JPH07231242A - Surface acoustic wave filter, branching filter and mobile radio equipment - Google Patents

Abstract

PURPOSE:To attain miniaturization and light weight by using part of a frequency band causing an inductive impedance for a pass band of the filter. CONSTITUTION:A surface acoustic wave resonator 4 and an inductive element pattern 9 are connected in series, one terminal connects to ground and a surface acoustic wave resonator 6 and a wire 10-3 used for the inductive element pattern are connected in series and one terminal connects to ground. Since the resonators 2-6 in use are arranged in this order from an input terminal, the length of the wire used for connecting the resonators 5 is reduced and then deterioration in a pass band insert loss attending a shift of the resonance frequency of the resonators 5 is reduced. Since part of the frequency band where the impedance is inductive is used for the pass band of the filter, the two surface acoustic wave resonators whose one-side terminal connects to ground are inductive for the pass band and the other side terminals of them are connected by a capacitive element to obtain a high pass filter in terms of an equivalent circuit. Thus, the surface acoustic wave filter in which the insertion loss for the pass band is small and the attenuation for the black band is high is formed in this way. A small branching filter easily realized and a subminiatured mobile radio equipment is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface wave filter formed on a piezoelectric substrate, a duplexer for a mobile radio device, and a mobile radio device.

[0002]

2. Description of the Related Art In a conventional surface wave filter, for example, as disclosed in Japanese Patent Application Laid-Open No. 63-132515, surface wave resonators are all capacitively coupled and arranged in the lateral direction. Further, as disclosed in, for example, Japanese Patent Laid-Open No. 61-22051, surface acoustic wave resonators are all connected in series. Further, as disclosed in, for example, Japanese Patent Laid-Open No. 3-205908, a method of combining various piezoelectric substrates is known.

A conventional duplexer is disclosed in, for example, Japanese Patent Laid-Open No. 62-17.
As shown in Japanese Patent No. 1327, each filter is combined with each circuit. Furthermore, Japanese Patent Application No. 4-21120
As disclosed in Japanese Unexamined Patent Publication (Kokai) No. 1, a comb-shaped electrode formed on a piezoelectric substrate, or a surface-wave filter formed by combining a comb-shaped electrode and a one-terminal pair surface-wave resonator composed of a reflector, At least two surface acoustic wave resonators whose terminals are connected to the ground side are used, and the other terminals of these two surface acoustic wave resonators are connected by a capacitive element. The resonance frequency is set to a higher frequency side including the pass band of the surface wave filter. Further, instead of connecting the other terminals of the two surface wave resonators with a capacitive element, connection is performed using a surface wave resonator whose resonance frequency is set to a higher frequency side than the pass band of the surface wave filter, At least one of the two surface acoustic wave resonators is grounded via an inductive element. The above surface wave filter and one terminal are grounded, and at least one surface wave resonator having a resonance frequency and an antiresonance frequency set outside the pass band of the surface wave filter is used, and these are inductively coupled,
The inductor used for this inductive coupling is formed on the same piezoelectric substrate.

[0004]

SUMMARY OF THE INVENTION The above-mentioned prior art has been proposed in the prior art because of the insertion loss of the pass band and the attenuation of the stop band due to the elastic and acoustic coupling between the surface acoustic wave resonators and the ground capacitance of the interdigital transducer. There was a problem in that. In addition, because the settings such as the resonance frequency of each surface acoustic wave resonator are not optimized, parts with a large shape are required to match the external circuit,
The number was not small. In addition, there is a problem that the size of the duplexer becomes large because surface acoustic wave filters having greatly different configurations are combined.

