JPH06350390A - Surface acoustic wave filter - Google Patents

Abstract

PURPOSE:To obtain a small sized surface acoustic wave filter with high performance in which the band width is set freely, a square ratio is increased without making the band width narrow and a temperature coefficient is made small. CONSTITUTION:At least two surface acoustic wave resonators 4, 5 having different anti-resonance frequencies fa1, fa2 and at least one inductor 6 are connected to a series arm 2 of a 2-terminal ladder circuit and a parallel resonator 3 causing parallel resonance at a frequency fp between the anti-resonance frequencies fa1, fa2 of the surface acoustic wave resonators 4, 5 of the series arm 2 is connected to a parallel arm 1 to form unit section. The inductor 6 connecting to the series arm 2 is formed of a thin wire, plural bonding pads formed in the surface acoustic wave resonator and plural bonding pads formed in a package accommodating the surface acoustic wave resonator are connected in zigzag shaped to obtain a desired inductance.

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. Generally, a surface acoustic wave device is composed of a piezoelectric substrate and a comb-shaped electrode provided on the piezoelectric substrate for converting a voltage into a surface acoustic wave or vice versa. As a function, a high frequency voltage is converted into a surface acoustic wave having a wavelength of about 10 ⁻⁵ times that of an electromagnetic wave by using a comb-shaped electrode, propagated on the surface of the piezoelectric substrate, and then converted into a voltage by the comb-shaped electrode again.

Since it is possible to have frequency selectivity by the shape of the interdigital transducer during the two conversions, it has a filter function or a resonator function. Also,
Since the propagation speed can be slowed down to about 10 ^{−5 of} electromagnetic waves, it can be used as a delay element. Utilizing these functions, they have already been applied to filters, resonators, and delay elements that are compact, inexpensive, and do not require adjustment.

An example of a product already commercialized is a TV.
, An IF filter, a resonator for a VTR oscillator, a VCO for a cordless telephone, and the like. Recently, it has been applied to mobile radio such as car phones and mobile phones by taking advantage of its small size and low price. To expand the needs in this field, improvement of pass characteristics and power characteristics are required. Is the main issue.

[0004]

2. Description of the Related Art Conventionally, a surface acoustic wave (Surface Acoustic Wave S) for automobiles and mobile phones is used.
Although a transversal type filter has been used as an (AW) filter, a resonator type surface acoustic wave filter has been developed as a solution to the drawback because the loss is limited.

Conventional broadband type filters using surface acoustic wave resonators are disclosed in Japanese Patent Publication No. 56-19765, Japanese Patent Application Nos. 3-281694 and 4-32270.
As can be seen in the specification, etc., one-terminal pair type surface acoustic wave resonators were connected in a ladder type.

FIG. 9 is an explanatory view of the principle of a conventional surface acoustic wave filter. In this figure, 61 is a parallel arm, 62 is a series arm, and 63 and 64 are surface acoustic wave resonators. In the basic section of the conventional surface acoustic wave filter, as shown in this figure, a surface acoustic wave resonator 63 is connected to the parallel arm 61 and a surface acoustic wave resonator 64 is connected to the series arm 62. .

FIG. 10 is a diagram for explaining the operation of a conventional surface acoustic wave filter. FIG. 10A shows frequency dependence of immittance, and FIG. 10B shows frequency dependence of attenuation. The horizontal axis of this figure shows the frequency, and the vertical axis shows the impedance of the surface acoustic wave resonator 64 of the series arm 62 and the immittance which means the admittance of the surface acoustic wave resonator 63 of the parallel arm 61. In order to simplify the explanation, it is assumed that the surface acoustic wave resonator is a reactance circuit without resistance, and the impedance of the surface acoustic wave resonator 64 of the series arm 62 of FIG.
= Jx, and the admittance of the surface acoustic wave resonator 63 of the parallel arm 61 is Y = jb.

According to the image parameter method, the input voltage in FIG. 9 is V ₁ , the input current is I ₁ , and the output voltage is V ₂ ,
Assuming that the output current is I ₂ , exp (γ) = (V ₁ · I ₁ / V ₂ · I ₂ ) ^1/2 (1) the image transmission amount γ (complex number) defined by , Tanh (γ) = tanh (α + β) = (B / C / A / D) ^1/2 ... (2) is an imaginary number, the two terminals of FIG. The whole pair circuit shows a pass characteristic, and a real number shows an attenuation characteristic.

