JP2000349589A - Surface acoustic wave filter - Google Patents

Abstract

(57) [PROBLEMS] To improve out-of-band attenuation by connecting a one-terminal-pair resonator to bus bars on both sides of an input electrode or an output electrode of a dual-mode resonator and using them as balanced terminals. SOLUTION: An interdigital electrode 1a for exciting a surface acoustic wave, an interdigital electrode 1b for receiving a surface acoustic wave, and reflectors arranged on both sides of the interdigital electrodes 1a, 1b on a piezoelectric substrate. In the two-terminal resonator type surface acoustic wave filter having the elements 3 and 3, the bus bars 2a and 2b on both sides of the IDT 1b receiving the surface acoustic wave. One-port resonators 5 were connected in series, and these were used as output terminals 7.

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 used for a communication device such as a mobile communication terminal.

[0002]

2. Description of the Related Art FIG.
FIG. 7 is a configuration diagram showing the conventional surface acoustic wave filter shown in FIG. 1 of No. 6. In the figure, reference numerals 1a and 1b denote IDTs arranged side by side, 2a and 2b denote bus bars,
Numeral 3 is a reflector positioned on both sides of the interdigital electrodes 1a and 1b, 4 is a two-port resonator composed of the interdigital electrodes 1a and 1b and the reflectors 3 and 5, and 5 is a one-terminal resonator. , 6 is an input terminal, and 7 is an output terminal. The interdigital electrode 1a has bus bars 2a and 2b arranged in parallel on the upper and lower sides, and a thin electrode and a bus bar 2 protruding from the bus bar 2a.
b are arranged alternately and in parallel with each other, and the interdigital electrodes 1b have busbars 2a and 2b arranged in parallel on the upper and lower sides, and the fine electrodes protruding from the busbar 2a and the busbar 2b. Protruding fine electrodes are alternately arranged in parallel. The input terminal 6 is connected to the bus bar 2a on the upper side of the IDT 1a via the one-port resonator 5, and the output terminal 7 is connected to the bus bar 2b of the IDT 1b. The bus bar 2b below the IDT 1a and the bus bar 2a above the IDT 1b are connected to ground. The reflectors 3, 3 are configured by connecting the upper and lower bus bars 3a, 3b with fine electrodes arranged in parallel.

In FIG. 12, two interdigital transducers 1a and 1b are arranged side by side on a piezoelectric substrate, and two reflectors 3 and 3 are arranged on both sides thereof to form a two-terminal pair resonator 4. ing. Furthermore, the interdigital transducer 1 on the left side of the two-port resonator 4
The one-terminal pair resonator 5 is connected in series to the bus bar 2a on the upper side of "a" to form an input terminal 6. The lower bus bar 2b on the right side of the interdigital electrode 1b is connected to the output terminal 7.

Next, the operation will be described. Input terminal 6
, The electric signal passes through the one-port resonator 5 and reaches the IDT 1a on the left side of the two-terminal resonator 4. Here, the electric signal is converted into a surface acoustic wave. The excited surface acoustic wave is reflected multiple times between the reflectors 3 arranged on both sides, and causes resonance. A part of the surface acoustic wave is received by the right interdigital electrode 1b, converted into an electric signal again, and taken out from the output terminal 7.

[0005] Considering the pass characteristics of only the two-port pair resonator 4 without connecting the one-port pair resonator 5, it is a low-loss band-pass filter. However, only the two-port resonator 4 may not provide sufficient out-of-band attenuation at a specific frequency outside the band.

A one-port resonator 5 shown in FIG. 12 is connected to improve the out-of-band attenuation characteristic. The pass characteristic of the one-port resonator 5 shows a characteristic having an attenuation pole at which the amount of attenuation increases at a specific frequency. By adjusting the frequency of the attenuation pole to a frequency at which the amount of out-of-band attenuation in the two-port resonator 4 cannot be sufficiently obtained, the amount of out-of-band attenuation at this frequency can be improved.

In recent years, a balanced type of a surface acoustic wave filter of this type is connected to an input terminal 6 or an output terminal 7 thereof.
That is, a balanced terminal may be required. This means that surface acoustic wave filters can be used for differential amplifiers and mixers.
This is to enable direct connection to a circuit having another balanced terminal. This eliminates the need for a balanced-unbalanced conversion circuit, a so-called balun, and makes it possible to reduce the size of the entire circuit.

