JPH07212184A - Surface acoustic wave convolver - Google Patents

Abstract

PURPOSE:To have high convolution efficiency and a wide band characteristic by arranging an interdigital electrode by considering the directivity of the electrode in an elastic convolver where the interdigital electrode having thickness on a piezoelectric or an electrostrictive substrate is provided. CONSTITUTION:On a piezoelectric or an electrostrictive substrate 1, a first interdigital electrode composed of a first surface acoustic wave converter 2 damping a surface acoustic wave and a second interdigital electrode composed of a second surface acoustic wave converter 3 are provided. These surface acoustic waves are detected and a convolution output is taken out as an electric signal from output power 8. At this stage, the first and second interdigital electrodes 2 and 3 have prescribed thickness, the electrode 2 has a positive/ negative electrode 4 whose electrode width and cycle gradually become shorter toward an output electrode 8, and the electrode 3 has positive/negative electrodes 6 and 7 whose electrode widths and periods gradually become longer toward the output electrode 8.

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 convolver which is a combination of surface acoustic wave converters provided with interdigital electrodes having different electrode widths and periods in the surface acoustic wave propagation direction.

[0002]

2. Description of the Related Art Conventionally, a surface acoustic wave converter having a comb-shaped electrode composed of positive and negative electrodes provided on a piezoelectric substrate (including a piezoelectric thin film substrate) or an electrostrictive substrate generally has an equi-periodic structure. The electrodes were arranged. FIG. 3A is a plan view showing a surface acoustic wave convolver using a conventional surface acoustic wave converter, and FIG. 3B is an XY sectional view thereof. Three
1 is a first surface acoustic wave converter for converting an electric signal into a surface acoustic wave, 32 is a second surface acoustic wave converter for converting a similar electric signal into a surface acoustic wave, and 33 is a surface acoustic wave converter 3
1 and 32 are output electrodes that detect the surface acoustic waves that have been generated and proceed and that extract the convolution output as an electric signal. Each of the interdigital electrodes of the surface acoustic wave converters 31 and 32 has an electrode arrangement structure with an equal period. That is,
When the electrode width of the interdigital transducer is m and the period is p, p is constant and m / p is a constant (mostly "0.5").

In the surface acoustic wave converter having such an electrode arrangement structure of equal period, the generated surface acoustic waves propagate in the left and right directions with substantially the same amplitude. Therefore, it can be said that they have similar insertion loss characteristics in both directions, that is, they have bidirectional characteristics.

On the other hand, as a technique for obtaining a unidirectional surface acoustic wave converter having a characteristic of low insertion loss in only one direction by using a surface acoustic wave converter having an electrode arrangement structure of equal periods,
Conventionally, for example, a method of using a 120-degree phase shifter, a method of using a 90-degree phase shifter, and an internal reflection type unidirectionality that obtains a unidirectional characteristic by arranging reflective electrodes asymmetrically between positive and negative electrodes at equal intervals There was a method such as a converter.

[0005]

A surface acoustic wave converter having an electrode arrangement structure with an equal period has a bidirectional characteristic, and a characteristic of low insertion loss in only one direction cannot be obtained. Therefore, even if a surface acoustic wave convolver is configured using such a surface acoustic wave converter, a convolver with high convolution efficiency cannot be obtained. Further, in the technique for obtaining the above-mentioned unidirectional surface acoustic wave converter, although the characteristic that the insertion loss is low in one direction is obtained, the surface acoustic wave converter having the electrode arrangement structure of the equal period is also used. Therefore, broadband characteristics cannot be obtained. Therefore, even if applied to a surface acoustic wave convolver, wide band characteristics cannot be obtained.

The present invention has been made in view of the above problems in the conventional example, and an object thereof is to provide a surface acoustic wave convolver having a high convolution efficiency and a wide band characteristic.

[0007]

In order to achieve the above object, the present invention provides first and second interdigital transducers for exciting surface acoustic waves on a piezoelectric or electrostrictive substrate, and these electrodes. In the surface acoustic wave convolver having an output electrode for detecting a surface acoustic wave of (1) and extracting a convolution output as an electric signal, the first and second interdigital transducers have a predetermined thickness, and the first electrode has a predetermined thickness. The interdigital electrodes are formed by alternately arranging positive and negative electrodes whose electrode width and period gradually decrease toward the output electrode.
The interdigital electrodes are characterized in that positive and negative electrodes whose electrode width and period gradually increase toward the output electrode are alternately arranged.

