JP3890668B2 - Surface acoustic wave filter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a surface acoustic wave filter, and more particularly to a ladder-type surface acoustic wave filter (hereinafter referred to as a ladder-type SAW filter) with improved attenuation on the high frequency side in a pass band.
[0002]
[Prior art]
A so-called ladder-type SAW filter in which a plurality of one-terminal-pair surface acoustic wave resonators (hereinafter referred to as SAW resonators) are connected in a ladder shape to an RF stage of a cellular phone or the like is used. The ladder-type SAW filter is characterized by the fact that it can realize filtering characteristics with low loss and steep attenuation gradient in addition to being smaller and lighter than dielectric filters, and has recently been widely used as an RF filter for mobile phones and the like. Has been.
[0003]
A ladder-type SAW filter is a filter in which SAW resonators are cascaded in a ladder shape. Since the ladder-type SAW filter is composed of high-Q SAW resonators, a filter with a low loss and a steep attenuation gradient can be obtained. FIG. 6 is a plan view of a conventional ladder-type SAW filter, and FIG. 7 is an electrical equivalent circuit diagram thereof. The SAW resonator formation method will be described by taking, as an example, a SAW resonator R3 (symbol Ri representing each SAW resonator at the left end of the piezoelectric substrate) disposed at the upper end of the piezoelectric substrate 20 shown in FIG. The IDT 21 and the reflectors 22a and 22b are arranged on both sides of the main surface along the propagation direction of the surface wave. The IDT 21 is composed of a pair of comb electrodes each having a plurality of electrode fingers interleaved with each other. One comb electrode constituting the IDT 21 is an input terminal, and the other comb electrode is an output terminal. The reflectors 22a and 22b arranged on both sides of the IDT 21 reflect the surface wave excited by the IDT 21 in the center direction of each IDT, thereby confining the vibration energy between the reflectors 22a and 22b and thereby forming a resonator. Constitute.
[0004]
A plurality of SAW resonators formed as described above are formed on the same piezoelectric substrate 20 with gaps that do not interfere with each other (six SAW resonators R1 to R6 in the example of FIG. 6). A ladder-type SAW filter element is formed by connecting each SAW resonator and between the SAW resonator and the ground pad. The ladder-type SAW filter element is accommodated in a ceramic package 23 having a recess in the center, and the bottom surface of the element and the package 23 are fixed with an adhesive or the like. The input / output electrode pads 24 and 25 of the ladder-type SAW filter element and the input / output electrodes 26 and 27 of the package are connected by bonding wires, respectively. Further, the ladder-type SAW filter element is completed by connecting the grounding electrode pads 28, 29 and 30 of the ladder-type SAW filter element and the ground electrode 31 of the package with bonding wires.
[0005]
As shown in FIG. 7, the ladder SAW filter has an electrical equivalent circuit in which the first SAW resonators R1, R3, and R5 are arranged in series arms, and the second SAW resonators R2, R4, and R6 are arranged in parallel arms. To configure. As is well known, a bandpass filter is configured by making the anti-resonance frequency of the SAW resonator of the parallel arm substantially coincide with the resonance frequency of the SAW resonator of the series arm. The pass band is between the resonance frequency of the parallel arm and the anti-resonance frequency of the series arm, and a ladder-type SAW filter having attenuation poles at the resonance frequency and the anti-resonance frequency can be configured. Note that it is known that the attenuation gradient of the filter, the amount of blocking attenuation, and the like greatly depend on the number of SAW resonators used in the filter configuration.
[0006]
[Problems to be solved by the invention]
However, when the ladder-type SAW filter is used as an RF filter for a mobile phone or the like, the transmission characteristic of a normal ladder-type SAW filter monotonously decreases with increasing frequency as shown in FIG. At this time, the series arms are the same SAW resonator, the IDT logarithm is 100 pairs, and there are 100 reflectors. The parallel arm SAW resonators R2 and R4 have 100 IDT pairs and 100 reflectors, respectively, R6 has 50 IDT pairs and 100 reflectors each. The center frequency is 946 MHz, the bandwidth is about 40 MHz, and the input / output impedance is 50Ω. As described above, the conventional ladder-type SAW filter has a low loss and a steep attenuation gradient in the vicinity of the pass band, but on the high frequency side of the pass band, it is twice the local oscillation frequency generated by the mixer. There is a drawback that it is not possible to secure an attenuation that suppresses three times the harmonics.
