JPH0714133B2 - IDT excitation 2-port resonator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to an IDT-excited two-port type using a wave that is excited on a piezoelectric substrate by an interdigital transducer (IDT) electrode such as a surface acoustic wave (SAW) resonator. The present invention relates to a resonator and a resonator filter using the resonator.

(Prior Art) Conventionally, a 2-port SAW resonator has been used in view of easiness of oscillation, especially in a high frequency region. This resonator has an input IDT on a piezoelectric substrate 1 as shown in FIG. The electrode 2 and the output IDT electrode 3 are arranged along the traveling direction of the SAW excited by the input IDT2, and reflectors 4 and 4'are provided on both sides of these two to confine vibration energy between the reflectors 4 and 4 '. It is common to do so. Between the reflectors 4 and 4 ', there are almost sinusoidal or cosine curve-like first-order modes and higher-order modes as standing waves along the propagation direction of the excited SAW. A response based on the vibration of these higher order modes is output from the output IDT3 and becomes a spurious. Generally, a spurious based on the vibration energy of a third order mode or higher is charged and separated from the fundamental wave and its level is also small, so there is no problem. Almost none.

In the resonator with such a structure, there is an energy confinement mode having a similar displacement distribution in the direction perpendicular to the SAW propagation direction, but spurious waves based on this energy confinement mode, for example, weight the IDT. It can be suppressed by means, so avoid further references.

However, in the two-port resonator constructed as described above, the spurious of the second mode is not only close to the response by the fundamental wave as shown in FIG. There was a defect that it was not very well applied to the filter.

(Object of the invention) The present invention has been made to eliminate the defects of the conventional two-port SAW resonator as described above, and is caused by an even-order energy confinement mode, especially a second-order energy confinement mode close to the fundamental frequency. It is an object of the present invention to provide an IDT-excited two-port resonator in which a spurious having a large level that removes the noise and a resonator filter using the same are provided.

(Summary of the Invention) In order to achieve the above object, a two-port resonator including an input / output IDT and reflectors on both sides of the input / output IDT along the traveling direction of a wave excited on a piezoelectric substrate by an interdigital transducer (IDT) electrode. In the above, the input / output ID
The input and output IDTs are divided in order to alternately divide the required number of Ts to suppress the occurrence of the secondary energy trapping mode vibration between the reflectors due to the excitation of the substrate.
Are arranged by adjusting the number and positions of the electrode fingers of the divided input / output IDTs so that they are asymmetric with respect to the center from the end faces of the both-side reflectors, and the generated vibration of the secondary energy trapping mode is generated. Output the charge excited due to
The divided input / output IDTs are connected so as to cancel the IDT electrode fingers when collecting them.

Embodiments of the Invention The present invention will be described in detail below with reference to embodiments shown in the drawings.

1 (a) and 1 (b) are conceptual diagrams for explaining the basic configuration of the two-port resonator according to the present invention together with its principle.

That is, FIG. 1 (a) shows that the generated electric charge based on the excitation energy of the primary mode and the secondary mode confined between the reflectors 4 and 4'by the input IDT2 is divided by the output IDT3 'and 3 "to collect electricity. Although it is output as a signal, regarding the charge due to the secondary confinement mode that is the cause of this spurious, collect the charge corresponding to the area of the hatched parts 5 and 5'in the split IDT electrode part. However, the polarities of 5 and 5'are opposite to each other, so 5
And the divided IDT so that the areas of 5'and 5'are equal.
It will be understood that if the positions and widths (number of electrode pairs) of 3'and 3 "are selected, the generated charges due to the excitation energy of the secondary mode are canceled out and are not output as an electric signal.

In addition, FIG. 2B shows the output IDT 3 ″ and the reflector 4 ′ that have been divided.
Since the non-electrode part generated between the
T is added and divided input IDTs 2'and 2 "are used for excitation.

According to the IDT arrangement of the two-port resonator according to the present invention as described above, even if the input / output IDTs are exchanged, the energy confinement in the even-order modes hardly occurs, and if the input IDT arrangement is unbalanced, it will be small. Even if the secondary mode electric charge is generated, the latter structure (FIG. 1 (b)) can cancel the collected electric charge, so that spurious can be sufficiently suppressed.

If you want to invert the phase between the input and output terminals for the fundamental wave (first order) mode vibration, either connect either the input terminal or the output terminal to each other, or set the IDT position to 1/2 the excitation wavelength. Just move.

A 2-port SA that was actually created based on the above idea.
The experimental result about how the spurious by the excitation energy of the secondary mode of the W resonator was suppressed is shown.

FIG. 4 (a) shows that the input / output IDT in the 2-port SAW resonator (resonance frequency 100 MHz) of the present invention is divided into two equal parts and each is connected to the input and output sides. The results shown in b) were obtained. As is clear from this figure, spurious is approximately 10 dB compared to the conventional 2-port SAW resonator.
It was proved that there was a decrease and a remarkable effect.

When the 2-port SAW resonator as shown in FIG. 4 (a) is actually mass-produced, the electrode structure as shown in FIG. 5 may be used.

That is, one of the electrode fingers of the input / output IDTs 2 ', 2 "and 3', 3" may be formed into a continuous pattern 6 and both ends thereof may be used as ground lines for the input / output ports.

By the way, according to the basic idea of the present invention as described above, various IDT arrangements and connections can be considered for the IDT-excited two-port resonator according to the present invention.

Needless to say, the IDT division as shown in FIG. 4 (a) may be further subdivided and connected in parallel from the end to the input side, output side, input side, ...

Next, when the excitation charges due to the vibration of the even-order, especially the second-order confinement mode are collected, it is sufficient to cancel them. Therefore, as shown in FIG. 6, the output IDT3 is placed at the center of the reflector 4, 4'spacing. For example, the right and left sides may be divided into an appropriate number so that the charge collection amounts on the left and right sides are equal, that is, in the case of the present embodiment, the curve of the quadratic mode is regarded as a sine curve. Therefore, the number and positions of electrode fingers of the IDT may be adjusted and distributed so that the hatched area (5) is equal to the area (5 ″ +5).

Finally, a resonator filter using the 2-port SAW resonator according to the present invention will be briefly described.

In the filter using the conventional two-port SAW resonator as shown in FIG. 2, spurious with a large level due to the vibration of the second-order confinement mode is generated in the vicinity of the pass band and the attenuation characteristic is deteriorated. As mentioned above, there was a defect.

On the other hand, as shown in FIG. 7, for example, in a filter according to the present invention in which two 2-port SAW resonators having the same characteristics are connected and a capacitance 6 is inserted between stages to set a required pass band, As shown by the solid line in FIG. 8, it has been confirmed that the spurious response in the vicinity of the pass band is significantly reduced and good filter characteristics are obtained. The dotted line in this figure shows the spurious level when the conventional 2-port SAW resonator is used.

The SAW resonator has been described above as an example, but the present invention is not necessarily limited to this, and other waves that can be excited by the IDT, such as a leaky surface acoustic wave, a Love wave, an SH wave or a slip wave, are also applicable. It will be obvious that the same applies.

Further, the effect of the division and connection of the IDT according to the present invention does not change even when applied to a 2-port resonator in which the IDT is weighted. In this case, the displacement distribution of the secondary mode (almost sine curve) is multiplied by the weight of the IDT to obtain the collected charge, and the IDT may be divided and connected so as to cancel this.

(Effects of the Invention) Since the present invention is configured as described above, even if the IDT fabrication pattern of the resonator is slightly changed, even-order, especially quadratic-order, generated in the vicinity of the fundamental wave frequency for which excitation is desired is generated. It is possible to significantly suppress the spurious caused by the vibration of the confinement mode of the device. Therefore, even when this is used as an oscillator or a resonator filter is configured, unnecessary vibration is eliminated and good characteristics are realized. Exerts a remarkable effect in doing.

[Brief description of drawings]

1 (a) and 1 (b) are conceptual explanatory views for explaining the basic structure and principle of an IDT-excited 2-port resonator according to the present invention, and FIG. 2 is a structure of a conventional 2-port SAW resonator. FIG. 3 is a plan view, FIG. 3 is a diagram of one experimental data showing the characteristics, and FIGS. 4 (a) and 4 (b) respectively show an embodiment of the IDT structure of the 2-port SAW resonator according to the present invention. FIG. 6 is a plan view and a diagram of experimental data showing its characteristics. FIG. 5 is a plan view showing an embodiment of an IDT structure of a 2-port SAW resonator according to the present invention.
FIG. 7 is a conceptual diagram showing another example of the IDT configuration of the IDT excitation type two-port resonator according to the present invention, and FIG. 7 is the IDT excitation type 2 according to the present invention.
FIG. 8 is a configuration diagram showing an embodiment of a resonator filter using a port resonator, and FIG. 8 is a diagram showing its general characteristics. 1 ... Piezoelectric substrate, 2,3,2 ', 3', 2 ", 3", 2 and 3 ...
Input / output IDT, 4,4 '... Reflector, 5,5' and 5 "... Split IDT
Amount of charge excited by

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Takefumi Kurosaki 753 Otani, Samukawa-cho, Takaza-gun, Kanagawa Prefecture Toyo Communication Equipment Co., Ltd. JP-A-54-60842 (JP, A) JP-A-57-202114 (JP, A)

Claims (2)

[Claims] 1. An interdigital transducer (ID
T) In a two-port resonator having an input / output IDT and reflectors on both sides of the input / output IDT along the traveling direction of the wave excited on the piezoelectric substrate, the input / output IDTs are alternately divided into a required number. , The divided input and output IDTs for suppressing the generation of the secondary energy trapping mode vibration between the reflectors due to the excitation of the substrate are asymmetric with respect to the center from the end faces of the both-side reflectors, respectively. The number of electrode fingers of the divided input / output IDT and the positions thereof are adjusted and arranged, and the charges excited due to the generated vibration of the secondary energy confinement mode are applied to the electrode fingers of the output IDT. An IDT-excited two-port resonator characterized in that the divided input / output IDTs are connected so as to cancel this when collecting. 2. An IDT excitation type 2 according to claim (1).
An IDT-excited two-port resonator, comprising a required number of port resonators connected to form a filter to obtain a desired pass band characteristic.