JP3379775B2 - Surface acoustic wave filter - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resonator type surface acoustic wave filter having a surface acoustic wave resonator and an inductance adding element.

Surface acoustic wave filters have hitherto been used as image filters represented by IF filters for televisions and videos. In recent years, mobile phones, cell phones, etc. have been moved by taking advantage of their small size and low cost. Demand for communication filters is increasing rapidly.

In a surface acoustic wave filter, a comb-shaped electrode for exciting a surface acoustic wave and a comb-shaped electrode for reception which are formed on a piezoelectric substrate make a pair, and conventionally, a plurality of comb-shaped electrodes are connected in multiple stages. The transversal type surface acoustic wave filter that has been used is often used.

On the other hand, recently, by resonating a surface acoustic wave with a surface acoustic wave resonator having reflectors on both sides of an exciting comb-shaped electrode, insertion loss is greatly improved and an external matching circuit is not required. Resonator type surface acoustic wave filters are promising.

In particular 800 to 900MH in the surface acoustic wave filter or the like of the current car phone or cellular phone is used in the _Z band, broadband and high degree of suppression maintaining low loss The addition of inductance SAW resonator It has been confirmed that this can be realized.

[0006] However, in the next-generation car phone and mobile phone has been studied for use in quasi-microwave band of 1.5GH _Z and 1.9GH _Z, maintaining broadband and high degree of suppression of the low-loss even in such regions There is a demand for the development of a surface acoustic wave filter that can realize the above.

[0007]

2. Description of the Related Art FIG. 6 is an equivalent circuit diagram showing an example of a resonator type surface acoustic wave filter disclosed in Japanese Patent Application No. 4-32270 (Japanese Patent Application Laid-Open No. 5-183380; Japanese Patent No. 280905). 8 is a plan view showing an example of a wave resonator, FIG.
Is a diagram qualitatively showing the frequency characteristic of the surface acoustic wave resonator, FIG. 9 is a diagram showing the filter characteristic of the two-terminal pair surface acoustic wave resonator, FIG. 10 is a diagram showing the characteristic of the inductance-added surface acoustic wave resonator, FIG. 11 is a perspective view showing a state where the surface acoustic wave filter shown in FIG. 6 is housed in a package.

In FIG. 6, the resonator type surface acoustic wave filter has a one-terminal pair surface acoustic wave resonator (hereinafter referred to as surface acoustic wave resonator) R, and the plurality of surface acoustic wave resonators R are series arms.
11, the parallel arm 12, the inductance element L, etc. are connected in series or in parallel.

Each of the surface acoustic wave resonators R has a pair of exciting comb-shaped electrodes 13 and a pair of receiving comb-shaped electrodes 14 as shown in FIG.
On both sides of the comb-shaped electrode 14, reflectors 16 composed of open-type or short-circuit type comb-shaped electrodes, strip-array electrodes, etc. are arranged.

In the resonator type surface acoustic wave filter shown in FIG. 6, the first surface acoustic wave resonators R ₁ and R ₂ are connected in series via the series arm 11 and are connected to the parallel arm 12 in the second direction. The surface acoustic wave resonators R ₃ and R ₄ are each grounded via an inductance element L.

The surface acoustic wave resonator has an impedance of FIG.
As shown in (a), 0 at resonance frequency f _r , anti-resonance frequency f
a maximum, 0 admittance at the antiresonance frequency f _a, as in FIG. 8 (b), a double resonance characteristic becomes maximum at the resonant frequency f _r in _a.

Such a surface acoustic wave resonator R is arranged in a series arm and a parallel arm as shown in FIG. 9 (a) to form a two-terminal pair surface acoustic wave resonator, and the anti-resonance frequency f of the parallel arm. _ap and a band pass filter can be formed by substantially coincides with the resonance frequency f _rs of the series arm.

FIG. 9 (b) shows the surface acoustic wave resonator R _s of the series arm.
Of the anti-resonance frequency f _ap of the resonance frequency f _rs ≒ parallel arm SAW resonator R _p, overlaid impedance characteristic curve and admittance characteristic curve of the surface acoustic wave resonator R _p of the surface acoustic wave resonator R _s It is a figure.

Now, the surface acoustic wave resonator R_sImpeda
Z = jx, surface acoustic wave resonator R _pAdmittance Y
= Jb, image of two-terminal surface acoustic wave resonator
Tanh (γ) = [bx / (bx-1)] for the transmission amount γ
^1/2The following expression holds.

