JPS5834048B2 - surface acoustic wave device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a surface acoustic wave device using a multi-strip coupler.

FIG. 1 shows a general surface acoustic wave filter using a multi-strip coupler.

In this surface wave filter, input and output quadrature reducers 2 and 3 are arranged on a piezoelectric body 1 with their respective propagation paths shifted, and a multi-strip coupler 4 is arranged between the input and output quadrature reducers 2 and 3 across both propagation paths. It has been established.

The multi-strip coupler 4 has a large number of electrode fingers 4a, 4b in the same direction as the electrode fingers of the input/output transducers 2, 3,
. . . 4n, and these electrode fingers 4a, 4b, . . . 4n are configured as floating electrodes.

In such a surface wave filter, a large number of electrode fingers 4a, 4b, . . . of the multi-strip coupler 4 are used.
Since 4n is a floating electrode, the input and output quadrant transducers 2 and 3 are electrically coupled by a large capacitor.

As a result, the signal applied to the input quadrature transducer 2 is directly transmitted to the output transducer 3 via the capacitance of the multi-strip coupler 4, that is, the level of the direct wave increases and spurious occurs in the filter characteristics.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a surface acoustic wave device that can obtain the effect of suppressing spurious waves caused by bulk waves, which is the original purpose of using a multi-strip coupler, and at the same time reduce the level caused by direct waves.

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

In FIG. 2, numeral 10 denotes a piezoelectric material, which is made of, for example, a piezoelectric thin film such as ZnO, a piezoelectric ceramic such as PZT, or a single crystal such as LiNbO2.

Reference numerals 11 and 12 denote an input/output quadrant transducer, which is constructed by forming interdigital electrodes in which a pair of comb-shaped electrodes are inserted into each other on the piezoelectric body 10.

Each comb-teeth electrode is usually formed on the piezoelectric body 10 using an electrode material such as A7 using a pattern forming technique such as vapor deposition or photo-etching.

The input/output quadrant transducers 11, 12 are arranged on the piezoelectric body 10 so that the propagation paths of the transducers 11, 12 do not overlap, with the electrode fingers parallel to each other, and separated by an appropriate distance.

Reference numeral 13 denotes a multi-strip coupler, which has a large number of electrode fingers 14, 15, 16, 17, 18, 1 arranged parallel to each other.
920.

The coupler 13 is connected between the input and output quadrant transducers 1L12, and its electrode fingers 14 to 20 are connected to the transducer 11.
, 12, and parallel to the electrode fingers 14 to 12.
The length of 20 is arranged so as to straddle both the propagation paths of the transducers 11 and 12.

Moreover, in the coupler 13, among the electrode fingers 14 to 20, the electrode fingers 14, 16, 18, 20 that are in the same phase are different from the other electrode fingers 15.
, 17° 19 toward the side surface of the piezoelectric body 10, and these extensions are electrically coupled to each other by an extraction electrode 21.

The lead 22 connected to this extraction electrode 21 is grounded, and the electrode fingers 14, 16.degree. 18.20 are grounded.

Which electrode fingers among a large number of electrode fingers have the same phase is determined by the pitch of the electrode fingers.

In other words, as shown in the figure, the pitch tends to vary (λ).

: the wavelength of the surface wave at the center frequency), the phase of each electrode finger is reversed, and each electrode finger is alternately in the same phase.

Although not shown, if the pitch is random, every two electrode fingers will be in the same phase alternately.

The coupler 13 and extraction electrode 21 are formed on the piezoelectric body 10 in the same manner as the comb-like electrodes of the transducers 1 and 12.

Input leads 23 and 24 are connected to the comb electrodes of the input juicer 1, and output leads 25 and 26 are connected to the comb electrodes of the output juicer 2.

In the above embodiment, among the electrode fingers 14 to 20 of the coupler 13, all of the electrode fingers 14, 16, 18, and 20 that are in the same phase are grounded, but the present invention is not limited to this, and only one electrode finger is grounded. , or several electrode fingers.

Further, in order to ground the electrode fingers, a grounding lead may be connected to each electrode finger individually, without having to take out the electrode finger and extend it to the electrode 21.

Next, the operation of the above embodiment will be explained.

First, when a signal is applied to the input quadratic transducer 1 through the leads 23 and 24, the transducer 1 is excited, and a surface wave is propagated from the transducer 1 along the surface of the piezoelectric body 10 in a direction perpendicular to the electrode finger. , when the unidirectional surface wave shown by arrow A reaches the coupler 13, the coupler 13 is also excited.

When the logarithm of this coupler 13 is set to a predetermined number, most of the surface waves excited by the coupler 13 propagate in the direction of arrow B, reach the output juicer 2, and are carried by the transducer 2 into the lead 25. The output voltage is derived between 26 and 26.

The coupler 13 forms a large capacitor like the coupler 4 in FIG. cadran juicer 11
, 12 becomes smaller, the level due to direct waves decreases.

Further, since the bulk wave generated by the input quadrature transducer 11 propagates through the piezoelectric body 10 in the direction of propagation of the transducer 11, it does not reach the output transducer 12, and almost no spurious waves are generated due to the bulk wave.

Moreover, in the above embodiment, only the electrode fingers of the same phase in the coupler 13 are grounded, so that the state in which the coupler 13 is excited by the surface wave from the input quadrature transducer 11 is as shown in FIG. 3a. It is in phase with the amplitude of the surface wave, and the surface wave is not adversely affected while passing through the coupler 13.

On the other hand, if electrode fingers having different phases are grounded, as shown in FIG. 3, surface wave propagation will be hindered and loss will increase.

However, the present invention is not limited to the case where only the electrode fingers of the same phase are grounded, and if the occurrence of surface wave distortion can be tolerated, the electrode fingers of different phases may be grounded.In short, at least one of the couplers The main electrode finger is grounded to reduce the level due to direct waves.

As explained above, in the present invention, at least one electrode finger of the multi-strip coupler disposed between the input and output quadrature transducers is grounded, so direct waves are suppressed, spurious waves are reduced, Furthermore, if the electrode fingers to be grounded are set to have the same phase, there is also the effect that generation of surface wave distortion due to the coupler can be suppressed.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing a conventional surface acoustic wave device, FIG. 2 is a plan view showing an embodiment of the surface acoustic wave device according to the present invention,
Figures 3a and 3b are diagrams showing the excitation state of the coupler. 10 is a piezoelectric body, 11 and 12 are transducers, 13 is a multi-strip coupler, and 14 to 20 are electrode fingers.

Claims (1)

[Scope of Claims] 1. A surface acoustic wave device in which a multi-strip coupler consisting of a large number of electrode fingers is provided between output quadrature reducers, characterized in that at least one electrode finger of the multi-strip coupler is grounded. surface acoustic wave device. 2. The surface acoustic wave device according to claim 1, wherein the number of electrode fingers to be grounded is at least two, and the electrode fingers are in the same phase.