JPH0918273A - Surface acoustic wave element, spread spectrum signal receiver adopting the element, and its communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress a timewisely shifted convolution peak in an output signal by allowing the unnecessary surface acoustic wave excited from an arcuate comb-shaped electrode to reflect on the end face but not to input to the output electrode. SOLUTION: When a signal having a carrier angular frequency ω is inputted to arcuate comb-shaped input electrodes 12, surface acoustic waves are excited by the piezoelectric effect of a piezoelectric substrate 11, and an output electrode 13 becomes a Δ V/V waveguide and they are propagated on the substrate 11 in opposite directions while being confined in this waveguide. Two waves strike on the electrode 13, abd a convolution signal having a frequency 2ω is taken out from the electrode 13 by the nonlinear effect of the substrate. At this time, two electrodes 12 are provided in such form that surface acoustic waves are concentrated to the electrode 13; and thereby, surface acoustic waves propagated in the direction opposite to the electrode 13, namely, waves propagated to both end faces 14 of the substrate 11 become unnecessary waves, and timewisely shifted signals are not inputted to the electrode 13, and thus, a timewisely shifted comvolution peak doesn't appear in the output signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention utilizes the physical non-linearity effect of a piezoelectric substrate or a substrate in which a piezoelectric material is formed on a non-piezoelectric material to extract the convolution of two input signals as an output signal. The present invention relates to a surface acoustic wave element in which a convolution characteristic is effectively improved in a surface acoustic wave convolver, and further relates to a spread spectrum receiver and a spread spectrum communication system using the same.

[0002]

2. Description of the Related Art At present, a surface acoustic wave (SAW) device is an electronic component that converts an electric signal into a surface wave that propagates on a solid surface once, and then converts the electric signal back into an electric signal for extraction. Has been done. Among them, the surface acoustic wave convolver, which applies the nonlinear effect of surface waves, is spread spectrum (S
S) As a key device for communication, its importance is increasing more and more.

FIG. 12 is a schematic view showing a conventional surface acoustic wave convolver. In the figure, 1301 is a piezoelectric substrate such as Y-cut (Z-propagation) lithium niobate, 130
Reference numeral 2 is a normal type comb-shaped input electrode (IDT: interdigital transducer) formed on the surface of the piezoelectric substrate 1301 and 1303 is an output electrode formed on the surface of the piezoelectric substrate 1301. Reference numeral 1304 denotes an end surface of the piezoelectric substrate 1301 in the surface acoustic wave convolver element. Reference numeral 1305 denotes the angle θ of the end surface of the piezoelectric substrate 1301.

The input / output electrodes 130 shown in the above
2, 1303 are made of a conductive material such as aluminum and are usually formed directly on the surface of the piezoelectric substrate 1301 by using a photolithography technique. Further, generally, as the piezoelectric substance, LiNbO3, LiTaO3, quartz and the like are recognized.

In the surface acoustic wave device having such a structure, when an electric signal of the carrier angular frequency ω is input to each of the two normal type comb input electrodes 1302, the surface acoustic wave is excited by the piezoelectric effect of the substrate. The output electrode 1303 acts as a waveguide, and these two surface acoustic waves propagate on the piezoelectric substrate 1301 in the directions of the output electrode 1303 and in the opposite directions while being confined in the output electrode.
In this way, the two surface acoustic waves hitting on the output electrode 1303 are extracted from the output electrode 1303 as a convolution signal of two input signals (carrier angular frequency 2ω) due to the physical nonlinear effect of the piezoelectric substrate 1301. Be done.

That is, two surface acoustic waves are

[0007]

[Equation 1]

Then, on the piezoelectric substrate 1301, it is the product of the nonlinear interaction.

[0009]

[Equation 2]

The surface acoustic wave of is generated. This signal is integrated in the output electrode length region L by providing a uniform output electrode,

[0011]

(Equation 3)

(Here, K is a constant coefficient) and is extracted as a signal. Here, the integration range L may be substantially ± ∞ when the interaction length is sufficiently larger than the signal length, and when τ = t− (x / v), the equation (3) is

[0013]

(Equation 4)

And the signal is a convolution of two input signals. As described above, in the surface acoustic wave convolver, each regular type comb input electrode 13 is
The surface acoustic wave excited from No. 02 propagates only in the direction of the output electrode 1303 is the originally most desirable propagation direction in the surface acoustic wave convolver.

However, it is clear from the characteristics of the comb-shaped electrodes that the normal-type comb-shaped input electrodes 1302 that excite surface acoustic waves have bidirectionality of propagating in both directions of the comb-shaped input electrodes. Comb-shaped input electrode 13
The surface acoustic wave excited from 02 also propagates in the direction opposite to the output electrode direction, which is the original propagation direction of the surface acoustic wave, that is, in the direction of the end surface 1304 of the piezoelectric substrate.

Such an unnecessary surface acoustic wave is reflected by the end surface 1304 of the piezoelectric substrate, and then the normal type comb input electrode 13 is formed.
Since it is re-excited by 02, it adversely affects convolution efficiency and the like. Therefore, an absorber (sound absorbing material) is conventionally added to the end surface 1304 of the piezoelectric substrate to suppress reflected waves, and End face 1304
Is obliquely formed at an angle θ1305, and the surface acoustic wave to be reflected is changed by changing the reflection direction of the surface acoustic wave.
02, the re-excitation at the normal comb input electrode 1302 is prevented and unnecessary surface acoustic waves are suppressed. Conventionally, the magnitude of the angle θ1305 of the end surface 1304 of the piezoelectric substrate at this time is preferably at least about 20 degrees.

As a method disclosed in the prior art for suppressing such unwanted waves, Japanese Patent Publication No. 61-32
No. 846, JP-A-58-120313, JP-A-57-197910 and the like. Further, the absorber method using the sound absorbing material is more generally used as a currently known one.

For example, FIG. 13 shows a block diagram of a convolver that suppresses reflected waves by using a sound absorbing material. In the figure, 14
01 is a substrate having piezoelectricity, 1402 is a comb-shaped input electrode,
1403 is an output electrode for taking out a convolution signal, 1404 is an end face arranged on both sides of the substrate 1401, 1
Reference numeral 405 is a region provided with a sound absorbing material which is an absorber.
This is to absorb the surface acoustic wave to the end surface 1404 of the substrate excited by the comb-shaped input electrodes 1402 by the sound absorbing material 1405 and to attenuate the reflected wave from the end surface 1404.

The convolution mechanism as described above is described in, for example, "Japan Society for the Promotion of Science, Acoustic Wave Element Technology No. 15".
0 Committee, "Surface acoustic wave element technology handbook", Ohmsha, (1991), "p145-p205, p371.
~ P374 and the like.

