JPH07226641A - Surface acoustic wave element, surface acoustic wave convolver using the element and communication system using the convolver - Google Patents

Abstract

PURPOSE:To excite surface acoustic waves in one direction with a single phase structure and to improve energy conversion efficiency by arranging bus bars for which plural electrode fingers for inputting the signals of the same phase are bundled and connected on the right and left of the electrode finger, cancelling one direction and strengthening the other direction. CONSTITUTION:In the three-phase type UDT of a comb-line electrode, the electrode fingers 121... are respectively connected to the bus bars 111 and 115 for connecting grounded electrodes and the bus bars 113 and 114 and 112 and 116 for high frequency signals provided with the phase difference of 60 deg. at a center frequency and arranged on the right and left. The phases of electric fields among the electrode fingers 127, 128... are shifted by 120 deg. each and thus, since the excited surface acoustic waves advancing in a right or left direction are strengthened or cancelled with each other between the electrodes, only the surface acoustic waves advancing in the right direction are excited. Thus, the three-phase UDT is realized with a single layer structure without the need of a gap cross electrode, loss is made small and highly efficient communication is performed.

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, a surface acoustic wave convolver using the same, and a communication system using the same.

[0002]

2. Description of the Related Art A surface acoustic wave element using a comb-shaped electrode (hereinafter referred to as IDT) as a piezoelectric transducer has been conventionally used for IDT.
Various unidirectional IDs to prevent loss due to
Research on T (UDT) has been conducted.

FIG. 8 shows an example of a UDT called a group type. As shown in the figure, the interdigital electrodes with a small number of logarithms are set as one group and the width of the ground electrode between the groups is
/ 2, and by arranging the ground electrodes of λ in a meandering line so that the waves excited between the groups have the same phase, and by applying an electric field of 0 ° and 90 ° phases, unidirectionality is obtained. Is getting FIG. 12 is a diagram simulating the intensity distribution in the traveling direction and the depth direction of the elastic wave excited by the group-type UDT of FIG. 8, and the bright part is the strong part.

In FIG. 9, a floating electrode is provided between the electrode fingers of the IDT, and the reflection of surface acoustic waves caused by the difference in the acoustic impedance under the electrode and the acoustic impedance under the electrode and the intermediate potential between the adjacent electrode fingers are shown. This is an example in which unidirectionality is obtained by acting as a holding electrode.

FIGS. 10 and 11 show a UDT called a polyphase type.
10 and 11 show a three-phase type in which unidirectionality is obtained by shifting the phase of the electric field applied between the electrode fingers by 120 °, and three electrode fingers are provided in a length corresponding to one wavelength. There is.

In the case of FIG. 10, the potentials of all three phases can be supplied to the electrode fingers by providing the void crossing electrodes. Also,
FIG. 11 shows a structure in which an electrode finger having one reference potential is made a meander line and meandered between electrode fingers having other two potentials.

These unidirectional IDT (UDT) diagrams 8 to
Regarding Fig. 10, elastic wave device technology handbook (edited by the Japan Society for the Promotion of Science, elastic wave device technology 150th Committee) p192-
195, FIG.
/ 7 Vol. See J61-BN0.7.

[0008]

However, in the case of the group type, the frequency bandwidth of the IDT becomes narrower, and as shown in the simulation diagram of FIG. 12, in addition to the surface acoustic wave, the bulk propagating in the depth direction is also used. The waves are excited, which causes losses. In the floating electrode type, reflection at the floating electrode is small and unidirectionality is small. Further, since the unidirectionality is small in the frequency band deviated from the center frequency where the reflection condition does not match, the frequency bandwidth becomes narrow. There was a problem such as. Further, in the case of FIG. 10, a void crossing electrode is required. Since this void is usually formed by a dielectric thin film,
Processes with more than two layers are required. The multi-phase type as shown in FIG. 11 has a single-layer structure that can be manufactured by a single process. However, in order to obtain a strong surface acoustic wave, there is a portion where the surface acoustic wave is hardly excited only by the return electrode for each wavelength. However, there is a problem that the number of electrode fingers is increased and the frequency bandwidth is narrowed.

