JPH0555862A - Surface acoustic wave device - Google Patents

Abstract

PURPOSE:To reduce the deterioration of frequency characteristics due to the movement of an impulse exciting source by arranging a part of electrode fingers in an interdigital electrode processed by sampling weighting on an area shifted from an arrangement area based upon a fixed pitch. CONSTITUTION:Piezo-electric base consisting of LiNbO3 monocrystal with 128 deg. Y axis cut is used as a surface acoustic wave base and the propagating direction of surface acoustic waves is set up to the X axis. The interdigital electrode has plural electrode fingers, interdigital electrodes 1a, 1b connecting the electrode fingers and electrode fingers 12a, 12b arranged most close to the end part of the interdigital electrode, holding the impulse exciting source between them and having mutually different polarity. An intermediate point 13a between the electrode fingers 12a, 12b is moved by distance r=3.3mum to the outside 13x of the interdigital electrode along the main propagation direction of the surface acoustic wave to set up the positions of the electrode fingers 12a, 12b. Since a response near the center frequency is approximately the same as that of the original frequency characteristics of the interdigital electrode and a side lobe level is reduced by 10dB at maximum, the deterioration of the side lobe level can be reduced.

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 device, and more particularly to a surface acoustic wave device using sampling weighting electrodes.

[0002]

2. Description of the Related Art Conventionally, as a comb-shaped electrode of a surface acoustic wave device such as a surface acoustic wave filter, comb-shaped electrodes having the same electrode width and the same gap are all inserted with the same electrode finger crossing width. Electrodes were used.

Further, when such a normal type electrode is used, an impulse response model (CS Hartman) is used.
et. al. IEEE Trans. Micro
wave Tech. , Vol. MTT-21, pp1
62-175, April 1973), the surface acoustic wave device has a frequency characteristic H represented by the following equation.
It is known to have (f).

H (f) = (sinX) / X * exp (−jωN / 2f ₀ ). ． ． ． ． ． (1) X = Nπ (f−f ₀ ) / f ₀ Here, N, π, f, f ₀ , and ω represent the number of electrode pairs, pi, center frequency, and angular frequency, respectively.

However, when the surface acoustic wave device using such a normal type electrode is used as a filter, there is a problem in practical use because the side lobe attenuation amount is small.

On the other hand, as a technique for improving the attenuation amount of the side lobes, a cross length weighted electrode (U.S.P. No. 3,663, 663, which changes the cross length of adjacent comb-teeth electrodes).
899 specification).

However, such a cross-length weighted electrode is easily affected by diffracted waves. Further, generally, of the two interdigital electrodes provided in the surface acoustic wave device, the cross length weighted electrode can be used for only one of them, and the other one needs to be the normal type electrode. That is, a multi-strip coupler (Multistrip)
Coupler), it is possible to use the crossed length weighted electrodes for both of the two interdigital electrodes of the surface acoustic wave device, in which case the chip size of the piezoelectric surface acoustic wave substrate is It gets bigger (FGM
arshallet al. IEEE Trans. M
TT-21, 4, 206 (1973)).

Therefore, by removing a part of the electrode fingers of the comb-teeth-shaped electrode, the surface acoustic wave device in which the excitation source of the impulse is partly removed, that is, the technique of the surface acoustic wave device using the extraction weighted electrode. Have been proposed (C.S.
Hartman; Proc. 1973 Ultraso
n. Symp. , Pp 423-426 (1973)).

According to such a surface acoustic wave device using the extraction weighted electrode, the multi-strip coupler can be used together with the cross length weighted electrode.

[0010]

However, in the conventional technique of the surface acoustic wave device using the extraction weighted electrodes, when the electrode fingers are extracted and the non-excited portions are formed, the periodicity of the arrangement of the electrode fingers is disturbed. The electric field distribution in the piezoelectric surface acoustic wave substrate is biased from the non-excited portion to the electrode finger group as compared with the case where the electrode fingers are not extracted.

In particular, the inventors have found that the excitation source closest to each end of the non-excited portion and the excitation source closest to each end of the interdigital transducer have electrode finger extractions. It has been found that, compared with the case where the step is not performed, the electrode moves to the electrode finger group from the non-excited part, and thus the desired frequency characteristic cannot be obtained and a problem occurs in practical use.

Therefore, the present invention provides a surface acoustic wave device using a sampling weighted electrode, which can reduce the deterioration of the frequency characteristic caused by the movement of the excitation source of the impulse generated by the sampling of the electrode finger. To aim.

[0013]

[Means for Solving the Problems] To achieve the above object,
A surface acoustic wave device having a surface acoustic wave substrate for propagating surface acoustic waves and a plurality of interdigital electrodes provided on the surface acoustic wave substrate, wherein at least one interdigital electrode among the plurality of interdigital electrodes. Is a part of the interdigital electrode in which the electrode fingers are arranged at a constant pitch on the surface acoustic wave substrate, and a part of the electrode fingers is removed, and a part of the electrode fingers is displaced from the arrangement area at the constant pitch. There is provided a surface acoustic wave device characterized by being a sampling weighting electrode having a structure arranged in a region.

