JPH0974330A - Surface acoustic wave element and communication system using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress spurious waves reflected on the end face of a piezoelectric substrate in the SAW convolver element using a circular-arcuate interdigital input electrode and to provide a surface acoustic wave(SAW) convolver element suitable for mass production. SOLUTION: In this SAW element which has one circular-arcuate interdigital input electrode 12 for exciting SAW and one output electrode 13 for a waveguide on the main surface of a piezoelectric substrate 11 at least, an electrode pad part 15 is provided at one part on the electrode finger of the circular- arcuate interdigital input electrode 12. Besides, in the area of the electrode pad part 15 on the SAW element, the central angle of the arcuate interdigital input electrode 15 is defined as an angle within the range where the propagation angle of SAW excited from the arcuate interdigital input electrode 12 (the angle formed by the waveguide direction of this waveguide and the propagation direction of group velocity of waves) is expressed by a wave surface angle (the angle formed by the waveguide direction of the waveguide and the propagation direction of phase velocity of waves) to be 0 deg..

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 having improved characteristics in a surface acoustic wave convolver, a receiving device using the same, and a communication system.

[0002]

2. Description of the Related Art Currently, surface acoustic wave (SAW) devices have been variously applied and researched. Among them, the surface acoustic wave convolver is a spread spectrum (SS) which has been attracting attention as a next-generation communication technology. ) It is becoming more and more important as a key device for communication.

This surface acoustic wave (SAW) is a surface acoustic wave that propagates on the surface of a propagation medium such as a piezoelectric substrate, and its energy is mostly contained within about one wavelength from the surface, and even with a relatively small input power. High-density elastic energy can be easily obtained, and the nonlinear effect becomes larger than that of the bulk wave, and its application as a communication device is expected.

As the nonlinear effect of this surface acoustic wave, harmonic generation, parametric mixing effect, parametric oscillation, direct current effect, convolution (Convolutio)
n) Effects and others are known, especially using surface acoustic waves
A surface acoustic wave device using a surface acoustic wave convolver for extracting convolution outputs of two input signals is a spread spectrum communication system (SS).
In recent years, its importance has been increasing and is being actively studied for application to signal processing devices such as n).

FIG. 5 is a schematic view showing a conventional surface acoustic wave convolver. In the figure, 51 is a piezoelectric substrate made of Y-cut (Z-propagation) lithium niobate or the like, and 52 is an arc-shaped comb-shaped input electrode (I) formed on the surface of the piezoelectric substrate 51.
DT: Interdigital Transducer), 53 is an output electrode (waveguide) formed on the surface of the piezoelectric substrate 51, 54
Is a piezoelectric substrate 51 in the surface acoustic wave convolver device.
Is the end face of.

[0006] These arc-shaped comb-shaped input electrodes 52 on both sides,
The output electrode 53 is made of a conductive material such as aluminum and is usually formed directly on the surface of the piezoelectric substrate 51 by using a photolithography technique.

In the surface acoustic wave device having such a structure,
When an electric signal having the carrier angular frequency ω is input to the two comb-shaped input electrodes 52, surface acoustic waves are excited by the piezoelectric effect of the piezoelectric substrate 51. These two surface acoustic waves propagate in opposite directions on the piezoelectric substrate 51 while being confined in the output electrode by the output electrode 53 acting as a waveguide.

The two surface acoustic waves colliding on the output electrode 53 in this way are output from the output electrode 53 as a convolution signal (carrier angular frequency 2ω) of two input signals due to the physical nonlinear effect of the piezoelectric substrate 51. Taken out.

That is, two surface acoustic waves are

[0010]

[Equation 1] Then, on the piezoelectric substrate 51, the product is obtained by nonlinear interaction.

[0011]

[Equation 2] Surface acoustic wave is generated. This signal is integrated in the region L in the length direction of the output electrode by providing a uniform output electrode.

[0012]

(Equation 3) Is taken out as a signal represented by. Here, the integration range L is substantially ± when the interaction length is sufficiently larger than the signal length.
If ∞ and τ = t− (x / v), then equation (3) becomes

[0013]

(Equation 4) And the signal is a convolution of two input signals.

The mechanism of convolution and bulk wave as described above is described, for example, in "Surface acoustic wave element technology handbook" edited by Japan Society for the Promotion of Science, 150th Committee, Surface acoustic wave element technology, Ohmsha, Ltd., (1991), p145. ~ P
205, p371-p374 and the like.

Further, in the above-mentioned conventional example, since the comb-shaped input electrode 52 for exciting the surface acoustic wave has an arc shape, the excited surface acoustic wave is focused on the end face of the output electrode 53, and the energy density is increased. Can be increased. As a result, the convolution efficiency (the ratio of the input signals P1, P2 and the output signal Pout: = Pout / P1 · P2) can be increased.

As described above, in the surface acoustic wave convolver, it is desirable that the surface acoustic waves excited from each arcuate comb-shaped input electrode 52 propagate only in the direction of the output electrode 53.