[0009]

In order to solve the above problems, according to the present invention, a unidirectionality for exciting a surface acoustic wave in one direction by inputting a plurality of phase-shifted high frequency signals onto a piezoelectric body. A surface acoustic wave device having a comb-shaped electrode (hereinafter referred to as a polyphase UDT), wherein the polyphase UDT bundles a plurality of electrode fingers to which signals of the same phase are to be input, and connects them to one bus bar. A surface acoustic wave device having a single layer structure, which is configured by arranging a plurality of bus bars on the left and right of an electrode finger.

Further, in the present invention, the electrode fingers for which it is difficult to supply the electric power by the bus bar are omitted by leaving at least two electrode fingers arranged within one wavelength.

[0011]

【Example】

(Embodiment 1) FIG. 1 is a schematic view of a piezoelectric transducer portion of a surface acoustic wave device for explaining the present invention. UD of this embodiment
T is a three-phase type. In the figure, 111 and 115 are bus bars for connecting a ground electrode which serves as a reference of electric potential,
Bus bars 113 and 114 for outputting the high frequency signals output from the signal source 101 and impedance-converted by the impedance matching circuit 102, and 112 and 116,
It is a bus bar for supplying a high-frequency signal that has passed through the delay circuit 103 that creates a delay corresponding to a phase difference of 60 ° at the center frequency with respect to the high-frequency signal supplied to 113 and 114.

[0012] The electrode fingers 127, 128, 129, 130. ． ． The electric field between the phases is 120 ° out of phase. Since surface acoustic waves are excited in proportion to this electric field strength, surface acoustic waves traveling to the right in the figure strengthen each other between the electrodes, and surface acoustic waves traveling to the left cancel each other out. Only surface acoustic waves traveling to the right are excited.

The spaces 123 and 126 do not have electrode fingers to which a high frequency signal is input, but the surface acoustic waves excited by the electrode fingers 127 to 132 are electrode fingers 121, 122 and.
Since it is in phase with the surface acoustic wave excited by the electrode fingers 124 and 125, there is almost no energy loss in exciting the surface acoustic wave. 133,13 for the same reason
Even if there are no electrode fingers in the spaces 6 and 143 and 146, there is almost no energy loss in exciting the surface acoustic waves.

In the UDT that realizes unidirectionality with a polyphase signal, it is not necessary to arrange all electrode fingers at equal intervals and to apply a polyphase alternating current, and at least two electrode fingers are included in one wavelength. If there is In the case of the three-phase type in which three electrode fingers are present in one wavelength as in the present embodiment, if the electrode fingers for which power supply is more difficult than the busbar are within one wavelength, the energy loss can be obtained even if thinning out. The surface acoustic wave can be excited with almost no.

FIG. 2 is a diagram simulating the intensity distribution in the traveling direction and the depth direction of the elastic wave excited by the three-phase UDT of FIG. As can be seen, the surface acoustic waves are efficiently excited in the traveling direction by the UDT of the present embodiment, and as can be seen from comparison with FIG. 12, bulk waves propagating in the depth direction are hardly generated, Most of the input electric energy is converted into surface acoustic wave energy.

In this embodiment, the electrode fingers are provided for 10 wavelengths in order to obtain a strong surface acoustic wave, but the electrode fingers 127 to 13 in FIG.
As can be seen from 2, it is possible to form a single layer structure without thinning out the electrode fingers if the wavelength is equal to or less than 2 wavelengths.