If the value obtained by the above equation is an imaginary number, then 2 in FIG.
The terminal-pair surface acoustic wave resonator exhibits a pass characteristic, and a real number exhibits an attenuation characteristic. That is, if 0 <bx <1 in the above equation, it becomes an imaginary number and shows the pass characteristic, and bx <0 or bx>
If it is 1, the damping characteristic is shown.

In other words, the two-terminal pair surface acoustic wave resonator shown in FIG. 9 (a) has a small amount of attenuation in the region exhibiting the pass characteristic as shown in FIG. 9 (c), and the amount of attenuation in the region exhibiting the attenuation characteristic. Can be said to have excellent characteristics as a bandpass filter that rapidly increases.

However, in the two-terminal SAW resonator, the bandwidth of the passage region and the steepness of the slope reaching the attenuation region, that is, the degree of suppression are mainly the resonance frequency _{frs of} each surface acoustic wave resonator. And the anti-resonance frequency f _ap .

Therefore, in the resonator type surface acoustic wave filter, as a means for realizing a wide band and high suppression of the pass band while maintaining low loss, an elastic wave forming a resonator type surface acoustic wave filter as shown in FIG. An inductance element L is added to the surface acoustic wave resonator R.

By adding an inductance element L in series with the surface acoustic wave resonator R, the impedance is shown in FIG.
As (a), the contribute to broadband and spacing of the resonant frequency f _r and the antiresonance frequency f _a lift ωL the original impedance + side is spread.

[0020] On the other hand, the admittance is the reciprocal of the impedance by adding an inductance element L in the surface acoustic wave resonator R, the resonant frequency as shown similarly to the impedance in FIG. 10 (b) f _r and the anti-resonance frequency f _a The widening of the interval contributes to widening the band.

Regarding the degree of suppression, the admittance value is increased by adding the inductance element L to the surface acoustic wave resonator R, and bx outside the pass band shown in FIG. It increases in the negative direction and contributes to high suppression.

Although the impedance value outside the pass band may be reduced by adding the inductance element L, the impedance value can be increased by connecting a plurality of the same surface acoustic wave resonators R in series. It is possible to

In the resonator type surface acoustic wave filter shown in FIG. 6, the filter chip 3 is mounted in the central recess of the package 2 as shown in FIG. 11, and the package 2 made of ceramic has the ground layer 21 in the central recess. A plurality of electrodes 22, 23, 24, 25 are formed on the periphery.

In the filter chip 3, for example, the first surface acoustic wave resonators R ₁ and R ₂ and the second surface acoustic wave resonators R ₃ and R _{4 form} a series arm or a parallel arm on the piezoelectric substrate 31. It is formed of Al or an Al-based alloy such as Al-Cu together with the conductors and electrodes 13, 14, 15, 16.

One of the first surface acoustic wave resonators R ₁ and R ₂ connected to the series arm has electrodes 13 and 14 respectively.
The electrodes 22 and 23 of the package 2 and the electrodes 13 and 14 on the filter chip 3 are connected to each other via the bonded wire 26.

Further, one of the second surface acoustic wave resonators R ₃ and R ₄ connected to the parallel arm has an electrode 15 and an electrode, respectively.
The electrodes 24 and 25 of the package 2 and the electrodes 15 and 16 on the filter chip 3 are connected to each other through the bonded wire 27.

[0027] For example, an inductance added to the surface acoustic wave resonators in the surface acoustic wave filter used in 800~ 900MH _Z zone length which is bonded between the electrodes is about 1~3nH of about 2mm It corresponds to the inductance of the wire.

That is, the wire 27 bonded to the electrode 24 and the electrode 15 and the electrode 25 and the electrode 16 also serves as the inductance element L. By adjusting the length of the wire 27, the wire 27 is added to the surface acoustic wave resonator. The size of the inductance is adjusted.

[0029]

However, as the passing area becomes wider, the area of bx> 1 shown in FIG. 9 increases and the steepness of the slope reaching the passing area deteriorates. The influence on the filter characteristics becomes more remarkable as the value of the inductance added to the surface acoustic wave resonator becomes too large.

Furthermore, especially the inductance value of the inductance element L is compared with the surface acoustic wave filters for 800～900MH _Z band is proportional to the frequency, effect on the resonator-type surface acoustic wave filter used in a quasi-microwave band There was a problem of getting bigger.

An object of the present invention is to provide a surface acoustic wave filter capable of maintaining a low loss in the quasi-microwave band and realizing a wide band and a high degree of suppression.

