JP3294496B2 - Surface acoustic wave device and communication device using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave device capable of simultaneously obtaining a sufficient out-of-band suppression degree and a wide pass band with a small chip size, and a communication device using the same.

[0002]

2. Description of the Related Art FIG. 12 is a schematic diagram showing a general surface acoustic wave device, wherein 1 is a piezoelectric substrate, 2 is a regular electrode, 3 'is a weighting electrode, 4 is a main slope, and 5 is a main slope. Is a side slope, 6 is a sound absorbing material, 7 is a metal film, and 8 is an envelope.

In FIG. 1, two input / output interdigital transducers in which every other electrode finger and every other electrode finger intersect in a comb shape on a piezoelectric substrate 1 made of YX LiNbO3 rotated by 128 degrees. Electrodes 2, 3 'are provided at a predetermined distance. One of the input / output interdigital transducers 2 is a regular electrode having a constant intersecting width of the interdigital transducers, and the other input / output interdigital transducer 3 ′ has a gap between the opposing electrode fingers due to a change in the electrode finger intersecting width. Is a weighting electrode having a lobe representing the trajectory. Such lobes include a main rope 4 located at the center of the weighting electrode 3 ′ and side lobes 5 arranged on both sides of the main rope 4. The maximum crossing width of the side lobes 5 is indicated by an envelope 8. In addition, the side lobe 5 on the end side of the weighting electrode 3 ′ is smaller. Here, only the outermost side lobe is shown.

Further, a sound absorbing material 6 for suppressing a reflected wave from an end face of the piezoelectric substrate 1 is coated on an end side of the input / output interdigital electrodes 2, 3 'on the piezoelectric substrate 1. ,
A metal film 7 for suppressing direct waves between the input and output interdigital electrodes 2 and 3 ′ is formed between the input and output interdigital electrodes 2 and 3 ′.

[0005]

Such a surface acoustic wave device obtains a desired frequency characteristic by utilizing a surface wave propagating between the input and output interdigital electrodes 2 and 3 '. The out-of-band suppression degree of such a surface acoustic wave device is closely related to the pass band frequency. Using conventional weighted electrodes, for example, "IEEE TRANSACTION ON MICROWAVE
THEORY AND TECHNIQUES ”Volume. MTT-21 No.4, Apr
As described in il 1973 pp. 162 to 175, it is well known that when the passband frequency is increased within a limited number of impulses, the degree of out-of-band suppression deteriorates. FIG.
Numeral 3 schematically shows this. When the pass band A is narrow as shown by the broken line, the degree of out-of-band suppression C can be sufficiently obtained. Then, the out-of-band suppression degree D deteriorates.

Therefore, in the conventional weighting electrode, the number of impulses (the number between electrode fingers in the traveling direction of the surface acoustic wave) must be increased in order to widen the passband frequency and secure the degree of suppression outside the band. However, there is a problem that the chip size becomes large as a result.

An object of the present invention is to solve such a problem and to obtain a sufficient degree of out-of-band suppression and a wide passband at the same time with a conventional weighted electrode or smaller chip size. It is another object of the present invention to provide a surface acoustic wave device and a communication device using the same.

[0008]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a method in which the outermost end of a side lobe of a weighting electrode is larger than the maximum electrode finger intersection width of the outermost side lobe. Electrode fingers at electrode finger intersections are provided.

With such a configuration, in the frequency amplitude characteristics of the weighting electrode, both shoulders of the pass band can be further raised, and the pass band of the surface acoustic wave device can be further expanded. In this case, the out-of-band characteristics are not significantly affected as a whole, so that the degree of out-of-band suppression is ensured and a wider pass bandwidth is obtained.

Further, according to the present invention, the rising portion outside the frequency amplitude characteristic band of the weighting electrode is set near zero frequency outside the frequency amplitude characteristic band of the IDT electrode facing the weighting electrode.