[0020]

Since the convolution efficiency is proportional to the square of the energy density, the width of the output electrode that operates as a waveguide is set to prevent higher-order propagation transverse modes and increase the energy density. There is a demand to make it as narrow as possible in the range where the volume output can be taken out (width of about 1 to 4 wavelengths of surface acoustic wave in the case of a waveguide type output electrode in which a metal thin film is deposited on Y-cut Z-propagation lithium niobate). . On the contrary, in order to achieve impedance matching and wide band of the input comb-shaped electrodes, there is a demand to increase the comb-shaped crossing width and reduce the number of comb-shaped pairs as much as possible. Therefore, in order to generate a surface acoustic wave with a large input comb-shaped electrode and concentrate the surface acoustic wave on a narrow output electrode, the input electrode is formed into an arc shape. A horn, an acoustic lens, and a multi-electrode are provided between the input electrode and the output electrode. It has been devised such as providing a strip coupler. However,
There has been no known countermeasure against the influence caused by the SAW excited by the arc-shaped input electrode traveling in the direction opposite to the desired propagation direction and being reflected at the end face. Especially,
SAW having waveguide type output electrode like convolver
In the device, the reflected wave from the end face is input to the arc-shaped input electrode and re-excited, but the effect is almost eliminated from the shape of the input electrode, but the normal type comb-shaped electrode (IDT) In the device having the above, the above means for preventing re-excitation of the reflected wave by the input IDT, that is, the structure in which the end face is formed obliquely or the sound absorbing material is provided, has been solved at the same time, but the reflected wave is output. There was a problem that it would be input to the electrode (normal IDT
In, in order to prevent re-excitation, if an angle is set on the end face so that the reflected wave does not face the input IDT, the reflected wave is not necessarily input to the output electrode. ).

In the present application, a SAW having an arc-shaped input electrode
To solve the problem of the reflected wave in the convolver, especially the problem that the reflected wave from the end face of the substrate is input to the output electrode and the convolution signal due to the reflected wave is time-shifted from the desired convolution signal. It is an issue.

If the end face of the SAW device is inclined, when a plurality of devices are taken from one wafer at the time of manufacturing the device, the device cutting line (dicing line) is made straight for simplification of the device cutting work. Then, it is an object to solve the problem that if the angle of the end face becomes large and steep, the number of SAW devices that can be obtained from one wafer decreases and the cost becomes high.

Further, when the sound absorbing material is used, the amount of the sound absorbing material is not necessary because there is a problem that the gas generated from the sound absorbing material itself and the outflow of the low molecular weight component contained in the sound absorbing material affect the reliability of the element. The problem is to reduce the reflected wave as much as possible within the range that can be suppressed.

[0024]

The above-mentioned object of the present invention is to use an arc-shaped comb-shaped input electrode as a surface acoustic wave element, and to generate a surface acoustic wave that is excited by the comb-shaped input electrode and propagates to the opposite side of the output electrode. Of a surface acoustic wave having a propagation angle of 0 degree, which is an angle formed by the direction of the group velocity and the first direction in which the surface acoustic wave is guided in the output electrode, the propagation angle remains 0 degree. This is solved by providing an anti-reflection means on the opposite side of the output electrode with respect to the comb-shaped input electrode.

In particular, in the present invention, the area where the preventing means is provided is only an area where the surface acoustic wave having the propagation angle of 0 degrees reaches, or the area where the propagation angle is 0 degree is reflected. Then, only the region where the reflected surface acoustic wave reaches the surface acoustic wave which is coupled to the 0th-order guided mode of the output electrode is required. Therefore, as a means for preventing this, the range in which the end face is inclined is narrow, so that the number of substrates obtained from the wafer is increased and the yield is extremely low.

Also, when the sound absorbing material is used, the area where the sound absorbing material is provided can be made extremely small, and the amount of the sound absorbing material used can be reduced. Further, even when using the scattering means or the reflector, the installation area thereof can be made extremely small. Also, when the entire end face is inclined, the inclination angle is the angle formed by the normal direction of the wavefront of the surface acoustic wave excited by a part of the comb-shaped input electrode and the first direction. Since it suffices that the propagation angle is equal to or greater than the maximum wavefront angle of the surface acoustic wave at which the propagation angle is 0 degree, for example, when a Y-cut lithium niobate piezoelectric substrate is used as the substrate, the Z direction is set to the first direction. As the direction, the angle may be 3 degrees or more, so that the influence on the yield can be extremely reduced. It is preferable to make the angle as small as possible because the yield can be improved.

Further, a communication system using this surface acoustic wave element and a receiver used therein are also considered as a solution means of the present application. According to the above configuration, the convolution signal due to the reflected wave is not generated, and the convolution signal that is temporally shifted is not generated in the output signal. In addition, more devices can be manufactured from one wafer, and cost can be reduced. Furthermore, by reducing the use of sound absorbing materials, the cost can be reduced, and the gas generated from the sound absorbing materials,
Reliability can also be improved because the outflow of low molecular weight components can be reduced.

The propagation angle and the wavefront angle referred to in the present application are in the range of 0 to 90 degrees, and the positive and negative of the direction of the group velocity, the direction of the normal of the wavefront and the direction of the waveguide of the waveguide are taken into consideration. do not do. For example, when the propagation angle of a certain surface acoustic wave is 0 degree, even if the direction of the group velocity of this surface acoustic wave is reversed, the propagation angle is not called 180 degrees, but is expressed as 0 degree.

[0029]

Embodiments of the present invention will be described below in detail with reference to the drawings. <First Embodiment> An embodiment of the present invention will be described below.

FIG. 1 is a schematic view showing a first embodiment of a surface acoustic wave convolver according to the present invention. In the figure,
Reference numeral 11 is a Y-cut (Z-propagation) lithium niobate piezoelectric substrate, 12 is two arc-shaped comb-shaped input electrodes formed on the surface of the piezoelectric substrate 11, and 13 is formed on the surface of the piezoelectric substrate 11. Output electrodes, 14 are end faces of the piezoelectric substrate 11 of the surface acoustic wave convolver element, and 15 is an angle φ at which the end faces of the piezoelectric substrate 11 are formed.

These input / output electrodes 12 and 13 are made of a conductive material such as aluminum and are usually formed directly on the surface of the piezoelectric substrate 11 by using a photolithography technique. Further, the piezoelectric substrate 11 may be a piezoelectric substrate itself using a piezoelectric substance material, or may be a piezoelectric substrate in which a piezoelectric substance is formed on a non-piezoelectric substance.

In the surface acoustic wave device having such a structure,
When an electric signal of the carrier angular frequency ω is input to the arc-shaped comb-shaped input electrode 12, surface acoustic waves are excited by the piezoelectric effect of the substrate, and the output electrode 13 acts as a ΔV / V waveguide, and the output electrode 13 (waveguide ), They propagate in opposite directions on the piezoelectric substrate 11. Then, the two waves collide with each other on the output electrode 13 and are extracted from the output electrode 13 as a 2ω convolution signal due to the physical nonlinear effect of the piezoelectric substrate 11.

