JPS594886B2 - surface acoustic wave filter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a surface acoustic wave filter having variable leakage characteristics.

An object of the present invention is to provide a surface acoustic wave filter with a simple configuration and variable leakage characteristics.

Conventionally, active filters using operational amplifiers have been common as filters with variable leakage characteristics, but they require a large number of circuit elements, making the configuration complicated, and it is difficult to adjust the constants of each element. The cost increases because of the need for

The present invention realizes a filter with variable leakage characteristics consisting of a single element by utilizing surface acoustic waves, and has a very simple configuration.

FIG. 1 shows an embodiment of a surface acoustic wave filter according to the present invention.

In FIG. 1, 1 is a piezoelectric material or a substrate having at least a piezoelectric material layer on the surface, 2 is a wave transmitting converter consisting of a crossed electrode 101, and 3 is a 45-degree angle with respect to the propagation direction of the surface acoustic wave generated by the wave transmitting converter. A reflection grating 4 is a reflection grating in which a plurality of reflectors 102 with continuously changing pitch intervals arranged at an angle of ° are arranged in the propagation direction. The receiving transducer is arranged at an angle of 45 degrees with respect to the arranged direction, and each interdigitated finger electrode 103 is perpendicular to the propagation direction X. 5 is one electrode of the receiving transducer 4, and 6 is a receiving transducer. The other electrode of the wave converter 4 is connected to each interdigital electrode 103 via a switch region 7 .

In FIG. 1, the reflection grating 3 has reflectors 102 at both ends thereof.
Let Wl and W2 be surface acoustic waves that are arranged so that the spacing takes the minimum and maximum values, and have wavelengths corresponding to both spacings, Wl is the reflection grating 3 that has the same reflector 1020 spacing as this wavelength. W2 is reflected at the left end of the wavelength and enters the receiving converter 4, whereas W2 is reflected at the left end of the wavelength
It is reflected at the right end with a gap and enters the receiving converter 4, but since the receiving converter 4 is perpendicular to the reflector 102, that is, at an angle of 45 degrees with the direction in which the reflection grating 3 is arranged,
The time required for Wl and W2 to be transmitted from the transmitting converter 2 and entering the receiving converter 4, that is, the delay time, is the same.

Similarly, the delay time of a surface acoustic wave having a frequency value intermediate between Wl and W2 also takes the same value as w11w2.

Moreover, since the spacing between the reflection grating 30 and the reflectors 1020 changes continuously, the propagation path of the reflected surface acoustic wave changes from the position Wl in FIG. 1 to W2 according to its frequency.
The position changes to .

Therefore, the signal input to the transmitting converter 4 converted into the frequency domain, that is, the Fourier transformed signal is
It is something that is developed in the direction.

Further, the pitch of the interdigitated electrodes 103 of the receiving converter 4 changes in exactly the same way as the distance between the reflectors 102, with the distance between the reflectors 1020 at both ends of the reflection grating 30 being the maximum and minimum values.

Further, a switch region 7 is provided between one electrode 6 of the wave receiving converter 4 and the interdigital electrodes.

The switch region 7 selectively connects each interdigital electrode 103 to one electrode 6, and connects and disconnects each interdigital electrode 103 in accordance with desired leakage characteristics.

An example of this switch area is shown in FIG.

In FIG. 2, 8 is one electrode of the wave receiving converter 4, 9 is a cross-finger electrode, and 10 is a connection part with the cross-finger electrode 9 in the switch area. It is selectively fused.

FIG. 3 shows another embodiment of the switch area.

In FIG. 3, 12 is a base, 13 is one electrode of a wave receiving converter, 14 is a crossed finger electrode, and 15 is a photoconductor film.

A sectional view taken along line A-A' is shown in FIG. In this configuration, by irradiating the photoconductor film 15 with a light beam pattern corresponding to the desired wave leakage characteristic, necessary locations are made conductive, and a part of the interdigitated finger electrode 9 and one electrode 13 are electrically connected. It is connected to

As shown above (in the surface acoustic wave filter according to the present invention, this leakage characteristic can be set arbitrarily, and once set, there is no need to adjust it, and the filter can be realized as a single element, resulting in low Highly practical as a low cost, small volume, programmable filter.

[Brief explanation of drawings]

Fig. 1 shows an embodiment according to the present invention, Fig. 2 shows an embodiment of the switch region, Fig. 3 shows another embodiment of the switch region, and Fig. 4 is a sectional view taken along line AA' in Fig. 3. . 1--Piezoelectric body or base, 2--Transmitting converter, meter--reflection grating, 4--Receiving converter, 5, 6... - Electrode, 7... Switch area, 8... Electrode, 9... Cross-finger electrode, 10... Connection part, 11... ...Optical system, 12... Base, 13... Electrode, 14
. . . Cross-finger electrode, 15 . . . Photoconductor film.

Claims (1)

[Claims] 1. Having a reflection grating arranged at an angle of 45° to the propagation direction of the surface acoustic wave generated by the transmitting transducer, and in which a plurality of reflectors with continuously changing pinch intervals are arranged in the propagation direction. Then, a receiving transducer in which the pitch of the interdigitated electrodes changes continuously is placed 4 times in the direction in which the reflection gratings are arranged.
5°, and the direction of the intersecting finger electrodes is parallel to the propagation direction, and the direction of the intersecting finger electrodes is parallel to the propagation direction. , a surface acoustic wave filter characterized in that the filters are connected via a switch region.