JPH0450652Y2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field] This invention relates to a resonator using surface acoustic waves.

[Conventional technology]

Figure 8 is a diagram showing a conventional surface acoustic wave resonator.
FIG. 8a is a plan view, FIG. 8b is a sectional view taken along the plane AA' of FIG. 8a, and FIG. 8c is a partial sectional view of FIG. 8b. These diagrams are for example
proceedings of the IEEE, vol.67, No.1, Jan.
1979, pp. 147-158, and in these figures 1 is a piezoelectric substrate, which is a propagation medium for surface acoustic waves. 2 is an interdigital electrode, 3 is a grating that acts as a surface acoustic wave reflector, and 4 is a grating that acts as a surface acoustic wave reflector.
5 is a groove provided on the surface of the substrate 1 to form the grating 3, and 5 is a lead wire. The interdigital electrode 2 is formed by etching a metal film deposited on the piezoelectric substrate 1.

When an oscillating voltage is applied to one interdigital electrode 2,
A surface acoustic wave corresponding to the oscillating voltage waveform applied to the surface of the piezoelectric substrate 1 is generated. This surface acoustic wave vibration propagates along the surface of the substrate 1. During this propagation, since the characteristics of the propagation medium are different at the entrance and exit of the structure 4, the light is reflected at these points. The reflected waves at a frequency (referred to as the resonant frequency) at which the reflected waves reflected at the entrance and exit points of many grooves 4 are all added in the same phase return to the weeping electrode 2 with maximum strength, where they become electrical oscillations. converted. At a frequency slightly different from this resonant frequency, the reflected waves are added at the entrance and exit points of each groove 4 with slightly different phases, resulting in the reflected waves being canceled out as a whole. That is, only at the resonant frequency, multiple reflections are repeated at the grating 3, and a standing wave is generated. By disposing the interdigital electrode 2 at a position corresponding to the antinode (loop) of this standing wave and extracting the induced voltage, it is possible to obtain a low loss, narrow band, that is, a high Q passing characteristic.

[Problem that the invention attempts to solve]

Since the conventional surface acoustic wave resonator is configured as described above, the resonant frequency is determined by the structural dimensions of the interdigital electrodes 2 and the grating 3 on the piezoelectric substrate 1, and the resonant frequency is finely adjusted from the outside. There was a problem that it could not be adjusted.

This invention was made to solve the above-mentioned problems, and its purpose is to obtain a surface acoustic wave resonator whose resonant frequency can be finely adjusted from the outside.

[Means for solving problems]

In this invention, an electric circuit is connected to an elastic vibrating body using a grating through interdigital electrodes, and the resonant frequency is finely adjusted by adjusting the circuit constant of the connected electric circuit.

[Effect]

It is a well-known method to represent a vibration circuit of elastic vibrations that can be converted into electric vibrations through a piezoelectric phenomenon by an equivalent electric circuit. Therefore, by connecting an electric circuit to the grating where elastic vibration exists through interdigital electrodes and adjusting the electric circuit constant, the circuit constant of the electric circuit, which is an equivalent circuit of elastic vibration, can be adjusted and resonance can be achieved. Frequency can be finely adjusted.

〔Example〕

Embodiments of this invention will be described below with reference to the drawings. Figure 1 is a drawing showing an embodiment of this invention.
FIG. 1a is a plan view, FIG. 1b is a sectional view taken along line AA' in FIG. 1a, and FIG. 1c is an enlarged view of section B in FIG. 1b.
In these drawings, the same reference numerals as in FIG. 8 indicate the same or corresponding parts, and 6 is an external electric circuit. In addition, in FIG. 1, the interdigital electrode 2 includes a grating 3 in addition to the two pairs of interdigital electrodes 2 shown in FIG.
Two pairs of interdigital electrodes 2 are provided which are connected to an external electrical circuit 6 in parallel.
connected to. The external electric circuit 6 is composed of a coil, a capacitor, or a reactive element whose circuit constant can be changed by combining a coil and a capacitor.

The resonance phenomenon in the surface acoustic wave resonator shown in FIG. 1 is the same as that described above with respect to FIG. Therefore, the surface acoustic wave vibration in the portion of the grating 3 induces an oscillating voltage in the interdigital electrode 2 in that portion, and this oscillating voltage causes an oscillating current to flow in the external electric circuit 6. The voltage between the interdigital electrodes 2 is determined, and this determined voltage will conversely generate surface acoustic wave vibrations in that part of the grating 3, so the circuit constants of the external electric circuit 6 are changed. The vibration phase of the surface acoustic wave vibration in the grating 3 changes the vibration current flowing therein, and therefore, by adjusting the circuit constant of the external electric circuit 6, the resonant frequency can be finely adjusted.

