JPH07162262A - Surface acoustic wave device and communication system using the device - Google Patents

Abstract

PURPOSE:To easily obtain a surface acoustic wave device capable of propagating only a reference mode even when the azimuth of crystal on a substrate is slightly shifted from the direction of an element and suppressing the generation of a primary mode and having high efficiency and high frequency characteristics at a low cost and high yield. CONSTITUTION:A surface acoustic wave element has two input convertes 12, 13 for exciting 1st and 2nd surface acoustic waves formed on a substrate 11 having a piezoelectric property and an output electrode 14 arranged between the converters 12, 13, acting as a waveguide for the 1st and 2nd surface acoustic waves and extracting convolution signals from respective surface acoustic wave signals. The maximum value of the width of the output electrode 14 acting as the waveguide is set up to width capable of practically propagating only a waveguide reference mode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave device for extracting a convolution signal of two signals and a communication system using the same.

[0002]

2. Description of the Related Art A surface acoustic wave element, especially a surface acoustic wave convolver, has recently been increasing in importance as a key device for performing spread spectrum communication and has been actively studied.

FIG. 6 is a conceptual diagram showing such a conventional surface acoustic wave element. In the figure, 61 is a piezoelectric substrate of Y-cut (Z-propagation) lithium niobate or the like, and 62, 6
Reference numeral 3 is a comb-shaped electrode formed on the surface of the piezoelectric substrate 61.
Reference numeral 64 is an output electrode formed on the surface of the piezoelectric substrate 1.

These electrodes are made of a conductive material such as aluminum and are usually formed by the 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 input comb-shaped electrode 62, the surface acoustic wave is excited by the piezoelectric effect of the substrate. Similarly, when an electric signal having a carrier angular frequency ω is input to the comb-shaped electrode 63, a surface acoustic wave is excited. When these two surface acoustic waves propagate in opposite directions on the piezoelectric substrate, the convolution signal (carrier angular frequency 2) of the two input signals is generated due to the physical nonlinear effect of the piezoelectric substrate.
ω) can be taken out from the output electrode.

In the coordinate system with the center of the output electrode as the x-axis and the left end of the output electrode as the origin, two surface acoustic waves are F (t-x / v) e ^{j (wt-kx)} and G (t + x / v) e ^{j (wt + kx)} is expressed by the product of F (t−x / v) · G (t + x / v) e ^j2wt, which is the product of the product due to the nonlinear interaction on the piezoelectric substrate 1. Surface acoustic waves are generated. This signal is integrated within the electrode length region by providing a uniform output electrode. Within the interaction length under the output electrode, it is taken out as a signal represented by S (t) = Ke ^j2wt ∫F (t−x / v) · G (t + x / v) dx (1). Here, the integration range may be substantially ± ∞ when the interaction length is sufficiently larger than the signal length, and when τ = t−x / v, the equation (1) is expressed as S (t) = − vKe ^j2wt ∫F (τ ) * G (2t- [tau]) d [tau] (2), and the signal is a convolution of the input signal.

The mechanism of such convolution is described in, for example, "Shibayama" Application of Surface Acoustic Wave "Television, 30, 457 (1976)".

As described above, in the convolver utilizing surface acoustic waves, the convolution output of the detected wave signal and the reference signal is obtained by the configuration as shown in FIG. When the metal thin film is vapor-deposited on the material having the piezoelectric effect, the surface of the piezoelectric body in that portion is short-circuited, and the velocity of the surface acoustic wave becomes slower. Of the surface acoustic wave due to the effect of concentrating on the surface and the mass load of the deposited metal, and the waveguide utilizing the effect of concentrating the surface acoustic wave (Because the surface acoustic wave is confined by the difference in speed, / V waveguide).

Since the convolution efficiency is proportional to the square of the energy density, the output electrode that operates as a waveguide is as narrow as possible in the range where the convolution output can be taken out in order to prevent higher-order propagation transverse modes and increase the energy density. Due to the requirement that the wavelength of the propagating elastic wave be λ, the Z-direction of Y-cut lithium niobate is A propagation convolver of about 1 to 4λ is suitable.

[0010]

In Y-cut lithium niobate, since the crystal anisotropy of the piezoelectric substrate is symmetrical with respect to the Z axis, surface acoustic waves excited symmetrically with respect to the Z axis are Z.
When propagating in the waveguide formed in the axial direction, ideally, the odd-order modes among the higher-order transverse modes do not propagate.

