by multiplying the characteristic of the unidirectional converter and the characteristic of the bidirectional converter. Therefore, the good characteristics of the bidirectional converter are utilized for the frequency characteristics, and the insertion loss and T.V.
T. E. FIG. With regard to the (Triple TransitEcho) level, a surface acoustic wave filter device utilizing the useful characteristics of the one-way converter can be realized. As a result, frequency characteristics, insertion loss and T.V. T. E. FIG. A surface acoustic wave filter device that satisfies all level requirements can be realized.

According to a fifth aspect of the present invention, there is provided a surface acoustic wave filter device having a piezoelectric substrate having an electromechanical coupling coefficient of 0.1 to 1.5%, and a bidirectional filter formed on the piezoelectric substrate. And a first unidirectional converter and a second unidirectional converter arranged on both sides of the propagation axis of the surface acoustic wave of the bidirectional converter. When the input-side converter is used, the first one-way converter and the second one-way converter are used as the output-side converter, and when the bidirectional converter is used as the output-side converter, The first one-way converter and the second one-way converter are input side converters, and each of the first one-way converter and the second one-way converter is provided on the piezoelectric substrate. A first electrode formed on the piezoelectric substrate, and a second electrode formed on the piezoelectric substrate so as to face the first electrode. Is the propagation wavelength of the basic surface acoustic wave, a first electrode finger having a width in the propagation direction of the surface acoustic wave of approximately λ / 12 between the first electrode and the second electrode; A second electrode finger having a center-to-center distance of λ / 6 and having a width in the propagation direction of the surface acoustic wave of approximately λ / 12, and a center-to-center distance of the first electrode finger being λ / 2. A third electrode finger having a width of approximately λ / 12 in the propagation direction of the surface acoustic wave, and a fourth electrode finger having a width of approximately λ / 12 in the propagation direction of the surface acoustic wave located at a distance of 2λ / 3 from the first electrode. Electrode fingers are periodically formed at a pitch of λ, a part of the pairs is a pair in which each of the first to fourth electrode fingers is connected to the first electrode, and the other pair is a first electrode. Connecting a finger to said first electrode;
An electrode finger and a fourth electrode finger are connected to each other to form a short-circuit type floating electrode, and the third electrode finger is connected to the second electrode in a pair.

In this way, the surface acoustic wave filter device according to the present invention can be constructed by arranging the unidirectional converter according to claim 1 on both sides of the bidirectional converter. The device is also particularly suitable for a surface acoustic wave filter device for CDMA.

When the unidirectional converters are arranged on both sides of the bidirectional converter in this manner, almost all of the energy excited by the bidirectional converter can be used effectively, and the insertion loss can be reduced. This is advantageous for a significant reduction.

In the surface acoustic wave filter device according to a sixth aspect of the present invention, the bidirectional converter is located at a center distance of λ / 4, and the width of the surface acoustic wave in the propagation direction is λ / 8.
A positive electrode in which a set of two electrode fingers is periodically formed at a pitch of λ, and similarly, with a center-to-center distance of λ / 4,
A set of two electrode fingers whose width in the propagation direction of the surface acoustic wave is λ / 8 is periodically formed at a pitch of λ, and each set of electrode fingers is set to λ with the set of adjacent electrode fingers of the positive electrode. And a negative electrode located at a center distance of / 2.

As a bidirectional converter, there is a converter in which the width of each of the positive and negative electrode fingers is set to λ / 4. This converter is very useful in terms of excitation efficiency. However, since the pitch between the respective ends of the electrode fingers is λ / 4, the reflected waves generated at the respective edges of the electrode fingers become in phase with each other, and as a result, a large ripple of 1 dB or more occurs. Therefore, when combined with a one-way converter, the frequency characteristics cannot be satisfied.

In the case of a bidirectional converter in which the width of each electrode finger is set to λ / 8, the excitation efficiency is lower than that of the λ / 4 type because the area of the electrode finger is smaller than that of the λ / 4 type. I do. In addition, since the phases of the reflected waves generated at the edges of the electrode fingers are shifted from each other, ripples occur in the frequency characteristics. Therefore, when combined with a unidirectional converter, satisfactory characteristics regarding insertion loss and frequency characteristics cannot be obtained.