However, since the arc-shaped comb input electrode 52 for exciting the surface acoustic wave has the bidirectionality of propagating in both directions of the comb-shaped input electrode due to the characteristics of the comb-shaped electrode, it is excited from the arc-shaped comb-shaped input electrode 52. The surface acoustic wave also propagates in the direction opposite to the direction of the output electrode 53, which is the desired propagation direction of the surface acoustic wave, that is, in the direction of the end surface 54 of the piezoelectric substrate 51.

Since the comb-shaped input electrode 52 has an arc shape, the surface acoustic wave propagating in the direction opposite to the desired propagation direction of the output electrode propagates while diffusing.

Therefore, the influence of unnecessary reflected waves at the end surface 54 of the piezoelectric substrate 51 is smaller than that of the piezoelectric substrate 51 having a regular comb input electrode, but some unnecessary surface acoustic waves are still generated. After being reflected by the end surface 54 of the above, the laser beam is re-excited by the arc-shaped comb-shaped input electrode 52, and various adverse effects are exerted on the convolution efficiency and the like.

As means for suppressing such unnecessary reflected waves, conventionally, an absorber (sound absorbing material) is placed on the end surface 54 of the piezoelectric substrate 51 to suppress the reflected wave, or the end surface 54 of the piezoelectric substrate 51 is slanted. And the method of changing the reflection direction of the surface acoustic wave was used.

Further, in addition to the one invented by the present inventors, the formation angle of the end face 54 of the piezoelectric substrate 51 is determined in consideration of the shape of the arc-shaped comb input electrode and the anisotropy of the substrate (Japanese Patent Application No. (Japanese Patent Application No. 7-103897), which limits the position of the sound absorbing component (absorber).
No.).

[0022]

However, in the surface acoustic wave convolver, the means for suppressing the unnecessary surface acoustic wave excited from the arc-shaped comb-shaped input electrode as shown in the above-mentioned conventional example has the following problems. And you have to solve them.

In the surface acoustic wave convolver, of the surface acoustic waves excited from the comb-shaped input electrode, those that propagate in the direction of the output electrode are reflected by the end surface of the piezoelectric substrate of the element and are output to the output electrode (waveguide). As unnecessary surface acoustic waves such as propagating, they greatly affect various characteristics of the surface acoustic wave convolver.

As a means for suppressing the unnecessary reflected waves of the surface acoustic waves, there is a method of using a sound absorbing material (absorber). The effect of suppressing unnecessary surface acoustic waves by using a sound absorbing material is very large and effective, but since the sound absorbing material is applied after the element is manufactured, the number of processes must be increased, which affects the cost etc. during mass production. But not very desirable.

In addition, it cannot be denied that the components generated from the sound absorbing material affect the piezoelectric substrate and the metal film on the surface to some extent, which leads to a reliability problem.

As another means, there is a method in which the end surface of the substrate of the element is formed obliquely so that unnecessary surface acoustic waves do not return to the comb-shaped input electrode even if they are reflected by the end surface. There is no problem in reliability without increasing the number of steps as in the case of using a sound absorbing material.

However, when the end face of the element is formed obliquely,
Conventionally, the oblique angle of the end face is required to be at least 45 ° or more from a plane perpendicular to the propagation direction of the surface acoustic wave, which limits the number of elements that can be taken out from one substrate (wafer). As a result, the manufacturing cost is reduced due to the decrease in the number of products (Japanese Patent Laid-Open No. 63-
301609).

Particularly in the surface acoustic wave convolver, the size of one element is larger than that of the filter element due to the length of the waveguide, so that the number of the elements is greatly affected, and the cost of one element increases. Therefore, it is not suitable for mass production.

The inventors of the present invention have previously devised a product suitable for mass production as compared with the conventional one by taking advantage of the characteristic of the circular arc shape to solve the above problems. However, the above problems have not been completely solved by using a sound absorbing material or forming the end surface of the piezoelectric substrate obliquely, although it is a minimum.

[0030]

SUMMARY OF THE INVENTION It is an object of the present invention to suppress an unnecessary wave reflected on an end surface of a piezoelectric substrate in a surface acoustic wave convolver element using an arcuate comb-shaped input electrode and to provide an elastic material suitable for mass production. To obtain a surface wave convolver device.

In order to achieve the above object, the present invention provides a surface acoustic wave convolver using an arc-shaped comb-shaped input electrode, in which a surface acoustic wave is generated due to the arc shape of the arc-shaped comb-shaped input electrode and the anisotropy of the piezoelectric substrate. This can be achieved by determining the range of the center angle of the arc shape when propagating perpendicularly to the element end face and using a part of the arc type comb-shaped input electrode within the angle range as an electrode pad.

According to the above invention, in the surface acoustic wave convolver using the arc-shaped comb-shaped input electrode, the unnecessary surface acoustic wave excited from the arc-shaped comb-shaped input electrode is reflected on the end face of the element, and then the output electrode (waveguide). ), It is possible to obtain a convolution output signal with good characteristics without ripple, and since it is not necessary to form the end face of the element obliquely, it is possible to use a single piezoelectric substrate. Since the number of elements that can be taken out is increased and there is no need to provide means for suppressing unnecessary reflected waves at the end face of the element such as sound absorbing material provided at the end face of the surface acoustic wave convolver, obtain an element suitable for mass production. You can

[0033]

Embodiments of the present invention will now be described in detail with reference to the drawings.