However, the values of A, B, C and D are: A = 1 B = jx C = jb D = 1-bx (3) Is. Therefore, the expression (2) becomes tanh (γ) = (bx / (bx−1)) ^1/2 (4).

From the equation (4), when 0 <bx <1, that is, when b and x have the same sign and a small value, the entire two-terminal pair circuit in FIG. 9 shows a pass characteristic, and bx <0 or bx>. 1, that is, when b and x have opposite signs, or b
It can be seen that when the x product has a large value, the damping characteristic is exhibited.

The surface acoustic wave resonators 63 and 64 connected to the parallel arm 61 and the series arm 62 of FIG. 9 have double resonance characteristics having a resonance frequency fr and an antiresonance frequency fa. Then, the surface acoustic wave resonators 63 and 64 having such double resonance characteristics are connected to the parallel arm 61 and the series arm 62, and the anti-resonance frequency fap of the surface acoustic wave resonator 63 connected to the parallel arm 61 is set to Surface acoustic wave resonator 64 connected to series arm 62
When the resonance frequency frs is substantially equal to the resonance frequency frs, the bandpass filter characteristic having the center frequency as the center frequency is exhibited.

The reason for this is as shown in the relationship between immittance and frequency in FIG.
In the vicinity of the center frequency of s, the relationship of 0 <bx <1 is satisfied, and therefore the pass band is obtained from the above condition, bx> 1 in the frequency region slightly away from the center frequency, and bx <0 in the region far away from the center frequency. , And both are in the attenuation range.

Therefore, the surface acoustic wave filter shown in FIG. 9 has a filter characteristic as shown in FIG. The frp shown in this figure is the parallel arm 61.
Is the resonance frequency of the surface acoustic wave resonator 63, and fas is the anti-resonance frequency of the surface acoustic wave resonator 64 connected to the series arm 62. Further, fc described in the frequency on the horizontal axis is the center frequency.

In addition to the surface acoustic wave filter described above,
As a surface acoustic wave filter of a resonator type, a double mode type filter design method is known (Technical Research Report of Institute of Electronics, Information and Communication Engineers, May 28, 1992, US92-8,
pp 7-14).

[0015]

The above-mentioned conventionally proposed filter in which the surface acoustic wave resonators are connected in a ladder type and the dual mode type filter have the following limitations.

The bandwidth has a limit determined by the electric coupling coefficient of the crystal. This band can be expanded a little, but if it does so, the input standing wave ratio (VSW
R) becomes worse.

There is a limit to the Q of the wideband resonator having a large electromechanical coupling coefficient, and the squareness ratio (S =
Bandwidth / frequency difference between the innermost attenuation poles outside the band S
It is difficult to bring the “Hap Factor” close to 1, and it is difficult to realize a steep cutoff characteristic. On the other hand, quartz or the like, which is a material having a high Q, has a small electromechanical junction coefficient, and thus cannot be used for a wide band with the conventional filter configuration.

A wide band filter having a large electromechanical coupling coefficient has a large temperature coefficient (30 to 80 ppm / ° C.), and there is a problem that the frequency greatly shifts when the operating temperature range is widened.

According to the present invention, the bandwidth can be freely set, and the squareness ratio can be increased without narrowing the bandwidth.
It is an object of the present invention to provide a high performance and small surface acoustic wave filter having a temperature coefficient of substantially 0 ppm / ° C.

[0020]

Elastic surface according to the invention
In the wave filter, different anti-resonance frequencies f_a1, F _a2
At least two surface acoustic wave resonators with
Connect one inductor to the series arm of a two terminal pair ladder circuit
Then, the anti-resonance frequency f of the surface acoustic wave resonator of the series arm is_a1，
f_a2Frequency f between_pParallel resonator that causes parallel resonance at
Adopted a configuration connected to parallel arms.

In this case, the parallel arms of the parallel arms can be made into a resonator which can be miniaturized and has a high Q and which confines electromagnetic waves for resonance. Further, the parallel resonator of the parallel arm can be formed by forming it in the lower part of the package that encloses the surface acoustic wave resonator of the series arm via the metal film for grounding. Further, the surface acoustic wave resonator of the series arm can be formed on the quartz plate.

Further, in this case, the inductor connected to the series arm is formed by a thin wire, and a plurality of wires for adjusting the inductance value are provided between the package and the chip forming the surface acoustic wave resonator. Can be connected.