Further, in Japanese Patent Application No. 4-211201, it is possible to solve the above-mentioned problems of the prior art and to realize a compact surface wave filter having a small insertion loss in the pass band and a large attenuation in the stop band. It is possible, but in order to obtain the required inductor value, the filter characteristics change due to the arrangement of the surface acoustic wave resonators that are configured and the inductor used for inductive coupling is formed on the same piezoelectric substrate as the surface acoustic wave resonator. In addition, the area occupied by the inductor becomes large, which causes an increase in chip size. In addition, there is a problem of deterioration of insertion loss in the pass band due to an increase in the dielectric constant of the piezoelectric substrate and the resistance component of the formed inductor. An object of the present invention is to solve the above-mentioned problems of the prior art, to realize a small surface wave filter with a small insertion loss in the pass band and a large attenuation amount in the stop band, and to configure a small duplexer. It is to realize a small and lightweight mobile wireless device.

[0006]

In a surface wave filter formed by combing a comb-shaped electrode formed on a piezoelectric substrate or a comb-shaped electrode and a one-terminal-pair surface wave resonator composed of a reflector, the input of the filter is used. A first surface wave resonator that is inductively coupled to the terminal and has one terminal of the interdigital transducer grounded, and a first surface wave resonator that is inductively coupled to the first surface wave resonator and has the other terminal of the interdigital transducer grounded. The second surface acoustic wave resonator is inductively coupled to the second surface acoustic wave resonator, and the other terminal of the interdigital transducer is connected to the third surface acoustic wave resonator via an inductive element or directly grounded, Of the third surface wave resonator, the fourth surface wave resonator connected to the terminal inductively coupled to the second surface wave resonator, and the fourth surface wave resonator connected to the output terminal of the filter. It is connected to the other terminal and the other terminal of the interdigital transducer is an inductor. Through the first surface acoustic wave resonator, or the fifth surface acoustic wave resonator grounded directly, in the order of the first, second, third, fourth and fifth surface acoustic wave resonators, or the first, third, fourth , The surface acoustic wave propagation paths of the surface acoustic wave resonators are parallel to each other in the order of the fifth and second surface acoustic wave resonators or in the order of the first, fifth, fourth, third and second surface acoustic wave resonators. So that the spiral coil is wound in the same direction as the inductive element or other inductive element for inductive coupling, using a spiral coil created on a different substrate from the surface wave resonator. To do. Further, a bonding wire for connecting the spiral coil and each surface acoustic wave resonator and a bonding wire for grounding the spiral coil are arranged in a direction in which the number of turns of the spiral coil increases. Further, a duplexer was constructed using the surface wave filter described above. In addition, a mobile wireless device is configured using the above-described duplexer.

[0007]

The impedance of the surface acoustic wave resonator is capacitive below the resonance frequency and above the anti-resonance frequency, and inductive between the resonance frequency and the anti-resonance frequency. In the present invention, a part of the inductive frequency band is used as the pass band of the filter. Therefore, in the pass band, the two surface wave resonators, one terminal of which is connected to the ground side, are inductive, and by connecting these other terminals with a capacitive element, an equivalent circuit becomes a high-pass filter. . Further, since the stop band is formed in the vicinity of the resonance frequencies of the two surface acoustic wave resonators, a filter having a steep shoulder characteristic can be realized. Also, instead of connecting the other terminals of the two surface wave resonators with a capacitive element, by connecting using a surface wave resonator whose resonance frequency is set to a higher frequency side than the pass band of the surface wave filter, A bandpass filter can be constructed. That is, the impedance of the surface acoustic wave resonator is not capacitive between the resonance frequency and the anti-resonance frequency, so that a stop band is formed.

In addition, one terminal is connected to the ground side 2
It suffices that each surface acoustic wave resonator be inductive in the pass band, and its resonance frequency can be changed by grounding it through an inductive element. That is, the stop band can be set to a desired frequency. Further, by inductively coupling the above surface wave filter and the surface wave resonator whose one terminal is grounded, it is possible to increase the attenuation amount of the stop band formed near the resonance frequency of the surface wave resonator. it can.

