JPS5950130B2 - acoustic surface wave electrical filter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to the design of so-called acoustic microwave circuits, which utilize surface wave standing waves to provide acoustic surface wave electrical filters at very high frequencies. .

The name "acoustic microwave" comes from the fact that the dimensions of the circuit structure are electromagnetic, in contrast to general electric circuits, where the dimensions of the circuit structure are sufficiently smaller than the wavelength of the electromagnetic field when the frequency handled by the circuit is viewed as an electromagnetic field. It was chosen because of its similarity to microwave circuits, which have dimensions comparable to the wavelength of the field.

In the acoustic microwave field, there are acoustic waves with wavelengths of several millimeters to several micrometers and accompanying electric fields with the same period.

However, unlike in the case of ordinary microwaves, the electromagnetic interaction is negligible.

Over the past five years, numerous research and invention articles have been published regarding the design of acoustic microwave circuits.

These announced inventions either concern the design of delay paths that take advantage of the fact that the speed of acoustoelectric waves is 10-5 slower than the speed of electromagnetic waves at the corresponding frequency, or are otherwise used to excite acoustoelectric waves. It concerns the design of filters that take advantage of the special frequency response of the coupling efficiency of the specially structured electrodes used.

The authors of these research publications and inventions do not seem to have taken into account the interesting behavior of acoustoelectric standing waves, especially in resonant conditions, in relation to circuit structures.

The inventors of this application seek to understand the interesting resonance phenomenon of acoustoelectric waves by augmenting the concepts used in laser optics.

In particular, the acoustic analogy of the so-called Fabry-Perot resonant cavity has played an important role in the development of the inventive concept.

Considering the above-mentioned speed ratio between acoustic electric waves and electromagnetic waves, it is most natural to adopt a structure similar to a Fabry-Perot cavity whose structural dimensions are much larger than the wavelength of the electromagnetic field.

In another sense, this invention relates to the extension of crystal resonators and crystal filters to high frequency ranges above 100 MHz.

Crystal resonators are widely used as high-Q resonators and therefore as elements of electrical filters.

However, in the frequency range exceeding 100 megahertz, the thickness of the crystal resonator becomes thinner than 30 micrometers, which is a critical limit in terms of manufacturing technology.

The invention further relates to the application of acoustic surface waves to electrical circuit design.

The term "surface wave" comes from the distant Lord Rayleigh.

He discovered two forms of surface elastic waves, one of which he named a surface wave, which moved along the earth's surface at a slightly slower speed than the other form of surface elastic wave, which he named a volume wave. and propagate.

This decrease in velocity can be explained by introducing a boundary condition along the free surface parallel to the direction of propagation of the elastic wave.

The properties of acoustic surface waves along the surfaces of acoustoelectric crystals have been extensively investigated both theoretically and experimentally, and are becoming an important component of acousto-microwave circuit materials.

In the case of acoustoelectric surface waves, interdigitated electrodes are photolithographically inscribed on the surface of the crystal and used for excitation of the acoustic waves.

An interlocking electrode is formed by equally spaced conductor fingers connected alternately to opposite terminals, and the pitch of the electrodes (i.e. twice the conductor finger spacing) is approximately equal to the wavelength of the acoustoelectric surface wave. equally chosen.

As a result of the development of manufacturing technology using photolithography, it is not difficult at all to form electrodes at a pitch of several micrometers.
Therefore, it is not difficult to generate gigahertz acoustoelectric surface waves.

Leather 2 Therefore, by incorporating the Fabry-Perot resonant cavity analogy into acoustic microwave circuit design, the present invention is capable of providing a The object of the present invention is to provide a means for realizing a high Q filter in a frequency domain above the input frequency.

The Fabry-Perot cavity concept is characterized by the phenomenon of multi-beam interference between a pair of highly reflective surfaces arranged perpendicular to the axis of wave propagation.

The distance between these two reflective surfaces is 1/2 wavelength (^/2
), the wave that has made one round trip between both reflecting surfaces has the same phase as the original wave.