In this case, the electrodes on the input side or the output side of the chip forming the surface acoustic wave resonator of the series arm are formed by a plurality of electrode portions which are insulated from each other, and at least one of them is a surface acoustic wave. The electrode on the package side is connected to the resonator, and the electrode on the package side is also formed by a plurality of electrodes insulated from each other. At least one of the electrodes is connected to the signal line of the package, and the electrode on the chip side and the electrode on the package side are connected. The wires can be alternately connected to obtain the desired inductance.

[0024]

FIG. 1 is an explanatory view of the structure of a filter using the surface acoustic wave resonator of the present invention. This figure shows an equivalent circuit of a basic section of a filter using the surface acoustic wave resonator of the present invention. In this figure, 1 is a parallel arm, 2 is a series arm,
3 is a parallel resonator, 3 ₁ is an inductor, 3 ₂ is a capacitor, 4 is a first surface acoustic wave resonator, 5 is a second surface acoustic wave resonator, and 6 is a series inductor.

The filter using the surface acoustic wave resonator of the present invention is a two-terminal pair ladder type circuit, and the parallel arm 1 on the input side thereof.
Is connected to a parallel resonator (R _p ) 3 having an inductor 3 ₁ and a capacitor 3 ₂ and having a parallel resonance frequency fp, and the series arm 2 has a first surface acoustic wave having an anti-resonance frequency f _a1. Resonator (R _s1 ) 4, second surface acoustic wave resonator (R _s2 ) 5 having anti-resonance frequency f _a2 , inductance L
Is connected to the series inductor (L) 6.

2A and 2B are operation explanatory views of a filter using the surface acoustic wave resonator of the present invention. FIG. 2A shows frequency dependence of immittance, and FIG. 2B shows frequency dependence of attenuation. . The horizontal axis of this figure shows the frequency, and the vertical axis shows the impedance jx of the series arm circuit and the immittance that means the admittance jb of the parallel arm circuit. To simplify the explanation, it is assumed that the surface acoustic wave resonator is a reactance circuit without a resistance component and the parallel resonator is a pure reactance.

The operation of the filter using the surface acoustic wave resonator of the present invention shown in FIG. 1 will be examined by the image parameter method like the filter using the surface acoustic wave resonator of the conventional example. The reason why the impedance characteristic of the series arm circuit becomes as shown in FIG. 2A will be described.

FIG. 3 is an explanatory diagram of impedance characteristics of the series arm circuit. (A) shows frequency dependence of impedance of individual circuit elements, and (B) shows frequency dependence of impedance obtained by adding individual circuit elements. Shows.

As shown in FIG. 3A showing the frequency dependence of the impedance of each circuit element, the first surface acoustic wave resonator R _s1 and the second surface acoustic wave connected to the series arm are connected. The resonator R _s2 exhibits double resonance characteristics and has resonance frequencies f _r1 and f _r2 and antiresonance frequencies f _a1 and f _a2 , respectively. The inductance of the series inductor L is ω
It is represented by L and increases as the frequency increases.

Further, the first surface acoustic wave resonator R _s1 and the second surface acoustic wave resonator R _s1
3B in which the impedances of the surface acoustic wave resonator R _s2 and the series inductor L are added, as a result of adding them, the resonance frequency f _{r2 of} the second surface acoustic wave resonator R _s2 becomes It moves to the low frequency side and comes to be located at an intermediate position f _c between f _a1 and f _a2 . This FIG. 3 (B) corresponds to FIG.
The frequency dependence of the impedance of the series circuit of (A) is shown.

Further, as shown in FIG.
Resonant frequency f of parallel arm circuit_pF _cAlmost matches
To design. The parallel arm circuit is a normal parallel resonator
Therefore, its admittance characteristic is
As described above, the straight line increases.

Assuming that the impedance of the series arm circuit of FIG. 1 is Z = jx and the admittance of the parallel arm circuit is Y = jb, the above-mentioned Japanese Patent Application No. 3-281694 and Japanese Patent Application No. 4-169494.
According to the image parameter method described in Japanese Patent No. 32270-3, when 0 <bx <1, that is, when b and x have the same sign and a small value, the entire two-terminal pair circuit in FIG. 1 exhibits pass characteristics. , Bx <0 or bx> 1, that is, when b and x have opposite signs, or when the bx product has a large value, the attenuation characteristic is exhibited.