On the other hand, a two-electrode finger having a width of λ / 8 is paired, and a positive / negative electrode finger is composed of two electrode finger pairs. For containers,
The area of the electrode finger is the same as that of the λ / 4 type, and high conversion efficiency can be obtained. In addition, since the reflected waves generated at the electrode finger edges are only the reflected waves whose phases are inverted from each other, an extremely good frequency characteristic without ripple can be obtained. Therefore,
If this bidirectional converter having a λ / 8 split type electrode structure is combined with a λ / 12 type unidirectional converter,
Insertion loss, frequency characteristics and T.V. T. E. FIG. The inherent drawbacks of each converter with respect to the attenuation level are complemented by each other, and as a result, a surface acoustic wave filter device having excellent characteristics can be realized.

The surface acoustic wave filter device according to a seventh aspect of the present invention is characterized in that the bidirectional converter has a weighted electrode structure.

By using a weighted electrode structure for the bidirectional converter as described above, a waveform having better frequency characteristics can be obtained.

In the surface acoustic wave filter device according to the present invention, the weighting electrode structure of the bidirectional converter may be configured such that an electrode finger of the positive electrode and a negative electrode are arranged along the propagation direction of the surface acoustic wave. The apodizing method in which the cross width with the electrode finger changes sequentially, or the cross width between the electrode finger of the positive electrode and the electrode finger of the negative electrode is uniform along the propagation direction of the surface acoustic wave, and the excitation intensity is changed. It is characterized by a thinning method in which weighting is performed by using

As a method of weighting, a Balibich method for changing the interval between electrode fingers is known. However, in this method, a phase shift occurs in the reflected wave from the electrode finger, which causes a ripple. On the other hand, in the apotize method, the length of the electrode finger in the direction orthogonal to the propagation direction of the surface acoustic wave is sequentially changed, so that the occurrence of ripple due to phase shift is prevented, and good frequency characteristics without ripple are obtained. It becomes easier to obtain a waveform. This also applies to the thinning method in which the intersection width between the electrode finger of the positive electrode and the electrode finger of the negative electrode is uniform along the propagation direction of the surface acoustic wave, and the excitation intensity is changed by thinning the electrodes. apply.
When weighting is performed by the thinning method, the sum of the electrode finger widths of each pair is the same in order to make the propagation speed of the surface acoustic wave in each pair coincide.

The surface acoustic wave filter device according to a ninth aspect of the present invention is characterized in that the piezoelectric substrate is a quartz substrate, a lithium tantalate substrate, a lithium borate substrate or a langasite substrate. .

Such a surface acoustic wave filter device has the same operation and effect as the surface acoustic wave filter device using the one-way converter according to the second aspect.

[0034]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a surface acoustic wave filter device and a unidirectional converter according to the present invention will be described in detail with reference to the drawings. The drawings are linear and are not to scale.

FIG. 1 is a diagram showing an embodiment of a one-way converter according to the present invention. When this one-way converter is used as an input-side converter, a surface acoustic wave propagates rightward in the figure, and when used as an output-side converter, a surface acoustic wave propagates leftward in the figure.

In this embodiment, a quartz substrate 1 is used as a piezoelectric substrate. Since the crystal substrate has a small change in the bandwidth with respect to the temperature change, the change in the pass frequency band due to the temperature change can be kept small.

This one-way converter has a positive electrode 2 as a first electrode and a negative electrode 3 as a second electrode. Some pairs (pair A in FIG. 1) have a width of λ /
Twelve first to fourth electrode fingers 4 to 7 are connected to the positive electrode 2. Note that the center-to-center distance between the first electrode finger 4 and the second electrode finger 5 is λ /
6, and an intermediate position between the first electrode finger 4 and the third electrode finger 6 is λ.
/ 2, and the center-to-center distance between the first electrode finger 4 and the fourth electrode finger 7 is 2λ / 3. Such pairs A are arranged regularly or irregularly according to desired characteristics.