If the frequency amplitude characteristic of the weighting electrode is set so as to widen the pass band of the frequency amplitude characteristic of the surface acoustic wave device, a swelling characteristic occurs outside the frequency amplitude characteristic band of the weighting electrode. However, in the present invention, by setting this raised portion near the zero frequency of the frequency amplitude characteristic of the other IDT, the raised portion is greatly attenuated, and a good suppression degree can be obtained.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram showing a main part of a first embodiment of a surface acoustic wave device according to the present invention, that is, a weighting electrode, where 3 is the weighting electrode, 9 is the outermost end of the electrode, and FIG. Are given the same reference numerals.

In FIG. 1, the outermost side lobes 5 do not reach the outermost end portions 9 of the electrodes on both sides of the weighting electrode 3, and a pair of electrode fingers are provided at the outermost end portions 9 of these electrodes. The electrode finger intersection width d2 is set to be larger than the maximum electrode finger intersection width d1 in the outermost side lobe 5.

This first embodiment is different from the surface acoustic wave device shown in FIG.
The weighting electrode 3 having the configuration shown in FIG.

FIG. 2 is a characteristic diagram showing a frequency amplitude characteristic of the first embodiment.

In FIG. 2, a dotted line 10 is a frequency amplitude characteristic 10 of the normal electrode 2 shown in FIG. 12, which is a mountain-shaped characteristic in which both shoulders are attenuated in the pass band,
The chevron-shaped characteristic having a periodic zero-point frequency 12 is repeated. The envelope of the characteristic outside these bands is a curve that attenuates away from the pass band.

On the other hand, a broken line 11 is a frequency amplitude characteristic 11 of the weighting electrode 3 shown in FIG. 1, and the weighting electrode 3 is configured so that both shoulders of the pass band are raised. Therefore, in the first embodiment, the attenuation of the shoulders in the pass band of the frequency amplitude characteristic 10 is caused by the swelling of the shoulders in the pass band of the frequency amplitude characteristic 11 by combining the frequency amplitude characteristics 10 and 11. Compensated, solid line 13
In the total frequency amplitude characteristic shown by, a wide pass band is obtained.

Of course, also in the weighting electrode 3 'shown in FIG. 12, as shown by a solid line 14 in FIG. 2, the shoulder of the pass band is raised so as to widen the pass band of the overall frequency amplitude characteristic. can do. However, if an attempt is made to obtain a wider pass band by increasing the swell, the degree of suppression outside the band deteriorates as described with reference to FIG.

Therefore, in the first embodiment, the electrode finger intersection width d2 of the pair of electrode fingers at the electrode outermost ends 9 on both sides of the weighting electrode 3 is set to the electrode finger intersection of the outermost end side lobe 5. It is made larger than the width d1. According to this, as shown in FIG. 2, both shoulder portions of the pass band in the frequency amplitude characteristic 11 of the weighting electrode 3 can be raised, and the raised portion is the frequency of the conventional weighting electrode 3 ′ indicated by a solid line 14. Even if the amplitude characteristic becomes larger than the amplitude characteristic, the degree of out-of-band suppression does not significantly deteriorate compared to the conventional weighting electrode 3 '.

However, if the electrode finger as described above is provided at the outermost end portion 9 of the electrode to widen the pass band in the total frequency amplitude characteristic of the surface acoustic wave device, as shown in FIG. Outside of the band, a characteristic 15 of a bulge that significantly degrades the degree of out-of-band suppression occurs. If the shoulder of the pass band of the frequency amplitude characteristic 11 of the weighting electrode 3 is made to bulge further, the bulge characteristic 15 outside this band becomes More excitement. As a result, the degree of out-of-band suppression is degraded.

