JPH0481114A - Surface acoustic wave convolver - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a surface acoustic wave convolver, and particularly to a split waveguide type surface acoustic wave convolver that extracts a convolution signal of two signals through a split waveguide. Regarding convolver.

[Prior art] Fig. 3 is a diagram of "Chuyo et al., Journal of the Institute of Electronics and Communication Engineers °86/2.
Vol. J69-C, No. 2. pp190-1
98J is a schematic plan view showing the configuration of a conventional split waveguide type surface acoustic wave convolver.

Note that the coordinate axes shown in this figure are added for convenience and do not mean the crystal axes of the substrate or the like.

In FIG. 3, numeral 1 is a piezoelectric substrate, and numerals 2 and 3 are two comb-shaped electrodes for excitation of surface acoustic waves, which are formed on the surface of the substrate 1, facing each other at an appropriate distance in the X direction.

Moreover, 4-1, 4-2, ... 4-n are these electrodes 2,
The waveguides are formed on the surface of the substrate 1 in parallel to each other and extending in the X direction between the two waveguides. Reference numeral 5 designates an output comb-shaped electrode formed on the surface of the substrate 1 at an appropriate distance from the waveguide in the X direction.

In this surface acoustic wave element, when an electric signal with an angular frequency ω is input to the comb-shaped electrodes 2 and 3 for exciting surface acoustic waves, a surface acoustic wave of that frequency is excited, and the surface acoustic waves and the waveguide 4-1. 4-2. ..., 4-n in opposite directions to each other in the X-axis direction, and in the waveguide, a surface acoustic wave with an angular frequency of 2ω is generated that propagates in the y-axis direction due to a parametric mixing phenomenon. This surface acoustic wave is transmitted to the output comb-shaped electrode 5.
, and a convolution electric signal of the above two input signals can be obtained at the output comb-shaped electrode.

[Problems to be Solved by the Invention] However, in the conventional split waveguide type surface acoustic wave convolver as described above, each split waveguide and the part where the waveguide is not formed (the part where the waveguide is formed) width ratio between
In other words, since the line and space ratio is 1:1,
Not all of the surface acoustic waves excited from each comb-shaped electrode for surface acoustic wave excitation toward the waveguides are incident on each waveguide, and nearly half of the surface acoustic waves are also between the waveguides. It was Therefore, there is a drawback that the incidence efficiency of surface acoustic waves into the waveguide is poor.

[Object of the Invention] An object of the present invention is to provide a split waveguide type surface acoustic wave convolver that allows surface acoustic waves excited by a comb-shaped electrode for surface acoustic wave excitation to enter a waveguide efficiently.

[Means and effects for solving the problem] The above object is to provide a horn-shaped waveguide having the same exit width as each waveguide between the comb-shaped electrode for excitation of surface acoustic waves and each waveguide. This is achieved by providing the same number of waveguides on both sides of the waveguide.

Further, the above-mentioned problem is solved by a surface acoustic wave convolver characterized in that the excitation electrode side entrances of the plurality of horn-shaped waveguides are all continuous.

In other words, in such a configuration, the surface acoustic waves excited by the comb-shaped electrodes for excitation of surface acoustic waves can be made to enter each waveguide efficiently (inject into each waveguide, and there is no leakage between the waveguides). Surface acoustic waves can be reduced.

In addition, by arranging the entrances of each horn-shaped waveguide one after the other without any gaps, the surface acoustic waves leaking between the waveguides can be similarly reduced, and the excited surface acoustic waves can be unnecessarily introduced into the waveguide. can do.

[Example] (First Example) FIG. 1 is a schematic plan view showing a first example of a surface acoustic wave element of the present invention.

Note that the coordinate axes in the figures are added for convenience and do not mean the crystal axes of the substrate or the like.

In FIG. 1, 1 is a piezoelectric substrate. As the piezoelectric substrate, for example, a piezoelectric substrate such as lithium niobate can be used.

Reference numeral 2.3 denotes surface acoustic wave excitation electrodes formed on the surface of the substrate 1 and facing each other at an appropriate distance in the X direction. The electrode 2.3 is a comb-shaped electrode made of a conductor such as aluminum, silver, or gold, and is provided so that surface acoustic waves propagate in the X direction.