<< First Embodiment >> FIG. 1 is a schematic view showing a first embodiment of a surface acoustic wave convolver according to the present invention.
In the figure, 11 is a piezoelectric substrate made of Y-cut (Z-propagation) lithium niobate, 12 is an arc-shaped comb-shaped input electrode formed on the surface of the piezoelectric substrate 11, and 13 is the piezoelectric substrate 1.
1, an output electrode (waveguide) formed on the surface of 1, an end surface of the piezoelectric substrate 11 of the surface acoustic wave convolver element, and 15
Is an electrode pad formed on a part of the electrode fingers of the arc-shaped comb-shaped input electrode 12.

The electrodes of the arc-shaped comb-shaped input electrode 12, the output electrode 13 and the electrode pad 15 are made of a conductive material such as aluminum, and are usually formed on the surface of the piezoelectric substrate 11 by the photolithography technique. Formed directly.

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 electrodes 12 on both sides, surface acoustic waves are excited by the piezoelectric effect of the piezoelectric substrate 11, and the output electrode 13 is ΔV / V.
They function as waveguides and propagate in opposite directions on the piezoelectric substrate 11 while being confined in the output electrode (waveguide). Then, the above two waves collide with each other on the output electrode 13,
Due to the physical non-linear effect of the piezoelectric substrate 11, a 2ω convolution signal is taken out from the output electrode 13.

Here, the ΔV / V waveguide is the piezoelectric substrate 11
By electrically short-circuiting the surface of, the propagation velocity of the surface acoustic wave is made lower than that of the free surface, and the surface acoustic wave is trapped in the short-circuited portion. Here, the velocity of the surface acoustic wave on the free surface without electrodes is V, and the velocity difference in which the velocity of the surface acoustic wave is delayed due to the presence of the output electrode 13 is ΔV. The larger the velocity difference, the stronger the waveguiding effect. Become.

At this time, the two arc-shaped comb-shaped input electrodes 12
, The surface acoustic waves are provided so as to concentrate on the output electrodes 13, respectively. However, the surface acoustic waves propagating in the opposite direction to the output electrodes 13, that is, the surface acoustic waves propagating to the end face 14 side of the piezoelectric substrate 11 are It becomes an unwanted wave.

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 as used herein refers to the angle between the Z direction of the piezoelectric substrate and the propagation direction of the wave phase velocity in the Y-cut (Z propagation) lithium niobate piezoelectric substrate. The propagation angle means an angle formed by the Z direction of the substrate and the propagation direction of the group velocity of waves. Further, in the present embodiment, the direction in which the surface acoustic waves excited from the arcuate comb-shaped input electrode are focused is made coincident with the Z direction of the piezoelectric substrate.

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 section and the output electrode section in the surface acoustic wave convolver using the arc-shaped comb-shaped input electrode. In the figure, 31 represents the propagation angle, and 32 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 0 ° to 3 °.
That is, when the arc-shaped comb-shaped input electrode 12 is used in the piezoelectric substrate 11 of Y-cut (Z-propagation) lithium niobate, unnecessary elasticity excited when the central angle of the arc is 0 ° to ± 3 °. Since the surface wave propagates straight in the direction of the output electrode without being affected by the anisotropy of the piezoelectric substrate 11, the end surface 14 of the piezoelectric substrate 11 is formed at right angles to the propagation direction of the surface acoustic wave. When it is present, it is reflected by the end surface 14 of the piezoelectric substrate 11 and propagates to the output electrode (waveguide).

On the other hand, when the center angle of the circular arc is equal to or larger than the angle in the range of 0 ° to ± 3 °, the propagation angle of the surface acoustic wave is not 0 °. The unnecessary surface acoustic wave excited by the
Even if the end surface 14 of the piezoelectric substrate 11 is formed at a right angle to the propagation direction of the surface acoustic wave, since the comb-shaped input electrode has an arc shape, unnecessary surface waves are generated by the end surface 14 of the piezoelectric substrate 11.
The unnecessary surface acoustic waves that are radially diffused in the direction of and are reflected by the end surface 14 of the piezoelectric substrate 11 due to the anisotropy of the piezoelectric substrate 11 do not propagate to the output electrode (waveguide) 13. .

From the above, Y cut (Z propagation)
When the arc-shaped comb-shaped input electrode 12 is used in the piezoelectric substrate 11 made of lithium niobate, the center angle of the arc shape is 0 ° to
Since only surface acoustic waves excited within a range of ± 3 ° propagate straight without being affected by the anisotropy of the piezoelectric substrate 11, an arc represented by a central angle of 0 ° to ± 3 °. Type comb-shaped input electrode 12 is partially covered with the electrode pad 15
By setting the
No propagation of surface acoustic waves in the direction of the end face 14 of 1 is generated,
Unnecessary surface acoustic waves propagating in the direction perpendicular to the end surface 14 of the piezoelectric substrate 11 can be completely suppressed. Further, even if the reflected wave from the end face 14 is reflected and inputted to the electrode pad 15, it is not re-excited and the influence of the unnecessary reflected wave is eliminated.

