JP2008054046A - Piezoelectric filter and duplexer using it, and communication device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric filter which makes the attenuation band variable independently from the pass band. <P>SOLUTION: The piezoelectric filter is provided with: one or more series piezoelectric resonators 3; and two or more parallel piezoelectric resonators 4a, 4b. It is provided with: a first inductor 5a arranged between the first parallel piezoelectric resonator 4a and a ground; a second inductor 5b which is arranged between the second parallel piezoelectric resonator 4b and the ground; and a bypass piezoelectric resonator 36 which is arranged between a connection point of the first parallel piezoelectric resonator and the first inductor and a connection point of the second parallel piezoelectric resonator and the second inductor. The capacitance value of the bypass piezoelectric resonator is variable. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a piezoelectric filter, a duplexer, and a communication device used in a mobile communication radio circuit such as a mobile phone or a wireless LAN.

  Components built in electronic devices such as portable devices are required to be smaller and lighter. For example, filters and duplexers used in portable devices are required to be small in size, precisely adjusted in frequency characteristics, and small in insertion loss. As one of filters that satisfy these requirements, a piezoelectric filter using a piezoelectric resonator is known.

  FIG. 17 shows an equivalent circuit diagram of a piezoelectric filter using a conventional piezoelectric resonator. In this piezoelectric filter, a first parallel variable capacitor 62a is arranged in parallel with the first series piezoelectric resonator 61a, and the first series piezoelectric resonator 61a and the first parallel variable capacitor 62a are connected in series with each other. Two series variable capacitors 63a are arranged, and the first series piezoelectric resonator group 64a is formed by the first series piezoelectric resonator 61a, the first parallel variable capacitor 62a, and the first series variable capacitor 63a. . Similarly, a second parallel variable capacitor 62b is arranged in parallel with the second series piezoelectric resonator 61b, and a second series is connected in series with respect to each of the second series piezoelectric resonator 61b and the second parallel variable capacitor 62b. A variable capacitor 63b is arranged to form a second series piezoelectric resonator group 64b, which is connected in series with the first series piezoelectric resonator group 64a.

  A third parallel variable capacitor 62c is disposed in parallel with the first parallel piezoelectric resonator 61c. A third series variable capacitor is connected in series to each of the first parallel piezoelectric resonator 61c and the third parallel variable capacitor 62c. The capacitor 63c is arranged to form the first parallel piezoelectric resonator group 64c. Similarly, a fourth parallel variable capacitor 62d is arranged in parallel with the second parallel piezoelectric resonator 61d, and a fourth series is connected in series to each of the second parallel piezoelectric resonator 61d and the fourth parallel variable capacitor 62d. A variable capacitor 63d is arranged to form a second parallel piezoelectric resonator group 64d.

  One end of the first parallel piezoelectric resonator group 64c and the second parallel piezoelectric resonator group 64d thus formed is connected to both ends of the second series piezoelectric resonator group 64b, and the other end is connected to the ground. Grounded. The input terminal 65a is connected to one end of the first series piezoelectric resonator group 64a that is not connected to the second series piezoelectric resonator group 64b, and the output terminal 65b is connected to the second series piezoelectric resonator group 64b. 1 is connected to one end not connected to the series piezoelectric resonator group 64a. As described above, the piezoelectric filter 66 using the conventional piezoelectric resonator is configured.

  The operation of the piezoelectric filter using the conventional piezoelectric resonator configured as described above will be described. FIG. 18A is a single characteristic of each piezoelectric resonator constituting the conventional piezoelectric filter, and FIG. 18B is a pass characteristic of the piezoelectric filter. The characteristic s1 indicated by the solid line in FIG. 18A is the single characteristic of the first parallel piezoelectric resonator group 64c or the second parallel piezoelectric resonator group 64d, and the characteristic s2 indicated by the broken line is the first characteristic. This is a single characteristic of the series piezoelectric resonator group 64a or the second series piezoelectric resonator group 64b. 70 is a resonance point of the parallel piezoelectric resonator group, and 71 is an anti-resonance point of the parallel piezoelectric resonator group. Reference numeral 72 denotes a resonance point of the series piezoelectric resonator group, and reference numeral 73 denotes an antiresonance point of the series piezoelectric resonator group. FIG. 18B shows the filter pass characteristic t. 74 is a pass band, 76 is a low-frequency attenuation band, 78 is a high-frequency attenuation band, 75 is a low-frequency attenuation pole, and 77 is a high-frequency attenuation pole.