When this is applied to the case of FIG. 2, 0 <bx <1 becomes a pass band in the vicinity of the frequency f _c , and bx> 1 or bx <0 in the frequency region outside thereof.
Becomes the attenuation range. As a result, as shown in FIG. 2B, the band pass characteristic centered on the frequency f _c is exhibited.

In such a surface acoustic wave filter of the present invention, the bandwidth is determined by the difference between the resonance frequencies of the two surface acoustic wave resonators in the series arm, and therefore the above-mentioned Japanese Patent Application No. 3-281.
Unlike the surface acoustic wave filter of the conventional configuration described in Japanese Patent No. 694 and Japanese Patent Application No. 4-32270, it is not determined by the value of the electromechanical junction coefficient of the surface acoustic wave resonator. Therefore, if the Q of the surface acoustic wave resonator is large to some extent, there is almost no design constraint on the bandwidth in principle. Further, if the Q of the surface acoustic wave resonator is large, the squareness ratio of the pass band approaches 1, and steep characteristics can be realized.

At this time, in the surface acoustic wave filter having the conventional structure, the bandwidth tends to be narrowed when Q is increased.
The surface acoustic wave filter having the configuration of the present invention does not have this problem. Therefore, according to the surface acoustic wave filter having the structure of the present invention, it is possible to realize a filter characteristic having a wide bandwidth and a steep squareness ratio.

[0036]

EXAMPLES Examples of the present invention will be described below. In describing the embodiments, the ET, which is the specification of British automobiles and mobile phones, is used as the specification of a filter that requires the widest bandwidth and steep squareness ratio that are currently in practical use.
A specific example is a method of selecting the ACS and realizing the reception (Rx) filter thereof.

FIG. 4 is an equivalent circuit diagram of a surface acoustic wave filter according to an embodiment of the present invention. In this figure, 11 is a parallel arm, 12 is a series arm, 13 is a first parallel resonator, and 13 ₁
Is a capacitor, 13 ₂ is an inductor, 14 is a first surface acoustic wave resonator, 15 is a second surface acoustic wave resonator, 16 is a series inductor, 17 is a second parallel resonator, 17 ₁ is a capacitor, 17 ₂ is an inductor.

In the surface acoustic wave filter of this embodiment,
Is the resonance frequency f on the series arm 12. _r1= 910 MHz,
Anti-resonance frequency f_a1= 1st elasticity table with = 911 MHz
Surface wave resonator R_s114 and the resonance frequency f_r2= 955MH
z, anti-resonance frequency f_a2= 2nd bullet with 956MHz
Surface acoustic wave resonator R_s215 and bonding wire
Series inductor L₁12 and series inductor L₂16
Are connected.

The parallel arm 11 has a capacitor 13 ₁
The first parallel resonator R _p1 13 _composed of the inductor 13 ₂ and the resonance frequency f _p1 and the second parallel resonator R _p2 17 _{composed of} the capacitor 17 ₁ and the inductor 17 ₂ and having the resonance frequency f _p2 are input. Side and output side are connected.

FIG. 5 is a structural explanatory view of a parallel resonator of parallel arms of a surface acoustic wave filter according to an embodiment of the present invention.
(A) is an equivalent circuit, (B) is a first form, (C) is a second form.
Shows the form of.

In this figure, the reference numerals of the equivalent circuits of the parallel arms of the parallel arms of (A) are the same as those of FIG. 4, and in the first form of (B) and the second form of (C), 21 Is a dielectric substrate, 22 is a conductor film, 22 ₁ is a horizontal portion of the conductor film, 22
₂ is a vertical portion of the conductor film, 23 is a dielectric, 24 is a central conductor, and 25 is an outer conductor film.

In the parallel resonator of the first embodiment, FIG.
In order to realize the equivalent circuit of the parallel resonator shown in FIG.
As shown in (B), on the dielectric substrate 21,
A configuration is adopted in which the conductor film 22 is formed of the horizontal portion 22 ₁ of the conductor film and the vertical portion 22 ₂ of the conductor film. Qualitatively speaking, a capacitance is provided between the horizontal portions 22 ₁ of the upper and lower conductor films, and an inductance is provided by the vertical portions 22 _{2 of the} conductor film.

