JP2764866B2 - Surface acoustic wave device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave device, and more particularly, to a surface acoustic wave convolver for extracting a convolution signal of two signals.

[Prior Art] FIG. 3 shows “Nakagawa et al., IEICE Transactions on '86 / 2, Vo
l. J69-C, No. 2, pp. 190 to 198 ”, which is a schematic plan view showing a configuration of a conventional surface acoustic wave device.

In FIG. 3, reference numeral 1 denotes a piezoelectric substrate, and reference numerals 2 and 3 denote two comb-shaped electrodes for surface acoustic wave excitation which are formed on the surface of the substrate 1 so as to face each other at an appropriate distance in the x direction.
.., 4-n are surface acoustic wave waveguides extending in the x direction between the electrodes 2 and 3 and formed on the surface of the substrate 1 in parallel with each other. Reference numeral 5 denotes an acousto-electric converter formed on the surface of the substrate 1 at an appropriate distance from the surface acoustic wave waveguide in the y-direction.

The coordinate axes shown in FIG. 3 are added for convenience, and do not mean the crystal axes of the substrate.

In this surface acoustic wave element, when an electric signal having an angular frequency ω is input to the surface acoustic wave excitation comb-shaped electrodes 2 and 3,
The surface acoustic wave having the frequency is excited, and the surface acoustic wave propagates through the surface acoustic wave waveguides 4-1, 4-2,..., 4-n in opposite directions in the x-axis direction. Generates a surface acoustic wave having an angular frequency of 2ω propagating in the y-axis direction due to the parametric mixing phenomenon. This surface acoustic wave reaches the acoustic-electric converter 5, and the convolution electric signal of the two input signals can be obtained by the acoustic-electric converter.

[Problem to be Solved by the Invention] However, in the above-described conventional example, a convolution electric signal due to a parametric mixing phenomenon different from that described above is also generated in the surface acoustic wave waveguide. This convolution electric signal reaches the acoustoelectric converter as an electromagnetic wave, interferes with the convolution electric signal converted from the surface acoustic wave into an electric signal by this acoustoelectric converter, and degrades the characteristics of the element. was there.

[Object of the Invention] An object of the present invention is to provide a surface acoustic wave device having improved characteristics by eliminating generation of electromagnetic waves from a surface acoustic wave waveguide.

[Means and Actions for Solving the Problems] The present invention provides, as means for achieving the above object, at least two excitation electrodes for exciting first and second surface acoustic waves on a piezoelectric substrate; A surface acoustic wave waveguide for propagating the first and second surface acoustic waves excited from the electrodes in opposite directions, and propagation of the first and second surface acoustic waves generated in the surface acoustic wave waveguide A surface acoustic wave device having at least one acousto-electric converter for converting a third surface acoustic wave propagating in a direction crossing the direction into an electric signal, wherein the surface acoustic wave waveguide is electrically grounded. An object of the present invention is to provide a surface acoustic wave device characterized by the following.

According to the above means of the present invention, in an electric circuit including a surface acoustic wave element, by grounding the surface acoustic wave waveguide of the surface acoustic wave element, electromagnetic waves from the surface acoustic wave waveguide Occurrence can be suppressed.

Example (First Example) FIG. 1 is a schematic plan view showing a first example of a surface acoustic wave device according to the present invention.

In FIG. 1, reference numeral 1 denotes a piezoelectric substrate. As the piezoelectric substrate, for example, a piezoelectric substrate of lithium niobate or the like can be used.

Reference numerals 2 and 3 denote surface acoustic wave excitation electrodes that are formed on the surface of the substrate 1 so as to face each other at an appropriate distance in the x direction. The electrodes 2 and 3 are comb-shaped electrodes and are made of a conductor such as aluminum, silver, and gold, and are provided so that surface acoustic waves propagate in the x direction.

.., 4-n are surface acoustic wave waveguides that extend in the x direction between the excitation electrodes 2 and 3 and are arranged parallel to each other on the surface of the substrate 1 at a constant pitch. .

The surface acoustic wave waveguide is described in detail in `` Surface Acoustic Wave Engineering '' supervised by Kazuo Shibayama, IEICE, 82-102, and there are thin film waveguides and topographic waveguides.
In the present invention, a Δv / v waveguide in which the substrate surface is covered with a conductor such as aluminum, silver, or gold is preferable.