If the rate of energy loss per one-way passage is δ, then the rate is 1/
δ waves are superimposed to form a composite wave.

If L deviates from N^/2 by δλ/2, the wave will have a completely opposite phase to the 1/δ pass restoration wave, and will no longer be effective for addition as a composite wave.

If multiple beam interference is considered in detail, the energy of the composite wave will be reduced to half of that when the phases are exactly matched, because the wavelength changes by the amount of δi2N tones.

This phenomenon is similar to the resonance of a high-Q electrically tuned circuit where Q=Nπ/δ.

The Fabry-Perot cavity concept is also characterized by the stability of the electric field distribution expressed by a Hermitian-Gaussian function.

According to the theory of Fourier transformation, a plane wave with an electric field distribution of Exp (-(x/a) 2) along a phase plane perpendicular to the wave propagation axis has an electric field distribution of Kx・^ with respect to the original phase plane. (
is expressed as a superposition of homogeneous plane waves with relative intensities of slope Exp (-(πKxa) 2) by radians).

These homogeneous plane waves propagate by a distance L, where X' is the distance from the wave propagation axis along the new phase plane, and as a result, they are recombined to become a plane wave with an electric field distribution force f:.

Here, if a=l) is set in equation (1), it can be seen that the electric field distributions of phase planes separated by a certain distance match each other.

The electric field distribution at Z=L of a plane wave reflected toward z20 by a plane perpendicular to the axis of travel of the wave is Exp(-
(x'/a))2), the original electric field distribution of the original plane wave at z=Q will be reshaped.

This electric field distribution is the lowest order of the family of Hermitian-Gaussian states.

Since these properties hold regardless of the physical properties of the wave, the relationship between the dimensions of the reflective structure and the wavelength is expressed by equation (1).
In the case of acoustoelectric surface waves, the existence of a two-dimensional analogy of Fabry-Perot cavity can be assumed as long as .

The electric field distribution Exp(-(X/a) 2) is such that the electric field with an energy density of e-2 times or more the value on the wave propagation axis is -a<x<
Therefore, no reflector is required in the X direction to confine the electric field energy within the cavity.

What this means is that any structure outside the range (-a, a) does not actually interfere with the electric field within the cavity.

Based on the above knowledge, the present invention provides an acoustoelectric crystal having a surface that forms a planar boundary with a gas, and a pair of electrodes provided on the crystal to generate an acoustic surface wave along the planar boundary. , provided on the surface of the crystal perpendicular to the direction of propagation of acoustic surface waves generated by the electrode and propagating along the planar boundary, resulting in an electric field distribution that appears at the planar boundary as a superposition of Hermitian-Gaussian functions. a pair of arc-shaped reflective boundaries, and the propagation phase between the pair of arc-shaped reflective boundaries is substantially an integral multiple of a half wavelength of the surface wave, and the pair of arc-shaped reflective boundaries It is characterized by being constructed as an isometric circuit element as seen from the electrode, which concentrates the acoustic surface waves at the center of the electrode and generates a strong electric field distribution. It is an attempt to provide a high-Q acoustic surface wave electrical filter in the frequency domain.

Hereinafter, the present invention will be explained in more detail based on the accompanying drawings.

FIG. 1A shows one example of a known structure for generating acoustoelectric surface waves.

FIG. 1B is a sectional view showing the structure on the yz plane indicated by the chain line in FIG. 1A.

FIG. 1C shows the depth dependence of stress S, strain T and electric field E.

In FIG. 1A, 0100 is a Y plate of a 3m symmetrical crystal with a large piezoelectric constant.

A typical example of this seed crystal is resumed niobate, in which the propagation velocity of the surface wave traveling in two directions is V
a is 3.47mm/# (mm per microsecond)
It is well known that

0111 and 0112 are terminals 0131 and 0132, respectively, in which electrode fingers extending in the X direction are arranged at equal intervals and alternately
are connected to form an interlocking electrode.