In the surface acoustic wave convolver using the arc-shaped comb-shaped electrodes, by providing the electrode pads 15 on a part of the comb-shaped electrode portions on the arc-shaped comb-shaped input electrode 12 as described above, the arc-shaped comb-shaped input electrodes are provided. Unnecessary surface acoustic waves excited from 12 can be completely suppressed, and a convolution output signal with good characteristics without ripples can be obtained.

Further, as compared with the conventional one using the sound absorbing material, the sound absorbing material is not used at all, so that the reliability can be improved and the number of steps is reduced, and the mass productivity is excellent.

In addition, since the shape of the end face of the element can be made perpendicular to the propagation direction of the surface acoustic wave without being inclined, the number of elements that can be obtained from one piezoelectric substrate is reduced to the conventional one. It is possible to increase the shape of the end face of the device more than the case where the end face is inclined, and it is possible to reduce the cost per element in mass production.

<Second Embodiment> FIG. 4 is a schematic view showing a second embodiment of the surface acoustic wave convolver according to the present invention.
In the figure, 41 is a Y-cut (Z-propagation) lithium niobate piezoelectric substrate, 42 is an arc-shaped comb-shaped input electrode formed on the surface of the piezoelectric substrate 41, and 43 is formed on the surface of the piezoelectric substrate 41. Output electrodes (waveguides), 44 is an end surface of the piezoelectric substrate 41 of the surface acoustic wave convolver element, 45 is an electrode pad formed on a part of the arc-shaped comb-shaped input electrode 42,
46 is a width d that represents the width of the end surface of the output electrode 43.

The arc-shaped comb-shaped input electrode 42, the output electrode 43, and the electrodes of the electrode pads are made of a conductive material such as aluminum, and are usually directly formed on the surface of the piezoelectric substrate 41 by a photolithography technique. It is formed.

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 42, surface acoustic waves are excited by the piezoelectric effect of the substrate, the output electrode 43 acts as a ΔV / V waveguide, and the inside of the output electrode (waveguide ), They propagate in opposite directions on the piezoelectric substrate 41. Then, the above two waves collide with each other on the output electrode 43 and are taken out from the output electrode 43 as a 2ω convolution signal due to the physical nonlinear effect of the piezoelectric substrate 41.

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 surface of the substrate, and the surface acoustic wave is trapped in the short-circuited portion. . In this case, the propagation velocity of the surface acoustic wave on the free surface without electrodes is set to V, and the propagation velocity of the surface acoustic wave in the waveguide of the output electrode becomes slow, and the difference in the propagation velocity is Δ.
Assuming V, the larger the velocity difference ΔV, the greater the waveguiding effect.

At this time, the two arc-shaped comb-shaped input electrodes 42
, The surface acoustic waves are provided so as to be concentrated on the output electrodes 43, respectively. However, the surface acoustic waves propagating in the opposite direction to the output electrodes 43, that is, on the end face 44 side of the piezoelectric substrate 41 are It becomes an unwanted wave.

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 the range of 0 ° to 3 °. That is, in the Y-cut (Z-propagation) lithium niobate piezoelectric substrate 41, the arc-shaped comb-shaped input electrode 4 is formed.
When 2, the unnecessary surface acoustic waves excited in the direction of both end surfaces 44 within the range of the central angle of the arc shape of 0 ° to ± 3 ° are not affected by the anisotropy of the piezoelectric substrate 41, Since the light propagates straight, when the end surface 44 of the piezoelectric substrate is formed at a right angle to the propagation direction of the surface acoustic wave, it is reflected by the end surface 44 of the piezoelectric substrate and propagates to the output electrode (waveguide). Will be done.

On the other hand, when the center angle of the circular arc is equal to or greater than 0 ° to ± 3 °, the propagation angle of the surface acoustic wave does not become 0 °. The unnecessary surface acoustic wave excited by the
Even if the end surface 44 of the piezoelectric substrate 41 is formed at a right angle to the propagation direction of the surface acoustic wave, since the comb-shaped electrode has an arc shape, unnecessary surface acoustic waves are radiated toward the end surface 44 of the piezoelectric substrate 41. The unnecessary surface acoustic waves diffused and reflected by the end surface 44 of the piezoelectric substrate 41 due to the anisotropy of the piezoelectric substrate 41 do not propagate to the output electrode 43 (waveguide).

From the above, Y cut (Z propagation)
When the arc-shaped comb-shaped input electrode 42 is used in the piezoelectric substrate 41 of lithium niobate, the central angle of the arc shape is 0 ° to
Since only the surface acoustic waves excited within the range of ± 3 ° propagate straight without being influenced by the anisotropy of the piezoelectric substrate 41, the central angle of the arc shape is represented by 0 ° to ± 3 °. A part of the comb-shaped electrode portion on the arc-shaped comb-shaped input electrode 42 is connected to the electrode pad 45.
By doing so, it is possible to completely suppress unnecessary surface acoustic waves propagating vertically in the direction of the element end face 44.

However, in the surface acoustic wave convolver having the arc-shaped comb-shaped input electrode 42, the arc-shaped comb-shaped input electrode 4 is used.
Due to the characteristic of the circular arc shape that 2 has, the excited surface acoustic wave concentrates its energy while the output electrode 43
Propagate to the end face entrance of (waveguide). That is, the width d of the width 46 of the end face of the output electrode is equal to the width d of the arc-shaped comb-shaped input electrode 4.
It is very small compared to the size of 2.