However, in the surface acoustic wave filter shown in FIG. 12, one of the upper and lower bus bars 2a and 2b of the interdigital transducer 1a on the left side of the two-terminal resonator 4 has only one upper side.
The terminal pair resonator 5 is connected, and the lower bus bar 2b is grounded. For this reason, the input terminal 6 is of an unbalanced type, that is, an unbalanced type. This is because the surface acoustic wave filter circuit viewed from the input terminal 6 is unbalanced. Therefore, in such a configuration, there is a problem that this terminal cannot be a balanced type terminal, and the circuit cannot be downsized.

[0009]

As described above, this type of conventional surface acoustic wave filter has a problem that a balanced terminal cannot be obtained. SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and it is an object of the present invention to obtain a low-loss, high-attenuation surface acoustic wave filter having balanced terminals.

[0010]

According to the first aspect of the present invention, at least one of the interdigital transducers for exciting a surface acoustic wave or the interdigital transducer for receiving a surface acoustic wave is provided on both sides of the interdigital transducer. , A one-port pair resonator was connected to each of these busbars, and these were used as balanced terminals as input terminals or output terminals.

According to the second aspect of the present invention, three electrodes are provided, one of which is an interdigital electrode for exciting a surface acoustic wave, and the other is an interdigital electrode for receiving a surface acoustic wave. In a two-terminal pair resonator type surface acoustic wave filter, among the interdigital transducers that excite a surface acoustic wave or the interdigital transducer that receives a surface acoustic wave, at least one of the interdigital transducers has a bus bar on both sides thereof. One-port resonators were connected, and these were used as balanced terminals as input terminals or output terminals.

According to the third aspect of the present invention, one terminal-pair resonator is provided on each of the bus bars on both sides of the IDT for exciting the SAW and the IDT for receiving the SAW. And the input terminal and the output terminal were both balanced terminals.

According to the fourth aspect of the present invention, the one-port resonator is connected in series to an input terminal or an output terminal.

According to a fifth aspect of the present invention, the one-port resonator is connected in parallel to an input terminal or an output terminal.

According to the sixth aspect of the present invention, of the plurality of one-port resonators connected to the two-port resonator,
The frequency at which the attenuation pole of at least one 1-port resonator is generated is different from the frequency at which the attenuation pole of the other 1-port resonator is generated.

According to the present invention, the two-port resonator and at least one of the one-port resonators are arranged on the same piezoelectric substrate.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIG. 1 is a configuration diagram showing Embodiment 1 of the present invention, and the same components as those in FIG. 12 are denoted by the same reference numerals. In the figure, reference numerals 1a and 1b denote left and right interdigital electrodes, 2a and 2b upper and lower bus bars, 3 a reflector, 4 a two-port resonator, 5, 5 a one-port resonator, and 6 Is an input terminal and 7, 7 are output terminals.

In FIG. 1, two interdigital transducers 1a and 1b are provided side by side on a piezoelectric substrate, and two reflectors 3 and 3 are disposed on both sides thereof.
Is composed. In the left interdigital electrode 1a,
The upper and lower bus bars 2a, 2 constituting the IDT 1a
The upper side of b is the input terminal 6, and the other is ground. Therefore, the input terminal 6 is an electrically unbalanced terminal. On the other hand, in the right-side interdigital electrode 1b, one-port resonators 5 and 5 are connected in series to both the upper and lower bus bars 2a and 2b, and the output terminals 7 and 7 are connected via these one-port resonators. Connected to Therefore, the output terminals 7, 7 are electrically balanced terminals. By mounting the two-port resonator 4 and the one-port resonators 5 and 5 on the same piezoelectric substrate, miniaturization is realized.

Next, the operation will be described. Input terminal 6
When a high-frequency electric signal is applied to the piezoelectric substrate, the electric signal is converted into a surface acoustic wave by the interdigital transducer 1a on the left side, and the surface acoustic wave is excited on the piezoelectric substrate. This surface acoustic wave is multiply reflected between the reflectors 3 and 3 arranged on both sides and resonates. A part of the resonated surface acoustic wave is again extracted as an electric signal at the right interdigital electrode 1b.

The frequency at which resonance occurs depends on the IDT 1
The electric signal applied to the input terminal 6 is efficiently extracted at the right interdigital electrode 1b near the frequency at which this resonance occurs, although it depends on the arrangement of the reflectors a, 1b and the reflectors 3, 3 and their respective structures. . Therefore, in the two-port resonator 4, the insertion loss of the pass characteristic at this frequency is reduced. In addition, when the electric signal is applied to the input terminal 6 at a frequency other than around the frequency at which resonance occurs, a small amount of the signal is extracted from the right interdigital electrode 1b, resulting in a large insertion loss. Thus, the two-port pair resonator 4
Is a band-pass filter that passes a signal of only a specific frequency.

