JP3384638B2 - Balanced 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 balanced surface acoustic wave filter used in communication equipment.

[0002]

2. Description of the Related Art In recent years, surface acoustic wave devices have been actively researched for use in filters. In particular, due to recent developments in mobile communication and higher frequencies, surface acoustic wave devices, particularly surface acoustic wave filters, have been actively developed. Conventionally, various methods have been proposed as a method of forming a filter in a high frequency band, particularly several hundreds of MHz by using a surface acoustic wave element. As a typical example thereof, a filter is constructed by using a plurality of surface acoustic wave resonators as disclosed in JP-A-52-19044 and JP-A-5-183380, and JP-A-58-58. A multi-electrode type as shown in Japanese Patent No. 154917, a type in which surface acoustic wave resonators as shown in Japanese Patent Laid-Open No. 3-222512 are installed adjacent to each other, and coupling between the resonators is used. is there.

[0003]

Most of the conventional surface acoustic wave filters are so-called unbalanced filters. Basically, the multi-electrode type filter can be used in a balanced type or an unbalanced type. However, normally, although four terminals are output from the filter, one of the input and output terminals is directly connected and is usually used as a ground terminal, so that only unbalanced signals can be processed. On the other hand, in a high frequency circuit such as an amplifier or a mixer, it is possible to improve the circuit characteristics by using a balanced signal. However, since the filter that is connected to it and is indispensable in the high frequency circuit does not adapt to the balanced circuit, the high frequency circuit in the balanced circuit needs to connect a balanced-unbalanced conversion circuit to the connection part with the filter. there were. As a result, the number of parts is increased and the cost is increased, and it is rarely actually used.

As a prior art reference for a balanced filter, there is a surface acoustic wave device disclosed in Japanese Utility Model Publication No. 58-29627. This uses the above-mentioned multi-electrode filter as a balanced filter, and equips the input and output with the balanced-unbalanced converter. Therefore, as described above, the number of parts is increased, and it is not usually used much. Further, as another example of the balanced filter, an example disclosed in Japanese Patent Laid-Open No. 1-208010 can be mentioned. This connects a surface acoustic wave resonator to a lattice type circuit. However, the resonator is a two-port resonator and has no means for controlling the resonance frequency and the anti-resonance frequency.

In order to solve the above-mentioned problems in the prior art, the present invention provides a balanced surface acoustic wave filter capable of achieving a balanced circuit of a high frequency circuit without connecting a balanced-unbalanced conversion circuit. To aim.

[0006]

To achieve the above object, according to an aspect of, configuration of the balanced type surface acoustic wave filter according to the present invention is to connect the four surface acoustic wave resonators in a symmetrical lattice type, the symmetric lattice Using at least one type circuit, and substantially (a) at least one selected from the lattice arm anti-resonance frequency and the series arm resonance frequency, and (b) the lattice arm resonance frequency and the series arm anti-resonance frequency. Is a balanced surface acoustic wave filter that is almost matched to the above, and as a means for adjusting the resonance frequency of the lattice arm and the series arm, the inductance of the connecting portion connecting the surface acoustic wave resonators of the lattice arm and the series arm are
The impedance of the connecting portion to be connected is different .

[0007]

[0008] In the above configuration of the present invention, as a connection portion of the surface acoustic wave resonators, (a) wiring electrodes on the substrate forming the surface acoustic wave resonator, and (b) an external circuit It is preferable to use at least one selected from the wires used for connection with.

[0009] In the above configuration of the present invention is preferably connected a symmetrical lattice-type circuit 2 stages. Further, in the above configuration of the present invention is preferably connected a symmetrical lattice-type circuit 3 stages.

[0010] In the above configuration of the present invention, among the four surface acoustic wave resonators, the two are arranged in the series arm, that the remaining two are arranged in a lattice arm preferable.

[0011]

SUMMARY OF According to configuration of the present invention, the grating arms and series arms
As a means of adjusting the resonance frequency of the
Inductance of the connection part that connects the surface wave resonator and the series arm
The surface acoustic wave resonator of the series arm and the elastic surface of the parallel arm are made different by changing the impedance of the connecting part
Even if the equivalent capacitance ratio of the wave resonator is changed from 1: 1,
(A) Anti-resonance frequency of lattice arm and resonance frequency of series arm, and
(B) Is the resonance frequency of the lattice arm and the anti-resonance frequency of the series arm?
It is possible to realize a balanced surface acoustic wave filter having at least one selected from the above-mentioned substantially substantially identical properties and having good characteristics. Further, since the high frequency circuit can be made into a balanced circuit without using the balanced-unbalanced conversion circuit,
It is possible to reduce the number of parts and costs .

