JPH10294640A - Surface acoustic wave filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide high inhibition attenuation quantity on the high area side of a pass area by making at least one of bonding wires wired between the ground electrode pads of IDT and the ground terminal of a package into plural wires and providing them between the bonding wires connected to an input electrode pad and an output electrode pad. SOLUTION: The two bonding wires 16a, 16b, 17a and 17b are connected between the ground electrode pads 11 and 12 provided for the surface acoustic wave resonators against one terminal R4 and R6 of parallel arms and the ground electrodes 13 and 13c of the package 4. The two bonding wires 16a, 16b, 17a and 17b are wiring-constructed so that electromagnetic leakage is insulated between input bonding wire 5 and output bonding wire 8. Thus, the level of a direct wave can considerably be reduced and inhibition area attenuation quantity on the high area-side of the pass area can considerably be 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, and more particularly to a ladder type surface acoustic wave filter (hereinafter referred to as a ladder type SAW filter) having improved attenuation on a high frequency side of a pass band.

[0002]

2. Description of the Related Art A so-called ladder-type SAW filter in which a plurality of one-port surface acoustic wave resonators (hereinafter, referred to as SAW resonators) are connected in a ladder type at an RF stage of a cellular phone or the like is used. The features of the ladder type SAW filter are that it is smaller and lighter than a dielectric filter or the like, and is capable of realizing a filtering characteristic having a low loss and a steep attenuation gradient, and has recently been widely used as an RF filter for a cellular phone or the like. Have been.

A ladder type SAW filter is a filter in which SAW resonators are cascaded in a ladder form, and has a high Q
Since the filter is composed of a resonator, a filter having 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.
A method of forming a SAW resonator will be described with reference to an example of a SAW resonator R3 (the symbol Ri representing each SAW resonator is described 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 reflectors 22a and 22b on both sides thereof are arranged on the main surface along the propagation direction of the surface wave. The IDT 21 is constituted by a pair of comb-shaped electrodes each having a plurality of electrode fingers interposed between each other.
One of the interdigital electrodes constituting DT21 is used as an input terminal,
The other comb electrode is an output terminal. The reflectors 22a and 22b disposed on both sides of the IDT 21 reflect the surface waves excited by the IDT 21 toward the center of each IDT, thereby reducing vibration energy to the reflectors 22a and 22b.
b to form a resonator.

[0004] A plurality of SAW resonators formed as described above are formed on the same piezoelectric substrate 20 with a gap not interfering with each other (in the example of FIG. 6, six SAW resonators R1 to R6). Depending on the lead electrode, between each SAW resonator and SAW
A ladder type SAW filter element is formed by connecting the resonator and the ground pad. The ladder-type SAW filter element is housed in a ceramic package 23 having a recess at the center,
The bottom surface of the element and the package 23 are fixed with an adhesive or the like. Ladder type SAW filter element input / output electrode pad 2
4 and 25 and the input / output electrodes 26 and 27 of the package are respectively connected by bonding wires. Ladder type S
The ground electrode pads 28, 29 and 30 of the AW filter element and the ground electrode 31 of the package are connected by bonding wires, respectively, to complete a ladder type SAW filter.

As shown in FIG. 7, an electrical equivalent circuit of the ladder type SAW filter has first SAW resonators R1, R
3 and R5 are arranged in a series arm, and the second SAW resonators R2 and R5
4, R6 are arranged on the parallel arm. As is well known, a bandpass filter is configured by making the anti-resonance frequency of the SAW resonator of the parallel arm substantially match 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 an attenuation pole at the resonance frequency and the anti-resonance frequency can be configured. It is known that the attenuation slope, the amount of rejection, and the like of a filter greatly depend on the number of SAW resonators used in the filter configuration.

[0006]

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 is such that the amount of rejection attenuation on the high frequency side is as shown in FIG. Decreases monotonically with increasing frequency. At this time, the serial arm is the same SAW
The resonator has 100 IDT pairs and 10 reflectors each.
There are zero. The SAW resonators R2 and R4 of the parallel arm have 100 pairs of IDT pairs and 100 reflectors each.
The IDT logarithm of No. 6 is 50 pairs and there are 100 reflectors each.
The center frequency is 946MHz, the bandwidth is about 40MHz,
The input / output impedance is 50Ω. As described above, the conventional ladder-type SAW filter has a low loss and a filter characteristic having a steep attenuation gradient near the pass band. However, on the high frequency side of the pass band, the local oscillation frequency twice as high as the local oscillation frequency generated by the mixer is obtained. There is a drawback in that it is not possible to secure a damping amount for suppressing triple harmonics. If the grounding is insufficient due to the miniaturization of the radio, the conventional ladder type SA
The W filter has a disadvantage that the attenuation characteristics on the high frequency side deteriorate. The present invention has been made in order to solve the above-mentioned drawbacks, and an object of the present invention is to provide a ladder-type SAW filter having a high rejection attenuation on a high band side of a pass band.

[0007]

In order to achieve the above object, a ladder type surface acoustic wave filter according to the present invention is characterized in that at least two IDTs and reflectors are arranged on a piezoelectric substrate. In the constituting surface acoustic wave filter,
At least one of the bonding wires to be wired between the ground electrode pad of the IDT and the ground terminal of the package is provided in a plurality, and between the bonding wire connected to the input electrode pad and the bonding wire connected to the output electrode pad. This is a surface acoustic wave filter provided. According to a second aspect of the present invention, there is provided a ladder type surface acoustic wave filter formed by forming a plurality of one-port pair surface acoustic wave resonators on a piezoelectric substrate and connecting them in a ladder form. At least one of the surface acoustic wave resonators is grounded by a plurality of bonding wires, and the bonding wires are disposed between a bonding wire connected to an input electrode pad and a bonding wire connected to an output electrode pad. This is a surface acoustic wave filter characterized by the following.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on an embodiment shown in the drawings. FIG. 1 is a plan view showing one embodiment of a ladder-type SAW filter according to the present invention,
FIG. 2 is an electrical equivalent circuit thereof.

