JPH0974332A - Surface acoustic wave device and communication system using the same - Google Patents

Abstract

(57) 【Abstract】 PROBLEM TO BE SOLVED: To increase the electromechanical coupling coefficient K ² of a surface acoustic wave excited from a comb-shaped input electrode, and further to output electrode (waveguide).
This is to squeeze and couple surface acoustic waves on the end faces. At least two comb-shaped input electrodes for exciting first and second surface acoustic waves are formed on a main surface of a piezoelectric substrate which is a piezoelectric substrate or a laminated substrate in which a piezoelectric substance is formed on a non-piezoelectric substance. A surface acoustic wave device having an output electrode for taking out the convolution signal of the two surface acoustic waves by utilizing the non-linear effect of the piezoelectric substrate, on the comb-shaped input electrode, and the comb-shaped input electrode and the output electrode. An insulative insulating film is formed on the substrate in the region between.

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 convolver and a communication system using the same.

[0002]

2. Description of the Related Art Currently, surface acoustic waves (SAW: Surface Ac)
Various applications and researches have been made on the oustic wave) element. Among them, the surface acoustic wave convolver is a spread spectrum (S) that has been attracting attention as a next-generation communication technology.
S) As a key device for communication, its importance is increasing more and more.

This surface acoustic wave (SAW) is an acoustic wave that propagates along the surface or boundary surface of a propagation medium such as a piezoelectric substrate, and its energy is mostly contained within about one wavelength from the surface. High-density elastic energy can be easily obtained even with extremely small input power, and the nonlinear effect becomes larger than that of bulk waves, 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. 4 is a schematic view showing a conventionally known surface acoustic wave convolver. In the figure, 51 is a piezoelectric material substrate such as a Y-cut (Z-propagation) lithium niobate or a laminated substrate in which a piezoelectric material is laminated on a non-piezoelectric material, and 52 is formed on the surface of the piezoelectric substrate 51. Standard comb-shaped input electrode (IDT: Interdigital Transduce
r) and 53 are output electrodes as waveguides formed on the surface of the piezoelectric substrate 51, and 54 is a parabolic horn provided in a region between the regular comb input electrode 52 and the output electrode 53.

The input / output electrodes and the parabolic horn are made of a conductive material such as aluminum and are 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, the surface acoustic wave is excited by the piezoelectric effect of the piezoelectric substrate.

These two surface acoustic waves are narrowed down by the parabolic horn 54, and the output electrode 53
To the end face of. The output electrode 53 functions as a waveguide, and the piezoelectric substrate 5 is enclosed while being confined in the output electrode.
1 propagates in the opposite directions.

The two surface acoustic waves hitting 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

[0011]

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

[0012]

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

[0013]

(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

[0014]

(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 Device Technology Handbook” edited by Japan Society for the Promotion of Science 150th Committee, Ohmsha, Ltd., (1991), p. ~ P
205, p371-p374 and the like.

[0016]

However, in order to increase the convolution efficiency of the surface acoustic wave convolver, the following points must be solved.

In the surface acoustic wave convolver,
There are several ways to increase solution efficiency
But one of them is the electromechanical coupling at the comb-shaped input electrode.
Coefficient K ²There is a way to increase the value of.

However, since the electromechanical coupling coefficient K ² usually greatly depends on the properties of the piezoelectric substrate itself, the value of the electromechanical coupling coefficient K ² is uniquely determined when the piezoelectric substrate is determined.

Therefore, as described in the above-mentioned conventional example, the surface acoustic wave excited from the normal type comb-shaped electrode is compressed by the parabolic horn, the energy density of the surface acoustic wave is increased and the surface acoustic wave is coupled to the end face of the waveguide, and the convolution efficiency is increased. Even if the value is increased, the value of the electromechanical coupling coefficient K ² is determined by the material type of the piezoelectric substrate, so further improvement in efficiency cannot be expected.

[0020]

SUMMARY OF THE INVENTION It is an object of the present invention to increase the electromechanical coupling coefficient K ² of a surface acoustic wave excited from a comb-shaped input electrode in a surface acoustic wave convolver device using a comb-shaped input electrode, and further output A surface acoustic wave is squeezed and coupled to the end face of the electrode (waveguide).