In addition, when grounding is insufficient due to the miniaturization of the radio, the conventional ladder-type SAW filter has a disadvantage that the attenuation characteristic on the high frequency side is deteriorated. The present invention has been made to solve the above-described drawbacks, and an object of the present invention is to provide a ladder-type SAW filter having a high blocking attenuation on the high frequency side of the pass band.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, a surface acoustic wave filter according to a first aspect of the present invention includes a surface acoustic wave element formed on a piezoelectric substrate and a package that accommodates the surface acoustic wave element. In the surface acoustic wave filter, the surface acoustic wave element includes an IDT and at least two SAW resonators having reflectors disposed on both sides of the IDT, and includes an input electrode pad, an output electrode pad, A ground electrode pad, and the package includes an input pad, an output pad, a first ground pad adjacent to the input pad, and a second ground pad adjacent to the output pad, At least one of the grounding electrode pads is connected to both the first grounding pad and the second grounding pad by grounding wire bonding, and the grounding bonding wire includes: An input bonding wire connected to the input electrode pad of the DT and the input pad of the package, and an output bonding wire connected to the output electrode pad of the IDT and the output pad of the package It is a surface acoustic wave filter characterized by these.
According to a second aspect of the present invention, there is provided a surface acoustic wave filter including a surface acoustic wave element formed on a piezoelectric substrate and a package that accommodates the surface acoustic wave element. A ladder-type surface acoustic wave filter configured by forming a terminal-pair surface acoustic wave resonator and connecting to a ladder type, comprising an input electrode pad, an output electrode pad, and a ground electrode pad, and the package includes an input pad And an output pad, a first ground pad adjacent to the input pad, and a second ground pad adjacent to the output pad, wherein at least one of the ground electrode pads is the first ground pad. The grounding wire is connected to both the pad and the second grounding pad, and the grounding bonding wire is connected to the input electrode pad of the IDT and the input pad of the package. A bonding wire connecting input, a surface acoustic wave filter being characterized in that disposed between the output bonding wire connected to said output pad of IDT of said output electrode pad and package.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.
FIG. 1 is a plan view showing an embodiment of a ladder-type SAW filter according to the present invention, and FIG. 2 is an electrical equivalent circuit thereof.
[0009]
SAW resonators Ri (i = 1 to 6 in the embodiment of FIG. 1) are arranged on the main surface of the piezoelectric substrate 1 with a predetermined gap so as not to interfere with each other by a desired number. Are connected by lead electrodes L to form a ladder-type SAW filter element, and the element is fixed to the recessed portion provided in the center of the ceramic package 4 using an adhesive or the like, similar to the conventional ladder-type filter. . The feature of the present invention resides in the connection using bonding wires between the pads of the ladder type SAW filter element and the input / output electrodes and the ground electrode of the package 4.
[0010]
Referring to FIG. 1, the bonding wire 5 electrically connects the input electrode pad 6 provided on the SAW resonator R1 on the piezoelectric substrate and the input pad 7 of the package 4 in FIG. The bonding wire 8 electrically connects the output electrode pad 9 provided on the SAW resonator R5 on the piezoelectric substrate and the output pad 10 of the package 4. Further, there are two ground electrode pads 11 provided on the parallel arm SAW resonator R4, two ground electrode pads 12 provided on the parallel arm SAW resonator R6, and two ground pads 13a and 13c of the package 4. Connect the bonding wire. The ground electrode pad 14 of the parallel arm SAW resonator R2 and the ground pad 13b of the package 4 are connected by a bonding wire 15a.
[0011]
As in this embodiment, the SAW resonators R4 and R6 have two ground bonding wires, that is, 16a, 16b and 17a, 17b are electromagnetically leaked between the input bonding wire 5 and the output bonding wire 10. It has become clear from various experimental results that the level of the direct wave can be greatly reduced by using a wiring structure that shields the wire, and that a large shielding effect can be obtained.
[0012]
FIG. 3 shows the amplitude transmission characteristic A of the ladder-type SAW filter manufactured based on FIG. 1 which is an example of the bonding wire wiring structure according to the present invention, and the conventional bonding wire wiring structure previously shown in FIG. FIG. 7 is a comparison of amplitude transmission characteristics C of a ladder-type SAW filter created based on FIG. 6. The design conditions of the filter based on FIG. 1 are the same as those of FIG. 8, and only the bonding wires are wired. As can be seen from the figure, the transmission characteristics of the conventional bonding wire wiring structure show that the amount of blocking attenuation decreases monotonously as the frequency increases on the high frequency side. It can be seen that the blocking attenuation is greatly improved over the conventional area.