[0014]

According to the surface acoustic wave device of the present invention, by arranging a part of the electrode fingers of the sampling-weighted interdigital electrodes in a region deviated from the arrangement region at the constant pitch, The movement of the impulse excitation source due to the deviation of the electric field distribution in the piezoelectric surface acoustic wave substrate is corrected.

[0015]

EXAMPLES Examples of the present invention will be described below.

First, a first embodiment of the present invention will be described.

FIG. 1 shows the structure of a surface acoustic wave device according to the first embodiment.

The surface acoustic wave device according to the first embodiment is a surface acoustic wave device provided with extraction weighted electrodes provided on a surface acoustic wave substrate, and converts electrical signals and surface acoustic wave signals. To do.

FIG. 1 shows the configuration of the interdigital electrode of the surface acoustic wave device according to the first embodiment.

In the first embodiment, as the surface acoustic wave substrate, a piezoelectric substrate made of 128 ° Y-axis cut LiNbO ₃ single crystal (hereinafter referred to as "lithium niobate substrate") was used. .. Further, the propagation direction of the surface acoustic wave is the X axis. As the surface acoustic wave substrate, for example, a LiTaO ₃ substrate (hereinafter, referred to as “lithium tantalate substrate”), a quartz substrate, or another material can be used.

In the first embodiment, the center frequency of the interdigital transducer having the maximum excitation efficiency is f ₀ = 36.3.
It has a double electrode structure of 6 MHz and an electrode width of 13.3 μm.
This was formed on a surface acoustic wave substrate by a photolithography technique from an aluminum vapor deposition film having a thickness of 6000Å.

FIG. 1 shows both ends of the interdigital electrode according to the first embodiment. Although not shown in the figure, a non-excited portion formed by removing the electrode fingers exists between the both ends.

As shown in the figure, the interdigital electrode has comb-teeth-shaped electrodes 1a and 1b each composed of a plurality of electrode fingers and a bus bar for connecting the electrode fingers. Then, electrode fingers 12a and 12b sandwiching the impulse excitation source closest to the electrode end portion and having mutually different electric polarities are 12a and 12b.

Now, in the conventional surface acoustic wave device using the sampling weighting electrodes, the positions where the electrode fingers having mutually different electric polarities sandwiching the impulse excitation source closest to the electrode end are shown. It is indicated by a broken line inside. As shown in the figure, conventionally, all the electrode fingers are arranged with a constant metallized ratio and electrode pitch. In the first embodiment, the metallized ratio is 0.5.

The inventors of the present invention have determined that the electrode finger sandwiching the impulse excitation source located closest to the electrode end is located along the main surface acoustic wave propagation direction from the conventional position shown above.
While moving parallel to the outside of the interdigital transducer, the side lobe level attenuation in the frequency characteristic of the interdigital electrode was measured. The result is shown in FIG.
Indicate.

Reference numeral 35a designates an intermediate point 13a of the electrode finger which is located closest to the electrode end and which sandwiches the impulse excitation source.
3 shows the relationship between the moving distance r and the side-lobe level attenuation of the frequency characteristics of the interdigital transducer when it is moved to the outside 13x of the interdigital transducer along the main propagation direction of the surface acoustic wave.

As shown in the figure, by setting the moving distance r to an appropriate value within the range of 0 <r <6.65 μm, it is possible to reduce the deterioration of the side lobe level as compared with the conventional case. Book first
In the example, the position r of the electrode finger was set at a distance r3.3 μm, which was the best result from the measurement results.

Here, the frequency characteristic of the interdigital transducer when the distance r is about 3.3 μm is shown by reference numeral 4a in FIG.
Further, reference numeral 4b indicates a conventional frequency characteristic. As shown in the figure, compared to the code 4b, the code 4a has almost the same response near the center frequency, and the maximum side lobe level is 10 or less.
It is lowered by dB.

In general, in the case of a double electrode structure,
The point 13a, the middle point 13b of the electrode finger that sandwiches the impulse excitation source that is the second closest to the electrode end, and the middle point 13c of the electrode finger that sandwiches the impulse excitation source that is the third closest to the electrode end are adjacent. When the matching distance is set to p, the moving distance r may be considered within the range of 0 <r <(p / 8), and the optimum position of the electrode finger may be obtained. p is represented by p = v / 2f ₀ by using the center frequency f ₀ of the interdigital transducer and the propagation velocity v of the surface acoustic wave.

The second embodiment of the present invention will be described below.

The surface acoustic wave device according to the second embodiment is a surface acoustic wave device provided with a sampling weighted electrode provided on a surface acoustic wave substrate, and converts an electric signal and a surface acoustic wave signal. To do.

FIG. 3 shows the configuration of the interdigital electrodes of the surface acoustic wave device according to the second embodiment.

In the second embodiment, a 128 ° Y-axis cut lithium niobate substrate was used as the surface acoustic wave substrate. Further, the propagation direction of the surface acoustic wave is the X axis. The surface acoustic wave substrate is made of lithium tantalum.
Substrates, quartz substrates, and other materials can also be used. Further, in this interdigital transducer, the center frequency at which the excitation efficiency is maximum is f ₀ = 36.36 MHz, and the electrode width is 13.
3μm double electrode structure, thickness of 6000Å
It was formed on the surface acoustic wave substrate by a photolithography technique from the aluminum vapor deposition film.

