JPH01180110A - Surface acoustic wave convolver - Google Patents

Abstract

PURPOSE:To suppress self-convolution by providing two center electrodes with different length side by side along the propagating direction of a surface acoustic wave. CONSTITUTION:A comb-line electrode 2 and center electrodes 3a, 3b are formed on a piezoelectric substrate 1. The electrodes 3a, 3b are formed in parallel along the direction of propagation of the surface acoustic wave radiated from the electrode 2 and the length of the electrode 3b is longer than the electrode 3a by L=L1+L2. When the surface of the substrate 1 is covered by the conductor, the velocity of the surface acoustic wave is reduced more than the velocity on the free surface due to electric field short-circuit effect and mass load effect. The difference L of the length between the electrodes 3a and 3b is set properly by utilizing the fact to enable the phase of the surface acoustic wave passing through the electrodes 3a, 3b by 180 deg.. Thus, the electric charge is neutralized by each electrode finger forming other comb-line electrode electrically and the reflection wave due to re-stimulation is not caused.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a surface acoustic wave convolver, and particularly to a surface acoustic wave convolver intended to suppress so-called large Ruff convolvers 71.

[Prior art]

FIG. 3 is a schematic diagram of a conventional surface acoustic wave convolver.

In the same figure, a pair of comb-shaped electrodes 2 are placed on a piezoelectric substrate l,
A central electrode 3 is provided between them.

The comb-shaped electrode 2 is an electrode for exciting surface acoustic wave signals, and the center electrode 3 is an electrode for propagating the surface acoustic wave signals in opposite directions and extracting an output signal.

When a signal F(t)6j'' is applied to one side of the comb-shaped electrode 2, and a signal G(t)ej'' is applied to the other side, two surface acoustic waves in opposite directions propagate on the surface of the piezoelectric substrate 1. . Here, ν is the surface acoustic wave velocity, and L is the length of the central electrode 3.

On this propagation path, a product component of the surface acoustic wave is generated due to nonlinear effects, which is integrated within the range of the central electrode 3 and extracted. If this output signal is H(t), it is expressed by the following equation.

$)-α-ej" 5 r(t--)-a(t-"
:2'-)dxν τ However, α is a proportionality constant.

In this way, two signals F(t) and C(t
) can get a Congoliesi attack signal.

[Problem to be Solved by the Invention] However, in the above conventional example, when the signal emitted from one comb-shaped electrode 2 passes through the center electrode 3 and reaches the other comb-shaped electrode 2, a part of it is reflected, The central electrode 3 is reached again. For this reason, the signal emitted from the negative comb-shaped electrode 2 and the signal reflected from the other comb-shaped electrode 2 overlap at the center electrode 3, resulting in a con? Licensing charges occur. This is usually referred to as a self-confidence scene.

In other words, is it self-contained in the past? There was a problem in that the unnecessary signal caused by the Liesi 1/ signal overlapped with the original signal of the Condeline signal.

[Means to solve the problem]

The surface acoustic wave converter according to the present invention has on a piezoelectric substrate,
It has at least a pair of excitation electrodes that excite surface acoustic wave signals, and first and second central electrodes that propagate surface acoustic waves from the excitation electrodes in mutually opposite directions and extract output signals. , the first and second central electrodes are provided adjacent to each other along the propagation direction of the surface acoustic wave, and each central electrode has a different length.

[Effect]

In this way, by providing the first and second central electrodes with different lengths, the signal radiated from one of the excitation electrodes is separated by the signal that propagated through the first central electrode and the signal that propagated through the second central electrode. This results in a phase shift between the two objects. Therefore, when the other excitation 1tffl&ζ is reached, they cancel each other out, making it possible to suppress the generation of reflected waves. In other words, the self-composite seal is killed by suppression.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic diagram of a first embodiment of a surface acoustic wave conderper according to the present invention.

In the same figure, a comb-shaped electrode 2 is formed on a piezoelectric substrate 1 by a conventional photolithography technique. Central electrodes 3& and 3b are formed.

The central electrodes 3a and 3b are formed parallel to each other and adjacent to each other along the propagation direction of the surface acoustic waves emitted from the comb-shaped electrode 2, and the central electrode 3b has a length ΔL! L
It is formed as long as l+L.

Note that the piezoelectric substrate 1 may be made of, for example, lithium niobate (
LINbO, ) is used, and a conductor such as aluminum, silver, or gold is used for the electrodes 2.31 and 3b.

In this way, when the surface of the piezoelectric substrate 10 is covered with a conductor, the speed of the surface acoustic wave decreases compared to the speed in a free surface trap due to the electric field short circuit effect and the mass load effect. By utilizing this phenomenon, it is possible to appropriately set the difference ΔL between the lengths of the central electrodes 3a and 3b to shift the phase of the surface acoustic waves that have passed through the central electrodes 3a and 3b by 180°. It becomes possible. The details will be explained below.

First, the difference in length ΔL between the center electrodes 3m and 3b is set and formed so as to satisfy the following equation.

△L・() = (n+2)・A... (
1) vmv.

Here, ν is the velocity of the surface acoustic wave on the conductor coating surface, νG is the velocity of the surface acoustic wave on the free surface, f is the center frequency of the input signal, and n is an integer.

If there is a length difference △L that satisfies equation (1), the surface acoustic waves excited in the same phase from one comb-shaped electrode 2 will reach the central electrode 3.
a and 3b, and when they reach the other comb-shaped electrode, the phase of the surface acoustic wave propagating through the center electrode 3a and the surface acoustic wave propagating through the center electrode 3b is 1.
80@ shifted state. This rounding is electrically neutralized by each electrode finger constituting the other comb-shaped electric current, and no reflected wave is generated due to re-excitation. Therefore, it is possible to suppress the problem of self-composition, which is a conventional problem.

