JP3948550B2 - Surface acoustic wave device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a surface acoustic wave device on which a surface acoustic wave element including a plurality of surface acoustic wave resonators formed on a piezoelectric substrate is mounted, and in particular, the surface acoustic wave resonators constitute a ladder type circuit. The present invention relates to a technique effective when applied to a surface acoustic wave device. The present invention is also applied to a dual filter and duplexer using a plurality of the surface acoustic wave elements.
[0002]
[Prior art]
In recent years, mobile communication terminals such as mobile phones have been rapidly developed. This terminal is desired to be particularly small and light because of its convenience for carrying around. In order to reduce the size and weight of the terminal, it is essential that the electronic components used in the terminal are also small and light. For this reason, the high-frequency part and intermediate-frequency part of the terminal have multiple surface acoustic wave resonances. A surface acoustic wave element having a ceramic (SAW resonator) formed on a piezoelectric substrate and advantageous for reduction in size and weight is widely used.
[0003]
Important characteristics required when a surface acoustic wave element is used as a filter include insertion loss and attenuation outside the passband. Here, the insertion loss affects the power consumption of the device, and the lower the loss, the longer the life of the battery. Therefore, the capacity of the battery can be reduced, contributing to a reduction in size and weight. Moreover, if the high out-of-band attenuation can be obtained with one filter, it contributes to the reduction in size and weight of the device.
[0004]
The surface acoustic wave element has a series arm between the input terminal and the output terminal, and a plurality of parallel arms are formed between the series arm and the reference potential terminal, and an appropriate elastic surface is formed between the series arm and the parallel arm. 2. Description of the Related Art A surface acoustic wave element that constitutes a ladder circuit having a wave resonator is known.
[0005]
In the surface acoustic wave device that constitutes the ladder circuit, by matching the resonance frequency of the surface acoustic wave resonator disposed in the series arm with the anti-resonance frequency of the surface acoustic wave resonator disposed in the parallel arm, In the vicinity of the matched frequency, the input / output impedance is matched with the characteristic impedance, thereby forming a pass band.
[0006]
By the way, a surface acoustic wave element used as a bandpass filter is strongly required to increase the attenuation in the frequency region outside the passband.
[0007]
Here, FIG. 4 shows a circuit diagram of a ladder-type surface acoustic wave element studied by the present inventors.
[0008]
In the illustrated surface acoustic wave element 111, a plurality of surface acoustic wave resonators 120 are arranged on a series arm 117. Further, between the input terminal 115 and the surface acoustic wave resonator 120 located closest to the input terminal 115, between the output terminal 116 and the surface acoustic wave resonator 120 located closest to the output terminal 116, A parallel arm 119 is formed between the surface acoustic wave resonators 120. A surface acoustic wave resonator 121 is arranged on each of these parallel arms 119.
[0009]
In FIG. 4, the symbol L represents an inductance component included between the chip of the surface acoustic wave element 111 and the package on which the chip is mounted (such as wiring, bumps, or bonding wires). Symbol Lp represents an inductance component included in the path from the connection pad on the package to the ground on the device side.
[0010]
In such a configuration, the value of the inductance component Lp is designed to be extremely small (0.03 nH or less), and the value of the inductance component L is selected appropriately, thereby ensuring a predetermined passband frequency and the passband frequency. The desired attenuation on the lower frequency side was obtained.
[0011]
This prior art means a technique that is the basis of the present invention recognized by the present inventor and does not mean a known technique in patent law. Nor does it abandon the pursuit of rights for what has been described here as prior art.
[0012]
[Problems to be solved by the invention]
However, with the above-described technique, it is practically difficult to reduce the value of the inductance component Lp due to wiring routing or the like.
[0013]
Further, since it is extremely difficult to measure the actual inductance component Lp, trial and error by actual measurement is indispensable. In particular, since the inside of the package has a three-dimensional structure, the design change required as a result of trial and error may be extremely difficult.
[0014]
If the value of the inductance component Lp cannot be made sufficiently small, the attenuation pole f _LP cannot take a sufficient amount of attenuation in FIG. 3, and only the characteristics shown by the broken line can be obtained. In the figure, the attenuation pole f _P is a resonance frequency by the surface acoustic wave resonator of the parallel arm. The attenuation pole f _S is a resonance frequency by the surface acoustic wave resonator of the series arm.
[0015]
SUMMARY OF THE INVENTION An object of the present invention is to provide a surface acoustic wave device that can increase the attenuation in a frequency region outside the passband without reducing the inductance component.