In the parallel resonator of the second embodiment, FIG.
In order to realize the equivalent circuit of the parallel resonator shown in FIG.
As shown in (C), a central conductor 24 is formed along a central axis of a columnar dielectric 23 having a square or rectangular cross section, and an outer conductor film 25 is formed outside the dielectric 23. The formed structure is adopted.

This is a short-circuit type coaxial resonator having an electric length of ¼ wavelength, and its resonance frequency f _p is determined by the length of the resonator, and its length d is d = 3 × 10 ¹⁰ / 4f _p ε
It becomes ^1/2 (cm). Here, ε is the relative permittivity of the dielectric, and the larger this value is, the smaller the resonator can be formed. Further, f _p is a resonance frequency. The surface acoustic wave filter of one embodiment of the present invention described later uses the parallel resonator of the second aspect.

Currently, Ba has a small temperature coefficient.
Ceramics using Ti ₂ O ₃ is often used. In this case, ε is 98, so f _p (= f _c ) = 934 M
In Hz, the dielectric length is 8 mm.

6A and 6B are structural explanatory views of a surface acoustic wave filter according to an embodiment of the present invention. FIG. 6A shows a disassembled state and FIG. 6B shows an assembled state. In this figure, I is the first dielectric member, II is the second dielectric member, III is the third dielectric member, IV is the fourth dielectric member, V is the metallic lid, and VI is elastic. Surface wave resonator chip,
31 is a through hole, 32 is a metal layer, 33 is a through hole, 34 is an input side conductor wiring layer, 35 is an output side conductor wiring layer, 36, 37, 38 and 39 are bonding pads,
Reference numerals 40, 44 and 45 are conductor layers, and 41, 42 and 43 are conductor wiring layers.

The constituent members of the surface acoustic wave filter of one embodiment of the present invention will be described with reference to FIG. 6 (A).

The first dielectric member I is a rectangular frame-shaped member formed of a dielectric material having a dielectric constant ε ₁ and a height of h ₁ , and through holes 31 are formed at its four corners. . Then, a metal layer 32 for adhering the metallic lid V is formed on the upper surface of the frame-shaped member.

Second Dielectric Member II A rectangular frame-shaped member formed of a dielectric having a dielectric constant ε _{1 and having} a frame width wider than that of the first dielectric member I having a height of h ₂ . Through holes 33 are formed at the four corners.
The input side conductor wiring layer 34, the output side conductor wiring layer 35, and the bonding pads 36, 37, 38, 39 are formed on the upper surface of the wide frame-shaped member.

Third Dielectric Member III A rectangular plate-shaped member formed of a dielectric having a dielectric constant ε ₂ and having a height of h ₃ , and a conductor serving as a ground conductor on the upper surface and the side surface in the long side direction. The layer 40 is formed. A conductor wiring layer 41 is formed on the side surface in the short side direction.

Fourth dielectric member IV is a rectangular plate member formed of a dielectric material having a dielectric constant ε ₂ and having a height of h ₄ , and the upper surface thereof has the first parallel resonator R on the input side.
A conductor wiring layer 42 serving as the center conductor of _{p1 and} a conductor wiring layer 43 serving as the center conductor of the second parallel resonator R _p2 on the output side are formed, and conductor wiring layers 44 and 45 serving as outer conductors are formed on the side surfaces.
Are formed.

VI is a surface acoustic wave resonator chip connected to the series arm of a two-terminal pair type surface acoustic wave filter, and has a high Q and an ST-cut quartz plate with a small frequency temperature dependence (the propagation direction is Al on the surface (direction perpendicular to the X direction)
A comb-shaped electrode is formed of a system alloy to form a first surface acoustic wave resonator R _s1 and a second surface acoustic wave resonator R _s2 , and together with an input electrode and an output electrode, as described later with reference to FIG. Bonding pads are formed. The first
Of the dielectric member I, the second dielectric member II, the third dielectric member III, and the fourth dielectric member IV are the same, and the length d in the long side direction is d = λ _p / 4 Is. However, this λ _p is the resonance wavelength.

FIG. 6B shows a state in which the constituent members of the surface acoustic wave filter described with reference to FIG. 6A are assembled. The first dielectric member I, the second dielectric member II, the third dielectric member III, and the fourth dielectric member IV, which are described above, are laminated, and the first dielectric member I and the second dielectric member IV are stacked. The third dielectric member III is passed through the opening in the frame of the body member II.
On the upper surface of the conductor layer 40 of the surface acoustic wave resonator chip V
By applying heat treatment while I is placed,
The dielectric member I, the second dielectric member II, the third dielectric member III, and the fourth dielectric member IV, and the conductor layer 40 on the upper surface of the third dielectric member III.
The surface acoustic wave resonator chip VI is fixed on the upper surface. Also,
A conductor is filled in the through holes 31 and 33 to connect the metal layer 32 and the conductor layer 40.