Although the size of the arc-shaped comb-shaped input electrode 42 varies depending on the radius of the arc-shaped comb-shaped input electrode 42 and the distance between the center point of the arc-shaped shape and the end face of the output electrode 43,
At this time, if the width represented by the central angle of the arc shape within the range of 0 ° to ± 3 ° is wider than the width d of the end face of the output electrode 43, unnecessary surface acoustic waves are reflected by the end face 44 of the piezoelectric substrate 41. However, not all of them are collected in the output electrode 43, so that it is possible to further narrow the range in which a part of the comb-shaped electrode portion on the arc-shaped comb-shaped input electrode 42 is used as the electrode pad 45.

In other words, the range where the comb-shaped electrode portion on the arc-shaped comb-shaped input electrode 42 is used as the electrode pad 45 is such that the central angle of the arc shape is within the range of 0 ° to ± 3 ° and the output electrode 43.
It is not necessary to make it larger than the width d of the end face of the electrode pad 45, and the shape of the electrode pad 45 does not necessarily need to be fan-shaped.

In the surface acoustic wave convolver using the arc-shaped comb-shaped electrodes, as shown above, a part of the comb-shaped electrode portion on the arc-shaped comb-shaped input electrode 42 does not exceed the width d of the end face of the output electrode 43. By providing the electrode pad 45 of the height, it is possible to completely suppress the unnecessary surface acoustic wave excited from the arcuate comb-shaped input electrode 42, and it is possible to obtain a convolution output signal with good characteristics without ripples.

Further, as compared with the conventional one using the sound absorbing material, the sound absorbing material is not used at all, so that the reliability can be enhanced and the number of steps is reduced, so that the mass productivity is excellent.

In addition, since the shape of the end face of the element can be made perpendicular to the propagation direction of the surface acoustic wave without being inclined, the number of elements that can be obtained from one piezoelectric substrate is conventionally It is possible to increase the shape of the end face of the device more than the case where the end face is inclined, and it is possible to reduce the cost per element in mass production.

The electrode pad portion 45 provided on a part of the comb-shaped electrode portion on the arc-shaped comb-shaped input electrode 42 shown in the second embodiment is represented by a rectangular shape, but the shape is not necessarily limited to this shape, and the electrode pad is not limited thereto. Even if the size changes in the middle of the portion 45, there is no problem as long as it meets the contents shown in the second embodiment, and any other one may be used.

In the above-mentioned first and second embodiments, the shape of the end face of the piezoelectric substrate of the surface acoustic wave convolver element is shown to be a right angle, but it may be formed at an angle and in an oblique manner. There is no change in the effect indicated by.

Further, the angle range showing the region of the electrode pad portion provided in a part of the comb-shaped electrode portion on the arc-shaped comb-shaped input electrode shown in the first and second embodiments, the central angle of the arc shape is 0 °. ~
The range of ± 3 ° is not necessarily limited to this range, and the effects shown in the examples can be obtained even if the value is within this range.

Further, the electrode pad portion provided on a part of the comb-shaped electrode portion on the arc-shaped comb-shaped input electrode shown in the first and second embodiments may be used for either the input signal or the ground.

In the first and second embodiments, an example in which 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 it is necessary that the electric signals have the same frequency. Alternatively, electric signals having different carrier angular frequencies 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 signals.

Furthermore, in the first and second embodiments, an example using the surface acoustic wave convolver is given, but if an arc-shaped comb-shaped electrode is used, another surface acoustic wave element, for example, a surface acoustic wave filter. As for the resonator and the like, the effect of suppressing unnecessary waves can be obtained as described in the embodiment.

The expression of the central angle of the arc-shaped comb-shaped input electrodes shown in the first and second embodiments is as follows: Y-cut (Z-propagation) Z of the piezoelectric substrate of lithium niobate from the center point of the arc shape. Although the angles are set in the plus direction and the minus direction with respect to the axial direction as a reference, other expressions may be used as long as an equivalent angle amount is expressed.

Although the piezoelectric substrates shown in the first and second embodiments use Y-cut (Z-propagation) lithium niobate, other piezoelectric materials and piezoelectric materials in other cutting directions are used. You may use the thing. In this case, the graph state of the propagation angle with respect to the wavefront angle of the surface acoustic wave shown in FIG. 2 is different, and therefore the graph of the other piezoelectric material itself is measured and displayed,
The shape such as the angle and width of the electrode pad is obtained from the wavefront angle at which the propagation angle is 0 °, and is formed on the piezoelectric substrate by the photolithography technique or the like.

Further, in the above-mentioned first and second embodiments, as the surface acoustic wave element, the example of using the elastic type has been shown, but the type is not limited to this, and the AE type may be used. Furthermore, it is needless to say that the piezoelectric substrate may be a piezoelectric substrate in which the angular dependence of the propagation velocity of the crystal orientation is symmetrical with respect to the propagation direction of the surface acoustic wave.

Further, the piezoelectric substrate shown in the first and second embodiments is not limited to that originally, but a substrate in which a piezoelectric substance is formed on a non-piezoelectric substance other than the piezoelectric substrate may be used.