FIG. 3 shows a non-exciting portion of the interdigital transducer of the surface acoustic wave device according to the second embodiment, both ends of which are not shown.

As shown in the figure, the interdigital electrode has comb-teeth-shaped electrodes 1a and 1b each composed of a plurality of electrode fingers and a bus bar for connecting the electrode fingers. The non-excitation part 7 is provided partially in the interdigital transducer.
Electrode fingers 25a and 25b having electrical polarities different from each other and sandwiching an impulse excitation source closest to the non-excitation part are provided.

Now, in the conventional surface acoustic wave device using the sampling weighting electrodes, the positions where the electrode fingers having mutually different electric polarities sandwiching the excitation source of the impulse closest to the non-excitation part are shown in the figure. It is indicated by a broken line. As shown in the figure, conventionally, all electrode fingers are arranged at a constant metallized ratio and electrode pitch. In the second embodiment, the metallized ratio is 0.5.

The inventors of the present invention have determined that the electrode fingers sandwiching the impulse excitation source located closest to the non-excited portion are located in the main surface acoustic wave propagation direction from the conventional position shown above.
The amount of side lobe level attenuation in the frequency characteristics of the interdigital transducer was measured while moving in parallel toward the non-excitation part 7. The result is indicated by reference numeral 35b in FIG.

The reference numeral 35b designates the intermediate point 23a of the electrode finger which sandwiches the impulse excitation source located closest to the non-excitation section.
2 shows the relationship between the moving distance r and the attenuation amount of the side lobe level of the frequency characteristic of the interdigital transducer when the surface acoustic wave is moved to the non-excitation portion side 23x along the main propagation direction.

As shown in the figure, by setting the moving distance r to an appropriate value within the range of 0 <r <6.65 μm, the deterioration of the side lobe level can be reduced as compared with the conventional case. Book second
In the example, the position r of the electrode finger was set at a distance r3.3 μm, which was the best result from the measurement results.

The frequency characteristic of the interdigital transducer when r is about 3.3 μm is shown by reference numeral 8a in FIG. Reference numeral 8b in FIG. 4 shows a conventional frequency characteristic. As shown in the figure, compared to the code 8b, the code 8a has a response near the center frequency
Almost the same, the side lobe level is reduced by up to 15 dB.

Incidentally, in the same manner as described in the first embodiment,
In the case of the double electrode structure, a point 23a, an intermediate point 23b of the electrode fingers sandwiching the impulse excitation source located second closest to the non-excitation section 7 and an impulse excitation source located third closest to the non-excitation section 7 Assuming that the distance between the midpoints 23c of the sandwiching electrode fingers is p, the moving distance r should be considered within the range of 0 <r <(p / 8). p is the center frequency f ₀ of the interdigital transducer and the propagation velocity v of the surface acoustic wave, and p = v /
It is represented by 2f ₀ .

The configuration shown in FIG. 3 has the non-excitation section 7
Is shown as having two impulse excitation sources extracted, but the number of excitation sources to be extracted is not limited to two.

The third embodiment of the present invention will be described below.

The surface acoustic wave device according to the third embodiment is a surface acoustic wave device provided with extraction weighted electrodes provided on a surface acoustic wave substrate, and converts electric signals and surface acoustic wave signals. To do.

FIG. 5 shows the configuration of the interdigital electrode of the surface acoustic wave device according to the third embodiment.

In the third embodiment, a 128 ° Y-axis cut lithium niobate substrate was used as the surface acoustic wave substrate. Further, the propagation direction of the surface acoustic wave is the X axis. The surface acoustic wave substrate is made of lithium tantalum.
Substrates, quartz substrates, and other materials can also be used. Further, in this interdigital transducer, the center frequency at which the excitation efficiency is maximum is f ₀ = 36.36 MHz, and the electrode width is 13.
3μm double electrode structure, thickness of 6000Å
It was formed on the surface acoustic wave substrate by a photolithography technique from the aluminum vapor deposition film.

FIG. 5 shows a non-exciting portion of the interdigital transducer of the surface acoustic wave device according to the third embodiment, both ends of which are not shown.

As shown in the figure, the interdigital electrode has comb-teeth-shaped electrodes 1a and 1b each composed of a plurality of electrode fingers and a bus bar for connecting the electrode fingers. The non-excitation part 10 is partially provided in the interdigital transducer. Electrode fingers 39a, 39b having different electrical polarities sandwiching the impulse excitation source closest to the non-excitation unit 10 are provided.
Is.

In the second embodiment described above, the non-excitation part of the interdigital electrode was sandwiched between the electrode fingers having the same electric polarity (see FIG. 3). In the interdigital transducer according to the third embodiment, the non-excited portion is sandwiched between electrode fingers having different electric polarities. So in this case,
Impulse excitation may occur at the center of the non-excitation unit 10.

