JPH06314946A - Surface acoustic wave element, its design method and signal receiver and communication system using the same - Google Patents

Abstract

PURPOSE:To obtain a high coupling efficiency by providing a shape corresponding to an angle dependency of a speed of a surface acoustic wave depending on a direction when the surface acoustic wave propagates on an isotropic piezoelectric substrate for an input electrode and to concentrate the surface acoustic wave to a narrow range. CONSTITUTION:A guide path 14 is an ideal path guiding a surface acoustic wave to a guide path end face (origin position) as if it were almost regarded as a point wave source. Part 12 of a wave front of a surface acoustic wave is outputted from an end face of the guide path 14. The shape of an interdigital input electrode 11 is obtained by calculating the behavior of the surface acoustic wave outputted from an end face of the guide path 14 and propagating on an isotropic piezoelectric substrate. Since the distance and angle of each observing point from a wave source are found out by setting observing points to be a mesh, the distance vector and the wave number vector are obtained and the complex amplitude is calculated. Contour lines of the complex amplitude indicate the wave front. Thus, the shape of the interdigital input electrode 11 is decided corresponding to the shape of the surface acoustic wave spread from a point wave source obtained in this way.

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, and particularly to improving its efficiency.

[0002]

2. Description of the Related Art A surface acoustic wave element, particularly a surface acoustic wave convolver for extracting a convolution signal of two surface acoustic wave signals, has recently been increasing in importance as a key device for performing spread spectrum communication. Has been actively studied.

FIG. 16 is a schematic view showing an example of such a conventional surface acoustic wave element. In the figure, 91 is a Y cut (Z
Propagation) A piezoelectric substrate such as lithium niobate, 92, 9
Reference numeral 3 is a comb-shaped input electrode formed on the surface of the piezoelectric substrate 91, and 94 is an output electrode formed on the surface of the piezoelectric substrate 91. These electrodes are made of a conductive material such as aluminum and are usually formed by using a photolithography technique. A test wave signal input circuit 96 is connected to the input electrode 92, and a reference signal generator 95 is connected to the input electrode 93.
Are connected.

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 electrode 92 from the signal input circuit 96, the surface acoustic wave is excited by the piezoelectric effect of the substrate. Similarly, when an electric signal having the carrier angular frequency ω is input to the input electrode 93 from the reference signal generator 95, the surface acoustic wave is excited by the piezoelectric effect of the substrate. These two surface acoustic waves propagate in opposite directions on the piezoelectric substrate 91 between the two input electrodes 92 and 93, and due to the physical nonlinear effect of the piezoelectric substrate, a convolution signal that is a correlation output of the two input signals. (Carrier angular frequency 2ω) can be taken out from the output electrode 94.

X in the direction connecting the two input electrodes 92, 93
An axis is taken and the origin is located between the two input electrodes 92 and 93, and two surface acoustic waves are F (tx / v) exp {j (ωt-kx)}, G (t +
x / v) exp {j (ωt + kx)}, the product F (tx / v) · G (t + x / v) on the piezoelectric substrate 91 is the product of the nonlinear interaction.
A surface-independent surface wave exp (2jωt) is generated. This signal is integrated within the electrode length region by providing a uniform output electrode 94. This interaction region length is T
Then, S (t) = Kexp (2jωt) ∫ _{-T / 2} ^{T / 2} F (tx / v) ・ G (t + x / v) dx ・ ・ ・ ・ ・ ・ (1) Is taken out as. Here, the integration range may be substantially −∞ to + ∞ when the interaction region length T is sufficiently larger than the signal length, and when τ = tx / v, the above equation (1) becomes S (t) =-vKexp (2jωt) ∫ _-I ^I F (τ) ・ G (2t-τ) dτ ・ ・ ・ ・ ・ ・ (2) (where I in the integration range indicates ∞), and the signal is input by two inputs. It becomes the convolution of the signal. Such a convolution mechanism is described in, for example, “Shibayama,“ Application of Surface Acoustic Wave ”, Television, 30, 45.
7 (1976) ”and the like.

