JPH0555863A - Cascade type surface acoustic wave device - Google Patents

Abstract

PURPOSE:To improve the degree of suppression of out-band components in the frequency characteristic of a cascade type surface acoustic wave device. CONSTITUTION:In the cascade type surface acoustic wave device having an input interdigital electrode 2, plural interdigital electrodes 3, 4 constituting an intermediate connection stage and an output interdigital electrode, sampling type interdigital electrodes having the same structure, satisfied with (B/Ga)<2>=1/H(omega)<2>-1 and processed by sampling weighting are used for the interdigital electrodes 3, 4. Provided that, H(omega) is a required frequency characteristic, Ga is the radiation conductance of each sampling type interdigital electrode and B is the susceptance component of each sampling type interdigital electrode.

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, and more particularly to improving the out-of-band characteristics of the surface acoustic wave device.

[0002]

2. Description of the Related Art As a technique for suppressing out-of-band components in a surface acoustic wave device, 1989 I-Y-Ultrasonics Symposium Proceedings, pp. 241, (198).
9 IEEE ULTRASONICS SYMPOS
IUM Proceedings, P.M. The technology described in 241) is known.

According to this technique, the surface acoustic wave filters are cascaded by using normal electrodes in two stages and an intermediate stage.

[0004]

However, according to the above-mentioned conventional technique, it is not always possible to sufficiently suppress the out-of-band component.

Therefore, an object of the present invention is to provide a cascade type surface acoustic wave device capable of sufficiently suppressing out-of-band components.

[0006]

[Means for Solving the Problems] To achieve the above object,
The present invention relates to an input interdigital electrode for converting an electric signal into a surface acoustic wave provided on a surface acoustic wave substrate and an output interdigital electrode for converting a surface acoustic wave converted by the input interdigital electrode into an electric signal. The pair has k (where k is an integer of 2 or more) stages, the n-th (where 0 <n <k is an integer satisfying 0) stage output comb-shaped electrode and the (n + 1) -stage input comb-shaped A cascade type surface acoustic wave device in which electrodes are electrically connected in parallel so that an electric signal converted by the output interdigital transducer is input to the input interdigital transducer, wherein the electrically connected input interdigital transducer A cascade type surface acoustic wave device, characterized in that at least one of the group of electrode-shaped electrodes and the group of output-shaped interdigital electrodes is a group of extraction-type interdigital electrodes weighted by changing density distribution of electrode fingers. ..

[0007]

According to the cascade type surface acoustic wave device of the present invention,
Extraction-type interdigital electrodes, in which at least one set of the electrically connected input interdigital electrode and output interdigital electrode has a radiation conductance outside the band smaller than that of a normal normal type electrode. It is a group of. The pass characteristic is also proportional to the ratio of susceptance and radiative conductance there. Therefore, according to the cascade type surface acoustic wave device of the present invention, the out-of-band suppression degree can be improved as compared with the related art.

[0008]

EXAMPLES Examples of the present invention will be described below.

First, one embodiment of the present invention will be described.

FIG. 1 shows the configuration of a cascade connection type surface acoustic wave device according to the first embodiment.

As shown in the figure, the cascade connection type surface acoustic wave device according to the present embodiment has a surface acoustic wave substrate 1, an input interdigital electrode 2 provided on the surface acoustic wave substrate 1, and a removal of an intermediate coupling stage. It has mold interdigital electrodes 3, 4 and output interdigital electrode 5. The input terminals 70 and 71 of the interdigital transducer electrode 60 and 61 are the output terminals of the interdigital transducer electrode 5. The input interdigital electrode 2 and the extraction type interdigital electrode 3 of the intermediate coupling stage constitute a first stage filter, and the extraction type interdigital electrode 4 of the intermediate coupling stage and the output interdigital electrode 5 are the second stage filters. Is composed of. Here, the withdrawal-shaped interdigital transducer is an electrode in which surface acoustic wave excitation parts are regularly arranged at equal pitches so that the adjacent excitation parts have different polarities (generally called normal-form electrodes). ), One or several excitation sources have been removed.