(Embodiment 2) FIG. 3 shows a unidirectional ID according to the present invention.
This is an example in which T (UDT) is applied to a convolver, and FIG. 4 is an enlarged view of the UDT portion of FIG. In case of convolver,
In order to increase the convolution efficiency, the output electrode,
At the same time, it is necessary to narrow the width of the waveguide and reduce the conversion loss at the portion where the surface acoustic wave signal is propagated to the waveguide. Especially the convolution efficiency is proportional to the elastic wave energy intensity input from both sides of the waveguide.
Preventing loss of elastic wave energy from the IDT (UDT) to the waveguide is important for improving the convolution efficiency.

In FIG. 3, 201 is a lithium niobate substrate, 202 is an output electrode and also serves as a waveguide, 205 and 206.
Is the UDT of the present invention. UDT 205, 20 of the present invention
6 is a shape in which the surface acoustic wave propagates only to the waveguide 202 side, and the surface acoustic wave generated by the UDT is further concentrated on the waveguide.
(In the present embodiment, it has an arc shape concave toward the waveguide side). In this embodiment, the substrate is a Y-cut Z-propagation lithium niobate substrate, and the end of the waveguide 202 is UDT 20.
It is not the center of curvature O of 5 and 206, but the position where the propagation efficiency of the surface acoustic wave is a maximum at a position slightly apart from the center of curvature O.

Since the signal converted from electric energy to elastic wave energy by this UDT is propagated to the waveguide with almost no loss, the convolution efficiency can be greatly improved.

Although the arc-shaped electrode is used in this embodiment, the shape may be such that the waveguide mode of the waveguide and the anisotropy of the substrate are taken into consideration. Alternatively, a horn or an acoustic lens may be used as a means for concentrating the surface acoustic waves on the waveguide.

In the first and second embodiments, the electrode index is 22.
Only the three-phase UDT of the book was used for the description, but with other configurations,
For electrode fingers for which power supply is more difficult than bus bars, at least two electrode fingers remain for one wavelength, and the electrode fingers are thinned out U
The same effect can be obtained for DT. Also, 123, 126, 133, 136, 143, 146 in FIG.
It is also possible to suppress the influence of the reflection of the surface acoustic wave by arranging the floating electrode in the above space and the space corresponding to that in FIG.

(Embodiment 3) 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, 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. The receiver 41 includes an antenna 411, a high frequency signal processing unit 412,
Synchronization circuit 413, code generator 414, spread demodulation circuit 41
5, 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 the surface acoustic wave device 413 described in the embodiment of the present invention.
1 and the modulation circuit 4132 that modulates the reference spread code input from the code generator 414 and the signal output from the surface acoustic wave device 4131, and the spread code synchronization signal and the clock synchronization signal for the transmission signal are generated by the code generator. And a signal processing circuit 4133 for outputting to 414. 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, if 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 transmission side, the surface acoustic wave device 4131
When the synchronization-specific spreading code component included in the received signal and the reference spreading code match on the waveguide of the surface acoustic wave device 4131, a correlation peak is output. Signal processing circuit 413
3, the correlation peak is detected from the signal input from the surface acoustic wave device 4131, the deviation amount of the code synchronization 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 are generated. The signal is 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. The signal output from the spread modulation / demodulation circuit 415 is
Since the signal is 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.

(Embodiment 4) FIGS. 6 and 7 are block diagrams respectively showing an example of a transmitter and a receiver of a communication system using the surface acoustic wave device as described above. In this embodiment, a CDM (Code Divis) is used as a communication method.
Ion multiplexing method is used. The details will be described below.