As described above, in the surface acoustic wave convolver,
With the configuration shown in FIG. 16, a convolution output signal of the detected signal and the reference signal is obtained. Output electrode 9 of FIG.
4 also serves as a waveguide. That is, when a metal thin film is vapor-deposited on a material having a piezoelectric effect, the propagation velocity of the surface acoustic wave in that portion is slowed down and the surface acoustic wave is concentrated there, and the surface acoustic wave is concentrated due to the mass load of the deposited metal. It is a waveguide that utilizes the effect.

Since the convolution efficiency is proportional to the square of the energy density, the output electrode operating as a waveguide should prevent a higher-order propagation transverse mode and increase the energy density, so that the convolution output should be taken out as much as possible. If the wavelength of the propagating surface acoustic wave is λ, the convolver for propagating the Y-cut lithium niobate in the Z direction is given by the requirement that the wavelength of the propagating surface acoustic wave be λ. 1.5-4λ
It is said that the degree is appropriate.

On the other hand, in the comb-shaped input electrode for converting an electric signal into a surface acoustic wave signal, in order to increase the ratio (coupling efficiency) of the energy of the surface acoustic wave generated there to the waveguide, the shape of the input electrode has been increased. A circular arc was devised.

[0009]

However, in an anisotropic piezoelectric substrate such as lithium niobate, the propagation velocity of a surface acoustic wave depends on the propagation direction, and therefore the energy of an arc-shaped electrode is limited to one point. There was a problem that it was difficult to concentrate and high coupling efficiency could not be obtained. That is, taking lithium niobate propagating in the Y-cut Z direction as an example, the relationship between the propagating direction and the propagating velocity is as shown in FIG. , The speed gradually decreases up to about ± 22 degrees. Therefore, when the arc of one part of the circle is made into the shape of the input electrode, the wave excited near the Z-axis of the electrode, that is, near the center of the arc is guided to the waveguide faster than the wave excited near the outside of the arc. It arrives and you can't concentrate the waves in a narrow area. Therefore, there is a problem that it is difficult to introduce many waves into the waveguide and high coupling efficiency cannot be obtained.

As one method for solving this problem,
USP No. In the 4649509, a frequency dispersive converter (comb-shaped input electrode) was installed in the vicinity of the waveguide, and the electrode shape was devised so that the surface acoustic waves in the waveguide mode of the waveguide would have equal wavefronts on the comb-shaped electrode. Although there are examples, it is very difficult to match the phase and intensity of surface acoustic waves in the vicinity of the waveguide with a wide frequency band.

[0011]

SUMMARY OF THE INVENTION Therefore, according to the present invention, by forming an input electrode having a shape corresponding to the angular dependence of the velocity of a surface acoustic wave propagating on a piezoelectric substrate, the surface acoustic wave can be narrowed. The purpose is to concentrate and obtain high coupling efficiency.

[0012]

According to the present invention, in order to achieve the above object, an input electrode is provided on an anisotropic piezoelectric substrate to generate a surface acoustic wave and concentrate the surface acoustic wave. In the surface acoustic wave element that is coupled to the waveguide by
The surface acoustic wave element is characterized in that the input electrode has a shape corresponding to the angular dependence of the velocity of the surface acoustic wave depending on the propagation direction when the surface acoustic wave propagates on the anisotropic piezoelectric substrate. To be done.

In one embodiment of the present invention, the input electrode is
It has a shape that is at least approximately equal to the equiphase surface of the surface acoustic wave emitted from the waveguide.

In one embodiment of the present invention, the input electrode is
The surface acoustic wave having the intensity distribution of the guided mode has a shape that is at least approximately equal to the equiphase surface of the surface acoustic wave when emitted from the waveguide. Here, there is a mode in which the input electrode is apodized according to the intensity distribution shown on the input electrode when the surface acoustic wave in the guided mode is emitted from the waveguide.

In another aspect of the invention, the impedance of the input electrode is matched to the impedance of the input circuit to the input electrode.

In one aspect of the present invention, the input electrode is a comb-shaped electrode. Here, there are a mode in which the comb-shaped electrode is a double electrode and a mode in which the comb-shaped electrode has unidirectionality.

