JPH01291511A - Surface acoustic wave convolver - Google Patents

Abstract

PURPOSE:To improve a characteristic by suppressing self convolution by providing at least one auxiliary electrode with different length in a direction of propagation between areas where a surface acoustic wave is propagated through first and second central electrodes, respectively. CONSTITUTION:The central electrodes 3a and 3b are formed on a piezoelectric substrate 1 along a direction where the surface acoustic wave radiated from an interdigital electrode 2 is propagated in parallel and adjacently with each other. Also, the auxiliary electrodes 4a and 4b are formed between the interdigital electrode 2 and the central electrodes 3a and 3b. And, for example, the area B of the auxiliary electrode 4a corresponding to the central electrode 3b is formed larger by DELTAl in the direction of propagation than the area A corresponding to the central electrode 3a. By covering the surface of the piezoelectric substrate 1 with a conductor of lithium niobate. etc., the speed of the surface acoustic wave is decreased compared with that of a free surface. And it is possible to shift the phase of the surface acoustic wave passing the areas A and B, respectively at, for example, 180 deg. by setting the difference DELTAl of the length at an appropriate level.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a surface acoustic wave converter, and more particularly to a so-called self-converter, a secondary surface acoustic wave converter M/I/P, which is entirely intended for suppression of self-consistency.

[Prior art]

FIG. 7 is a schematic diagram of a conventional surface acoustic wave converter.

In the figure, a pair of comb-shaped electrodes 2 are placed on a piezoelectric substrate 1,
A central electrode 3 is provided between them.

The comb-shaped electrode 2 is an electrode that excites surface acoustic wave signals, and the center electrode 3 is an electrode that propagates the surface acoustic wave signals in opposite directions and extracts an output signal.

When a signal 14t)lj'' is applied to one side of this comb-shaped electrode 2 and a signal ((the''te) is applied to the other side, two surface acoustic waves in opposite directions propagate on the surface of the piezoelectric substrate l.Here, ν is the surface acoustic wave velocity, and L is the length of the central electrode 3.

On this propagation path, components of the surface acoustic wave are generated due to nonlinear effects, which are integrated within the range of the central electrode 3 and extracted. This output signal sound) (1) is expressed by the following equation.

However, α is a proportionality constant.

In this way, a composite signal of two signals 1) and C(t) can be obtained from the central electrode 3.

[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 the signal is reflected and returns to the center electrode 3.
reach. For this reason, the signal emitted from the - side comb-shaped electrode 2 and the signal reflected by the other comb-shaped electrode 2 and returned are overlapped at the center electrode 3, and as described above, a composite signal and a -signal signal are generated. occurs. This is usually called self-commelusion.

That is, the conventional system has had a problem in that an unnecessary signal due to the self-converting signal is superimposed on the original compensating signal.

[Means to solve the problem]

The surface acoustic wave convolver according to the present invention has a piezoelectric substrate on which
at least one pair of excitation electrodes for exciting surface acoustic waves; first and second center electrodes for propagating surface acoustic waves from the excitation electrodes in opposite directions and extracting output signals; and the pair of excitation electrodes. and the central electrode, the surface acoustic wave is provided between a region where the surface acoustic wave propagates through the first central electrode and a region where the surface acoustic wave propagates through the second central electrode, substantially in the propagation direction. and at least one auxiliary electrode having different lengths.

[Effect]

By providing the auxiliary electrode, the signal emitted from one of the excitation electrodes has a phase shift between the signal propagated through the first central electrode and the signal propagated through the second central electrode. Therefore, when they reach the other excitation electrode, they cancel each other out, making it possible to suppress the generation of reflected waves.

In other words, it is possible to suppress self-commerusion and improve characteristics.

〔Example〕

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

FIG. 1 shows the first surface acoustic wave conger quantity according to the present invention.
FIG. 1 is a schematic configuration diagram of an example.

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

The center'FJ1 poles 3a and 3b are formed parallel to each other and adjacent to each other along the direction in which the surface acoustic waves radiated from the comb-shaped electrode 2 propagate.

! In addition, auxiliary electrodes 4a and 4b are formed between the comb-shaped electrode 2 and the center electrodes 3a and 3b, and here, the region B of the auxiliary electrode 4a corresponding to the center electrode 3b is larger than the region A corresponding to the center electrode 3a. It is formed to be longer by Jt in the propagation direction.

Note that as the piezoelectric substrate l, for example, lithium niobate (
LINbO,) is used, and electrodes 2, 3 & and 3bK#
i Conductors such as aluminum, silver, and gold are used.

