JPS6145403B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a surface acoustic wave device whose performance is improved by removing unnecessary reflected signal waves.

FIG. 1 is a diagram showing the configuration of a conventionally used surface acoustic wave device. As shown in the figure, in the conventional device, an input transducer 2 is located close to one end of a piezoelectric substrate 1 and converts an electrical signal into a surface acoustic wave signal, and an input transducer 2 is located close to the other end and converts a surface acoustic wave signal. An output converter 4 for converting into an electrical signal is provided, and a surface acoustic wave propagation path 3 is formed between the input converter 2 and the output converter 4.

Further, a power source 5 is connected to the input converter 2, and a load 6 is connected to the output converter 4.

In this case, the input transducer 2 or the output transducer 4 usually includes a first comb-shaped electrode 7 as shown in FIG.
A blind-shaped electrode is used in which second comb-shaped electrodes 8 are arranged facing each other.

In a surface acoustic wave device using a screen-shaped electrode having such a shape, the band characteristics when used as a filter are determined by the electrode finger spacing of each comb-shaped electrode constituting the screen-like electrode and the intersecting width thereof. (CS
Hartmann etal IEEE TransMTT−21,4
(1973) 162) Furthermore, in order for a surface acoustic wave to propagate as a plane wave using a surface acoustic wave device, the surface acoustic waves must be in the same phase on a vertical plane at any point in the traveling direction of the surface acoustic wave. is desirable.

In this case, as a method for reducing the phase difference between the center and the periphery of surface acoustic waves, the
It is possible to use a surface acoustic wave device equipped with a blind electrode with an auxiliary electrode as presented in No. 3,699,364.

FIG. 3 is a diagram showing the structure of a blind electrode having an auxiliary electrode used in this case.

In this screen-like electrode, an auxiliary electrode 10 is disposed across the entire area of the weighting electrode, facing the weighting electrode section 9, and is connected to a terminal with a polarity opposite to that of the weighting electrode section 9, so that the auxiliary electrode 10 is parallel to the weighting electrode section 9. It has an arranged structure.

However, in a surface acoustic wave device using a screen-like electrode having an auxiliary electrode, when used as a filter, a reflected signal is generated from a part of the auxiliary electrode at a time slightly delayed from the main signal due to its time axis characteristics. ,
This has the disadvantage that it becomes a large undulation ripple and deteriorates its frequency characteristics.

The surface acoustic wave device according to the present invention solves the problems of the conventional devices, removes unnecessary reflected signals, and makes it possible to improve its frequency characteristics and time axis characteristics.

Hereinafter, the surface acoustic wave device according to the present invention will be described in detail based on examples thereof.

FIG. 4 shows the first surface acoustic wave device according to the present invention.
It is a figure showing the composition of an example.

As shown in the figure, in the first embodiment, blind-shaped electrodes in which auxiliary electrodes are arranged opposite to the respective weighting electrodes are arranged on the piezoelectric substrate over the entire area of the weighting electrode section 11. It has a unique structure.

Furthermore, auxiliary electrode parts 21 and 2 on the effective propagation path side of surface acoustic waves that face other screen-like electrodes, with the electrode finger having the maximum cross width of the weighting electrodes as the border.
In No. 2, the electrode fingers of the auxiliary electrode are formed parallel to the electrode fingers of the weighting electrode. Further, in the auxiliary electrode parts 23 and 24 on the side of the surface acoustic wave ineffective propagation path facing the end face of the piezoelectric substrate, with the electrode finger having the maximum cross width of the weighting electrode as the border, the electrode fingers of the auxiliary electrode are weighted. It is formed to have a predetermined angle with the electrode finger of the electrode.

With this configuration, the reflected waves generated at the auxiliary electrodes will not re-enter the weighting electrode section with the same phase, making it possible to remove the reflected waves.

In this first embodiment, the angles 31 and 32 formed by the electrode fingers of the auxiliary electrode parts 23 and 24 on the surface acoustic wave effective propagation path side facing the end face of the piezoelectric substrate and the effective propagation direction of the surface acoustic wave are as follows: A center line 12 that bisects the intersecting width of the electrode fingers of the weighting electrode section 11;
12', one side is set at 90°<θ<180° and the other side is set at -180°<θ<-90°.

A second implementation of the surface acoustic wave device according to the present invention is as follows:
This is an example of using this as a surface acoustic wave filter for video intermediate frequency of a television receiver.

In this case, a 127.8° rotated Y-cut lithium niobate was used as the piezoelectric substrate, and the input transducer and output transducer were formed by applying photolithography technology to an aluminum vapor-deposited film of about 8000 Å.

In this second embodiment, in this case approximately 60μ
The wavelength of the surface acoustic wave of m is λ, the electrode width and electrode pitch of the electrode fingers constituting the weighting electrode part and the auxiliary electrode are formed to λ/4, and the electrode fingers whose intersection width of the weighting electrodes has the maximum value are formed. The electrode finger of the auxiliary electrode on the side of the ineffective propagation path of the surface acoustic wave facing the end surface of the piezoelectric substrate is aligned with the center line 12, 1 in FIG.
Above and below 2', the angles 31 and 32 formed with respect to the propagation direction of the surface acoustic wave are -105° and 105°, respectively.
It is formed so that it becomes ゜.

FIG. 5 shows the third surface acoustic wave device according to the present invention.
It is a figure showing the composition of an example.

This third embodiment is also an example of use as a surface acoustic wave filter for video intermediate frequencies of a television receiver.