[0012]

[0013]

[0014]

Further, in the above-described structure of the present invention, according to a preferable example in which the symmetrical lattice type circuits are connected in two stages, there is no portion where the wiring intersects on the substrate, and the wire bonding becomes easy. Further, in this case, a sufficient out-of-band attenuation amount can be obtained as compared with the case of one stage.

According to a preferred example of connecting the symmetrical lattice type circuits in three stages in the configuration of the present invention, it is possible
As in the case of step connection, there is no portion where the wiring intersects on the substrate, and wire bonding becomes easy. Also,
Also in this case, a sufficient out-of-band attenuation amount can be obtained as compared with the case of one stage. In addition, the half-width is smaller than that in the case where two stages are connected.

[0017]

EXAMPLES The present invention will be described in more detail below with reference to examples. <First Embodiment> First, a first embodiment of the present invention will be described. 1 is a configuration diagram showing a first embodiment of a balanced surface acoustic wave filter according to the present invention, and FIG. 2 is an equivalent circuit diagram of the balanced surface acoustic wave filter shown in FIG. The circuits wired as shown in FIG. 2 are collectively called "symmetrical lattice type circuit".

Resonators 101 and 102 were manufactured by using a 36 ° rotation Y-cut X-propagation lithium tantalate (LiTaO ₃ ) substrate as a substrate and aluminum as an electrode. Then, as shown in FIGS. 1 and 2, a balanced surface acoustic wave filter was manufactured by connecting two series arm resonators 101 and two parallel arm resonators 102 in a symmetrical lattice type. . 103, 104 in FIG.
Is a connecting portion connecting the respective resonators, and a wiring electrode on the substrate is used as this connecting portion. Further, in FIGS. 1 and 2, 109 is an inductor, which is connected in series to all the resonators. Also, 10
Reference numerals 5 and 106 are input terminals, and 107 and 108 are output terminals. Since the connection lines of the input terminals 105 intersect on the substrate, they are connected at the time of wire bonding in this embodiment. Of course, semiconductor technology may be used to intersect on the substrate. The number of electrode pairs and the number of reflector pairs of the resonator are determined by the characteristics of the piezoelectric substrate. still,
In this embodiment, both the number of electrode pairs and the number of reflector pairs are about 1.
Although it is preferable that the number of electrodes is 00, the number of electrode pairs and the number of reflectors of the resonator are reduced for the convenience of drawing.

The factors that determine the characteristics of the balanced surface acoustic wave filter configured as described above are the resonance frequency and anti-resonance frequency of each resonator and the equivalent parallel capacitance of each resonator. Here, when the equivalent circuit of the resonator is shown in FIG. 3, 201 is a parallel capacitance, 202 is a series capacitance, and
The parallel capacitance 201 when 203 is a series inductor and 204 is a resonance resistance. In this case, the equivalent capacitance ratio of the resonator 101 of the series arm and the resonator 102 of the parallel arm is about 1: 1, and the anti-resonance frequency of the lattice arm (same as the parallel arm) and the resonance frequency of the series arm are substantially equal to each other. Almost matches.
FIG. 4 shows frequency characteristics of the resonators 101 and 102. As shown in FIG. 4, the resonance frequency of the resonator 102 of the parallel arm is lower than the resonance frequency of the resonator 101 of the series arm.

The above-mentioned balanced surface acoustic wave filter was converted into an unbalanced type using the circuit shown in FIG. 5, and its characteristics were measured. In FIG. 5, 501 is a balun for balanced-unbalanced conversion. The reason why the present balanced type surface acoustic wave filter is converted to the unbalanced type is that the measuring instrument used here is a measuring instrument for measuring an unbalanced circuit. FIG. 6 shows the measurement result. As shown in FIG. 6, it can be seen that a balanced surface acoustic wave filter having good frequency characteristics is realized.

<Second Embodiment> Next, a second embodiment of the present invention will be described. FIG. 7 is a configuration diagram showing a second embodiment of the balanced surface acoustic wave filter according to the present invention.
This is a configuration in which the configuration shown in the first embodiment is connected in two stages, and is implemented when it is difficult to obtain sufficient out-of-band attenuation with one stage. When two-stage connection is made in this way, there are no crossing points on the board,
There is an advantage that wire bonding becomes easy.
Then, in this case, as shown in FIG. 8, a balanced surface acoustic wave filter having a sufficiently high out-of-band attenuation as compared with the case of the first stage of the first embodiment (see FIG. 6) is realized. I was able to.

<Third Embodiment> Next, a third embodiment of the present invention will be described. In the first and second embodiments, since no consideration is given to the wire or wiring electrode connecting the resonator, an inductor component may be inserted in series with the resonator depending on the arrangement or the design of the resonator. Since the size of the inductor differs for each resonator, the resonance frequency may change, which may deteriorate the characteristics of the filter. Looking at the equivalent circuit of the resonator shown in FIG. 3, it can be seen that the inductor 203 connected in series with the resonator changes the resonance frequency. Therefore, the wiring on the substrate was designed and prototyped so that the inductor components connected in series to all the resonators were almost the same. As a result, the anti-resonance frequency of the lattice arm and the resonance frequency of the series arm were almost the same regardless of the design of the resonator, and a balanced surface acoustic wave filter having good characteristics could be realized.