Here, the ΔV / V waveguide is intended to trap the surface acoustic wave in the short-circuited portion by lowering the propagation velocity of the surface acoustic wave as compared with the free surface by electrically short-circuiting the substrate surface. . At this time, the two arcuate comb-shaped input electrodes 12 are provided in such a shape that the surface acoustic waves are concentrated toward the output electrode 13, respectively.
Surface acoustic waves propagating in the opposite direction, that is, the surface acoustic waves propagating to both end surfaces 14 of the piezoelectric substrate 11 become unnecessary waves.

The graph of FIG. 2 is a graph showing the relationship between the wavefront angle of a surface acoustic wave and the propagation angle in a Y-cut (Z propagation) lithium niobate piezoelectric substrate. The horizontal axis represents the wavefront angle of the surface acoustic wave, and the vertical axis represents the propagation angle of the surface acoustic wave. The wavefront angle referred to here is an angle formed by the wavefront normal direction and the propagation principal axis of the surface acoustic wave (Z axis in the case of a Y-cut (Z-propagation) lithium niobate piezoelectric substrate). Indicates the angle formed between the Z direction of the principal axis of propagation of the substrate and the propagation direction of the group velocity of the surface acoustic waves.

FIG. 3 is an explanatory diagram of the wavefront angle and the propagation angle shown by using an enlarged view of the arc-shaped comb-shaped input electrode portion and the output electrode portion in the present invention. In the figure, 31 indicates a propagation angle, 3
2 represents the wavefront angle. From the graph of FIG. 2, it can be seen that the range of the wavefront angle at which the propagation angle is 0 degree is the range of 0 ° to 3 °. That is, when the arc-shaped comb-shaped input electrode is used in the Y-cut (Z-propagation) lithium niobate piezoelectric substrate, unnecessary surface acoustic waves excited within the range of the central angle of the circular arc of 0 ° to ± 3 ° are generated. Since it propagates straight regardless of the anisotropy of the piezoelectric substrate, the end face of the piezoelectric substrate enters the output electrode, the desired convolution signal, the convolution signal by the end face reflected wave overlaps,
Convolution peaks that are shifted in time appear in the output signal.

On the other hand, for angles other than the angle in which the central angle of the circular arc shown above is in the range of 0 ° to ± 3 °, the propagation angle of the surface acoustic wave does not become 0 °, so the circular arc type comb input is performed. Unwanted surface acoustic waves excited by the electrodes are unnecessary surface acoustic waves because the comb-shaped electrodes are arc-shaped even if the end surface of the piezoelectric substrate is formed at a right angle to the output electrode. Unnecessary surface acoustic waves that are radially diffused in the direction of the end surface of the flexible substrate and are reflected by the end surface of the piezoelectric substrate do not enter the output electrode, and a time-shifted signal is not input to the output electrode. Convolution peaks that are shifted in time do not appear in the output signal.

The graph of FIG. 4 shows that in the surface acoustic wave convolver device using the arc-shaped comb-shaped electrodes manufactured by using the Y-cut (Z-propagation) lithium niobate piezoelectric substrate, the angle of the end face of the piezoelectric substrate is 5 °. 7 is a graph of the time response of the convolution output signal 41 of the surface acoustic wave convolver obtained by measuring the convolution output signal 41 when it is formed at an angle of, and the signal 42 of the unnecessary reflected wave reflected by the end surface of the piezoelectric substrate.

From this graph, it can be seen that the level of the unnecessary reflected wave signal reflected by the end surface of the piezoelectric substrate is significantly attenuated with respect to the main convolution signal. From the above, the angle φ15 at which the end surface 14 of the piezoelectric substrate 11 shown in FIG. 1 is formed is an unnecessary surface acoustic wave propagating in the direction opposite to the center direction of the arc of the arc-shaped comb-shaped input electrode 12. However, it must be formed at an angle that does not return to the output electrode 13 after being reflected by the end surface 14 of the piezoelectric substrate 11, that is, an angle of at least 3 degrees or more.

In the surface acoustic wave convolver using the arc-shaped comb electrodes, the end face angle can be made smaller than before,
The number of elements that can be obtained from the piezoelectric substrate per wafer is increased more than ever before, and the cost can be reduced. Further, the design of the arc-shaped comb input electrode is not greatly influenced because it does not depend on the size of the cross width of the arc-shaped comb input electrodes.

<Second Embodiment> The second embodiment of the present invention will be described below. FIG. 5 is a schematic view showing a second embodiment of the surface acoustic wave convolver according to the present invention. In the figure, 61 is a Y-cut (Z-propagation) lithium niobate piezoelectric substrate, 62 is two arc-shaped comb-shaped input electrodes formed on the surface of the piezoelectric substrate 61, and 63 is formed on the surface of the piezoelectric substrate 61. Output electrodes 64, 64 are both end faces of the piezoelectric substrate 61 of the surface acoustic wave convolver element, and 65 is an angle δ at which the end faces of the piezoelectric substrate 61 are obliquely formed.

The input / output electrodes 62 and 63 are made of a conductive material such as aluminum, and are usually formed directly on the surface of the piezoelectric substrate 61 by the photolithography technique. The piezoelectric substrate 61 may be a piezoelectric substrate itself, or may be a piezoelectric substrate in which the above-mentioned Y-cut (Z propagation) lithium niobate piezoelectric substance is formed on a non-piezoelectric substance.

In the surface acoustic wave device having such a structure, when an electric signal of the carrier angular frequency ω is input to the arc-shaped comb-shaped input electrode 62, the surface acoustic waves are excited by the piezoelectric effect of the substrate, and the output electrode 63 is ΔV. It acts as a / V waveguide and propagates in opposite directions on the piezoelectric substrate 61 while being confined in the output electrode (waveguide). Then, the above two waves collide with each other on the output electrode 63, and the piezoelectric substrate 6
Due to the physical nonlinear effect of 1, a convolution signal of 2ω is taken out from the output electrode 63. Where ΔV
The / V waveguide is as described in the first embodiment.

At this time, the two arcuate comb-shaped input electrodes 62 are provided in such a shape that the surface acoustic waves are concentrated toward the output electrode 63, but in the opposite direction to the output electrode 63, that is, piezoelectricity. The surface acoustic wave propagating to the end surface 64 side of the substrate 61 becomes an unnecessary wave. From FIG. 2 of the first embodiment, Y
It can be seen that in the cut (Z propagation) lithium niobate piezoelectric substrate, the range of the wavefront angle at which the propagation angle is 0 degree is 0 ° to 3 °. That is, when the arc-shaped comb-shaped input electrode is used, the center angle of the arc shape is excited within the range of 0 ° to ± 3 °, and even unnecessary surface acoustic waves traveling toward the end face side of the surface acoustic wave element are 3 ° or more. If it is reflected by the inclined end surface,
The unnecessary surface acoustic wave does not enter the output electrode, and the time-shifted signal is not input to the output electrode, so that the time-shifted convolution peak does not appear in the output signal.