Then, the input side conductor wiring layer 34 and the output side conductor wiring layer 35 formed on the wide frame of the second dielectric member II, and the input electrode of the surface acoustic wave resonator chip VI. The output electrodes are connected by a bonding wire.

At this time, in order to obtain the inductance required to form the inductor connected to the series arm, the input side conductor wiring layer 34 of the second dielectric member II and the surface acoustic wave resonator chip VI are formed. The input electrode or the output-side conductor wiring layer 35 of the second dielectric member II and the output electrode of the surface acoustic wave resonator chip VI are not directly connected by a bonding wire, but the second dielectric member II is not connected. After the bonding pads 36, 37, 38, 39 of No. 3 and the bonding pads of the surface acoustic wave resonator chip VI are connected to each other in a zigzag shape by a bonding wire as many times as necessary, the input side conductivity of the second dielectric member II. The body wiring layer 34 and the input electrode of the surface acoustic wave resonator chip VI, or the output side conductor wiring layer 35 of the second dielectric member II and the surface acoustic wave resonator chip V. It can be connected between the output electrode. Finally, it is sealed with a metal lid V having a thickness of 0.2 mm.

For example, h ₁ = 0.5 mm, h ₂ = 0.3
When mm, h ₃ = 1 mm, h ₄ = 1 mm, the total thickness including the lid is about 3 mm, the short side s is 3 mm, and the long side d (= λ _p / 4) is 8 mm, which is small. Can be converted. Note that ε ₁ = ε ₂ = 98.

FIG. 7 is an explanatory view of a resonance chip of a surface acoustic wave filter according to an embodiment of the present invention and a connecting method thereof. In this figure, II is a second dielectric member, VI is a surface acoustic wave resonator chip, 34 is an input side conductor wiring layer, 35 is an output side conductor wiring layer, and 36, 37, 38, 39 are bonding pads. , 51 is an input electrode, 52 is an output electrode, 5
3, 54, 55 and 56 are bonding pads, and w is a bonding wire.

In this embodiment, the first surface acoustic wave resonator Rs ₁ has 240 pairs, the aperture length is 320 μm and the period is 5.11 μm, and the second surface acoustic wave resonator R _s2 is
The logarithm and the aperture length are the same as those of the first surface acoustic wave resonator R _s1 ,
Only the period is shortened to 4.87 μm. As a result, the two surface acoustic wave resonators have different resonance frequencies and antiresonance frequencies.

As shown in this figure, the surface of an ST-cut quartz plate (propagation direction is a direction perpendicular to the X direction) having a size of about 3 mm × 1 mm and a thickness of 0.3 mm is made of Al alloy. A comb-shaped electrode is formed to form a first surface acoustic wave resonator R _s1 and a second surface acoustic wave resonator R _s2 in parallel, and the opposite sides are connected by a conductor wiring layer 51. An input electrode 52 and an output electrode 53 are provided on the outer side of the bonding pad 5 on the input side and the output side.
4, 55, 56 and 57 are formed.

In addition to the input side conductor wiring layer 34 and the output side conductor wiring layer 35, the second dielectric member II has bonding pads 36, 37, as well as the surface acoustic wave resonator chip VI. 38 and 39 are formed. In this embodiment, the input side conductor wiring layer 34 of the second dielectric member II is used.
And the inductance L ₁ between the input electrode 52 of the surface acoustic wave resonator chip VI, the output side conductor wiring layer 35 of the second dielectric member II, and the output electrode 53 of the surface acoustic wave resonator chip VI. The inductance L ₂ of both is 2.5n
H.

Then, the inductance L ₁ and the inductance L ₂ are realized by a bonding wire. 25
Since the bonding wire of Al of μmφ is about 0.5 nH in the length of 1 mm, 5 mm of this bonding wire is used.
Books and zigzags were connected in series.