In addition, if the electrode finger configuration is made into a double electrode, the effect of suppressing reflected waves will be further increased, and the control effect will be increased. It is possible to improve the characteristics of Lupa.

To explain in more detail, in FIG.
The left end of & is assumed to be X=O, and the X axis is taken to the right of the page.

In the figure, two surface acoustic waves propagating in opposite directions through the center electrode 3 are expressed by the following equation.

However, 0≦X≦L (2) On the other hand, two surface acoustic waves propagating in opposite directions through the center electrode 3b are expressed by the following equation.

However, −L1≦X≦L−)−L.

Since two surface acoustic waves propagating in opposite directions are superimposed on each of the central electrodes 3 and 3b, the signals a, (t) and H are generated due to nonlinear effects.
2(t) are generated, and each is expressed by the following equation.

Here, according to equations (1) and (3), Δt1+Δt2=(n+ ”)・1f, and Δt and Δt2 are F(t) and G(t
With α sufficiently small compared to the fluctuation of l, therefore, Hl(t) and H! Since the phase is 180° different from that of (t), it is sufficient to extract the output signal in differential form.

FIG. 2 is a schematic diagram of a second embodiment of the present invention.

In this embodiment, in addition to the structure of the first embodiment, an auxiliary conductor film 4 is provided.

As shown in FIG. 2, the auxiliary conductor film 4 is provided on a propagation path other than the area where the surface acoustic waves generated by the comb-shaped electrode 2 propagate through the central electrodes 3a and 3b, and its width is equal to the width of the propagation path. The length is 1/2 and the total length is ΔL, which satisfies equation (1).

By providing such an auxiliary conductor film 4, even in surface acoustic waves propagating through areas other than the central electrodes 31 and 3b,
Since the phase differs by 1800 depending on whether or not it passes through the auxiliary conductor film 4 when reaching the other comb-shaped electrode, reflected waves can be suppressed.

Therefore, in this embodiment, in addition to the first embodiment, there is a self-control function. It can suppress the Liesin Cason and improve its characteristics as a Conqueror.

Although the auxiliary conductor film 4 is provided in the illustrated position in this embodiment, the present invention is not limited thereto.

If the surface acoustic waves excited from both of the comb-shaped electrodes 2 are on a propagation path other than the region where they propagate through the central electrodes 3a and 3b,
The auxiliary conductor film 4 may be provided anywhere, and may be divided into a plurality of parts as long as it is on the same propagation path.

〔Effect of the invention〕

As described above in detail, the surface acoustic wave converter according to the present invention is characterized in that first and second central electrodes having different lengths are provided. As a result, it is possible to suppress the surface acoustic waves emitted from one excitation electrode from being reflected by the other excitation electrode.
Hold down the con? It is possible to achieve improvements in the characteristics of the entire system.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a first embodiment of a surface acoustic wave convolver according to the present invention, FIG. 2 is a schematic diagram of a second embodiment of the present invention, and FIG. 3 is a diagram of a conventional surface acoustic wave convolver. FIG. 2 is a schematic configuration diagram of a wave converter Plupa. 1... Piezoelectric substrate, 2... Comb-shaped electrode, 3m, 3b.
... Central electrode, 4... Auxiliary conductor film. Agent Patent attorney Seki Yamashita Children 1 Figure 2 Figure 3 Procedure Um official letter (spontaneous) April 6, 1985 Commissioner of the Patent Office Kunito Ogawa 1, Indication of the case 1988 Patent application No. 3211 No. 2.9! Name: Surface Acoustic Wave Convolver 3, Relationship with the person making the amendment Patent applicant address: 3-30-2 Shimomaruko, Ota-ku, Tokyo Name (+0
0) Canon Co., Ltd. 4, Agent 5, Claims column and Detailed Description of the Invention column 6 of the specification to be amended, Contents of the amendment (1) The claims are amended as shown in the attached sheet. (2) “With a small a” on the bottom line of page 8 of the specification
correct it to "because it's small." Claims (1) On a piezoelectric substrate, at least a pair of excitation electrodes for exciting surface acoustic wave signals, and a first electrode for propagating surface acoustic waves from the excitation electrodes in mutually opposite directions and extracting an output signal. and a second central electrode, the first and second central electrodes are provided adjacent to each other along the propagation direction of the surface acoustic wave, and each central electrode has a different length. surface acoustic wave convolver. (2) The surface acoustic wave convolver according to claim 1, wherein the difference ΔL between the lengths of the first and second central electrodes substantially satisfies the following expression. However, (2) is the surface acoustic wave propagation velocity on the substrate surface covered with the central electrode, (2). is the surface acoustic wave propagation velocity on the free surface, f is the center frequency of the signal input to the excitation electrode, and n is an integer.

Claims (2)

[Claims] (1) At least a pair of excitation electrodes for exciting surface acoustic wave signals on a piezoelectric substrate, and first and second excitation electrodes for propagating surface acoustic waves from the excitation electrodes in mutually opposite directions and extracting output signals. a center electrode, the first and second center electrodes are provided adjacent to each other along the propagation direction of the surface acoustic wave, and each center electrode has a different length. Convolver. (2) The surface acoustic wave convolver according to claim 1, wherein the difference ΔL between the lengths of the first and second central electrodes substantially satisfies the following formula. △L・1/(Vm)-1/(V0)=n+1/2・1/
f, where Vm is the surface acoustic wave propagation velocity on the substrate surface covered with the central electrode, V0 is the surface acoustic wave propagation velocity on the free surface, f is the center frequency of the signal input to the excitation electrode, and n is an integer. .