[0032]

FIG. 1 is a perspective view showing a resonator type surface acoustic wave filter according to the present invention. Note that the same object is denoted by the same symbol throughout the drawings.

The above-mentioned problem is to store the piezoelectric substrate and the piezoelectric substrate.
Package and a predetermined package provided on the piezoelectric substrate.
The first elasticity that becomes a series arm so that it has a closed path characteristic.
A surface acoustic wave resonator and a second surface acoustic wave resonator serving as a parallel arm;
Have a plurality of surface acoustic wave resonators connected in a ladder shape
In the surface acoustic wave filter, the second surface acoustic wave
Connection between each of the shakers and the ground electrode of the package
Minute, multiple bonding wires are provided
Will be solved by.

[0034]

In FIG. 1, when three wires having inductances L ₁ , L ₂ and L ₃ are connected in parallel between the same electrodes, the combined inductance L of the inductance elements is 1 / L = 1 / It can be calculated from the formula L ₁ + 1 / L ₂ + 1 / L ₃ .

If the electrodes on the package formed for bonding the three wires and the electrodes on the filter chip are parallel to each other, L ₁ , L ₂ and L ₃ are almost equal to each other and the combined inductance element inductance L is equal to L _1/3.

That is, the inductance L of the inductance element is proportional to the inductance of one wire and inversely proportional to the number of wires. Therefore, the inductance of the inductance element can be freely adjusted by changing the number of wires.

Moreover, each wire constituting the inductance element is long, and the inductance can be adjusted with high precision. That is, it is possible to realize a surface acoustic wave filter that can maintain a low loss in the quasi-microwave band and realize a wide band and a high degree of suppression.

[0038]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 2 is a diagram showing a filter characteristic in the embodiment,
3 is a perspective view showing another embodiment of the present invention, FIG. 4 is a view showing a filter characteristic in another embodiment, and FIG. 5 is a view showing a filter characteristic in a modification of the present invention.

One embodiment of the surface acoustic wave filter according to the present invention is, as shown in FIG. 1, in which the filter chip 5 is mounted in the central recess of the package 4, and the package 4 made of ceramic is used.
Has a ground layer 41 in the central recess and has a plurality of electrodes 42, 4 around it.
3, 44, 45 are formed.

In the filter chip 5, for example, the first surface acoustic wave resonators R ₁ and R ₂ and the second surface acoustic wave resonators R ₃ and R _{4 form} a series arm or a parallel arm on the piezoelectric substrate 51. It is formed of Al or an Al-based alloy such as Al-Cu together with the conductors and electrodes 52, 53, 54, 55 and the like.

One of the first surface acoustic wave resonators R ₁ and R ₂ connected as a series bowl has an electrode 52 and an electrode 5 respectively.
3, the electrodes 42 and 43 of the package 4 and the electrodes 52 and 53 on the filter chip 5 are connected to each other via the bonded wire 56.

Further, one of the second surface acoustic wave resonators R ₃ and R ₄ connected in parallel to each other is connected to the electrode 54 and the electrode 55, respectively, and an elongated electrode 54 capable of bonding a plurality of wires thereto. , 55 are formed in parallel with the electrodes 44, 45 of the elongated package 4 as well.

In this embodiment, a parallel bowl-shaped surface acoustic wave resonator R is used.
₃ and R ₄ are grounded via the inductance element L, and a plurality of wires 57 are bonded as the inductance element L between the parallel electrodes 44 and 45 and the electrodes 54 and 55.

FIG. 2 (a) shows the pass characteristics of the filter when one wire (inductance about 1 nH) is added to the surface acoustic wave resonator R. FIG. 2 (a) shows 10 wires connected in parallel (inductance about 0.1 nH). Figure 2 (b) shows the pass characteristics of the filter when) is added.

According to the pass characteristics of the two filters, when 10 wires are added as compared with the case where one wire is added to the surface acoustic wave resonator R, the bandwidth of the pass region is slightly narrowed and the suppression degree is deteriorated. The rising characteristic from the attenuation region to the pass region is improved.

Another embodiment of the surface acoustic wave filter according to the present invention is such that the filter chip 7 is mounted on the package 6 as shown in FIG.
Has a ground layer 61 in the central recess and is surrounded by a plurality of electrodes 62, 6
3, 64, 65 are formed.

