JP2011146768A - Ladder type elastic wave filter and antenna duplexer using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress Q value deterioration of a ladder type elastic wave filter. <P>SOLUTION: The ladder type elastic wave filter is a ladder type elastic wave filter in which a serial resonator and a parallel resonator are connected in the shape of a ladder, and includes: a first parallel resonator which is connected between a signal route and ground and forms an attenuation pole in a frequency being double passband or more and a triple passband or less of the ladder type elastic wave filter and an inductor connected serially to the first parallel resonator; and a second parallel resonator 19 connected between the signal route and the ground and having a capacity smaller than that of the first parallel resonator, wherein the second parallel resonator 19 is provided with a plurality of input and output IDT electrode pairs 25, 26 and 27 which are acoustically coupled, and the plurality of input and output IDT electrode pairs 25, 26 and 27 are connected in series. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a ladder-type elastic wave filter and an antenna duplexer using the same.

  A conventional ladder type acoustic wave filter will be described with reference to the drawings. FIG. 5 is a circuit block diagram of an antenna duplexer equipped with a conventional ladder type acoustic wave filter.

  In FIG. 5, a conventional antenna duplexer 101 is, for example, an antenna duplexer for band 1 of the UMTS system, and has a pass band (2110 MHz) on the high frequency side of the transmission filter 102 and the pass band (1920 MHz to 1980 MHz) of the transmission filter 102. To 2170 MHz). The transmission filter 102 is connected between the input terminal 104 and the antenna terminal 105, receives a transmission signal from the input terminal 104, and outputs it from the antenna terminal 105. The reception filter 103 includes, for example, a longitudinal mode coupling filter 118 connected between the antenna terminal 105 and the output terminal 106, and receives a reception signal from the antenna terminal 105 and outputs it from the output terminal 106. Further, the antenna duplexer 101 includes a phase shifter 107 connected between the transmission filter 102 and the reception filter 103. With this phase shifter 107, the other passband is set to a high impedance between transmission and reception. I try to improve isolation.

  The transmission filter 102 is a ladder type acoustic wave filter in which a series resonator 108 and parallel resonators 109 and 110 are connected in a ladder shape. In addition, by connecting a capacitor 113 in parallel to the series resonator 108 closest to the antenna terminal 105, the antiresonance frequency of the series resonator 108 is controlled to be lower than the pass band of the reception filter 103, and a reception filter having a desired characteristic is obtained. 103 is realized.

  Further, the transmission filter 102 includes, in order from the antenna terminal 105 side, a first parallel resonator 109 connected between the signal path and the ground, a first inductor 111 connected in series thereto, a signal path and a ground. And a third parallel resonator 110 connected in between and a third inductor 112 connected in series therewith.

  As shown in FIG. 6, the first parallel resonator 109 and the first inductor 111 connected in series form an attenuation pole 114 in the adjacent frequency band on the low frequency side of the pass band of the transmission filter 102 and the transmission filter. The attenuation pole 115 is formed at a frequency that is not less than 2 times and not more than 3 times the pass band of 102.

  In addition, the third parallel resonator 110 and the third inductor 112 connected in series form an attenuation pole 116 in the frequency band on the low frequency side of the pass band of the transmission filter 102 and increase the pass band of the transmission filter 102. An attenuation pole 117 is formed in the adjacent frequency band on the band side. The vertical axis shown in FIG. 6 indicates the insertion loss (unit dB) of the filter, and the horizontal axis indicates the frequency (unit MHz) (hereinafter the same in the filter characteristic diagram).

  For example, Patent Literature 1 and Patent Literature 2 are known as prior literature relating to this application.

JP-T-2005-521319 JP-A-9-8598

  In such a conventional antenna duplexer 101, the amount of attenuation in the frequency band (3840 MHz to 3960 MHz and 5760 MHz to 5940 MHz) that is twice and three times the pass band (1920 MHz to 1980 MHz) of the transmission filter 102 is a characteristic of the transmission filter 102. It was necessary to ensure. This is because harmonic noise is generated in a power amplifier (not shown) connected to the input side of the transmission filter 102 at integer multiples of the frequency of the transmission signal, particularly at frequencies twice and three times.

  Therefore, as means for ensuring attenuation in frequency bands twice and three times the pass band of the transmission filter 102, the first parallel resonator is provided between the first parallel resonator 109 and the third parallel resonator 110. A method of moving the attenuation pole 115 to the low frequency side by connecting a parallel resonator (not shown) whose capacity is sufficiently smaller than 109 is conceivable. It is necessary to make the capacity of this parallel resonator sufficiently small. When the capacity of this parallel resonator is large, the insertion loss of the transmission filter 102 increases and the attenuation pole 115 moves greatly to the low frequency side. This is because there are two disadvantages that it is impossible to secure an attenuation amount in a frequency band three times the pass band of the transmission filter 102.