Further, the input interdigital electrode 2 and the output interdigital electrode 5 are interdigitally weighted interdigital electrodes to correct the frequency characteristic. In addition, the interleaved extraction type interdigital transducers 3 and 4 are connected to the coupling lines 80 and 81, respectively.
Are electrically connected by. Further, in order to suppress the reflected wave from the end face of the substrate, sound absorbing materials 90 and 91 are applied to the end face of the substrate.

An electric signal input from the input terminals 60 and 61 is converted into a surface acoustic wave by the input interdigital electrode 2, and is converted into an electric signal by the interdigital electrode 3 of the intermediate coupling stage. It is converted into a surface acoustic wave by the interdigital transducer 4 in the intermediate coupling stage, and finally converted into an electric signal by the output interdigital electrode 7 and output to the output terminals 70 and 71.

In the first embodiment, the center distance l ₁ between the input interdigital electrode 2 of the first stage filter and the extraction type interdigital electrode 3 of the intermediate coupling stage, and the second stage filter. The difference between the center-to-center distance l ₂ between the extraction type interdigital transducer 4 and the output interdigital transducer 5 in the intermediate coupling stage is set to 1/4 of the wavelength of the surface acoustic wave at the filter center frequency. This is to cancel the reflected wave generated in the first stage and the reflected wave generated in the second stage.

Next, FIG. 2 shows an equivalent circuit of the intermediate coupling stage.

As shown in the figure, the equivalent circuits 10 and 11 of the interdigital electrodes 2 and 3 of the intermediate coupling stage have radiative conductances 12 and 15, radiative susceptances 13 and 16, respectively.
It is represented by capacitances 14 and 17.

The value of the radiation conductance 12 is G
a0, the value of the radiation conductance 12 is Ga1, the value of the radiation susceptance 13 is Ba0, the value of the radiation susceptance 16 is Ba1, the value of the capacitance 14 is Ct0, and the value of the capacitance 14 is Ct1. When the pass characteristic is calculated in consideration of the loss, the expected value of the pass characteristic is H
(Ω) is

[0018]

[Equation 1]

It is expressed as follows. (Ω is the angular frequency) where, if the first and second stage interdigital electrodes have the same structure,
Is

[0020]

[Equation 2]

Is represented as In addition, put together the susceptance portion,

[0022]

[Equation 3]

Putting,

[0024]

[Equation 4]

Then, further,

[0026]

[Equation 5]

It is simplified as follows. When the equation (5) is modified, (B / Ga0) ² = 1 / H (ω) ² -1 ... (Equation 6) is obtained.

That is, in order to obtain a desired frequency characteristic H (ω) at the intermediate coupling stage, the radiation conductance and the susceptance may be determined so as to satisfy the equation (6). As described above, the passage characteristics in the intermediate stages 3 and 4 are characterized by being determined only by the ratio of the susceptance of the interdigital transducer and the radiation conductance.

Therefore, in the first embodiment, as the interdigital electrodes 3 and 4 of the intermediate coupling stage, the interleaved interdigital electrodes are used to perform appropriate extraction weighting. This allows
For example, the radiative conductance of the second side lobe in the frequency characteristic of the intermediate coupling stage is 1 /
A value of 4 can be easily reduced. Therefore,
From (Equation 6), it is possible to easily improve the out-of-band suppression degree of the pass characteristic of the intermediate stage by about 10 dB as compared with the normal type electrode. Since a method of designing a sampling-shaped interdigital transducer having such characteristics is well known, its description is omitted here.

As described above, the use of this embodiment makes it possible to obtain a surface acoustic wave device which has a small ripple due to reflection and has excellent characteristics with suppressed out-of-band characteristics.

The second embodiment of the present invention will be described below.

FIG. 3 shows the structure of a cascade connection type surface acoustic wave device according to the second embodiment.