In FIG. 6, reference numeral 501 denotes a serial-parallel converter for converting data input in series into n parallel data, 5
02-1 to n are multiplier groups for multiplying each parallelized data and n spread codes output from the spread code generator,
Reference numeral 503 is a spreading code generator that generates n different spreading codes and spreading codes dedicated to synchronization, and 504 is a spreading code dedicated to synchronization output from the spreading code generator 503 and n pieces of multiplier groups 502-1 to 502-1. 505 that adds the outputs of the
Is a high frequency stage for converting the output of the adder 504 into a transmission frequency signal, and 506 is a transmission antenna. Also, FIG.
In the figure, 601 is a receiving antenna, 602 is a high frequency signal processing unit, 603 is a synchronizing circuit for capturing and maintaining synchronization with the spreading code and clock on the transmitting side, and 604 is a synchronizing circuit 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 reproduction circuit that reproduces a carrier signal from the carrier reproduction spread code and the output of the high-frequency signal processing unit 602, and 606 is an output of the carrier reproduction circuit 605, an output of the high-frequency signal processing unit 602, and an output of the spread code generator 604. a baseband demodulation circuit for demodulating in the baseband using n spread codes, 60
Reference numeral 7 denotes a parallel-serial converter that parallel-serial converts n parallel demodulated data output from the baseband demodulation circuit 606.

In the above structure, on the transmitting 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, and is directly input to the adder 504 without being modulated by the parallel data. The remaining n spread codes are modulated by n parallel data in the multiplier groups 502-1 to 502-1 and input to the adder 504. The adder 504 linearly adds the n + 1 input signals and outputs the added baseband signal to the high frequency stage 505. The baseband signal is subsequently fed to the high frequency stage 5
At 05, it is converted into a high frequency signal having an appropriate center frequency and transmitted from the transmitting antenna 506.

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. The signal is input to the synchronizing circuit 603. The synchronization circuit 603 processes the signals output from the surface acoustic wave device 6031 and the modulation circuit 6032 for modulating the reference spread code input from the code generator 604 and the surface acoustic wave device 6031 described in the embodiment of the present invention. , A signal processing circuit 6033 for outputting a spread code synchronization signal and a clock synchronization signal for the transmission signal to a spread code generator 604. Surface acoustic wave element 603
An output signal from the high frequency signal processing unit 602 and an output signal from the modulation circuit 6032 are input to 1 and a convolution operation of two input signals is performed. If the reference spreading code input from the code generator 604 to the modulation circuit 6032 is a time-reversed code of the synchronization-only spreading code transmitted from the transmitting side, the surface acoustic wave device 6031 has
A correlation peak is output when the synchronization-specific spreading code component and the reference spreading code included in the received signal match on the waveguide of the surface acoustic wave device 6031. Signal processing circuit 603
In 3, the correlation peak is detected from the signal input from the surface acoustic wave device 6031, the deviation amount of the code synchronization 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 are generated. The signal is output to the spread code generator 604. After the synchronization is established, the spreading code generator 604 generates a spreading code group in which the clock and the spreading code phase match the spreading code group on the transmitting side. Of these code groups, the spread code PN0 dedicated to synchronization is input to the carrier reproduction circuit 605. The carrier reproduction circuit 605 despreads the reception signal converted to the transmission frequency band or the intermediate frequency band which is the output of the high frequency signal processing unit 602 by the synchronization-dedicated spreading code PN0 and reproduces the carrier wave in the transmission frequency band or the intermediate frequency band. As the configuration of the carrier reproducing circuit 605, 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 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 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 bandpass filter from the voltage controlled oscillator. The signal is output as a reproduced carrier wave. The reproduced carrier wave is input to the baseband demodulation circuit 606. In the baseband demodulation circuit, a baseband signal is generated 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 which are the outputs of the spreading code generator 604, and then data demodulation is performed. The parallel demodulated n demodulated data are converted into serial data by the parallel-serial converter 607 and output.

In the present embodiment, the CDM method is used as the communication method, and since a plurality of signals can be bundled and transmitted, the transmission capacity can be increased.

The present embodiment is a case of binary modulation,
Other modulation methods such as quadrature modulation may be used.

[0030]

As described above, according to the present invention, it is possible to realize a broadband multi-phase (three-phase) UDT in a single process (with a single layer structure) without the need for a void crossing electrode, A surface acoustic wave device having a wide band and low loss can be realized. Further, the convolver of the present invention can perform convolution efficiently in a wide band, and the communication system of the present invention can perform efficient communication in a wide band.