Therefore, as shown in FIG. 5, when the central angle of the arc shape of the comb-shaped input electrode is equal to or larger than the crossing width of the arc-shaped comb-shaped input electrode corresponding to the angle in the range of 0 ° to ± 3 °, the extension line is extended. If the end surface of the piezoelectric substrate is formed at an angle of 3 ° or more, the other end surface of the piezoelectric substrate may be horizontal to the output electrode.

In addition, if the end face of the piezoelectric substrate is formed horizontally with respect to the output electrode, the end face is perpendicular to the output electrode, and a cutout portion having an angle δ of 3 ° or more is provided in a part of the end face. Since this is sufficient, the number of devices that can be obtained from one wafer is significantly increased, and mass production performance is improved.

(Third Embodiment) An embodiment of the present invention will be described below. FIG. 6 is a schematic diagram showing a first embodiment of a surface acoustic wave convolver according to the present invention. In the figure,
Reference numeral 71 is a Y-cut (Z-propagation) lithium niobate piezoelectric substrate, 72 is an arc-shaped comb-shaped input electrode formed on the surface of the piezoelectric substrate 71, 73 is an output electrode formed on the surface of the piezoelectric substrate 71, 74 is an end surface of the piezoelectric substrate 71 of the surface acoustic wave convolver element, and 75 is an arc-shaped input electrode on the surface of the piezoelectric substrate 71 and in a direction opposite to the direction in which the surface acoustic waves of the arc-shaped comb-shaped input electrode 72 are focused. A sound absorbing material region is provided at a position not overlapping 72, and 76 is a width of the sound absorbing material region 75.

These electrodes are made of a conductive material such as aluminum, and are usually formed directly on the surface of the piezoelectric substrate 71 using a photolithography technique.
In the surface acoustic wave device having such a configuration, when an electric signal having the carrier angular frequency ω is input to the arc-shaped comb-shaped input electrode 72,
Surface acoustic waves are excited by the piezoelectric effect of the substrate,
The output electrode 73 acts as a ΔV / V waveguide and propagates in opposite directions on the piezoelectric substrate 71 while being confined in the output electrode (waveguide). Then, the two waves collide with each other on the output electrode 73 and are extracted from the output electrode 73 as a 2ω convolution signal due to the physical nonlinear effect of the piezoelectric substrate 71.

Here, the ΔV / V waveguide is intended to trap the surface acoustic wave in the short circuit portion by lowering the propagation velocity of the surface acoustic wave as compared with the free surface by electrically shorting the surface of the substrate. . At this time, the two arcuate comb-shaped input electrodes 72 are provided in such a shape that the surface acoustic waves are concentrated toward the output electrode 73, respectively.
The surface acoustic wave propagating in the opposite direction, that is, the surface acoustic wave propagating to the end face 74 side of the piezoelectric substrate 71 becomes an unnecessary wave.

From FIG. 2 described in the first embodiment, in the Y-cut (Z-propagation) lithium niobate piezoelectric substrate, the range of the wavefront angle at which the propagation angle becomes 0 degree is the range of 0 ° to ± 3 °. I understand. That is, when the arc-shaped comb-shaped input electrode is used, the center angle of the arc shape is excited within the range of 0 ° to ± 3 °, and even the unnecessary surface acoustic wave that moves toward the end face of the surface acoustic wave element is absorbed by the sound absorbing material. By doing so, unnecessary surface acoustic waves
Since the time-shifted signal does not enter the output electrode and is not input to the output electrode, the time-shifted convolution peak does not appear in the output signal.

Therefore, as shown in FIG. 6, a region 75 provided with a sound absorbing material formed on the surface of the piezoelectric substrate 71.
Is required to be equal to or greater than the size of the intersection width of the arc-shaped comb-shaped input electrodes whose center angle of the arc-shaped comb-shaped input electrodes is in the range of 0 ° to ± 3 °. In the surface acoustic wave convolver using the arc-shaped comb-shaped electrodes, it is possible to suppress unnecessary surface acoustic waves excited from the arc-shaped comb-shaped input electrodes by limiting the area where the sound absorbing material is provided as shown above. , The convolution output signal which is deviated in time from the output signal does not appear.

Further, since the amount of the sound absorbing material used is smaller than that of the conventional one using the normal type input electrode, the reliability can be enhanced and the mass productivity is excellent. In addition, it is possible to make the shape of the end face of the device perpendicular to the propagation direction of the surface acoustic wave without making the shape of the end face of the wafer 1.
The number of elements that can be taken from the piezoelectric substrate per sheet,
It can be made easier than the conventional end face having a slanted shape, and the cost can be reduced.

The type of the sound absorbing material shown in the third embodiment may be any material as long as it suppresses unnecessary reflected waves at the end face of the element, and in particular, epoxy resin, silicon resin, phenol resin, ultraviolet curing resin, An ink material used in screen printing or the like may be used.

There are various methods for installing the sound absorbing material shown in the third embodiment, such as a patterning method using a mask, a stamping method, a screen printing method, and a mechanical coating method. Any method may be used. Also, some examples of the types of sound absorbing materials were given, but in order to improve the absorption of unnecessary surface acoustic waves, in order to improve the absorption of unnecessary surface acoustic waves, silicon-based powder, epoxy powder, niobium oxide powder etc May be included.

(Fourth Embodiment) An embodiment of the present invention will be described below. FIG. 7 is a schematic diagram showing a fourth embodiment of the surface acoustic wave convolver according to the present invention.

In FIG. 7, 81 is Y cut (Z propagation).
A lithium niobate piezoelectric substrate, 82 is an arc-shaped comb-shaped input electrode formed on the surface of the piezoelectric substrate 81, 83 is an output electrode formed on the surface of the piezoelectric substrate 81, and 84 is a surface acoustic wave convolver element. The end surface of the piezoelectric substrate 81, 85 is located on the surface of the piezoelectric substrate 81 and in a position opposite to the direction in which the surface acoustic waves of the arc-shaped comb-shaped input electrode 82 are focused so as not to overlap the arc-shaped input electrode 82. Area of the rough surface provided,
86 is the width of the area 85 in which the rough surface portion is provided.

