JPS5834975B2 - Surface acoustic wave filter device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a surface acoustic wave filter device, in which when interdigital electrodes for transmitting and receiving surface acoustic waves are composed of a very large number of pairs, the effective length in the propagation direction of surface acoustic waves can be reduced. The present invention attempts to provide a device in which the length of a piezoelectric substrate in the propagation direction of surface waves is shortened by compressing the piezoelectric substrate, and a device in which the passband characteristics of a filter can be controlled by controlling the irradiation of light onto the electrode mounting surface. It is.

As a surface acoustic wave filter device for processing filtrate of various electrical signals, in order to realize the desired passband characteristics as faithfully as possible, an interdigitated surface acoustic wave filter device for transmitting and receiving surface acoustic waves (hereinafter referred to as ESW) is used. The structure of the electrode can be expressed in simple normal form (
Merely setting the electrode finger crossing width (constant) is insufficient to achieve the above characteristics, and it is necessary to employ various weighting electrodes.

Therefore, the electrode often becomes elongated in the ESW propagation direction, and the piezoelectric substrate may become elongated.

On the other hand, although it is strongly desired to change the passband characteristics of a filter depending on the input signal waveform and its level, there are no devices that do this by controlling the irradiation of light onto the electrode mounting surface for ESW transmission and reception. So far, unknown.

Of course, there are some functions that involve light in the functions of signal processing devices using ESW, but they are different from light waves and ESW.
This is mainly due to mutual interference with light modulation, light deflection,
Furthermore, there are only image input/output devices and the like.

However, there is nothing that can change the processing function by controlling the irradiation of light using light and regardless of the mutual interference between the light wave and the ESW.

The present invention realizes a bandpass filter device that eliminates the above-mentioned problems and drawbacks of the prior art.

The basic configuration of the device according to the present invention is that at least one interdigital electrode is disposed on a piezoelectric body, a plurality of interdigital electrodes are connected in parallel to each other in the length direction of the electrode fingers, and further, there is a connection between the electrodes. An electromechanical coupler in the form of a charged electrode is provided on the propagation path of the ESW to be transmitted and received, and the ESW is transmitted and received between the former electrode and the latter electrode via the electromechanical coupler.
In effect, the latter electrodes are electrically connected in parallel and acoustically connected in cascade, thereby dividing the electro-mechanical coupler.

Hereinafter, the configuration and effects of the device of the present invention will be specifically explained with reference to the drawings.

1 and 2 are basic configuration diagrams of a surface acoustic wave filter device according to the present invention, and FIGS. 3 to 6 show a device whose pass characteristics as a filter are variable by controlling light radiation. 3 and 5 correspond to FIG. 1, and FIG. 4 and FIG. 6 correspond to FIG. 2, respectively.

Common to each figure, 1 is the first electrode (
1) interdigital electrodes.

However, illustration of the piezoelectric body is omitted.

All of the following components are provided on the same piezoelectric body as the electrode 1.

2.3.4 means three sets of interdigital electrodes connected in parallel to each other in the length direction of the electrode fingers.

The number of sets is not necessarily limited to three, but may be any number of sets.

Reference numerals 5 and 6.7 refer to electrical-mechanical couplers in the form of charged electrodes, which are equally spaced between electrode 1 and electrodes 2 and 3.4 so that ESW can be exchanged. The spacing is not necessarily the same as that of electrodes 1-4.

Furthermore, a gap W is maintained between the coupler 5 and the other coupler 6°γ, and each gap serves as an opening for the ESW transmitted and received between the electrodes 1 and 2, and the coupler 6 The ESW energy is approximately the same as the ESW energy exchanged between the electrodes 1 and 4 via the electrodes 1 and 3 and the coupler 1.
energy flows through the gap W.

Thermal, the number of electro-mechanical couplers corresponds to the number of ESW propagation paths.

Note that when ESW is transmitted and received between electrodes 3 and 4 and electrode 1 at the positions of broken line blocks 3' and 4', respectively, without going through the coupler 6.7, virtual electrode 3' and electrode 3 The relative center distances of the electro-mechanical couplers 5, 6 and 5, 7 correspond to the center distances of the virtual electrode 4' and the electrode 4, respectively, as shown in FIGS. In the configuration shown in the figure, they are both l, and in the configurations of FIGS. 2, 4, and 6, they are 11 and 12, respectively.

Although the distance d is drawn relatively large in the figure,
In reality, it may be sufficiently small as long as the charged electrode phases in each coupler 5, 6.7 are not short-circuited to each other.

Numerals 8 and 9 in FIGS. 3 and 4 and 8' and 9' in FIGS. 5 and 6 indicate the gap W and the coupler 5.
6.7 refers to a photoconductive thin film attached to cover each band-shaped electrode finger, and when each is sufficiently irradiated with light and becomes highly conductive, the thin film 8 or 9 is attached to the coupler 5. 6
Alternatively, the strip-shaped electrode fingers of couplers 5, 6, and 7 are electrically short-circuited to each other so that they no longer function as a coupler, and the strip-shaped electrode fingers of couplers 5, 6, and 7 are coupled to each other in the thin film 8'. They are arranged as if they were not divided but functioned as a single electromechanical coupler.

