JPH07283685A - Trap circuit - Google Patents

Abstract

PURPOSE:To obtain a trap circuit having plural trap frequencies and in which the attenuation amount in each trap frequency is large. CONSTITUTION:By forming interdigital transducers(IDT) 23 and 24 on a piezoelectric substrate 22, first and second resonance parts of end face reflection type for which an SH type surface wave is used are composed. Weighing is performed for the IDT23 and 24 so that each of the first and second resonance parts may have two resonance characteristics and an inductance element 35 is connected between the first and second resonance parts to form a trap circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a trap circuit constructed by using a piezoelectric resonator utilizing SH type surface waves, and more particularly to a trap circuit having a plurality of trap frequencies.

[0002]

2. Description of the Related Art Television receivers and video tape recorders
At the video intermediate frequency stage of the
The trap characteristics shown in Fig. 1 are used to prevent
A trap circuit is used. Next to this circuit
Closed channel video signal frequency f _ap(American NTSC
Method 39.75MHz) and adjacent channel voice signal
No. frequency f_as(The American NTSC system is 47.25.
MHz) it is necessary to sufficiently attenuate the signal
is there.

In order to realize the above trap characteristics, conventionally, there are two traps, one having an attenuation point at the adjacent channel video signal frequency f _ap and the other having an attenuation point at the adjacent channel audio signal frequency f _as . A trap is used, and each trap is composed of an LC resonance circuit, a piezoelectric resonator, or the like.

As a piezoelectric resonator used for such an application, a piezoelectric resonator utilizing an SH type surface wave such as a BGS wave has been receiving attention. FIG. 2 shows an end surface reflection type surface wave resonator utilizing BGS waves.

The end surface reflection type surface acoustic wave resonator 1 is composed of a piezoelectric substrate 2 having a quadrangular planar shape. The piezoelectric substrate 2 is made of a piezoelectric material such as lead zirconate titanate-based piezoelectric ceramics, LiNbO ₃ piezoelectric single crystal, or LiTaO ₃ piezoelectric single crystal. In the case of piezoelectric ceramics, the piezoelectric substrate 2 is polarized in the direction of arrow P shown in the figure. Is being processed.
On the upper surface 2a of the piezoelectric substrate 2, a pair of comb-teeth electrodes 3 and 4 are formed, which constitutes an interdigital transducer. The comb electrodes 3 and 4 have a plurality of electrode fingers 3a to 3c and 4a to 4c, respectively.

In the end surface reflection type surface acoustic wave resonator 1, by applying an AC voltage from the comb-teeth electrodes 3 and 4, a BGS wave is excited and the BGS wave is propagated in the arrow X direction shown in the figure. This BGS wave is reflected by the end surface of the piezoelectric substrate 2.

In the end face reflection type surface wave resonator 1, effective resonance characteristics are obtained by matching the frequency spectrum determined by the interdigital transducer with the frequency determined by the dimension between the end faces.

Attenuation amount of the end face reflection type surface wave resonator 1-
Frequency spectrum characteristics and impedance-frequency characteristics are shown in FIGS. 3 (a) and 3 (b). 3 (a) and 3 (b)
As is apparent from the above, the end surface reflection type surface acoustic wave resonator 1 also has a single resonance characteristic, like the conventional LC resonance circuit and other types of piezoelectric resonators.

[0009]

As described above, as described above,
For example, in order to realize the trap characteristics shown in FIG. 1, it is necessary to prepare and connect two resonance circuits, piezoelectric resonators, and the like. Even if two resonant circuits, piezoelectric resonators, etc. are connected as described above, it is difficult to realize a sufficient amount of attenuation at each trap frequency.