Other pairs (for example, pair B in FIG. 1)
The first electrode finger 8 was connected to the positive electrode 2, the second electrode finger 9 and the fourth electrode finger 10 were connected to each other to form a short-circuit floating electrode 11, and the third electrode 12 was connected to the negative electrode 3. Make a pair. Also in this case, the center distance between the first electrode finger 8 and the second electrode finger 9 is λ / 6, the center distance between the first electrode finger 8 and the third electrode finger 12 is λ / 2, The center distance between the electrode finger 8 and the fourth electrode finger 10 is 2λ / 3.

The logarithm of the positive electrode 2 and the negative electrode 3 is set to, for example, 200 pairs. This logarithm can be set to an optimum condition as appropriate according to the required converter characteristics. In addition, the number of pairs A and pairs B can be appropriately set to optimal conditions according to required converter characteristics.

The operation of this embodiment will be described. The one-way converter shown in FIG. 1 is used for an input-side converter to which an electric signal is input from terminals 13 and 14, and the distance between the centers of the first electrode finger and the second to fourth electrode fingers is set to be an elastic surface. Λ / 6, λ / 2 and 2λ / in the direction opposite to the wave propagation direction, respectively.
A surface acoustic wave filter device using a one-way converter having the same configuration as the output-side converter except that it is arranged to be 3 will be considered.

FIG. 2 is a diagram for explaining the phase relationship between the excitation wave and the reflected wave in the pair B of FIG. 1, and FIG. 3 is a vector diagram of the phase relationship in FIG. FIG.
FIG. 5 is a diagram for explaining the phase relationship between the excitation wave and the reflected wave in the pair B in FIG. 1, and FIG. 5 is a vector diagram of the phase relationship in FIG. In the pair B, since the potential at the position where the short-circuit type floating electrode is arranged is forcibly made zero,
When the electric field distribution formed on the surface of the piezoelectric substrate (in this case, the quartz substrate) changes, the excitation center of the electrode finger Fp1 shifts, thereby causing a phase shift between the excitation wave and the reflected wave that is close to an ideal state. Can be generated, and the electrode finger of the short-circuit type floating electrode is displaced by λ / 12 from an intermediate position between the electrode finger of the positive electrode and the electrode finger of the negative electrode in a direction opposite to the propagation direction of the surface acoustic wave. The best results are obtained if they are arranged in a vertical position.

As described above, by using the short-circuit type floating electrode, the excitation center is shifted to the left in FIG. 2 from the center of the positive electrode. As a result, each of the electrode fingers Fs1 to Fs1,
Each of the reflected waves rs1, rn, rs2, and rp incident on Fn, Fs2, and Fp2 and reflected rightward has a smaller phase delay with respect to the excitation wave E1. As a result, the combined reflected wave R1 reflected to the right has substantially the same phase as the excitation wave E1.
On the other hand, as shown in FIGS. 4 and 5, each of the reflected waves rs1, rn, rs2, and rp reflected in the left direction is the excitation wave E2.
, The phase is further delayed. As a result, the combined reflected wave R2 reflected to the left has substantially the opposite phase to the excitation wave E2. As a result, almost ideal one-way state is achieved.

FIG. 6 is a diagram for explaining the phase relationship between the excitation wave and the reflected wave in the pair A in FIG. 1, and FIG. 7 is a vector diagram of the phase relationship in FIG. Electrode finger Fp
Since Fs1, Fs3, Fs4, and Fs5 are all connected to the positive electrode, no excitation wave is generated, and the electrode fingers Fp1, Fs3, Fs
s4, Fs5 reflected waves rp1, rs3, rs4, rs5
Only occurs. In the pair A, an excitation wave generated in the pair B upstream thereof and a reflected wave of the pair B are generated, and these reflected waves rp
Since the direction of the vector sum R3 of 1, rs3, rs4, and rs5 is the same as the direction of the excitation wave generated in the upstream pair B,
In the pair A, the reflected wave propagates only in the direction of the output converter. Further, for the pair B, the electrode fingers Fp1 and Fp are applied only to the positive electrode.
Since the electrode finger width of each pair is the same due to the thinned electrode structure connecting s3, Fs4, and Fs5, the propagation speed of the surface acoustic wave propagating through pair A is equal to the propagation speed of surface acoustic wave propagating through pair B. And the characteristics of the surface acoustic wave filter device are not adversely affected.