FIG. 3B shows the frequency characteristics of the two-port resonator 4. A low-loss passband occurs at fo near the frequency at which resonance occurs. However, in this type of two-port resonator 4, as shown in FIG. 3B, at a frequency fs slightly higher than the pass band fo, it is known that spurious-like mountain-like pass characteristics occur. Therefore, at this frequency, the out-of-band attenuation deteriorates.

The one-port resonator 5 shown in FIG. 1 has the configuration shown in FIG. 2 in order to improve the deterioration of the out-of-band attenuation. FIG. 2 is a diagram showing a detailed configuration of the one-port resonator 5. In FIG. 2, reference numeral 1c denotes a parallel arrangement in which fine electrodes projecting from upper and lower bus bars 1m and 1n are alternately arranged in parallel. The constituted IDTs 3, 3 are reflectors disposed on the left and right of the IDT 1c.

One bus bar 1 of the one-port resonator 5
When an electric signal is applied to m through the terminal 1x, the surface acoustic wave excited by the interdigital electrode 1c is multiply reflected between the reflectors 3 and 3, and resonance occurs. This is the same as the two-port resonator 4 in FIG. However, the one-port resonator 5 operates as an impedance element because the electrical terminals are one-terminal pairs.

The pass frequency characteristic between the one terminal and the terminal of the resonator 5 is as shown in FIG. At a specific frequency fr determined by the arrangement and structure of the interdigital transducer 1c and the reflectors 3 and 3, the impedance of the one-port resonator 5 becomes close to 0, and the insertion loss in the pass characteristics also decreases. At a frequency fa slightly higher than the frequency fr, the impedance of the one-port resonator 5 approaches infinity. For this reason, the insertion loss in the transmission characteristics increases, and an attenuation pole is generated.

In the surface acoustic wave filter shown in FIG. 1, the bus bars 2a and 2b of the IDT 1b on the right side of the two-port resonator 4 are used.
One terminal pair resonators 5, 5 are connected in series between b and the output terminals 7, 7, respectively. As shown in FIG. 3, the passband fo of the two-port resonator 4 and the frequency fr at which the one-terminal resonator 5 has low loss are set to be substantially the same frequency. The frequency fs at which the spurious of No. 4 occurs and the attenuation pole fa of the one-port resonator 5 are set to have substantially the same frequency. Therefore,
As shown in FIG. 3 (c), the overall frequency characteristics are to maintain the low-loss characteristics in the pass band, and to significantly improve the out-of-band attenuation by the effect of the attenuation pole at the frequency at which spurs have occurred. Can be.

Further, in FIG. 1, both upper and lower bus bars 2a, 2b of the IDT 1b on the right side of the two-terminal resonator 4 are shown.
Are connected to one-port resonators 5 and 5, respectively, and these are output terminals 7 and 7, respectively. At this time, looking at the surface acoustic wave filter from the output terminals 7, 7, the circuit is well balanced. Therefore, the output terminals 7, 7 can be taken out as balanced terminals.

As described above, the surface acoustic wave filter according to the first embodiment of the present invention shown in FIG. 1 has a small insertion loss in the pass band, a good out-of-band attenuation, and has a balanced output terminal. There is an effect that a wave filter can be obtained.

In this type of surface acoustic wave filter,
The so-called reciprocity theorem in network theory holds. That is, even if the input terminal 6 and the output terminals 7 and 7 are exchanged, the pass characteristics become completely the same. In other words, the effects of the present invention can be similarly obtained by a configuration in which an electric signal is input from a balanced terminal and extracted from an unbalanced terminal.

Embodiment 2 FIG. 4 is a configuration diagram showing the second embodiment of the present invention. In the figure, 1e, 1f,
1g is an interdigital transducer in which fine electrodes protruding from the upper and lower bus bars 2a and 2b are alternately arranged in parallel, and three of them are juxtaposed. 2a, 2b are upper and lower busbars, 3, 3
Are reflectors installed on the left and right of the interdigital transducers 1e, 1f, 1g, 4 is a two-port resonator, 5, 5 is a one-port resonator, 6 is an input terminal, 7, 7 are output terminals. It is.