Now, in the surface acoustic wave device using the conventional sampling and weighting electrodes, the positions where electrode fingers having different electric polarities sandwiching the excitation source of the impulse closest to the non-excitation part are arranged in the figure. It is indicated by a broken line. As shown in the figure, conventionally, all the electrode fingers are arranged with a constant metallized ratio and electrode pitch. In the third embodiment, this metallized ratio is 0.5.

Now, the inventors of the present invention have placed the electrode fingers sandwiching the impulse excitation source closest to the non-excited portion from the conventional position shown above along the main surface acoustic wave propagation direction.
While moving parallel to the non-excitation part 10, the side lobe level attenuation amount in the frequency characteristic of the interdigital transducer was measured.

Now, when the intermediate point 33a of the electrode fingers sandwiching the impulse excitation source closest to the non-excitation section is moved to the non-excitation section 10 side 33x along the main propagation direction of the surface acoustic wave, the moving distance is As for the relationship between r and the attenuation amount of the side lobe level of the frequency characteristic of the interdigital transducer, the frequency characteristic of the interdigital electrode is the best when r is about 3.3 μm, as in the second embodiment. The response near the center frequency was almost the same, and the side lobe level was reduced by about 15 dB compared to the frequency characteristic when the was not moved.
Therefore, in the third embodiment, the distance r3.3 μm, which gives the best effect from the measurement result, is set as the position of the electrode finger.

As described above, even when the non-excited portion 10 is sandwiched between the electrode fingers 39a and 39b having different electric polarities, the side positions can be determined by arranging the optimum positions of the electrode fingers by measurement. -It is possible to improve the attenuation amount of the sub-level.

The fourth embodiment of the present invention will be described below.

In the fourth embodiment, the movement of the electrode fingers performed in the second and third embodiments is performed by another method.

This moving method is shown in FIGS. 6, 7 and 8. It should be noted that in each figure, only the vicinity of the boundary with the non-excitation part is shown.

Further, in the surface acoustic wave device using the conventional sampling and weighting electrodes, the positions where the electrode fingers having mutually different electric polarities sandwiching the excitation source of the impulse closest to the non-excitation part are shown in each figure. Is indicated by a broken line. Also, 41a and 41b in FIG. 6 and 73a and 7b in FIG.
Reference numeral 3b, and 46a and 46b in FIG. 8 denote electrode fingers sandwiching the impulse excitation source located closest to the non-excitation portion.

The inventors of the present invention have determined that the electrode fingers sandwiching the impulse excitation source closest to the non-excited portion are closer to the non-excited portion 7 side along the main surface acoustic wave propagation direction than the conventional position shown above. The amount of side lobe level attenuation in the frequency characteristic of the interdigital transducer was measured while moving parallel to.

However, in the case shown in FIG. 6, the position of the side 42 of the electrode finger 41a on the opposite side of the impulse excitation source closest to the non-excitation portion is kept fixed.

Further, in the case shown in FIG. 7, the electrode finger 7 on the opposite side of the impulse excitation source located closest to the non-excited portion is used.
The position of the side 44 of 3a and the position of the side 45 of the electrode finger 73b on the opposite side of the impulse excitation source closest to the non-excited portion were kept fixed.

Further, in the case shown in FIG. 8, the electrode finger 4 on the opposite side of the impulse excitation source located closest to the non-excited portion is used.
The position of the side 47 of 6b was kept fixed.

In each case, the intermediate point 43a of the electrode finger sandwiching the impulse excitation source located closest to the non-excitation section is located along the main propagation direction of the surface acoustic wave on the non-excitation section 7 side of the interdigital electrode. The relationship between the moving distance r when moved to 43x and the attenuation amount of the side lobe level of the frequency characteristic of the interdigital transducer is that r is about 3 as in the case of the second and third embodiments described above. In the case of 0.3 μm, the frequency characteristic of the interdigital transducer is the best, and compared with the frequency characteristic when the point 43a is not moved, the response near the center frequency is almost the same and the side lobe level is reduced by about 15 dB. Therefore, also in the fourth embodiment, the position of the electrode finger is set to the distance r3.3 μm at which the best effect is obtained from the measurement result.

As described above, also by such a moving method, it is possible to improve the attenuation amount of the side lobe level by arranging the optimum positions of the electrode fingers by experiments.

Next, a fifth embodiment of the present invention will be described.

The surface acoustic wave device according to the fifth embodiment is a surface acoustic wave device provided with extraction weighted electrodes provided on a surface acoustic wave substrate, and converts electrical signals and surface acoustic wave signals. To do.

FIG. 9 shows the configuration of the interdigital transducer of the surface acoustic wave device according to the fifth embodiment.

In the fifth embodiment, a 128 ° Y-axis cut lithium niobate substrate is used as the surface acoustic wave substrate. Further, the propagation direction of the surface acoustic wave is the X axis. For the surface acoustic wave substrate, for example, a lithium tantalate substrate, a quartz substrate, or another material can be used.

In the fifth embodiment, the center frequency of the interdigital transducer having the maximum excitation efficiency is f ₀ = 36.3.
It has a single electrode structure of 6 MHz and an electrode width of 26.6 μm. This was formed on a surface acoustic wave substrate by a photolithography technique from an aluminum vapor deposition film having a thickness of 6000Å.