On the other hand, as a surface acoustic wave resonator utilizing Rayleigh waves, one having two resonance characteristics in a single resonator has been shown (for example, International Electric Technical Report N.
o. 16, p. 1 to p. 7, 1992). That is, in the surface wave resonator filter using the Rayleigh wave,
A dual mode resonator utilizing a secondary longitudinal mode (basic mode) and a secondary longitudinal mode is known, and two resonance characteristics are obtained here. However, in the above dual mode resonator, two or more interdigital transducers and a reflector are required to obtain two resonance characteristics. Further, in the above dual mode resonator, its resonance characteristic is determined by the reflection coefficient-frequency characteristic of the reflector. However, since the frequency region where the reflection coefficient is large is narrow, the difference between the two resonance points is about 1 MHz. It was so small that the trap filter as shown in FIG. 1 could not be constructed with only the dual mode resonator.

An object of the present invention is a trap circuit constructed by using a piezoelectric resonator utilizing SH type surface waves, and it is possible to realize a sufficiently large attenuation amount at a plurality of trap frequencies. To provide.

[0012]

According to a first aspect of the present invention, there is provided a piezoelectric substrate, and two resonance portions each having two resonance characteristics on the piezoelectric substrate. And a pair of interdigital transducers connected to each other, wherein the two resonators are electrically connected in parallel, and a piezoelectric resonator utilizing an SH type surface wave is provided. , Which is a trap circuit.

That is, the invention described in claim 1 is SH
In a piezoelectric resonator using a surface acoustic wave of a type, two sets of IDTs are formed so as to form two resonance parts, and the two resonance parts are connected in parallel. Therefore,
In the trap circuit of the present invention, it is sufficient to prepare only a single piezoelectric resonator as an element for realizing two trap frequencies, and two traps are formed by the single piezoelectric resonator and the inductance element. A trap circuit having a frequency is constructed.

Preferably, as described in claim 2, an inductance element is further connected between the two resonance parts or at least one of the preceding stages of the part where the two resonance parts are provided. Be prepared.

The invention according to claim 3 is provided with a piezoelectric substrate and an interdigital transducer formed on the piezoelectric substrate and electrically connected in parallel to each other so as to have two resonance characteristics. And a first and second piezoelectric resonators using SH type surface waves.

According to the third aspect of the invention, the first and second piezoelectric resonators utilizing SH type surface waves are connected in parallel. Therefore, although the first and second piezoelectric resonators, that is, the two piezoelectric resonators are used, it is possible to realize a sufficiently large attenuation amount at a plurality of trap frequencies as described later.

Preferably, as in claim 4, an inductance connected between the first and second piezoelectric resonators or at least one of the preceding stages of the portion where the first and second piezoelectric resonators are provided. An element is further provided.

[0018]

The inventors of the present invention have proposed a Japanese Patent Application No.
-34415, a piezoelectric resonator using SH type surface waves, in which the IDT is configured to have at least two resonance characteristics, is proposed. This structure will be described with reference to FIGS.

The piezoelectric resonator 11 is composed of a piezoelectric substrate 12 having a rectangular planar shape. The piezoelectric substrate 12 is made of an appropriate piezoelectric material such as lead zirconate titanate-based piezoelectric ceramics. Piezoelectric substrate 12
Is polarized in a direction indicated by an arrow P, that is, parallel to the main surface and in a direction parallel to the extending direction of the electrode fingers.

On the upper surface of the piezoelectric substrate 12, the comb-teeth electrode 1
An interdigital transducer (hereinafter abbreviated as IDT) 15 including 3 and 14 is formed. Each of the comb-teeth electrodes 13 and 14 has a plurality of electrode fingers 13
a, 13b, 13c, 13d and 14a to 14i. That is, the IDT 15 is configured in the form of thinned electrodes by thinning out some of the plurality of electrode fingers that are inserted into each other.

More specifically, between the electrode fingers 14c to 14g, the electrode fingers on the other side of the comb electrode 13 are thinned out. In this case, in the inter-electrode finger area, the area where the electrode fingers on both sides are connected to different potentials, that is, the area where the voltage is applied from the electrode fingers on both sides to excite the BGS wave is “1”, Since the electrode fingers are thinned out, the electrode fingers on both sides have the same potential, that is, the inter-electrode finger region in which the BGS wave is not excited is expressed as “0”. In the piezoelectric resonator 11, 1 from the electrode finger 14a to the electrode finger 14i
The two regions are, in order, 1, 1, 1, 1, 0, 0, 0,
It is represented by 0, 1, 1, 1, 1.