These electrodes are made of a conductive material such as aluminum and are usually formed directly on the surface of the piezoelectric substrate 81 by using a photolithography technique. In the surface acoustic wave device having such a configuration, when an electric signal having the carrier angular frequency ω is input to the arc-shaped comb-shaped input electrode 82, the surface acoustic waves are excited by the piezoelectric effect of the substrate, and the output electrode 83 is guided by the ΔV / V conductor. The piezoelectric substrate 81 acts as a waveguide and is confined in the output electrode (waveguide).
Propagate in the opposite direction to each other. Then, the two waves collide with each other on the output electrode 83 and are extracted from the output electrode 83 as a 2ω convolution signal due to the physical nonlinear effect of the piezoelectric substrate 81.

Here, the ΔV / V waveguide is intended to confine the surface acoustic wave in the short-circuited portion by electrically short-circuiting the surface of the substrate to reduce the propagation velocity of the surface acoustic wave as compared with the free surface. . At this time, the two arcuate comb-shaped input electrodes 82 are provided in such a shape that the surface acoustic waves are concentrated toward the output electrode 83, respectively.
Surface acoustic waves propagating in the opposite direction, that is, to the end surface 84 side of the piezoelectric substrate 81 become unnecessary waves.

From the graph of FIG. 2 of the first embodiment, it can be seen that the range of the wavefront angle at which the propagation angle is 0 degree is 0 ° to 3 °. That is, when the arc-shaped comb-shaped input electrode is used, the surface angle of the unnecessary portion of the surface acoustic wave element, which is excited within the range of 0 ° to ± 3 ° of the central angle of the circular arc shape, is provided. , If the surface acoustic wave is scattered, the unnecessary surface acoustic wave does not enter the output electrode, and the time-shifted signal is not input to the output electrode. Does not appear.

Therefore, as shown in FIG. 7, in the region 85 where the rough surface portion formed on the surface of the piezoelectric substrate 81 is provided, the center angle of the comb-shaped input electrode is within the range of 0 ° to ± 3 °. The intersection width of the arc-shaped comb input electrodes may be 86 or more. In the surface acoustic wave convolver using the arc-shaped comb-shaped electrodes, it is possible to suppress unnecessary surface acoustic waves excited from the arc-shaped comb-shaped input electrode by limiting the area where the rough surface is provided as shown above. , Convolution peaks that are shifted in time do not appear in the output signal.

Further, since it is possible to make the shape of the end face of the element perpendicular to the propagation direction of the surface acoustic wave without making the shape of the end face oblique, the number of elements that can be obtained from one piezoelectric substrate is reduced to the conventional one. The shape of the end surface can be increased more than that of the inclined shape, and the cost per element can be reduced during mass production.

As for the rough surface portion shown in the fourth embodiment, it is sufficient that the substrate surface is roughened in order to suppress unnecessary reflected waves at the element end face, and the roughening method is chemically roughened. Method such as wet etching, a method of spraying a fine grain size using a blasting device that mechanically roughens, and a method of rubbing with a roughened surface such as paper file There are a roughening method by reverse sputtering using a vacuum apparatus such as a sputtering apparatus, a roughening method by ashing, and the like, but other than this, any method for roughening the substrate surface may be used.

(Fifth Embodiment) An embodiment of the present invention will be described below. FIG. 8 is a schematic view showing a surface acoustic wave convolver according to a fifth embodiment of the present invention. In the figure, 91 is a Y-cut (Z-propagation) lithium niobate piezoelectric substrate, 92 is an arc-shaped comb-shaped input electrode formed on the surface of the piezoelectric substrate 91, and 93 is formed on the surface of the piezoelectric substrate 91. An output electrode, 94 is an end face of the piezoelectric substrate 91 of the surface acoustic wave convolver element, 95 is an arc on the surface of the piezoelectric substrate 91 and in a direction opposite to the direction in which the surface acoustic waves of the arc-shaped comb-shaped input electrode 92 are focused. The area of the reflector provided at a position where it does not overlap the mold input electrode 92, and 96 is the width of the area 95 where the reflector is provided.

These input / output electrodes 92 and 93 are made of a conductive material such as aluminum, and are usually formed directly on the surface of the piezoelectric substrate 91 using a photolithography technique. In the surface acoustic wave device having such a configuration, when an electric signal of the carrier angular frequency ω is input to the arc-shaped comb-shaped input electrode 92, the surface acoustic wave is excited by the piezoelectric effect of the substrate and the output electrode 93 conducts the ΔV / V conduction. It acts as a waveguide and propagates in opposite directions on the piezoelectric substrate 91 while being confined in the output electrode (waveguide). Then, the two waves collide with each other on the output electrode 93, and the piezoelectric substrate 9
Due to the physical non-linear effect of 1, it is taken out from the output electrode 93 as a 2ω convolution signal.

In the ΔV / V waveguide, the propagation speed of the surface acoustic wave is made lower than that of the free surface by electrically short-circuiting the substrate surface, and the surface acoustic wave is confined in the short-circuited portion. . At this time, the two arcuate comb-shaped input electrodes 92 are provided in such a shape that the surface acoustic waves are concentrated toward the output electrode 93, respectively.
Surface acoustic waves propagating in the opposite direction, that is, to the end surface 94 side of the piezoelectric substrate 91 become unnecessary waves.

From the graph of FIG. 2 described in the first embodiment, in the Y-cut (Z propagation) lithium niobate piezoelectric substrate, the range of the wave front angle at which the propagation angle becomes 0 degree is 0 ° to 3 °.
It can be seen that the range is °. That is, when the arc-shaped comb-shaped input electrode 92 is used, the central angle of the arc shape is 0 ° to ± 3.
Even if unnecessary surface acoustic waves are excited in the range of ° and directed toward the end surface side of the surface acoustic wave element, a reflector is provided to reflect the surface acoustic waves, so that unnecessary surface acoustic waves do not enter the output electrode. As a time-shifted signal is not input to the output electrode, a time-shifted convolution peak does not appear in the output signal.

From the above, the size 96 of the region 95 provided with the reflector formed on the surface of the piezoelectric substrate 91 shown in FIG. 8 is such that the center angle of the arc-shaped comb-shaped input electrode 92 is The crossing width of the arc-shaped comb-shaped input electrodes 92 corresponding to an angle in the range of 0 ° to ± 3 ° may be greater than or equal to the width.

The reflector described above means an angle of at least 3 ° or more with respect to the propagation direction of the surface acoustic wave excited in the range of the central angle 0 ° to ± 3 ° of the arc shape of the arc-shaped comb input electrode. It is necessary to have at least one or more, and the effect of reflecting unnecessary waves is improved by forming a plurality of them.

In the surface acoustic wave convolver using the arc-shaped comb-shaped electrode, the unnecessary surface acoustic wave excited from the arc-shaped comb-shaped input electrode is suppressed by limiting the area where the reflector is provided as described above. It is possible to obtain a convolution output signal with less ripples and good characteristics.

Further, since the shape of the end face of the element can be made perpendicular to the propagation direction of the surface acoustic wave without making the shape of the end surface oblique, the number of elements that can be obtained from one piezoelectric substrate is reduced to the conventional one. The shape of the end surface can be increased more than that of the inclined shape, and the cost per element can be reduced during mass production.