According to the present invention, in order to achieve the above object, an input electrode is provided on an anisotropic piezoelectric substrate to generate a surface acoustic wave, and the surface acoustic wave is concentrated on a waveguide. A method of designing an input electrode of a surface acoustic wave element to be coupled, comprising calculating an angular dependence of a velocity of the surface acoustic wave depending on a propagation direction when the surface acoustic wave propagates on the anisotropic piezoelectric substrate, There is provided a method of designing an input electrode of a surface acoustic wave device, characterized in that the shape of the input electrode is determined according to the calculated angle dependency.

In one aspect of the present invention, the angle dependence is calculated by calculating the equiphase surface of the surface acoustic wave when the surface acoustic wave is emitted from the waveguide.

In one aspect of the present invention, the angle dependence is calculated by calculating an equiphase surface of the surface acoustic wave when the surface acoustic wave having the intensity distribution of the guided mode is emitted from the waveguide. To do.

Further, according to the present invention, there is provided a signal receiver for generating a convolution signal using the surface acoustic wave device of the present invention as described above and a communication system using the signal receiver.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of the present invention will be described below with reference to the drawings.

[Embodiment 1] FIG. 1 is a partially enlarged view of a first embodiment of a surface acoustic wave device such as a convolver according to the present invention, and particularly shows a comb-shaped input electrode. In FIG. 1, 15-16 is the center line of the element. Reference numeral 11 is a comb-shaped input electrode for converting an electric signal into a surface acoustic wave, reference numeral 13 is an electrode pad for wire bonding, and reference numeral 14 is a surface acoustic wave which can be almost regarded as a point wave source at the end face of the waveguide (origin position). It is an ideal waveguide to make waves. Reference numeral 12 is a part of the wavefront of the surface acoustic wave output from the end face of the waveguide 14.

The shape of the comb-shaped input electrode 11 is obtained by calculation means for calculating how the surface acoustic wave is output from the waveguide and propagates on the anisotropic piezoelectric substrate. Such calculation is described in "Surface Acoustic Wave Engineering; The Institute of Electronics and Communication Engineers; Supervised by Mikio Shibayama.
As described in "Chapter 3", the elastic equations of (3) and (4) and Maxwell's equations of (5) and (6) below are solved by solving them according to the respective conditions. can: ▽ · T = jω p - F ······ (3) ▽ s v = jω S ······ (4) ▽ × E = -jω B ······ (5 ) ▽ H = jω D + J (6) where T is stress, j is imaginary unit, ω is angular frequency, p is momentum, F is external force, v is particle velocity, and S is Distortion, E is electric field,
B is the magnetic flux density, H is the magnetic field, D is the electric flux density, and J is the current density (note that the underline indicates a vector: the same applies below).

It is extremely difficult to find the exact solution of the above equation. So, for example, simply use "JBGreen et
al., IEEE Transactions on sonics and ultrasonics,
vol.30. No.1, January 1983, p 43- ", the anisotropy is taken into account in the wave theory using the Huygens theorem of surface acoustic waves. It can be approximated: a = exp {j (ωt− k · r )} / | r | ^1/2 (7) where a is the complex amplitude at the measurement point and ω is the angle of the surface acoustic wave. Frequency, k is a wave number vector, r is a distance vector from the point source to the observation point.

If the observation points are set in a mesh pattern, the distance and angle from each wave source of each observation point can be known.
r and the wave number vector k obtained by k = 2πf / v are obtained, and the complex amplitude a can be calculated. The contour line of this complex amplitude a shows the wavefront. In the case of Y-cut lithium niobate, the speed in the Z-axis direction is about 3488 m / s, whereas it is about 3430 m at the slowest speed of ± 22 °.
/ S, the wavefront of the surface acoustic wave from the actual point source is close to a circle, but in FIG. 1, the wavefront distortion due to the angular dependence of the propagation velocity is emphasized to explain the present invention. I am drawing. Since the propagation of surface acoustic waves is reversible, if surface acoustic waves are excited toward the point source from the entire surface of the surface acoustic wave spreading from the point source, the surface acoustic waves will concentrate near the center. The coupling efficiency with the waveguide is improved. That is, the shape of the comb-shaped input electrode 11 is determined corresponding to the shape of the surface of the surface acoustic wave spreading from the point wave source obtained as described above.