[0016]
[Means for Solving the Problems]
In order to solve the above problems, a surface acoustic wave device according to the present invention includes a ladder type having a series arm between an input terminal and an output terminal and a plurality of parallel arms between the series arm and a reference potential terminal. A surface acoustic wave device on which surface acoustic wave elements constituting a circuit are mounted, wherein the first surface acoustic wave resonators disposed on the series arm and the parallel arms are disposed respectively. A second surface acoustic wave resonator having an anti-resonance frequency that matches the resonance frequency of the surface acoustic wave resonator of the first surface acoustic wave resonator, and the second surface acoustic wave resonator of the parallel arm located closest to the input terminal. Predetermined capacitance means disposed between a reference potential terminal side and a reference potential terminal side of the second surface acoustic wave resonator of the parallel arm located closest to the output terminal; The second surface acoustic wave resonator in the arm An inductance component included between a reference potential terminal side and a connection point on the reference potential terminal side where the parallel arms are connected to each other; a connection point on the reference potential terminal side where the parallel arms are connected to each other; and the reference And an inductance component included between the potential terminal and the potential terminal.
[0017]
According to such an invention, since the capacitive means is arranged between the parallel arm located closest to the input terminal and the parallel arm located closest to the output terminal, without reducing the inductance component, The attenuation in the frequency region outside the passband can be greatly increased.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described more specifically with reference to the drawings. Here, in the accompanying drawings, the same reference numerals are given to the same members, and duplicate descriptions are omitted. The embodiment of the invention is a particularly useful embodiment in which the present invention is implemented, and the present invention is not limited to the embodiment.
[0019]
FIG. 1 is a sectional view showing a surface acoustic wave device in which a surface acoustic wave element according to an embodiment of the present invention is packaged. FIG. 2 shows an equivalent circuit of the surface acoustic wave element according to an embodiment of the present invention. FIG. 3 is a graph showing attenuation frequency characteristics of the surface acoustic wave device shown in FIG.
[0020]
A surface acoustic wave filter device (surface acoustic wave device) 10 shown in FIG. 1 has a pair of cross fingers (comb teeth) that generate a surface acoustic wave by an electric field or convert the surface acoustic wave into an electric signal. A surface acoustic wave filter (surface acoustic wave element) 11 in which a plurality of surface acoustic wave resonators composed of electrodes (not shown) are arranged at predetermined positions on a piezoelectric substrate is composed of a single layer or a plurality of layers and has a predetermined wiring. It is mounted on a ceramic or resin mounting board 12 on which a pattern or circuit pattern is formed.
[0021]
In the case shown in the figure, the element forming surface of the surface acoustic wave filter 11 is disposed opposite to the mounting substrate 12, and the surface acoustic wave filter 11 and the mounting substrate 12 are flip-chip connected via bumps 13. Both may be connected by wire bonding.
[0022]
Here, reflectors that amplify the surface acoustic waves are provided on both sides of the pair of electrodes described above. The piezoelectric substrate is made of a piezoelectric single crystal such as LiNbO3, LiTaO3 or quartz, or a piezoelectric ceramic such as a lead zirconate titanate piezoelectric ceramic. However, a piezoelectric substrate in which a piezoelectric thin film such as a ZnO thin film is formed on an insulating substrate may be used.
[0023]
A cap 14 is adhered to the mounting substrate 12 so as to surround the surface acoustic wave filter 11, and the surface acoustic wave filter 11 is protected from dust and mechanical shocks.
[0024]
As shown in FIG. 2, the surface acoustic wave filter 11 mounted on the surface acoustic wave filter device 10 has a series arm 17 between the input terminal 15 and the output terminal 16. Further, a plurality of parallel arms 19 are connected between the series arm 17 and the reference potential terminal 18, and such a series arm 17 and the parallel arm 19 constitute a ladder type circuit.
[0025]
A plurality of first surface acoustic wave resonators 20 are arranged in series on the series arm 17. In the present embodiment, there are two first surface acoustic wave resonators 20, but two or four or more may be arranged in series.
[0026]
The parallel arm 19 is connected between a connection point between the input terminal 15 and the first surface acoustic wave resonator 20 located closest to the input terminal 15 and the reference potential terminal 18, and between the output terminal 16 and the output terminal. 16 between the connection point between the first surface acoustic wave resonator 20 and the reference potential terminal 18 located between the first surface acoustic wave resonator 20 and the two first surface acoustic wave resonators 20 adjacent to each other. It is provided between the reference potential terminal 18.
[0027]
Each parallel arm 19 is provided with a second surface acoustic wave resonator 21. These second surface acoustic wave resonators 21 have an anti-resonance frequency that matches the resonance frequency of the first surface acoustic wave resonator 20.
[0028]
In this specification, “an anti-resonance frequency that matches the resonance frequency of the first surface acoustic wave resonator” means that both frequencies do not have to match exactly, and a predetermined function such as a filter is exhibited. It is enough if it matches to the extent possible.
[0029]
Further, between the parallel arm 19 positioned closest to the input terminal 15 and the parallel arm 19 positioned closest to the output terminal 16, capacitive means 24 having a predetermined capacitance is disposed. Here, the capacitance means 24 may be formed on a chip as a part of the circuit of the surface acoustic wave filter 11, may be formed on the mounting substrate 12 on which the surface acoustic wave filter 11 is mounted, or the mounting substrate 12. You may form by mounting components, such as a chip capacitor, on it.