AC voltage V with frequency f is applied to terminals 0131 and 0132 □
When applied, a periodic electric field E as shown by the arrow in FIG. 1B
y occurs.

The spatial period of this electric field Ey is equal to the pitch p of the meshing electrodes.

This spatially periodic electric field is concentrated within a depth of 1/2πp from the crystal surface.

The piezoelectric constant is determined by the six components of the strain and stress matrix, Si and T.
is the proportionality constant between i and the ゛'3 commandments Ej and Dj of the electric field and displacement vectors, and is expressed as: Si= d re , +EJt Dj= d if 1
The piezoelectric constant of Ti(2) resume niobate is expressed in matrix form as follows (unit: Coulomb per newton): As can be seen from equation (3), in the case of this seed crystal, d4゜2
and d5,1 are significantly large.

Here, to make these quantities easier to understand visually,
Let Syz and Ey replace S4 and b.

The parallelepiped shown by the dotted line 0140 in FIG. 1B is an exaggerated depiction of how the rectangular portion of the crystal properties of Syz deforms.

Here, the wavelength of the new acoustic surface liquid that travels in two directions ^=
If Va/f is almost equal to p, the surface wave is the first
It propagates as illustrated in an exaggerated manner by the dotted line 0150 in Figure B, accompanied by electric fields Ey and Ez.

0160 in FIG. 1C is a curve representing stress Tyz, strain Syz, and electric fields Ey, Ez as a function of distance from the crystal surface.

This curve 0160 decreases exponentially in the −X direction at a rate of 2π/λ.

Figures 2A and 2B show, in plan and side view, the basic configuration of the invention consisting of an acoustoelectric crystal, a pair of electrodes, and a pair of reflective boundaries.

In FIG. 2A, 0200 is an acoustoelectric crystal, and 021
1 and 0212 are the first and second electrodes, respectively, and the crystal 02
00 surface by photolithography.

0211 and 0212 form interlocking electrodes, and each conductor finger extends in the X direction and is equally spaced.

Electrodes 0211 and 0212 are connected to terminals 0231 and 0231, respectively.
and 0232.

Here, an AC voltage V of frequency f is applied to terminals 0231 and 023.
2 and the wavelength λ=Va/f of the surface wave is almost equal to the pitch p of the electrodes, a new surface liquid is generated as already explained.

0221 and 0222 are first and second reflection boundaries extending in the X direction, where the surface waves are reflected under the following boundary conditions.

That is: In Figure 2B, 0250 is b1=b2
-0 and the distance between the two boundaries is an integer multiple of the half wavelength ^/2, and the surface deformation of the crystal due to the surface waves reflected at both boundaries 0221 and 0222 is exaggeratedly shown.

The resonance characteristic of the above structure is Q.

Figures 3A and 3B are top and side views, in which the reflective boundary is realized by grooves cut on the surface of the acoustoelectric crystal.

In FIG. 3A, 0300 is an acoustoelectric crystal, and 031
1 and 0312 are the first and second electrodes, respectively, and the crystal 03
00 surface by photolithography.

0311 and 0312 form interlocking electrodes, and each conductor finger extends in the X direction and is equally spaced.

Electrodes 0311 and 0312 are connected to terminals 0331 and 0, respectively.
332.

Here, the AC voltage V of frequency f is applied to terminals 0331 and 033.
2 and the wavelength of the surface wave = Va/f is almost equal to the pitch p of the electrodes, a new surface liquid is generated as already explained.

032al and 032a2 are first and second grooves extending in the X direction, respectively, which can be carved on the surface of crystal 03000 by photolithography and ion sputtering techniques or simply by micro-abrasives.

The surface wave is reflected in the first and second grooves under the following boundary conditions.

Namely: This is a special case of equation (4).

In Fig. 3B, 0350 is the surface of the crystal caused by the surface waves reflected by the first and second grooves when b1=b2=■ and the distance between both grooves is an integral multiple of half wavelength λ/2. This is an exaggerated illustration of the deformation.