As described above, by connecting the first to fourth electrode fingers 9 to 12 (FIG. 1) to only the positive electrode 2 (FIG. 1) for a part of the pair A, a one-way converter can be controlled. In addition, it is possible to configure a thinned-out weighted electrode structure that satisfies various characteristics while making full use of the unidirectional characteristics. Note that the same operation and effect can be obtained even when such a one-way converter is used as the output-side converter.

FIG. 8 is a diagram showing a first embodiment of a surface acoustic wave filter device according to the present invention. Also in the present embodiment, the quartz substrate 21 is used as the piezoelectric substrate. An electric signal is externally input to the surface of the quartz substrate 21 through terminals 22 and 23, and an input-side converter 24 for converting the electric signal into a surface acoustic wave, a shield electrode 25, and an input-side converter 24. An output converter 28 that converts the excited surface acoustic wave into an electric signal and outputs the electric signal to the outside through terminals 26 and 27 is formed along the propagation direction of the surface acoustic wave.

The input-side converter 24 is the same as the one-way converter having the thinned-out electrode structure shown in FIG. The output-side converter 28 outputs the first to fourth electrode fingers for each pair in a direction in which the center-to-center distance between the first and second electrode fingers is opposite to the propagation direction of the surface acoustic wave. 6, λ / 2 and 2
It has the same structure as the one-way converter shown in FIG. 1 except that it is arranged to be λ / 3.

In such a surface acoustic wave filter device,
The same operation and effect as those of the surface acoustic wave filter device obtained by combining the one-way converter shown in FIG. 1 and the one-way converter having the same configuration as above are provided.

FIG. 9 is a diagram showing a surface acoustic wave filter device according to a second embodiment of the present invention. In the present embodiment, the input converter 35 has the same configuration as the input converter 24 in FIG. The output-side converter 36 is bidirectional in a split electrode structure having a positive electrode 37 and a negative electrode 38 in which a plurality of pairs of two electrode fingers arranged at a center distance of λ / 4 are periodically formed at a pitch of λ. Sex transducer,
The pair of electrode fingers of the positive electrode 37 is set so as to be located at a center-to-center distance of λ / 2 with the pair of electrode fingers of the negative electrode 38. In the present embodiment, the width of the electrode fingers of the positive electrode 37 and the negative electrode 38 is set to λ / 8 in order to improve the conversion efficiency of the surface acoustic wave. With this configuration, the intervals between the electrode fingers adjacent to each other are all set to λ / 8. The logarithm of the output side converter 36 is set to, for example, 300 pairs.

The output side converter 36 is weighted by the apodizing method, and the width of the intersection between the electrode finger of the positive electrode 37 and the electrode finger of the negative electrode 38, that is, the opening length is determined by the propagation of the surface acoustic wave. It changes along the direction.

As described above, the surface acoustic wave filter device according to the present invention can be configured by combining the unidirectional converter according to the present invention with the bidirectional converter. Particularly, it is suitable for a surface acoustic wave filter device for CDMA.

The frequency characteristic of the electric signal obtained by such a surface acoustic wave filter device is a characteristic obtained by multiplying the characteristic of the unidirectional converter and the characteristic of the bidirectional converter. Therefore, the good characteristics of the bidirectional converter are utilized for the frequency characteristics, and the insertion loss and T.V.
T. E. FIG. As for the level, it is possible to realize a surface acoustic wave filter device utilizing the useful characteristics of the one-way converter. As a result, frequency characteristics, insertion loss and T.V. T.
E. FIG. A surface acoustic wave filter device that satisfies all level requirements can be realized.

FIG. 10 is a diagram showing a surface acoustic wave filter device according to a fourth embodiment of the present invention. In the present embodiment, first and second output converters 40 and 41 are arranged on both sides of the input converter 39. Input side converter 39
Is the same as the output-side converter 36 in FIG. 9, the first output-side converter 40 is the same as the input-side converter 24 in FIG. 8, and the second output-side converter 41 is It is the same as the output converter 28 of FIG. 2 except that the positive electrode is a negative electrode and the negative electrode is a positive electrode.