[0030]
In such a circuit, an inductance component L is present between the chip of the surface acoustic wave filter 11 and the package on which the chip is mounted (wiring, bumps, bonding wires, etc.) from the connection pads on the package to the device side. There is an inductance component Lp in the path to the ground.
[0031]
Next, the attenuation frequency characteristic of the surface acoustic wave filter 11 of the present embodiment will be described with reference to FIG.
[0032]
In such a surface acoustic wave filter 11, as shown in FIG. 3, an attenuation pole f _P , an attenuation pole f _S and an attenuation pole f _LP appear. Here, the attenuation pole f _P is a resonance frequency by the second surface acoustic wave resonator 21. Further, the attenuation pole f _S is a resonance frequency by the first surface acoustic wave resonator 20. The attenuation pole f _LP is formed by the capacitance of the first surface acoustic wave resonator 20, the capacitance of the second surface acoustic wave resonator 21, and the inductance component Lp.
[0033]
Here, in the present embodiment, since the capacitive means 24 is disposed between the parallel arm 19 positioned closest to the input terminal 15 and the parallel arm 19 positioned closest to the output terminal 16, As indicated by the solid line 3, the attenuation pole f _LP can take a sufficient attenuation. Therefore, it is possible to significantly increase the attenuation in the frequency region outside the passband without reducing the inductance component.
[0034]
Since such a capacitive means 24 can be easily formed, the value of the inductance component Lp (inductance component included in the path from the connection pad on the package to the ground on the device side) is extremely small. Thus, it is possible to reliably obtain a sufficient amount of attenuation outside the passband without designing the circuit.
[0035]
In the above description, the surface acoustic wave filter device 10 on which one surface acoustic wave filter 11 is mounted is shown. However, for example, two surface acoustic wave filters 11 having mutually different band center frequencies are mounted. Therefore, the surface acoustic wave filter of the present invention can be applied to various types of surface acoustic wave filter devices.
[0036]
Furthermore, the scope of application of the present invention is not limited to filters, and can be applied to various surface acoustic wave devices other than the filter field in which one or a plurality of surface acoustic wave elements are mounted.
[0037]
【The invention's effect】
As is apparent from the above description, the present invention can provide the following effects.
[0038]
(1). Capacitance means is arranged between the parallel arm located nearest to the input terminal and the parallel arm located nearest to the output terminal, so that the inductance component is not reduced and the outside of the passband is reduced. The attenuation in the frequency domain can be greatly expanded.
[0039]
(2) Since the capacitance means can be easily formed, it is possible to reliably obtain a sufficient amount of attenuation outside the passband without designing the inductance component value to be extremely small.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a surface acoustic wave device in which a surface acoustic wave element according to an embodiment of the present invention is packaged.
FIG. 2 is a circuit diagram showing an equivalent circuit of a surface acoustic wave element according to an embodiment of the present invention.
3 is a graph showing attenuation frequency characteristics of the surface acoustic wave device of FIG. 2;
FIG. 4 is a circuit diagram showing an equivalent circuit of a surface acoustic wave element that the present inventor studied.
[Explanation of symbols]
10 Surface acoustic wave filter device (surface acoustic wave device)
11 Surface acoustic wave filter (surface acoustic wave device)
12 mounting substrate 13 bump 14 cap 15 input terminal 16 output terminal 17 serial arm 18 reference potential terminal 19 parallel arm 20 first surface acoustic wave resonator 21 second surface acoustic wave resonator 24 capacitor means 111 surface acoustic wave element 115 Input terminal 116 Output terminal 117 Series arm 119 Parallel arm 120 Surface acoustic wave resonator 121 Surface acoustic wave resonator

Claims (3)

A surface acoustic wave device including a surface acoustic wave device having a ladder circuit having a series arm between an input terminal and an output terminal and having a plurality of parallel arms between the series arm and a reference potential terminal. There,
A plurality of first surface acoustic wave resonators disposed in the series arm;
A second surface acoustic wave resonator disposed on each of the parallel arms and having an anti-resonance frequency that matches a resonance frequency of the first surface acoustic wave resonator;
Recently the reference potential terminal side of the second surface acoustic wave resonators in parallel arms located near, recently the second surface acoustic wave resonator of the parallel arm positioned beside said output terminal of said input terminals Predetermined capacity means arranged between the reference potential terminal side of the device,
In each of the parallel arms, an inductance component included between a reference potential terminal side of the second surface acoustic wave resonator and a connection point on the reference potential terminal side where the parallel arms are connected to each other;
An inductance component included between a connection point on the reference potential terminal side where the parallel arms are connected to each other and the reference potential terminal;
A surface acoustic wave device comprising:   2. The surface acoustic wave device according to claim 1, wherein the capacitive means is provided on the surface acoustic wave element.   3. The surface acoustic wave device according to claim 2, wherein the surface acoustic wave device is a duplexer on which the two surface acoustic wave elements having mutually different band center frequencies are mounted.

Images