  The parallel piezoelectric resonators 61c and 61d and the series piezoelectric resonators 61a and 61b theoretically have unit characteristics having resonance points 70 and 72 where the impedance is 0 and antiresonance points 71 and 73 where the impedance is infinite. The Δf indicating the difference between the resonance frequency at the resonance point and the antiresonance frequency at the antiresonance point is generally determined by the material of the piezoelectric body constituting the normal piezoelectric resonator. The anti-resonance point 71 of the parallel piezoelectric resonator groups 64c to 64d and the resonance point 72 of the series piezoelectric resonator groups 64a to 64b are made to substantially coincide with each other, and each of the piezoelectric resonators is configured as a ladder type. As a result, between the input terminal 65a and the output terminal 65b, as shown in FIG. 18B, the low frequency side of the pass band 74 has a low frequency corresponding to the resonance point 70 of the parallel piezoelectric resonator groups 64c to 64d. A side attenuation pole 75 is formed, and a low-frequency attenuation band 76 is disposed. Further, on the high band side of the pass band 74, a high band attenuation pole 77 is formed at a frequency corresponding to the antiresonance point 73 of the series piezoelectric resonator groups 64a to 64b, and a high band attenuation band 78 is disposed.

FIG. 19 shows the change in the filter pass characteristic when the variable capacitance of the piezoelectric filter using the conventional piezoelectric resonator is changed. By adjusting the parallel variable capacitors 62a to 62d and the series variable capacitors 63a to 63d arranged in the respective piezoelectric resonator groups 64a to 64d constituting the piezoelectric filter 66, the pass characteristics of the piezoelectric filter 66 are 79 to 82, respectively. It changes and operates as a passband variable filter (see Patent Document 1).
JP 2005-217852 A

  However, in the conventional configuration, when the pass band of the piezoelectric filter is changed by the parallel variable capacitors 62a to 62d and the series variable capacitors 63a to 63d, the attenuation bands 75 and 77 change simultaneously with the pass band 74, and the desired attenuation band is obtained. The attenuation characteristic at is not obtained.

  Therefore, an object of the present invention is to provide a piezoelectric filter capable of making the attenuation band variable independently of the pass band.

  The piezoelectric filter of the present invention includes, as a basic configuration, one or more series piezoelectric resonators and two or more parallel piezoelectric resonators.

  In order to solve the above-described problem, a piezoelectric filter having a first configuration according to the present invention includes a first inductor disposed between the first parallel piezoelectric resonator and the ground, and a second parallel piezoelectric resonator. A second inductor disposed between the ground, a connection point between the first parallel piezoelectric resonator and the first inductor, and a connection point between the second parallel piezoelectric resonator and the second inductor; The bypass piezoelectric resonator is disposed, and a capacitance value of the bypass piezoelectric resonator is variable.

  A piezoelectric filter having a second configuration according to the present invention includes a first inductor disposed between the first parallel piezoelectric resonator and the ground, and a second inductor disposed between the second parallel piezoelectric resonator and the ground. And a bypass piezoelectric resonator disposed between the connection point of the first parallel piezoelectric resonator and the first inductor and between the connection point of the second parallel piezoelectric resonator and the second inductor. And a variable capacitor arranged in parallel with the bypass piezoelectric resonator.

  The piezoelectric filter of the third configuration of the present invention includes a first inductor disposed between the first parallel piezoelectric resonator and the ground, and a second inductor disposed between the second parallel piezoelectric resonator and the ground. And a reactance element disposed between a connection point between the first parallel piezoelectric resonator and the first inductor, and between a connection point between the second parallel piezoelectric resonator and the second inductor. The reactance value of the reactance element is variable.