[Brief description of drawings]

FIG. 1 is a schematic view of a piezoelectric transducer part of a surface acoustic wave device for explaining the present invention.

FIG. 2 is a diagram showing the intensity distribution of elastic waves excited in the three-phase UDT of FIG.

FIG. 3 is a diagram showing an example in which the present invention is applied to a convolver.

FIG. 4 is an enlarged view of the UDT portion of FIG.

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 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 receiver of a communication system using the surface acoustic wave device of the present invention.

FIG. 8 is a diagram showing a configuration of a UDT called a group type of a conventional example.

FIG. 9 is a diagram showing a configuration of a UDT including a conventional floating electrode.

FIG. 10 is a diagram showing a configuration of a multi-phase UDT using a void crossing electrode of a conventional example.

FIG. 11 is a diagram showing a configuration of a multiphase UDT in which a conventional electrode is meandered.

12 is a diagram showing the intensity distribution of elastic waves excited by the group type UDT of FIG.

[Explanation of symbols]

101 Signal Source 102 Impedance Matching Circuit 103 Delay Circuit 111, 115 Bus Bar 113, 114 for Connecting to Ground Electrode Bus Bar 112, 116 for Supplying High Frequency Signal Central frequency 60 from the high frequency signal supplied to Bus Bar 113, 114 Bus bars 121, 122, 124, 125, 127 to 132, 1 for supplying high-frequency signals whose phases are shifted by
34, 135, 137 to 142, 144, 145, 14
7, 148 Electrode fingers 123, 126, 133, 136, 143, 146 Space where no electrode fingers are arranged 201 Lithium niobate substrate 202 Output electrode and waveguide 205, 206 Arc-shaped UDT 40 transmitter 401 of the present invention 401 Transmitting antenna 41 Receiver 411 Receiving antenna 412 High frequency signal processing unit 413 Synchronizing circuit 414 Code generator 415 Spreading demodulating circuit 415, 416 Demodulating circuit 501 Serial-parallel conversion 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 Transmitting antenna 601 Receiving antenna 602 High frequency signal processing unit 603 Synchronizing circuit 604 Spreading code generator 605 Carrier reproducing circuit 606 Baseband demodulating circuit 607 Parallel Serial converter

Front Page Continuation (72) Inventor Takahiro Hachisu 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Akane Yokota 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Akihiro Koyama 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (8)

[Claims] 1. A surface acoustic wave in which a unidirectional comb-shaped electrode (hereinafter referred to as a polyphase UDT) for exciting a surface acoustic wave in one direction by inputting a plurality of phase-shifted high frequency signals is formed on a piezoelectric body. In the element, the multi-phase type UDT is configured by bundling a plurality of electrode fingers to which signals of the same phase are input and connecting them to one bus bar, and arranging a plurality of the bus bars on the left and right of the electrode finger. A surface acoustic wave device having a single-layer structure. 2. The surface acoustic wave device according to claim 1, wherein the electrode fingers of the polyphase UDT are omitted so that at least two electrode fingers arranged within one wavelength remain. . 3. The phase between the plurality of high frequency signals is 120.
3. The surface acoustic wave device according to claim 1, wherein the surface acoustic wave device is offset from each other. 4. The surface acoustic wave device according to claim 1, wherein the surface acoustic wave device has a waveguide, and the polyphase UDT couples the surface acoustic wave to the waveguide. A surface acoustic wave device characterized by the above. 5. The surface acoustic wave device according to claim 1, wherein the surface acoustic wave device has a waveguide, and the polyphase UDT concentrates and couples the surface acoustic wave to the waveguide. A surface acoustic wave device having a shape. 6. The surface acoustic wave device according to claim 2, wherein a floating electrode is provided in a portion where the electrode fingers are omitted. 7. A surface acoustic wave convolver using the surface acoustic wave device according to claim 1. Description: 8. A communication system using the surface acoustic wave convolver according to claim 8.