  However, if the crossing width of the IDT electrodes in the parallel resonator is reduced or the logarithm is reduced in order to reduce the capacitance of the parallel resonator, ripples are generated in the pass band of the transmission filter 102 or the Q value is deteriorated due to loss. The problem that this occurs can occur.

  Accordingly, an object of the present invention is to suppress the Q value deterioration of a ladder-type elastic wave filter and to secure an attenuation amount in frequency bands twice and three times the pass band of the ladder-type elastic wave filter.

  In order to achieve this object, the ladder-type elastic wave filter of the present invention is a ladder-type elastic wave filter in which a series resonator and a parallel resonator are connected in a ladder shape, and is provided between a signal path and a ground. A first parallel resonator that is connected and forms an attenuation pole at a frequency that is not less than 2 times and not more than 3 times the passband of the ladder-type acoustic wave filter; an inductor connected in series to the first parallel resonator; and a signal path and a ground And a second parallel resonator having a smaller capacity than the first parallel resonator, the second parallel resonator having a plurality of input / output IDT electrode pairs acoustically coupled to each other, and A plurality of input / output IDT electrode pairs are connected in series.

  Even if strong harmonic noise is generated in the power amplifier connected to the input side of the ladder-type elastic wave filter with an integer multiple of the frequency of the transmission signal, particularly twice and three times the frequency, the ladder-type elasticity It is possible to secure attenuation in frequency bands twice and three times the pass band of the wave filter. Further, even if the capacity of the second parallel resonator is sufficiently smaller than the capacity of other parallel resonators, for example, an increase in insertion loss due to ripple or Q value deterioration can be suppressed, and good transmission filter characteristics can be obtained.

1 is a circuit block diagram of an antenna duplexer equipped with a ladder-type elastic wave filter according to Embodiment 1 of the present invention. Transmission filter characteristics of the same acoustic wave device Top view of the acoustic wave device Another top view of the same acoustic wave device Circuit block diagram of a conventional antenna duplexer equipped with a ladder type acoustic wave filter Filter characteristics diagram of the same acoustic wave device

(Embodiment 1)
Hereinafter, the acoustic wave device according to the first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a circuit block diagram of an antenna duplexer 1 on which a ladder type acoustic wave filter according to Embodiment 1 is mounted.

  In FIG. 1, an antenna duplexer 1 equipped with a transmission filter 2 that is a ladder type acoustic wave filter of the present invention is an antenna duplexer for band 1 of a UMTS system, for example, and includes a transmission filter 2 and a pass band of the transmission filter 2. And a reception filter 3 having a pass band (2110 MHz to 2170 MHz) on the high frequency side (1920 MHz to 1980 MHz). The transmission filter 2 is connected between the input terminal 4 and the antenna terminal 5, receives a transmission signal from the input terminal 4, and outputs it from the antenna terminal 5. Further, the reception filter 3 includes, for example, a longitudinal mode coupling filter 18 connected between the antenna terminal 5 and the output terminal 6, and receives a reception signal from the antenna terminal 5 and outputs it from the output terminal 6. The reception filter 3 may have two output terminals 6 and may use these to balance output the reception signal. Furthermore, the reception filter 3 may include a resonator connected in series to the signal path on the antenna end side, the reception end side, or both. Further, the antenna duplexer 1 includes a phase shifter 7 connected between the transmission filter 2 and the reception filter 3. With this phase shifter 7, the other passband is set to a high impedance between transmission and reception. I try to improve isolation.

  The transmission filter 2 is a ladder type acoustic wave filter in which a series resonator 8 and parallel resonators 9, 10, and 19 are connected in a ladder shape. In addition, by connecting a capacitor 13 in parallel to the series resonator 8 closest to the antenna terminal 5, the antiresonance frequency of the series resonator 8 is controlled to be lower than the pass band of the reception filter 3, and a reception filter having a desired characteristic is obtained. 3 is realized.

  Further, the transmission filter 2 includes, in order from the antenna terminal 5 side, a first parallel resonator 9 (2.96 pF) connected between the signal path and the ground, and a first inductor 11 (1 .5 nH), a second parallel resonator 19 (0.0747 pF) connected between the signal path and the ground, a second inductor 20 (1.4 nH) connected in series with the second parallel resonator 19 (0.0747 pF), a signal path and the ground And a third parallel resonator 10 (0.6 pF) connected in between and a third inductor 12 (1.8 nH) connected in series therewith.