When the electrode width of the interdigital transducer is m and the period is p, the first interdigital electrode has 0.2 ≦ m / p ≦ 0.
7 and the second interdigital electrode is 0.72 ≦ m / p ≦
It is preferably set to 0.9. When the acoustic impedance of the metal film of the interdigital transducer is Zm and the acoustic impedance of the electrode gap is Zg, Zm / Zg of the first interdigital electrode is smaller than 1 and the acoustic impedance of the second interdigital electrode is less than 1. It is preferable that Zm / Zg be greater than 1.

[0009]

[Operation] Positive and negative electrodes having different periods are arranged in the propagation direction,
When the film thickness of the electrode is thick, the phase of excitation and the phase of reflection of the electrode can be the same in one propagation direction and the opposite phase in the other propagation direction. A surface acoustic wave convolver (filter) is obtained by aligning the surface acoustic wave converters having such unidirectional characteristics in the same direction and forming output electrodes between them. In particular, in the above-mentioned configuration, the first interdigital transducer has a shape of 0.2 ≦ m / p ≦ 0.
7 and the second interdigital electrode is 0.72 ≦ m / p ≦
When it is set to 0.9, the second electrode has substantially bidirectional characteristics, and a convolver with high convolution efficiency can be obtained.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a plan view of a surface acoustic wave convolver according to an embodiment of the present invention. Reference numeral 2 is an excitation-side first surface acoustic wave converter arranged on the piezoelectric substrate, and reference numeral 3 is an excitation-side second surface acoustic wave converter arranged on the piezoelectric substrate. The first surface acoustic wave converter 2 has a positive electrode 4 and a negative electrode 5 (first interdigital transducer). The second surface acoustic wave converter 3 has a positive electrode 6 and a negative electrode 7 (second interdigital transducer). Reference numeral 8 represents an output electrode. The positive electrodes 4 and the negative electrodes 5 are alternately arranged so that the electrode width m and the period p gradually decrease toward the output electrode. The positive electrodes 6 and the negative electrodes 7 are alternately arranged so that the electrode width m and the period p gradually increase toward the output electrode. Here, Y-cut Z-propagation lithium niobate was used as the piezoelectric substrate 1, and aluminum films were used as the electrodes 4, 5, 6, 7.

Graph 21 in FIG. 2 shows the relationship between m / p and insertion loss in the surface acoustic wave converter. Graph 21 shows the insertion loss characteristics of the surface acoustic wave converter in the forward direction (the direction in which a surface acoustic wave having a larger amplitude is obtained). Graph 22
On the contrary, shows the insertion loss characteristic in the backward direction of the surface acoustic wave converter (the direction in which a surface acoustic wave having a smaller amplitude is obtained). From FIG. 2, the insertion loss in the backward direction is larger than the insertion loss in the forward direction, and the magnitude of the insertion loss is m.
It can be seen that it depends on / p. Note that the advancing direction may be opposite depending on the cut and propagation of the crystal of the piezoelectric body and the type of the deposited film.

It is preferable that one surface acoustic wave converter on the excitation side has a strong unidirectional property and the other surface acoustic wave converter has a weak unidirectional property and is almost bidirectional. Therefore, from FIG. 2, one surface acoustic wave converter has 0.2 ≦ m / p ≦ 0.7,
On the other hand, it is preferable that 0.72 ≦ m / p ≦ 0.9. In the convolver of FIG. 1, the positive electrode 4 and the negative electrode 5 are
Is m / p = 0.5, and the positive electrode 6 and the negative electrode 7 are m / p =
It was set to 0.8. As described above, a surface acoustic wave convolver having high convolution efficiency and wide band characteristics can be obtained. In fact, the surface acoustic wave convolver of FIG. 1 had a bandwidth of 30% or more and a convolution efficiency of -60 dBm or less.

It should be noted that the present invention has for the first time found that the surface acoustic wave converter has directivity by positively utilizing the reflection at the electrodes arranged on the piezoelectric substrate. The surface acoustic wave convolver having a wide bandwidth and a high convolution efficiency is constructed by utilizing this property. In this case, the electrode needs to have a certain thickness so that the surface acoustic wave is reflected at the electrode. When the thickness of the electrode is H and the wavelength of the surface acoustic wave is λ, it is preferable that 0.01 ≦ H / λ ≦ 0.10.