In view of the above object, the present invention forms an insulating film such as SiO ₂ (silicon oxide film) on the upper surface of the comb-shaped input electrode portion of the surface acoustic wave convolver element, and further provides a space between the comb-shaped input electrode and the output electrode. S on the area and output electrode (waveguide)
It is characterized in that a parabolic horn is formed by an insulating film such as iO ₂ .

According to the above structure, in the surface acoustic wave convolver element, the electromechanical coupling coefficient K ^{2 of the} surface acoustic wave excited by the comb-shaped input electrode portion is increased, and the surface acoustic wave excited by the comb-shaped input electrode is further increased. Since it is compressed, the energy density is increased and the energy is coupled to the end face of the waveguide, which leads to improvement in convolution efficiency.

At the same time, since it also serves as a protective film on the pattern surface of the input electrode and the output electrode, the performance and reliability as a surface acoustic wave convolver are improved.

Further, as a structure of the present invention, in the surface acoustic wave element, a region on the output electrode is added to a portion where the insulating film is formed. Further, in the surface acoustic wave device, the insulating film is formed of a silicon oxide film. Further, the insulating film formed in the region between the comb-shaped input electrode and the output electrode has a shape that focuses surface acoustic waves excited from the comb-shaped input electrode to the output electrode inlet end surface. It is characterized by The shape of the insulating film formed in the region between the comb-shaped input electrode and the output electrode is
It is characterized by having a parabolic horn shape. Further, it is characterized in that an arc shape is used for the comb-shaped input electrode. Further, Y-cut Z-propagation lithium niobate is used for the piezoelectric substrate.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION

 << First Embodiment >> An embodiment of the present invention will be described below.

FIG. 1 is a schematic diagram showing a first embodiment of a surface acoustic wave convolver according to the present invention. In the figure, 1
Reference numeral 1 denotes a piezoelectric substrate such as a Y-cut (Z propagation) lithium niobate or a laminated substrate in which a piezoelectric substance is laminated on a non-piezoelectric substance, and 12 is a regular substrate formed on the surface of the piezoelectric substrate 11. Type comb-shaped input electrode, 13 is an output electrode as a waveguide formed on the surface of the piezoelectric substrate 11, and 14 is an S electrode.
An insulating film such as iO ₂ (silicon oxide film).

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

The insulating film 14 is also formed by photolithography in the region up to the upper end of the regular comb input electrode 12 and the end face of the waveguide 13, and its shape is excited from the regular comb input electrode 12. The surface acoustic wave has a shape such that it is compressed and coupled to the end face of the waveguide 13, for example, a shape like a horn.

In the surface acoustic wave element having such a structure,
Comb-shaped input electrodes 1 arranged near both ends of the piezoelectric substrate 11
When an electric signal of the carrier angular frequency ω is input to 2, surface acoustic waves are excited by the piezoelectric effect of the piezoelectric substrate 11, the output electrode 13 acts as a ΔV / V waveguide, and the output electrode as a waveguide While being confined, they propagate in opposite directions on the piezoelectric substrate 11. Then, the two waves collide with each other on the output electrode 13 and are taken out from the output electrode 13 as a convolution signal having an angular frequency 2ω due to the physical nonlinear effect of the piezoelectric substrate 11.

Here, the ΔV / V waveguide has a surface of the piezoelectric substrate electrically short-circuited to reduce the propagation velocity of the surface acoustic wave as compared with the free surface and confine the surface acoustic wave to the short-circuited portion. Is.

FIG. 2 is a simulation graph showing the magnitude of the amplitude intensity with respect to the time change of a surface acoustic wave at a certain point on a Y-cut (Z-propagation) lithium niobate substrate.

The horizontal axis represents time and the vertical axis represents the amplitude of the surface acoustic wave at each time. At this time, the unit of the magnitude of the vertical axis is arbitrary because it is proportional to the magnitude of the voltage of the input signal input to the comb-shaped input electrode.

In the figure, 21 indicates the magnitude of the amplitude when the insulating film is not formed on the piezoelectric substrate, and 22 indicates the thickness of the SiO ₂ film on the piezoelectric substrate. 1
It represents the magnitude of the amplitude when μm is formed.

When an insulating film SiO ₂ film of 1 μm is formed on the piezoelectric substrate from 21 and 22 in the figure, the surface acoustic wave is delayed in time as compared with a free surface without an insulating film. You can see that it has arrived.

This means that since the SiO ₂ film is formed on the surface of the surface acoustic wave element, the velocity of the surface acoustic wave changes slower than that of the surface of the piezoelectric substrate which is a free surface. .