In FIG. 4, a two-terminal resonator 4 is constituted by three interdigital electrodes 1e, 1f, 1g on a piezoelectric substrate and two reflectors 3, 3 arranged on both sides thereof. , A two-terminal resonator 4 having a so-called three-electrode configuration. In the center interdigital electrode 1f, the upper terminal of the upper and lower bus bars 2a and 2b constituting the interdigital electrode 1f is used as the input terminal 6, and the other is used as the ground. Therefore, the input terminal 6 is an electrically unbalanced terminal. On the other hand, the left and right two interdigital electrodes 1e and 1g serve as receiving sides, and sandwich the exciting interdigital electrode 1f. In the interdigital electrodes 1e and 1g, the upper and lower bus bars 2a and 2b are connected to each other.
One terminal pair resonators 5 are connected in series to both lower bus bars 2a and 2b, respectively. In addition, both of these
The terminal pair resonators 5 are output terminals 7. Therefore, the output terminal 7 is an electrically balanced terminal. In this case, the one-port resonators 5 and 5 are mounted on the piezoelectric substrate on which the two-port resonators 4 are mounted.

Next, the operation will be described. Input terminal 6
When a high-frequency electric signal is applied to the piezoelectric substrate, the electric signal is converted into a surface acoustic wave at the center interdigital electrode 1f, and the surface acoustic wave is excited on the piezoelectric substrate. This surface acoustic wave is multiply reflected between the reflectors 3 and 3 arranged on both sides and resonates. A part of the resonated surface acoustic wave is again extracted as an electric signal at the left and right interdigital electrodes 1e and 1g. These operations are almost the same as those in the first embodiment of the present invention shown in FIG.

However, it is known that the two-terminal resonator 4 having a three-electrode configuration shown in FIG. 4 can have a wider passband than the two-electrode configuration shown in FIG. This is described in, for example, the document "Transactions of the Institute of Electronics, Information and Communication Engineers, A, Vol. J76-A, No. 2, pp. 227-
235. (1993) ", and details of the principle will not be described here. Thus, the two-terminal pair resonator 4 having the three-electrode configuration shown in FIG.
Is a bandpass filter having a small loss and a wide passband.

However, also in this case, FIG.
As described above, the frequency f slightly higher than the pass band fo
In s, a mountain-like passage characteristic due to spurious noise occurs. For this reason, only the two-port resonator 4 degrades the out-of-band attenuation.

In FIG. 4, the upper and lower busbars 2 of the left and right interdigital electrodes 1e and 1g of the two-terminal resonator 4 are shown.
a, 2b, and these upper and lower bus bars 2a, 2b
Are connected in series with one-port resonators 5 and 5, respectively.

Also in this case, as shown in FIG. 3, the pass band f0 of the two-port resonator 4 and the frequency fr at which the one-terminal resonators 5 and 5 have low loss are set to be substantially the same frequency. Further, the frequency fs at which spurious of the two-port resonator 4 is generated and the attenuation pole fa of the one-port resonators 5 and 5 are set to be substantially the same frequency. Therefore, the overall frequency characteristics are similar to those shown in FIG. 3C, while maintaining low-loss and wide-band characteristics in the passband, and out-of-band attenuation due to the effect of the attenuation pole at the frequency at which spurious components are generated. The amount can be greatly improved.

Further, in FIG.
Both upper and lower bus bars 2 of the right interdigital electrodes 1e, 1g
One-terminal pair resonators 5 and 5 are connected to a and 2b, respectively, and these are used as output terminals 7 and 7. Therefore, output terminals 7 and 7 can be taken out as balanced terminals.

As described above, the surface acoustic wave filter according to the second embodiment of the present invention shown in FIG. 4 has a small insertion loss in the pass band, a wide band, good attenuation outside the band, and a balanced output terminal. There is an effect that a surface acoustic wave filter can be obtained.

As in the case of the first embodiment, in this type of surface acoustic wave filter, the input terminal 6 and the output terminal 7,
Even if 7 is replaced, the pass characteristics become completely the same. That is, the effect of the present invention can be similarly obtained by a configuration in which an electric signal is input from the balanced terminal and extracted from the unbalanced terminal.

Embodiment 3 FIG. 5 is a configuration diagram showing a third embodiment of the present invention, and the same components as those in FIG. In the figure, 1e, 1f, 1g are interdigital electrodes, 2a, 2b are busbars, 3, 3 are reflectors, 4 is 2
Terminal-pair resonators, 5 and 5 are one-port pair resonators, 6 is an input terminal, and 7, 7 are output terminals.

In FIG. 5, a two-terminal pair resonator 4 is constituted by three interdigital electrodes 1e, 1f, 1g on a piezoelectric substrate and two reflectors 3, 3 arranged on both sides thereof. , A two-terminal resonator 4 having a so-called three-electrode configuration. The left and right interdigital transducers 1e and 1g are on the excitation side, and are positioned so as to sandwich the interdigital transducer 1f on the receiving side. In the interdigital electrodes 1e and 1g, the upper and lower bus bars 2a and 2b are connected to each other, and the upper one of the upper and lower bus bars 2a and 2b is used as the input terminal 6, and the other is ground. Therefore, the input terminal 6 is an electrically unbalanced terminal. On the other hand, in the center interdigital electrode 1f, both the upper and lower bus bars 2a and 2b that constitute the interdigital electrode 1f have
One terminal pair resonators 5 and 5 are connected respectively. Further, these one-port resonators 5 and 5 are output terminals 7 and 7, respectively. Therefore, the output terminals 7, 7 are electrically balanced terminals.

Next, the operation will be described. Input terminal 6
When a high-frequency electric signal is applied to the
The surface is converted into a surface acoustic wave by the right interdigital electrodes 1e and 1g, and is again output as an electric signal at the center interdigital electrode 1f. Since the two-port resonator 4 has a three-electrode configuration, a broadband and low-loss transmission characteristic can be obtained as in the second embodiment. Further, the one-terminal-pair resonators 5 and 5 are connected to both the upper and lower bus bars 2a and 2b of the center interdigital electrode 1f, and these are used as the output terminals 7 and 7, respectively. alike,
The spurious response of the two-port resonator 4 can be suppressed, and an unbalanced input / balanced output surface acoustic wave filter with good out-of-band attenuation can be obtained.

Also in this case, the input terminal 6 and the output terminals 7 and 7 are exchanged, and an electric signal is input from the balanced terminal.
The effect of the present invention can be obtained in the same manner even if the configuration is taken out from the unbalanced terminal.

Embodiment 4 FIG. FIG. 6 is a configuration diagram showing a fourth embodiment of the present invention, and the same components as those in FIG. In the figure, 1e, 1f, 1g are interdigital electrodes, 2a, 2b are busbars, 3, 3 are reflectors, 4 is 2
The terminal-pair resonator 5 is a one-terminal-pair resonator, and four resonators are provided. 6 is an input terminal and 7, 7 are output terminals.

In FIG. 6, a two-terminal resonator 4 is constituted by three interdigital electrodes 1e, 1f, 1g on a piezoelectric substrate and two reflectors 3, 3 arranged on both sides thereof. In this case, a two-terminal resonator 4 having a so-called three-electrode configuration is used. The interdigital transducers 1e and 1g on both sides serve as receiving sides, and are positioned so as to sandwich the interdigital transducer 1f on the excitation side. In the center interdigital electrode 1f on the excitation side,
The upper and lower bus bars 2a, 2b constituting the interdigital electrode 1f
b, one-port pair resonators 5 and 5 are connected, respectively,
These two 1-port resonators 5 and 5 are input terminals 6. Therefore, the input terminal 6 is an electrically balanced terminal. On the other hand, the upper and lower bus bars 2a and 2b are also connected to each other in the two interdigital electrodes 1e and 1g, and both the upper and lower bus bars 2a and 2b are connected to each other.
Respective one-port resonators 5 and 5 are connected, and these one-port resonators 5 and 5 are output terminals 7 and 7, respectively. Therefore, the output terminals 7, 7 are also electrically balanced terminals.

Next, the operation will be described. By connecting the one-terminal pair resonator 5 to the two-terminal pair resonator 4 having a three-electrode configuration, as in the second and third embodiments,
A surface acoustic wave filter with low loss, wide band, and good out-of-band attenuation can be obtained.

Further, in the fourth embodiment, the output terminals 7,
Not only 7 but also the input terminals 6 and 6 can be balanced terminals. Also in this case, the input terminals 6 and 6 and the output terminals 7 and 7
The same effect can be obtained even if the configuration is changed.

Embodiment 5 FIG. 7 is a configuration diagram showing Embodiment 5 of the present invention, and the same components as those in FIG. In the figure, 1e, 1f, 1g are interdigital electrodes, 2a, 1b are busbars, 3, 3 are reflectors, 4 is 2
Terminal-pair resonators, 5 and 5 are one-port pair resonators, 6 is an input terminal, and 7, 7 are output terminals.