However, Z of the lithium niobate substrate
When the direction of the output electrode of the convolver is deviated from the axis, the primary mode can be propagated when the output electrode width is 2.5λ or more. The eigenmode of a surface acoustic wave propagating in a waveguide in which a metal thin film is deposited on a piezoelectric substrate is the metal deposition surface (electrical short-circuit surface).
Then, it is derived from the boundary condition of the surface on which nothing is vapor-deposited (electrically open surface). Strictly speaking, the eigenmode of the surface acoustic wave propagating in this waveguide is obtained by "Koshiba, Suzuki, Theory of Science (B), J61-B, p689 (1978)" and the like. For lithium,
"R.V. Schmidt & L.A. Coldre
n, IEEE Transaction onsoni
cs and ultrasonics. Vol. su
-22. No. 2, March 1975, p115
Calculation by scalar potential approximation like "-" may be performed.

Reference numeral 71 in the graph of FIG. 7 indicates the output electrode width = 3λ.
Represents the amplitude distribution of the 0th mode (fundamental mode) when
72 shows the amplitude distribution of the first-order mode under the same conditions.

FIG. 8 shows a YZ-lithium niobate substrate,
When the output electrode of the convolver and the substrate are deviated from each other by 0.5 ° in the direction of the Z axis, an arc-shaped IDT having a radius of curvature R = 80λ of the electrode finger closest to the output electrode of the IDT and a center of curvature O of the arc of the IDT. The result of having calculated the relationship between the distance L of an output electrode and the relative value of the propagation characteristic in the center frequency of a 0th-order mode and a 1st-order mode is shown. Around L = 80λ, that is, IDT
The propagation efficiency of the 0th-order mode is maximum near 160λ between the output electrode and the output electrode, but at this point, the difference from the propagation efficiency of the 1st-order mode is only about 4 dB.

In FIG. 9, the waveguide width is 2.5λ and L = 80.
An IDT with a radius of curvature R = 80λ arranged at the point of λ is
It is the measurement result of the time response of the propagation characteristic between the input electrodes of the element when formed slightly deviating from the crystal axis of the substrate. In the figure, the first-order mode is seen a little earlier than the 0th-order mode (basic mode).

FIG. 10 shows the measurement result of the frequency characteristic of the convolution output of the element shown in FIG. In the figure, it can be seen that ripples occur in the frequency characteristics and the characteristics of the element are significantly deteriorated.

Therefore, in order to produce a surface acoustic wave device having good characteristics, a substrate having a high orientation flat (orientation flat) and a high orientation of the substrate is used. It is necessary to strictly align the orientation flat marks so that the Z axis of the substrate and the direction of the output electrode of the convolver are aligned, which increases the cost of the substrate and deteriorates the yield of the device.

[Object of the Invention] The object of the present invention is to propagate only the fundamental mode and suppress the generation of the primary mode even if the crystal orientation of the substrate and the direction of the element are slightly deviated. It is to obtain a convolver of frequency characteristics easily, at low cost, and with good yield.

[0018]

As a means for solving the above problems, the present invention provides two input converters for exciting first and second surface acoustic waves formed on a substrate having piezoelectricity. And an output electrode sandwiched between the two input transducers and placed along the propagation axis of the surface acoustic wave, serving as a waveguide of the surface acoustic wave and extracting a convolution signal of the two surface acoustic wave signals. In the surface acoustic wave device having the above-mentioned, there is provided a surface acoustic wave device characterized in that the maximum value of the width of the output electrode acting as the waveguide is a width capable of substantially propagating only the guided fundamental mode.

That is, in the present invention, the width of the output integrating electrode that operates as a waveguide (the length in the direction perpendicular to the propagation direction of the elastic wave; hereinafter, the waveguide width) is the first-order lateral direction of the waveguide mode. The width of the waveguide is narrower than the width in which the modes are generated, and the width of the waveguide is set to be equal to or larger than the width of the waveguide in which the change in the convolution efficiency with the frequency does not pose a problem within the required band.

Particularly, in a so-called Y-cut Z-propagation lithium niobate (hereinafter YZ-lithium niobate) substrate, when the wavelength of the surface acoustic wave propagating in the Z-axis direction is λ, the waveguide width is 2λ or less, Make it 1 λ or more.