Therefore, in FIG. 1, if the SiO ₂ film is provided in the region between the comb-shaped input electrode 12 and the waveguide 13, and the shape is such that it is coupled to the end face of the waveguide 13, the SiO ₂ film is formed. Since there is a difference in the velocity of the surface acoustic wave between the free surface and the free surface, and the surface acoustic wave energy can be confined to the slow speed region, that is, the part where the SiO ₂ film is formed, the parabolic horn Can be used as

It is also seen from FIG. 2 that when the SiO ₂ film is formed to a thickness of 1 μm on the piezoelectric substrate, the amplitude of the surface acoustic wave is larger than that of a free surface on which the insulating film is not formed. That is, by forming an insulating film such as a SiO ₂ film on the upper part of the comb-shaped input electrode, the electromechanical coupling coefficient K ² increases and the energy of the surface acoustic wave increases.

From the above, in the surface acoustic wave convolver having the normal type comb-shaped input electrode and the output electrode (waveguide) formed on the surface of the piezoelectric substrate such as the Y-cut (Z-propagation) lithium niobate substrate, the normal type By forming an insulating film such as a SiO ₂ film on the upper part of the comb-shaped input electrode and the region up to the end face of the waveguide, the electromechanical coupling coefficient K ^{2 of the} surface acoustic wave excited from the normal-shaped comb-shaped input electrode can be changed to the normal-shaped comb-shaped electrode. A surface acoustic wave which is improved on the input electrode and has a large amplitude (large surface acoustic wave energy) is obtained. Furthermore, SiO
Confined to a parabolic horn formed by an insulating film such as ₂ films, increasing the surface acoustic wave energy density,
Coupling to the end face of the waveguide.

As a result, the convolution efficiency (generally, the electric input power input to the input electrodes on both sides is P
If the output power that can be taken out from the central output electrode is POUT, the convolution efficiency F is F =
It is represented by (POUT / P1, P2). ) Is improved, and in addition, it also serves as a protective film for the pattern surface, which has been used as a conventionally well-known one, so that not only the performance as a surface acoustic wave convolver but also the reliability is improved.

<< Second Embodiment >> An embodiment of the present invention will be described below.

FIG. 3 is a schematic view showing a second embodiment of the surface acoustic wave convolver according to the present invention.

In the figure, 31 is a Y-cut (Z-propagation) lithium niobate piezoelectric substrate, 32 is a regular comb-shaped input electrode formed on the surface of the piezoelectric substrate 31, and 33 is the piezoelectric substrate 3.
An output electrode as a waveguide formed on the surface of 1.
Is an insulating film such as SiO ₂ (silicon oxide film).

The electrodes of the normal type comb-shaped input electrode 32 and the output electrode 33 are made of a conductive material such as aluminum, and are usually formed directly on the surface of the piezoelectric substrate 31 by a photolithography technique.

The insulating film is also formed by photolithography on the output electrode 33 and the region up to the end face of the regular comb input electrode 32 and the end face of the output electrode 33, and the shape thereof is the regular comb input electrode. The surface acoustic wave excited from 32 is compressed to the end surface of the output electrode 33 and is coupled, for example, a shape like a horn.

In the surface acoustic wave device having such a structure,
When an electric signal of the carrier angular frequency ω is input to the comb-shaped input electrodes 32 on both sides, the surface acoustic waves are excited by the piezoelectric effect of the substrate, and the output electrode 33 acts as a ΔV / V waveguide, and the output electrode 33 (waveguide) ), They propagate in opposite directions on the piezoelectric substrate 31. Then, the above two waves collide with each other on the output electrode 33 and are extracted from the output electrode 33 as a 2ω convolution signal due to the physical nonlinear effect of the piezoelectric substrate 31.

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 FIG. 2, as described above, a simulation graph showing the magnitude of the amplitude intensity with respect to the time change of the surface acoustic wave at one point on the Y-cut (Z-propagation) lithium niobate substrate is shown. SiO on the piezoelectric substrate
_The surface acoustic waves 22 propagating through the _two films represent that the piezoelectric substrate arrives later than the one having a free surface on the piezoelectric substrate.

This is because there is a difference in the velocity of the surface acoustic wave between the portion where the SiO ₂ film is formed on the piezoelectric substrate and the free surface which is not so that the slow velocity region, that is, the SiO ₂ film is formed. It is shown that the surface acoustic wave energy can be confined in the existing part.