5 is the surface acoustic wave waveguide 4-1 on the surface of the substrate 1.
These are acousto-electric transducers that are arranged at an appropriate distance from .about.4-n in the y direction. The acoustoelectric transducer is made of a conductor such as aluminum, silver, or gold, and is provided so that surface acoustic waves propagating in the y-direction can be efficiently converted into electric signals.

Reference numeral 7 denotes a hermetic seal as a conductive fixing member for fixing the piezoelectric substrate 1, and 6-1 to 6-n electrically connect the surface acoustic wave waveguides 4-1 to 4-n to the hermetic seal 7. Bonding wire.

In the surface acoustic wave element of the present embodiment, when an electric signal having a central angular frequency ω is input to one of the excitation electrodes 2,
The first surface acoustic wave is excited, propagates in the positive direction of x, and enters the surface acoustic wave waveguides 4-1 to 4-n. Similarly, when an electric signal having the central angular frequency ω is input to the other excitation electrode 3, the second surface acoustic wave is excited, and x
And enters the surface acoustic wave waveguides 4-1 to 4-n. The first and second surface acoustic waves propagate from opposite ends of the surface acoustic wave waveguides 4-1 to 4-n in opposite directions.
Due to the mixing phenomenon, a third surface acoustic wave having a central angular frequency of 2ω propagating in the y-axis direction is generated, and this third surface acoustic wave is converted into an electric signal by the acoustoelectric converter 5, and the two inputs A convolution electrical signal of the signal is obtained.

On the other hand, when the first and second surface acoustic waves propagate in opposite directions to the surface acoustic wave waveguides 4-1 to 4-n, the surface acoustic wave waveguide 4-1 A convolution electric signal of the above two input signals having a central angular frequency of 2ω is generated on −1 to 4-n. Was causing.

However, the surface acoustic wave waveguides 4-1 to 4-1 of this embodiment
4-n is electrically connected to the hermetic seal 7 by bonding wires 6-1 to 6-n, and the hermetic seal 7 is electrically grounded to a housing (not shown). Generation of electromagnetic waves from the surface acoustic wave waveguide is suppressed.

Thereby, the interference by the electromagnetic wave in the acoustoelectric converter 5 is suppressed, and the characteristics of the element are improved.

Second Embodiment FIG. 2 is a schematic plan view showing a surface acoustic wave device according to a second embodiment of the present invention. In this drawing, the same members as those in FIG. 1 are denoted by the same reference numerals.

In FIG. 2, reference numeral 8 denotes a surface acoustic wave waveguide 4-1 to 4-
A conductor band 9 connecting n is a conductor pattern connected to the conductor band 8 and extending to the end of the piezoelectric substrate 1.

The conductor band 8 and the conductor pattern 9 are made of, for example, aluminum, silver, gold, or the like, and are formed on the piezoelectric substrate 1.

The end of the conductor pattern 9 is electrically connected to the hermetic seal 7 as a conductive fixing member by conductive rubber or the like at the end of the piezoelectric substrate 1. The seal 7 is grounded to a casing or the like (not shown).

Also in the device of the present embodiment, since the surface acoustic wave waveguides 4-1 to 4-n are grounded similarly to the device of the first embodiment, the electromagnetic wave from the waveguides 4-1 to 4-n are not grounded. Generation is suppressed.

Further, the conductor band 8 and the conductor pattern 9 of the present embodiment are:
Since the excitation electrodes 2 and 3 and the surface acoustic wave waveguides 4-1 to 4-n can be formed at the same time, and the multiple wire bondings 6-1 to 6-n shown in FIG. It is possible to shorten the yield and improve the yield.

In the present embodiment, the connection is made to the hermetic seal 7 by the conductor pattern 9 extending to the end of the piezoelectric substrate 1, but it may be directly connected to the hermetic seal 7 by the conductor band 8, or The conductive pattern 9 that does not extend to the end of the piezoelectric substrate 1 may be connected to the hermetic seal 7 by a bonding wire or the like. Even in this case, since it can be formed by one wire bonding,
The process can be shortened and the yield can be improved.

Further, in the present embodiment, the conductor band 8 is formed so as to be connected at the end of the surface acoustic wave waveguide. However, the same effect can be obtained even if the conductor band 8 is connected at another portion.