In the above filter structure, the length of the wire used for connection can be adjusted by changing the order of arrangement of the constituent surface acoustic wave resonators, and the degree of freedom in filter characteristics is increased. In addition, by using a spiral coil created on a substrate different from the surface wave resonator as an inductive element for inductive coupling and other inductive elements, a large inductor value can be obtained in a small area and As shown in FIG. 13, a bonding wire for connecting each surface acoustic wave resonator and a bonding wire for grounding from the spiral coil are arranged in a direction in which the number of turns of the spiral coil increases, and the spiral coil is wound in the same direction. By doing so, the inductor component of the wire can be effectively utilized, and as shown in FIG. 14, the directions of the current loops of adjacent spiral inductors can be made the same direction, and the magnetic field generated from the spiral inductors can be canceled. ,
With respect to the filter characteristics, it is possible to reduce deterioration of the out-of-band suppression degree particularly in the high frequency range.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIG.

On the piezoelectric substrate 1, surface acoustic wave resonators 2, 3, 4,
Configure 5 and 6. Reference numerals 7, 8 and 9 are spiral coil patterns formed on the alumina substrate of the inductive element, and the spiral coil patterns are arranged in the same winding direction. Surface wave resonators 2, 3 and 6 terminals 2-1 and 3-
1, 6-1 are grounded via wires 10-1, 10-2, 10-3. The terminal 2-2 of the surface acoustic wave resonator 2 is the wire 1
It is connected to the input terminal 11 through 0-4, the inductive element pattern 7, and the wire 10-5, and is used for connection with an external circuit. The terminals 2-2 and 3-2 of the surface acoustic wave resonators 2 and 3 are connected to the wire 10-.
Inductive element patterns 8 are coupled to each other through 6, 10-7. The terminal 3-2 of the surface wave resonator 3 is connected to the terminal 4-2 connecting the surface wave resonators 4 and 5 via the wire 10-8. The terminal 4-1 of the surface acoustic wave resonator 4 is connected to the wire 10
-9, the inductive element pattern 9, and the wire 10-10 are grounded. Terminal 5 for connecting the surface wave resonators 5 and 6
2 is connected to the output terminal 11 via the wire 10-11,
Used to connect to external circuits. Since the wire 10-3 is used as an inductive element, the wire length is long. In addition, the wires 10 connected to the inductive elements 7, 8 and 9 respectively
-4,10-5,10-6,10-7,10-9,10
-10 is connected in a direction in which the number of turns of the spiral coil, which is an inductive element, increases, and the winding directions of the spiral coil are the same.

A block diagram of this embodiment is shown in FIG. That is, the surface acoustic wave resonator 4 and the inductive element pattern 9 are connected in series and one end is grounded. Similarly, the surface wave resonator 6 and the wire 10-3 used as the inductive element pattern
Are connected in series and one end is grounded.

The filter frequency characteristics of the first embodiment of the present invention are as shown in FIGS. The pass band is the range of markers 1 and 2 (810 to 826 MHz), and the stop band is the range of markers 3 and 4 (940 to 956 MHz). Conventionally, the layout of the resonators used is 2, 3, 5, from the input terminal side.
In the present invention, the used resonators are arranged in the order 2, 3, 4, 5, 6 from the input terminal side, so that the wire length connected to the resonator 5 is short. Therefore, deterioration of the pass band insertion loss due to the shift of the resonance frequency of the resonator 5 is reduced. Also, by connecting the connecting wire in the direction in which the number of turns of the spiral coil increases,
Since the inductor component of the wire can be used effectively,
The spiral coil pattern, which is an inductive element, can be made smaller. Further, since the spiral coil patterns are arranged in the same winding direction, the magnetic field generated between the adjacent spiral coils can be canceled, and the out-of-band suppression degree after 1 GHz is improved in the filter frequency characteristic shown in FIG. .