In the comb electrodes 13 and 14, the width of each region between the electrode fingers is λ / 4 when the wavelength λ of the excited BGS wave is λ / 4, and the electrode finger 1
The width of the remaining electrode fingers other than 4a and 14i is also λ / 4. In addition, the electrode fingers 14a and 14i located on the outermost sides
Has a width of λ / 8, and the electrode fingers 14a and 14i are arranged along the edges between the end surfaces 12a and 12b of the piezoelectric substrate 12 and the upper surface.

For the comb-teeth electrodes 13 and 14 as described above, for example, a piezoelectric substrate having a larger width direction than the piezoelectric substrate 12 is prepared, and a large number of electrode fingers having a width λ / 4 are formed at a λ / 4 pitch. By dicing the piezoelectric substrate so that the comb electrodes 13 and 14 are obtained, that is, the electrode fingers 1
4a and 14i are λ / 4 by the above dicing.
It can be formed by cutting an electrode finger having a width of 4 to a half width. In this way, the IDT 15 and
The piezoelectric resonator 11 having the end faces 12a and 12b can be obtained.

In the piezoelectric resonator 11, as in the case of the end face reflection type surface wave resonator 1 utilizing the conventional SH type surface wave shown in FIG. , A BGS wave propagating in a direction orthogonal to the extending direction of the electrode fingers is excited, and the BGS wave is excited by the end face 12
It is reflected between a and 12b.

Therefore, the piezoelectric resonator 11 is an end face reflection type surface wave resonator utilizing BGS waves. Piezoelectric resonator 1
The impedance-frequency characteristic of No. 1 is shown in FIG.

As is apparent from FIG. 6, the piezoelectric resonator 11
Then, the two resonance points Fr₁And Fr ₂Appears. Sanawa
Then, two resonance characteristics can be obtained. This is IDT15
However, as described above, 1,1,1,1,0,0,0,0,
Consists of thinning electrodes thinned out by 1, 1, 1, 1.
It is because it has been. That is, between the above forms
Since the IDT 15 is composed of the pulling electrode,
Designed two main lobes for the determined frequency spectrum
As a result, two resonance characteristics can be obtained.

In this case, two resonance points Fr ₁ and Fr ₂
The frequency difference between them is about 8 MHz. That is, two resonance characteristics with a large frequency difference can be obtained as compared with the case of the dual mode resonator filter using the Rayleigh wave described above. It is considered that this is because two main lobes of the frequency spectrum determined by IDT could be designed. Therefore, by adjusting the material and size of the piezoelectric substrate 12 and the mode of the thinned electrodes in the IDT 15 and the size of the electrode fingers,
Two resonance points 11 having a relatively large appropriate frequency difference
It is possible to provide a piezoelectric resonator having

Therefore, the piezoelectric resonator 11 can be preferably used as a trap filter in the intermediate video frequency stage of the television receiver or the video tape recorder shown in FIG. 1, for example. That is, the piezoelectric resonator 11 is a single element and can be used as a trap element having two trap frequencies.

As described above, the piezoelectric resonator 11 is a single element but has two trap frequencies. Therefore, by using the piezoelectric resonator 11, the structure of the trap circuit can be simplified. However, when the piezoelectric resonator 11 is used as the trap filter of the television receiver, for example, the attenuation amounts at the trap frequencies of the adjacent channel video frequency f _ap and the adjacent channel audio frequency f _as are 13 dB and 15 respectively.
There was a problem that it was about dB and still not sufficient.