The resonance characteristics of this structure are similar to those described with respect to FIG.

Figures 4A and 4B are top and side views in which the reflective boundary is realized by a polished edge of the acoustoelectric crystal.

In Figure 4A, 0400 is an acoustoelectric crystal, 0411 and 0
Reference numeral 412 denotes the first and second electrodes 0431 and 0432, which are terminals of each electrode, and are operated in the relationship λ=Va/f=p.

042bl and 042b2 are unique parts of this example,
The X-direction edge of the crystal has been carefully polished to a sufficiently fine precision compared to the wavelength of the surface wave.

The surface wave is reflected at both edges due to the boundary condition shown in equation (4a).

In FIG. 4B, 0450 shows an exaggerated degree of deformation of the crystal surface.

As another example, one employing a structure similar to a quarter-wavelength multilayer reflector in optics will be shown, but this type of reflector will first be explained.

The reflector is constructed by alternating layers of two different dielectric materials.

One dielectric has a large refractive index n□ (therefore the speed of light is slow and the wavelength is short), and the other dielectric has a small refractive index n (therefore the speed of light is fast and the wavelength is long).

The thickness of each layer is equal to 174 wavelengths within it.

When the logarithm of the two types of dielectrics is n and the refractive index of the substrate layer is nb, the combined reflectance R is as follows.

When a heavy metal strip is attached on the crystal surface perpendicular to the traveling direction of the surface waves, the heavy metal strip reflects the surface waves to a small extent.

The presence of this metal piece changes the boundary conditions, so the speed of the surface wave also changes.

This is the so-called load effect. For example, if a 50 nm (nanometer) thick layer of gold is placed on a Y-plate of resumed niobate, the surface shedding liquid traveling in two directions will have a velocity of 11%.
descend.

Reflection of surface waves occurs at the edge of this load region, but
This corresponds to light being reflected on a surface whose refractive index changes at a ratio equal to the ratio of surface wave velocities before and after the end of the load region.

FIG. 5 shows the phase relationship of waves reflected from each load area on the crystal surface, and when each reflected wave overlaps, it becomes a considerably large combined reflected wave.

0500 is an acoustoelectric crystal.

052CO is a sequence of load regions where the speed changes.

0551°0553.0555 and 0557 indicate the relative phases of the surface waves incident on the first, second, third and fourth regions, respectively, and 0552,0554°0556
and 0558 indicate the relative phases of waves reflected from the first, second, third and fourth regions, respectively.

Although the phase change is exaggerated in the figure, the actual phase change between the incident wave and the reflected wave is small when the load is light.

If the load is sufficiently small, the amplitude of the transmitted wave is almost equal to the amplitude of the incident wave, and the reflected waves from the front end of each load region have equal amplitude and sinusoidal phase.

When these are superimposed and added, it becomes a considerably large combined reflected wave.

Reflections also occur at the rear end of each load region, but are not shown in FIG. 5 to avoid unnecessary complication.

If the width of the load region is represented by the phase of the traveling wave and is π/2, the reflected wave from the rear end of the load region has the same amplitude and phase as the reflected wave from the front end of the load region.

For this π/2 loading, for the reflection of acoustic surface waves from a set of loading regions, the ratio of refractive indices (n
, /n,) with the speed ratio (V, /V,) and n5 is 1
After making the following modifications, it becomes the following.

Equation (7a) provides the reflectance for the number n of load regions arranged in a case where the wavelength is equal to 2p.

When the wavelength changes, equation (7a) needs to be modified to take into account the phase mismatch between the reflected waves.

As n becomes larger, (v
, /v1) 2n approaches 0.

Therefore, for large n, R approaches 1.

However, even if n is quite large, R rapidly drops to O at some value of phase mismatch.

FIG. 6 shows the reflectance R of the load region arrangement as a function curve with respect to the surface wave wavelength λ for some arrangement numbers n.

0661.0662,0663,0664,0665,
'0666 and 0667 are n=1゜n=2, respectively.
．． n=4. n=6. n=8. Figure 3 is a curve showing λ versus R for n=10 and n=12.