In the reflector shown in the fifth embodiment, the effect is obtained by using a conductive material such as aluminum like a metal strip line or by scraping the substrate surface like a groove. Some of them are shown, but other than the above may be used as long as they have the effect of reflecting and scattering unnecessary surface acoustic waves.

In Embodiments 2 to 5 described above, the width of the region where the means for suppressing unnecessary surface acoustic waves is provided has been described, but the shape of the region is not limited as long as it has the width of the region. Further, it may be formed at any portion between the arc-shaped comb-shaped input electrode and the end face of the element.

In the above-described first to fifth embodiments, the example in which the electric signals of the same carrier angular frequency ω are input to the respective comb-shaped input electrodes of the surface acoustic wave convolver has been shown, but they do not have to have the same frequency and are different from each other. An electric signal of the carrier angular frequency may be input, and the output signal obtained from the output electrode at that time is the sum of the carrier angular frequencies of the input signal.

In the above-described first to fifth embodiments, the example using the surface acoustic wave convolver has been described. However, other surface acoustic wave elements such as surface acoustic wave filters and resonators can be used as long as arc-shaped comb electrodes are used. Also, the effect of suppressing unnecessary waves can be obtained as described in the embodiment.

The way of expressing the central angle of the arc-shaped comb-shaped input electrode shown in the above-mentioned first to fifth embodiments is represented by Y from the center point of the arc shape.
Cut (Z propagation) The Z axis direction of the lithium niobate piezoelectric substrate is used as a reference, and angles are set in the plus direction and the minus direction, respectively, but if the equivalent angle amount is expressed, another expression is used. May be.

The piezoelectric substrate 1 shown in the first to fifth embodiments uses Y-cut (Z-propagation) lithium niobate, but other piezoelectric materials and piezoelectric materials with other cutting directions are used. May be. Further, in the above-described Embodiments 1 to 5, the surface acoustic wave element has been shown as an example using the elastic type, but it is not limited to this, and the AE type may be used.

The piezoelectric substrate shown in the above-mentioned first to fifth embodiments is not limited to the one originally having piezoelectricity, but a substrate in which a piezoelectric substrate is formed on a non-piezoelectric substance other than the piezoelectric substrate. You may use. In addition, in the above-described Embodiments 1 to 5, all surface acoustic waves having a propagation angle of 0 degrees have a propagation angle of 0 degrees.
The surface acoustic wave is reflected at an angle not equal to or the surface acoustic wave having a propagation angle of 0 degree is absorbed and scattered. However, in the surface acoustic wave element using the arc-shaped comb-shaped electrodes, the width of the output electrode can be made sufficiently small, and therefore it is not necessary to reflect, absorb, or scatter all the surface acoustic waves having a propagation angle of 0 degree. At least what is necessary is to prevent the surface acoustic wave that is coupled to the waveguide mode of the waveguide-type output electrode among the unnecessary surface acoustic waves that is reflected by the end face from being reflected at the propagation angle of 0 degree. At this time, what is needed is not the width of the output electrode but 0
Consider coupling to the next guided mode. Therefore, in Embodiments 1 to 5, when the width of the spread of the guided mode is narrower than the intersection width of the electrode fingers of the portion that excites the surface acoustic wave having a propagation angle of 0 degree, the width of the end face to be angled The width of the region where the sound absorbing material, the rough surface portion and the reflector are provided may be at least the width of the spread of the waveguide mode of the output electrode.

<Sixth Embodiment> FIG. 9 is a block diagram showing an example of a communication system using the surface acoustic wave device as described above. In the figure, 100 indicates a transmitter. This transmitter uses a spreading code to transmit the signal
It is spread spectrum modulated and transmitted from the antenna 1001. The transmitted signal is received by the receiver 101 and demodulated. The receiver 101 includes an antenna 1011, a high frequency signal processing unit 1012, a synchronization circuit 1013, and a code generator 1.
014, a spread demodulation circuit 1015, and a demodulation circuit 1016. In the receiver 101, the antenna 101
The received signal received at 1 is the high frequency signal processing unit 1012.
Is appropriately filtered and amplified, and is output as it is as the transmission frequency band signal or as an appropriate intermediate frequency band signal. The high frequency signal is input to the synchronization circuit 1013. The synchronization circuit 1013 is a modulation circuit 1013 that modulates the reference spread code input from the surface acoustic wave device 10131 and the code generator 1014 described in the embodiment of the present invention.
2 and a signal processing circuit 10133 that processes the signals output from the surface acoustic wave device 10131 and outputs the spread code synchronization signal and the clock synchronization signal for the transmission signal to the code generator 1014. An output signal from the high frequency signal processing unit 1012 and an output signal from the modulation circuit 10132 are input to the surface acoustic wave element device 10131, and a convolution operation of the two input signals is performed. Here, when the reference spreading code input from the code generator 1014 to the modulation circuit 10132 is a code obtained by time-reversing the spreading code transmitted from the transmitting side, the surface acoustic wave device 10131 has a high frequency included in the received signal. A peak is output when the synchronization-specific spreading code component from the signal processing unit 1012 and the reference spreading code from the modulation circuit 10132 match on the waveguide of the surface acoustic wave element device 10131. However, by using the surface acoustic wave element that reduces the influence of the reflected wave due to the end surface on the piezoelectric substrate described in the first to fifth embodiments in the surface acoustic wave element device 10131,
The convolution peak as shown in can be detected at a high level.

In the signal processing circuit 10133, the correlation peak is detected from the signal input from the surface acoustic wave device 10131, and the code synchronization deviation amount is calculated from the time from the code start of the reference spreading code to the correlation peak output. The indexing, code synchronization signal and clock signal are output to the code generator 1014. After the synchronization is established, the code generator 1014 generates a spread code having the same clock and spread code phase as the spread code on the transmission side. This spread code is used by the spread demodulation circuit 10
The signal input to 15 is restored to the signal before being spread-modulated. Since the signal output from the spread demodulation circuit 1015 is a signal modulated by a commonly used modulation method such as so-called frequency modulation or phase modulation, data demodulation is performed by the demodulation circuit 1016 known to those skilled in the art.

<Fourth Embodiment> FIGS. 10 and 11 are block diagrams showing an example of a transmitter and a receiver of a communication system using the surface acoustic wave element as described above. FIG.
In 0, 1101 is a serial-parallel converter for converting serially input data into n parallel data, 1102-1 to 1102-1.
n is a group of multipliers that multiply each parallelized data by n spread codes output from the spread code generator, and 1103 is a spread code that generates n different spread codes and a spread code dedicated to synchronization. Generator 1104 is a spread code generator 1
Synchronous spreading code output from 103 and multiplier group 11
Adder for adding n outputs 02-1 to n, 1105
Is a high frequency stage for converting the output of the adder 1104 into a transmission frequency signal, and 1106 is a transmission antenna.