[Embodiment 2] FIG. 2 is a partially enlarged view of a second embodiment of a surface acoustic wave element according to the present invention, and particularly shows a comb-shaped input electrode. The difference between this embodiment and the first embodiment is that a wave source having the same width as the waveguide is assumed in this embodiment. In FIG. 2, 15-16
Is the centerline of the device. Reference numeral 11 is a comb-shaped input electrode that converts an electric signal into a surface acoustic wave, 13 is an electrode pad for wire bonding, and 24 is a wave source whose waveguide width is equal to the waveguide width, and the intensity of the wave source is constant within this width. This is an ideal waveguide for propagating a linear surface acoustic wave. Reference numeral 22 is a part of the wavefront of the surface acoustic wave output from the end face of the waveguide 24. In this case, the complex amplitude of the mesh-shaped observation points for obtaining the wavefront 22 is expressed by the following equation (8) by integrating the equation (7) with the size of the wave source (width of the waveguide 24). Is obtained: a = ∫ [exp {j (ωt− k · r )} / | r | ^1/2 ] dσ ··· (8) where dσ is a minute section of the wave source.

The surface acoustic wave excited by the comb-shaped input electrode having a shape corresponding to the shape of the wavefront thus obtained has a high coupling efficiency with the waveguide of a predetermined width and a finite size.

[Embodiment 3] Next, a third embodiment will be described. The difference of this embodiment from the second embodiment is that the guided mode of the surface acoustic wave propagating in the waveguide is taken into consideration.

The eigenmode of the surface acoustic wave propagating in the waveguide in which the metal thin film is deposited on the piezoelectric substrate is the boundary between the metal deposition surface (electrically short-circuited surface) and the surface on which nothing is deposited (electrically open surface). It is derived from the conditions, and the amplitude intensity distribution as shown in FIG. 5 is obtained. The eigenmode of the surface acoustic wave propagating in this waveguide is
"Koshiba, Suzuki, Theology (B), J61-B, p689
(1978) ”and the like. Also, YZ
-For lithium niobate, see `` RV Schmidt & L.
A. Coldren, IEEE Transactions on sonics and ultras
onics, vol.su-22. No.2, March 1975, p115- ".

The surface acoustic wave having this waveguide mode is output from the waveguide and propagates on the piezoelectric substrate. A small section of each wave source is guided to the waveguide entrance by the integration method similar to the equation (8). It can be obtained by calculating the velocity and phase of the surface acoustic wave at each measurement point when it has the same intensity as the mode. Figure 3
FIG. 3 is a partially enlarged view of a surface acoustic wave device of the present invention having an input electrode matched to a phase surface of a surface acoustic wave thus obtained, and particularly a comb-shaped input electrode. In FIG. 3, members having the same functions as those in FIGS. 1 and 2 may be designated by the same reference numerals. In this embodiment, the isophase surface of the surface acoustic wave output from the waveguide having a width of 2λ at the center frequency of 200 MHz has a radius of curvature r =
The shape of the input electrode 11 was determined by calculating and correcting how much it deviated from the arc of 171 λ and the central angle θ = 6.0 °.

By the way, the electric impedance of the comb-shaped input electrode is proportional to the length of the intersecting portion of the paired electrodes, and the number of pairs of electrodes is inversely proportional to the bandwidth. Since the wavefront can be calculated as described in Examples 1 to 3, the length of the electrode is uniquely determined. For example, in YZ-lithium niobate, when the center frequency is 200 MHz, the bandwidth is 40 MHz, and the impedance is 50Ω, the electrode length (intersection width) is about 0.8 mm and the logarithm is about 3.5.