4-1.4-2. ..., 4-n are waveguides extending in the X direction and arranged parallel to each other at a constant pitch on the surface of the substrate 1 between the electrodes 2 and 3.

Waveguides are described in detail in "Surface Acoustic Wave Engineering" edited by Kenio Shibayama, Institute of Electronics and Communication Engineers, pp. 82-102.
Although there are thin film waveguides and topographic waveguides, in the present invention, a Δv/v waveguide whose substrate surface is coated with a conductor such as aluminum, silver, or gold is preferable.

5 is the waveguide 4-1 to 4-n to y on the surface of the substrate 1.
These output comb-shaped electrodes are arranged at appropriate distances in the y-direction, and are made of a conductor such as aluminum, silver, or gold, and are capable of efficiently converting surface acoustic waves propagating in the y-direction into electrical signals. It is set up so that it can be converted.

7-1 to 7-n, 8-1 to 8-n are located between the electrode 2 and the waveguides 4-1 to 4-n on the surface of the substrate l, and between the electrode 3 and the waveguide 4-n. These are horn-shaped waveguides arranged respectively between 1 and 4-n.

Regarding horn-type waveguides, see A Rayleigh Wave Beam Co by MANAS K, ROY.
mpressor UsingΔv/v-Type G
uidance J IEEE Trans, on 5
onicsand Llltrasonics, Vol.
, 5Ll-23, July 1976.276-279
It is detailed on page.

Horn waveguides include thin film waveguides and topographic waveguides, but in the present invention, ΔV/V waveguides in which the substrate surface is coated with a conductor such as aluminum, silver, or gold are preferred. Here, the horn-shaped waveguides 7-1 to 7-n,
and 8-1 to 8-n are surface acoustic wave excitation electrodes 2 and 3
The side entrance end faces are continuous, and the width of the tip of the horn is equal to the width of each waveguide.

In the surface acoustic wave convolver of this embodiment, when an electric signal with a center angular frequency ω is input to one excitation comb-shaped electrode 2, a surface acoustic wave is excited from the excitation electrode 2, and
The light propagates in the positive direction and enters one of the horn waveguides 7-1 to 7-n whose incident side end faces are continuous.

The surface acoustic waves are transmitted through the horn waveguides 7-1 to 7-n.
The beam propagates while being reflected at the boundaries of the waveguides, and is emitted with a beam width equal to that of each waveguide.
4-n and propagates.

Here, the shape of the horn-shaped waveguide is such that the incident angle θ when the surface acoustic wave is reflected at the boundary of the horn-shaped waveguide is sinθ>V
+/Vo (V+ is the surface acoustic wave velocity on the surface of the horn-shaped waveguide, ■. is the surface acoustic wave velocity on the free surface)
By arranging and forming the horn-shaped waveguide so that it satisfies
The beam width of surface acoustic waves can be efficiently converted. Therefore, the surface acoustic waves excited by the surface acoustic wave excitation comb-shaped electrode 2 are all incident on the waveguides 4-1 to 4-n via the horn-shaped waveguides 7-1 to 7-n, and propagate therein.

Similarly, when an electrical signal with a center angular frequency ω is input to the other excitation comb-shaped electrode 3, a surface acoustic wave is excited from the excitation electrode 3 and propagates in the negative direction of Horn-shaped waveguides 8-1 to 8-n with continuous end faces
The light is incident on the waveguides 4-1 to 4-n via the waveguides 4-1 to 4-n, and propagates.

In this way, two surface acoustic waves propagate in opposite directions from both ends of the waveguides 4-1 to 4-n, and due to the parametric mixing phenomenon in the waveguides, the central angular frequency 2ω propagates in the y-axis direction. surface acoustic waves are generated. This surface acoustic wave reaches the output comb-shaped electrode 5, where a convolution electric signal of the above two input signals can be obtained.

The waveguides 4-1 to 4-n are arranged so that the arrangement pitch of the waveguides 4-1 to 4-n is the same as an integral multiple of the wavelength of the surface acoustic wave generated in the waveguide. By forming such a waveguide element, the surface acoustic waves generated in each waveguide element overlap in the same phase, and can be efficiently excited.