In this way, when the surface of the piezoelectric substrate l is covered by a conductor, the velocity of the surface acoustic wave decreases compared to the velocity on the free surface due to the electric field short circuit effect and the mass loading effect. By utilizing this phenomenon, the length difference Δz'6 of regions A and B in the auxiliary electrode 4a is set appropriately, and the regions ^ and Bi
It is possible to shift the phases of the surface acoustic waves that have passed through each by 180 degrees.

The details will be explained below.

First, the length difference Δt is expressed as approximately /il! Auxiliary electrodes 4a and 4b'ft are formed on the piezoelectric substrate 1.

Δt-f・----n+-...(1) vrI, fo madashi, ya. is the velocity of the surface acoustic wave on the conductor coating surface, is the velocity of the surface acoustic wave on the free surface, f is the center frequency of the input signal, and n#i is an integer.If there is a length difference Δt that satisfies equation (1), For example, surface acoustic waves excited in the same phase from one comb-shaped electrode 2 are out of phase with each other while passing through the auxiliary electrode 4at.

The phase of the Yuzen surface wave passing through regions A and B is 180
It reaches the other comb-shaped electrode 2 in a shifted state.

For this reason, it is electrically neutralized by the ☆ electrode fingers constituting the other comb-shaped electrode, and no reflected waves are generated due to re-excitation. Therefore, self-composition, which is a conventional problem, can be suppressed.

Note that if the electrode fingers are configured as double electrodes, the effect of suppressing reflected waves is further increased, and the characteristics as a convolver can be improved.

To explain in more detail, in FIG.
It is assumed that the left end of a is t-x-0, and the X axis is taken to the right of the page.

In the same figure, two surface acoustic waves propagating in opposite directions at the central electrode 3mg are expressed by the following equation.

However, it is ω-2πf.

On the other hand, two surface acoustic waves propagating in opposite directions through the center electrode 3b are expressed by the following equation.

F (t---c) eja+(t -,, -Jt)
and m In each of the central electrodes 3a and 3b, since two surface acoustic waves propagating in opposite directions are superimposed, the confluence signals a, (t) and H are generated due to nonlinear effects.
Jt) is generated, and each is expressed by the following equation.

Here, Jt wealth (n+ 2 ) · a, and Jt is sufficiently small compared to the fluctuation of F(t), so the following equation is obtained. Therefore, since H,(t) and H2(t) have a phase difference of 1800, the output signal is
and 3b in the form of a differential.

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

In this embodiment, the difference in length between the area and B of the auxiliary electrode 4a is Jt1, that of the auxiliary electrode 4b is Jt2, and Δt,
and Δt2t− are set to have the following equation.

That is, in equation (1) in the first embodiment, Δ1−Δt,
+Δt2. As a result, as in the first embodiment, the surface acoustic waves propagated in the area At and the surface acoustic waves propagated in the area Bi have a phase difference of 180°,
When reaching the other comb-shaped electrode 2, these two surface acoustic waves are electrically neutralized and no reflected waves are generated due to re-excitation.

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

On the other hand, two surface acoustic waves propagating in mutually opposite directions on the center electrode 3bi are expressed by the following equation.

As already mentioned, congelus signals H,(t) and H2(t) are generated at the center electrodes 3& and 3b.

and Δt1. Δ121-1 each F1t),
This is sufficiently small compared to the fluctuation of G(t).

becomes. Therefore, since the phases of H2(t) and H2(t) differ by 1800, the output signals can be extracted from the central electrodes 3a and 3b in a differential manner.

Note that the shape of the auxiliary electrodes 4a and 4b is not limited to the above embodiments, and in regions other than regions A and B, any shape may be used as shown below.

Figures 3(,) to (c) are 3 to g5 of the present invention, respectively.
FIG. 1 is a schematic configuration diagram of an example.

In the same figure (&), auxiliary electrodes 4 and 4 are connected to the outside of the propagation path.
It has a step-like shape in which the area A is widened and shortened by Δt1 and Δt2, respectively.

In the same figure (b), the space between regions A and B is formed diagonally.

In the same figure (c), the auxiliary electrode 4b is divided into 4b and 4b2, and the electrode 4b2? has a length Δt. It is formed on the area B side.

In each of these embodiments, the same effects as in the first embodiment can be obtained.

FIGS. 4(-) and 4(b) are schematic diagrams of the sixth and seventh embodiments of the present invention.