The above phenomenon is a kind of confinement effect and is a thin film ribbon waveguide used in a so-called waveguide, ΔV.
It can be considered as a phenomenon similar to that of the / V waveguide.

Therefore, as shown in FIG. 3 of this embodiment, S
By providing an insulating film such as iO ₂ on the output electrode (waveguide), the waveguide 33 is excited by the comb-shaped input electrode 32.
The surface acoustic wave coupled to the end surface of the wave propagates while suppressing the radiation mode of confining the surface of the waveguide 33 and having a large effect, that is, radiating the surface acoustic wave energy to the outside of the waveguide.

Further, as shown in the first embodiment, in FIG. 1, a SiO ₂ film is provided in a region between the comb-shaped input electrode 12 and the waveguide 13, and the shape is coupled to the end face of the waveguide 13. With such a horn shape, there is a difference in the velocity of the surface acoustic wave between the portion where the SiO ₂ film is formed and the free surface where it is not formed, and the slow velocity region, that is, SiO
_Since surface acoustic wave energy can be confined in the part where _two films are formed, it can be used as a parabolic horn.

As shown in FIG. 2, Si is formed on the piezoelectric substrate 31.
When the O ₂ film is formed to a thickness of 1 μm, the amplitude of the surface acoustic wave is larger than that of a free surface on which the insulating film 34 is not formed. Therefore, the insulating film 34 such as a SiO ₂ film is formed on the upper portion of the comb-shaped input electrode 32. The electromechanical coupling coefficient K ² is increased due to the formation of γ, and the energy of the surface acoustic wave increases.

From the above, the regular comb input electrode 32 and the output electrode (waveguide) 3 formed on the surface of the piezoelectric substrate 31 such as the Y-cut (Z-propagation) lithium niobate substrate.
In the surface acoustic wave convolver having No. 3, by forming an insulating film 34 such as a SiO ₂ film on the normal type comb-shaped input electrode 32 and the region up to the end face of the waveguide 33 and on the output electrode 33, The electromechanical coupling coefficient K ^{2 of the} surface acoustic wave excited from the input electrode 32 is improved on the normal type comb-shaped input electrode 32, and a surface acoustic wave having a large amplitude (large surface acoustic wave energy) is obtained. Further, it is confined in a parabolic horn formed by an insulating film 34 such as a SiO ₂ film to increase the surface acoustic wave energy density and couple it to the end face of the waveguide 33. On the waveguide 33, the surface acoustic wave energy is prevented from radiating to the outside of the waveguide 33 by keeping the radiation mode of the surface acoustic wave low.

As a result, the convolution efficiency is improved and, in addition, it also serves as a protective film for the pattern surface which has been conventionally used. Therefore, not only the performance as a surface acoustic wave convolver but also the reliability is improved. Becomes

Although the insulating film shown in the description of the first and second embodiments is an example in which a SiO ₂ film (silicon oxide film) is used, it is not limited to this and the Al ₂ O ₃ film (oxidation film is not limited to that. A film such as an aluminum film), a Si ₃ N ₄ film (silicon nitride film), or a ZnO film (zinc oxide film) may be used.

The thickness of the SiO ₂ film (silicon oxide film) which is the insulating film described in the first and second embodiments is 1 μm.
Although an example of the case of m is shown, the film thickness is not limited to this, and may be any film thickness capable of exhibiting the effects described in the present embodiment.

Further, although the shape of the comb-shaped input electrode shown in the first and second embodiments is a regular shape, a comb-shaped input having a circular arc shape or a shape for focusing the surface acoustic wave on the output electrode (waveguide). Also in the surface acoustic wave convolver using electrodes, the same effects as those shown in the present embodiment can be obtained.

In the first and second embodiments, an example in which the electric signals having 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 the same frequency is required. Alternatively, electric signals having different carrier angular frequencies may be input, and at that time, the angular frequency component of the output signal obtained from the output electrode becomes the frequency component of the sum of the carrier angular frequencies of the input signal.

The piezoelectric substrates 1 shown in the first and second embodiments use Y-cut (Z-propagation) lithium niobate, but other piezoelectric materials and piezoelectric materials in other cutting directions are used. You may use the thing.

Further, in the above-mentioned first and second embodiments, the example in which the elastic surface acoustic wave element uses the elastic type is shown, but it is not limited to this, and the AE type may be used.