Therefore, in the first embodiment, the swelling characteristic 15 outside the band of the frequency amplitude characteristic 11 of the weighting electrode 3 is further changed to the zero frequency 12 outside the band of the frequency amplitude characteristic 10 of the normal electrode 2. The weighting electrodes 3 are configured so as to match. As a result, as shown in FIG. 2, the swelling characteristic 15 outside the band of the frequency amplitude characteristic 11 of the weighting electrode 3 is sufficiently attenuated, and the overall frequency amplitude characteristic 13 can obtain a sufficient degree of suppression uniformly outside the band. Will be done.

Thus, in the first embodiment, even if the pass band is widened, the degree of suppression outside the band can be increased at the same time.

FIG. 3 is a characteristic diagram showing the overall frequency amplitude characteristics of the first embodiment and the conventional surface acoustic wave device as shown in FIG. 12 at the same number of impulses. The dotted line 17 indicates the total frequency amplitude characteristic of the conventional surface acoustic wave device. The solid line 16 'is an enlarged view of the ± 5 dB portion of the total frequency amplitude characteristic 16 of the first embodiment.
7 'is the total frequency amplitude characteristic 17 of the conventional surface acoustic wave device.
5 is an enlarged view of the ± 5 dB portion of FIG.

As is apparent from FIG. 3, when the degree of out-of-band suppression is equal, the overall frequency amplitude characteristic 1 of the first embodiment is obtained.
It can be seen that the pass band at 6 (16 ') can be made wider than the pass band at the total frequency amplitude characteristic 16 (16') of the conventional surface acoustic wave device.

FIG. 4 shows a second embodiment of the surface acoustic wave device according to the present invention.
2 is a configuration diagram showing a main part of the embodiment, that is, a weighting electrode. Parts corresponding to FIG. 1 are denoted by the same reference numerals, and redundant description is omitted.

In the second embodiment, in the electrode outermost end portions 9 on both sides of the weighting electrode 3, the electrode finger intersection width d3 is set to the maximum value of the outermost side lobe 5 by two pairs of electrode fingers. This is larger than the electrode finger intersection width d1.

In the second embodiment, both shoulders of the pass band in the frequency amplitude characteristic 11 shown in FIG. 2 can be made larger than the first embodiment shown in FIG. In order to obtain good out-of-band suppression with a wide pass bandwidth similar to the embodiment shown in FIG.
The design margin of the weighting electrode 3 is increased.

In the second embodiment, the number of electrode finger pairs at the outermost end portion 9 of the electrode may be three or more.

FIG. 5 shows a third embodiment of the surface acoustic wave device according to the present invention.
FIG. 2 is a configuration diagram showing a main part of the embodiment, that is, a weighting electrode, and portions corresponding to FIG. 1 are denoted by the same reference numerals.

In the third embodiment, a weighting electrode 3 is a so-called tilt type electrode in which side lobes 5 on both sides of a main lobe 4 are arranged on opposite sides with respect to a surface acoustic wave propagation center axis 18. Is what you do.

If the center axes of the surface acoustic wave propagation of all the side lobes are made to coincide with each other as in the previous embodiment, the surface wave intensities on both sides of the center axis are offset on the weighting electrode 3, and the weighting is performed. The surface acoustic wave propagating on the electrode 3 has difficulty in obtaining a desired frequency amplitude characteristic due to the weight loss. The tilt type electrode is designed to prevent this, and the surface wave intensity is weighted so that the propagation speed of the surface acoustic wave in the opening direction of the electrode 3 can be made uniform and the weight loss can be improved.

Further, the weighting electrode 3
As shown in FIG. 5, the electrode cross width d4 at the outermost end portion 9 of the electrode can be increased as compared with the first embodiment shown in FIG.
In order to obtain a wide passband and a sufficient degree of out-of-band suppression, restrictions on electrode design are alleviated.

In the third embodiment, as in the second embodiment shown in FIG. 4, the number of pairs of electrode fingers at the outermost end portion 9 of the weighting electrode 3 can be set to two or more.

FIG. 6 shows a fourth embodiment of the surface acoustic wave device according to the present invention.
1 is a block diagram showing an embodiment of the present invention, and portions corresponding to the above-mentioned drawings are denoted by the same reference numerals.