FIG. 9 shows both ends of the interdigital transducer according to the fifth embodiment. Although not shown in the figure, a non-excited portion formed by removing the electrode fingers exists between the both ends.

As shown in the figure, the interdigital electrode is composed of two comb-teeth-shaped electrodes each composed of a plurality of electrode fingers and a bus bar for connecting the electrode fingers. Then, electrode fingers 98a and 98b sandwiching the impulse excitation source closest to the electrode end portion and having mutually different electric polarities are 98a and 98b.

Now, in the surface acoustic wave device using the conventional sampling and weighting electrodes, the positions where the electrode fingers having different electric polarities sandwiching the impulse excitation source closest to the electrode end are arranged are shown in FIG. It is indicated by a broken line inside. As shown in the figure, conventionally, all the electrode fingers are arranged with a constant metallized ratio and electrode pitch. In the fifth embodiment, this metallized ratio is 0.5.

Now, the inventors of the present invention have placed the electrode fingers sandwiching the impulse excitation source closest to the end of the electrode from the conventional position shown above along the main surface acoustic wave propagation direction.
While moving parallel to the outside of the interdigital transducer, the side lobe level attenuation in the frequency characteristic of the interdigital electrode was measured. The result is shown in FIG.

In FIG. 12, the intermediate point 93a of the electrode fingers sandwiching the impulse excitation source, which is the closest to the electrode end, is located outside the interdigital electrode 93 along the main propagation direction of the surface acoustic wave.
It shows the relationship between the movement distance r and the attenuation amount of the side lobe level of the frequency characteristics of the interdigital transducer when moved to x.

As shown in the figure, by setting the moving distance r to an appropriate value within the range of 0 <r <13 μm, the deterioration of the side lobe level can be reduced as compared with the conventional case. Book 5
In the example, the position of the electrode finger was set at a distance r6.5 μm, which was the best result from the measurement results.

Here, the distance r is about r and about 6.5.
When μm, the frequency characteristics of the interdigital transducer are the best, and compared with the conventional frequency characteristics, the response near the center frequency is
Almost the same, the side lobe level is reduced by about 15 dB.

Generally, in the case of a single electrode structure, a point 93a, an intermediate point 93b of an electrode finger sandwiching an impulse excitation source located at the second closest position to the electrode end, and 3 at the electrode end.
Assuming that the distance between the intermediate points 93c of the electrode fingers sandwiching the impulse excitation source located next to the next is p, the moving distance r is considered within the range of 0 <r <(p / 4). It is sufficient to find the optimum position of. p is represented by p = v / 2f ₀ by using the center frequency f ₀ of the interdigital transducer and the propagation velocity v of the surface acoustic wave.

In the fifth embodiment, the end portion of the interdigital electrode having the single electrode structure is described. However, the non-excited portion inside the interdigital electrode has the double electrode structure in the second and third embodiments. Results are obtained with those shown for the interdigital electrodes. In addition, in this case, the portion from which the impulse excitation source is extracted may be arbitrary.

Next explained is the sixth embodiment of the invention.

The surface acoustic wave device according to the sixth embodiment is a surface acoustic wave device provided with a sampling weight electrode provided on a surface acoustic wave substrate, and performs conversion between an electric signal and a surface acoustic wave signal. ..

FIG. 10 shows the configuration of the interdigital electrode of the surface acoustic wave device according to the sixth embodiment.

In the sixth embodiment, a 128 ° Y-axis cut lithium niobate substrate is used as the surface acoustic wave substrate. Further, the propagation direction of the surface acoustic wave is the X axis. The surface acoustic wave substrate is made of lithium tantalum.
Substrates, quartz substrates, and other materials can also be used. Further, in this interdigital transducer, the center frequency at which the excitation efficiency is maximum is f ₀ = 36.36 MHz, and the electrode width is 13.
3μm double electrode structure, thickness of 6000Å
It was formed on the surface acoustic wave substrate by a photolithography technique from the aluminum vapor deposition film.

FIG. 10 shows a non-exciting portion of the interdigital transducer of the surface acoustic wave device according to the sixth embodiment, and both ends thereof are not shown.

As shown in the figure, the interdigital electrode has two comb-teeth electrodes each of which is composed of a plurality of electrode fingers and a bus bar for connecting the electrode fingers. Then, electrode fingers 119a and 119b sandwiching the impulse excitation source closest to the non-excitation portion and having different electrical polarities are 119a and 119b.

Now, in the conventional surface acoustic wave device using the sampling weighted electrodes, the positions where the electrode fingers having different electric polarities sandwiching the excitation source of the impulse closest to the non-excited portion are arranged in the drawing. It is indicated by a broken line. As shown in the figure, conventionally, all electrode fingers are arranged at a constant metallized ratio and electrode pitch. In the sixth embodiment, this metallized ratio is 0.5.

Now, the inventors of the present invention have placed the electrode fingers sandwiching the impulse excitation source closest to the non-excited portion from the conventional position shown above along the main surface acoustic wave propagation direction.
While moving parallel to the non-excitation part 107 side, the side lobe level attenuation amount in the frequency characteristic of the interdigital transducer was measured.