As for the connection method, as shown in FIG. 7, for the input side, the input side conductor wiring layer 34 → bonding pad 55 → bonding pad 36 → bonding pad 54 → bonding pad 37 → input electrode 5
2 and zigzag connection with a bonding wire w. If one side of the zigzag of the bonding wire w is about 1 mm, the total length is 5 mm, and an inductance of 2.5 nH can be realized as L ₁ .

Also on the output side, the output-side conductor wiring layer 35
→ bonding pad 57 → bonding pad 38 →
By connecting the bonding pad 56 → bonding pad 39 → output electrode 53 in a zigzag manner with the bonding wire w, an inductance of 2.5 nH can be realized as L ₂ . In addition, R _s11 , R _s12 , R _s21 , and R _s22 shown in this figure improve the conversion efficiency,
It is a reflector for adjusting the ripple of the frequency characteristic of the attenuation amount.

By adopting the above configuration, L₁+ L
₂Can be set to 5 nH, and the
In the impedance characteristic of the vibration circuit, the resonance frequency f_c
F _a1And f_a2I was able to move to the middle of. In particular,
f_a1= 911 MHz, f_a2= 956 MHz, f_c= 9
It became 34 MHz.

Further, the first parallel resonator and the second parallel resonator of the parallel arms of the two-terminal pair type surface acoustic wave filter shown in FIG. 4 are mounted, and the surface acoustic wave resonator is mounted as shown in FIG. It was realized as a structure in which a coaxial resonator using a dielectric was built in the lower part of the package.

That is, as shown in this figure, the third
The third dielectric member III and the fourth dielectric member IV are dielectric resonators, and the surroundings are covered with the grounded outer conductor composed of the conductor layers 40, 44, 45, and the third dielectric member III.
In the fourth dielectric member IV, the conductor wiring layers 42 and 43 serving as the conductors for the coaxial line of the first parallel resonator R _p1 on the input side and the second parallel resonator R _p2 on the output side are made of copper. , Tungsten, etc. are formed by screen printing.

FIG. 8 is a characteristic diagram of a surface acoustic wave filter according to an embodiment of the present invention. In this figure, the horizontal axis represents frequency and the vertical axis represents attenuation. In this figure, 36
The characteristics of the conventional Rx filter for E-TACS formed on the Y-cut X-propagation LiTiO ₃ are shown by broken lines for comparison. The characteristic of the surface acoustic wave filter of one embodiment of the present invention is shown by the solid line, but the squareness ratio becomes steeper than that of the conventional filter, and the bandwidth capable of securing low loss can be widened. It shows that.

In this embodiment, since the bandwidth is determined by the difference between the resonance frequencies of the two surface acoustic wave resonators as described above, only the design of the period of the interdigital electrodes of the individual surface acoustic wave resonators is required. Can be set freely. In addition, the temperature coefficient also reflects the temperature characteristics of the crystal, and the conventional filter has 3
The surface acoustic wave filter according to one embodiment of the present invention has a significant improvement of 1 ppm / ° C or less, while it is 2 ppm / ° C.

As described above, in the E-TACS Rx filter specification, the loss is 3d in the band of 917 MHz to 950 MHz.
Below B, the out-of-band suppression is required to be 30 dB or more at 905 MHz and 962 MHz, but this is realized by the filter of the present invention, and the frequency shift due to temperature does not occur.

Although two surface acoustic wave resonators are connected to the series arm of the two-terminal pair ladder type circuit in the above embodiment, three or more surface acoustic wave resonators are used to adjust the pass band. It is also possible to connect a resonator. The inductors connected to the series arms can be integrated into one piece or can be formed in a dispersed manner at a plurality of locations.

[0071]

As described above, according to the present invention,
Since the bandwidth is determined by the difference between the anti-resonance frequencies of the two surface acoustic wave resonators, the width can be freely designed. If a surface acoustic wave resonator having a high Q such as crystal is used, a filter having a large squareness ratio can be designed without sacrificing the bandwidth. Further, the temperature coefficient can be set to almost 0 ppm / ° C. by using crystal, and a high-performance and small-sized filter can be realized.

[Brief description of drawings]

FIG. 1 is a structural explanatory view of a filter using a surface acoustic wave resonator of the present invention.

FIG. 2 is an operation explanatory view of a filter using the surface acoustic wave resonator of the present invention, (A) shows frequency dependence of immittance, and (B) shows frequency dependence of attenuation amount.

FIG. 3 is an explanatory diagram of impedance characteristics of a series arm circuit,
(A) is the impedance characteristic of each circuit element, (B)
Indicates the impedance characteristic obtained by adding the individual circuit elements.