<Fourth Embodiment> Next, a fourth embodiment of the present invention will be described. In the third embodiment, the wiring on the substrate is designed so that the inductor components connected to all the resonators are almost the same, but the resonator 10 of the series arm is designed.
1 and the equivalent capacitance ratio of the resonator 102 in the parallel arm are, for example, 1:
When the ratio was changed from 1 to 2: 1, it was confirmed that the filter characteristics deteriorated, which is also considered to be due to the change in the resonance frequency. This cause is also due to the inductor component, and in the third embodiment, the equivalent parallel capacitance of the resonator was almost the same for both the series arm and the lattice arm, so the same inductor could be used.
When the equivalent parallel capacitance is different, it is necessary to change the value of the inductor for each series arm and lattice arm.

In consideration of this, the equivalent capacitance ratio between the resonator 101 of the series arm and the resonator 102 of the parallel arm is set to 2: 1 [that is, the equivalent parallel capacitance of the resonator is the one having the higher resonance frequency of the resonator]. (The resonator 101 of the series arm is made larger than that of the lower resonator (the resonator 102 of the parallel arm) (see FIG. 4)], and the inductance of the connecting portion connecting the resonators of the lattice arm A balanced surface acoustic wave filter was designed by differentiating the impedance of the connection part connecting the and the series arm. The frequency characteristic in this case is shown in FIG. Although the out-of-band attenuation is worse than in the case of the first embodiment,
It can be seen that the pass band width is slightly wider. Even when the equivalent capacitance ratio of the resonator 101 of the series arm and the resonator 102 of the parallel arm is changed from 1: 1 as described above, the inductance of the connecting portion connecting the resonators of the lattice arm and the connection connecting the series arms are connected. By making the impedances of the parts different, the anti-resonance frequency of the lattice arm and the resonance frequency of the series arm substantially matched, and a balanced surface acoustic wave filter having good characteristics could be realized.

<Fifth Embodiment> Next, a fifth embodiment of the present invention will be described. In this embodiment, wires are used instead of the wiring electrodes of the third embodiment, and the wiring on the substrate is designed so that the inductors that are in series with all the resonators are substantially the same. As a result, the anti-resonance frequency of the lattice arm and the resonance frequency of the series arm substantially coincide with each other, and good characteristics are obtained irrespective of the design of the resonator as compared with the case where the inductor is not taken into consideration as in the third embodiment. It was possible to realize a balanced surface acoustic wave filter having

<Sixth Embodiment> Next, a sixth embodiment of the present invention will be described. FIG. 10 is a configuration diagram showing a sixth embodiment of the balanced surface acoustic wave filter according to the present invention. This is a configuration in which the configuration shown in the first embodiment is connected in three stages, and is implemented when it is difficult to obtain a sufficient out-of-band attenuation amount in one stage or two stages. When three stages are connected in this way, two stages are connected (Fig. 7).
Similar to (1), there is no portion where the wiring intersects on the substrate, and there is an advantage that wire bonding becomes easy. And in this case also, as shown in FIG.
It was possible to realize a balanced surface acoustic wave filter having a sufficiently high out-of-band attenuation as compared with the case of the first stage (see FIG. 6) of the embodiment. Further, the half-width is slightly smaller than that in the case of the second stage of the second embodiment (see FIG. 8).

If the structure shown in the first embodiment is connected in four stages or more, wire bonding becomes difficult because the portion where the wiring intersects again appears on the substrate. Further, if the number of stages is increased too much, the substrate becomes large and the filter cannot be downsized.

<Seventh Embodiment> Next, a seventh embodiment of the present invention will be described. In this embodiment, the case where the equivalent capacitance ratio of the resonator of the fourth embodiment is changed is shown. Specifically, the series-arm resonator 101 and the parallel-arm resonator 102
The equivalent capacity ratio of was set to 1: 2. That is, the equivalent parallel capacitance of the resonator is such that the lower resonance frequency of the resonator (the parallel arm resonator 102) is the higher resonator (the series arm resonator 10).
It was made larger than that in 1) (see FIG. 4). In this case, as shown in FIG. 12, an attenuation pole is formed near the pass frequency of the filter, which is particularly advantageous when a high attenuation amount is required.

In each of the above embodiments, the anti-resonance frequency of the lattice arm and the resonance frequency of the series arm are substantially matched, but the resonance frequency of the lattice arm and the anti-resonance frequency of the series arm are substantially equal to each other. It is possible to obtain a good filter characteristic even when the values are substantially matched with.