When the intermediate point 103a of the electrode finger sandwiching the impulse excitation source located closest to the non-excited portion is moved to the non-excited portion side 103x along the main propagation direction of the surface acoustic wave, the moving distance r and When the relationship of the side lobe level attenuation amount of the frequency characteristic of the interdigital transducer is obtained, the frequency characteristic of the interdigital electrode is the best when r is about 3.3 μm, as in the second embodiment, and the conventional frequency characteristic. Compared with, the response near the center frequency is almost the same, and
The level is about 15 dB lower.

Therefore, in the sixth embodiment, the position r of the electrode finger is set to the distance r3.3 μm where the best effect is obtained from the measurement result.

As described above, it is possible to improve the side lobe level attenuation amount by arranging the optimum position of the electrode finger obtained by measurement.

By the way, in the non-excitation part where the excitation source is removed, the piezoelectric substrate is exposed. And
The propagation velocity of the surface acoustic wave propagating on the substrate surface of the non-excited portion is higher than that in the state where the electrode fingers are formed in the non-excited portion. For example, in a lithium niobate substrate, a propagation velocity difference of about 3% occurs between the case where the surface is covered with aluminum and the case where the surface is not covered with aluminum.

Therefore, in the interdigital transducers in each of the first to sixth embodiments, the exposure width of the non-excited portion is widened so that the apparent speed difference becomes zero. May be.

In this case, in the interdigital electrode corrected as described above, the electrode fingers may be moved as described above to obtain the optimum arrangement position.

Even in such a case, the frequency characteristics of the interdigital electrode have substantially the same response in the vicinity of the center frequency as compared with the frequency characteristics when the electrode fingers are not moved, and the side-row frequency characteristics are the same.
The level can be improved by about 15 dB.

In the surface acoustic wave device shown in each of the above embodiments, it is assumed that there is no change in the electric field distribution of the non-excited part due to the removal of the electrode fingers of the interdigital transducer. Except for the period corresponding to the excitation unit and at least one of the time point of the impulse excitation and the time points of the earliest and final impulse excitation that are adjacent to the period corresponding to the non-excitation unit, the time response of the impulse excitation is Occurring at a constant time interval and at least one of an impulse excitation time point and an earliest and final impulse excitation time point which are adjacent to each other in the period corresponding to the non-excitation section, and the impulse excitation which is adjacent to the time point. The electrode fingers can be designed so that the time interval from the point of time is larger than the fixed time interval.

Next explained is the seventh embodiment of the invention.

FIG. 13 shows the structure of the surface acoustic wave filter according to the seventh embodiment.

This surface acoustic wave filter is based on T of West Germany.
The center frequency corresponding to the standard of the V receiver is f ₀ = 36.3.
It is a 6 MHz intermediate frequency filter, and has a comb-shaped input electrode 122 and output electrode 123. Also,
As the surface acoustic wave substrate, a 128 ° Y axis cut lithium niobate substrate is used, and the propagation direction of the surface acoustic wave is the X axis. The surface acoustic wave substrate 121 may be made of, for example, a lithium tantalate substrate, a quartz substrate, or another material.

Further, in the seventh embodiment, the interdigital input electrodes 122 are the interdigital electrodes shown in the first to sixth embodiments.

That is, the input electrode 122 sandwiches the comb-teeth-shaped electrode fingers 124a and 124b which interdigitate with each other and the impulse excitation source closest to the end of the interdigital electrode, and the electrode fingers 125a and 125 having different electric polarities.
b. In addition, the electrode finger 126 in the input-shaped electrode 22
A non-excitation part 107 is provided between a and 126b. Also,
Compared to the arrangement pitch of the other electrode fingers, the electrode fingers 125a, 12a
5b is at a position moved to the end side of the input electrode 122,
The arrangements of 6a and 126b are arranged at positions moved to the non-excitation portion 107 side.

In the seventh embodiment, the output electrode 123
The crossing length weighting electrode is used for the first to sixth embodiments.
The interdigital electrodes shown in the embodiments may be used.

Next, as an eighth embodiment of the present invention, a TV receiver using the surface acoustic wave filter according to the seventh embodiment as an intermediate frequency filter will be described.

FIG. 14 shows the structure of the receiving section of the TV receiver according to the eighth embodiment.

In the figure, numeral 129 is a tuner block, 13
0 is a surface acoustic wave filter, 131 is a detection block, 13
2 is a video signal output, 133 is an audio signal output, and 134 is an antenna.

In such a receiving portion of the TV receiver, the surface acoustic wave filter 130 extracts a signal for one channel from the intermediate frequency signal sent from the tuner block 129, and the detection block 131. Then, the video signal output 132 and the audio signal output 133 are separately output.

FIG. 15 shows the frequency characteristic 135a of the intermediate frequency filter in the eighth embodiment.

As shown in the figure, by using the surface acoustic wave filter according to the seventh embodiment as an intermediate frequency filter, the conventional extraction weighting electrode in which electrode fingers are arranged at a constant pitch is used as an input electrode. The out-of-band characteristic is improved by about 10 dB as compared with the characteristic 135b.