In the transmission filter 2, the series resonator 8, the first parallel resonator 9, the third parallel resonator 10, and the capacitor 13 are formed on the piezoelectric substrate. Further, the first inductor 11 and the third inductor 12 may be formed in a multilayer filter on which the piezoelectric substrate is mounted, or may be formed on a dielectric layer stacked on the piezoelectric substrate. The piezoelectric substrate is, for example, a lithium niobate (LiNbO ₃ ) -based or lithium tantalate (LiTaO ₃ ) -based piezoelectric single crystal substrate, and when the dielectric layer is formed on the piezoelectric substrate, the dielectric layer Is, for example, silicon oxide (SiO ₂ ), silicon nitride (SiN), aluminum nitride (AlN), or a laminated structure thereof.

  Further, the comb-shaped electrodes constituting the series resonator 8, the first parallel resonator 9, and the third parallel resonator 10 are made of, for example, aluminum, copper, silver, gold, titanium, tungsten, molybdenum, platinum, or chromium. A single metal, an alloy containing these as a main component, or a laminated structure thereof. The comb-shaped electrode may be an electrode that excites a surface acoustic wave such as an SH (Shear Horizontal) wave or Rayleigh as a main wave, or an electrode that excites a bulk wave such as a Lamb wave. good.

  As shown in FIG. 2, the first parallel resonator 9 and the first inductor 11 ensure attenuation in a DCS (Digital Cellular System) frequency band (1710 MHz to 1880 MHz) on the low frequency side of the pass band of the transmission filter 2. In order to form an attenuation pole 14 and to ensure attenuation at a frequency twice (1920 MHz to 1980 MHz) and three times (3840 MHz to 3960 MHz) of the pass band of the transmission filter 2, a frequency of 2 to 3 times Attenuation pole 15 is formed.

  In addition, the second parallel resonator 19 and the second inductor 20 form an attenuation pole 21 slightly below the attenuation pole 14 in order to further secure an attenuation amount in the DCS frequency band, and a transmission filter. An attenuation pole (not shown) is formed at a frequency three times or more of the pass band of 2. Further, the attenuation pole 15 is moved to the low frequency side by the second parallel resonator 19 having a capacity sufficiently smaller than that of the first parallel resonator 9, and the attenuation in the frequency band twice and three times the pass band of the transmission filter 2. Can be sufficiently secured at 20 dB or more. The attenuation pole 15 moves to the low frequency side because there is a path in which the first parallel resonator 9 and the second parallel resonator 19 are electrically connected to each other via the inductor 11 and the inductor 20 via the ground. This is probably because of this.

  In addition, the capacity of the second parallel resonator 19 needs to be sufficiently small in addition to the disadvantage that the insertion loss on the low frequency side of the transmission filter 2 increases when the capacity of the second parallel resonator 19 is large, This is because the attenuation pole 15 moves too much to the low frequency side, and it becomes impossible to secure an attenuation amount in a frequency band three times the pass band of the transmission filter 2.

  The third parallel resonator 10 and the third inductor 12 are attenuation poles in order to secure an attenuation amount in the GPS (Global Positioning System) frequency band (1575.42 MHz) on the lower side of the pass band of the transmission filter 2. 16 is formed, and an attenuation pole 17 is formed in order to secure an attenuation amount in the pass band of the reception filter 3 on the high frequency side of the pass band of the transmission filter 2.

  In the power amplifier connected to the input side of the transmission filter 2 by the second parallel resonator 19, even if strong harmonic noise is generated at an integer multiple of the frequency of the transmission signal, particularly twice and three times the frequency, It is possible to ensure attenuation in frequency bands twice and three times the pass band of the transmission filter 2.

  FIG. 3 shows a schematic top view of the second parallel resonator 19 in the ladder type acoustic wave filter of the present embodiment. In FIG. 3, the second parallel resonator 19 includes three input / output IDT electrode pairs 25, 26, and 27 that are connected in series between the input unit 23 and the output unit 24 and are acoustically coupled to each other. These input / output IDT electrode pairs 25, 26, 27 are arranged side by side in the propagation direction of the main elastic wave, and the grating reflectors 22 are arranged at both ends of these input / output IDT electrode pairs 25, 26, 27.