In addition, in this embodiment, the horn-shaped waveguides 7-1 to 7-
n and 8-1 to 8-n are continuous on the incident end face on the side of the comb-shaped electrodes 2 and 3 for surface acoustic wave excitation, respectively, but the horn-shaped waveguides 7-1 to 7-n and 8-1 ~8-n may be separated from each other. In such a surface acoustic wave convolver having a horn-shaped waveguide in which the individual incident end faces are placed apart from each other, the incidence of the surface acoustic wave into the waveguide is reduced to the extent that the surface acoustic wave leaks between the horn-shaped waveguides that are separated from each other. Efficiency decreases, but
Even so, compared to the conventional split waveguide type surface acoustic wave convolver, the incidence efficiency is sufficiently improved.

(Second Example) FIG. 2 is a schematic plan view showing a second example of the surface acoustic wave element according to the present invention. In this figure, members similar to those in FIG. 1 are given the same reference numerals.

In this embodiment, an output comb-shaped electrode 6 similar to the output comb-shaped electrode 5 is provided on the surface of the substrate 1 from the waveguides 4-1 to 4-n in the y direction on the opposite side to the comb-shaped electrode 5. The only difference from the first embodiment is that they are arranged and formed at the same distance.

In this embodiment, the same effects as in the first embodiment can be obtained, but in this embodiment, the surface acoustic waves generated in the waveguide propagating in both directions of the y-axis are
By receiving the output from the two output comb-shaped electrodes 5 and 6 and combining these outputs, it is possible to obtain an output twice that of the first embodiment.

In addition, the waveguides 4-1 to 4- of the two output comb-shaped electrodes 5.6
By varying the distances from n, the output from one output comb-shaped electrode 5 can be delayed by an appropriate time with respect to the output from the other output comb-shaped electrode 6.

Furthermore, by using the surface acoustic wave excitation electrodes 2 and 3 in the first and second embodiments as double electrodes (split electrodes), reflection of surface acoustic waves at the surface acoustic wave excitation electrodes 2.3 is suppressed. can.

Similarly, by making the output comb-shaped electrodes 5 and 6 double electrodes (split electrodes), reflection of surface acoustic waves at the output comb-shaped electrodes 5 and 6 is suppressed, and the characteristics of the device are further improved. can do.

Furthermore, in the first and second embodiments described above, the substrate 1 is not limited to a piezoelectric single crystal such as lithium niobate (
Any material and structure that has a parametric mixing effect may be used, such as a structure in which a piezoelectric film is added on a semiconductor glass substrate.

[Effects of the Invention] As described above, according to the present invention, the number of horn-shaped waveguides whose exit width on the waveguide side is equal to the width of the waveguide is provided between the excitation electrode and the waveguide. By providing the
Thereby, the efficiency of incidence of surface acoustic waves into the waveguide can be improved.

In addition, by arranging the end faces of the entrances on the excitation electrode side of the individual horn-shaped waveguides continuously, it is possible to significantly reduce the surface acoustic waves leaking between the waveguides. The effect of improving the incidence efficiency of surface acoustic waves on the surface can be obtained.

[Brief explanation of the drawing]

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. 1 is a substrate, 2 and 3 are excitation electrodes, 4-1 to 4-n are waveguide elements, 5.6 is an output electrode, 7-1 to 7-n, 8-1 to
8-n is a horn waveguide.

Claims (2)

[Claims] (1) At least two excitation electrodes that excite first and second surface acoustic waves on a piezoelectric substrate, and the first and second surface acoustic waves excited from the excitation electrodes are arranged in opposite directions. a plurality of waveguides for propagation, and at least one output electrode for converting a third surface acoustic wave propagating in a direction crossing the first and second surface acoustic waves generated in the waveguides into an electrical signal; In the surface acoustic wave convolver having a surface acoustic wave convolver, the same number of horn-shaped waveguides as the number of waveguides are provided between the excitation electrode and the waveguide, and the width of the exit on the waveguide side is equal to the width of the waveguide. surface acoustic wave convolver. (2) The surface acoustic wave convolver according to claim 1, wherein the excitation electrode side entrances of the plurality of horn-shaped waveguides are all continuous.