In addition, the piezoelectric substrate shown in the first and second embodiments is not limited to this, and 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. 5 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 41 and demodulated. The receiving device 41 includes 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 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 output from the synchronization circuit 41
Input to 3.

The synchronization 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 signal and a clock synchronization signal for the transmission signal to the code generator 414. Surface acoustic wave element 413
In 1, the output signal from the high frequency signal processing unit 412 and the output signal from the modulation circuit 4132 are input to the surface acoustic wave element 4131, and the convolution operation of the two input signals is performed. Here, the modulation circuit 413 from the code generator 414
Assuming that the reference spreading code input to 2 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 dedicated signal included in the received signal. Code component and modulation circuit 41
The reference spread code from 32 is the surface acoustic wave element 413.
When they coincide with each other on the waveguide of the No. 1 output electrode, the correlation peak is output.

In this case, the convolution efficiency is improved because the electromechanical coupling coefficient K ² can be increased by covering the output electrode with an insulating film between the comb-shaped input electrode and the end surface of the output electrode or in addition to the above.

Next, the signal processing circuit 4133 detects the 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 spreading 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 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.
The signal output from the spread modulation / demodulation circuit 415 is so-called frequency modulation or phase modulation (PSK: Phase Shift Keying).
Since the signal is modulated by a modulation method such as, the data is demodulated by the corresponding demodulation circuit 416.

The surface acoustic wave convolver, which is the surface acoustic wave element 4131 used in the present configuration, has a large surface area by slowing down the propagation velocity of the surface acoustic wave by covering the piezoelectric substrate with an insulating film in a predetermined shape. The volume signal can be obtained.

<Fourth Embodiment> FIGS. 6 and 7 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. 6 showing a block diagram of the transmitting apparatus, 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. 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. 7 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 the clock on the transmitting side, and 604 is Synchronization circuit 60
A spreading code generator for generating n + 1 spreading codes and a reference spreading code, which are the same as the spreading code group on the transmission side, according to the code synchronization signal and the clock signal input from the reference numeral 3, and 605 is output from the spreading code generator 604. A carrier reproducing circuit for reproducing a carrier signal from the carrier reproducing spread code PN0 and the output of the high frequency signal processing unit 602, and 606 is an output of the carrier reproducing circuit 605, an output of the high frequency signal processing unit 602 and an output of the spread code generator 604. Some n spreading codes P
A baseband demodulation circuit that demodulates the baseband using N1 to PNn, and a parallel-serial converter 607 that parallel-serial converts n parallel demodulated data output from the baseband demodulation circuit 606.

In the above configuration, on the transmission side, the input data is first 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 multiplied and 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 high-frequency stage 505.
The baseband signal added to is output. 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 section 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 synchronization circuit 603 outputs the signals output from the surface acoustic wave element 6031 described in the embodiment of the present invention, the modulation circuit 6032 that modulates the reference spread code input from the code generator 604, and the surface acoustic wave element 6031. The spread code generator 604 processes the spread code sync signal and the clock sync signal for the transmission signal.
, And a signal processing circuit 6033 for outputting the signal.

The surface acoustic wave element 6031 includes the first and
The signal from the high frequency signal processing unit 602 and the output signal from the modulation circuit 6032 are input using any one of the surface acoustic wave convolver elements shown in the second embodiment, and the convolution operation of the 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, the code synchronization signal and the clock signal are generated, and the spread code generator 6
It is output to 04.

After the synchronization is established, the spreading code generator 604 generates a spreading code group having the same clock and spreading code phase with respect to the transmitting side spreading code group. 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 a phase locked loop, for example. 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.

In this embodiment, binary modulation is used, but 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.
It can be stored in the same package and used 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, a transmitter and a receiver are provided in the same package, the same carrier is used by differentiating the spreading code for synchronization, and it is possible to perform communication with the configuration of the communication device being almost the same, By using the above-mentioned surface acoustic wave element for the receiving device, the establishment of synchronization can be achieved at high speed and reliably, so that a highly reliable communication system is enabled.