<< Third Embodiment >> FIG. 6 is a block diagram showing an example of a communication system using the surface acoustic wave device as described above. In the figure, reference numeral 40 denotes a transmitting device.
The transmitter 40 spread-spectrum modulates a signal to be transmitted using a spread code and transmits the signal from an antenna 401. The transmitted signal is received by the receiving device 400 and demodulated. The receiving device 400 includes an antenna 411, a high frequency signal processing unit 412, a synchronizing circuit 413, and a code generator 41.
4, a spread demodulation circuit 415 and a demodulation circuit 416. The reception signal received by the antenna 411 is appropriately filtered and amplified by the high frequency signal processing unit 412, and is output as it is as a transmission frequency band signal or as an appropriate intermediate frequency band signal. The signal is input to the synchronizing circuit 413.

The synchronizing circuit 413 is the above-mentioned first and second circuits of the present invention.
The surface acoustic wave device 4131 shown in the second embodiment, the modulation circuit 4132 for modulating the reference spread code input from the code generator 414, and the signal output from the surface acoustic wave device 4131 are processed, The signal processing circuit 4133 outputs a spread code synchronization signal and a clock synchronization signal for the transmission signal to the code generator 414. Surface acoustic wave element 4
An output signal from the high frequency signal processing unit 412 and an output signal from the modulation circuit 4132 are input to the surface acoustic wave element 413.
1, and the convolution operation of two input signals is performed. Here, the modulation circuit 4 is generated by the code generator 414.
Assuming that the reference spreading code input to 132 is a code obtained by time-reversing the spreading code transmitted from the transmitting side, the surface acoustic wave element 4131 using the surface acoustic wave convolver element spreads only the synchronization signal included in the received signal. When the code component and the reference spreading code from the modulation circuit 4132 match on the waveguide of the output electrode of the surface acoustic wave element 4131, a correlation peak is output.

At this time, since the surface acoustic wave element 4131 is a surface acoustic wave convolver element that suppresses unnecessary waves reflected on the end surface of the piezoelectric substrate and is suitable for mass production, the convolution efficiency is improved. , A high output level of the correlation peak is obtained, and a low cost one is applied.

Next, the signal processing circuit 4133 detects a correlation peak from the signal input from the surface acoustic wave element 4131, and shifts the code synchronization in the time from the code start of the reference spread code to the correlation peak output. The amount is calculated, and the code synchronization signal and the clock signal are output to the code generator 414.

After the synchronization is established, the code generator 414 generates a spreading code in which the clock and the spreading code phase match with the spreading code on the transmitting side. This spreading code is a spreading demodulation circuit 41.
The signal before being input to the signal 5 and subjected to spread modulation is restored.
Since the signal output from the spread modulation / demodulation circuit 415 is a signal that has been modulated by a modulation method such as so-called frequency modulation (FSK: Frequency Shift Keying) or phase modulation (PSK: Phase Shift Keying), the corresponding demodulation circuit 41
Data demodulation is performed by 6.

The surface acoustic wave convolver, which is the surface acoustic wave element 4131 used in this configuration, uses electrode pads in a predetermined shape on the piezoelectric substrate to prevent adverse effects of reflected waves from both end surfaces of the piezoelectric substrate. , A large convolution signal can be obtained.

<< Fourth Embodiment >> FIGS. 7 and 8 show the first and second embodiments.
It is a block diagram which shows an example of a transmitter and a receiver of a communication system using the surface acoustic wave element described in the second embodiment.

In FIG. 7 showing a block diagram of the transmitting device, 501 is a serial-parallel converter for converting serially input data into n parallel data, and 502-1 to n are parallelized data and spread data. A multiplier group for multiplying n spread codes output from the code generator, 503 is n different spread codes PN1 to PNn and a spread code PN dedicated to synchronization.
A spreading code generator for generating 0, 504 is an adder for adding the synchronization dedicated spreading code PN0 output from the spreading code generator 503 and n outputs of the multiplier groups 502-1 to 502-n, 50
Reference numeral 5 is a high frequency stage for converting the output of the adder 504 into a transmission frequency signal, and 506 is a transmission antenna.

In FIG. 8 showing a block diagram of the receiving apparatus, 601 is a receiving antenna, 602 is a high frequency signal processing section, 603 is a synchronizing circuit for capturing and maintaining synchronization with the spreading code and clock on the transmitting side, and 604 is a synchronizing circuit. Circuit 603
By the code synchronization signal and clock signal input from
A spreading code generator for generating the same n + 1 spreading codes as the spreading code group on the transmitting side and a reference spreading code, and 605, a carrier reproducing spreading code PN0 output from the spreading code generator 604 and a high frequency signal processing unit 602. , A carrier reproducing circuit for reproducing a carrier signal from the output of the carrier generating circuit 606, n outputs of the carrier reproducing circuit 605, the output of the high-frequency signal processing unit 602, and the output of the spreading code generator 604.
˜PNn is used to demodulate the base band, and 607 is a parallel-serial converter that parallel-serial converts n parallel demodulated data output from the base band demodulation circuit 606.

In the above configuration, on the transmission side, first, the input data is converted by the serial-parallel converter 501 into n pieces of parallel data equal to the number of code division multiplexes. On the other hand, the spreading code generator 503 generates n + 1 pieces of spreading codes PN0 to PNn having the same code period but different from each other. Of these, PN0 is dedicated to synchronization and carrier reproduction, is not modulated by the parallel data, and is directly input to the adder 504. The remaining n spread codes PN1 to PNn are modulated by n parallel data in the multiplier groups 502-1 to 50n and input to the adder 504. The adder 504 linearly adds the input n + 1 signals and outputs the added baseband signal to the high frequency stage 505. Subsequently, the baseband signal is converted into a high-frequency signal having an appropriate center frequency in the high-frequency stage 505 and transmitted from the transmission antenna 506.

Next, on the receiving side, the signal received by the receiving antenna 601 is appropriately filtered and amplified by the high frequency signal processing unit 602, and is output as it is as a transmission frequency band signal or as an appropriate intermediate frequency band signal. It The signal is input to the synchronization circuit 603. The synchronizing circuit 603 is the surface acoustic wave device 60 described in the first and second embodiments of the present invention.
31, a modulation circuit 6032 for modulating the reference spread code input from the code generator 604, and a surface acoustic wave element 60.
The signal processing circuit 6033 processes the signal output from the output terminal 31, and outputs a spread code synchronization signal and a clock synchronization signal for the transmission signal to the spread code generator 604.

The surface acoustic wave element 6031 includes the first and
An output signal from the high frequency signal processing unit 602 and a signal from the modulation circuit 6032 are input using any one of the surface acoustic wave convolver elements shown in the second embodiment, and a convolution operation of two input signals is performed.

Here, the modulation circuit 60 is supplied from the code generator 604.
If the code string of the reference spreading code input to 32 is a code string obtained by time-reversing the synchronization-dedicated spreading code transmitted from the transmission side, the surface acoustic wave element 6031 has the synchronization-dedicated spreading code included in the reception signal. A correlation peak is output when the code string of the component and the code string of the reference spreading code match on the waveguide of the output electrode of the surface acoustic wave element 6031.

Next, in the signal processing circuit 6033, the correlation peak is detected by the signal output from the surface acoustic wave element 6031, and the code synchronization shifts in the time from the code start of the reference spreading code to the correlation peak output. The amount is calculated, and the code synchronization signal and the clock signal are output to the spread code generator 604.

After the synchronization is established, the spreading code generator 604 generates a spreading code group in which the clock and the spreading code phase match with the spreading code group on the transmitting side. Of these code groups, the spread code PN0 dedicated to synchronization is input to the carrier reproduction circuit 605. The carrier reproduction circuit 605 despreads the reception signal converted to the transmission frequency band or the intermediate frequency band which is the output of the high frequency signal processing unit 602 by the synchronization-dedicated spreading code PN0, and reproduces the carrier wave in the transmission frequency band or the intermediate frequency band. .

The carrier reproducing circuit 605 has a structure using, for example, a phase locked loop. The received signal and the synchronization-dedicated spreading code 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-specific synchronization-specific spreading code PN0 match, and the transmission-side synchronization-specific spreading code is not modulated with data. Is despread at, and a carrier component appears at the 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 consisting of a phase detector, a loop filter and a voltage controlled oscillator, and a phase is applied to a carrier component output from the voltage controlled oscillator through a bandpass filter. The locked signal is output as a reproduced carrier wave.

The reproduced carrier wave is input to the baseband demodulation circuit 606. The baseband demodulation circuit 606 generates a baseband signal from the reproduced carrier wave and the output of the high frequency signal processing unit 602. The baseband signal is divided into n pieces and despreaded for each code division channel by the spreading code groups PN1 to PNn output from the spreading code generator 604, and subsequently data demodulation is performed. The parallel demodulated n demodulated data is converted into serial data by the parallel-serial converter 607, and the signal input to the transmission device is output.

Although the present embodiment is a case of binary modulation, other modulation methods such as quadrature modulation may be used. Further, the present invention can be applied to any of the DS (direct spread) method, the FH (frequency hopping) method, and the TH (time hopping) method in a spread spectrum communication system.

Further, in the above embodiment, an example in which the transmission device and the reception device are separated into a communication system has been described.
Both devices can be stored in the same package as a communication device. Further, in the case of the communication device, mutual communication can be performed by changing the codes of the used code strings. In that case,
The transmitter and the receiver are provided in the same package, and the same carrier is used by differentiating the spreading code for synchronization, so that the communication device can perform communication with almost the same configuration. Further, since the surface acoustic wave element described above is used for the receiving device, synchronization can be achieved reliably at high speed.
It enables a highly reliable communication system.

[0091]

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 are provided on the main surface of the piezoelectric substrate and the piezoelectric substrate. In a surface acoustic wave element having an output electrode for taking out the convolution signal of the two surface acoustic waves by utilizing non-linearity, an electrode pad portion provided on a part of the arc-shaped comb-shaped input electrode is The central angle of the arc shape in the range where the surface acoustic wave excited from the arc-shaped comb electrode propagates straight without being influenced by the anisotropy of the piezoelectric substrate, that is, in the range of the wave front angle where the propagation angle is 0 degree. The surface acoustic wave is formed within a range represented by an angle, whereby unnecessary surface acoustic waves excited from the arc-shaped comb-shaped electrode can be suppressed.

From the above, in the surface acoustic wave convolver using the arc-shaped comb-shaped electrodes, by providing the electrode pads on a part of the comb-shaped electrode portions on the arc-shaped comb-shaped input electrodes,
Unnecessary surface acoustic waves excited from the arc-shaped comb-shaped input electrode can be completely suppressed, and a convolution output signal with good characteristics without ripples can be obtained.

Further, as compared with the conventional one using the sound absorbing material, the sound absorbing material is not used at all, so that the reliability can be enhanced and the number of steps is reduced, and the mass productivity is excellent.

In addition, since the shape of the end face of the element can be made perpendicular to the propagation direction of the surface acoustic wave without being inclined, the number of elements that can be obtained from one piezoelectric substrate is reduced to the conventional one. It is possible to increase the shape of the end face of the device more than the case where the end face is inclined, and it is possible to reduce the cost per element in mass production.

Further, by using the above-mentioned surface acoustic wave element in a communication system, a convolution output signal having no ripple and good characteristics can be obtained, so that the stability and reliability of communication can be improved.

[Brief description of 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 in the present invention.

FIG. 4 is a schematic view showing a second embodiment of the surface acoustic wave convolver according to the present invention.

FIG. 5 is a schematic view showing a conventional surface acoustic wave convolver.

FIG. 6 is a block diagram showing an example of a communication system using the surface acoustic wave device of the present invention.

FIG. 7 is a block diagram illustrating an example of a transmission device of a communication system using the surface acoustic wave device of the present invention.

FIG. 8 is a block diagram illustrating an example of a receiving device of a communication system using the surface acoustic wave device of the present invention.

[Explanation of symbols]

11, 41, 51 Piezoelectric substrate 12, 42, 52 Arc-shaped comb-shaped input electrode 13, 43, 53 Output electrode 14, 44, 54 End surface of surface acoustic wave device 15, 45 Electrode pad 46 Output electrode end surface width d 31 Propagation Angle 32 Wavefront angle 40 Transmitter 401 Transmitting antenna 400 Receiving device 411 Receiving antenna 412 High frequency signal processing unit 413 Synchronizing circuit 414 Code generator 415 Spreading demodulation circuit 416 Demodulation circuit 501 Data input in series to n parallel data To parallel converter 502-1 to n multiplier group 503 spreading code generator 504 adder 505 high frequency stage 506 transmitting antenna 601 receiving antenna 602 high frequency signal processing unit 603 synchronization circuit 604 spreading code generator 605 carrier regeneration circuit 606 Baseband demodulation circuit 607 Parallel-serial converter

Front page continued (72) Inventor Tadashi Eguchi 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Akira Torizawa 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Akane Yokota 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (8)

[Claims] 1. A piezoelectric substrate or at least two substantially arc-shaped comb-shaped input electrodes for exciting first and second surface acoustic waves on a main surface of a substrate on which a piezoelectric substance is formed on a non-piezoelectric substance, and the substrate. A surface acoustic wave device having an output electrode also serving as a waveguide for taking out the convolution signal of the two surface acoustic waves by utilizing the non-linear effect of A surface acoustic wave device having a pad portion. 2. A propagation angle of a surface acoustic wave excited by the arc-shaped comb-shaped input electrode (where the center angle of the arc-shaped comb-shaped input electrode is equal to the propagation direction of the surface acoustic wave excited by the wave-guiding direction of the waveguide) in the region of the electrode pad portion. The angle formed by the group velocity and the propagation direction of the group velocity is 0 ° (the angle formed by the waveguide direction of the waveguide and the propagation direction of the phase velocity of the wave). The surface acoustic wave element according to claim 1, which is characterized in that. 3. The electrode width of the electrode pad portion (length in the direction perpendicular to the propagation direction of the surface acoustic wave) is at least approximately equal to or greater than the width of the inlet end face of the waveguide. The surface acoustic wave device according to claim 1 or 2, which is characterized. 4. The electrode pad portion is used as an electrode pad for an input signal, and the electrode pads provided on both sides of the arc-shaped comb-shaped input electrode are grounded.
The surface acoustic wave device according to any one of the above items. 5. The substrate according to claim 1, wherein the piezoelectric substrate is a substrate in which a propagation velocity of a surface acoustic wave has a symmetrical angular dependence due to a crystal orientation. Surface acoustic wave device. 6. A Y-cut (Z-propagation) is formed on the piezoelectric substrate.
The surface acoustic wave device according to any one of claims 1 to 5, wherein a piezoelectric substrate of lithium niobate is used. 7. A Y-cut (Z-propagation) is formed on the piezoelectric substrate.
A region of the electrode pad portion provided on a part of the electrode finger on the arc-shaped comb-shaped input electrode using a piezoelectric substrate of lithium niobate has a central angle of 0 ° to 0 ° 7. The surface acoustic wave device according to claim 1, wherein the surface acoustic wave device is a region represented by ± 3 °. 8. A communication system using the surface acoustic wave device according to claim 1. Description: