JPH0258915A - Surface acoustic wave resonator - Google Patents

Abstract

PURPOSE:To dispense with the inductance portion of an external fitting such as a coil for expanding by forming the inductance in the part of a reflector and connecting it to an IDT electrode electrically in series. CONSTITUTION:In a surface acoustic wave resonator 12, a connection between plural metallic strips 151a and 151b to compose reflectors 15a and 15b, respectively, is executed in a snaking shape so that they can be made all serial, respectively, and simultaneously, the one edge sides are connected to the one edge side of an IDT electrode 4, respectively. In the surface acoustic wave resonator 12, the inductances are formed in the parts of the reflectors 15a and 15b, respectively, and they are electrically connected to both sides of the IDT electrode 4 in series, respectively. Thus, the inductance portion of the external fitting such as the coil for expanding can be made unnecessary.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a surface acoustic wave resonator suitable for use in, for example, a voltage controlled oscillator.

[Conventional technology]

As shown in FIG. 5, the conventional surface acoustic wave resonator 2 is constructed by providing an IDT electrode 4 on the surface of a piezoelectric substrate 3 and grid-shaped reflectors 5a and 5b on both sides thereof. 6a,
6'b is an electrical terminal.

In a voltage controlled oscillator using such a surface acoustic wave resonator 2, for example, as shown in FIG. Applied voltage V
By changing c, the signal frequency appearing at the output terminal is controlled.

However, since the surface acoustic wave resonator 2 as described above alone does not have a sufficient inductance variable range, the frequency variable range is usually increased by connecting an extension coil 7 in series therewith.

[Problem to be solved by the invention]

However, if this is done, the number of parts increases by the amount of the extension coil 7, and the inductance of the extension coil 7 itself must be adjusted, which leads to a problem of increased cost.

In contrast, there are examples of surface acoustic wave resonators in which spiral coils are formed on the same piezoelectric substrate, but such devices do not require an increase in the number of components and do not require adjustment because the inductance is determined by the pattern. However, the area of the piezoelectric substrate becomes thicker due to the coil (therefore, there is a problem that the surface acoustic wave resonator becomes larger and the cost becomes higher.

SUMMARY OF THE INVENTION An object of the present invention is to provide a surface acoustic wave resonator that eliminates the need for an external inductance such as an extension coil, and also eliminates the need to increase the size of the piezoelectric substrate.

[Means to solve the problem]

In order to achieve the above object, the surface acoustic wave resonator of this invention connects a plurality of metal strips constituting at least one reflector so that at least some of them are connected in series, and one end of the metal strips is connected to an IDT electrode. It is characterized by being connected to one end of the.

(Function) According to the above configuration, an inductance is formed in the portion of the reflector connected as described above, and this inductance is electrically connected in series with the IDT electrode.

〔Example〕

1 to 4 are plan views showing surface acoustic wave resonators according to embodiments of the present invention, respectively. Components equivalent to those in the example shown in FIG. 5 are given the same reference numerals, and the differences from the conventional example will be mainly explained below.

In the surface acoustic wave resonator 12 shown in FIG.
A plurality of metal strungs 151a each forming part 5b.
, 151b are connected in a meandering manner so that they are all in series, and one end thereof is connected to the IDT electrode 4.
are connected to one end of each.

The TDT electrode 4 and the reflectors 15a and 15b are both made of aluminum alloy 11 or an aluminum alloy containing several percent of copper, for example.
b is 1/ of the wavelength of the surface wave that magnetizes the surface of the piezoelectric substrate 3.
The metal strips 151a, 1 are arranged at 2 pitches.
51b are arranged in a grid pattern. Reflector 25 to be described later
The same applies to a, 25b, 35a, 35b, 45a, and 45b.

In such a surface acoustic wave resonator 12, the reflector 1
Inductances are formed in the portions 5a and 15b, and these are electrically connected in series to both sides of the IDT electrode 4.

Therefore, when such a surface acoustic wave resonator 12 is used in a voltage controlled oscillator as shown in FIG. 6, for example, by connecting electric terminals 6a and 6b to both ends of the reflectors 15a and 15b, respectively. Since inductance is generated between the electric terminals 6a and 6b, the extension coil 7 is not necessary. That is, even without using the external extension coil 7,
The frequency variable range can be increased.

Furthermore, since the reflectors 15a and 15b also serve as inductance, unlike the case where a separate coil is formed, it is not necessary to increase the size of the piezoelectric substrate 3, and the accompanying cost increase can be avoided.

Next, another embodiment will be described focusing mainly on the differences from the surface acoustic wave resonator 12 described above. In the surface acoustic wave resonator 22 of FIG. The metal strips 251a and 251b are connected in a meandering manner so that several metal strips (two in the illustrated example) are connected in series, and one end of them is connected to one end of the DT electrode 4. are connected to each.

This has the advantage that the electrical resistance in the reflectors 25a, 25b can be reduced when viewed as an inductance component.

In the surface acoustic wave resonator 32 shown in FIG.
A plurality of metal strips 351 each forming part 5b
a and 351b are spirally connected so that they are all in series, and one end thereof is connected to one end of the IDT electrode 4, respectively.

This has the advantage that the inductance at the reflectors 35a and 35b increases.

In the surface acoustic wave resonator 42 shown in FIG.
A plurality of metal strips 451 each forming part 5b
Several lines (two lines in the illustrated example) between a and 451b.
The electrodes connected in parallel are spirally connected in series, and one end of each is connected to one end of the IDT electrode 4.

This has the advantage that the inductance at the reflectors 45a, 45b becomes relatively large, and the electrical resistance at the reflectors 45a, 45b can be reduced when viewed as an inductance component.

Moreover, since the metal pattern connecting the metal strips 451a, 451b, etc. is formed almost uniformly over a large area, the surface waves between the part that substantially constitutes the reflector and the other parts are reduced. Another advantage is that there is a large difference in the speed of sound, and therefore the energy trapping effect of surface waves is large.

Note that it is not always necessary to connect both reflectors as in each of the above embodiments, and depending on the required inductance, only one reflector may be connected as in each of the above embodiments. .

Furthermore, the surface acoustic wave resonator as described above can be used in voltage controlled oscillators of types other than those shown in FIG. 6.

〔Effect of the invention〕

As described above, according to the present invention, an inductance is formed in the reflector portion and is electrically connected in series with the IDT electrode, so that such a surface acoustic wave resonator can be used in a voltage controlled oscillator, etc. If used for this purpose, external inductance such as an extension coil becomes unnecessary.

Moreover, since the reflector also serves as an inductance,
Unlike the case of forming a separate coil, there is no need to increase the size of the piezoelectric substrate, and the associated cost increase can also be avoided.

[Brief explanation of the drawing]

1 to 4 are plan views showing surface acoustic wave resonators according to embodiments of the present invention, respectively. Figure 5 shows
FIG. 2 is a plan view showing an example of a conventional surface acoustic wave resonator. FIG. 6 is a circuit diagram showing an example of a voltage controlled oscillator. 3... Piezoelectric substrate, 4... IDT electrode, 12, 22
．． 32.42...Surface acoustic wave resonator according to Example, 1
5a, 15b, 25a, 25b, 35a. 35b, 45a, 45b--Reflector, 151a. 151b, 251a, 251b, 351a, 3
51b, 451a, 45Lb --- Metal strip. Figure 1

Claims (1)

[Claims] (1) In a surface acoustic wave resonator in which an IDT electrode and a lattice-shaped reflector are provided on the surface of a piezoelectric substrate, at least some of the metal strips forming at least one of the reflectors are connected in series. What is claimed is: 1. A surface acoustic wave resonator characterized in that the surface acoustic wave resonator is connected such that the surface acoustic wave resonator is connected to the surface acoustic wave resonator, and one end thereof is connected to one end of an IDT electrode.