  According to the above configuration, a piezoelectric filter having attenuation characteristics necessary for a desired attenuation band can be obtained even when the pass band is varied.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 shows an equivalent circuit diagram of a piezoelectric filter 8 using a piezoelectric resonator according to a first embodiment of the present invention. Between the input terminal 1 and the output terminal 2, a first series piezoelectric resonator 3a, a second series piezoelectric resonator 3b, and a third series piezoelectric resonator 3c are arranged in series. One end of the first parallel piezoelectric resonator 4a is connected between the first series piezoelectric resonator 3a and the second series piezoelectric resonator 3b, and the other end is connected to the ground via the first parallel inductor 5a. Grounded. One end of the second parallel piezoelectric resonator 4b is connected between the second series piezoelectric resonator 3b and the third series piezoelectric resonator 3c, and the other end is connected to the ground via the second parallel inductor 5b. Grounded.

  A bypass piezoelectric resonator 6 is connected between a connection point between the first parallel piezoelectric resonator 4a and the first parallel inductor 5a and between a connection point between the second parallel piezoelectric resonator 4b and the second parallel inductor 5b. The variable capacitor 7 is arranged in parallel with the bypass piezoelectric resonator 6. As described above, the piezoelectric filter 8 using the piezoelectric resonator is configured.

  FIG. 2 shows changes in the passage characteristics when the variable capacitor 7 of the piezoelectric filter 8 having the above configuration is changed. The filter waveform a1 is a reference pass characteristic, a2 is when the variable capacitor 7 is increased by 0.1 pF, a3 is increased by 0.2 pF, a4 is increased by 0.3 pF, and a5 is increased by 0.4 pF And a6 shows the pass characteristics when increased by 0.5 pF.

  As can be seen from FIG. 2, the passband 9 and the poles on the high band side away from the passband 9 without greatly changing the low band closest poles of the passband 9 and the high band closest poles of the passband 9. Is greatly changed to change the high band side attenuation band of the pass band 9. That is, by changing the variable capacitor 7, it is possible to vary the high band side attenuation characteristic of the pass band 9 without degrading the pass characteristic in the pass band 9.

  The piezoelectric filter using the piezoelectric resonator of the present embodiment can be used in a filter used in a reception tuner of a digital television. That is, in the configuration of the conventional piezoelectric filter, when the pass band is varied according to the desired channel, the attenuation band changes, and the attenuation amount in the fixed frequency band of the mobile phone of other systems, for example, deteriorates. On the other hand, by using the piezoelectric filter configuration of this embodiment, the attenuation band can be independently adjusted as desired, and a filter waveform corresponding to each channel can be obtained. In various wireless systems, the attenuation band can be tuned according to interference waves and unnecessary signals.

  The configuration of the filter circuit 8 is an example, and is not limited thereto. For example, the same effect can be obtained by a configuration using four piezoelectric resonators in which the first series piezoelectric resonator 3a and the third series piezoelectric resonator 3c are omitted. can get.

  FIG. 3 shows a change in pass characteristics when the capacitance value of the variable capacitor 7 is changed for a piezoelectric filter having the same circuit configuration as that of FIG. The filter waveform b1 is a reference pass characteristic, b2 is when the variable capacitor 7 is increased by 0.1 pF, b3 is increased by 0.2 pF, b4 is increased by 0.3 pF, and b5 is 0.4 pF. The pass characteristic of the piezoelectric filter 8 when increased is shown.

  As can be seen from FIG. 3, the passband 10 and the lower-band closest pole of the passband 10 and the higher-band nearest pole of the passband 10 are not greatly changed, and the lower pole far from the passband 10 is changed. Is greatly changed to change the low band attenuation band of the pass band 10. That is, by changing the variable capacitor 7, it is possible to vary the low band side attenuation characteristic of the pass band 10 without deteriorating the pass characteristic in the pass band 10.

  As described above, the attenuation band can be adjusted similarly on the low band side and the high band side of the pass band.

  In addition, the piezoelectric filter described above can be used in any piezoelectric resonator such as a thin film acoustic wave resonator (FBAR) or a surface acoustic wave (SAW) as a piezoelectric resonator. The same effect can be obtained by applying the configuration.

(Second Embodiment)
FIG. 4 shows an equivalent circuit diagram of the piezoelectric filter 12 using the piezoelectric resonator according to the second embodiment of the present invention. The same components as those in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted.