  When a resonator having an extremely small capacitance, such as the second parallel resonator 19, is created, it is necessary to reduce the logarithm of IDT extremely or to reduce the crossing width in the conventional resonator structure. It was. However, when the logarithm of IDT is extremely reduced, there is a problem that the Q value is lowered due to the resistance loss of the electrode fingers, or ripples are generated due to the small logarithm. Further, when the crossing width is made extremely small, there is a problem that a transverse mode ripple occurs in a piezoelectric substrate material in which transverse mode spurs such as a decrease in Q value due to leakage of main elastic waves and lithium niobate are liable to occur. As in the present invention, since the second parallel resonator 19 is connected in series and has a plurality of input / output IDT electrode pairs 25, 26, and 27 that are acoustically coupled to each other, two IDT electrode pairs are provided. Compared to a conventional resonator sandwiched between two reflectors, when a resonator having the same capacitance is made, the IDT electrode pair per one becomes large. Is obtained. Thereby, it is possible to suppress the ripple in the pass band of the transmission filter 2 and to suppress the deterioration of the Q value due to the loss. Further, with this configuration, even if the capacity of the second parallel resonator 19 is sufficiently smaller than the capacities of the other first and third parallel resonators 9 and 10, the power durability of the second parallel resonator 19 is deteriorated. It can be suppressed.

  As shown in FIG. 3, the second parallel resonator 19 has at least three input / output IDT electrode pairs 25, 26, 27 that are acoustically coupled to each other, and these at least three input / output IDT electrode pairs 25, 26. 27 are preferably connected in series. By connecting at least three input / output IDT electrode pairs 25, 26, 27 in series, the capacity of the second parallel resonator 19 can be made sufficiently smaller than the capacities of the other first and third parallel resonators 9, 10. It can be done.

  Further, as shown in FIG. 1, the second parallel resonator 19 is connected between the first parallel resonator 9 and the third parallel resonator 10 having a larger capacity than the second parallel resonator 19. desirable. Thereby, it can suppress that the 2nd parallel resonator 19 with small capacity | capacitance deteriorates by the reflected wave of the input wave from the input terminal 4, and the output wave from an antenna end.

  Further, as shown in FIG. 4, the second parallel resonator 19 has a plurality of input / output IDT electrode pairs 25, 26, 27 that are acoustically coupled to each other and are connected in series. It is desirable. As a result, the capacity of the second parallel resonator 19 can be further reduced. Further, although the capacity can be reduced by increasing the number of stages in the conventional resonator, the configuration shown in FIG. 4 has an advantage that a resonator having a desired capacity can be realized with a much smaller area.

  The pitches of the input / output IDT electrode pairs 25, 26, 27 constituting the second parallel resonator 19 shown in FIGS. 3 and 4 are not necessarily constant. For example, any of the input / output IDT electrode pairs 25, 26 27, the pitch of the input / output IDT electrode pairs 25 and 27 located at the ends of the input / output IDT electrodes 27 is made smaller than the pitch of the other input / output IDT electrode pairs 26 to increase the Q value at the resonance frequency of the second parallel resonator 19 it can.

  The ladder-type acoustic wave filter according to the first embodiment includes a semiconductor integrated circuit element (not shown) connected to the filter and a reproducing device connected to the semiconductor integrated circuit element (not shown). You may mount in the provided electronic device. Thereby, the communication quality in an electronic device can be improved.

  The ladder-type elastic wave filter according to the present invention has a feature of suppressing the Q value deterioration, and can be applied to an electronic device such as a mobile phone.

1 antenna duplexer 2 transmission filter 3 reception filter 4 input terminal 5 antenna terminal 6 output terminal 7 phase shifter 8 series resonator 9 first parallel resonator 10 third parallel resonator 11, 12, 20 inductor 13 capacitor 18 longitudinal mode Coupling filter 19 Second parallel resonator

Claims (5)

A ladder-type acoustic wave filter in which a series resonator and a parallel resonator are connected in a ladder shape,
A first parallel resonator connected between the signal path and the ground, and forming an attenuation pole at a frequency not less than twice and not more than three times the pass band of the ladder-type acoustic wave filter, and an inductor connected in series to the first parallel resonator When,
A second parallel resonator connected between the signal path and the ground and having a capacity smaller than that of the first parallel resonator;
The second parallel resonator includes a plurality of input / output IDT electrode pairs acoustically coupled to each other, and the plurality of input / output IDT electrode pairs are connected in series. 2. The ladder-type elasticity according to claim 1, wherein the second parallel resonator has at least three input / output IDT electrode pairs acoustically coupled to each other, and the at least three input / output IDT electrode pairs are connected in series. Wave filter. 2. The ladder-type elastic wave filter according to claim 1, wherein the second parallel resonator is connected between a third parallel resonator having a capacity larger than that of the second parallel resonator and the first parallel resonator. . 2. The ladder-type elastic wave filter according to claim 1, wherein the second parallel resonator includes a plurality of input / output IDT electrode pairs acoustically coupled to each other and is connected in series. An antenna duplexer comprising a transmission filter and a reception filter having a pass band on the high side of the pass band of the transmission filter,
The said transmission filter is an antenna sharing device provided with the ladder type | mold elastic wave filter of Claim 1.

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