As described above, the surface acoustic wave filter according to the seventh embodiment can be used not only as a TV receiver but also as an intermediate frequency filter for various communication devices.

The application examples to the interdigital transducer intermediate frequency filters shown in the first to sixth embodiments have been described above. The interdigital electrodes shown in the first to sixth embodiments are oscillators. Also, the present invention can be applied to a correlator, an RF filter, and the like. As described above, according to this embodiment, the electrode finger crossing length of the adjacent comb-teeth-shaped electrodes is not changed, and Without increasing the element chip size, the amount of movement of the impulse excitation position is apparently zero at the end of the electrode finger extraction part, and the amount of impulse excitation position movement is apparent at the end of the interdigital electrode. The excitation intensity of the surface acoustic wave can be changed to zero.
As a result, it is possible to obtain the same effect as that of the conventional weighting electrode in which the crossing length is changed, the side lobe level can be significantly improved, and the characteristics of the surface acoustic wave filter can be improved.

Also, regarding the characteristics within the pass band, since both the input and output electrodes can be weighted, the degree of freedom in designing elements such as filters is greatly improved.

[0109]

As described above, according to the present invention, the elasticity using the sampling weighted electrode which can improve the deterioration of the frequency characteristic due to the movement of the excitation source position of the impulse caused by the sampling of the electrode finger is used. A surface acoustic wave device can be provided.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a configuration of a surface acoustic wave device according to a first embodiment of the present invention.

FIG. 2 is a characteristic diagram showing frequency characteristics of the surface acoustic wave device according to the first embodiment of the present invention.

FIG. 3 is an explanatory diagram showing a configuration of a surface acoustic wave device according to a second embodiment of the invention.

FIG. 4 is a characteristic diagram showing frequency characteristics of a surface acoustic wave device according to a second embodiment of the invention.

FIG. 5 is an explanatory diagram showing a configuration of a surface acoustic wave device according to a third embodiment of the present invention.

FIG. 6 is an explanatory diagram showing a first configuration of a surface acoustic wave device according to a fourth embodiment of the present invention.

FIG. 7 is an explanatory diagram showing a second configuration of the surface acoustic wave device according to the fourth embodiment of the present invention.

FIG. 8 is an explanatory diagram showing a third configuration of the surface acoustic wave device according to the fourth embodiment of the present invention.

FIG. 9 is an explanatory diagram showing a structure of a surface acoustic wave device according to a fifth embodiment of the present invention.

FIG. 10 is an explanatory diagram showing a structure of a surface acoustic wave device according to a sixth embodiment of the present invention.

FIG. 11 is a characteristic diagram showing the relationship between the side lobe level attenuation amount and the electrode finger movement amount of the surface acoustic wave device according to the first embodiment of the present invention and the surface acoustic wave device according to the second embodiment. is there.

FIG. 12 is a characteristic diagram showing a relationship between a side lobe level attenuation amount and an electrode finger movement amount of a surface acoustic wave device according to a fifth embodiment of the present invention.

FIG. 13 is an explanatory diagram showing a structure of a surface acoustic wave device according to a seventh embodiment of the present invention.

FIG. 14 is a block diagram showing a configuration of a TV receiver according to an eighth embodiment of the present invention.

FIG. 15 is a characteristic diagram showing frequency characteristics of a surface acoustic wave filter according to an eighth embodiment of the present invention.

[Explanation of symbols]

 1a, 1b electrode, 7, 10 non-excitation part, 121 surface acoustic wave substrate, 122 input electrode, 123 output electrode, 130 surface acoustic wave filter.

Claims (12)