In the figure, the same parts as those in the cascade connection type surface acoustic wave device (see FIG. 1) according to the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

The difference in structure between the cascade connection type surface acoustic wave device according to the second embodiment and the cascade connection type surface acoustic wave device according to the first embodiment is that the interdigitated interdigital transducers 3, 4 are provided.
The point is that the inductor 19 is connected in parallel with.

In the second embodiment, the inductance value of the inductor 19 is set to a value that cancels out the susceptance of the interdigital transducers 2 and 3 at the intermediate coupling stage at the center frequency of the cascade type surface acoustic wave device. By doing so, as is clear from (Equation 4), the pass characteristic H (ω ₀ ) at the center frequency can be brought close to 1, and the loss due to signal transmission can be reduced.

As described above, according to the second embodiment, the transmission loss due to the intermediate coupling stage can be reduced.

FIG. 4 shows the structure of a cascade connection type surface acoustic wave device according to the third embodiment.

In the figure, the same parts as those of the cascade connection type surface acoustic wave device (see FIG. 1) according to the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

The difference in structure between the cascade connection type surface acoustic wave device according to the third embodiment and the cascade connection type surface acoustic wave device according to the first embodiment is that the interdigital transducer comb-shaped electrodes 3, 4 are provided.
The capacitor 20 is connected in parallel with.

In the third embodiment, when the capacitance of the capacitor 20 is added to increase B in the formula (5), the formula (5) approximates H (ω) ² = Ga0 ² It can be expressed as / B ² ... (Equation 5).

Therefore, H (ω) can be almost determined by Ga0 of the interdigital transducers 3 and 4 in the intermediate coupling stage.

As described above, according to the third embodiment, it is possible to easily design the pass characteristic of the intermediate coupling stage.

The fourth embodiment of the present invention will be described below.

FIG. 5 shows the configuration of a cascade connection type surface acoustic wave device according to the fourth embodiment.

In the figure, 22a to 22c are input interdigital electrodes, 23a to 23b and 24a to 24b are interdigital electrodes at the intermediate coupling stage, and 25a to 25c are output interdigital electrodes. Further, 21 is an input terminal and 26 is an output terminal. The interdigitated interdigital electrodes 23a and 24a, 23b and 24
The intermediate comb-shaped electrode according to the above-described first, second or third embodiment is used for b. In addition, input interdigital electrodes 22a to 22c and output interdigital electrodes 25a to 25c.
The frequency characteristic is corrected by using a comb-shaped electrode with a cross width weighted to c.

Now, the signal input from the input terminal 21 is converted into surface acoustic waves by the input interdigital electrode groups 22a to 22c, and the interdigital electrode interdigital electrodes 23a to 23c.
It is converted into an electric signal by 3b. Further, it is converted into surface acoustic waves by the interdigital electrodes 24a to 24b of the second intermediate coupling stage, converted into electric signals by the output interdigital electrode groups 25a to 25c, and output to the output terminal 26.

At this time, for example, the input interdigital transducer 2
The surface acoustic wave propagating from 2b in the horizontal direction in the figure is converted into an electric signal by the interdigital transducers 23a and 23b of the intermediate coupling stage, so that the surface acoustic wave is transmitted in both directions of the filter stage. The directional loss is reduced and the loss of the device is suppressed.

As described above, by using this embodiment, it is possible to reduce the loss of the device.

The fifth embodiment of the present invention will be described below.

The fifth embodiment is a unidirectional electrode as shown in FIG. 6 as a take-out interdigital electrode of the second stage filter of the cascade type surface acoustic wave device according to the first to third embodiments. 27 is used. In addition, in FIG.
1 shows a unidirectional unidirectional electrode.

As shown in the figure, in the intermediary coupling step extraction type interdigital electrode according to the fifth embodiment, the sending electrode 28 and the reflecting electrode 30 are arranged so as to sandwich the meander electrode 30. Further, the extraction unit 31 of the excitation source is provided to improve the out-of-band suppression degree. An unillustrated phase shifter is installed between each electrode to radiate more surface acoustic waves in one direction to reduce bidirectional loss.