Further, in this embodiment, since the surface acoustic wave waveguides are connected by the conductor band 8, the surface acoustic waves at the bonding joints generated when wire bonding is directly performed on the waveguides 4-1 to 4-n. Can be prevented from scattering, and is suitable for an element operating at a high frequency.

In the first and second embodiments, the acoustoelectric transducer 5 is provided only on one side of the waveguides 4-1 to 4-n, but may be provided on both sides.

In this case, the surface acoustic waves generated by the surface acoustic wave waveguide propagate in both directions in the y-axis direction. 1. It is possible to obtain twice the output of the second embodiment.

The two acoustic-electric transducers 5 use the surface acoustic wave waveguide 4-
By making the distances from 1 to 4-n different, the output from one acoustoelectric converter can be appropriately delayed with respect to the output from the other acoustoelectric converter.

Further, the surface acoustic wave excitation electrodes 2, 3 in the first and second embodiments are formed as double electrodes (split electrodes), thereby suppressing the reflection of surface acoustic waves at the surface acoustic wave excitation electrodes 2, 3. As a result, the characteristics of the device can be further improved. Similarly, by making the acoustoelectric transducer 5 a double electrode (split electrode), it is possible to suppress the reflection of surface acoustic waves at the surface acoustic wave excitation electrodes 2 and 3,
The characteristics of the element can be further improved.

The coordinate axes shown in FIGS. 1 and 2 are added for convenience, and do not mean the crystal axes of the substrate.

Further, in the first and second embodiments, the substrate 1 is not limited to a piezoelectric single crystal such as lithium niobate. For example, a parametric mixing such as a structure in which a piezoelectric film is added on a semiconductor or glass substrate is used. Any material and structure that are effective can be used.

Further, in the first and second embodiments, the surface acoustic wave excited by the surface acoustic wave exciting electrode is guided to the surface acoustic wave waveguide as it is, but between the exciting electrode and the surface acoustic wave waveguide. A beam width compressor such as a horn waveguide or a multistrip coupler may be provided.

[Effects of the Invention] As described above, according to the present invention, since the surface acoustic wave waveguide is grounded, generation of electromagnetic waves from the surface acoustic wave waveguide can be suppressed. The interference of the convolution signal generated in the electric converter can be suppressed. Therefore, the effect that the characteristics of the surface acoustic wave element can be improved is obtained.

[Brief description of the drawings]

FIG. 1 is a schematic plan view showing a first embodiment of a surface acoustic wave device according to the present invention. FIG. 2 is a schematic plan view showing a second embodiment of the surface acoustic wave device according to the present invention. FIG. 3 is a schematic plan view showing a conventional example. DESCRIPTION OF SYMBOLS 1 ... Piezoelectric substrate, 2, 3 ... Exciting electrode, 4-1-4-n ... Surface acoustic wave waveguide, 5 ... Acoustoelectric transducer, 6-1-6-n ...
Bonding wire, 7: Hermetic seal (conductive fixing member), 8: Conductor band, 9: Conductor pattern

Claims (5)

(57) [Claims] 1. At least two excitation electrodes for exciting first and second surface acoustic waves on a piezoelectric substrate, and the first and second surface acoustic waves excited from the excitation electrodes are turned in opposite directions. A surface acoustic wave waveguide to be propagated, and at least a third surface acoustic wave generated in the surface acoustic wave waveguide and propagated in a direction transverse to a propagation direction of the first and second surface acoustic waves, is converted into an electric signal. A surface acoustic wave device having one acoustoelectric transducer, wherein the surface acoustic wave waveguide is electrically grounded. 2. The surface acoustic wave device according to claim 1, wherein the surface acoustic wave waveguide comprises a plurality of waveguides, and the plurality of waveguides are electrically connected to each other. 3. The surface acoustic wave device according to claim 2, wherein the plurality of waveguides are electrically connected to each other by a conductor pattern formed on the piezoelectric substrate. 4. The surface acoustic wave device according to claim 1, wherein said surface acoustic wave waveguide is electrically grounded via a conductive fixing member for fixing said piezoelectric substrate. 5. The surface acoustic wave device according to claim 4, wherein said surface acoustic wave waveguide is electrically connected to said conductive fixing member by conductive rubber.