Similar to the second embodiment, as a piezoelectric substrate
Using 127.8° rotated Y-cut lithium niobate, the input transducer and output transducer were formed by applying photolithography technology to an approximately 8000 Å aluminum evaporated film.

In this third embodiment, in this case approximately 60μ
The electrode width and electrode pitch of the electrode fingers constituting the weighting electrode portion and the auxiliary electrode are set to λ/4, where the wavelength of the surface acoustic wave is λ.

In addition, the electrode fingers of the auxiliary electrodes on the side of the ineffective propagation path of the surface acoustic wave facing the end face of the piezoelectric substrate are aligned with the center line 12 in FIG. Above and below 12', the angles 31 and 32 formed with respect to the propagation direction of the surface acoustic wave are formed at 160° and -160°, respectively, and the electrode index is half that of the second embodiment. .

FIG. 6 shows the fourth surface acoustic wave device according to the present invention.
It is a figure showing the composition of an example.

This fourth embodiment is also an example of use as a surface acoustic wave filter for video intermediate frequencies of a television receiver.

As the piezoelectric substrate, a 127.8° rotated Y-cut lithium niobate is used, and the input transducer and output transducer are formed by applying photolithography technology to an aluminum vapor-deposited film of about 8000 Å.

In this case, the wavelength of the surface acoustic wave, which is about 60 μm, is set to λ, and the electrode width and electrode pitch of the electrode fingers constituting the weighting electrode part and the auxiliary electrode are formed to λ/8, and a double electrode structure (AJDeVries et al. al,
(see IEEE US Symposium 353 (1972)),
The configuration is such that a deviation is given depending on the necessity for frequency characteristics.

The auxiliary electrode is arranged so that, on the side of the surface acoustic wave ineffective propagation path facing the end face of the piezoelectric substrate, with the electrode finger having the maximum cross width of the weighting electrode as the border, the electrode finger is connected to the cross width of the electrode finger of the weight electrode part It is formed so that one side is 110 degrees and the other is -110 degrees with respect to the center line that bisects the width.

FIG. 7 is a diagram showing observation of time axis characteristics using a burst signal of a surface acoustic wave device.

In conventional surface acoustic wave devices, the seventh
Reflection signal 4 from the auxiliary electrode for the main signal 41 in the figure
2 was observed at approximately -30dB.

On the other hand, in the second and third embodiments of the surface acoustic wave device according to the present invention, the reflected signal 42 is about -
40 dB, and about -45 dB in the fourth embodiment.If the surface acoustic wave device according to the present invention is used as a surface acoustic wave filter for video intermediate frequency of a television receiver, the signal reflected from the auxiliary electrode It is possible to significantly reduce the ghosting that occurs on the television screen.

As described above in detail, the surface acoustic wave device according to the present invention can significantly reduce unnecessary reflected signals from the auxiliary electrode on the time axis of the surface acoustic wave, and can reduce the unnecessary reflection signal as a wave in the frequency characteristic. If ripples are removed and used as a surface acoustic wave filter for video intermediate frequencies in television receivers, for example,
Ghosts on the screen of a television receiver can be removed.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the configuration of a conventionally used surface acoustic wave device, Figure 2 is a diagram showing the structure of a blind electrode, Figure 3 is a diagram showing the structure of a blind electrode having an auxiliary electrode, FIG. 4 is a diagram showing the configuration of the first embodiment of the surface acoustic wave device according to the present invention, FIG. 5 is a diagram showing the configuration of the third embodiment of the surface acoustic wave device according to the present invention, and FIG. is the fourth surface acoustic wave device according to the present invention.
FIG. 7 is a diagram showing the structure of an embodiment of the present invention, and FIG. 7 is a diagram showing observation of time axis characteristics using a burst signal of a surface acoustic wave device. Explanation of symbols, 1... Piezoelectric substrate, 2... Input transducer, 3... Propagation path, 4... Output transducer, 5... Power supply, 6
...load, 7...first comb-shaped electrode, 8...second comb-shaped electrode,
9... Weighting electrode part, 10... Auxiliary electrode, 11... Weighting electrode part, 21, 22, 23, 24... Auxiliary electrode part, 41... Main signal, 42... Reflected signal.

Claims (1)

[Scope of Claims] 1. A surface acoustic wave device having a plurality of screen-shaped electrodes each having a pair of comb-shaped electrodes facing each other and having a conversion function between an electric signal and a surface acoustic wave on a piezoelectric substrate. At least one of the blind electrodes is formed of a weighting electrode, and the weighting electrode extends from a side of the blind electrode having the weighting electrode opposite to another blind electrode to an electrode finger having a maximum crossing width of the weighting electrode. is formed perpendicularly to the propagation direction of the surface acoustic wave, and is outside an envelope formed by the intersection of the weighting electrodes from the side opposite to the end surface of the piezoelectric substrate of the blind electrode having the weighting electrodes to the electrode fingers. is formed at a specific angle that is not perpendicular to the propagation direction of the surface acoustic wave. 2. The surface acoustic wave device according to claim 1, wherein the specific angle is larger than 90° and smaller than 180°. 3. Claim 1, wherein the specific angles of one of the weighting electrodes and the other of the weighting electrodes are symmetrical with respect to the central axis of the surface acoustic wave device in the propagation direction of surface acoustic waves. Or the surface acoustic wave device according to item 2. 4. The surface acoustic wave device according to claim 1 or 2, wherein the weighting electrode comprises a weighting electrode section and an auxiliary electrode section facing the weighting electrode section.