The surface acoustic wave resonator of the present invention uses the interdigital transducer alone as shown in FIG. 5, uses the interdigital electrode and the reflector 13 in combination as shown in FIG. 6, and FIG. There is known one using a weighted interdigital transducer as shown. Further, it is possible to use a series connection of these surface wave resonators or a resonator as shown in Japanese Patent Laid-Open No. 1-157109, but in this embodiment, the surface wave resonance as shown in FIG. 5 is used. I have a child.
An example of impedance characteristics of these surface wave resonators is shown in FIG.
Shown in. It is capacitive at frequencies below the resonance frequency Fs and above the anti-resonance frequency Fa, and inductive between the resonance frequency Fs and the anti-resonance frequency Fa.

In the embodiment of the present invention, the surface acoustic wave resonators 4 and 6 are used.
The pass band of the filter is a part of the frequency band that is inductive due to the impedance characteristic of. In the pass band, each resonance frequency is set so that the impedance characteristics of the surface wave resonators 2, 3, 5 are capacitive. Therefore, the equivalent circuit in the pass band is as shown in FIG. 9, which has good matching with an external circuit having a characteristic impedance of 50 ohms. That is, since the entire filter acts equivalently to the matching circuit in the pass band, the insertion loss is small. Further, if the parasitic impedance due to the package or the like can be ignored, no matching element is required.

The stop band on the frequency side lower than the pass band is
It is formed near the resonance frequency of the surface wave resonators 4 and 6. The resonance frequency of the surface wave resonators 4 and 6 is the same as that of the induction element pattern 9
Also, the degree of freedom in designing the stop band is large because it can be adjusted by the length of the wires 10-3 and 10-10.

The stop band on the higher frequency side than the pass band is
It is formed in a band where the impedance characteristic of the surface wave resonator 5 becomes non-capacitive, that is, between the resonance frequency and the anti-resonance frequency of the surface wave resonator 5 and in the vicinity thereof and in the vicinity of the resonance frequency of the surface wave resonators 2 and 3.

In this embodiment, the terminal 2 of the surface acoustic wave resonators 2 and 3 is used.
Since -1, 3-1 are grounded, the amount of attenuation can be increased,
There is also an advantage that the reflection coefficient and the input impedance seen from the terminal can be increased. Therefore, it is suitable for a duplexer configured by connecting other filters having different pass bands in parallel. Further, by arranging the surface acoustic wave resonators so that the resonance frequencies thereof are slightly shifted, an optimum amount of attenuation can be obtained. The surface wave resonators 2 and 3 become capacitive except near the resonance frequency and the antiresonance frequency, and the spiral coils 7 and 8 of the inductive element,
Since the LC low-pass filter is configured with the wire 10-8 used as the inductive element, the high frequency can be attenuated.

Although many reports have been made on the type of piezoelectric substrate 1 and the surface waves that can be used, SH waves or Love waves on a lithium tantalate substrate or a lithium niobate substrate may be used, for example. Further, since the electrode material of the surface acoustic wave resonator requires power resistance, Al-Ti was used, but other Al-based alloys having excellent power resistance may be used.

Since the electrodes of the surface acoustic wave resonator are as fine as about 1 μm, the RIE (dry etching) technique was used for forming the electrodes.

FIG. 10 shows a second embodiment of the present invention.

The present invention is shown in the first embodiment of the present invention.
Surface acoustic wave resonators 2, 3, 4, 5, formed on the piezoelectric substrate 1.
The arrangement order of 6 is changed to the order of 2, 4, 5, 6, 3. With the above configuration, the terminal 3 of the surface acoustic wave resonator 3
The length of the wire 10-3 used for grounding -1 is shortened, the resonance frequency shift of the surface acoustic wave resonator can be suppressed, and the insertion loss in the pass band is improved.

FIG. 11 shows a third embodiment of the present invention.