Further, when Zm is the acoustic impedance of the electrode metal and Zg is the acoustic impedance of the electrode gap, the directionality of the surface acoustic wave converter is determined according to the value of Zm / Zg.

In FIG. 5, the thickness of the electrode made of Al is 200
It is a figure which shows the frequency characteristic and arrangement | positioning of an electrode for demonstrating the directivity of the chirp type transducer by an equivalent circuit analysis when it is set to 0 angstrom and Zm / Zg = 0.98. As shown in FIG. 5B, an up-chirp IDT 73 in which the density of the positive and negative electrodes is gradually increased is adjacent to the IDT (interdigital transducer, interdigital transducer) 74 having a pair of positive and negative electrodes. With this configuration, the frequency characteristic is as shown by the solid line 71 in FIG. On the contrary, as shown in FIG. 5C, a down-chirp ID in which the arrangement density of the positive and negative electrodes gradually becomes coarser toward the IDT 76 having a pair of positive and negative electrodes.
In the configuration in which the T75s are adjacent to each other, the frequency characteristic is as shown by the broken line 72 in FIG. As for the frequency characteristic, the solid line 71 is better than the broken line 72. Therefore, I
The DT73 has the directionality shown by the arrow 73D, and the IDT75
It can be seen that has the directionality shown by the arrow 75D.

FIG. 6 is a diagram showing the frequency characteristics and the arrangement of electrodes for explaining the directivity of the chirp type transducer by the equivalent circuit analysis when Zm / Zg = 1.00. As shown in FIG. 6B, in the configuration in which the IDTs 83 having a pair of positive and negative electrodes are arranged adjacent to each other with the up-chirp IDT 83 in which the density of the arrangement of the positive and negative electrodes is gradually increased, The frequency characteristic is as shown by the solid line 81. Further, as shown in FIG. 6C, a down-chirp IDT in which the arrangement density of the positive and negative electrodes gradually becomes coarser toward the IDT 86 having a pair of positive and negative electrodes.
Also in the configuration in which 85 are adjacent to each other, the solid line 8 in FIG.
The frequency characteristic shown in FIG. Therefore, it is understood that the IDT 83 and the IDT 85 have no directivity.

FIG. 7 is a diagram showing the frequency characteristics and the arrangement of electrodes for explaining the directivity of the chirp type transducer by the equivalent circuit analysis when Zm / Zg = 1.02. As shown in FIG. 7B, in the configuration in which the IDTs 93 having a pair of positive and negative electrodes are arranged adjacent to each other with the up-chirp IDTs 93 such that the arrangement density of the positive and negative electrodes is gradually increased, The frequency characteristic is as shown by the solid line 91. On the contrary, as shown in FIG. 7C, a down-chirp IDT in which the arrangement density of the positive and negative electrodes gradually becomes coarser toward the IDT 96 having a pair of positive and negative electrodes.
In the configuration in which 95 are adjacent to each other, the frequency characteristic is as shown by a broken line 92 in FIG. The broken line 9 shows the frequency characteristics.
2 is better than solid line 91. Therefore, the ID
It can be seen that T93 has a directionality shown by an arrow 93D and IDT95 has a directionality shown by an arrow 95D.

As a result of investigating the directivity of the chirp type transducer under various conditions as described above, in the chirp type transducer, when Zm / Zg <1, the arrangement density of the positive and negative electrodes becomes coarse to dense. It has directionality, and when Zm / Zg = 1, it has no directionality and Zm / Z
It was found that when g> 1, the arrangement density of the positive and negative electrodes has a directivity in a direction from dense to coarse. Therefore, if the convolver is configured in consideration of the directionality of such a transducer, it is possible to have a low insertion loss and a wide band characteristic.

In FIG. 4, the thickness of the electrode made of Al is 200
It is a figure which shows the frequency characteristic and arrangement | positioning of an electrode for demonstrating the directivity of the chirp type filter by an equivalent circuit analysis at 0 angstrom and Zm / Zg = 0.98. In other words, it shows the frequency characteristics and the like in the case of configuring a filter in which the transducers used in the example of FIG. 5 are arranged. As shown in FIG. 4B, the IDT 63 of the up-chirp
With the configuration in which the IDT64 of Upchirp is adjacent to
The frequency characteristic is as shown by the solid line 61 in FIG.
On the contrary, as shown in FIG. 4C, the down chirp IDT6
In the configuration in which the No. 5 and the down-chirp IDT 66 are adjacent to each other, the frequency characteristic is as shown by the broken line 62 in FIG. The difference in the frequency characteristics is caused because the IDTs 63, 64, 65, 66 have the directivities shown by the arrows 63D, 64D, 65D, 66D, respectively, as described in FIG.