FIG. 4 is an equivalent circuit diagram of a surface acoustic wave filter according to an embodiment of the present invention.

5A and 5B are configuration explanatory views of a parallel resonator of parallel arms of a surface acoustic wave filter according to an embodiment of the present invention, where FIG. 5A is an equivalent circuit, FIG. 5B is a first mode, and FIG. 2 is shown.

6A and 6B are configuration explanatory views of a surface acoustic wave filter according to an embodiment of the present invention, in which FIG. 6A shows a disassembled state and FIG. 6B shows an assembled state.

FIG. 7 is an explanatory diagram of a resonance chip of the surface acoustic wave filter of the embodiment of the present invention and a connecting method thereof.

FIG. 8 is a characteristic diagram of a surface acoustic wave filter according to an embodiment of the present invention.

FIG. 9 is a diagram illustrating the principle of a conventional surface acoustic wave filter.

10A and 10B are operation explanatory views of a conventional surface acoustic wave filter, FIG. 10A shows frequency dependence of immittance, and FIG. 10B shows frequency dependence of attenuation amount.

[Explanation of symbols]

1 parallel arm 2 series arm 3 parallel resonator 3 ₁ inductor 3 ₂ capacitor 4 first surface acoustic wave resonator 5 second surface acoustic wave resonator 6 inductor 11 parallel arm 12 series arm 13 first parallel resonator 13 ₁ Capacitor 13 ₂ Inductor 14 First Surface Acoustic Wave Resonator 15 Second Surface Acoustic Wave Resonator 16 Series Inductor 17 Second Parallel Resonator 17 ₁ Capacitor 17 ₂ Inductor 21 Dielectric Substrate 22 Conductive Film 22 ₁ Conductive Horizontal part of body film 22 ₂ Vertical part of conductor film 23 Dielectric 24 Center conductor 25 External conductor film 31 Through hole 32 Metal layer 33 Through hole 34 Input side conductor wiring layer 35 Output side conductor wiring layer 36, 37 , 38, 39 Bonding pads 40, 44, 45 Conductor layer 41, 42, 43 Conductor wiring layer 51 Input electrode 52 Output electrode 53, 5 , 55, 56 Bonding pad I First dielectric member II Second dielectric member III Third dielectric member IV Fourth dielectric member V Metal lid VI VI surface acoustic wave resonator chip w Bonding wire 61 Parallel arm 62 Series arm 63,64 Surface acoustic wave resonator

Front page continuation (72) Inventor Toshihiro Nishihara 1015 Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa, Fujitsu Limited (72) Inventor Mitsuo Takamatsu 1015 Kamedota, Nakahara-ku, Kawasaki, Kanagawa Prefecture, Fujitsu Limited

Claims (6)

[Claims] 1. At least two surface acoustic wave resonators having different antiresonance frequencies f _a1 and f _a2 and at least one inductor are connected to a series arm of a two-terminal pair ladder type circuit, and the elasticity of the series arm is connected. A surface acoustic wave filter comprising a parallel arm connected to a parallel arm that causes parallel resonance at a frequency f _p between the anti-resonance frequencies f _a1 and f _a2 of the surface wave resonator. 2. The surface acoustic wave filter according to claim 1, wherein the parallel resonator of the parallel arms is a resonator having a structure for confining and resonating electromagnetic waves. 3. The parallel resonator of the parallel arm is built in a lower portion of a package that encloses the surface acoustic wave resonator of the series arm via a metal film for grounding. The surface acoustic wave filter described in 1. 4. A surface acoustic wave resonator of a series arm is formed on a quartz plate.
The surface acoustic wave filter according to any one of items 1 to 7. 5. The inductor connected to the series arm is formed by a thin wire, and the package and the chip forming the surface acoustic wave resonator are connected by a plurality of wires for adjusting the inductance value. The surface acoustic wave filter according to claim 1, wherein the surface acoustic wave filter is provided. 6. A chip forming a surface acoustic wave resonator of a series arm comprises a plurality of electrode portions on an input side or an output side which are insulated from each other, and at least one of them is a surface acoustic wave resonator. The electrode on the package side is also composed of a plurality of electrodes insulated from each other, and at least one of the electrodes is connected to the signal line of the package. The surface acoustic wave filter according to claim 5, wherein wires are alternately connected to the electrodes.