[0013]
FIG. 4 shows another embodiment of the present invention. The difference from the wiring structure shown in FIG. 1 is between the ground electrode pad 14 of the SAW resonator R2 and the ground pad 13b of the package 4 provided on the piezoelectric substrate. The additional point is that a bonding wire 15b is additionally provided. That is, the wiring structure is such that two bonding wires are connected to the grounding electrode pad 14 of the SAW resonator R2. All the grounding electrode pads of the SAW resonator provided on the piezoelectric substrate are connected to the grounding electrode of the package by two bonding wires, and a grounding bonding wire is provided between the input and output bonding wires. It is that the wiring structure is to shield.
A curve B shown in FIG. 3 is a transmission characteristic when a ladder-type SAW filter is prototyped using the present embodiment, and the blocking attenuation amount is improved on the high frequency side in the same manner as the transmission characteristic A of the wiring structure of FIG. It turns out that it has improved from the curve A to the high region side.
[0014]
【The invention's effect】
Since the present invention has the wiring structure as described above, the stopband attenuation on the high side of the pass band is greatly improved while maintaining the low loss and steep attenuation characteristics of the ladder-type SAW filter. Therefore, when used in an RF stage of a mobile phone or the like, it is possible to sufficiently suppress twice or three times the local oscillation frequency generated by the mixer, so that the elastic surface according to the present invention uses a filter as a mobile phone terminal. Excellent effect when used.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration method of bonding wires in a ladder-type SAW filter according to an embodiment of the present invention.
FIG. 2 is a diagram showing an electrical equivalent circuit of FIG. 1;
3 is a diagram comparing transmission characteristics of a ladder-type SAW filter created using the configuration method of FIG. 1 of the present invention and transmission characteristics of a conventional configuration method.
FIG. 4 is a diagram showing a bonding wire configuration method in a ladder-type SAW filter according to another embodiment of the present invention.
5 is a diagram showing an electrical equivalent circuit of FIG. 4;
FIG. 6 is a diagram illustrating a configuration method of bonding wires in a conventional ladder-type SAW filter.
7 is an electrical equivalent circuit of FIG. 6;
8 is a diagram illustrating transmission characteristics of the ladder-type SAW filter of FIG. 6. FIG.
[Explanation of symbols]
1 ・ ・ Piezoelectric substrate 2 ・ ・ IDT
3a, 3b ... Reflector 4 ... Package 5, 8, 15a, 15b, 16a, 16b, 17a, 17b ... Bonding wire 6, 9, 11, 12, 14 ... Electrode pad 7 ... Input electrode 10 ... -Output electrodes 13a, 13b, 13c-Ground electrode L-Lead electrodes R1, R2, R3, R4, R5, R6-SAW resonators

Claims (2)

In a surface acoustic wave filter comprising a surface acoustic wave element formed on a piezoelectric substrate and a package for housing the surface acoustic wave element,
The surface acoustic wave element includes an IDT and at least two SAW resonators in which reflectors are arranged on both sides of the IDT, and includes an input electrode pad, an output electrode pad, a ground electrode pad, With
The package includes an input pad, an output pad, a first ground pad adjacent to the input pad, and a second ground pad adjacent to the output pad;
At least one of the ground electrode pads is connected to both the first ground pad and the second ground pad by ground wire bonding,
The ground bonding wire includes: an input bonding wire connected to the input electrode pad of the IDT and the input pad of the package; an output bonding wire connected to the output electrode pad of the IDT and the output pad of the package; A surface acoustic wave filter characterized by being disposed between the two. In a surface acoustic wave filter comprising a surface acoustic wave element formed on a piezoelectric substrate and a package for housing the surface acoustic wave element,
The surface acoustic wave element is a ladder type surface acoustic wave filter formed by forming a plurality of one-terminal surface acoustic wave resonators and connecting them to a ladder type, and includes an input electrode pad, an output electrode pad, and a ground electrode pad And
The package includes an input pad, an output pad, a first ground pad adjacent to the input pad, and a second ground pad adjacent to the output pad,
At least one of the ground electrode pads is connected to both the first ground pad and the second ground pad by ground wire bonding,
The ground bonding wire includes: an input bonding wire connected to the input electrode pad of the IDT and the input pad of the package; an output bonding wire connected to the output electrode pad of the IDT and the output pad of the package; A surface acoustic wave filter characterized by being disposed between the two.

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