[0021]

According to the present invention, even if the crystal orientation of the substrate and the direction of the element are slightly deviated, only the fundamental mode can be propagated, the generation of the primary mode can be suppressed, and a convolver with high efficiency and good frequency characteristics can be provided. can get.

[0022]

[Embodiment 1] FIG. 1 is a view showing a convolver according to an embodiment of the present invention. In FIG. 1, 11 is a Y-cut (Z-propagation) lithium niobate substrate (hereinafter, YZ-lithium niobate substrate), and 12 and 13 are input comb electrodes (Int).
erDigital Transducer; IDT)
The input converter (hereinafter referred to as IDT) 14 is an output electrode (hereinafter referred to as waveguide) that functions as a waveguide. Here, the width of the waveguide 14 (here, the width of the waveguide is the length of the electrode in the direction perpendicular to the propagation direction of the surface acoustic wave, and YZ−
For a lithium niobate substrate, this is the length of the electrode in the X-axis direction. ) Is 1.5λ, where λ is the wavelength of the surface acoustic wave propagating in the Z-axis direction on the surface of the electrically released YZ-lithium niobate substrate. ID here
Aluminum having a small mass loading effect is used for the T and the waveguide.

FIG. 2 shows the potential approximation theory
6 is a graph showing the relationship between the waveguide width and the phase velocity of an elastic wave traveling in the waveguide in the Z-axis direction, using each mode as a parameter. In FIG. 2, the mass effect of the metal thin film of the waveguide is not considered. Considering the mass effect, if the waveguide width is smaller than approximately 2λ, the first-order mode does not reliably propagate, and only the fundamental mode (zero-order mode) can be guided in the waveguide.

By the way, since the convolution is obtained by the non-linear effect of the elastic wave (electromagnetic wave accompanying the elastic wave) propagating as two guided modes traveling in opposite directions, the convolution efficiency of the convolver propagates in both directions. It is proportional to the product of the energy densities of two surface acoustic waves. If the energy densities of both are equal, it is proportional to the square of the energy density of the surface acoustic wave.

FIG. 3 shows the relationship between the square of the component under the waveguide of the fundamental mode of the waveguide mode and the waveguide width. Figure 3
In the figure, the vertical axis is a value obtained by integrating the square of the component under the waveguide of the waveguide mode so that it becomes 1 when the entire waveguide mode (fundamental mode) in each waveguide width is integrated. When this value is set to 1 when the width is 1.6λ, the value of each waveguide width is expressed in percent. If only the elastic wave (electromagnetic wave accompanying the elastic wave) under the waveguide can be integrated and extracted as an output among the guided modes, the convolution efficiency is proportional to the component on the vertical axis in FIG. Therefore, the optimum value of the waveguide width is 1.6λ. Also,
From FIG. 3, the convolution efficiency drops sharply when the waveguide width is 1λ or less. This means that when a surface acoustic wave having a wide frequency band propagates in a waveguide, the difference between the upper and lower surface acoustic wave convolution efficiencies in the band becomes large. Therefore, in order to obtain a good convolution output with a small difference in convolution efficiency with respect to frequency,
It is preferable to avoid making the waveguide width 1λ or less.

Therefore, in combination with 2λ which is the preferable upper limit of the waveguide width described above with reference to FIG. 2, the waveguide width is approximately 1λ.
It can be seen that by setting the distance to 2λ or less, only the fundamental mode can be propagated and the characteristics can be improved.

FIG. 4 is a measurement result of the time response of the propagation characteristic between the input electrodes of the convolver of the present invention. ID of this embodiment
T is an arc-shaped IDT with the radius of curvature R = 80λ of the electrode finger closest to the output electrode of the same IDT as in the conventional example, and the curvature center O of the arc of the IDT and the distance L = 80λ between the waveguide, that is, I
The distance between DT and the output electrode is around 160λ. The convolver is formed slightly displaced from the crystal axis of the substrate, but in this figure, unlike in FIG. 12, the first-order mode is not seen.

FIG. 5 shows the measurement result of the frequency characteristic of the convolution output of the element shown in FIG. It can be seen that, since there is no first-order mode, the frequency characteristic becomes flat and the element characteristic is improved.