In FIG. 11, reference numeral 1201 is a receiving antenna, 1202 is a high frequency signal processing unit, 1203 is a synchronizing circuit for capturing and maintaining synchronization with the spread code and clock on the transmitting side, 1204 is a code input from the synchronizing circuit 1203. A spread code generator 1205 that generates the same n + 1 spread codes and reference spread code as the spread code group on the transmission side by the synchronization signal and the clock signal, and the spread code generator 1
A carrier reproduction circuit that reproduces a carrier signal from the carrier reproduction spread code output from 204 and the output of the high-frequency signal processing unit 1202 is a carrier reproduction circuit 1205.
, A high-frequency signal processing unit 1202 output, and a spreading code generator 1204 output using n spreading codes, a baseband demodulation circuit for demodulating in a baseband 1207.
Is a parallel-to-serial converter that parallel-serial converts n parallel demodulated data output from the baseband demodulation circuit 1206.

In the above structure, the input data is first converted into n parallel data equal to the number of code division multiplexes by the serial-parallel converter 1101 on the transmission side. On the other hand, the spread code generator 1103 generates n + 1 code codes having the same code period but different spread codes PN0 to PNn.
Of these, PN0 is dedicated to synchronization and carrier reproduction, and is directly input to the adder 1104 without being modulated by the parallel data. The remaining n spreading codes are the multiplier group 1102.
Adder 1 modulated by n parallel data from -1 to n
It is input to 104. The adder 1104 receives the input n +
One signal is added linearly and the added baseband signal is output to the high frequency stage 1105. The baseband signal is subsequently converted into a high frequency signal having an appropriate center frequency in the high frequency stage 1105 and transmitted from the transmitting antenna 1106.

On the receiving side, the signal received by the receiving antenna 1201 is appropriately filtered and amplified by the high frequency signal processing section 1202, and is output as it is as a transmission frequency band signal or as an appropriate intermediate frequency band signal. The transmission frequency band signal or the intermediate frequency band signal is transferred to the synchronization circuit 12
03 is input. The synchronization circuit 1203 outputs the signals output from the surface acoustic wave element device 12031 described in the embodiment of the present invention, the modulation circuit 12032 that modulates the reference spread code input from the code generator 1204, and the surface acoustic wave element device 12031. The signal processing circuit 12033 processes and outputs the spread code synchronization signal and the clock synchronization signal for the transmission signal to the spread code generator 1204. The output signal from the high frequency signal processing unit 1202 and the output signal from the modulation circuit 12032 are input to the surface acoustic wave device 12031, and the convolution operation of the two input signals is performed.

Here, the modulation circuit 1 is output from the code generator 1204.
If the reference spreading code input to 2032 is a code obtained by time-reversing the synchronization dedicated spreading code transmitted from the transmission side, the surface acoustic wave device 12031 has the synchronization dedicated spreading code component and the reference spread included in the received signal. A correlation peak is output when the code and the sign match on the waveguide of the surface acoustic wave device 12031. In particular, as shown in FIG. 4, for example, a convolution output signal of two input signals can obtain a high-level correlation peak output signal with respect to an unnecessary reflected wave signal, so that a malfunction in the latter stage can be prevented. , Effective in achieving accurate synchronization. In the next signal processing circuit 12033, the correlation peak is detected from the signal input from the surface acoustic wave element device 12031, and from the time from the code start of the reference spreading code to the correlation peak output,
The deviation amount of code synchronization is calculated, and the code synchronization signal and the clock signal are output to the spread code generator 1204. After the synchronization is established, the spreading code generator 1204 generates a spreading code group having the same clock and spreading code phase as the spreading code group on the transmitting side. Of these code groups, the spreading code P dedicated to synchronization
N0 is input to the carrier reproduction circuit 1205.

The carrier reproducing circuit 1205 despreads the received signal converted to the transmission frequency band or the intermediate frequency band which is the output of the high frequency signal processing unit 1202 by the synchronization-dedicated spreading code PN0, and then despreads the transmission frequency band or the intermediate frequency band. Play carrier wave. The carrier regenerating circuit 1205 uses, for example, a circuit utilizing a phase locked loop. The received signal and the spread code for synchronization PN0 are multiplied by the multiplier. After the synchronization is established, the clock and code phase of the synchronization-specific spreading code in the received signal and the reference synchronization-specific spreading code match, and the transmitter-side synchronization-specific spreading code is not modulated with data. It is despread and carrier components appear at its output. The output is then input to a bandpass filter, and only the carrier component is extracted and output. The output is then input to a well-known phase locked loop composed of a phase detector, a loop filter and a voltage controlled oscillator, and the phase is locked to the carrier component output from the band pass filter from the voltage controlled oscillator. The generated signal is output as a reproduced carrier wave.

The reproduced carrier wave is input to the baseband demodulation circuit 1206. Baseband demodulation circuit 1206
Then, a baseband signal is generated from the reproduced carrier wave and the output of the high frequency signal processing unit 1202. The baseband signal is divided into n signals and is despread for each code division channel by the spreading code groups PN1 to PNn output from the spreading code generator 1204, and subsequently data demodulation is performed. The parallel demodulated n demodulated data are converted into serial data by the parallel-serial converter 1207 and output.

Although the present embodiment has been described for the case of binary modulation, when the surface acoustic wave is used not only for the convolution of the receiver by the SS system but also for other modulation systems such as quadrature modulation for the convolution. Of course, elements may be used.

[0087]

As described above, according to the present invention, at least two arc-shaped comb-shaped input electrodes for exciting the first and second surface acoustic waves on the main surface of the piezoelectric substrate and the piezoelectric substrate. In the surface acoustic wave element having an output electrode for taking out the convolution signal of the two surface acoustic waves by utilizing the nonlinearity of the, the angle forming the end face of the piezoelectric substrate in the surface acoustic wave element is When the surface acoustic wave excited from the arc-shaped comb-shaped electrode is formed to have an angle equal to or more than a range in which the surface acoustic wave propagates straight, that is, an angle in a range of a wavefront angle at which the propagation angle is 0 degree, The excited unnecessary surface acoustic wave does not enter the output electrode even if it is reflected by the end face, and a time-shifted signal is not input to the output electrode. It does not appear.

Since the number of elements that can be obtained from the piezoelectric substrate per wafer is increased, the cost can be reduced. Further, when the sound absorbing material is used, the decrease in reliability due to the gas generated from the sound absorbing material and the outflow of low-molecular components can be reduced by reducing the amount of the sound absorbing material used.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a first embodiment of a surface acoustic wave convolver according to the present invention.

