JPS63250908A - Surface acoustic wave device - Google Patents

Abstract

PURPOSE:To prevent the adverse effect of a diffraction effect from being generated and to stabilize a characteristic, by providing an intermediate electrode of meander shape not being connected to an external circuit between a positive electrode and a negative electrode on one or plural IDT electrodes for transmission/reception of a surface acoustic wave, and specifying the interval between the electrode fingers of the positive electrode and the negative electrode. CONSTITUTION:The intermediate electrode of meander shape not being connected to the external circuit is provided between the positive electrode 1 and the negative electrode 2, and the interval of the electrode fingers of the positive electrode 1 and the negative electrode 2 are set as (2n+1)lambda/2(n=1, 2, 3,...). By constituting a device in such way, it is possible to quadruple impedance without separating the electrode into plural sections compared with a conventional IDT electrode. Since no electrode is separated into plural numbers, the high impedance of a weight electrode not being realized in a conventional device can be realized, and also, no adverse effect of the diffraction effect is given because no track separation is performed. For example, by providing an aperture with a pitch of lambda/8 on the electrode 3 of meander shape in the propagation path 10 of a surface acoustic wave and setting the effective acoustic velocity of the acoustic waves between the positive and negative electrodes 11 and 13 and between meander electrode sections 12 equal, the change of the characteristic can be prevented from being generated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a surface acoustic wave device, and relates to a method of configuring an IDT electrode suitable for increasing the impedance of the IDT electrode to a high impedance.

[Conventional technology]

A conventional technique for achieving high impedance is to divide the electrode into two parts and connect them in series (Japanese Unexamined Patent Publication No. 51-5
No. 0592, Japanese Unexamined Patent Publication No. 153318/1982),
How to divide the electrode into multiple tracks and connect them in series (
! % Publication No. 50-120993).

[Problem that the invention seeks to solve]

The problem with the above conventional technology is that the method of dividing the electrode into two requires that the two electrodes have exactly the same characteristics.
There is a problem in that the voltage applied to each electrode is not equal and the characteristics change, and for example, it could not be applied to left-right asymmetric weighted electrodes (TV IP filters, etc.). Furthermore, in the method of dividing into a plurality of tracks, there is a problem that the aperture length of each track becomes small, which is adversely affected by the diffraction effect, and the characteristics change.

An object of the present invention is to solve the above-mentioned problems and to propose a new electrode structure whose characteristics change little even when the impedance is increased.

[Means for solving problems]

The above object is achieved by providing a meandering intermediate electrode between the positive electrode and the negative electrode and connecting the electrodes in series without dividing the electrodes into a plurality of sections as in the prior art.

[Effect]

FIG. 1 shows the basic electrode structure of the present invention. A meandering intermediate electrode 3 that is not connected to the outside is provided between a positive electrode 1 and a negative electrode 2. The distance between the lightning pole fingers is (2rL+1)λ/2 (n = t2
3...). With this configuration, the conventional IDT shown in FIG.
The impedance can be quadrupled compared to the % pole. Since ia is not divided into a plurality of parts, it is possible to make the weight row electrodes high impedance, which was previously impossible, and since there is no track division, there is no adverse effect of diffraction effects.

〔Example〕

The present invention will be explained in detail below. FIG. 3 shows an example using a split electrode, which is currently most commonly used. Here, the meandering electrode 3 in the surface wave propagation path 10
The reason why openings with a pitch of λ/8 are provided is to equalize the effective sound speed of the surface waves in the positive and negative electrode sections 1113 and the meander electrode section 12, and to prevent characteristic changes. In the case of solid electrodes, the same effect can be obtained by providing openings with a pitch of λ/4. Also, 14 indicates the impulse response characteristic. If the spacing between positive and negative electrode fingers is 3/2λ, 3 Although pulse omissions 15 occur for each pulse, since the omissions occur at equal intervals, there is almost no change in the characteristics due to this omission.

Further, as shown in FIG. 4, by using a mixture of several types of positive and negative electrode finger spacing, it is also possible to actively apply variable weighting. Figure 5 shows 5AWI for TV and VTR to which the present invention is applied.
F7 (this is an example of a router).

As shown in FIG. 6, the 5AW IF filter generally has a configuration in which a regular type electrode 15 is used to obtain a high adjacent trap characteristic, and one weighted row electrode 16 is used to achieve an asymmetrical amplitude characteristic. Note that 17 is a shield electrode that suppresses direct waves between input and output electrodes. TV, V'l'R IP
In the circuit, the output impedance of the tuner on the input side of the SAW is 75Ω, which is a low impedance, and the output impedance of the tuner on the output side is 75Ω.
The input impedance of IFIC is 15 to 3. OKΩ and high impedance. Therefore, it is best to set the electrode impedance of the SAW filter to be low on the input side and high on the output side accordingly. However, in the conventional configuration shown in FIG. 6, the impedance is similar to that of the input and output electrodes, and the above cannot be achieved. , the impedance of the output pledge can be increased approximately 4 times without changing the amplitude characteristics and group delay time characteristics, and the optimal matching conditions with the external circuit can be obtained. Even when using a weight row electrode, the same effect can be obtained by applying the present invention to the weight row electrode.

〔Effect of the invention〕

According to the present invention, the electrode impedance can be increased approximately four times without changing the amplitude characteristics and group delay time characteristics of the conventional IDT electrode shown in FIG. 2, so the impedance of the external circuit is high and the SAW filter If matching cannot be achieved without making the impedance high, this electrode can be applied to achieve optimal matching without changing the characteristics.

Moichi 4th show the blind weight electrode structure according to the present invention.
...Positive electrode, 2...Negative electrode, 3...Meandering electrode, 4...Intermediate electrode, 5...Divided ¥ into poles 1, 6...
Split electrode 2゜7...Track 1, 8...Track 2
, 9... opening.

10...Surface wave propagation path, 11...Positive electrode section, 12
... Meander electrode section, 13 ... Negative electrode section, 14
...Impulse response, 15...Regular 2! ! ! Murogoku,
16... Weighted electrode (-217... Shield electrode, 1
8... Input terminal, 19... Output terminal, 20... Electrode according to the present invention.

謬　／　口 2nd bath No.) Mouth

Claims (1)

[Claims] One or more IDs for surface acoustic wave transmission on a piezoelectric substrate.
T electrode and one or more surface acoustic wave receiving IDs
In a surface acoustic wave device in which a T electrode is formed, one or more of the IDT electrodes has a meandering intermediate electrode that is not connected to an external circuit between the positive electrode and the negative electrode, and The electrode finger spacing of the negative electrode is [(2n+1)
/2] λ (n=1.2...').