[Claims] 1. A surface acoustic wave substrate for propagating a surface acoustic wave,
In a surface acoustic wave device having a plurality of interdigital transducers provided on a surface acoustic wave substrate, at least one interdigital transducer among the plurality of interdigital electrodes is arranged at a constant pitch on the surface acoustic wave substrate. An extraction weighting electrode having a structure in which a part of the electrode fingers of the interdigital electrode in which the electrode fingers are arranged is extracted, and a part of the electrode fingers is arranged in a region deviated from the arrangement region at the constant pitch. A surface acoustic wave device characterized by the above. 2. A surface acoustic wave substrate for propagating surface acoustic waves,
In a surface acoustic wave device having a plurality of interdigital transducers provided on a surface acoustic wave substrate, at least one interdigital transducer among the plurality of interdigital electrodes is arranged at a constant pitch on the surface acoustic wave substrate. Part of the electrode fingers of the interdigital electrode in which the electrode fingers are arranged are removed, and a part of the electrode fingers is displaced from the arrangement area at the constant pitch, and the non-excitation part is removed. A surface acoustic wave characterized by being an extraction weighting electrode having a structure arranged in an area in which the position of the partial excitation source is close to the position of the excitation source when the extraction of some of the electrode fingers is not performed. apparatus. 3. A surface acoustic wave substrate for propagating a surface acoustic wave,
In a surface acoustic wave device having a plurality of interdigital transducers provided on a surface acoustic wave substrate, at least one interdigital transducer among the plurality of interdigital electrodes is arranged at a constant pitch on the surface acoustic wave substrate. Part of the electrode fingers of the interdigital electrode in which the electrode fingers are arranged are removed, and a part of the electrode fingers is displaced from the arrangement area at the constant pitch, and the non-excitation part is removed. A surface acoustic wave device, characterized in that it is a sampling weighting electrode having a structure arranged in a region in which the electric field distribution of a portion approaches the electric field distribution when a part of the electrode fingers is not extracted. 4. A surface acoustic wave substrate for propagating a surface acoustic wave,
In a surface acoustic wave device having a plurality of interdigital transducers provided on a surface acoustic wave substrate, at least one interdigital transducer among the plurality of interdigital electrodes is arranged at a constant pitch on the surface acoustic wave substrate. A part of the interdigital electrode in which the electrode fingers are arranged is extracted, and the electrode fingers sandwiching the excitation source adjacent to the non-excitation part generated by the extraction of the part of the electrode fingers are set to the constant pitch. The surface acoustic wave device is a sampling weighting electrode having a structure arranged in a region displaced from the arrangement region in the direction of the non-excitation part by the above. 5. A surface acoustic wave substrate for propagating a surface acoustic wave,
In a surface acoustic wave device having a plurality of interdigital transducers provided on a surface acoustic wave substrate, at least one interdigital transducer among the plurality of interdigital electrodes is arranged at a constant pitch on the surface acoustic wave substrate. Arrangement of electrode fingers sandwiching the excitation source adjacent to the end portion of the interdigital transducer in which the electrode fingers are arranged and part of the electrode fingers are extracted and the surface acoustic wave propagation direction of the interdigital electrode is arranged at the constant pitch. A surface acoustic wave device, which is a sampling weighting electrode having a structure arranged in a region displaced in a direction of an end portion of a surface acoustic wave propagation direction of the interdigital electrode from the region. 6. The surface acoustic wave device according to claim 4, wherein the extraction weighting electrode has a multi-electrode structure, and an arrangement area of electrode fingers sandwiching an excitation source of the extraction weighting electrode is an excitation source. The distance r between the middle point of the electrode fingers that sandwich the electrode and the middle point of the electrode fingers that sandwich the excitation source when the electrodes are arranged at the constant pitch is 0 <r <v /
16f ₀ (where f ₀ is the center frequency f ₀ of the interdigital transducer,
The surface acoustic wave device is characterized in that v is a region that satisfies a surface acoustic wave propagation velocity relationship. 7. The surface acoustic wave device according to claim 4, wherein the sampling weighting electrode has a single electrode structure, and an arrangement area of electrode fingers sandwiching the excitation source of the sampling weighting electrode is an excitation source. The distance r between the middle point of the electrode fingers that sandwich the electrode and the middle point of the electrode fingers that sandwich the excitation source when the electrodes are arranged at the constant pitch is 0 <r <v /
8f ₀ (where f ₀ is the center frequency f ₀ , v of the interdigital transducer)
The surface acoustic wave device is a region that satisfies the relationship of (propagation velocity of surface acoustic waves). 8. An intermediate frequency filter as claimed in claim 1,
A communication device comprising the surface acoustic wave filter according to 3, 4, 5, 6 or 7. 9. An intermediate frequency filter as claimed in claim 1,
A television receiver comprising the surface acoustic wave filter according to 3, 4, 5, 6 or 7. 10. A comb-shaped electrode weighted by extraction is provided by extracting a part of electrode fingers arranged at a constant pitch on a surface acoustic wave substrate to provide a non-excitation part sandwiched between excitation parts. A method of designing a surface acoustic wave device, comprising: a part of the electrode fingers of the comb-shaped electrodes subjected to the extraction weighting, which is a region displaced from the arrangement region at the constant pitch, and a part of the electrode fingers. A method for designing a surface acoustic wave device, characterized in that the surface acoustic wave device is arranged in a region in consideration of a change in electric field distribution in a portion excluding the non-excited portion caused by the removal of. 11. A comb-shaped electrode for performing extraction weighting by extracting a part of electrode fingers arranged at a constant pitch on a surface acoustic wave substrate to provide a non-excitation part sandwiched between excitation parts. A method of designing a surface acoustic wave device, wherein it is assumed that there is no change in the electric field distribution of the non-excitation section due to the extraction of the electrode fingers of the comb-shaped electrodes subjected to the extraction weighting, the non-excitation section The period corresponding to
Except for at least one of the time points of the first and last impulse excitations and the time points of impulse excitations adjacent to each other in the period corresponding to the non-excitation section, the time response of the impulse excitation occurs at constant time intervals, And, at least one of the time points of the impulse excitation and the earliest and last time points of the impulse excitation that are adjacent to each other in the period corresponding to the non-excitation section, and the time interval between the time point and the time point of the adjacent impulse excitation. A method of designing a surface acoustic wave device, wherein the electrode fingers are arranged so as to be larger than the predetermined time interval. 12. An extraction weighting electrode, wherein only the remaining electrode fingers excluding the extraction points of the electrode fingers and some of the electrode fingers are arranged at a constant pitch.