The present invention is directed to Japanese Patent Application No. 6-344 as described above.
The piezoelectric resonator disclosed in No. 15 has been found as a result of further investigation to expand the attenuation amount at two trap frequencies. As described above, in the invention according to claim 1, the resonance is achieved. Since the parts are connected in parallel, in the invention according to claim 3, the first and second piezoelectric resonators are connected in parallel, thereby increasing the attenuation amount. Further, as described above, in the invention according to claim 2, by connecting the inductance element between the two resonance parts or at least one of the preceding stages,
According to the invention described in claim 4, by connecting an inductance element between the first and second piezoelectric resonators or at least one of the preceding stages thereof, the amount of attenuation can be increased and the high level within two trap frequencies can be achieved. It is prevented that the amount of attenuation on the band side, that is, the video carrier frequency becomes large.

As described above, the two resonance parts, or the two resonance parts
The reason why the attenuation amount is increased by connecting two piezoelectric resonators in parallel is that the impedance at the resonance point is halved by connecting two resonant parts or two piezoelectric resonators in parallel. It depends. In addition, the inductance element is provided between the two resonance parts, at least one of the preceding stages of the part where the two resonance parts are provided, or between the two piezoelectric resonators, or the two piezoelectric resonators. The reason why the attenuation amount is increased by connecting to at least one of the preceding stages of the portion where is provided, and the increase amount at the high frequency side within the two trap frequencies, that is, at the video carrier frequency is prevented is increased. 2 resonators or 2
This is because the peak of the resonance characteristic formed by the capacitance component of each piezoelectric resonator and the inductance element exists near the video carrier frequency.

[0032]

Therefore, in the invention described in claim 1, 2
Since the resonance parts are connected in parallel, the amount of attenuation at the two trap frequencies can be sufficiently increased. Moreover, in the invention according to claim 1, since the two resonance parts are configured in a single piezoelectric resonator,
When constructing a trap circuit having a plurality of trap frequencies, two resonators and two resonant circuits are not required. Therefore, the configuration of the trap circuit can be simplified.

Further, according to the second aspect of the invention, since the inductance element is connected between the two resonance parts or at least one of the preceding stages thereof, it is necessary to further increase the attenuation amount at the two trap frequencies. In addition, it is possible to prevent the amount of attenuation on the high frequency side within the two trap frequencies, that is, on the video carrier frequency from increasing.

According to the third aspect of the invention, by connecting the first and second piezoelectric resonators utilizing SH type surface waves in parallel as described above, attenuation at two trap frequencies is achieved. The amount is expanded. Therefore, similarly to the invention described in claim 1, it becomes possible to easily provide a trap circuit having a large amount of attenuation at two trap frequencies.

Further, in the invention according to claim 4, since the inductance element is connected between the two piezoelectric resonators or at least one of the preceding stages thereof, the attenuation amount at the two trap frequencies is further increased. And the high frequency side within the two trap frequencies,
That is, it is possible to prevent the amount of attenuation at the image carrier frequency from increasing.

[0036]

Description of Embodiments Embodiments will be described below with reference to the drawings. FIG. 7 is a plan view showing a piezoelectric resonator used to construct the trap circuit according to the first embodiment of the present invention. The piezoelectric resonator 21 is configured by using a rectangular piezoelectric substrate 22. The piezoelectric substrate 22 is made of a piezoelectric material such as lead zirconate titanate-based piezoelectric ceramics or LiNbO ₃ piezoelectric single crystal or LiTaO ₃ piezoelectric single crystal. In the case of piezoelectric ceramics, the direction indicated by arrow P in the figure is used. Is polarized. That is, the polarization process is performed in a direction parallel to the principal surface and orthogonal to the surface wave propagation direction described later.

On the upper surface of the piezoelectric substrate 22, two sets of IDTs 2 are formed.
3, 24 are configured. The IDT 23 has a pair of comb-teeth electrodes, and each comb-teeth electrode has a plurality of electrode fingers 23a and 23b. Similarly, the IDT 24 also has a pair of comb-teeth electrodes, and each comb-teeth electrode has a plurality of electrode fingers 24a and 24b.