In this embodiment, the waveguide is made of aluminum on the YZ-lithium niobate substrate, but the waveguide may be made of other metals. Also, other cuts, propagation directions, and other substrate materials may be used. However, since different metals have different mass loading effects, it is necessary to recalculate the guided mode. If the cut, the propagation direction, and the substrate are different, it is necessary to recalculate the guided mode. At this time,
The upper limit of the waveguide width is a range in which the first-order mode is not generated as the guided mode, and the lower limit is a range in which the frequency characteristic of the convolution efficiency is not a problem within the required band due to the frequency characteristic.

In the surface acoustic wave device described above,
Since the surface acoustic wave energy is concentrated by the waveguide, the IDT can be formed into a concave electrode as seen from the waveguide, for example, an arc-like shape as in the first embodiment. It is also possible to provide a means for concentrating the surface acoustic waves, such as a horn, an acoustic lens, or a multistrip coupler, between the IDT and the waveguide.

In the above embodiment, a monolithic piezoelectric substrate is used as the substrate, but a substrate having a layered structure in which a piezoelectric thin film is formed on a non-piezoelectric substrate may be used.

In the above embodiment, the elastic type convolver is shown as an example. However, a system using other nonlinear effects such as an AE type may be used.

In the present invention, it is also possible to use an IDT having double electrodes and suppressing reflection at the electrodes.

Further, in the present invention, it is also possible to use a so-called unidirectional IDT which inputs electric signals of three or more phases and excites surface acoustic waves unidirectionally. [Embodiment 2] FIG. 11 is a block diagram showing an example of a communication system using the surface acoustic wave device as described above. In the figure, 40 indicates a transmitter. This transmitter 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 receiver 41 and demodulated. Receiver 41
Is composed of an antenna 411, a high frequency signal processing unit 412, a synchronization circuit 413, a code generator 414, a spread demodulation circuit 415, and a demodulation circuit 416. The received 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 the transmission frequency band signal or converted into an appropriate intermediate frequency band signal.
The signal is input to the synchronizing circuit 413.

The synchronizing circuit 413 is a surface acoustic wave device 4131 according to the embodiment of the present invention and a modulation circuit 4132 for modulating the reference spread code input from the code generator 414 and a signal output from the surface acoustic wave device 4131. Signal processing circuit 4133 for processing the transmission signal and outputting the spread code synchronization signal and the clock synchronization signal for the transmission signal to the code generator 414.

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 4131, and a convolution operation of the two input signals is performed. Here, when the reference spreading code input from the code generator 414 to the modulation circuit 4132 is a code obtained by time-reversing the spreading code transmitted from the transmitting side, the surface acoustic wave device 4131 uses only the synchronization signal included in the reception signal. The spread code component and the reference spread code are the surface acoustic wave device 4
When they match on the waveguide 131, the correlation peak is output.

In the signal processing circuit 4133, the correlation peak is detected from the signal input from the surface acoustic wave device 4131, and the deviation amount of the code synchronization is calculated from the time from the code start of the reference spread code to the correlation peak output. , 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 spread code having the same clock and spread code phase as the spread code on the transmission side. This spread code is input to the spread demodulation circuit 415, and the signal before spread modulation is restored.

Since the signal output from the spread modulation / demodulation circuit 415 is a signal that has been modulated by a commonly used modulation method such as so-called frequency modulation or phase modulation, data demodulation is performed by the demodulation circuit 416 known to those skilled in the art. Done. [Third Embodiment] FIGS. 12 and 13 are block diagrams showing an example of a transmitter and a receiver of a communication system using the surface acoustic wave device as described above.

In FIG. 12, reference numeral 101 denotes a serial-parallel converter for converting data input in series into n pieces of parallel data,
Reference numerals 102-1 to 10-n are multiplier groups for multiplying each parallelized data by n spread codes output from the spread code generator, and 103 is n different spread codes and a spread code dedicated to synchronization. A spreading code generator to be generated, 104 is an adder for adding the synchronization-only spreading code output from the spreading code generator 103 and n outputs of the multiplier groups 102-1 to 102-n, 1
Reference numeral 05 is a high frequency stage for converting the output of the adder 104 into a transmission frequency signal, and 106 is a transmission antenna.