FIGS. 7A and 7B are top and side views in which the reflective boundary is realized by a load zone and an arrangement provided on the surface of the acoustoelectric crystal.

In Figure 7A, 0700 is an acoustoelectric crystal, 0711 and 0
712 are the first and second electrodes, 0731 and 0732 are the terminals of each electrode, and they are configured in the same way as in the case of Figures 3A and 3B, and similarly operate with the relationship ^=Va/f=p. .

072C1 and 072C2 are unique parts of this example,
configured as first and second reflective arrays extending in the X direction;
Here, the surface wave is reflected with the reflectance shown in FIG.

In this example, there is a reflectance R of the load region arrangement that can be practically considered to be 1 within a certain range of the wavelength of the surface wave.

In this case, by selecting a distribution value of p and a large value of n, it is possible to set R within a range of R=1-δ, which is slightly smaller than ■, over a certain range of surface wave wavelengths.

Furthermore, in this example, various loading methods are used.

For example, attaching a thin strip of material with density and compliance nearly equal to that of a crystal changes the boundary conditions for the surface waves, thereby changing the velocity of the surface waves to approach that of a volume wave.

Another example is applying a thin strip of high stiffness or low compliance material as a load.

In any case, the method of loading changes the boundary conditions for the surface waves or the effective acoustic impedance of the composite thin layer through which the surface waves travel.

FIG. 8 shows a first embodiment of the present invention, which is characterized in that the reflective boundary is arcuate.

In Figure 8, 0800 is an acoustoelectric crystal, 0811 and 08
Reference numeral 12 indicates the first and second electrodes, and 0831 and 0832 indicate the terminals of each electrode, which are constructed in the same manner as in the case of each side described above, and are operated in the same manner as ^=Va/f=p.

082C1 and 082C2 are parts unique to this embodiment, and are the load region arrangement of the curvature radii R1 and R2, respectively.

The center of curvature is on the Z axis along which surface waves propagate.

General Fupley-Bello Cavity Theory by Boyd and Kogelnick (1962, Bell System Technical
Journal Vol. 41, p. 1347),
The relationship between the radius of curvature and the coordinates on the two axes of the first reflection area is expressed as follows.

Here, bo is R in the case of confocal.

02 of the lowest order Hermitian-Gaussian configuration in the reflection alignment
The radius of the point, illustrated in Figure 8, is 2z =
d in bo=R and z=Q.

There are =2rte. As explained above, the electric field of the acoustic surface electric wave propagating along the plane boundary is concentrated within the radius r of equation (9) around the axis passing substantially through the center of the electrode.

Therefore, by providing a strong concentrated electric field distribution,
It is possible to obtain an electric filter that resonates efficiently and has a high Q.

FIG. 9 shows a second embodiment of the invention, in which the number of reflection rows in the load area is chosen appropriately so that the surface waves are partially transmitted.

FIG. 9A shows its structure, and FIG. 9B shows a transmission coefficient curve as a four-terminal network.

In Figure 9A, 0900 is an acoustoelectric crystal, 0911 and 0
912 is an input electrode that has a meshing structure with the first and second electrodes provided on the crystal 0900, and 0913 and 0
Reference numeral 914 forms an interlocking structure with third and fourth electrodes provided on the crystal 0900, and serves as an output electrode.

0931 and 0932 are input terminals, each connected to electrode 091.
1 and 0912, and 0933 and 0934 are output terminals connected to electrodes 0913 and 0914, respectively.

When an alternating voltage V is applied between terminals 0931 and 0932, a surface wave is generated.

092C1 and 092C2 are reflection lines, and the reflectance is slightly less than 1 within the wavelength range of the surface wave, and R=1−δ.

If the cavity formed by the two reflection lines 092C1 and 092C2 is far from the resonance condition expressed by equation (6),
A portion of the acoustic energy δ2 is transmitted through both reflection arrays.