As described above, when the unidirectional electrode is used, the loss can be reduced without increasing the chip size as compared with the multi-electrode type shown in the fourth embodiment.

As described above, according to the fifth embodiment, it is effective in downsizing the device and reducing the loss.

The sixth embodiment of the present invention will be described below.

FIG. 3 shows the configuration of a cascade connection type surface acoustic wave device according to the sixth embodiment.

In the figure, the same parts as those of the cascade connection type surface acoustic wave device (see FIG. 1) according to the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

In the cascade connection type surface acoustic wave device according to the sixth embodiment, the first stage filters 2 and 3 and the second stage filters 3 and 4 are provided on different surface acoustic wave substrates 32 and 32, respectively.
It is created on 33. Then, the surface acoustic wave substrate 32,
Each of the 33 is separately die-bonded on the same stem.

As shown in the figure, in the cascade connection type surface acoustic wave device according to the sixth embodiment, one electrode of the extraction type interdigital transducer 3 at the intermediate coupling stage is grounded by the wire 34, and similarly, the intermediate type. One electrode of the extraction-type interdigital transducer 4 of the coupling stage is also grounded by the wire 35. Further, the other electrodes of the extraction-type interdigital transducers 3 and 4 of the intermediate coupling stage are connected by a wire 36.

By thus forming the first-stage and second-stage filters on different substrates, the electromagnetic coupling wave (direct wave) directly transmitted from the input terminals 60 and 61 to the output terminals 70 and 71. Can be suppressed.

As described above, according to the sixth embodiment, since the direct wave can be suppressed, there is a further effect of suppressing the out-of-band.

As shown in FIG. 8, surface acoustic wave substrates 32 and 3 in which first-stage and second-stage filters are formed, respectively.
3 may be mounted on separate stems 37 and 38, and the interdigital electrodes 3 and 4 of the intermediate coupling stage may be connected by external wiring.

In FIG. 8, input terminals 360 and 361 are provided.
A signal input from the first stage surface acoustic wave device 37 passes through, and a second stage surface acoustic wave device 39 outputs an output terminal 40.
It is output to 0 and 401. A matching inductor 38 is arranged in the intermediate coupling stage to improve loss.

In this way, by using separate devices for the first-stage filter and the second-stage filter, it is possible to further suppress the influence of the direct wave and to further suppress the out-of-band component. You can

As a seventh embodiment of the present invention, a television receiver using the cascade type surface acoustic wave device described in the first to sixth embodiments will be described below.

FIG. 9 shows the structure of the television receiver according to the seventh embodiment.

As shown, the television receiver is
It has an antenna 41, a tuner section 42, a cascade connection type surface acoustic wave device 43, a demodulation section 44, and terminals 45 and 46.

The signal input from the antenna 41 is converted into an intermediate frequency (IF) by the tuner section 42, passes through the surface acoustic wave device 43, and the demodulation section 44 outputs the video signal to the terminal 45 and the audio signal. The signal is output to the terminal 46.

As described above, since the surface acoustic wave device 43 having the large out-of-band suppression degree described in the first to sixth embodiments is used for the intermediate frequency filter, the interference from the adjacent channel is small.

As described above, the use of this embodiment makes it possible to obtain a television receiver having excellent characteristics that are resistant to interference characteristics.

As an eighth embodiment of the present invention, a satellite broadcast receiver using the cascade type surface acoustic wave device described in the first to sixth embodiments will be described below.

FIG. 9 shows the configuration of a satellite broadcast receiver according to the seventh embodiment.

As shown in the figure, the satellite broadcasting receiver according to the seventh embodiment includes a parabolic antenna 47 and an outdoor unit 4.
8 has an indoor unit 49. The indoor unit 49 includes the front end 50 and the surface acoustic wave device 5.
1, a demodulator 52, and terminals 53 and 54.

The signal input from the parabolic antenna 47 is converted into the first intermediate frequency by the outdoor unit 48 and sent to the indoor unit 49. In the indoor unit 49, it is converted to the second intermediate frequency by the front end 50, passes through the surface acoustic wave device 51, and the demodulation unit 52 outputs the video signal to the terminal 53 and the audio signal to the terminal 54.

As described above, since the surface acoustic wave device 51 having the large out-of-band suppression degree described in the first to sixth embodiments is used for the intermediate frequency filter, the interference from the adjacent channel is small.

As described above, according to the seventh embodiment, it is possible to obtain the satellite broadcast receiver having excellent characteristics that are strong against interference characteristics.

Although the application examples of the surface acoustic wave device described in the first to sixth embodiments as an intermediate frequency filter have been described above, the first to sixth embodiments will be described. The surface acoustic wave device described above can also be applied to an oscillator, a correlator used for a receiver for receiving communication by a spread spectrum communication system, an RF filter, and the like.

According to the embodiment described above, a surface acoustic wave device having a large degree of out-of-band suppression can be obtained, so that the performance of the surface acoustic wave device and the interference characteristic of the communication device can be improved.

[0078]

As described above, according to the present invention, it is possible to provide a cascade connection type surface acoustic wave device capable of sufficiently suppressing an out-of-band component.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a configuration of a cascade connection type surface acoustic wave device according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing an equivalent circuit of an intermediate coupling stage of the cascade connection type surface acoustic wave device according to the first embodiment of the present invention.

FIG. 3 is an explanatory diagram showing a configuration of a cascade connection type surface acoustic wave device according to a second embodiment of the present invention.

FIG. 4 is an explanatory diagram showing a configuration of a cascade connection type surface acoustic wave device according to a third embodiment of the present invention.

FIG. 5 is an explanatory diagram showing a configuration of a cascade connection type surface acoustic wave device according to a fourth embodiment of the present invention.

FIG. 6 is an explanatory diagram showing a partial configuration of an intermediate coupling stage of a cascade connection type surface acoustic wave device according to a fifth embodiment of the present invention.

FIG. 7 is an explanatory diagram showing a configuration of a cascade connection type surface acoustic wave device according to a sixth embodiment of the present invention.

FIG. 8 is an explanatory view showing another configuration of the cascade connection type surface acoustic wave device according to the sixth embodiment of the present invention.

FIG. 9 is a block diagram showing the structure of a television receiver according to a seventh embodiment of the present invention.

FIG. 10 is a block diagram showing a configuration of a satellite broadcast receiver according to an eighth embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 32, 33 Surface acoustic wave substrate, 3, 4 Extraction type interdigital electrode, 23, 24 Extraction type interdigital electrode group, 27 Unidirectional electrode, 43, 44 Surface acoustic wave device

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shozuna Yubara, 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa, Ltd. Hitachi Media Co., Ltd. Media Research Laboratory

Claims (12)

[Claims] 1. An input interdigital transducer for converting an electric signal into a surface acoustic wave provided on a surface acoustic wave substrate and an output interdigital transducer for converting the surface acoustic wave converted by the input interdigital transducer into an electric signal. K pairs (where k is an integer of 2 or more)
The output interdigital electrode of the pair of output interdigital electrodes of the nth stage (where n is an integer satisfying 0 <n <k) and the input interdigital electrode of the (n + 1) th stage have electric signals converted by the output interdigital electrode. A cascade type surface acoustic wave device that is electrically connected in parallel so as to be input to an input interdigital transducer, wherein at least one of a set of the input interdigital electrode and the output interdigital electrode that are electrically connected. The cascade type surface acoustic wave device, wherein the group is a group of extraction type interdigital transducers weighted by changing the density distribution of the electrode fingers. 2. The cascade type surface acoustic wave device according to claim 1, wherein at least one of the interdigital electrodes other than the set of the extraction interdigital electrodes is cross-width weighted by the apodization method. A cascade type surface acoustic wave device characterized by being an electrode. 3. The cascade type surface acoustic wave device according to claim 1, wherein the input interdigital electrode and the output interdigital electrode in the set of the interleaved interdigital electrodes are interleaved interdigital electrodes having the same structure. A cascade type surface acoustic wave device characterized by being present. 4. The cascaded surface acoustic wave device according to claim 1, wherein at least two pairs of the input interdigital electrode and the output interdigital electrode in the k stages have surface acoustic wave propagation paths. The distance between the centers of the input interdigital transducer and the output interdigital transducer in each pair is the same and is 1/4 of the surface acoustic wave wavelength at the central frequency of the cascade type surface acoustic wave device. Cascade type surface acoustic wave device characterized by: 5. The cascaded surface acoustic wave device according to claim 1, wherein at least one pair of the input interdigital electrode and the output interdigital electrode among the pair of the input interdigital electrode and the output interdigital electrode in the k stages. A cascade type surface acoustic wave device, wherein an inductor is electrically connected in parallel to the strip electrodes. 6. The cascaded surface acoustic wave device according to claim 1, wherein at least one pair of the input interdigital electrode and the output interdigital electrode among the pair of the input interdigital electrode and the output interdigital electrode of the k stages. A cascade type surface acoustic wave device characterized in that a capacitor is electrically connected in parallel to the strip electrodes. 7. The cascaded surface acoustic wave device according to claim 1, wherein at least one pair of the input interdigital electrode and the output interdigital electrode in the k stages is one input interdigital electrode. And a surface acoustic wave propagating bidirectionally from the input interdigital electrode, which is a pair including a plurality of output interdigital electrodes electrically connected in parallel. Cascade type surface acoustic wave device. 8. The cascade type surface acoustic wave device according to claim 1, wherein at least one of the sets of extraction-type interdigital transducers.
A cascade type surface acoustic wave device, wherein at least one of the interleaved electrode and the interleaved electrode of the two sets is a unidirectional interdigital electrode. 9. The cascaded surface acoustic wave device according to claim 1, wherein a pair of the input interdigital electrode and the output interdigital electrode in the k stages are a plurality of surface acoustic wave substrates bonded on the same stem. A cascade type surface acoustic wave device, characterized in that one or a plurality of pairs are provided above. 10. The cascaded surface acoustic wave device according to claim 1, wherein the k-step input interdigital electrode and output interdigital electrode pairs are a plurality of surface-bonded surfaces bonded to different stems. A cascade type surface acoustic wave device, characterized in that it is provided on the wave substrate in a divided manner for every one or more pairs. 11. An intermediate frequency filter as claimed in claim 1,
A communication device, particularly a television receiver or a satellite broadcast receiver, comprising the cascade type surface acoustic wave device according to 3, 4, 5, 6, 7, 8, 9 or 10. 12. An input interdigital transducer provided on a surface acoustic wave substrate for converting an electric signal into a surface acoustic wave and an output interdigital transducer converting the surface acoustic wave converted by the input interdigital transducer into an electric signal. Has k (where k is an integer of 2 or more) stages, and the n-th (the integer satisfying 0 <n <k) output comb-shaped electrodes and the (n + 1) -th stage input blind A method of designing a cascaded surface acoustic wave device, wherein the striped electrodes are electrically connected in parallel so that an electric signal converted by the output interleaved electrode is input to the input interleaved electrode. The set of the input interleaved electrodes and the output interleaved electrodes are set as the set of interleaved interleaved electrodes of the same structure, the weight of each interleaved interleaved electrode is set to the desired transfer characteristic H (ω), and The radiant conductance of the electrode of Ga A method of designing a cascade type surface acoustic wave device, characterized in that the relationship of (Bt / Ga) ² = 1 / H (ω) ² −1 is satisfied when the septum is Bt.