The comb-shaped input electrodes of Examples 1 to 3 are manufactured according to the electrode length thus determined. FIG. 7 is a three-dimensional graph showing the intensity of surface acoustic waves excited by the comb-shaped input electrode designed in Example 3. In the figure, 11 is a comb-shaped input electrode of the present invention. For comparison, a simple arc-shaped comb-shaped electrode 61 (r
= 83.3λ, θ = 14 °), the intensity of the surface acoustic wave excited is shown in FIG. In the example shown in the figure, the surface acoustic wave spreads without concentrating on one point where the amplitude is large. However, in the comb input electrode of the present invention, the surface acoustic wave concentrates near the center and is guided from the comb input electrode. The coupling efficiency with the waveguide is improved.

[Embodiment 4] FIG. 4 is a partially enlarged view of a surface acoustic wave device according to a fourth embodiment of the present invention, particularly showing a comb-shaped input electrode. In FIG. 4, reference numeral 15-16 is the center line of the element. Reference numeral 41 is a comb-shaped input electrode for converting an electric signal into a surface acoustic wave, and the electrode fingers of the electrode 41 have a plurality of different intersecting widths.

In the comb-shaped input electrode 41, surface acoustic waves are excited only at the intersecting portions of the electrode fingers. Example 1 above
In the comb-shaped input electrodes as shown in FIGS. 3 to 3, since the electromechanical coupling coefficient differs depending on the angle of each part of the input electrode, the surface acoustic wave having the amplitude intensity as shown in FIG. 9A is excited. On the other hand, the amplitude intensity of the surface acoustic wave output from the waveguide has a distribution as shown in FIG. 9B on the comb-shaped input electrode.

In this embodiment, in the comb-shaped input electrode, the surface acoustic wave having the amplitude intensity of the eigenmode of the waveguide is emitted from the end face of the waveguide, and the intensity distribution in the input electrode portion (see FIG. 9).
(A)) When parts of the comb-shaped electrode generate surface acoustic waves proportional to the angle-dependent electromechanical coupling coefficient, the parts that do not match the above intensity distribution (FIG. 9B) are compensated as much as possible. Are apodized. In the vicinity of the electrode of FIG. 4 of the present invention, a surface acoustic wave having an amplitude intensity distribution as shown in FIG. 9C is excited, and the surface acoustic wave propagates with the intensity distribution shown in FIG. By changing the crossing width of the electrode fingers in accordance with the intensity distribution in which the waveguide mode is shown on the comb-shaped electrode as in this embodiment,
The coupling efficiency is further improved as compared with the third embodiment.

Although the center frequency, the bandwidth and the electric impedance of the comb-shaped input electrode in the above-described embodiments have concrete numerical values, these do not limit the present invention.

Further, in the present invention, the comb-shaped input electrode may be a double electrode as shown in FIG. 10 to suppress reflection of surface acoustic waves at the electrode. In FIG. 10, 1
Reference numeral 11 is a double comb-shaped input electrode, 113 is an electrode pad, and 114 is a waveguide.

Further, in the comb-shaped input electrode of the present invention, for example, as shown in FIG. 11, a so-called unidirectional comb-shaped electrode for inputting electric signals of three or more phases and exciting surface acoustic waves unidirectionally. It is also possible to In FIG. 11, 121 is a comb-shaped input electrode, 123 is an electrode pad, and 124 is a waveguide. By thus exciting the surface acoustic wave only in one direction, the efficiency can be further improved.

In the above embodiments of the present invention, for simplification, the calculation method which does not take into consideration the change in the waveguide end face of the waveguide mode and the phase change when the surface acoustic wave is output from the waveguide has been described. However, it is also possible to use a calculation method using the finite element method or the boundary element method satisfying the boundary conditions satisfying the above expressions (3) to (6).

[Embodiment 5] FIG. 12 is a block diagram showing an example of a communication system using the surface acoustic wave device as described above. In the figure, 120 indicates a transmitter. This transmitter spread-spectrum-modulates a signal to be transmitted using a spread code and transmits the signal from an antenna 1201.
The transmitted signal is received by the receiver 121 and demodulated. The receiver 121 includes an antenna 1211, a high frequency signal processing unit 1212, a synchronization circuit 1213, and a code generator 121.
4, a spread demodulation circuit 1215 and a demodulation circuit 1216. The reception signal received by the antenna 1211 is appropriately filtered and amplified by the high frequency signal processing unit 1212, 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 synchronization circuit 1213.