One of the comb-teeth electrodes of the IDT 23 has a plurality of electrode fingers 23a and a common electrode 25 commonly connecting the plurality of electrode fingers 23a. The common electrode 25 is formed along one edge of the piezoelectric substrate 22. Also, IDT
The other comb-shaped electrode of 23 is a plurality of electrode fingers 23b,
And a common electrode 26.

Similarly, on the IDT 24 side, one comb tooth electrode has a plurality of electrode fingers 24a and a common electrode 26. The common electrode 26 is used as the other comb-shaped electrode on the IDT 23 side. The other comb-shaped electrode of the IDT 24 includes a plurality of electrode fingers 24b and a common electrode 27.
Have and. The common electrode 27 is formed along the other edge of the piezoelectric substrate 22.

Each of the common electrodes 25 to 27 also functions as a terminal electrode, and the terminals a, b, and
connected to c. The first and second resonators formed by forming the IDTs 23 and 24 have the same structure as the SH-type surface acoustic wave end face reflection type piezoelectric resonator 11 described above. That is, the plurality of electrode fingers 23a, 23b, 24a, 24b are λ / 4 (however, λ / 4) except for the electrode fingers along the edges of the end surfaces 21a, 21b of the piezoelectric substrate 21 and the upper surface of the piezoelectric substrate 21. Are formed in the width of the surface wave) and at a λ / 4 pitch, and only the electrode fingers along the above-mentioned edge are formed in the width of 8 / λ.

Further, the first and second resonating portions composed of the IDTs 23 and 24 are each constructed to have two resonance characteristics, like the piezoelectric resonator 11 shown in FIG. There is. In other words, the piezoelectric resonator 21 corresponds to a configuration in which the piezoelectric resonator 11 shown in FIG. 4 is divided into two by forming the common electrode 26.

Further, in each of the IDTs 23 and 24, as described above, each IDT has two resonance characteristics.
The DTs 23 and 24 are weighted. Regarding this weighting, similarly to the piezoelectric resonator 11 shown in FIG. 4, dummy electrode fingers are appropriately arranged, and the areas between the electrode fingers are weighted as shown by the expressions "1" and "0". By doing so, the first and second resonating portions each have two resonance characteristics.

In the piezoelectric resonator 21, the terminal a and the terminal c are connected to the ground potential, and the terminal b is connected between the input and the output to form a trap circuit of the television receiver. This circuit configuration is shown in FIG. In FIG. 8, the resonators 28 and 29 are respectively composed of the above-mentioned first and second resonators.

A resistor 31 is provided in front of the piezoelectric resonator 21.
Is connected between the input end IN and the input end IN, and the resistor 32 is connected between the input end IN and the resistor 31 and the ground potential. On the other hand, at the subsequent stage of the piezoelectric resonator 21, the output end O
A resistor 33 is connected to the UT, and a resistor 3 is connected between the connection point between the resistor 33 and the output terminal OUT and the ground potential.
4 is connected.

FIG. 9 shows the attenuation-frequency characteristic of the trap circuit. As described above, in the trap circuit in which the terminal a and the terminal c are connected between the input and output ends and the terminal b is connected to the ground potential, as is apparent from FIG. 9, traps are formed at two frequency positions, 15 dB and 17 d at trap frequencies f _ap and f _as , respectively.
B and the amount of attenuation were obtained. However, the amount of attenuation is high on the high frequency side within the two trap frequencies, that is, on the video carrier frequency.

Next, as shown by the broken line in FIG. 7, the inductance element 35 is connected between the terminal a and the terminal c of the piezoelectric resonator 21 and the terminal b is connected to the ground potential. The trap circuit shown in FIG. This trap circuit constitutes a trap circuit according to an embodiment of the present invention.

In the trap circuit shown in FIG. 10, the inductance element 3 is provided between the terminals a and c of the piezoelectric resonator 21.
5 is connected. The piezoelectric resonator 21 is shown in FIG.
Since it is the same as the trap circuit shown in FIG. 3, the same parts are designated by the same reference numerals.