When the cavity is just in a resonant condition, a larger portion of the acoustic energy reaches the output electrode and the terminal 0933-09
34, a considerable output voltage V' is generated.

In FIG. 9B, 0961 and 0962 are the numbers of functions for the surface wave frequency of the voltage transmission coefficient 171 large l=V'/V for two types of δ values.

As can be seen from equation (6), the transmission coefficient exhibits sharp resonance with a period of Va/2L.

FIG. 10 shows a third embodiment of the present invention, in which two resonators are coupled in the above-mentioned partially transmissive reflection arrangement, and exhibits coupled resonator characteristics.

FIG. 10A shows the structure, and FIG. 10B shows the frequency response curve of impedance between the electrode pair.

The properties of coupled filters are well known both as electrical filters and as mechanical filters.

In an electric circuit, two resonant circuits having the same resonant frequency coupled by mutual inductance or a coupling capacitor exhibit three different frequency responses depending on the coupling coefficient.

That is, critical coupling, overcoupling, and loose coupling.

As mentioned above, since the resonator of the present invention exhibits high Q characteristics, it is easy to realize that an electric circuit in which two resonators are coupled with a capacitor can be used to obtain the characteristics of a coupled resonator. It can be inferred that

However, this embodiment proposes another expedient, taking advantage of the semi-transparent nature of the reflective alignment of the loaded area.

In the first OA diagram, 1000 is an acoustoelectric crystal, 1011 and 1012 are first and second electrodes forming interlocking electrodes on the surface of the crystal 1000, and 1031 and 1032 are first and second electrodes connected to each electrode. 1 and the second terminal.

When an alternating current voltage is applied between terminals 1031 and 1032, a surface wave is generated.

A portion of the acoustic energy passes through the transflective or coupling array 102CO.

102C1 and 102C2 are reflection rows at both ends.

A first resonator R1 formed by a first reflection row 102C1 and a coupling row 102CO, and a second reflection row 102C2.
and the second resonator R2 formed by the coupling array 102CO have the same resonance frequency and are coupled by the coupling array 102CO.

In FIG. 10B, 1061, 1062, and 1063 are terminals 1031-1 for overcoupling, critical coupling, and loose coupling, respectively.
The frequency response of the impedance between 0.032 and 0.032 is shown.

FIG. 11 shows a modification of the third embodiment, in which three resonators are transflected and coupled.

FIG. 11A shows the structure, and FIG. 11B shows the frequency response of the impedance between the electrode pairs.

In FIG. 11A, 1100 is an acoustoelectric crystal, 1111 and 1112 are first and second electrodes forming interlocking electrodes on the surface of the crystal 1100, and 1131 and 1132 are first and second electrodes connected to each electrode. 1 and the second terminal.

When an alternating current voltage is applied between the terminals 113, 1 and 1132, a surface wave is generated.

A portion of the acoustic energy passes through the transflective or coupling array 112CO.

112C1, 112C2, and 112C3 are reflection rows.

A first resonator R1 formed by a first reflection row 112C1 and a coupling row 112CO, and a second reflection row 112C2.
The second resonator R2 formed by the coupling arrangement 112CO and the third resonator R3 formed by the third reflection arrangement 112C3 and the coupling arrangement 112CO have slightly medium, high, and low resonant frequencies, respectively. They are offset and connected by bonding sequence 112CO.

In FIG. 11B, 1160 indicates the frequency response of the impedance between the terminals 1131 and 1132.

FIG. 12 shows an example in which a two-terminal network is assembled as the first application of this invention.

In this example, the resonator is used as a parallel element of a general grid type two-terminal network.

Acoustoelectric crystal 1201. Intermeshing electrodes 1211 and 12
12, reflection rows 122C1 and 122C2 are the first
The acoustoelectric crystal 1202, interlocking electrodes 1213 and 1214, reflection arrays 122C3 and 122C4 constitute a high-Q resonant circuit exhibiting a resonant impedance Xr1 of
A high-Q resonant circuit exhibiting a second resonant impedance Xr2 is constructed.