Thus, by arranging the one-way converter shown in FIG. 1 on both sides of the two-way converter, a surface acoustic wave filter device particularly suitable for a surface acoustic wave filter device for CDMA is constructed. can do. Also, by arranging the unidirectional converters on both sides of the bidirectional converter in this way, almost all of the energy excited by the bidirectional converter can be effectively used, and the insertion loss can be greatly reduced. It is advantageous to reduce.

Next, the characteristics of the surface acoustic wave filter device according to the present invention shown in FIG. 8 will be compared with the characteristics of the conventional surface acoustic wave filter device shown in FIG. Note that FIG.
In the surface acoustic wave filter device shown in FIG.
The electrode finger was connected to the positive electrode or the negative electrode, the second electrode finger and the fourth electrode finger were connected to each other to form a short-circuit type floating electrode, and the third electrode finger was connected to the negative electrode or the positive electrode. Pair
Other pairs are pairs without the first to fourth electrode fingers, and the arrangement of some and other pairs has a thinned-out electrode structure similar to that of the surface acoustic wave filter device shown in FIG. Shall be.

FIG. 12 is a characteristic diagram of the surface acoustic wave filter device of FIG. In this case, it is understood that the weighting is performed so that the one-way property is sufficiently utilized and the desired characteristics are satisfied, whereby the insertion loss is sufficiently reduced and the desired characteristics (in this case, a wide band) are obtained.

FIG. 13 is a characteristic diagram of the surface acoustic wave filter device of FIG. When the thinning-out weighting as shown in FIG. 13 is performed, the phase difference between the excitation wave and the reflected wave generated in each of the pairs is caused by the propagation speed between some pairs and the other pairs. It can be seen that strong ripples and deterioration of attenuation amount occur.

The present invention is not limited to the above embodiment, and many modifications and variations are possible. For example, in the above embodiment, a quartz substrate was used as the piezoelectric substrate, but a lithium tantalate substrate (LiTa
O ₃ ), a lithium borate substrate (Li ₃ B ₄ O ₇ ) or a langasite substrate 8 (La ₃ Ga ₅ SiO ₁₄ ) can be used instead.

Further, the first surface acoustic wave filter device of the first embodiment
In the third to third embodiments, the input-side converter can be used as the output-side converter, and the output-side converter can be used as the input-side converter.

In weighting the bidirectional converter, weighting may be performed by a thinning method instead of the apotizing method. In this case, in order to make the propagation speed of the surface acoustic wave in each pair coincide, the sum of the electrode fingers of each pair is the same.

The surface acoustic wave filter device can also be constructed by combining the one-way converter shown in FIG. 1 with a conventionally known converter.

Further, the positive electrode of the one-way converter and the bidirectional converter may be a negative electrode, and the negative electrode may be a positive electrode.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of a one-way converter according to the present invention.

FIG. 2 is a diagram for explaining a phase relationship between an excitation wave and a reflected wave in a pair A of FIG. 1;

FIG. 3 is a vector diagram of a phase relationship in FIG. 2;

FIG. 4 is a diagram for explaining a phase relationship between another excitation wave and a reflected wave in the pair A of FIG. 1;

FIG. 5 is a vector diagram of a phase relationship in FIG. 4;

FIG. 6 is a diagram for explaining a phase relationship between an excitation wave and a reflected wave in pair B of FIG. 1;

FIG. 7 is a vector diagram of a phase relationship in FIG. 6;

FIG. 8 is a diagram showing a first embodiment of a surface acoustic wave filter device according to the present invention.

FIG. 9 is a diagram showing a surface acoustic wave filter device according to a second embodiment of the present invention.

FIG. 10 shows a third example of the surface acoustic wave filter device according to the present invention.
It is a figure showing an embodiment.

FIG. 11 is a diagram showing a conventional surface acoustic wave filter device.

12 is a characteristic diagram of the surface acoustic wave filter device of FIG.