In the figure, the weighting electrode 3 is the same as that of the embodiment shown in FIGS. 1, 4 and 5, and in the fourth embodiment, the surface acoustic wave propagation center of the weighting electrode 3 is further increased. The axis 16 is shifted from the central axis 19 of the surface acoustic wave propagation of the normal electrode 2.

The piezoelectric substrate 1 has a sound velocity anisotropy, and the propagation speed of the surface acoustic wave differs depending on the propagation direction. Therefore, the weighting electrode 3 receives surface acoustic waves having different propagation speeds from the normal electrode 2. The frequency amplitude characteristics of the weighting electrode 3 are also affected by the distribution of surface acoustic waves having different propagation speeds.

Therefore, in the fourth embodiment, the amount of deviation between the center axis 16 of the surface acoustic wave propagation of the weighting electrode 3 and the center axis 19 of the surface acoustic wave propagation of the normal type electrode 2 is appropriately set, whereby It is possible to obtain a more excellent out-of-band suppression degree than in each embodiment. In this case, the pass band is hardly affected by the displacement of the shafts 16 and 19. Therefore, as in the previous embodiment,
A wide pass band is obtained.

Further, there is a trade-off with the out-of-band suppression degree.
The ripple in the pass band can be improved. Therefore, the characteristics of the surface acoustic wave device can be improved by setting the amount of displacement between the axes 16 and 19 so that the degree of out-of-band suppression and the improvement of ripple in the pass band are optimized. .

FIG. 7 shows a fifth embodiment of the surface acoustic wave device according to the present invention.
FIG. 2 is a block diagram showing an embodiment of the present invention, wherein 2 ′ is a sampling electrode, and portions corresponding to the above-mentioned drawings are denoted by the same reference numerals.

In the figure, the weighting electrode 3 has the same configuration as in each of the above embodiments. In the fifth embodiment, the regular electrode is the extraction electrode 2 ′ with the electrode finger partially removed. In this embodiment, the same effects as those of the first, second, and third embodiments can be obtained.

A structure in which some electrode fingers are thinned out is called a sampling electrode. In general, an electrode having such a structure has a higher degree of suppression of side lobes than a normal electrode.

In the fifth embodiment, the extraction electrode 2 'is used as a regular electrode, and the same effect as that of the previous embodiment can be obtained.

FIG. 8 shows a sixth embodiment of the surface acoustic wave device according to the present invention.
1 is a block diagram showing an embodiment of the present invention, and portions corresponding to the above-mentioned drawings are denoted by the same reference numerals.

In the figure, one input / output interdigital electrode is a weighting electrode 3 having the same structure as in each of the above embodiments, but the other input / output interdigital electrode sandwiching the metal film 7 is shown in FIG. A conventional weighting electrode 3 'as shown in FIG.

The frequency amplitude characteristic of the weighting electrode 3 is shown in FIG.
As shown in FIG. 2, the frequency-amplitude characteristic of the conventional weighting electrode 3 'is the same as that of the conventional dashed-dotted line 11, but there is almost no swelling portion 15 shown in FIG.

In the sixth embodiment, the zero-point frequency outside the band of the frequency amplitude characteristic of the weighting electrode 3 ′ and the zero frequency outside the band of the frequency amplitude characteristic of the weighting electrode 3 are shifted from each other, and the characteristic is shifted from each other at the zero frequency part. Thus, a sufficient degree of out-of-band suppression can be obtained even when the conventional weighting electrode 3 'is used instead of the normal electrode.

Here, the pass band of the frequency amplitude characteristic of the conventional weighting electrode 3 'is set as a characteristic 10 in FIG. 2, and the pass band of the frequency amplitude characteristic of the weight electrode 3 is set as the characteristic 11 of FIG. Needless to say. This allows
A wide pass band can be obtained.