The SAW resonator Ri (in the embodiment of FIG. 1, i =
1 to 6) 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. This is similar to a conventional ladder filter in that the element is fixed to a recess provided in the center of the ceramic package 4 using an adhesive or the like. The feature of the present invention resides in the connection of each pad of the ladder type SAW filter element to the input / output electrode of the package 4 and the ground electrode using a bonding wire.

The wiring structure of the bonding wire, which is a feature of the present invention, will be described. In 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 to each other. The bonding wire 8 electrically connects the output electrode pad 9 provided on the SAW resonator R5 on the piezoelectric substrate to the output pad 10 of the package 4. Also, the ground electrode pad 11 provided on the parallel arm SAW resonator R4 and the parallel arm SA
Two bonding wires are connected between the ground electrode pad 12 provided on the W resonator R6 and the ground pads 13a and 13c of the package 4, respectively. Parallel arm SAW
The ground electrode pad 14 of the resonator R2 and the ground pad 13b of the package 4 are connected by a bonding wire 15a.

As in the present embodiment, SAW resonators R4 and R6
Two ground bonding wires, ie, 16a,
16b and 17a, 17b are connected to the input bonding wire 5
It is possible to greatly reduce the level of direct waves by providing a wiring structure that shields electromagnetic leakage between the output bonding wire 10 and the output bonding wire 10. It became clear from the experimental results.

FIG. 3 shows an amplitude transmission characteristic A of a ladder type SAW filter manufactured based on FIG. 1 which is an example of a bonding wire wiring structure according to the present invention, and a conventional bonding wire wiring shown in FIG. 7 is a diagram comparing amplitude transmission characteristics C of a ladder type SAW filter created based on FIG. 6 which is a structure. The design conditions of the filter based on FIG. 1 are the same as those of FIG. 8, and only the wiring of the bonding wires is different. As is clear from the figure, the transmission characteristics of the conventional bonding wire wiring structure show that the attenuation decreases monotonically with increasing frequency on the high frequency side. It can be seen that the amount of stop attenuation is greatly improved over the region over the conventional one.

FIG. 4 shows another embodiment of the present invention. The difference from the wiring structure shown in FIG. 1 is that the ground electrode pad 14 of the SAW resonator R2 provided on the piezoelectric substrate and the ground pad 13b of the package 4 are provided. Is that a bonding wire 15b is additionally provided between them. That is, the wiring structure is such that two bonding wires are connected to the ground electrode pad 14 of the SAW resonator R2. All the ground electrode pads of the SAW resonator provided on the piezoelectric substrate are connected to the ground electrode of the package by two bonding wires, and a ground bonding wire is provided between the input and output bonding wires. Is a wiring structure that shields the light. A curve B shown in FIG. 3 is a transmission characteristic when a ladder-type SAW filter is experimentally manufactured using the present embodiment. As in the case of the transmission characteristic A of the wiring structure in FIG. It can be seen that the curve A is improved to the higher frequency side.

[0014]

According to the present invention, since the wiring structure as described above is employed, the attenuation of the stop band on the high band side of the pass band while maintaining the characteristics of the low loss and steep attenuation characteristics of the ladder type SAW filter. Can be greatly improved,
When used in the RF stage of a mobile phone or the like, since the local oscillation frequency generated by the mixer can be sufficiently suppressed twice or three times, the elastic surface according to the present invention is excellent when the filter is used for a mobile phone terminal. It has the effect.

[Brief description of the drawings]

FIG. 1 is a view showing a configuration method of a bonding wire in a ladder type SAW filter showing an embodiment of the present invention.

FIG. 2 is a diagram showing an electrical equivalent circuit of FIG.

3 is a diagram comparing the transmission characteristics of a ladder-type SAW filter created using the configuration method of FIG. 1 of the present invention with those of a conventional configuration method.

FIG. 4 is a view showing a method of forming a bonding wire in a ladder type SAW filter showing another embodiment of the present invention.

FIG. 5 is a diagram showing an electrical equivalent circuit of FIG. 4;

FIG. 6 is a diagram showing a method of forming a bonding wire in a conventional ladder-type SAW filter.

FIG. 7 is an electrical equivalent circuit of FIG.

FIG. 8 is a diagram illustrating transmission characteristics of the ladder-type SAW filter of FIG. 6;

[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 electrode 13a, 13b, 13c earth electrode L lead electrode R1, R2, R3, R4 R5, R6 ··· SAW resonator

Claims (2)

[Claims] 1. A surface acoustic wave filter comprising at least two SAW resonators each having an IDT and a reflector disposed on both sides of the IDT on a piezoelectric substrate, and a ground electrode pad and a package of the IDT. At least one of the bonding wires to be wired between the bonding wire and the ground terminal, and is disposed between the bonding wire connected to the input electrode pad and the bonding wire connected to the output electrode pad. Surface acoustic wave filter. 2. A ladder type surface acoustic wave filter comprising a plurality of one-port pair surface acoustic wave resonators formed on a piezoelectric substrate and connected in a ladder form, wherein one-port pair surface acoustic waves connected to a parallel arm. At least one of the resonators is grounded by a plurality of bonding wires, and the bonding wires are disposed between a bonding wire connected to an input electrode pad and a bonding wire connected to an output electrode pad. Surface acoustic wave filter.