In FIG. 7, a two-terminal resonator 4 is constituted by three interdigital electrodes 1e, 1f, 1g on a piezoelectric substrate and two reflectors 3, 3 arranged on both sides thereof. In this case, a two-terminal resonator 4 having a so-called three-electrode configuration is used. In the center interdigital electrode 1f, the upper and lower bus bars 2a, 2b constituting the interdigital electrode 1f are arranged.
Of these, the upper side is the input terminal 6, and the other is the ground. Therefore, the input terminal 6 is an electrically unbalanced terminal. On the other hand, the upper and lower bus bars 2a and 2b are connected to each other in the two left and right interdigital electrodes 1e and 1g, and the one-terminal pair resonators 5 and 5 are respectively connected to both the upper and lower bus bars 2a and 2b. They are connected in parallel, and these two one-port resonators 5 and 5 are output terminals 7 and 7, respectively.
Therefore, the output terminals 7, 7 are electrically balanced terminals.

Next, the operation will be described. In FIG. 7, one-port resonators 5 are connected in parallel to output terminals 7. At this time, the transmission characteristics of only the one-port resonators 5 and 5 are as shown in FIG. That is, 1
At the frequency fr at which the impedance of the terminal pair resonators 5 and 5 is close to 0, the insertion loss of the pass characteristics increases and an attenuation pole is generated. Frequency fa slightly higher than this frequency fr
In, the impedance of the one-port pair resonators 5, 5 approaches infinity, and the insertion loss of the pass characteristics decreases.

In the surface acoustic wave filter shown in FIG.
The passband fo of the two-port resonator 4 shown in FIG.
The frequency fa at which the one-port resonators 5, 5 shown in FIG. Therefore, as shown in FIG.
In the pass band, the attenuation characteristic especially at a frequency lower than the pass band can be improved by the effect of the attenuation pole of the one-port pair resonator 5 while maintaining a wide band with low loss. In addition, the balance of the circuit viewed from the surface acoustic wave filter from the output terminals 7, 7 is maintained, and the output terminals 7, 7 can be balanced terminals.

In FIG. 7, the effect of the present invention can be similarly obtained by replacing the input terminal 6 with the output terminals 7 and 7 and inputting an electric signal from the balanced terminal and extracting the electric signal from the unbalanced terminal. Needless to say,

Embodiment 6 FIG. FIG. 9 is a configuration diagram showing a sixth embodiment of the present invention, in which the same components as those in FIG. In the figure, 1e, 1f, 1g are interdigital electrodes, 2a, 2b are busbars, 3, 3 are reflectors, 4 is 2
Terminal-pair resonators, 5 and 5 are one-port pair resonators, 6 is an input terminal, and 7, 7 are output terminals.

In FIG. 9, a two-terminal resonator 4 is constituted by three interdigital electrodes 1e, 1f, 1g on a piezoelectric substrate and two reflectors 3, 3 arranged on both sides thereof. In this case, a two-terminal resonator 4 having a so-called three-electrode configuration is used. In the center interdigital electrode 1f, the upper and lower bus bars 2a, 2b constituting the interdigital electrode 1f are arranged.
Of these, the upper side is the input terminal 6, and the other is the ground. Therefore, the input terminal 6 is an electrically unbalanced terminal. On the other hand, the upper and lower busbars 2a and 2b are connected to each other at the two left and right interdigital electrodes 1e and 1g, and the upper and lower busbars 2a and 2b are connected to the one-terminal pair resonators 5 and 5 respectively. 5 is connected. Further, these one-port resonators 5 and 5 are output terminals 7 and 7, respectively. Therefore, the output terminals 7, 7 are electrically balanced terminals. These configurations correspond to the third embodiment shown in FIG.
The configuration is the same as

However, in FIG. 9, the frequencies at which the respective attenuation poles are generated in the upper and lower two one-port resonators 5 are different from each other.

FIG. 10A shows the pass frequency characteristic of the one-port resonator 5. In the figure, the solid line and the broken line represent the pass characteristics of the one-port pair resonators 5 and 5 shown in the upper and lower parts of FIG. 9, respectively, and the frequencies of these attenuation poles are different. The frequency fa at which this attenuation pole occurs is shown in FIG.
Since the frequency fs is substantially matched to the frequency fs at which the spurious of the two-port resonator 4 shown in FIG. 10B occurs, the overall frequency characteristic is as shown in FIG. As it is, a surface acoustic wave filter with good out-of-band attenuation can be obtained. These effects are similar to those of the third embodiment. However, at this time, since the attenuation poles of the one-port resonator 5 and 5 are generated at two different frequencies, the spurious of the two-port resonator 4 is more effectively suppressed as compared with the third embodiment. can do.
Therefore, the out-of-band attenuation can be significantly improved at this frequency.