In the above embodiment, the piezoelectric substrate 1
Using 128 degree rotated YX LiNbO3, but other materials such as 112 degree YX LiTaO3, LiNbO3, LiT
Similar effects can be obtained by using a piezoelectric substrate such as aO3 or quartz.

FIG. 9 is a block diagram showing a first embodiment of a communication device using a surface acoustic wave device according to the present invention, wherein 20 is an antenna, 21 is a tuner unit, 22 is an intermediate frequency filter, and 23 is demodulation. And 24 and 25 are output units.

In the figure, in the first embodiment, the communication device is a television receiver, and the surface acoustic wave device according to the present invention is used as the intermediate frequency filter 22.

The television signal received from the antenna 20 is converted into an intermediate frequency signal by the tuner 21, and is filtered by the intermediate frequency filter 22. The intermediate frequency signal from the intermediate frequency filter 22 is demodulated into a video signal and an audio signal by the demodulation unit 23, and the video signal is output from the output unit 24.
Audio signals are output from the output unit 25, respectively.

Since the surface acoustic wave device according to the present invention is used as the intermediate frequency filter 25,
Compared with the case of using the conventional surface acoustic wave device, filtering of the intermediate frequency signal becomes better, and a television receiver which can be made smaller and has excellent demodulation performance can be realized.

FIG. 10 is a block diagram showing a second embodiment of the communication apparatus using the surface acoustic wave device according to the present invention, wherein 26 is a parabolic antenna, 27 is an outdoor unit, and 2 is an outdoor unit.
8 is an indoor unit, 29 is a mixer, 30 is an oscillator, 31
Is an intermediate frequency filter, 32 is a demodulation unit, and 33 and 34 are output units.

In the figure, in the second embodiment, the communication device is a satellite broadcast receiving device, and the surface acoustic wave device according to the present invention is used for the intermediate frequency filter 22.

The satellite broadcast signal received by the parabolic antenna 26 is converted into a high-frequency signal by the outdoor unit 27 and supplied to the indoor unit 28. In the indoor unit 28, the high frequency signal is combined with the output signal of the oscillator 30 by the mixer 29 and converted into an intermediate frequency signal. This intermediate frequency signal is filtered by an intermediate frequency filter 31 and demodulated by a demodulation unit 32 into a video signal and an audio signal.
The video signal is output from the output unit 33, and the audio signal is output from the output unit 34.
Is output from each.

Here, since the surface acoustic wave device according to the present invention is used as the intermediate frequency filter 34,
Compared with the case of using the conventional surface acoustic wave device, filtering of the intermediate frequency signal becomes better, and a satellite broadcast receiver that can be made smaller and has excellent demodulation performance can be realized.

FIG. 11 is a block diagram showing a third embodiment of a communication device using a surface acoustic wave device according to the present invention, wherein 35 is a cable terminal, 36 is a tuner, 37 is an intermediate frequency filter, and 38 is The demodulation units 39 and 40 are output units.

In the figure, in the third embodiment, the communication device is a CATV receiver, and the above-described surface acoustic wave device according to the present invention is used for the intermediate frequency filter 37.

The input signal from the cable terminal 35 is converted into an intermediate frequency signal by the tuner section 36 and filtered by the intermediate frequency filter 37. The intermediate frequency signal from the intermediate frequency filter 37 is demodulated into a video signal and an audio signal by a demodulation unit 38, and the video signal is output from an output unit 39 and the audio signal is output from an output unit 40.

Since the surface acoustic wave device according to the present invention is used as the intermediate frequency filter 37,
It is possible to realize a CATV receiver that has better filtering of the intermediate frequency signal, can be more compact, and has excellent demodulation performance.

[0061]

As described above, according to the present invention,
In the surface acoustic wave device, the pass band can be widened and the degree of out-of-band suppression can be increased without increasing the number of impulses, and good frequency amplitude characteristics can be obtained with a limited chip size.

According to the present invention, good demodulation performance can be realized in a communication device.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a weighting electrode in a first embodiment of a surface acoustic wave device according to the present invention.