As explained earlier, the operation of the interdigital electrode 2 connected to the external electric circuit 6 is caused by the piezoelectric effect of the piezoelectric substrate 1 due to the surface acoustic wave vibration propagating on the piezoelectric substrate 1. The oscillating voltage generated on the piezoelectric substrate 1 is derived and applied to the external electric circuit 6, and the oscillating voltage between the interdigital electrodes 2 is applied to the piezoelectric substrate 1 to generate surface acoustic wave vibration. Any type of interdigital electrode may be formed in any position and connected to the external electric circuit 6 as long as this operation is possible. Various embodiments of this invention that are different from the embodiment shown in FIG. 1 will be described below. The present invention is not limited to those shown in the embodiments described in .

FIG. 2 is a plan view showing another embodiment of this invention, in which the same reference numerals as in FIG. 1 indicate the same or corresponding parts, and in the embodiment of FIG. Although the groove 4 was provided avoiding the groove 4, in the embodiment shown in FIG. 2, it was provided in the groove 4.

FIG. 3 is a plan view showing another embodiment of this invention, in which the same reference numerals as in FIG. 1 indicate the same or corresponding parts. It is formed in a position that covers a part of the body.

FIG. 4 is a plan view showing another embodiment of this invention, in which the same reference numerals as in FIG. 4, and a grating that reflects surface acoustic waves is also formed in this portion.

FIG. 5 is a plan view showing another embodiment of this invention, in which the same reference numerals as in FIG. 4 indicate the same or corresponding parts, and in the embodiment of FIG. However, in the embodiment of FIG. 5, the interdigital electrode 2 is provided within the groove 4.

FIG. 6 is a plan view showing another embodiment of this invention, in which the same reference numerals as in FIG. 1 indicate the same or corresponding parts. In this embodiment, two external electric circuits 6 are provided.
This is an example in which interdigital electrodes 2 are provided which are respectively connected to external electric circuits 6.

FIG. 7 is a plan view showing another embodiment of this invention. In the figure, the same reference numerals as in FIG. An example of application is shown.

It is clear that in the embodiments shown in FIGS. 2 to 7 as well, the resonance frequency can be finely adjusted by adjusting the external electric circuit 6, as in the embodiment shown in FIG.

In all of the embodiments described above, a so-called normal type electrode with a fixed cross width is used as the interdigital interdigital electrode 2, but a so-called apodized type electrode with a weighted cross width is used. Good too. There is also a structure of a surface acoustic wave resonator in which the length, width, and depth of the grooves 4 of the grating 3 are different for each groove 4, and this idea can also be applied to a surface acoustic wave resonator with such a structure. I can do it.

[Effect of idea]

As described above, according to this invention, the interdigital electrode 2 is formed on the grating 3, connected to the external electric circuit 6, and the resonant frequency is finely adjusted by changing the circuit constant of the external electric circuit 6. This has the advantage that the resonant frequency can be precisely adjusted after the surface acoustic wave resonator is manufactured.

[Brief explanation of the drawing]

Figure 1 shows an embodiment of this invention, Figure 2 shows an example of this invention.
3, 4, 5, 6 and 7 are plan views showing other embodiments of this invention, respectively.
FIG. 8 is a diagram showing a conventional surface acoustic wave resonator. 1 is a piezoelectric substrate, 2 is an interdigital electrode, 3 is a grating, 4 is a groove, 5 is a lead wire, and 6 is an external electric circuit. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims for Utility Model Registration] A first interdigital electrode configured on a piezoelectric substrate, which converts input electric vibrations into surface acoustic wave vibrations on the piezoelectric substrate, and converts the surface acoustic wave vibrations into output electric vibrations. and a grating formed on the piezoelectric substrate to reflect surface acoustic waves propagating on the piezoelectric substrate, the grating comprising a large number of grooves, a second interdigital electrode coupled to the grating is formed in a region of the grating near the first interdigital electrode, an external interdigital electrode connected to the second interdigital electrode and capable of varying a circuit constant thereof; A surface acoustic wave resonator characterized by being equipped with an electric circuit.