  In the piezoelectric filter 12 of the present embodiment, the connection point between the first parallel piezoelectric resonator 4a and the first parallel inductor 5a and the connection point between the second parallel piezoelectric resonator 4b and the second parallel inductor 5b. Only the variable capacitor 11 is arranged. Even with the same components, the circuit constants are different from those of the piezoelectric filter 8 of FIG.

  FIG. 5 shows changes in pass characteristics when the variable capacitor 11 of the piezoelectric filter 12 having the above-described configuration is changed. The filter waveform c1 shows the pass characteristics when the variable capacitor 11 is increased by 1 pF, c2 is increased by 2 pF, c3 is increased by 3 pF, c4 is increased by 4 pF, and c5 is increased by 5 pF. Show.

  As can be seen from FIG. 5, the passband 13 and the passband 13 can be reduced by changing the pole on the low frequency side far from the passband 13 without greatly changing the passband 13 and the high frequency nearest neighbor of the passband 13. The band side attenuation band is changed. That is, by changing the variable capacitor 11, it is possible to make the low band side attenuation characteristic of the pass band 13 variable without deteriorating the pass characteristic in the pass band 13.

  As in the first embodiment, the attenuation band can be adjusted on the low band side or the high band side of the pass band 13 by changing the circuit constants constituting the filter.

(Third embodiment)
FIG. 6 shows an equivalent circuit diagram of the piezoelectric filter 15 using the piezoelectric resonator according to the third embodiment of the present invention. The same components as those in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted.

  In the piezoelectric filter 15 of FIG. 6, the connection point between the first parallel piezoelectric resonator 4a and the first parallel inductor 5a and the connection point between the second parallel piezoelectric resonator 4b and the second parallel inductor 5b are not provided. A variable inductor 14 is arranged. Even with the same components, the circuit constants are different from those of the piezoelectric filter 8 of FIG.

  FIG. 7 shows the pass characteristics of the piezoelectric filter 15 configured as described above. The filter waveform d1 is a pass characteristic when the variable inductor 14 is increased by 2 nH, d2 is increased by 4 nH, d3 is increased by 6 nH, d4 is increased by 8 nH, and d5 is increased by 10 nH. Show properties.

  As can be seen from FIG. 7, the passband 16 and the passband 16 can be reduced by changing the pole on the low frequency side far away from the passband 16 without greatly changing the passband 16 and the high frequency nearest neighbor of the passband 16. The band side attenuation band is changed. That is, by changing the variable inductor 14, it is possible to vary the high band side attenuation characteristic of the pass band 16 without degrading the pass characteristic in the pass band 16.

  As in the first embodiment, the attenuation band can be adjusted on the low band side or the high band side of the pass band 16 by changing the circuit constants constituting the filter.

(Fourth embodiment)
FIG. 8 is an equivalent circuit diagram of the piezoelectric filter 17 using the piezoelectric resonator according to the fourth embodiment of the present invention. In the piezoelectric filter 17, the series piezoelectric resonator 3 is arranged in series between the input terminal 1 and the output terminal 2. One end of the first parallel piezoelectric resonator 4a is connected between the input terminal 1 and the series piezoelectric resonator 3, and the other end is grounded via the first parallel inductor 5a. One end of the second parallel piezoelectric resonator 4b is connected between the series piezoelectric resonator 3 and the output terminal 2, and the other end is grounded via the second parallel inductor 5b. A bypass piezoelectric resonator 6 is connected between a connection point between the first parallel piezoelectric resonator 4a and the first parallel inductor 5a and between a connection point between the second parallel piezoelectric resonator 4b and the second parallel inductor 5b. The variable capacitor 7 is arranged in parallel with the bypass piezoelectric resonator 6.

  FIG. 9A is a top view of a piezoelectric filter when a thin film acoustic wave resonator is used as the piezoelectric resonator in the configuration of FIG. 9B is a cross-sectional view taken along line AA in FIG. 9A. 9A and 9B, the same components as those in FIG. 8 are denoted by the same reference numerals, and the description thereof is omitted.

  21 is a substrate, 22 is an green body layer, 23a to 23c are first to third lower electrode layers, 24a and 24b are piezoelectric layers, 25a to 25c are upper electrode layers, 26a and 26b are frequency adjustment layers, 27a 27b are cavities, and 28 is a ferroelectric layer.

The substrate 21 is made of a silicon or glass substrate, and an insulator layer 22 made of silicon dioxide (SiO ₂ ), silicon nitride (Si ₃ N ₄ ), or the like is formed. On the green body layer 22, the first lower electrode layer 23a, the first piezoelectric layer 24a, the first upper electrode layer 25a, and the first frequency adjustment layer 26a are formed so as to cover the first cavity 27a. Are formed in order to form the series piezoelectric resonator 3.

The first lower electrode layer 23a is made of molybdenum (Mo), aluminum (A1), silver (Ag), tungsten (W), platinum (Pt), or the like. The first piezoelectric layer 24a is composed of aluminum nitride (AlN), zinc nitride (ZnO), lead zirconate titanate (PZT), lithium niobate (LiNbO ₃ ), lithium tantalate (LiTaO ₃ ), potassium niobate ( KNbO ₃ ) and the like. The first upper electrode layer 25a is made of molybdenum (Mo), aluminum (A1), silver (Ag), tungsten (W), platinum (Pt), or the like. The first frequency adjustment layer 26a is made of silicon dioxide (SiO ₂ ), silicon nitride (Si ₃ N ₄ ), aluminum nitride (AIN), zinc nitride (znO), or the like.

  The second lower electrode layer 23b, the second piezoelectric layer 24b, the second upper electrode layer 25b, and the second frequency adjustment layer 26b are sequentially formed so as to cover the second cavity 27b with the same material as described above. The bypass piezoelectric resonator 6 is formed.

Further, a ferroelectric layer 28 made of a third lower electrode layer 23c, barium strontium titanate (Ba _x Sr _1-x TiO ₃ ), etc. on the green body layer 22 at a location not corresponding to the cavity of the substrate 21, and The third upper electrode layer 25c is formed, and the variable capacitor 7 is configured.

  The input terminal 1 is connected to the lower electrode layer of the first parallel piezoelectric resonator 4 a and the lower electrode layer 23 a of the series piezoelectric resonator 3. The output terminal 2 is connected to the upper electrode layer 25a of the series piezoelectric resonator 3 and the upper electrode layer of the second parallel piezoelectric resonator 4b. The first parallel inductor 5a formed in a spiral shape is connected to the upper electrode layer of the first parallel piezoelectric resonator 4a, the upper electrode layer 25b of the bypass piezoelectric resonator 6, and the upper electrode layer 25c of the variable capacitor 7. The The second parallel inductor 5b is connected to the lower electrode layer of the second parallel piezoelectric resonator 4b, the lower electrode 23b of the bypass piezoelectric resonator 6, and the lower electrode 23c of the variable capacitor 7. The parallel inductors 5a and 5b are grounded to GND.

  The parallel inductors 5a and 5b are formed in a spiral shape on the substrate 21 in the above configuration. However, the shape is not limited to this, and the shape may be a meander shape or other shapes, or on another chip or substrate, or You may form with a bonding wire or a wiring electrode.

  Each piezoelectric resonator operates as a resonator by applying an electric field between the upper electrode layer and the lower electrode layer to polarize and distort the piezoelectric layer to generate mechanical resonance and electrically extract this. . The resonance frequency of the resonator is mainly determined by the film thicknesses of the vibrating parts constituted by the lower electrode layers 23a and 23b, the piezoelectric layers 24a and 24b, the upper electrode layers 25a and 25b, and the frequency adjustment layers 26a and 26b and their thicknesses. Determined by mass loading effect. By making the film thickness of the frequency adjustment layers 26a and 26b different between the piezoelectric resonators, the resonance frequency of each piezoelectric resonator is adjusted to a desired value. Although not shown, the same applies to the parallel piezoelectric resonators 4a and 4b. Piezoelectric resonators having three different resonance frequencies have the lowest resonance frequency of the bypass piezoelectric resonator 6, the next highest resonance frequency of the parallel piezoelectric resonators 4a and 4b, and the highest resonance frequency of the series piezoelectric resonator 3. They can be formed on the same substrate.