13 is a characteristic diagram of the surface acoustic wave filter device of FIG.

[Explanation of symbols]

1,21 quartz substrate, 2,37 positive electrode, 3,38 negative electrode, 4,9 first electrode finger, 5,10 second electrode finger,
6,12 fourth electrode finger, 7,29 short-circuit type floating electrode,
8, 11 Third electrode finger, 13, 14, 22, 23, 2
6, 27 terminals, 24, 35, 39, 42 input converter, 25 shield electrode, 28, 36 output converter,
40 first output converter, 41 second output converter

Claims (9)

[Claims] 1. A one-way transducer for a surface acoustic wave filter device, comprising: a piezoelectric substrate having an electromechanical coupling coefficient of 0.1 to 1.5%; and a first piezoelectric substrate formed on the piezoelectric substrate. A first electrode and a second electrode formed on the piezoelectric substrate so as to face the first electrode, wherein λ is a propagation wavelength of a basic surface acoustic wave;
A first electrode finger having a width in the propagation direction of the surface acoustic wave of approximately λ / 12 between the electrode and the second electrode, and a surface acoustic wave having a center distance of λ / 6 between the first electrode finger and the first electrode finger; And a third electrode finger having a width in the propagation direction of a surface acoustic wave located at a center-to-center distance of λ / 2 between the second electrode finger having a width of approximately λ / 12 and the first electrode finger having a width of approximately λ / 12. When the distance between the electrode finger and the first electrode is 2λ / 3, the width of the surface acoustic wave in the propagation direction is approximately λ.
/ 12 and the fourth electrode fingers are periodically formed at a pitch of λ, and some of the pairs are pairs in which each of the first to fourth electrode fingers is connected to the first electrode. Connecting the first electrode finger to the first electrode, connecting the second electrode finger and the fourth electrode finger to each other to form a short-circuit type floating electrode, and connecting the third electrode finger to the second electrode finger. A one-way converter characterized by a pair connected to an electrode. 2. The unidirectional converter according to claim 1, wherein said piezoelectric substrate is a quartz substrate, a lithium tantalate substrate, a lithium borate substrate or a langasite substrate. 3. A piezoelectric substrate having an electromechanical coupling coefficient of 0.1 to 1.5%, an electric signal formed on the piezoelectric substrate, an electric signal being input from outside, and converting the electric signal into a surface acoustic wave. And an output converter formed on the piezoelectric substrate, converts the surface acoustic wave excited by the input converter to an electric signal, and outputs the electric signal to the outside. A first electrode formed on the piezoelectric substrate and a second electrode formed on the piezoelectric substrate so as to face the first electrode; When λ is the propagation wavelength of the basic surface acoustic wave,
A first electrode finger whose width in the direction of propagation of the surface acoustic wave is approximately λ / 12 and a center-to-center distance between the first electrode and the second electrode is λ / 6. A second electrode finger having a width of approximately λ / 12 in the propagation direction of the surface acoustic wave, and a width of approximately λ / 12 in the propagation direction of the surface acoustic wave located at a center distance of λ / 2 from the first electrode finger; And a fourth electrode finger having a width of approximately λ / 12 in the propagation direction of the surface acoustic wave located at a distance of 2λ / 3 from the first electrode at a pitch of λ. , Some pairs are pairs in which each of the first to fourth electrode fingers is connected to the first electrode, and the other pairs are the first electrodes.
An electrode finger was connected to the first electrode, the second electrode finger and the fourth electrode finger were connected to each other to form a short-circuit type floating electrode, and the third electrode finger was connected to the second electrode. A surface acoustic wave filter device comprising a pair of unidirectional transducers. 4. A piezoelectric substrate having an electromechanical coupling coefficient of 0.1 to 1.5%, an electric signal formed on the piezoelectric substrate, an electric signal being input from the outside, and converting the electric signal into a surface acoustic wave. And an output converter formed on the piezoelectric substrate, converts the surface acoustic wave excited by the input converter to an electric signal, and outputs the electric signal to the outside. A first electrode formed on the piezoelectric substrate, and a first electrode formed on the piezoelectric substrate facing the first electrode. When two electrodes are provided and λ is the propagation wavelength of the basic surface acoustic wave, the width of the surface acoustic wave in the propagation direction is