The synchronizing circuit 1213 includes the surface acoustic wave element (surface acoustic wave device) 12131 described in the embodiment of the present invention.
A modulation circuit 12132 for modulating the reference spread code input from the code generator 1214, and a surface acoustic wave device 121.
The code generator 1 processes the signal output from 31 to generate a spread code synchronization signal and a clock synchronization signal for the transmission signal.
And a signal processing circuit 12133 for outputting to 214.

An output signal from the high frequency signal processing unit 1212 and an output signal from the modulation circuit 12132 are input to the surface acoustic wave element 12131, and a convolution operation of the two input signals is performed. Here, the code generator 121
4 that the reference spreading code input to the modulation circuit 12132 is a code obtained by time-reversing the spreading code transmitted from the transmitting side, the surface acoustic wave device 12131 has the synchronization dedicated spreading code component included in the reception signal. And the reference diffusion code match on the waveguide of the surface acoustic wave device 12131, the correlation peak is output.

In the signal processing circuit 12133, the correlation peak is detected from the signal input from the surface acoustic wave device 12131, the shift amount of the code synchronization is calculated from the time from the code start of the reference spread code to the output of the correlation peak, and the code is calculated. The sync signal and the clock signal are output to the code generator 1214. After the synchronization is established, the code generator 1214 generates a spread code having the same clock and spread code phase as the spread code on the transmitting side. This spread code is input to the spread demodulation circuit 1215, and the signal before spread modulation is restored.

Since the signal output from the spread demodulation circuit 1215 is a signal modulated by a generally used modulation method such as so-called frequency modulation or phase modulation, data demodulation is performed by the demodulation circuit 1216 well known to those skilled in the art. Done.

[Embodiment 6] FIGS. 13 and 14 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, respectively.
In this embodiment, the communication method is CDM (Code Di).
The vision multiplexing method is used. The details will be described below.

In FIG. 13, reference numeral 1301 is a serial-parallel converter for converting serially input data into n pieces of parallel data, and 1302-1 to 1302-n are parallelized data and outputs from the spread code generator. A spreader code group for multiplying n spread codes generated by the spread code generator 1303, a spread code generator for generating n different spread codes and a spread code dedicated for synchronization, and 1304 for output from the spread code generator 1303. Synchronous spreading code and multiplier groups 1302-1 to 1302-
An adder for adding the n outputs of n, a high-frequency stage 1305 for converting the output of the adder 1304 into a transmission frequency, and a transmission antenna 1306.

In FIG. 14, reference numeral 1401 is a receiving antenna, 1402 is a high frequency signal processing section, 1403 is a synchronizing circuit for supplementing and maintaining synchronization with the spread code and clock on the transmitting side, 1404 is a code input from the synchronizing circuit 1403. A spreading code generator that generates (n + 1) spreading codes and reference spreading codes that are the same as the spreading code group on the transmission side according to the synchronization signal and the clock signal, and 1405 is a carrier reproduction spreading output from the spreading code generator 1404. A carrier reproducing circuit for reproducing a carrier signal from the code and the output of the high-frequency processed signal section 1402, 1406 is a carrier reproducing circuit 140.
5, a baseband demodulation circuit for performing demodulation in the baseband using the n spread codes output from the high-frequency signal processing unit 1402 and the spread code generator 1404, 140
Reference numeral 7 is a parallel-serial converter for parallel-serial converting the n pieces of parallel demodulated data output from the baseband demodulation circuit 1406.

In the above configuration, on the transmission side, first, the input data is converted by the serial / parallel converter 1301 into n parallel data equal to the number of code division multiplexes. On the other hand, the spread code generator 1303 generates (n + 1) spread codes PN0 to PNn having the same code synchronization but different from each other. Of these, PN0 is dedicated to synchronization and carrier reproduction, and is directly input to the adder 1304 without being modulated by the parallel data. The remaining n spread codes are modulated by n parallel data in the multiplier groups 1302-1 to 1302-n and input to the adder 1304.
The adder 1304 linearly adds the (n + 1) input signals and adds the added baseband signals to the high frequency stage 1
Output to 305. The baseband signal is subsequently converted into a high frequency signal having an appropriate center frequency in the high frequency stage 1305 and transmitted from the transmission antenna 1306.

On the receiving side, the signal received by the receiving antenna 1401 is appropriately filtered and amplified by the high frequency signal processing section 1402 and is output as it is 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 1403. The synchronization circuit 1403 includes a surface acoustic wave element (surface acoustic wave device) 14031 described in the embodiment of the present invention, and a code generator 1404.
Modulation circuit 14 for modulating the reference spread code input from
032 and a signal processing circuit 14033 which processes the signal output from the surface acoustic wave device 14031 and outputs a spread code synchronization signal and a clock synchronization signal for the transmission signal to the code generator 1404. Surface acoustic wave element 14
An output signal from the high-frequency signal processing unit 1402 and an output signal from the modulation circuit 14032 are input to 031, and convolution calculation of two input signals is performed. Here, assuming that the reference spreading code input from the code generator 1404 to the modulation circuit 14032 is a code obtained by time-reversing the synchronization dedicated spreading code transmitted from the transmitting side, the surface acoustic wave device 14031 receives the received signal. Of the synchronization-dedicated spreading code component and the reference spreading code included in the surface acoustic wave device 14
When they coincide with each other on the waveguide 031, the correlation peak is output. In the signal processing circuit 14033, the surface acoustic wave device 1
The correlation peak is detected from the signal input from 4031,
The shift amount of code synchronization is calculated from the time from the code start of the reference spread code to the output of the correlation peak, and the code synchronization signal and the clock signal are output to the spread code generator 1404.
After the synchronization is established, the spread code generator 1404 generates a spread code group having the same clock and spread code phase as the spread code group on the transmission side. The spreading code PN0 dedicated to synchronization of these code groups is input to the carrier reproducing circuit 1405.
The carrier reproduction circuit 1405 uses the synchronization-dedicated spreading code PN0.
Then, 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 1402, is despread and the carrier wave in the transmission frequency band or the intermediate frequency band is reproduced. For the configuration of the carrier reproduction circuit 1405, for example, a circuit using a phase locked loop is used. The received signal and the spread code for synchronization PN0 are multiplied by the multiplier. After synchronization is established, the clock and code phase of the synchronization dedicated spreading code in the received signal and the reference synchronization dedicated spreading code match, and the synchronization dedicated spreading code on the transmission side is not modulated with data. Is despread and the carrier component appears 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 consisting 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 1406. In the baseband demodulation circuit, a baseband signal is generated from the reproduced carrier wave and the output of the high frequency signal processing section 1402. The baseband signal is divided into n pieces and despreaded for each code division channel by PN1 to PNn of the spread code group which is the output of the spread code generator 1404, and then data demodulation is performed. The parallel demodulated n demodulated data are converted into serial data by the parallel-serial converter 1407 and output.

By using the CDM method as the communication method, a plurality of data can be bundled and transmitted, and the transmission capacity can be increased.

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

[0052]

As described above, according to the present invention, the surface acoustic wave is narrowed by forming the input electrode into a shape corresponding to the angular dependence of the velocity of the surface acoustic wave propagating on the piezoelectric substrate. High coupling efficiency can be obtained by concentrating on the range. In particular, in a convolver that uses the physical nonlinear effect, the output is proportional to the product of two surface acoustic waves, and the output efficiency is proportional to the square of the coupling efficiency between both ends of the waveguide (output electrode) and the input electrode. Therefore, the improvement of the coupling efficiency between the waveguide and the input electrode has a great influence.

By using the surface acoustic wave device of the present invention in a signal receiver or a communication system, efficient communication can be performed.

[Brief description of drawings]

FIG. 1 is a partially enlarged view of a surface acoustic wave device according to a first exemplary embodiment.

FIG. 2 is a partially enlarged view of a surface acoustic wave device according to a second embodiment.

FIG. 3 is a partially enlarged view of a surface acoustic wave device according to a third embodiment.

FIG. 4 is a partial enlarged view of a surface acoustic wave device according to a fourth exemplary embodiment.

FIG. 5 is a diagram showing eigenmodes of surface acoustic waves propagating in a waveguide in which a metal thin film is deposited on a piezoelectric substrate.

FIG. 6 is a three-dimensional graph showing the intensity of surface acoustic waves excited by a comb-shaped input electrode.

FIG. 7 is a three-dimensional graph showing the intensity of surface acoustic waves excited by a comb-shaped input electrode.

FIG. 8 is a three-dimensional graph showing the intensity of a surface acoustic wave excited by a comb-shaped input electrode.

FIG. 9 is a diagram showing the amplitude intensity of a surface acoustic wave excited by a comb-shaped input electrode.

FIG. 10 is a partially enlarged view in which the input electrode of Example 3 is a double electrode.

FIG. 11 is a partially enlarged view in which the input electrode of Example 3 is a unidirectional electrode.

FIG. 12 is a configuration diagram of a signal receiver and a communication system using the surface acoustic wave device of the present invention.

FIG. 13 is a configuration diagram of a transmitter of the communication system according to the sixth embodiment.

FIG. 14 is a configuration diagram of a receiver of the communication system according to the sixth embodiment.

FIG. 15 is a diagram showing a relationship between a propagation direction and a propagation velocity of Y-cut Z-direction propagating lithium niobate.

FIG. 16 is a schematic view showing an example of a conventional surface acoustic wave element.

[Explanation of symbols]

 11, 41 Comb-shaped input electrodes 12, 22, 32 Wavefront 13 Electrode pad 14, 24, 34 Waveguide (output electrode)

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

Claims (13)

[Claims] 1. A surface acoustic wave device in which an input electrode is provided on an anisotropic piezoelectric substrate to generate a surface acoustic wave, and the surface acoustic wave is concentrated and coupled to a waveguide. A surface acoustic wave element having a shape corresponding to the angular dependence of the velocity of the surface acoustic wave depending on the propagation direction when the surface acoustic wave propagates on a piezoelectric substrate. 2. The surface acoustic wave device according to claim 1, wherein the input electrode has a shape that is at least approximately equal to an equiphase surface of the surface acoustic wave emitted from the waveguide. 3. The input electrode has a shape at least approximately equal to an equiphase surface of a surface acoustic wave having a waveguide mode intensity distribution when the surface acoustic wave is emitted from the waveguide. The surface acoustic wave element according to claim 1. 4. The input electrode according to claim 3, wherein the input electrode is apodized according to the intensity distribution shown on the input electrode when the surface acoustic wave of the guided mode is emitted from the waveguide. Surface acoustic wave device. 5. The surface acoustic wave device according to claim 1, wherein the impedance of the input electrode is matched with the impedance of the input circuit to the input electrode. 6. The surface acoustic wave device according to claim 1, wherein the input electrode is a comb-shaped electrode. 7. The surface acoustic wave device according to claim 6, wherein the comb-shaped electrode is a double electrode. 8. The surface acoustic wave device according to claim 6, wherein the comb-shaped electrode has unidirectionality. 9. A method of designing an input electrode of a surface acoustic wave element, comprising: providing an input electrode on an anisotropic piezoelectric substrate to generate a surface acoustic wave; and concentrating and coupling the surface acoustic wave to a waveguide. The angular dependence of the velocity of the surface acoustic wave depending on the propagation direction when the surface acoustic wave propagates on the anisotropic piezoelectric substrate is calculated, and the shape of the input electrode is determined according to the calculated angular dependence. A method for designing an input electrode of a surface acoustic wave device, comprising: 10. The elasticity according to claim 9, wherein the angle dependence is calculated by calculating an equiphase surface of the surface acoustic wave when the surface acoustic wave is emitted from the waveguide. Design method of input electrode of surface acoustic wave device. 11. The angle dependence is calculated by calculating an equiphase surface of a surface acoustic wave having a waveguide mode intensity distribution when the surface acoustic wave is emitted from the waveguide. A method for designing an input electrode of a surface acoustic wave device according to claim 9. 12. A signal receiver using the surface acoustic wave device according to claim 1 for generating a convolution signal. 13. A communication system using the surface acoustic wave device according to claim 1 for generating a convolution signal.