The present invention is shown in the first embodiment of the present invention.
Surface acoustic wave resonators 2, 3, 4, 5, formed on the piezoelectric substrate 1.
The arrangement order of 6 is changed to the order of 2, 6, 5, 4, and 3. With the above configuration, the length of the wire 10-3 used for grounding the terminal 3-1 of the surface wave resonator 3 is shortened as in the second embodiment, and the shift of the resonance frequency of the surface wave resonator is suppressed. It is possible to improve the insertion loss in the pass band.

In the embodiment of the present invention, the spiral coils are formed on separate substrates used as inductive elements, but it is needless to say that the spiral coils can be formed on the same substrate to achieve a small size. .

FIG. 12 shows an embodiment of an antenna demultiplexer of a mobile radio system constructed by using the surface wave filter of the present invention. Transmission filter 14 and reception filter 1 of this duplexer
5 uses a surface wave filter, and the transmission filter 14,
Each reception filter 15 is connected to an antenna 17 via a branch circuit 16. A surface wave filter used in a mobile radio system requires power resistance, has a high pass band of 800 to 900 MHz, and has very low loss as filter characteristics and sharp shoulder characteristics. The impedance characteristics of the wave resonator and the inductive element pattern are important factors. Therefore, by using the surface wave filter of the present invention in an antenna duplexer of a mobile radio system, good duplexer characteristics can be realized.

[0027]

As described above, according to the present invention,
It is possible to realize a small surface acoustic wave filter with a small insertion loss in the pass band and a large attenuation in the stop band. Therefore, the applicable range is wide and, for example, a small-sized duplexer can be easily realized.
Also, by using this duplexer, it is possible to realize a very small mobile radio device.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention.

FIG. 2 is a block diagram showing first, second and third embodiments of the present invention.

FIG. 3 is a filter frequency characteristic (narrow band) diagram of the first embodiment of the present invention.

FIG. 4 is a filter frequency characteristic (wide band) diagram of the first embodiment of the present invention.

FIG. 5 is a diagram showing an example of a surface acoustic wave resonator used in an example of the present invention.

FIG. 6 is a diagram showing another example of the surface acoustic wave resonator.

FIG. 7 is a diagram showing another example of the surface acoustic wave resonator.

FIG. 8 is a diagram showing an example of impedance characteristics of a surface acoustic wave resonator used in the present invention.

FIG. 9 is an equivalent circuit diagram in the pass band of the first, second and third embodiments of the present invention.

FIG. 10 is a diagram showing a second embodiment of the present invention.

FIG. 11 is a diagram showing a third embodiment of the present invention.

FIG. 12 is a diagram showing an antenna duplexer of a mobile wireless device using the present invention.

FIG. 13 is a layout view of spiral coils according to an embodiment of the present invention.

FIG. 14 is a magnetic field distribution diagram in the arrangement of spiral coils in the example of the present invention.

[Explanation of symbols]

1 ... Piezoelectric substrate, 2, 3, 4, 5, 6 ... Surface wave resonator, 2
-1,2-2,3-1,3-2,4-1,4-2,5-
2, 6-1 ... Terminal of surface wave resonator, 7, 8, 9 ... Spiral coil, 10-1, 10-2, 10-3, 10-
4, 10-5, 10-6, 10-7, 10-8, 10-
9, 10-10, 10-11 ... Wire, 11 ... Input terminal, 12 ... Output terminal, 13 ... Reflector, 14 ... Transmit filter, 15 ... Receive filter, 16 ... Branch circuit, 17 ... Antenna.