In each of the above embodiments, the case where lithium tantalate is used as the substrate has been described as an example, but the present invention is not necessarily limited to this.
A substrate having the same piezoelectricity, for example, a quartz substrate or a lithium niobate (LiNbO ₃ ) substrate may be used. That is, if it is a piezoelectric body, a balanced surface acoustic wave filter having similarly good characteristics can be realized.

In each of the above embodiments, the case where aluminum is used as the electrode has been described as an example, but the present invention is not limited to this. Even when aluminum mixed with copper or titanium is used in consideration of durability, a balanced surface acoustic wave filter having similarly good characteristics can be realized.

[0032]

As described in the foregoing, according to the balanced type surface acoustic wave filter over according to the present invention, the grating arms and series arms
Each elastic surface of the lattice arm as a means of adjusting the resonance frequency
The inductance of the connection part that connects the wave resonator and the series arm
By changing the impedance of the connecting part to be connected, the surface acoustic wave resonator of the series arm and the surface acoustic wave of the parallel arm can be changed.
Even if the equivalent capacitance ratio of the resonator is changed from 1: 1,
(A) Anti-resonance frequency of lattice arm and resonance frequency of series arm, and
(B) Is the resonance frequency of the lattice arm and the anti-resonance frequency of the series arm?
It is possible to realize a balanced surface acoustic wave filter having at least one selected from the above-mentioned substantially substantially identical properties and having good characteristics. Further, since the high frequency circuit can be made into a balanced circuit without using the balanced-unbalanced conversion circuit,
It is possible to reduce the number of parts and costs .

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a first embodiment of a balanced surface acoustic wave filter according to the present invention.

FIG. 2 is an equivalent circuit diagram of the balanced surface acoustic wave filter shown in FIG.

FIG. 3 is an equivalent circuit diagram of a resonator used in the balanced surface acoustic wave filter shown in FIG.

FIG. 4 is a frequency characteristic diagram of a resonator used in the balanced surface acoustic wave filter shown in FIG.

FIG. 5 is a measurement circuit diagram of a filter.

FIG. 6 is a frequency characteristic diagram of the balanced surface acoustic wave filter shown in FIG.

FIG. 7 is a configuration diagram showing a second embodiment of the balanced surface acoustic wave filter according to the present invention.

8 is a frequency characteristic diagram of the balanced surface acoustic wave filter shown in FIG.

FIG. 9 is a frequency characteristic diagram of the fourth embodiment of the balanced surface acoustic wave filter according to the present invention.

FIG. 10 is a configuration diagram showing a sixth embodiment of a balanced surface acoustic wave filter according to the present invention.

11 is a frequency characteristic diagram of the balanced surface acoustic wave filter shown in FIG.

FIG. 12 is a frequency characteristic diagram of a seventh embodiment of the balanced surface acoustic wave filter according to the present invention.

[Explanation of symbols]

101 series arm resonator 102 Parallel arm resonator 103, 104 connection 105, 106 input terminals 107, 108 output terminals 109 inductor 201 parallel capacity 202 series capacitance 203 series inductor 204 resonance resistance 501 Balun for balanced-unbalanced conversion

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shunichi Seki 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) Reference JP-A-2-127810 (JP, A) JP-A-48- 96045 (JP, A) JP-A-7-66676 (JP, A) JP-A-6-250876 (JP, A) Actually developed 55-133617 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) H03H 9/64 H03H 9/145

Claims (5)

(57) [Claims] 1. Four surface acoustic wave resonators are connected in a symmetric lattice type, and at least one symmetric lattice type circuit is used, and (a) an antiresonance frequency of a lattice arm and a resonance frequency of a series arm, and (B) A balanced surface acoustic wave filter in which at least one selected from the resonance frequency of the lattice arm and the anti-resonance frequency of the series arm is substantially matched, and the resonance frequencies of the lattice arm and the series arm are adjusted. As a means
A balanced surface acoustic wave filter characterized in that an inductance of a connecting portion connecting each surface acoustic wave resonator of a lattice arm is made different from an impedance of a connecting portion connecting a series arm. 2. The connection portion of each surface acoustic wave resonator is selected from (a) a wiring electrode on a substrate on which the surface acoustic wave resonator is formed, and (b) a wire used for connection with an external circuit. The balanced surface acoustic wave filter according to claim 1 , wherein at least one of them is used. Wherein the symmetric lattice-type circuit connecting two stages claim 1
The balanced surface acoustic wave filter described in 1. 4. A connecting three stages a symmetrical lattice-type circuit according to claim 1
The balanced surface acoustic wave filter described in 1. 5. Of the four surface acoustic wave resonators, two are arranged in the series arm, balanced type surface acoustic wave according to claim 1 the remaining two are disposed in a lattice arm filter.