FIG. 2 is a graph showing a relationship between a wavefront angle of a surface acoustic wave and a propagation angle in a Y-cut (Z-propagation) lithium niobate piezoelectric substrate according to the present invention.

FIG. 3 is an explanatory diagram of a wavefront angle and a propagation angle shown by using an enlarged view of an arc-shaped comb-shaped input electrode section and an output electrode section in the present invention.

FIG. 4 is a graph of a time response of a convolution output signal of a surface acoustic wave convolver using an arc-shaped comb-shaped input electrode manufactured by using a Y-cut (Z-propagation) lithium niobate piezoelectric substrate according to the present invention.

FIG. 5 is a schematic plan view showing a second embodiment of the surface acoustic wave convolver according to the present invention.

FIG. 6 is a schematic plan view showing a third embodiment of the surface acoustic wave convolver according to the present invention.

FIG. 7 is a schematic plan view showing a fourth embodiment of a surface acoustic wave convolver according to the present invention.

FIG. 8 is a schematic plan view showing five embodiments of the surface acoustic wave convolver according to the present invention.

FIG. 9 is a block diagram showing an example of a communication system using the surface acoustic wave device of the present invention.

FIG. 10 is a block diagram showing an example of a transmitter of a communication system using the surface acoustic wave device of the present invention.

FIG. 11 is a block diagram showing an example of a receiver of a communication system using the surface acoustic wave device of the present invention.

FIG. 12 is a schematic view showing a conventional surface acoustic wave convolver.

FIG. 13 is a schematic view showing a conventional surface acoustic wave convolver.

[Explanation of symbols]

11, 61, 71, 81, 91 Piezoelectric substrate 12, 62, 72, 82, 92 Arc-shaped comb-shaped input electrode 13, 63, 73, 83, 93 Output electrode 14, 64, 74, 84, 94 Surface acoustic wave device End face of piezoelectric substrate in 65, 65 Forming angle of end face of piezoelectric substrate in surface acoustic wave element 31 Propagation angle 32 Wavefront angle 100 Transmitter 101 Receiver 1001 Transmitting antenna 1011 Receiving antenna 1012 High frequency signal processing unit 1013 Synchronous circuit 1014 Code generator 1015 Spreading demodulation circuit 1016 Demodulation circuit 1101 Serial-parallel converter for converting data input in series into n parallel data 1102-1 to n Multiplier group 1103 Spreading code generator 1104 Adder 1105 High frequency stage 1106 Transmission antenna 1201 Reception antenna 1202 High frequency signal processing unit 203 synchronizing circuit 1204 spreading code generator 1205 carrier reproduction circuit 1206 baseband demodulation circuit 1207 serializer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koichi Egara 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Akira Torizawa 3-30-2 Shimomaruko, Ota-ku, Tokyo Kya Non-Incorporated (72) Inventor Akane Yokota 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (15)

[Claims] 1. A surface acoustic wave having a comb-shaped input electrode for exciting a surface acoustic wave on a substrate having piezoelectricity, and an output electrode for receiving and guiding the surface acoustic wave excited by the comb-shaped input electrode. In the device, the substrate has anisotropy, the comb-shaped input electrode has a concave arc shape toward the output electrode, and the side opposite to the output electrode is excited by the comb-shaped input electrode. A surface acoustic wave having a propagation angle of 0 degree, which is an angle formed by the direction of the group velocity of the surface acoustic waves propagating to the first direction and the first direction in which the surface acoustic wave is guided in the output electrode, A surface acoustic wave device, characterized in that the surface acoustic wave device is provided with a preventing means for preventing the reflection from being reflected while its propagation angle is 0 degree, on the side opposite to the output electrode with respect to the comb input electrode. 2. The surface acoustic wave element according to claim 1, wherein the area where the preventing means is provided is only an area where the surface acoustic wave having the propagation angle of 0 degrees reaches. 3. The reflected surface acoustic wave is provided in the area where the preventing means is provided, when the surface acoustic wave having the propagation angle of 0 degree reaches the area where the propagation angle is reflected at 0 degree. 3. The surface acoustic wave device according to claim 2, wherein is only a region where a surface acoustic wave coupled to the 0th-order guided mode of the output electrode reaches. 4. The preventing means is realized by inclining the end face of the substrate by a predetermined angle with respect to the radial direction of the first direction, and the predetermined angle is one of the comb-shaped input electrodes. The propagation angle is equal to or greater than the maximum wavefront angle of the surface acoustic wave at which the propagation angle becomes 0 degrees, when the angle formed by the first direction and the normal direction of the wavefront of the surface acoustic wave excited at the section is defined as the wavefront angle. Item 4. The surface acoustic wave device according to any one of items 1 to 3. 5. The surface acoustic wave element according to claim 2, wherein the preventing means is a sound absorbing material provided in a region where the preventing means is provided. 6. The preventing means is a surface acoustic wave scattering means provided in a region where the preventing means is provided.
The surface acoustic wave device described in 1. 7. The surface acoustic wave device according to claim 6, wherein the surface acoustic wave scattering means has a roughened substrate in a region where the surface acoustic wave scattering means is provided. 8. The preventing means is a surface acoustic wave reflector provided in a region where the preventing means is provided, and the reflector causes the surface acoustic wave reaching the reflector to a predetermined direction with respect to the first direction. Is reflected in different directions, and the predetermined angle is defined as an angle formed by the normal direction of the wavefront of the surface acoustic wave excited by a part of the comb-shaped input electrode and the first direction. The surface acoustic wave element according to claim 2 or 3, wherein the propagation angle is equal to or larger than the maximum wavefront angle of the surface acoustic wave at which the propagation angle becomes 0 degree. 9. The surface acoustic wave device according to claim 8, wherein the predetermined angle is formed as small as possible. 10. The Y-cut lithium niobate piezoelectric substrate is used as the substrate, according to claim 1.
The surface acoustic wave device according to item. 11. A Y-cut lithium niobate piezoelectric substrate is used as the substrate, and the predetermined angle is 3
The surface acoustic wave device according to claim 4, wherein the surface acoustic wave device has a degree of rotation of not less than 10 degrees. 12. The surface acoustic wave element has two comb-shaped input electrodes, and the output electrode has the two comb-shaped input electrodes.
The comb-shaped input electrodes generate convolution signals of two surface acoustic wave signals respectively excited, and the preventing means is provided for at least one of the two comb-shaped input electrodes. 11. The surface acoustic wave device according to any one of 11 above. 13. The surface acoustic wave device according to claim 12, wherein the output electrode permits only a 0th-order guided mode. 14. A spread spectrum signal receiver using the surface acoustic wave device according to claim 12 or 13 for obtaining a convolution signal of a spread spectrum signal and a reference signal. 15. A spread spectrum communication system comprising a transmitter for transmitting a spread spectrum signal and the spread spectrum signal receiver according to claim 14.