Further, in FIG. 13, 201 is a receiving antenna, 202 is a high frequency signal processing unit, 203 is a synchronizing circuit for capturing and maintaining synchronization with the spread code and clock on the transmitting side, and 204 is a code input from the synchronizing circuit 203. A spreading code generator that generates n + 1 spreading codes and a reference spreading code that are the same as the spreading code group on the transmission side according to the synchronization signal and the clock signal, and 205 is a carrier recovery spreading code output from the spreading code generator 204. And high-frequency signal processing unit 20
A carrier reproduction circuit for reproducing a carrier signal from the output of 2.
Reference numeral 206 denotes a baseband demodulation circuit that performs demodulation in the baseband using the output of the carrier reproduction circuit 205, the output of the high-frequency signal processing unit 202, and the output of the spreading code generator 204, which is n in number. Circuit 20
6 is a parallel-to-serial converter that performs parallel-to-serial conversion of n pieces of parallel demodulated data, which are the outputs of 6.

In the above-mentioned configuration, the transmitter first inputs
Data obtained by the serial / parallel converter 101
Is converted into n pieces of parallel data. Meanwhile, the diffusion mark
The code generator 103 has the same n + 1 code synchronization and
Different spreading code PN₀~ PN _nIs occurring. This
Chi PN₀Is dedicated to synchronization and carrier reproduction.
Input to the adder 104 without being modulated by the data
It The remaining n spreading codes are assigned to the multiplier groups 102-1 to 10n.
Modulated by n parallel data and input to adder 104
To be done. The adder 104 outputs the input n + 1 signals as lines.
Shaped baseband signal added to the high frequency stage 105
No. is output. The baseband signal is subsequently fed to the high frequency stage 1
It is converted to a high frequency signal with an appropriate center frequency at 05.
And transmitted from the transmitting antenna 106.

On the receiving side, the signal received by the receiving antenna 201 is appropriately filtered and amplified by the high frequency signal processing section 202, 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 203.

The synchronizing circuit 203 is a surface acoustic wave device 2031 according to the embodiment of the present invention and a modulation circuit 2032 for modulating the reference spread code input from the code generator 204 and a signal output from the surface acoustic wave device 2031. Signal processing circuit 203 for processing the signal and outputting the spread code synchronization signal and the clock synchronization signal for the transmission signal to the spread code generator 204.
It consists of three. An output signal from the high-frequency signal processing unit 202 and an output signal from the modulation circuit 2032 are input to the surface acoustic wave element 2031 and a convolution operation of the two input signals is performed.

Here, the modulation circuit 20 is supplied from the code generator 204.
If the reference spreading code input to 32 is a code obtained by time-reversing the synchronization dedicated spreading code transmitted from the transmitting side, the surface acoustic wave device 2031 has the synchronization dedicated spreading code component and the reference spreading code included in the received signal. A correlation peak is output when the code and the code match on the waveguide of the surface acoustic wave device 2031. In the signal processing circuit 2033, the surface acoustic wave device 2
The correlation peak is detected from the signal input from 031,
The code synchronization deviation amount is calculated from the time from the code start of the reference spreading code to the correlation peak output, and the code synchronization signal and the clock signal are output to the spreading code generator 204.

After the synchronization is established, the spreading code generator 204 generates a spreading code group in which the clock and the spreading code phase match the spreading code group on the transmitting side. Of these code groups, the spread code PN _{0 for} synchronization is input to the carrier reproduction circuit 205. The carrier reproduction circuit 205 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 202, by the synchronization-dedicated spreading code PN _0, and reproduces the carrier wave in the transmission frequency band or the intermediate frequency band. .

As the structure of the carrier reproducing circuit 205, for example, a circuit using a phase locked loop is used. The received signal and the spread code for synchronization PN ₀ 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 synchronization-specific spreading code on the transmitting side is not modulated with data. It is despread and carrier components appear in 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 a carrier component output from the band pass filter from the voltage controlled oscillator. The phase locked signal is output as the reproduced carrier wave. The reproduced carrier wave is input to the baseband demodulation circuit 206.

In the base band demodulation circuit, a base band signal is generated from the reproduced carrier wave and the output of the high frequency signal processing section 202. The baseband signal is divided into n pieces and spread code groups PN _{1 to} P which are outputs of the spread code generator 204.
Decoding is performed for each code division channel by N _n , and data demodulation is subsequently performed. The parallel demodulated n pieces of demodulated data are converted into serial data by the parallel-serial converter 207 and output.