In the filter chip 7, for example, the first surface acoustic wave resonators R ₁ and R ₂ and the second surface acoustic wave resonators R ₃ and R _{4 form} a series arm or a parallel arm on the piezoelectric substrate 71. It is formed of Al or an Al-based alloy such as Al-Cu together with the conductors and electrodes 72, 73, 74, 75 and the like.

Unlike the above embodiment, an inductance element L is added to the _first surface acoustic wave resonators R ₁ and R ₂ connected to the series arm, and the electrodes 62, 63, 64 and 65 of the package 6 and the filter chip are added. The seven electrodes 72, 73, 74, 75 are each connected via a wire 56.

Further, electrodes 76, 77, 78, 79 formed in parallel between the series bowls R ₁ and R ₂ and the parallel bowls R ₃ and R _4.
Is formed, and a plurality of wires 57 are bonded as the inductance element L between the electrodes 76 and 77 and between the electrodes 78 and 79.

FIG. 4 (a) shows the pass characteristics of the filter when one wire (inductance of about 1 nH) is added to the surface acoustic wave resonator R. FIG. 4 (a) shows 10 wires connected in parallel (inductance of about 0.1 nH). Figure 4 (b) shows the pass characteristics of the filter when) is added.

The bandwidth is slightly narrower when 10 wires are added than when one wire is added to the surface acoustic wave resonator R, but the degree of suppression is one when the wire is added to the surface acoustic wave resonator R. It is clearly improved when 10 wires are added compared to when the wires are added.

A modification of the surface acoustic wave filter according to the present invention is a wire 57 of two inductance elements L in FIG.
The number of lines is changed to shift the inductance of the inductance element L added to the surface acoustic wave resonators R ₃ and R ₄ connected to the parallel arm.

FIG. 5 (a) shows the pass characteristics when four wires (inductance of about 0.25 nH) are added to both surface acoustic wave resonators R. One wire has two wires and the other wire has four wires ( Figure 5 (b) shows the pass characteristics when the inductance is about 0.5 nH and about 0.25 nH).

From the pass characteristics of the two filters, there is only one attenuation pole on the low frequency side of the pass characteristics when the two inductances are equal. However, if the inductance of the two inductance elements L is changed, two attenuation elements on the low frequency side are attenuated. A pole is generated and the range of the attenuation range moves.

[0055]

As described above, according to the present invention, it is possible to provide a surface acoustic wave filter capable of maintaining a low loss in the quasi-microwave band and realizing a wide band and a high degree of suppression.

[Brief description of drawings]

FIG. 1 is a perspective view showing a resonator type surface acoustic wave filter according to the present invention.

FIG. 2 is a diagram showing filter characteristics in the example.

FIG. 3 is a perspective view showing another embodiment of the present invention.

FIG. 4 is a diagram showing filter characteristics in another embodiment.

FIG. 5 is a diagram showing a filter characteristic in a modified example of the present invention.

FIG. 6 is an equivalent circuit diagram showing an example of a resonator type surface acoustic wave filter.

FIG. 7 is a plan view showing an example of a surface acoustic wave resonator.

FIG. 8 is a diagram qualitatively showing frequency characteristics of a surface acoustic wave resonator.

FIG. 9 is a diagram showing a filter characteristic of a two-terminal pair surface acoustic wave resonator.

FIG. 10 is a diagram showing characteristics of an inductance-added surface acoustic wave resonator.

11 is a perspective view showing a state where the resonator type surface acoustic wave filter shown in FIG. 6 is housed in a package.

[Explanation of symbols]

4, 6 Package 5, 7
Filter tip 41, 61 Ground layer 42, 43,
44, 45 Electrodes 51, 71 Piezoelectric substrates 52, 53,
54, 55 electrodes 56, 57 wires 62, 63,
64, 65 electrodes 72, 73, 74, 75 electrodes 76, 77,
78, 79 electrodes R ₁ , R ₂ , R ₃ , R ₄ surface acoustic wave resonator L inductance element

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields investigated (Int.Cl. ⁷ , DB name) H03H 9/00 H03H 9/64

Claims (2)

(57) [Claims] 1. A plurality of surface acoustic wave resonators
The parallel and series arms of are connected in a ladder shape,
A surface acoustic wave filter having pass characteristics, comprising:
Connect multiple bonding wires in series to each of the parallel arms of
A surface acoustic wave filter characterized by being continued . 2. A plurality of buttons provided in each of the parallel bowls.
Claim that the number of bonding wires is different
Item 2. The surface acoustic wave filter according to item 1.