FIG. 2 is a diagram showing a frequency amplitude characteristic in the first embodiment shown in FIG.

FIG. 3 is a characteristic diagram showing a comparison between the frequency amplitude characteristic of the first embodiment shown in FIG. 1 and the frequency amplitude characteristic of a conventional surface acoustic wave device.

FIG. 4 is a configuration diagram showing weighting electrodes in a surface acoustic wave device according to a second embodiment of the present invention.

FIG. 5 is a configuration diagram showing weighting electrodes in a third embodiment of the surface acoustic wave device according to the present invention.

FIG. 6 is a configuration diagram showing a fourth embodiment of the surface acoustic wave device according to the present invention.

FIG. 7 is a configuration diagram showing a fifth embodiment of the surface acoustic wave device according to the present invention.

FIG. 8 is a configuration diagram showing a sixth embodiment of the surface acoustic wave device according to the present invention.

FIG. 9 is a block diagram showing a first embodiment of a communication device using the surface acoustic wave device according to the present invention.

FIG. 10 is a block diagram showing a second embodiment of a communication device using the surface acoustic wave device according to the present invention.

FIG. 11 is a block diagram showing a third embodiment of a communication device using the surface acoustic wave device according to the present invention.

FIG. 12 is a configuration diagram illustrating an example of a conventional surface acoustic wave device.

FIG. 13 is a schematic diagram showing a relationship between a pass band and a degree of out-of-band suppression in a conventional surface acoustic wave device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Piezoelectric substrate 2 Regular type electrode 2 'Extraction electrode 3 Weighting electrode 4 Main lobe 5 Side lobe 6 Sound absorbing material 7 Metal film 8 Envelope 9 Electrode outermost end 10 Frequency amplitude characteristic of normal type electrode 11 Frequency amplitude of weighting electrode Characteristic 12 Zero frequency 13 Total frequency amplitude characteristic 15 Rise part 20 Antenna 21 Tuner part 22 Intermediate frequency filter 23 Demodulation part 24, 25 Output part 26 Parabolic antenna 27 Outdoor unit 28 Indoor unit 26 Mixer 30 Oscillator 31 Intermediate frequency filter 32 Demodulation part 33, 34 output section 35 cable terminal 36 tuner section 37 intermediate frequency filter 38 demodulation section 39, 40 output section

Continuation of the front page (72) Inventor Jin Yanagihara 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Hitachi, Ltd. Multimedia System Development Division (56) References JP-A-60-1913 (JP, A) (58) Field surveyed (Int.Cl. ⁷ , DB name) H03H 9/145 H03H 9/64 H04B 1/26

Claims (6)

(57) [Claims] An input interdigital electrode and an output interdigital electrode are formed on a piezoelectric substrate, and one of the interdigital electrodes is provided.
In a surface acoustic wave device in which a pole is a normal type electrode and the other interdigital electrode comprises a weighting electrode having a main lobe and one or more side lobes, the outermost end of the weighting electrode is outside the side lobe. Wherein the outermost electrode finger intersection width is formed to be larger than the maximum electrode finger intersection width of the outermost end side lobe. 2. The surface acoustic wave device according to claim 1, wherein a bulging portion outside the frequency amplitude characteristic band of the weighting electrode is out of the frequency amplitude characteristic band of the interdigital electrode facing the weighting electrode. A surface acoustic wave device, wherein the surface acoustic wave device is set near a zero frequency. 3. The surface acoustic wave device according to claim 1, wherein the interdigital transducer facing the weighting electrode is a regular electrode. 4. The surface acoustic wave device according to claim 1, wherein the interdigital transducer facing the weighting electrode is a sampling electrode. 5. The surface acoustic wave device according to claim 1, wherein the interdigital transducer facing the weighting electrode is a weighting electrode. 6. A communication device using the surface acoustic wave device according to claim 1, 2, 3, 4, or 5.