  Similarly, in the variable capacitor 7, when an electric field is applied between the upper electrode layer 25 c and the lower electrode layer 23 c and the applied voltage is changed, the relative dielectric constant of the ferroelectric layer 28 is changed and the capacitance is changed. The film configuration of the present embodiment is an example, and the electrode may be composed of a plurality of materials or a dielectric layer may be added, and is not limited to this. The variable capacitor 7 uses a ferroelectric material, but a variable capacitor diode or the like can also be used.

  FIG. 10 is a top view of a piezoelectric filter when a surface acoustic wave resonator is used as the piezoelectric resonator in the configuration of FIG. The same components as those in FIG. 8 are denoted by the same reference numerals, and the description thereof is omitted.

  The surface acoustic wave resonator is configured by arranging an interdigital transducer electrode and a reflector electrode on a piezoelectric substrate close to the propagation direction. On the piezoelectric substrate 29, the parallel piezoelectric resonators 4a and 4b, the series piezoelectric co-photographer 3, and the bypass piezoelectric resonator 6 are formed and connected by wiring electrodes on the piezoelectric substrate 29. Further, a variable capacitor 7 composed of a voltage variable capacitor diode is formed in parallel with the bypass piezoelectric resonator 6 between the two parallel piezoelectric resonators 4a and 4b facing each other. Parallel inductors 5a and 5b are formed at both ends of the bypass piezoelectric resonator 6, and the parallel inductors 5a and 5b are grounded. Here, the resonance frequency of the surface acoustic wave resonator is optimally set to obtain desired filter characteristics by adjusting the electrode finger pitch, the metallization ratio, or the electrode film thickness.

  As described above, the piezoelectric filter in the case where the piezoelectric resonator is composed of the thin film acoustic wave resonator and the case where the piezoelectric resonator is composed of the surface acoustic wave resonator is shown. Similarly, the resonator can be replaced with a piezoelectric resonator to form a filter, and the same effect can be obtained.

  Note that a DC (direct current) voltage must be applied between the terminals in both the variable capacitor 7 using the ferroelectric layer 28 of FIG. 9B and the variable capacitor 7 using the voltage variable capacitor diode of FIG. . However, in the configuration of FIG. 8, both ends are connected to GND in terms of DC and have the same potential, and a bias cannot be applied. Therefore, in the actual circuit, as in the configuration of the piezoelectric filter 30 shown in FIG. 11A, the low frequency band is not connected between the connection points of the bypass piezoelectric resonator 6 and the first parallel inductor 5a, and the high frequency band is not connected. For example, a large capacitance 31 of 5 nF or more is arranged so as to be connected. The location where the capacitor is connected may be between the GNDs of either one of the variable capacitors 7. Alternatively, as in the configuration of the piezoelectric filter 32 in FIG. 11B, the capacitor 33 may be disposed between the connection points of the variable capacitor 7 and the bypass piezoelectric resonator 6, or may be between the parallel inductor and the GND ground.

  FIG. 12 shows pass characteristics of the piezoelectric filter according to this embodiment configured as described above. The filter waveform e1 shows that when the variable capacitor 7 is increased by 0.1 pF, e2 is increased by 0.2 pF, e3 is increased by 0.3 pF, e4 is increased by 0.4 pF, and e5 is 0. When the value is increased by 5 pF, and e6 indicates the pass characteristic when the value is increased by 0.6 pF.

  As can be seen from FIG. 12, the high-frequency side attenuation band of the pass band 34 is changed. That is, by changing the variable capacitor 7, it is possible to make the high band side attenuation characteristic of the pass band 34 variable without deteriorating the pass characteristic in the pass band 34.

  As described above, the number of filter stages, that is, the number of piezoelectric resonators, can be variously set such as the four stages in FIG. 8 or the six stages in FIG. If the stage circuit configuration is included, a desired effect can be obtained regardless of the number of stages.