In the sixth embodiment shown in FIG. 3(a), an auxiliary electrode 4 having a length Δt is provided only on one side of the region B, and this length Δt is determined by the formula (1).
It is set to substantially satisfy the requirements.

In the seventh embodiment shown in FIG. 3B, auxiliary electrodes 41 and 4bt-Δt, +Δt2×Δt, are provided in regions B on both sides of the central electrode 3b, respectively, with lengths Δt and Δt2.

In the sixth and seventh embodiments, the output signals may be extracted differentially from the center electrodes 3a and 3b. In either embodiment, it is possible to obtain the same effects as in the first embodiment already described.

FIGS. 5(a) and 5(b) are schematic diagrams of the eighth and ninth embodiments of the present invention. Also in these examples,
An auxiliary electrode is provided only on the region B side.

In the eighth embodiment shown in FIG. 3A, the auxiliary electrode 4t has a length Δt and is formed on one side of the central electrode 3b, and extends to areas other than area B.

In the ninth embodiment shown in FIG. 4B, the auxiliary electrodes 4a and 4
b are provided on both sides of the central electrode 3b, and Δt and Δ
The length is set to t2.

However, Δ1 - Δt, +Δt2, and Δt is according to formula (1)
It is a length that substantially satisfies .

FIGS. 6(a) and 6(b) show the tenth and eleventh embodiments of the present invention.
FIG. 1 is a schematic configuration diagram of an example.

In the tenth embodiment shown in the same figure (,), auxiliary electrodes 4a and 4b'fl are provided obliquely with respect to the propagation path to suppress the influence of reflected waves by the auxiliary electrodes.

In the eleventh embodiment shown in FIG. 6B, by providing a sound absorbing material 5t in the region between regions A and B, it is possible to suppress the propagation of excess surface acoustic waves and improve the characteristics.

Note that Δt and Δt2 are as already described.

In each of the above embodiments, if the comb-shaped electrode 2 has a double electrode structure, reflected waves can be further suppressed and self-convolution can be suppressed.

Furthermore, in each of the embodiments, the surface acoustic waves generated by the comb-shaped electrode 2 are propagated with the same beam width, but the beam width may be compressed using a multi-strip coupler, a horn-shaped waveguide, or the like. .

〔Effect of the invention〕

As explained in detail above, the surface acoustic wave convolver according to the present invention is provided with auxiliary electrodes having different lengths in the propagation direction, so that the signal emitted from one excitation electrode propagates through the first central electrode. This results in a phase shift between what is transmitted through the second central electrode and what is transmitted through the second central electrode. Therefore, when the waves reach the other excitation electrode, they cancel each other out, making it possible to suppress the generation of reflected waves. In other words, it is possible to suppress self-convolution and improve characteristics.

[Brief explanation of the drawing]

1 to 6 are schematic configuration diagrams of first to eleventh embodiments of a surface acoustic wave convolver according to the present invention, and FIG. 7 is a schematic configuration diagram of a conventional surface acoustic wave convolver. . l...Piezoelectric substrate 2...Comb-shaped electrode 3m, 3b...Central electrode 4t4as4b...Auxiliary electrode 5...Sound absorbing agent agent Patent attorney Seki Yamashita Figure 1 Figure 2 Figure 41 shoes af++Δ! 2 Figure 4 (0) Figure 4 (b) ΔIl 414 smell 12 Figure 5 (a) Figure 5 (b) Figure 6 (CI) Figure 6 (b) Figure 7

Claims (2)

[Claims] (1) At least a pair of excitation electrodes for exciting surface acoustic waves on a piezoelectric substrate; first and second centers for propagating the surface acoustic waves from the excitation electrodes in mutually opposite directions and extracting output signals; an electrode, and provided at least on one side between the pair of excitation electrodes and the center electrode, and between a region where the surface acoustic wave propagates through the first center electrode and a region where the surface acoustic wave propagates through the second center electrode. A surface acoustic wave convolver comprising: at least one auxiliary electrode having different substantial lengths in the propagation direction. (2) The surface acoustic wave convolver according to claim 1, wherein the substantial length difference Δl between the regions in the auxiliary electrode satisfies the following formula. Δl・f・{(1/V_m)−(1/V_o)}=n+
(1/2) where V_m is the surface acoustic wave propagation velocity on the substrate surface covered with the auxiliary electrode, V_o is the surface acoustic wave propagation velocity on the free surface, f is the center frequency of the signal input to the excitation electrode, n is an integer.