In particular, as one method, it is possible to adjust the value of Zm / Zg by providing a floating electrode as shown in FIG. 8, and thereby it is possible to give directionality to the transducer. In FIG. 8, a transducer 102, which is a surface acoustic wave converter, includes a positive electrode 10 and a negative electrode 10.
4,105. Furthermore, these positive and negative electrodes 10
The floating electrode 106 is provided in the gap between the electrodes 4, 106. Every other floating electrode 106 is short-circuited. By including such a short-circuited floating electrode 106, Zm / Zg of this transducer 102 became smaller than 1. Further, although not shown, by providing the floating electrode 106 opened without short-circuiting the floating electrode 106,
The Zm / Zg of this transducer 102 became larger than 1.

[0022]

As described above, according to the present invention,
In a surface acoustic wave convolver that has a comb-shaped electrode having a thickness on a piezoelectric or electrostrictive substrate, it is arranged in consideration of the directionality of the comb-shaped electrode, resulting in high convolution efficiency and wide band characteristics. A surface acoustic wave convolver having is obtained.

[Brief description of drawings]

FIG. 1 is a plan view of a surface acoustic wave convolver according to an embodiment of the present invention.

FIG. 2 is a graph showing the relationship between m / p and insertion loss.

FIG. 3 is a plan view and a cross-sectional view of a filter using a conventional surface acoustic wave converter.

FIG. 4 is a diagram showing a frequency characteristic and an arrangement of electrodes for explaining the directivity of a chirp filter with Zm / Zg = 0.98.

FIG. 5 is a diagram showing a frequency characteristic and an arrangement of electrodes for explaining the directivity of a chirp type transducer having Zm / Zg = 0.98.

FIG. 6 is a diagram showing a frequency characteristic and an arrangement of electrodes for explaining the directivity of a chirp type transducer having Zm / Zg = 1.00.

FIG. 7 is a diagram showing frequency characteristics and arrangement of electrodes for explaining the directivity of a chirp type transducer with Zm / Zg = 1.02.

FIG. 8 is a plan view showing a transducer using a floating electrode.

[Explanation of symbols]

2, 31 ... First surface acoustic wave converter, 3, 32 ... Second surface acoustic wave converter, 4, 6 ... Positive electrode, 5, 7 ... Negative electrode,
8, 33 ... Output electrodes.

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] July 5, 1991

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Claims

[Correction method] Change

[Correction content]

[Claims]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0016

[Correction method] Change

[Correction content]

FIG. 5 shows that the thickness of the electrode made of Al is 2
It is a figure which shows the frequency characteristic for demonstrating the directivity of a chirp type transducer by an equivalent circuit analysis at 000 angstrom, and Zm / Zg = 0.98, and arrangement | positioning of an electrode. As shown in FIG. 5B, a down-chirp IDT 7 in which the arrangement density of the positive and negative electrodes gradually increases toward the IDT (interdigital transducer, interdigital transducer) 74 having a pair of positive and negative electrodes.
In the configuration in which 3 are adjacent to each other, the frequency characteristic is as shown by the solid line 71 in FIG. On the contrary, as shown in FIG.
In the configuration in which the IDTs 75 having a pair of positive and negative electrodes are adjacent to the IDT 75 of the up-chirp where the density of the arrangement of the positive and negative electrodes is gradually increased, the frequency characteristics as shown by the broken line 72 in FIG. Become. As for the frequency characteristic, the solid line 71 is better than the broken line 72. Therefore, the IDT 73 has the direction shown by the arrow 73D, and the ID
It can be seen that T75 has the directionality shown by the arrow 75D.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0017

[Correction method] Change

[Correction content]