  It should be noted that a part of the configuration shown in FIG. 8 can be changed to configure the piezoelectric filter 35 as shown in FIG. In this configuration, instead of the bypass piezoelectric resonator 6 in FIG. 8, a variable capacitance bypass piezoelectric resonator 36 having a variable capacitance value is used, and the variable capacitor 7 is deleted. 14A and 14B show a configuration corresponding to FIGS. 9A and 9B. The variable capacitance bypass piezoelectric resonator 36 has a piezoelectric effect such as lead zirconate titanate (PZT) or bismuth titanate (BIT) as the piezoelectric layer 37, and the relative dielectric constant changes depending on the DC (direct current) voltage. By using the material, the capacitance value can be made variable.

  In the above embodiment, a single piezoelectric filter has been described. However, the piezoelectric filter having the configuration of each embodiment can be used for a duplexer, a communication device, and the like as follows.

  FIG. 15 is a block diagram of the duplexer 47 using a piezoelectric filter. The transmission terminal 41, the reception terminal 42, and the antenna terminal 43 are provided, and the transmission filter 44, the phase shift circuit 45, and the reception filter 46 are arranged in this order between the transmission terminal 41 and the reception terminal 42. An antenna terminal 43 is connected between the transmission filter 44 and the phase shift circuit 45. At least one of the transmission filter 44 and the reception filter 46 is provided with any of the piezoelectric filters in the above embodiment.

  FIG. 16 is a block diagram of a communication device using a piezoelectric filter. The signal input from the transmission terminal 51 passes through the baseband unit 52, the signal is amplified by the power amplifier 53, passes through the duplexer 54, is filtered by the transmission filter, and the radio wave is transmitted from the antenna 55. The signal received by the antenna 55 is filtered by the reception filter through the duplexer 54, amplified by the LNA 56, and transmitted to the reception terminal 57 through the baseband unit 52. At least one of the transmission filter and the reception filter included in the duplexer 54 is provided with any of the piezoelectric filters in the above embodiment.

  The piezoelectric resonator and the piezoelectric filter of the present invention can be realized with a small size, low loss characteristics and low cost, and are useful as a filter in a wireless circuit in a mobile communication terminal such as a mobile phone, a wireless LAN, and a digital TV reception tuner. It is. Moreover, it can be applied to uses such as a filter for a radio base station according to the specification.

1 is an equivalent circuit diagram of a piezoelectric filter according to a first embodiment of the present invention. The figure which shows the passage characteristic of the piezoelectric filter which concerns on the 1st Embodiment of this invention. The figure which shows the passage characteristic of the piezoelectric filter which concerns on the 1st Embodiment of this invention. The equivalent circuit diagram of the piezoelectric filter which concerns on the 2nd Embodiment of this invention The figure which shows the passage characteristic of the piezoelectric filter which concerns on the 2nd Embodiment of this invention. Equivalent circuit diagram of a piezoelectric filter according to a third embodiment of the present invention The figure which shows the passage characteristic of the piezoelectric filter which concerns on the 3rd Embodiment of this invention. Equivalent circuit diagram of piezoelectric filter according to Embodiment 4 of the present invention 8 is a top view of a piezoelectric filter when a thin film acoustic wave resonator is used as the piezoelectric resonator in the configuration of FIG. Sectional drawing along the AA line of FIG. 9A 8 is a top view of a piezoelectric filter when a surface acoustic wave resonator is used as the piezoelectric resonator in the configuration of FIG. Equivalent circuit diagram showing an improved example of the piezoelectric filter of FIG. Equivalent circuit diagram showing another improved example of the piezoelectric filter of FIG. The figure which shows the passage characteristic of the piezoelectric filter which concerns on the 4th Embodiment of this invention Equivalent circuit diagram showing a modification of the piezoelectric filter of FIG. 13 is a top view of a piezoelectric filter when a thin film acoustic wave resonator is used as the piezoelectric resonator in the configuration of FIG. Sectional drawing along the BB line of FIG. 14A Block diagram of duplexer using piezoelectric filter according to an embodiment of the present invention The block diagram of the communication apparatus using the piezoelectric filter which concerns on embodiment of this invention Equivalent circuit diagram of a conventional piezoelectric filter using a piezoelectric resonator (A) is a figure which shows the single-piece | unit characteristic of each piezoelectric resonator which comprises the conventional piezoelectric filter, (b) is a figure which shows the passage characteristic of the conventional piezoelectric filter. The figure which shows the filter passage characteristic of the piezoelectric filter which uses the conventional piezoelectric resonator