In FIG. 9, unlike FIG. 5, the impedance of the two 1-port resonators 5 is not completely the same at each frequency. Strictly, not perfectly balanced. However, the difference in impedance between the upper and lower two 1-port resonators 5 is small at each frequency, and there is no problem even if the output terminals 7, 7 are treated as substantially balanced terminals.

As described above, the surface acoustic wave filter according to the sixth embodiment of the present invention shown in FIG. 9 has a small insertion loss in the pass band, a wide band, very good out-of-band attenuation, and a balanced output. Is obtained.

The attenuation pole frequency of the one-port resonator 5 can be freely changed by appropriately setting the arrangement of the IDTs 1c and the reflectors 3 constituting the one-port resonator 5 and their structures. be able to. Specifically, as a method of making the attenuation pole frequency different, a widely known method for designing a resonator of this type may be used. Also, in FIG.
Obviously, the input terminal 6 and the output terminals 7 and 7 may be exchanged, and an electric signal may be input from the balanced terminal and extracted from the unbalanced terminal.

When the attenuation pole frequency of the one-port resonator 5 is made different, for example, as shown in FIG. 6 shown in the fourth embodiment, both the input terminal 6 and the output terminal 7 have one terminal. In the configuration in which the resonator 5 is connected, the input terminal 6 side,
The attenuation pole frequency of the upper and lower one-terminal pair resonator 5 on the output terminal 7 side may be different from that of the input terminal 6 side.
The attenuation pole frequency of the terminal-to-resonator 5 and the one-port to-resonator 5 on the output terminal 7 side may be made different. As described above, by making at least one attenuation pole frequency different from the others in the plurality of one-port resonators 5 connected to the two-port resonator 4, the bandwidth can be increased similarly to the sixth embodiment. The effect of improving the outside damping characteristics can be obtained.

In the surface acoustic wave filters according to the present invention described in the first to sixth embodiments, the two-port resonator 4 and the one-port resonator 5 are arranged on different piezoelectric substrates. Alternatively, they may be arranged on the same piezoelectric substrate. Also, a part of the one-port resonator 5 is replaced with a two-port resonator 4.
May be arranged on the same piezoelectric substrate, and the other one-terminal pair resonator 5 may be arranged on a different piezoelectric substrate.

When arranged on different piezoelectric substrates, by selecting and connecting resonators having good characteristics, a surface acoustic wave filter having a good production yield can be obtained. Further, when they are arranged on the same piezoelectric substrate, there is an effect that the whole size can be reduced and a small surface acoustic wave filter can be obtained.

In the present invention, in addition to the configurations shown in the first to sixth embodiments, the two-port resonators 4 and 1
Various combinations are conceivable for the method of connecting the terminal-pair resonator 5 and the method of setting the input terminal and the output terminal to the balanced terminal or the unbalanced terminal. Is obtained.

As shown in FIG. 11, one-port resonators 5 and 5 are connected to the upper and lower bus bars 2a and 2b, respectively, of the IDT 1a, and the one-port resonators are connected to the input side. You may attach 5,5. In this case, as shown in FIG. 3, the frequency characteristics of the entire surface acoustic wave filter are obtained by combining the characteristics of the one-port resonator and the characteristics of the two-terminal resonator. At this time, the order in which the electric signal passes through the one-port resonator or the two-port resonator first does not significantly affect the electrical characteristics. Therefore, even when the one-port resonator is provided on the input side of the two-port resonator, the same effect as when the one-port resonator is provided on the output side can be obtained.

[0064]

According to the first aspect of the present invention, at least one of the interdigital transducers for exciting a surface acoustic wave or the interdigital transducer for receiving a surface acoustic wave is provided with a bus bar on both sides of the interdigital transducer. One-port resonators are connected to each other, and these are used as balanced terminals as input terminals or output terminals. Therefore, balanced terminals can be realized, and downsizing can be realized.

According to the second aspect of the present invention, in the three-electrode two-terminal resonator type surface acoustic wave filter, the interdigital transducer for exciting the surface acoustic wave or the interdigital transducer for receiving the surface acoustic wave is used. Among them, one-port resonators were connected to the bus bars on both sides of at least one of the interdigital transducers, respectively, and these were used as balanced terminals as input terminals or output terminals. Terminals can be used, and miniaturization can be realized.