FIG. 6 is a diagram showing a frequency characteristic and an arrangement of electrodes for explaining the directivity of the chirp type transducer by an equivalent circuit analysis when Zm / Zg = 1.00. As shown in FIG. 6B, in the configuration in which the IDTs 83 having a pair of positive and negative electrodes are adjacent to each other with the down-chirp IDTs 83 such that the arrangement density of the positive and negative electrodes is gradually increased, the configuration shown in FIG. The frequency characteristic is as shown by the solid line 81. Further, as shown in FIG. 6C, an up-chirp I in which the arrangement density of the positive and negative electrodes becomes gradually coarser toward the IDT 86 having a pair of positive and negative electrodes.
Even with the configuration in which the DTs 85 are adjacent to each other, the frequency characteristic shown by the solid line 81 in FIG. Therefore, IDT8
It can be seen that both 3 and IDT85 have no directivity.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0018

[Correction method] Change

[Correction content]

FIG. 7 is a diagram showing a frequency characteristic and an arrangement of electrodes for explaining the directivity of the chirp type transducer by the equivalent circuit analysis when Zm / Zg = 1.02. As shown in FIG. 7B, in the structure in which the down-chirp IDT 93 in which the density of the arrangement of the positive and negative electrodes is gradually increased toward the IDT 94 having the pair of positive and negative electrodes is shown in FIG. The frequency characteristic is as shown by the solid line 91. On the other hand, as shown in FIG. 7C, the up-chirp I of which the arrangement density of the positive and negative electrodes gradually becomes coarser toward the IDT 96 having the pair of positive and negative electrodes.
In the configuration in which the DTs 95 are adjacent to each other, the broken line 92 in FIG.
The frequency characteristics are as shown in. Regarding the frequency characteristic, the broken line 92 is better than the solid line 91. Therefore,
The IDT 93 has the direction shown by the arrow 93D, and
It can be seen that 5 has the directionality shown by the arrow 95D.

[Procedure Amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0020

[Correction method] Change

[Correction content]

FIG. 4 shows that the thickness of the electrode made of Al is 2
It is a figure which shows the frequency characteristic and arrangement | positioning of an electrode for demonstrating the directivity of the chirp type filter by an equivalent circuit analysis at 000 angstrom and Zm / Zg = 0.98. In other words, it shows the frequency characteristics and the like in the case of configuring a filter in which the transducers used in the example of FIG. 5 are arranged. As shown in Fig. 4 (b), the IDT of down chirp
In the configuration in which 63 and the down-chirp IDT 64 are adjacent to each other, the frequency characteristic is as shown by the solid line 61 in FIG. Conversely, as shown in FIG.
In the configuration in which the T65 and the up-chirp IDT 66 are adjacent to each other, the frequency characteristic is as shown by the broken line 62 in FIG. The difference in the frequency characteristics is caused because the IDTs 63, 64, 65, 66 have the directivities shown by the arrows 63D, 64D, 65D, 66D, respectively, as described in FIG.

[Procedure correction 6]

[Document name to be corrected] Drawing

[Name of item to be corrected] Fig. 4

[Correction method] Change

[Correction content]

[Figure 4]

[Procedure Amendment 7]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 5

[Correction method] Change

[Correction content]

[Figure 5]

[Procedure Amendment 8]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 6

[Correction method] Change

[Correction content]

[Figure 6]

[Procedure Amendment 9]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 7

[Correction method] Change

[Correction content]

[Figure 7]

Claims (3)

[Claims] 1. A first or second interdigital transducer that excites a surface acoustic wave on a piezoelectric or electrostrictive substrate, and these surface acoustic waves are detected to output a convolution output as an electric signal. In a surface acoustic wave convolver having an output electrode, the first and second interdigital transducers have a predetermined thickness, and the first interdigital transducer gradually has an electrode width and a period toward the output electrode. Positive and negative electrodes are alternately arranged, and the second interdigital transducer is alternately arranged with positive and negative electrodes whose electrode width and period gradually increase toward the output electrode. And a surface acoustic wave convolver. 2. When the electrode width of the interdigital transducer is m and the period is p, the first interdigital electrode has 0.2 ≦ m.
/P≦0.7, and the second interdigital transducer is 0.7
The surface acoustic wave convolver according to claim 1, wherein 2 ≦ m / p ≦ 0.9. 3. When the acoustic impedance of the metal film of the interdigital transducer is Zm and the acoustic impedance of the electrode gap is Zg, Zm / Zg of the first interdigital electrode.
Is less than 1, and Zm / Zg of the second interdigital transducer is
The surface acoustic wave convolver according to claim 1 or 2, wherein is greater than 1.