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Input terminal 2 Output terminal 3, 3a, 3b, 3c Series piezoelectric resonator 4a, 4b Parallel piezoelectric resonator 5a, 5b Parallel inductor 6 Bypass piezoelectric resonator 7, 11 Variable capacity 8, 12, 15, 17, 30, 32 , 35 Piezoelectric filter 9, 10, 13, 16, 34 Passband 14 Variable inductor 21 Substrate 22 Insulator layers 23a, 23b, 23c Lower electrode layers 24a, 24b, 37 Piezoelectric layers 25a, 25b, 25c Upper electrode layer 26a, 26b Frequency adjustment layer 27a, 27b Cavity 28 Ferroelectric layer 29 Piezoelectric substrate 31, 33 Capacitance 36 Capacity variable piezoelectric filter 41, 51 Transmission terminal 42, 57 Reception terminal 43 Antenna terminal 44 Transmission filter 45 Phase shift circuit 46 Reception filter 47, 54 Duplexer 52 Baseband 53 Power Amplifier 55 Antenna 56 LNA
61a, 61b Series piezoelectric resonators 62a, 62b, 62c, 62d Parallel variable capacitors 63a, 63b, 63c, 63d Series variable capacitors 64a, 64b Series piezoelectric resonator group 65a Input terminal 65b Output terminal 66 Piezoelectric filter 70 Parallel piezoelectric resonator group Resonant point 71 Anti-resonant point 72 of parallel piezoelectric resonator group Resonant point 73 of series piezoelectric resonator group Anti-resonant point 74 of series piezoelectric resonator group Pass band 75 Low-frequency attenuation pole 76 Low-frequency attenuation band 77 High frequency Side attenuation pole 78 High side attenuation band 79, 80, 81, 82 Filter pass characteristics a1 to a6, b1 to b5, c1 to c5, d1 to d10, e1 to e6 Filter waveform s1 Single unit characteristic s2 of the parallel piezoelectric resonator group Single unit characteristics of series piezoelectric resonator group t Filter pass characteristics

Claims (5)

In a piezoelectric filter comprising one or more series piezoelectric resonators and two or more parallel piezoelectric resonators,
A first inductor disposed between the first parallel piezoelectric resonator and ground;
A second inductor disposed between the second parallel piezoelectric resonator and ground;
A connection point between the first parallel piezoelectric resonator and the first inductor, and a bypass piezoelectric resonator disposed between the connection point between the second parallel piezoelectric resonator and the second inductor,
A piezoelectric filter, wherein a capacitance value of the bypass piezoelectric resonator is variable. In a piezoelectric filter comprising one or more series piezoelectric resonators and two or more parallel piezoelectric resonators,
A first inductor disposed between the first parallel piezoelectric resonator and ground;
A second inductor disposed between the second parallel piezoelectric resonator and ground;
A bypass piezoelectric resonator disposed between a connection point of the first parallel piezoelectric resonator and the first inductor, and a connection point of the second parallel piezoelectric resonator and the second inductor;
A piezoelectric filter comprising: a variable capacitor arranged in parallel with the bypass piezoelectric resonator. In a piezoelectric filter comprising one or more series piezoelectric resonators and two or more parallel piezoelectric resonators,
A first inductor disposed between the first parallel piezoelectric resonator and ground;
A second inductor disposed between the second parallel piezoelectric resonator and ground;
A reactance element disposed between a connection point of the first parallel piezoelectric resonator and the first inductor, and a connection point of the second parallel piezoelectric resonator and the second inductor;
A reactance value of the reactance element is variable. A transmission terminal and a reception terminal;
An antenna terminal connected between the transmission terminal and the reception terminal;
A transmission filter disposed between the transmission terminal and the antenna terminal;
A reception filter disposed between the reception terminal and the antenna terminal;
The duplexer in which the piezoelectric filter according to any one of claims 1 to 3 is used for at least one of the transmission filter and the reception filter. An antenna,
A transmitting device;
A receiving device;
The communication apparatus provided with the duplexer of Claim 4 arrange | positioned in the connection part of the said antenna, the said transmitter, and the said receiver.

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