Common to each figure, the reference numerals 10 and 20 respectively refer to input or output electrical signals, which are interchangeable, as is generally allowed for linear elements of this type.

Furthermore, although the details of the structure of the interdigital electrodes are omitted in each figure, they may be of any structure as long as they can transmit and receive ESW.

Now, the functions of the apparatus configured as described above will be explained below.

First, the configurations shown in FIGS. 1 and 2 will be explained.

an input electrical signal 10 is converted into ESW by the electrode 1;
Considering the time response when that energy is received by the electrodes 2 to 4, the ESW leaving the electrode 1 is first received by the electrode 3 via the electro-mechanical coupler 6, and then by the coupler 5.6. Then, the wave passes through the gap W between 5 and 1 and is received by the electrode 2.

After a further delay, the signal is received by the electrode 4 via the coupler 1.

By the way, since the electrodes 3 and 4 are electrically connected in parallel to the electrode 2, the output electrical signal 20 taken out based on the above-mentioned time response is effectively generated by the electrodes 3 and 4, respectively. This is equivalent to the case where virtual electrodes 3' and 4' are electrically connected in parallel and acoustically connected in cascade with the electrode 2.

Therefore, in the apparatus having the configurations shown in FIGS. 1 and 2, the size of the electrodes arranged along the ESW propagation direction can be effectively reduced, and the size of the piezoelectric substrate Φ on which the electrodes are attached can be reduced. It becomes possible to shorten the ESW along the propagation direction.

Next, the appropriation shown in FIGS. 3 and 4 will be described.

The input/output signal responses when the photoconductive films 8, 9 are not irradiated with light are almost the same as those in FIGS. 1 and 2, but when the films 8, 9 are irradiated with light and the response is high When it becomes conductive, its response changes as follows.

That is, if the photoconductive film 8 is first irradiated with light, the coupler 6 will lose its function.
The ESW emitted from the electrode does not reach the electrode 3 and is received by the electrodes 2 and 4.

When only the photoconductive film 9 is irradiated with light, the coupler 1 similarly does not lose its function, and the ESW emitted from the electrode 1 is received by the electrodes 2 and 3.

Furthermore, as can be easily understood from the above, if both the photoconductive films 8 and 9 are irradiated with light to increase their conductivity,
Only electrode 2 acts as an effective receiving electrode,
Although the device has one type of electrode arrangement, it functions as a filter with four different pass characteristics by controlling light irradiation.

In the configurations shown in FIGS. 5 and 6, when the photoconductive film 8' becomes highly conductive due to light irradiation, the electro-mechanical couplers 5 to γ work together, and the 10 inputs The response of the output signal 20 to the signal 10 is effectively equal to that when the ESW is exchanged between the electrode 1 and the electrodes 3 and 4. The response will be completely different from the response when all of the above are working.

In other words, the above-described operation makes the passage characteristics of the filter device variable by controlling the irradiation of light.

As can be easily understood from the above description, the device of the present invention is capable of controlling either the transmission or reception of the ESW by disposing an electro-mechanical coupler in the form of a divided charged electrode between the transmission and reception electrodes of the ESW. The size of the electrode can be effectively reduced along the wave propagation direction.

Furthermore, by dividing the electro-mechanical coupler, placing photoconductive films on the two couplers, and selectively irradiating these photoconductive films with light, they can be operated as filters with various pass characteristics. Can be done.

[Brief explanation of the drawing]

FIGS. 1 to 6 are diagrams each showing a representative example of the basic configuration of a surface acoustic wave filter device based on the present invention. 1.2, 3, 4... Interdigital electrodes 3/, 4/
,...virtual placement locations of electrodes 3 and 4, 5, 6,
7...Charged electrode-like electrical-mechanical coupler, 8.8',
9... Photoconductive film, 10, 20... Input or output electrical signal.

Claims (1)

[Scope of Claims] 1. On a piezoelectric body, an interdigital electrode, a plurality of interdigital electrodes connected in parallel to each other in the electrode finger length direction, and an intersection between the former interdigital electrode and the latter interdigital electrode. It has an electro-mechanical coupler disposed on a propagation path of surface acoustic waves transmitted and received between each of the finger-shaped electrodes, and the electro-mechanical coupler is divided to connect the latter Φ interdigital electrodes. A surface acoustic wave filter device characterized by acoustically cascade-connecting. 2. On the piezoelectric body, an interdigital electrode, a plurality of interdigital electrodes connected in parallel to each other in the electrode finger length direction, and between each of the former interdigital electrode and the latter interdigital electrode. an electro-mechanical coupler disposed on a propagation path of surface acoustic waves transmitted and received by the electro-mechanical coupler, and the latter interdigital electrodes are acoustically connected in cascade by dividing the electro-mechanical coupler, and A surface acoustic wave filter device characterized in that a photoconductive film is provided for electrically short-circuiting the divided electro-mechanical couplers by light irradiation.