approximately λ / 12 between the first electrode and the second electrode. A first electrode finger, a second electrode finger having a center-to-center distance between the first electrode finger and λ / 6, Forming a third electrode finger whose center distance to the finger is λ / 2 and a fourth electrode finger whose distance to the first electrode is 2λ / 3 at a pitch of λ; A pair of parts is a pair in which each of the first to fourth electrode fingers is connected to the first electrode, and the other pair is a pair in which the first electrode finger is connected to the first electrode and the second electrode finger is connected to the second electrode finger. And the fourth electrode fingers are connected to each other to form a short-circuit type floating electrode;
A surface acoustic wave comprising: a one-way converter having a pair of electrode fingers connected to the second electrode; and the other of the input-side converter and the output-side converter being a bidirectional converter. Filter device. 5. A piezoelectric substrate having an electromechanical coupling coefficient of 0.1 to 1.5%, a bidirectional converter formed on the piezoelectric substrate, and a surface acoustic wave of the bidirectional converter. A first one-way converter and a second one-way converter arranged on both sides of the propagation axis of the first direction. The first unidirectional converter and the second one-way converter when the one-way converter and the second one-way converter are the output-side converter and the two-way converter is the output-side converter. The converter is an input-side converter, and each of the first unidirectional converter and the second unidirectional converter includes a first electrode formed on the piezoelectric substrate and a first electrode formed on the piezoelectric substrate. A second electrode formed on the piezoelectric substrate so as to face the first substrate, wherein λ is a propagation wavelength of a basic surface acoustic wave;
A first electrode finger having a width in the propagation direction of the surface acoustic wave of approximately λ / 12 between the electrode and the second electrode, and a surface acoustic wave having a center distance of λ / 6 between the first electrode finger and the first electrode finger; And a third electrode finger having a width in the propagation direction of a surface acoustic wave located at a center-to-center distance of λ / 2 between the second electrode finger having a width of approximately λ / 12 and the first electrode finger having a width of approximately λ / 12. When the distance between the electrode finger and the first electrode is 2λ / 3, the width of the surface acoustic wave in the propagation direction is approximately λ.
/ 12 and the fourth electrode fingers are periodically formed at a pitch of λ, and some of the pairs are pairs in which each of the first to fourth electrode fingers is connected to the first electrode. Connecting the first electrode finger to the first electrode, connecting the second electrode finger and the fourth electrode finger to each other to form a short-circuit type floating electrode, and connecting the third electrode finger to the second electrode finger. A surface acoustic wave filter device comprising a pair connected to an electrode. 6. The two-way transducer according to claim 1, wherein said bidirectional transducer is positioned with a center distance of λ / 4, and a pair of two electrode fingers having a width of λ / 8 in the propagation direction of the surface acoustic wave is formed at a pitch of λ. A pair of two electrode fingers, which are similarly positioned at a center distance of λ / 4 and have a width in the propagation direction of the surface acoustic wave of λ / 8, are periodically arranged at a pitch of λ. 6. A method according to claim 4, wherein each pair of electrode fingers includes a pair of adjacent electrode fingers of the positive electrode and a negative electrode located at a center-to-center distance of λ / 2. The surface acoustic wave filter device according to any one of the above items. 7. The surface acoustic wave filter device according to claim 6, wherein said bidirectional converter has a weighted electrode structure. 8. A weighting electrode structure of the bidirectional converter is formed by an apotizing method in which an intersection width between the electrode finger of the positive electrode and the electrode finger of the negative electrode sequentially changes along the propagation direction of the surface acoustic wave, or The crossing width between the electrode finger of the positive electrode and the electrode finger of the negative electrode is uniform along the propagation direction of the surface acoustic wave, and is configured by a thinning method of performing weighting by changing the excitation intensity. A surface acoustic wave filter device according to claim 7. 9. A surface acoustic wave filter according to claim 3, wherein said piezoelectric substrate is a quartz substrate, a lithium tantalate substrate, a lithium borate substrate, or a langasite substrate. apparatus.