FIG. 11 shows the attenuation-frequency characteristic of the trap circuit configured as described above. In FIG. 11, the attenuation amounts at f _ap and f _as are 22d, respectively.
B and 27.5 dB. Therefore, as apparent from comparison with FIG. 9, by connecting the inductance 35 between the terminals a and c of the piezoelectric resonator 21, the adjacent channel video frequency f _ap and the adjacent channel audio frequency f _{as are obtained.}
At 9 dB and 12.5 dB, respectively.
It turns out that it can be expanded. Further, as is clear from the comparison between FIG. 9 and FIG. 11, it is prevented that the attenuation amount at the video carrier frequency becomes small and the attenuation amount at the video carrier frequency becomes large.

Further, as shown in FIG. 12, the inductance element 35 was connected between the terminals a and c, and the inductance element 30 was connected in front of the piezoelectric resonator 21 to form a trap circuit. FIG. 13 shows the attenuation-frequency characteristics of the trap circuit shown in FIG. As is clear from FIG. 13, in this configuration, the attenuation amounts at the adjacent channel video frequency f _ap and the adjacent channel audio frequency f _as are 26 dB and 33 dB, respectively.
It can be seen that the amount of attenuation at each trap frequency can be further expanded as compared with the trap circuit shown in FIG.

The attenuation amounts at the adjacent channel video frequency f _ap and the adjacent channel audio frequency f _as of the trap circuits shown in FIGS. 8, 10 and 12 are shown in Table 1 below.
Are shown together.

Further, in the above-mentioned embodiment, the trap circuit in which the inductance element 35 is connected between the piezoelectric resonators 28 and 29, or the inductance element 35 is connected between the piezoelectric resonators 28 and 29 and the preceding stage of the piezoelectric resonator is provided. Although the trap circuit in which the inductance element 30 is connected is shown in FIG. 6, the trap circuit in which the inductance element 30 is connected in the preceding stage of the piezoelectric resonator also has a larger attenuation amount as compared with the trap circuit shown in FIG. In addition, it is possible to prevent the amount of attenuation on the high frequency side of the two trap frequencies, that is, on the video carrier frequency, from increasing. That is, at the adjacent channel video frequency f _ap and the adjacent channel audio frequency f _as , each is 21 dB.
And 24 dB.

[0052]

[Table 1]

In the embodiments shown in FIGS. 8, 10 and 12, in a single piezoelectric resonator 21, an inductance element is connected between two resonance parts, and if necessary, the piezoelectric resonator 21 Although the inductance element 30 is connected in the preceding stage, it is possible to use two piezoelectric resonators instead of the piezoelectric resonator 21.

That is, two piezoelectric resonators 11 utilizing the SH type surface wave having the two resonance characteristics shown in FIG. 4 are prepared, and the piezoelectric resonators 11 in the trap circuit shown in FIGS. The first and second piezoelectric resonators 28 and 29 may be formed by the piezoelectric resonators 11. That is, two piezoelectric resonators 11 using SH type surface waves having two resonance characteristics are prepared, an inductance element 35 is connected between them, and an inductance element 30 is connected to the preceding stage as required. By doing so, or by connecting the inductance element 30 only to the preceding stage thereof, the attenuation amount at the two trap frequencies can be effectively improved as in the above embodiment.

For simplification of the circuit structure, it is preferable to use the above-mentioned piezoelectric resonator 21 because a single element can be used as a resonance component. However, as described above, even when the two piezoelectric resonators 11 utilizing SH type surface waves are used, the attenuation amount at the trap frequency can be effectively increased as in the above-described embodiment. Therefore, it is possible to provide a trap circuit which can realize a larger amount of attenuation as compared with the conventional trap circuit using the LC resonance circuit.