Although the present embodiment is a case of binary modulation, other modulation methods such as quadrature modulation may be used.

[0050]

As described above, by setting the width of the output electrode to be the width that propagates substantially only the fundamental mode, it is possible to use a low cost ordinary piezoelectric substrate without using an expensive piezoelectric substrate with high orientation flat accuracy. Since a piezoelectric substrate with an orientation flat accuracy can be used, a convolver with high cost competitiveness can be realized.

Further, since it is not necessary to adjust the angle between the crystal orientation of the substrate and the direction of the output electrode of the convolver at the time of producing the device, it is possible to provide a convolver excellent in mass productivity.

Further, the frequency characteristic of the convolution output is flattened, and the element characteristic is improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a surface acoustic wave device (convolver) according to an embodiment of the present invention.

FIG. 2 is a graph showing the relationship between the waveguide width and the phase velocity of an elastic wave propagating in the waveguide in the Z-axis direction, which is obtained by potential approximation theory, using each mode as a parameter.

[Fig. 3] Two of the components under the waveguide of the fundamental mode of the guided mode
It is a graph (normalized with a value when the waveguide width is 1.6λ) showing the relationship between the power (convolution efficiency) and the waveguide width.

FIG. 4 is a measurement result of time response of propagation characteristics between input electrodes of the convolver of the present invention having a waveguide width of 1.5λ.

5 is a measurement result of frequency characteristics of the convolution output of the convolver of the present invention in FIG.

FIG. 6 is a conceptual diagram showing a surface acoustic wave element (convolver).

FIG. 7 shows amplitude-amplitude distributions of the 0th-order mode (basic mode) and the 1st-order mode when the output electrode width = 3λ.

FIG. 8 shows a conventional convolver in which the IDT when the output electrode of the convolver and the Z-axis of the crystal axis are deviated by 0.5 °.
In the arc-shaped IDT having the radius of curvature R = 80λ of the electrode finger closest to the output electrode, the distance L between the curvature center O of the arc of the IDT and the output electrode, and the relative value of the propagation characteristics at the center frequencies of the 0th-order mode and the 1st-order mode The result of having calculated the relationship of is shown.

FIG. 9 is a measurement result of the time response of the propagation characteristic between the input electrodes of the element when the conventional convolver having a waveguide width of 2.5λ is formed slightly deviated from the crystal axis of the substrate.

10 is a measurement result of frequency characteristics of the convolution output of the convolver of FIG.

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

FIG. 12 is a block diagram showing an example of a transmitter and a receiver of a communication system using the surface acoustic wave device of the present invention.

FIG. 13 is a block diagram showing an example of a transmitter and a receiver of a communication system using the surface acoustic wave device of the present invention.

[Explanation of symbols]

11 YZ-lithium niobate substrate 12 input comb-shaped electrode 13 electrode pad 14 waveguide (output electrode) 61 piezoelectric substrate 62, 63 input comb-shaped electrode 64 output electrode (Δv / v waveguide) T integration time 71 output electrode width = 3λ Amplitude distribution of zero-order mode (fundamental mode) when 72 Output electrode width = 3λ, first-order mode amplitude distribution

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takahiro Hachisu 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Koichi Egara 3-30-2 Shimomaruko, Ota-ku, Tokyo Kya Non Inc. (72) Inventor Norihiro Mochizuki 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (4)

[Claims] 1. An input transducer for exciting first and second surface acoustic waves formed on a substrate having piezoelectricity, and a propagation axis of the surface acoustic wave sandwiched between the two input transducers. Placed along the surface of the surface acoustic wave waveguide and the surface acoustic wave
In a surface acoustic wave device having an output electrode for taking out a convolution signal of two surface acoustic wave signals, the maximum value of the width of the output electrode acting as the waveguide is set such that only the guided fundamental mode can be propagated. A characteristic surface acoustic wave device. 2. The piezoelectric substrate is Y-cut lithium niobate, the output electrode acting as a waveguide provided in the Z-axis direction is formed of a metal thin film, and the output electrode width is Z-axis. The surface acoustic wave device according to claim 1, wherein the wavelength of the surface acoustic wave in the direction is approximately 1λ or more and 2λ or less. 3. The surface acoustic wave device according to claim 2, wherein the metal thin film is aluminum. 4. A communication system using the surface acoustic wave device according to claim 1.