[0081]

As described above, according to the present invention, at least two normal type comb 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 (waveguide) for taking out the convolution signal of the two surface acoustic waves by utilizing nonlinearity, SiO is formed on the comb-shaped input electrode on the surface of the surface acoustic wave element. An insulating film such as a ₂ film (silicon oxide film) is formed, and an insulating film such as a SiO ₂ film is formed in the region between the comb-shaped input electrode and the output electrode (waveguide). An elastic surface excited from the comb-shaped input electrode is formed by forming a shape converging on the end face, that is, a parabolic horn shape, and by additionally forming an insulating film such as a SiO ₂ film on the output electrode (waveguide). electro-mechanical coupling coefficient K ² of the wave By improving the surface acoustic wave with large amplitude (large surface acoustic wave energy), and confining it to the parabolic horn, the surface acoustic wave raises the surface acoustic wave energy density to the end face of the output electrode (waveguide). Join. On the output electrode (waveguide), the surface acoustic wave energy can be prevented from radiating to the outside of the output electrode (waveguide) by suppressing the radiation mode of the surface acoustic wave to a low level.

As a result, the convolution efficiency is improved, and in addition, the convolution efficiency plays a role as a protective film for the pattern surface, which has been conventionally well known. Therefore, not only the performance as the surface acoustic wave convolver but also the element Deterioration is prevented and reliability is improved.

By using this surface acoustic wave element, a high correlation peak as a surface acoustic wave convolver can be detected in a spread spectrum communication system.
It is possible to quickly establish mutual synchronization and improve the stability and reliability of the communication system.

[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 the ratio of the amplitude intensity to the time change of the surface acoustic wave at one point on the Y-cut lithium niobate piezoelectric substrate.

FIG. 3 is a schematic view showing a second embodiment of the surface acoustic wave convolver according to the present invention.

FIG. 4 is a schematic view showing a conventional surface acoustic wave convolver.

FIG. 5 is a block diagram showing an example of a communication system using the surface acoustic wave device of the present invention.

FIG. 6 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. 7 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, 31, 51 Piezoelectric substrate 12, 32, 52 Input electrode 13, 33, 53 Output electrode 14, 34 Insulating film such as SiO ₂ film (silicon oxide film) 54 Parabolic horn made of a conductive material 21 Magnitude of amplitude when free surface is formed without insulating film on piezoelectric substrate 22 Magnitude of amplitude when SiO ₂ film (silicon oxide film) is formed to 1 μm on piezoelectric substrate 40 Transmitter 401 Transmitting antenna 41 Receiving device 411 Receiving antenna 412 High frequency signal processing unit 413 Synchronizing circuit 414 Code generator 415 Spreading demodulating circuit 416 Demodulating circuit 501 Serial-parallel converter 502 for converting data input in series into n parallel data 502 -1 to n multiplier group 503 spreading code generator 504 adder 505 high-frequency stage 506 transmission antenna 601 reception Antenna 602 high-frequency signal processing section 603 synchronizing circuit 604 spread code generator 605 carrier reproducing circuit 606 baseband demodulation circuit 607 serializer

 ─────────────────────────────────────────────────── ─── Continued Front Page (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 Incorporated (72) Inventor Akane Yokota 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (8)

[Claims] 1. At least two comb-shaped input electrodes for exciting first and second surface acoustic waves on a main surface of a piezoelectric substrate, which is a laminated substrate in which a piezoelectric substance is formed on a piezoelectric substrate or a non-piezoelectric substance. And a waveguide / output electrode for taking out the convolution signal of the two surface acoustic waves by utilizing the non-linear effect of the piezoelectric substrate, on the comb-shaped input electrode and the comb-shaped input. A surface acoustic wave element, wherein an insulating insulating film is formed on the piezoelectric substrate in a region between an electrode and the output electrode. 2. In a portion where the insulating film is formed,
The surface acoustic wave device according to claim 1, wherein a region on the output electrode is added. 3. The surface acoustic wave device according to claim 1, wherein the insulating film is formed of a silicon oxide film. 4. The insulating film formed in a region between the comb-shaped input electrode and the output electrode has a shape for focusing a surface acoustic wave excited from the comb-shaped input electrode to an inlet end face of the output electrode. The surface acoustic wave element according to any one of claims 1 to 3, wherein 5. The elastic surface according to claim 4, wherein the insulating film formed in the region between the comb-shaped input electrode and the output electrode has a parabolic horn shape. Wave element. 6. The surface acoustic wave device according to claim 1, wherein the comb-shaped input electrode has a substantially arc shape. 7. The surface acoustic wave device according to claim 1, wherein Y-cut Z-propagation lithium niobate is used for the piezoelectric substrate. 8. A communication system using the surface acoustic wave device according to claim 1. Description: