JPH08139564A - Surface acoustic wave filtering device - Google Patents

Abstract

PURPOSE: To further improve the frequency characteristics of a surface acoustic wave filter device. CONSTITUTION: The negative electrodes of the transmission side converters 13 and 15 of first and second filtering stages 11 and 12 are connected to a ground-connected common bonding pad 29 and the negative electrodes of the reception side converters 14 and 16 of the first and second filtering stages 11 and 12 are connected to the bonding pad 31 positioned at the diagonal position of a package 27 holding a piezoelectric substrate 10 there between to the bonding pad 29. By performing connection and arrangement in such a manner, the electric characteristics of the entire package 27 are balanced, appropriate balance performance is secured and out-of-band attenuation characteristics are substantially improved.

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 filter device, and more particularly to a surface acoustic wave filter device with improved out-of-band attenuation characteristics.

[0002]

2. Description of the Related Art A surface acoustic wave filter device for extracting a signal in a specific frequency band by forming an interdigital transmitter and receiver on a piezoelectric substrate has been put into practical use. In such a surface acoustic wave filter device, unidirectional transducers are used as transmitter and receiver converters in order to minimize insertion loss. The surface acoustic wave filter device using the unidirectional transducer has a relatively small insertion loss and is highly useful because it can appropriately limit the phase characteristic and the frequency characteristic.

In order to put the surface acoustic wave filter device into practical use, it is necessary to obtain good out-of-band attenuation characteristics. As a method for improving the out-of-band attenuation characteristic, it is considered that several filter stages are formed on the piezoelectric substrate and these filter stages are connected in cascade. For example, when two surface acoustic wave filter devices are configured by connecting two filter stages in cascade, the obtained out-of-band attenuation characteristic is a characteristic obtained by multiplying the out-of-band characteristic of the two filter stages. The out-of-band attenuation characteristic can be significantly improved. An example of such a surface acoustic wave filter device is described in Japanese Patent Application No. 5-41220 proposed by the present applicant. In this surface acoustic wave filter device, two filter stages consisting of a transmitter-side converter and a receiver-side converter are formed in parallel with each other on a single piezoelectric substrate, and the positive side of the receiver-side converter of the first filter stage is formed. The electrode and the positive electrode of the transmitter transducer of the second filter stage are interconnected by a conductor pattern formed on the substrate.

[0004]

The two-stage cascade connection type surface acoustic wave filter device described above has an advantage that the out-of-band attenuation characteristic can be greatly improved. However, when the surface acoustic wave filter device is mounted on a printed circuit board and is actually used, the out-of-band attenuation characteristics, particularly the attenuation characteristics on the higher frequency side than the center frequency, have a problem.

An object of the present invention is to provide a surface acoustic wave filter device which can achieve the original filter characteristics of a two-stage cascade type surface acoustic wave filter device and has excellent filter characteristics.

[0006]

A surface acoustic wave filter device according to the present invention includes a piezoelectric substrate, an interdigital transmitter and an interdigital receiver, which are formed on the piezoelectric substrate. The package includes first and second filter stages each having a converter, a substrate housing space for housing the piezoelectric substrate, and a substantially rectangular package body, and a cap member made of a conductive material. A main body, a signal input terminal formed on a first side wall portion parallel to a central axis of a surface acoustic wave propagation direction, a signal output terminal formed on a second side wall portion facing the first side wall portion; First and second ground terminals respectively formed at both ends of the first side wall portion or in the vicinity thereof, and third and fourth ground terminals respectively formed at both ends of the second side wall portion or in the vicinity thereof.
Ground terminals, fifth and sixth ground terminals formed respectively at substantially the centers of the surface acoustic waves in the first and second side wall propagation directions, and a signal input pad formed on the first pad formation surface. And the first ground pad, the signal output pad and the second ground pad formed on the second pad formation surface, and the bottom surface of the substrate housing space, and a part of the first and second side wall portions is formed. First extending through to the outer peripheral surface
Of the conductor layer and the first or second side wall portion to the outer peripheral surface, the signal input terminal, the signal output terminal and the second
A second conductor layer connecting the third and third ground terminals to the signal input pad, the signal output pad, and the first and second ground pads, respectively, and a third conductor layer formed on the upper end surface of the package body, The positive electrode of the transmitter converter of the first filter stage is connected to the signal input pad, and the positive electrode of the receiver converter of the second filter stage is connected to the signal output pad. The negative electrode of the transmitting side converter of the filter stage and the negative electrode of the transmitting side converter of the second filter stage are connected to the second ground pad, and the negative electrode of the receiving side converter of the first filter stage and The negative electrode of the receiver converter of the second filter stage is connected to the first ground pad, and the positive electrode of the receiver converter of the first filter stage is connected to the transmitter electrode of the second filter stage. The positive electrode is interconnected, and the first and The third ground terminals are respectively arranged on the upstream side in the propagation direction of the surface acoustic wave with respect to the second and fourth ground terminals, and the signal input terminals are the first ground terminal and the fifth ground terminal. And the signal output terminal is disposed between the fourth ground terminal and the sixth ground terminal, and the first, second, third, fourth, fifth, and sixth The ground terminal is directly connected to the first conductor layer and the third conductor layer.

In the surface acoustic wave filter device according to the present invention, in order to balance the potentials of the entire package by appropriately setting the connection relationship of the converters and the arrangement position of the terminals, the transmitter side converter of the first filter stage. The positive electrode of the second filter stage is connected to the signal input pad, the positive electrode of the receiving converter of the second filter stage is connected to the signal output pad, and the negative electrode of the transmitting side converter of the first filter stage and the second filter are connected. The negative electrode of the transmitter side converter of the first stage is connected to the second ground pad, and the negative electrode of the receiver side converter of the first filter stage and the negative electrode of the receiver side converter of the second filter stage are connected to the first electrode. Connect to the ground pad of. By connecting and arranging in this way, the potentials of the entire package are balanced and proper balance performance is ensured, and the out-of-band attenuation characteristics can be greatly improved.

Further, in the surface acoustic wave filter device according to the present invention, the ground terminals connected to the first and third conductor layers are provided at substantially the center of the first and second side wall portions, and these ground terminals are connected to each other. It is connected to the ground pad. By providing the ground pad in this manner, there is electrical isolation between the transmitter and receiver converters of the first and second filter stages, thus significantly reducing electromagnetic coupling in the package and out of band. The damping characteristic can be improved significantly.

According to another embodiment of the surface acoustic wave filter device of the present invention, the side wall portions are formed on the third and fourth side wall portions located between the first side wall portion and the second side wall portion. The ground terminals are formed in a direction orthogonal to the propagation direction of the surface acoustic wave, and these ground terminals are directly connected to the first and third conductor layers.

By providing the ground pad in this manner, the first filter stage and the second filter stage are electrically separated from each other, so that the electromagnetic coupling in the package is further greatly reduced and the out-of-band attenuation characteristic is further improved. It can be further improved.

[0011]

Embodiments of a surface acoustic wave filter device according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing a filter circuit including a surface acoustic wave filter device according to the present invention. A signal input terminal 1 to which a signal to be filtered is input is connected to the first inductance 2 and the surface acoustic wave filter device 3. The surface acoustic wave filter device 3 is a two-stage cascade connection type filter device having a first filter stage 3a and a second filter stage 3b. The input signal is filtered by the first filter stage 3a, and the filtered signal is further filtered. It is filtered in the second filter stage 3b. A second inductance 4 for canceling a capacitive component is connected between the first filter stage 3a and the second filter stage 3b. The third inductance 5 is connected to the output section of the surface acoustic wave filter device 3 and the signal output terminal 6 is connected, and the filtered signal is taken out from this signal output terminal.

FIG. 2 is a diagrammatic plan view showing the configuration of an example of the surface acoustic wave filter device shown in FIG. A rectangular crystal substrate 10 is used as the piezoelectric substrate, and two first and second filter stages 11 and 12 are formed on the crystal substrate 10. The first filter stage 11 comprises a first transmitter side converter 13 and a first receiver side converter 14, and the second filter stage 12 comprises a first transmitter side converter 15 and a second receiver side converter 16. Equipped. These four converters 13 to 16 are all unidirectional converters having the same structure. First transmitting side converter 1
3 is a positive electrode 17 and a negative electrode 18, and these positive electrodes 17
And a floating electrode 19 arranged between the electrode fingers of the negative electrode 18.

The widths of the electrode fingers of the positive electrode 17, the negative electrode 18, and the floating electrode 19 are set to λ / 12. Here, λ is a fundamental surface acoustic wave. Positive electrode 17 and negative electrode 18
Each electrode finger of the positive electrode 17 is formed with a pitch of λ.
The center-to-center distance between the electrode finger of (1) and the electrode finger of the adjacent negative electrode 18 is set to λ / 2. In addition, the electrode finger of the floating electrode 19 is, for example, λ / 1 on the upstream side in the propagation direction of the surface acoustic wave from the intermediate position between the electrode fingers of the adjacent positive electrode 17 and negative electrode 18.
The unidirectionality is enhanced by arranging so as to deviate by two. Similarly, the first receiving-side converter 14 also has a positive electrode 20, a negative electrode 21, and a floating electrode arranged between the electrode fingers of the positive electrode 20 and the negative electrode 21. Further, the second transmitter-side converter 15 similarly has the positive electrode 22, the negative electrode 23, and the positive electrode 2 as well.
2 and a floating electrode disposed between the electrode fingers of the negative electrode 23. Further, the second receiving side converter 16 also has a positive electrode 24, a negative electrode 25, and a floating electrode arranged between the electrode fingers of the positive electrode 24 and the negative electrode 25. The number of electrodes of each converter is set to the same number of logs, and the first filter stage 11
And the second filter stage 12 are electrically balanced so that the input side and the output side of the second filter stage 12 are equal to each other. However, the number of pairs of electrodes may be changed according to the characteristics.

The converters 13 to 16 comprise a first filter stage 11
Are arranged so that the propagation direction of the surface acoustic wave and the propagation direction of the second filter stage 12 are parallel and in the same direction. The first filter stage 11 and the second filter stage 12 are arranged in parallel in the direction orthogonal to the surface acoustic wave propagation direction. Further, in the first transmitter converter 13, the bus bar 17a of the positive electrode 17 is arranged so as to directly face one edge of the crystal substrate 10, and in the first receiver converter 14, the positive electrode 20 is arranged. And the arrangement of the negative electrode 21 is reversed. In the second transmitter converter 15, the bus bar of the negative electrode 23 directly faces the opposite edge of the crystal substrate 10, and in the second receiver converter 16, the positive electrode 24 and the negative electrode 25. Reverse the placement of. Converters 13-1
6 positive electrodes 17, 20, 23 and 24 and negative electrode 1
By arranging 8, 21, 22, and 25 in this way, the signal input electrode of the transmitter side converter 13 of the first filter stage 11 and the signal output electrode of the receiver side converter 16 of the second filter stage 12 are located farthest. Since they can be separated from each other, electromagnetic coupling between input and output can be effectively prevented.

In this example, a sound absorbing member 26 (shown by a broken line in the figure) is applied between the first filter stage 11 and the second filter stage 12 on the quartz substrate 10, and the elastic surface generated in one filter stage is applied. Prevents the wave from entering the transducer of the other filter stage. By applying the sound absorbing material in this way,
It is possible to prevent the generation of noise and improve the attenuation characteristic.

The crystal substrate 10 is housed and supported in a package 27 made of an electrically insulating material such as alumina. The package 27 has a plurality of bonding pads, the electrodes of each converter are connected to these bonding pads, and the electrodes are interconnected or connected to a printed circuit board via the bonding pads. In this example, the connection between each electrode and the bonding pad is made via a bonding wire.

The positive electrode 17 of the first transmitter 13 is connected to the bonding pad 28 by a bonding wire. One end of the bonding wire is coupled to the intermediate position of the bus bar 17a of the positive electrode 17 in the surface acoustic wave propagation direction.
Further, the negative electrode 18 is connected to the bonding pad 29 arranged at the upper corner of the package 27 and connected to the ground terminal via a bonding wire.
In this case as well, one end of the bonding wire is similarly coupled to the intermediate position of the bus bar 18a of the negative electrode 18.

The positive electrode 20 of the first receiving side converter 14 is connected to the bonding pad 30 by a bonding wire, and the negative electrode 21 thereof is arranged at the lower corner of the package 27 and connected to the ground terminal. The bonding pad 31 is connected to the bonding pad 31 via a bonding wire. In this case as well, one end of the bonding wire is similarly connected to the positive electrode 2
It connects to the middle position of the bus bar of 0 and the negative electrode 21.

The positive electrode 23 of the second transmitting side converter 15 is connected to the bonding pad 30 by a bonding wire, and the negative electrode 22 thereof is connected to the bonding pad 29. In this case as well, one end of the bonding wire is similarly coupled to the intermediate position of the bus bar between the positive electrode 23 and the negative electrode 22.

The positive electrode 24 of the second receiving side converter 16 is connected to the bonding pad 32 by a bonding wire, and the negative electrode 25 thereof is connected to the bonding pad 31 via the bonding wire. In this case as well, one end of the bonding wire is similarly coupled to the intermediate position of the bus bar between the positive electrode 24 and the negative electrode 25. Further, in this example, the bonding pads 33 and 34 arranged at the corners of the package body and connected to the ground terminal are provided.

As described above, in this example, the negative electrodes of the transmitter side converters 13 and 15 of the first and second filter stages 11 and 12 are both connected to the bonding pad 29 connected to the ground terminal, and The first and second filter stages 11 and 12 are connected to a bonding pad 31 connected to a ground terminal at a diagonal position of the package 27 with the piezoelectric substrate 10 sandwiched between the bonding pad 29 and the bonding pad 31.
The negative electrodes of the receiving side converters 13 and 15 are connected together.
By connecting and arranging in this way, the potential of the entire package 27 can be balanced, proper balance performance can be ensured, and the out-of-band attenuation characteristic can be greatly improved.

Further, in this example, the edge 10 of the piezoelectric substrate 10 is
Bonding pads 35 and 36 connected to the ground terminal are provided along a and 10b. By providing the bonding pads 35 and 36 in this way, there is an electrical isolation between the transmitter converters 13 and 15 and the receiver converters 14 and 16 of the first and second filter stages 11 and 12, and thus The electromagnetic coupling in the package 27 can be greatly reduced, and the out-of-band attenuation characteristics can be greatly improved.

3 to 4 show the structure of an example of the surface acoustic wave filter device according to the present invention, FIG. 3 is an exploded perspective view, and FIG. 4 is a perspective view showing a form after assembly. The Kovar ring 40 is attached to the upper end surface of the package 27, and the conductive cap 41 is welded to the Kovar ring 40. As shown in FIG. 3, the package 2
7 is a three-layer structure, including a bottom layer 42 and a square-shaped intermediate layer 4
3 and a square-shaped uppermost layer 44. In addition, in FIG. 3, the conductor layer is shown by a region indicated by a black dot. Bottom layer 42
The first conductor layer 45 is formed on the first conductor layer 45 except the portions where the signal input terminal and the signal output terminal are formed and the portion in the vicinity thereof.

The intermediate layer 43 constitutes a pad forming portion, and second conductor layers 46a to 46g (only on one side portion) for connecting each bonding pad to a signal input terminal, a signal output terminal and a ground terminal. Numbered). A third conductor layer 47 is formed on the uppermost layer 44 over the entire upper surface thereof. These bottom layer 42 and intermediate layer 43
And the uppermost layer 44 is fired to be an integrated body.

As shown in FIG. 4, a signal input terminal 48, a signal output terminal 49, and ground terminals 50, 51 and 52 (only three ground terminals are shown in this example) are formed on the outer wall of the package 27. Then, the package ground terminals 53, 54 and 55 are formed. The package ground terminals 54 and 55 can also be used as ground terminals. The signal input terminal 48 and the signal output terminal 49 are connected to the second conductor layers 46f and 46b (FIG. 3), and the ground terminals 50 to 52 and the package ground terminals 53 and 54.
And 55 are second conductor layers 46g, 46d, 46a, 46
e and 46c and the first conductor layer 45 (FIG. 3). Therefore, the first conductor layer 45 (FIG. 3) and the cap 41 (FIG. 3) supporting the crystal substrate 10 (FIG. 2).
Are interconnected by terminals 50, 51, 52, 53, 54 and 55 and a plurality of conductor layers 45, 46a, 46c, 46e, 46g and 47 (FIG. 3).

FIG. 5 is a diagram showing frequency characteristics of the surface acoustic wave filter device according to the present invention. In FIG. 5, the horizontal axis represents frequency and the vertical axis represents attenuation. In this example, the center frequency is set to 250 MHz. As shown in FIG. 5, according to the surface acoustic wave filter device of the present invention, good out-of-band attenuation characteristics can be obtained.

The present invention is not limited to the above-mentioned embodiments, but various modifications and variations are possible. For example, although a quartz substrate is used as the piezoelectric substrate in the above-described embodiments, it can be applied to a substrate material such as Li ₂ B ₄ O ₇ having an electromechanical coupling coefficient as small as that of quartz.

The present invention can also be applied to a filter device using unidirectional converters of all forms as converters. For example, unidirectional converters having electrode fingers having a width of λ / 8 and It can also be applied when using a unidirectional converter using an open floating electrode.

[0029]

As described above, according to the surface acoustic wave filter device of the present invention, the negative electrodes of the transmitter-side converters of the first and second filter stages are connected to a common bonding pad and the bonding pad is used. With respect to the package, by arranging so that the negative electrodes of the receiving side converters of the first and second filter stages are connected to the bonding pads at diagonal positions of the package body with the piezoelectric substrate sandwiched therebetween, The entire potential is balanced and proper balance performance is secured, and the out-of-band attenuation characteristics can be greatly improved.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a filter circuit including a surface acoustic wave filter device according to the present invention.

FIG. 2 is a diagrammatic plan view showing the configuration of an example of the surface acoustic wave filter device shown in FIG.

FIG. 3 is an exploded perspective view of a surface acoustic wave filter device according to the present invention.

FIG. 4 is a perspective view showing an assembled state of the surface acoustic wave filter device according to the present invention.

FIG. 5 is a diagram showing frequency characteristics of the surface acoustic wave filter device according to the present invention.

[Explanation of symbols]

1 input terminal, 2, 4, 5 inductance, 3 surface acoustic wave filter device, 3a, 11 first filter stage, 3
b, 12 second filter stage, 6 output terminal, 10 quartz substrate, 13, 15 transmitter side converter, 14, 16 receiver side converter, 17, 20, 23, 24 positive electrode, 18, 2
1, 22, 25 Negative electrode, 17a, 18a Bus bar, 1
9 floating electrode, 26 sound absorbing member, 27 package, 2
8, 29, 30, 31, 32, 33, 34, 35, 36
Bonding pad, 40 Kovar ring, 41
Cap, 42 bottom layer, 43 middle layer, 44 top layer, 45, 46a, 46b, 46c, 46d, 46e,
46f, 46g, 47 conductor layers, 48 signal input terminals,
49 signal output terminal, 50, 51, 52 ground terminal, 53, 54, 55 package ground terminal

Claims (2)

[Claims] 1. A first and a second filter stage formed on the piezoelectric substrate and having an interdigital transmission side converter and an interdigital type reception side converter, respectively. A package housing having a substrate housing space for housing the piezoelectric substrate, the package body having a substantially rectangular shape, and a cap member made of a conductive material, wherein the package body is parallel to the central axis of the surface acoustic wave propagation direction. A signal input terminal formed on one side wall portion, a signal output terminal formed on a second side wall portion facing the first side wall portion, and a first output terminal formed on both ends of the first side wall portion or in the vicinity thereof. And a second ground terminal, third and fourth ground terminals respectively formed at both ends of the second side wall portion or in the vicinity thereof, and in the propagation direction of the surface acoustic wave of the first and second side wall portions. Almost in the center Formed 5th
A sixth ground terminal, a signal input pad and a first ground pad formed on the first pad formation surface, and a second ground terminal.
A signal output pad and a second ground pad formed on the pad forming surface of the substrate, and a bottom surface of the board housing space,
A part of the first conductor layer extends to the outer peripheral surface via the first and second side wall portions, and a part of the first conductor layer extends to the outer peripheral surface via the first or second side wall portion. A second conductor layer that connects the output terminal and the second and third ground terminals to the signal input pad, the signal output pad, and the first and second ground pads, respectively, and a third conductor layer formed on the upper end surface of the package body. And the positive electrode of the transmitter side converter of the first filter stage is connected to the signal input pad, and the positive electrode of the receiver side converter of the second filter stage is connected to the signal output pad. Connecting the negative electrode of the transmitting side converter of the first filter stage and the negative electrode of the transmitting side converter of the second filter stage to the second ground pad, and converting the receiving side conversion of the first filter stage. -Side conversion of negative electrode of filter and second filter stage Connecting the negative electrode of the converter to the first ground pad and interconnecting the positive electrode of the receiving converter of the first filter stage with the positive electrode of the transmitting converter of the second filter stage, The first and third ground terminals are respectively arranged on the upstream side in the propagation direction of the surface acoustic wave with respect to the second and fourth ground terminals, and the signal input terminal is connected to the first ground terminal and the fifth ground terminal. And the signal output terminal is arranged between the fourth ground terminal and the sixth ground terminal, and the first, second, third, fourth and fifth terminals are arranged between the fourth ground terminal and the sixth ground terminal. And a sixth ground terminal, which are directly connected to the first conductor layer and the third conductor layer, respectively. 2. The third and fourth side wall portions located between the first side wall portion and the second side wall portion are respectively grounded in a direction orthogonal to a propagation direction of surface acoustic waves of the side wall portions. The surface acoustic wave filter device according to claim 1, wherein terminals are formed and the ground terminals are directly connected to the first and third conductor layers.