In the piezoelectric resonator 11 shown in FIG. 4,
The IDT is weighted by arranging the dummy electrode fingers as described above, thereby realizing two resonance characteristics. However, the method of weighting the IDT of the piezoelectric resonator using SH type surface waves so as to have two resonance characteristics is not limited to the method using dummy electrode fingers. For example, as shown in FIG.
In the piezoelectric resonator 41, the IDT 45 including the comb-teeth electrodes 43 and 44 may be weighted by cross width weighting. Here, the piezoelectric substrate 42 is polarized in the direction of the arrow P, and a resonator using the SH type, for example, a piezoelectric resonator that reflects BGS waves is configured between the end faces 42a and 42b.

In the IDT 45, the lengths of the plurality of electrode fingers of the comb-teeth electrodes 43 and 44 are appropriately made different, so that the portions (intersections) of the adjacent electrode fingers that overlap with each other in the surface wave propagation direction. The width (intersection width) is changed along the surface wave propagation direction. As described above, it has been confirmed that two resonance points appear in the piezoelectric resonator 41 using the IDT with the cross width weighted, similarly to the piezoelectric resonator 11 shown in FIG. And this 2
It has been confirmed that the difference between the two resonance points is as large as about 8 MHz as in the case of the piezoelectric resonator 11 shown in FIG. Therefore, in the present invention, the trap circuit can be configured using the piezoelectric resonator 41. Further, in the piezoelectric resonator 41, as in the piezoelectric resonator 21, two sets of IDTs 45 are formed on the piezoelectric substrate so as to form a plurality of resonance parts, and the same configuration as the embodiment shown in FIG. Is also possible.

[Brief description of drawings]

FIG. 1 is a diagram showing an attenuation-frequency characteristic of a trap circuit used in a video intermediate frequency stage of a television receiver.

FIG. 2 is a perspective view showing an end surface reflection type surface acoustic wave resonator using an SH type.

3 (a) and 3 (b) are attenuation amount-frequency spectrum and impedance-of the surface acoustic wave resonator shown in FIG.
It is each figure which shows a frequency characteristic.

FIG. 4 is a plan view showing an end face reflection type piezoelectric resonator having two resonance characteristics.

5 is a perspective view of the piezoelectric resonator shown in FIG.

6 is a diagram showing impedance-frequency characteristics of the piezoelectric resonator shown in FIGS. 4 and 5. FIG.

FIG. 7 is a plan view for explaining a piezoelectric resonator used in an embodiment of the present invention.

8 is a circuit diagram showing an example of a trap circuit configured using the piezoelectric resonator shown in FIG.

9 is a diagram showing an attenuation-frequency characteristic of the trap circuit shown in FIG.

FIG. 10 is a circuit diagram for explaining a trap circuit according to an embodiment of the present invention.

11 is a diagram showing an attenuation-frequency characteristic of the trap circuit shown in FIG.

FIG. 12 is a circuit diagram for explaining a trap circuit according to another embodiment of the present invention.

13 is a diagram showing an attenuation-frequency characteristic of the trap circuit shown in FIG.

FIG. 14 is a plan view for explaining another example of the piezoelectric resonator used in the present invention.

[Explanation of symbols]

 21 ... Piezoelectric resonator 22 ... Piezoelectric substrate 23, 24 ... IDT 28, 29 ... 1st, 2nd resonance part 30, 35 ... Inductance element 41 ... Piezoelectric resonator 42 ... Piezoelectric substrate 45 ... IDT

Claims (4)

[Claims] 1. A piezoelectric substrate, and two sets of interdigital transducers connected to each other so as to form two resonant portions each having two resonant characteristics on the piezoelectric substrate. And a piezoelectric resonator using an SH type surface wave, wherein the two resonators are electrically connected in parallel. 2. The trap circuit, further comprising an inductance element connected between the two resonance parts or at least one of the preceding stages of the part where the two resonance parts are provided. 3. An SH type surface wave, which has a piezoelectric substrate and an interdigital transducer formed on the piezoelectric substrate and is electrically connected in parallel to each other so as to have two resonance characteristics, is used. A trap circuit comprising the first and second piezoelectric resonators. 4. An inductance element connected between the first and second piezoelectric resonators or at least one of the preceding stages of the portion where the first and second piezoelectric resonators are provided. Yes, the trap circuit.