According to the third aspect of the present invention, one terminal pair resonator is provided on each of the bus bars on both sides of the IDT electrode for exciting the surface acoustic wave and the IDT electrode for receiving the surface acoustic wave. Are connected, and both the input terminal and the output terminal are balanced terminals, so that both the input terminal and the output terminal can be balanced terminals, and downsizing can be realized.

According to the fourth aspect of the invention, since the one-port resonator is connected in series to the input terminal or the output terminal, a balanced terminal can be easily realized.

According to the fifth aspect of the invention, since the one-port resonator is connected in parallel to the input terminal or the output terminal, a balanced terminal can be easily realized.

According to the sixth aspect of the present invention, of the plurality of one-port resonators connected to the two-port resonator,
Since the frequency at which the attenuation pole of at least one 1-port resonator is generated is different from the frequency at which the attenuation pole of the other 1-port resonator is generated, the out-of-band attenuation can be improved.

According to the seventh aspect of the present invention, the two-port resonator and at least one of the one-port resonators are arranged on the same piezoelectric substrate. The size can be further reduced.

[Brief description of the drawings]

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

FIG. 2 is a circuit diagram showing a main part of one embodiment of the present invention.

FIG. 3 is a characteristic diagram showing the operation of the embodiment of the present invention.

FIG. 4 is a circuit diagram showing another embodiment of the present invention.

FIG. 5 is a circuit diagram showing another embodiment of the present invention.

FIG. 6 is a circuit diagram showing another embodiment of the present invention.

FIG. 7 is a circuit diagram showing another embodiment of the present invention.

FIG. 8 is a characteristic diagram for explaining the operation of the present invention.

FIG. 9 is a circuit diagram showing another embodiment of the present invention.

FIG. 10 is a circuit diagram for explaining the operation of the present invention.

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

FIG. 12 is a circuit diagram showing an example of a conventional circuit.

[Explanation of symbols]

1a, 1b, 1c, 1e, 1f, 2g interdigital electrodes,
2a, 2b busbar, 3 reflectors, 4 2-port resonator, 51-port resonator, 6 input terminals, 7 output terminals.

Claims (7)

[Claims] 1. An interdigital transducer for exciting a surface acoustic wave and an interdigital transducer for receiving a surface acoustic wave are arranged side by side on a piezoelectric substrate, and reflectors are arranged on both sides of the interdigital transducer. In the configured two-terminal resonator type surface acoustic wave filter, at least one of the interdigital transducers for exciting the surface acoustic waves or the interdigital transducers for receiving the surface acoustic waves has busbars on both sides thereof. , A one-port pair resonator is connected to each of them, and these are used as an input terminal or an output terminal as balanced terminals. 2. An interdigital transducer for exciting a surface acoustic wave and an interdigital transducer for receiving a surface acoustic wave on a piezoelectric substrate, and reflectors are arranged on both sides of the interdigital transducer. Comprising, interdigital transducers that excite the surface acoustic waves,
In a three-electrode two-terminal resonator type surface acoustic wave filter in which one of the interdigital electrodes for receiving the surface acoustic wave is provided so as to sandwich the other, the interdigital transducer for exciting the surface acoustic wave The electrodes or the interdigital transducers receiving the surface acoustic wave, each connected to a bus bar on both sides of at least one of the interdigital transducers, a one-terminal pair resonator,
A surface acoustic wave filter characterized in that these are balanced terminals and used as input terminals or output terminals. 3. A one-terminal-pair resonator is connected to each of bus bars on both sides of both an interdigital electrode for exciting the surface acoustic wave and an interdigital electrode for receiving the surface acoustic wave. 3. The surface acoustic wave filter according to claim 1, wherein both the output terminal and the output terminal are configured as balanced terminals. 4. The surface acoustic wave filter according to claim 1, wherein the one-port resonator is connected in series to an input terminal or an output terminal. 5. The surface acoustic wave filter according to claim 1, wherein the one-port pair resonator is connected in parallel to an input terminal or an output terminal. 6. The method according to claim 1, wherein, among the plurality of one-port resonators connected to the two-port resonator, the frequency at which the attenuation pole of at least one one-port resonator is generated is reduced by the attenuation of the other one-port resonator. The surface acoustic wave filter according to any one of claims 1 to 5, wherein the frequency is different from a frequency at which a pole is generated. 7. The resonator according to claim 1, wherein the two-port resonator and at least one of the plurality of one-port resonators are arranged on the same piezoelectric substrate.
A surface acoustic wave filter according to any one of the above.