Claims (7)

[Claims] 1. A surface wave filter comprising a comb-shaped electrode formed on a piezoelectric substrate, or a combination of a comb-shaped electrode and a one-terminal-pair surface-wave resonator composed of a reflector. The filter has an input terminal and a comb. One terminal of the electrode electrode is inductively coupled, the other terminal of the interdigital electrode is grounded to the first surface wave resonator, and the first surface wave resonator is inductively coupled,
A second surface acoustic wave resonator having the other terminal of the interdigital transducer grounded and inductively coupled to the second surface acoustic wave resonator, and the other terminal of the interdigital transducer via the inductive element or directly. A grounded third surface wave resonator, and a fourth surface wave resonator connected to a terminal inductively coupled to the second surface wave resonator in the third surface wave resonator, A fifth surface acoustic wave resonator connected to the other terminal of the fourth surface acoustic wave resonator connected to the output terminal of the filter and having one terminal of the interdigital transducer connected to the inductive element or directly grounded. ,
The first, second, third, fourth and fifth surface acoustic wave resonators are arranged in this order on the same substrate so that the surface acoustic wave propagation paths of the respective surface acoustic wave resonators are parallel to each other. Surface wave filter. 2. A surface wave filter comprising a comb-shaped electrode formed on a piezoelectric substrate, or a combination of a comb-shaped electrode and a one-terminal-pair surface-wave resonator composed of a reflector, wherein a filter input terminal and a comb One terminal of the electrode electrode is inductively coupled, the other terminal of the interdigital electrode is grounded to the first surface wave resonator, and the first surface wave resonator is inductively coupled,
A second surface acoustic wave resonator having the other terminal of the interdigital transducer grounded and inductively coupled to the second surface acoustic wave resonator, and the other terminal of the interdigital transducer via the inductive element or directly. A grounded third surface wave resonator, and a fourth surface wave resonator connected to a terminal inductively coupled to the second surface wave resonator in the third surface wave resonator, A fifth surface acoustic wave resonator connected to the other terminal of the fourth surface acoustic wave resonator connected to the output terminal of the filter and having one terminal of the interdigital transducer connected to the inductive element or directly grounded. ,
The first, third, fourth, fifth and second surface acoustic wave resonators are arranged in this order on the same substrate so that the surface acoustic wave propagation paths of the respective surface acoustic wave resonators are parallel to each other. Surface wave filter. 3. A surface wave filter comprising a comb-shaped electrode formed on a piezoelectric substrate, or a combination of a comb-shaped electrode and a one-terminal-pair surface-wave resonator composed of a reflector, wherein an input terminal of the filter and a comb. One terminal of the electrode electrode is inductively coupled, the other terminal of the interdigital electrode is grounded to the first surface wave resonator, and the first surface wave resonator is inductively coupled,
A second surface acoustic wave resonator having the other terminal of the interdigital transducer grounded and inductively coupled to the second surface acoustic wave resonator, and the other terminal of the interdigital transducer via the inductive element or directly. A grounded third surface wave resonator, and a fourth surface wave resonator connected to a terminal inductively coupled to the second surface wave resonator in the third surface wave resonator, A fifth surface acoustic wave resonator connected to the other terminal of the fourth surface acoustic wave resonator connected to the output terminal of the filter and having one terminal of the interdigital transducer connected to the inductive element or directly grounded. ,
The first, fifth, fourth, third and second surface acoustic wave resonators are arranged in this order on the same substrate so that the surface acoustic wave propagation paths of the respective surface acoustic wave resonators are parallel to each other. Surface wave filter. 4. The surface wave filter according to claim 1, claim 2 or claim 3, which is formed on a substrate different from a surface wave resonator as an inductive element for inductive coupling and other inductive elements. A surface acoustic wave filter using a spiral coil and having the same winding direction of the spiral coil. 5. The surface acoustic wave filter according to claim 4,
A surface wave filter, wherein a bonding wire for connecting the spiral coil and each surface wave resonator and a bonding wire for grounding the spiral coil are arranged in a direction in which the number of turns of the spiral coil increases. 6. Claim 1, claim 2, claim 3, claim 4
Alternatively, a duplexer for a mobile radio device, wherein the surface wave filter according to claim 5 is used. 7. A mobile radio apparatus using the duplexer for a mobile radio according to claim 6.