Resonance impedance Xr1. Xr2 as the first. As a second parallel element, capacitances C1 and C2 of capacitors 1271 and 1272 are connected to the first parallel element. As the second series element, terminal 1
It constitutes a two-terminal network viewed from 231 and 1232.

FIG. 13 shows a first example of a four-terminal network assembled as a second application of the invention.

In this example, the resonator is used as a parallel element in a T-shaped four-terminal network.

Acoustoelectric crystal 1300, interlocking electrodes 1311 and 13
12, reflection arrays 132C1 and 132C2 constitute a high-Q resonant circuit exhibiting a resonant impedance Xr.

The resonance impedance Xr is used as a parallel element, and the capacitor 1
371 and 1372 as input side and output side series elements, input side terminal pair 1331-1
T type 4 between 332 and output side terminal pair 1333-1334
It constitutes a terminal network.

FIG. 14 shows a second example of the second application of the invention.

In this example, a resonator (see FIG. 9) with a pair of transflective arrays and input and output electrodes is used to form something similar to a transformer coupling in a general circuit.

1400 is an acoustoelectric crystal, 1411 and 1412 are first and second electrodes provided on the crystal 1400 that form an interlocking structure and serve as input electrodes, and 1413 and 1414 are third electrodes provided on the crystal 1400. and a fourth electrode form an interlocking structure and serve as an output electrode.

142C1 and 142C2 are reflective arrays with reflectances slightly less than 1.

In this way, a transformer is formed in which the resonance impedance seen from the input terminal side is Xr, the resonance impedance seen from the output terminal side is Xr2, and the coupling impedance is Mr.

The input electrodes are connected to input terminal pairs 1431 and 1432, and the output electrodes are connected to output terminal pairs 1433 and 1434.

A capacitor 1471 with a capacitance C1 and a capacitor 1472 with a capacitance C2 are connected in parallel to the input electrode and the output electrode, respectively.

The reciprocal of the constant A of the four-terminal network between the input terminal and the output terminal pair exhibits a resonance characteristic as shown in FIG. 9B.

As described above, according to the present invention, circuits with various frequency responses can be assembled using a monolithic structure, which is extremely useful.

[Brief explanation of the drawing]

Figures 1A and 1B are diagrams showing a known acoustoelectric surface wave generation structure, Figures 2A and 2B are diagrams showing the basic configuration of the present invention, and Figures 3A and 3B and Figures 4A and 4B are the premises of the present invention. FIG. 5 is an explanatory diagram showing another basic configuration, FIG. 6 is a function graph showing its reflection characteristics, and FIGS. 7A and 7B are the premise of the present invention. A plan view and a side view showing other basic configurations; FIG. 8 is a diagram showing the first embodiment of the invention; FIGS. 9A and 9B are diagrams showing the second embodiment of the invention; FIGS. 10A and 10B are diagrams showing the second embodiment of the invention. The figure shows a third embodiment of the present invention, Figures 11A and 11B are diagrams showing modifications thereof, and Figures 12, 13, and 14 are circuit diagrams showing examples of circuits to which the invention is applied. 0200...Acoustic electric crystal, 0211,02
12...Meshing electrode, reflection boundary between 0221, 0222...

Claims (1)

[Claims] 1. An acoustoelectric crystal having a surface forming a planar boundary with a gas, a pair of electrodes provided on the crystal to generate acoustic surface waves along the planar boundary, and an acoustic surface wave generated by the electrodes along the planar boundary. a pair of arc-shaped reflective boundaries provided on the surface of the crystal perpendicular to the direction of propagation of the propagating acoustic surface waves to provide an electric field distribution appearing as a superposition of Hermitian-Gaussian functions on the plane boundary; The propagation phase between the pair of arcuate reflective boundaries is substantially an integral multiple of a half wavelength of the surface wave, and the pair of arcuate reflective boundaries are configured as equally constrained circuit elements when viewed from the pair of electrodes. An acoustic surface wave electric filter characterized by: