JP4734751B2 - Balanced surface acoustic wave filter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a surface acoustic wave filter, and more particularly to a balanced surface acoustic wave filter in which a phase difference error and an amplitude difference error between a pair of balanced terminals are improved.
[0002]
[Prior art]
In recent years, surface acoustic wave filters (hereinafter referred to as SAW filters) have been widely used in the communication field, and are widely used particularly in mobile phones and the like because they have excellent characteristics such as high performance, small size, and mass productivity. In recent mobile phones, it is necessary to accommodate digital circuits and analog circuits in a very small space, and therefore it is necessary to reduce noise from other circuits as much as possible. For this reason, means for reducing noise by making the input / output circuits of the RF circuit and IF circuit balanced is adopted, and the devices used for the RF and IF circuits are also required to be balanced. .
[0003]
FIG. 16A shows a surface acoustic wave filter in which two longitudinally coupled primary-third-order dual-mode surface wave filters (hereinafter referred to as double-mode SAW filters) using longitudinal-first-order-third-order modes are connected in cascade. It is a top view which shows the electrode pattern structure of this. The IDT electrodes 101, 102, 103 are arranged close to each other along the propagation direction of the surface wave on the main surface of the piezoelectric substrate (not shown), and grating reflectors (hereinafter referred to as reflections) are arranged on both sides of the IDT electrodes 101, 102, 103. 104a and 104b are provided to form a dual mode SAW filter F1. Further, IDT electrodes 101 ′, 102 ′, 103 ′ having almost the same configuration as the filter F1 are arranged close to each other on the same piezoelectric substrate in parallel with the dual mode SAW filter F1, and reflectors 104′a are arranged on both sides thereof. , 104′b are provided to form a dual mode SAW filter F2. Then, the comb electrodes near the center of the piezoelectric substrate of the IDT electrodes 102, 103 and 102 ′, 103 ′ on both sides of the dual mode SAW filters F1 and F2 are connected by lead electrodes formed on the same piezoelectric substrate. To do. Further, comb electrodes on the outer side of the piezoelectric substrate of the IDT electrodes 101 and 101 ′ in the center are connected to the input terminal IN and the output terminal OUT using bonding wires, respectively, and the other comb electrodes are connected to the ground. Construct a connected dual mode SAW filter.
[0004]
The IDT electrodes 101, 102, and 103 of the SAW filter F1 and the IDT electrodes 101 ', 102', and 103 'of the SAW filter F2 are each formed of a pair of comb electrodes having a plurality of electrode fingers that are interleaved with each other. In order to widen the bandwidth of the dual mode SAW filters F1 and F2, the widths of the outermost electrode fingers (referred to as electrode fingers S1 and S2) in the IDT electrodes 101 and 101 ′ at the respective centers of the filters are set. It is wider than others.
[0005]
FIG. 16B shows a balanced type output side of the unbalanced cascaded double mode SAW filter shown in FIG. 16A, and the configuration of the input side dual mode SAW filter F1 is the same. However, the comb-shaped electrodes of the central IDT electrode 105 forming the output-side filter F2 and the two output terminals OUT1 and OUT2 are connected to form a balanced configuration.
FIGS. 17A, 17B, and 17C are respectively the filter characteristics of the input unbalanced-output balanced cascaded dual mode SAW filter shown in FIG. 16B, and two balanced output terminals OUT1. , OUT2 phase difference characteristic, amplitude difference characteristic. The center frequency is set to 942.5 MHz, the bandwidth is set to 35 MHz, and the piezoelectric substrate is 39 ° Y-X LiTaO_ThreeThe electrode period λ is 4.1846 μm, the electrode thickness h is 8.7% λ, the center IDT electrodes 101 and 101 ′ are 17.5 pairs, and the IDT electrodes 102, 103, 102 ′, and 103 ′ on both sides are 11 This is a filter characteristic when .5 pairs, the crossing width is set to 50λ, and the number of reflectors 104a, 104b, 104′a, 104′b is set to 60.
[0006]
FIG. 18 is a circuit diagram for measuring the filter characteristics of the SAW filter. When both the input and output impedances of the SAW filter are 50Ω, the impedance ratio n of the balun (BALUN, impedance matching unit) is 1. When the output impedance of the filter is larger than 50Ω, the value of n is changed and measured. FIG. 19 is a circuit diagram for measuring the phase difference and amplitude difference between the two balanced output terminals OUT1 and OUT2 of the balanced SAW filter. When both the input / output impedances of the SAW filter are 50Ω, R1, R2 is 25Ω, and when it is larger than 50Ω, the values of R1 and R2 may be set as appropriate.
[0007]
FIG. 20 is a plan view showing a configuration of an input unbalanced / output balanced cascaded dual mode SAW filter having different input / output impedances. That is, the input / output impedance is made different by making the number of pairs of the IDT electrodes 106 at the center of the output side SAW filter F2 different from the number of pairs of the IDT electrodes 101 at the center of the input side SAW filter F1. The example of FIG. 20 is an example in which the logarithm of the IDT electrode 106 is reduced in order to increase the output impedance. The IDT electrode configuration of the SAW filter F1 on the input side is the same as the IDT electrode configuration of the SAW filter F1 shown in FIG. The IDT electrodes 106 and 107 (108 is symmetrical with 107 about the center of the electrode) of the SAW filter F2 on the output side are a predetermined number in order from the outermost electrode fingers S1 of the IDT electrode 101 at the center of the SAW filter F1. The electrode finger is formed by separating from the central IDT electrode 101 and connecting to one of the comb electrodes of the outer IDT electrode 102.
[0008]
21 (a), (b) and (c) respectively show the filter characteristics and two balanced output terminals of the input unbalanced / output balanced cascaded dual mode SAW filter having different input / output impedances shown in FIG. These are phase difference characteristics and amplitude difference characteristics between OUT1 and OUT2. The center frequency is set to 942.5 MHz, the bandwidth is set to 35 MHz, and the piezoelectric substrate is 39 ° Y-X LiTaO_ThreeThe electrode film thickness h is 8.7% λ, the IDT electrode 101 at the center of the SAW filter F1 on the input side is 16.5 pairs, the IDT electrodes 102 and 103 on both sides are 10.5 pairs, the crossing width is 50λ, The number of reflectors 104a and 104b is set to 60, and a predetermined electrode index is separated from both ends so that the logarithm of the IDT electrode 106 at the center of the SAW filter F2 on the output side matches the output impedance. This is a filter characteristic when connected to the IDT electrodes 107 and 108, the crossing width is set to 50λ, and the number of reflectors 109a and 109b is set to 60.
[0009]
[Problems to be solved by the invention]
However, in the conventional input unbalanced / output balanced cascaded dual mode SAW filter as shown in FIG. 16B or FIG. 20, as shown in FIG. 17B or 21B. The phase difference between the two balanced output terminals OUT1 and OUT2 was not exactly 180 °, and a phase difference error of about 10.5 ° or about 6 ° occurred. Further, the amplitude difference between OUT1 and OUT2 does not accurately become 0 dB, and an amplitude error of about 1.5 dB or about 3.3 dB occurs, and there is a problem that reception quality deteriorates when used for a mobile phone or the like.
The present invention has been made to solve the above-mentioned problem, and is an input unbalanced-output balanced type in which the phase error and the amplitude error from the phase difference of 180 ° between the two balanced terminals are significantly smaller than the conventional one. It is an object of the present invention to provide a cascade connection type dual mode SAW filter.
[0010]
[Means for Solving the Problems]
[Application Example 1]
  Along the direction of propagation of surface waves on a piezoelectric substrateIt consists of a central IDT electrode and IDT electrodes on both sidesA primary-third-order longitudinally coupled double mode in which three IDT electrodes are arranged close to each other and grating reflectors are arranged on both sides thereof.BulletSurface acoustic wave filtersThe aboveConfigure the central IDT electrodeOneComb electrodeAnd the other comb electrodeHave the same number of electrode indicesYes, the central IDT electrode was connected to a balanced terminalA balanced surface acoustic wave filter characterized by that.
[Application Example 2]
  bandWide electrode fingers to widen the areaThe bothConnect to the IDT electrode on the sideOctopusAnd featuresAs described in Application Example 1Balanced surface acoustic wave filter.
[Application Example 3]
  in frontOne of the IDT electrodes on both sides has a higher electrode index than the other by an odd numberNoIt is characterized byAs described in Application Example 1 or Application Example 2Balanced surface acoustic wave filter.
[Application Example 4]
  The widthWideElectrode fingers and saidBetween the central IDT electrodeConnected to at least one of the IDT electrodes on both sides.Odd numberThe electrode fingers were providedIt is characterized byAs described in Application Example 2Balanced surface acoustic wave filter.
[Application Example 5]
  SaidCentral IDT electrodeBetween the IDT electrodes on both sides and one of the IDT electrodes on both sides.Provided with multiple electrode fingersIt is characterized byAs described in any one of Application Examples 1 to 4Balanced surface acoustic wave filter.
[Application Example 6]
  SaidOne polarity of IDT electrodes on both sidesNokuDiamond electrodeThe multiple connected to theElectrode fingerofNumber, One of the IDT electrodes on both sidesotherWithOnly an odd numberIs differentIt is characterized byAs described in Application Example 5Balanced surface acoustic wave filter.
[Application Example 7]
  7. The balanced elasticity according to any one of application examples 1 to 6, wherein among the electrode fingers connected to the IDT electrodes on both sides, an electrode finger adjacent to the central IDT electrode is grounded. Surface wave filter.
[Application Example 8]
  A surface acoustic wave resonator in which an IDT electrode and grating reflectors are arranged on both sides thereof is connected in series to a terminal on an unbalanced side of the balanced surface acoustic wave filter according to any one of Application Examples 1 to 7. A balanced surface acoustic wave filter.
[Application Example 9]
  VerticalConnectedAt least one of the two primary-third-order longitudinally coupled double-mode surface acoustic wave filters is the balanced surface acoustic wave filter according to any one of Application Examples 1 to 8.With featuresDoBalanced surface acoustic wave filter.
[Application Example 10]
  IA surface acoustic wave resonator with a DT electrode and grating reflectors on both sidesTwo cascaded primary-cubic longitudinally coupled dual mode bulletsIt is characterized by providing at least one between the stages of the surface acoustic wave filter and connecting them in seriesAs described in Application Example 9Balanced surface acoustic wave filter.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.
FIG. 1 is a plan view showing an electrode pattern configuration of a cascaded double mode SAW filter of input unbalanced / output balanced type according to the present invention, and propagation of surface waves on the principal surface of a piezoelectric substrate (not shown). The IDT electrodes 1, 2, and 3 are arranged close to each other along the direction, and the reflectors 4a and 4b are disposed on both sides of the IDT electrodes 1, 2, and 3 to form the dual mode SAW filter F1. Further, IDT electrodes 1 ', 2', and 3 'having substantially the same configuration are arranged close to each other on the same piezoelectric substrate in parallel with the SAW filter F1, and reflectors 4'a and 4'b are provided on both sides thereof. Arrange to form a dual mode SAW filter F2. Furthermore, the comb electrodes near the center of the piezoelectric substrate of the IDT electrodes 2, 3 and 2 ', 3' on both sides of the dual mode SAW filters F1 and F2 are respectively formed by lead electrodes formed on the same piezoelectric substrate. Connecting. Then, a comb-shaped electrode closer to the outside of the central IDT electrode 1 of the SAW filter F1 is connected to the input terminal IN using a bonding wire or the like, and each comb-shaped electrode of the central IDT electrode 1 ′ of the SAW filter F2 is balanced output. Each of the terminals OUT1 and OUT2 is connected by a bonding wire or the like, and the other comb electrodes are grounded to constitute an input unbalanced / output balanced type cascaded double mode SAW filter.
[0012]
The IDT electrodes 1, 2, and 3 of the SAW filter F1 and the IDT electrodes 1 ', 2', and 3 'of the SAW filter F2 are each formed of a pair of comb electrodes having a plurality of electrode fingers that are interleaved with each other. In order to widen the bandwidth of the SAW filters F1 and F2, in the SAW filter F1, the outermost electrode fingers S1 and S2 of the central IDT electrode 1 are wider than the widths of the other electrode fingers, and the SAW filter F2 Is wide on the innermost electrode finger widths S1 and S2 of the IDT electrodes 2 'and 3' on both sides.
[0013]
A feature of the present invention is the electrode pattern configuration of the SAW filter F2, in which wide electrode fingers S1 and S2 for widening the band are separated from the central IDT electrode 1 ′, and one of the IDT electrodes 2 ′ and 3 ′ on both sides is separated. Connected to the comb-shaped electrode and thinned or increased the electrode index of each comb-shaped electrode forming the central IDT electrode 1 ′ to the same number to achieve geometric symmetry of the IDT electrode 1 ′ It is. Further, by moving the wide electrode fingers S1 and S2 to the IDT electrodes 2 ′ and 3 ′ on both sides, the geometric symmetry of the dual mode SAW filter F2 is achieved with respect to the center of the center IDT electrode 1 ′. That is. However, since the phase of the surface wave propagating through the SAW filter F2 is shifted by 180 ° as it is, the signals of the respective comb electrodes and the ground are connected reversely in the IDT electrode 3 of the SAW filter F1 as compared with FIG. To.
2 (a), 2 (b), and 2 (c) show an input unbalanced-output balanced type cascaded dual mode SAW filter with a center frequency of 942.5 MHz and a bandwidth of 35 MHz, respectively, as shown in FIG. These are the filter characteristics of the filter prototyped based on the above and the phase difference characteristics and amplitude difference characteristics between the two balanced output terminals OUT1 and OUT2. The various constants are the same as in FIG. 17, but the number of pairs of the central IDT electrodes 1 'of the output side SAW filter F2 is set to 17, and the electrode index of each comb electrode is set to be the same.
Comparing FIG. 2 with FIG. 17, the phase difference error is reduced from about 10.5 ° to about 2.5 °, and the amplitude difference error is greatly reduced from about 3.3 dB to about 0.3 dB. found.
[0014]
FIG. 3 shows a second embodiment of the present invention. The outermost electrode fingers S1, S2 of the central IDT electrode 1 constituting the SAW filter F1 on the input side of the cascaded dual mode SAW filter shown in FIG. The IDT electrode 5 in which one electrode finger is thinned out or increased so that the number of each comb electrode is the same number, and S1 and S2 separated from the central IDT electrode are respectively connected to the IDT electrodes 2 and 3 on both sides. The IDT electrodes 6 and 7 are connected. Further, by making the SAW filter F2 on the output side the same as the configuration of the SAW filter F2 shown in FIG. 1, the electrode indices of the comb-shaped electrodes of the central IDT electrodes are the same, and symmetry is maintained. Furthermore, since the wide electrode fingers S1 and S2 are connected to the IDT electrodes on both sides of the input / output SAW filter, impedance matching between the two SAW filters is improved.
[0015]
FIG. 4 shows a third embodiment according to the present invention, in which IDT electrodes 11, 12, and 13 are arranged close to each other along the surface wave propagation direction of a piezoelectric substrate (not shown) and reflected on both sides thereof. It is a primary-third-order longitudinally coupled double mode SAW filter configured by arranging the devices 14a and 14b. The comb electrodes on the upper side of the IDT electrodes 12 and 13 are connected and used as inputs, and the comb electrodes of the center IDT electrode 11 are connected to the two balanced output terminals OUT1 and OUT2, and the other electrode fingers are grounded. To do. A feature of the present invention is that the number of comb-shaped electrode indexes of the central IDT electrode 11 is the same, and an electrode finger 15 for phase shift is provided between the electrode 11 and the outer IDT electrode 13, thereby providing a surface. The phase of the wave can be shifted by 180 °.
[0016]
FIG. 5 shows a cascaded double-mode SAW filter of input unbalance-output balance type according to the fourth embodiment of the present invention. A conventional dual-mode SAW filter is used as the SAW filter F1 on the input side. The output side SAW filter F2 is a filter configured by cascading using the dual mode SAW filter shown in FIG. By using the electrode fingers 15 for 180 ° phase shift, a signal and grounding configuration can be achieved in the same manner as the outer IDT electrode 103 shown in FIG. This point is different from the configuration of the outer IDT electrode 3 in FIG.
[0017]
FIGS. 6A, 6B, and 6C show filter characteristics and two balanced outputs of an input unbalanced-output balanced cascaded dual-mode SAW filter that were prototyped using the electrode pattern of FIG. The phase difference characteristic and the amplitude difference characteristic between the terminals OUT1 and OUT2. The various constants are almost the same as those in FIG. 17, but the output side SAW filter F2IDT electrode 11 is 17 pairs, and the electrode index of each comb electrode is the same number. As a result, it can be understood that the phase difference error is 8 ° in the phase difference characteristic and the amplitude difference error is 1 dB in the amplitude characteristic, which is greatly improved compared to the conventional characteristic.
[0018]
FIG. 7 shows an input unbalanced-output balanced type cascaded dual mode SAW filter according to the fifth embodiment of the present invention, which is the center of the IDT electrode 16 of the input side SAW filter F1 shown in FIG. The outermost electrode fingers S1 and S2 are cut off to form the IDT electrode 21, and connected to the outer IDT electrodes 17 and 18, and the input side SAW filter F1 is formed as the IDT electrodes 22 and 23, and the output side SAW filter is illustrated. A cascaded double mode SAW filter is configured using the balanced filter shown in FIG. Also in this example, the electrode indexes of the comb-shaped electrodes of the IDT electrode 11 on the output side are the same number and maintain symmetry. Furthermore, since the wide electrode fingers S1 and S2 are both present on the outer IDT electrodes, the impedance matching of the SAW filters F1 and F2 is improved.
[0019]
FIG. 8 shows a sixth embodiment of the present invention, which is an input unbalanced / output balanced cascaded double mode SAW filter having different input / output impedances. The SAW filter F1 on the input side uses the SAW filter F1 shown in FIG. 1, and the SAW filter F2 on the output side is separated from the central IDT electrode 1 ′ by the same number on the left and right sides based on the SAW filter F2 shown in FIG. The IDT electrodes 31 and 33 on both sides are formed by connecting the separated electrode fingers to one of the comb electrodes of the IDT electrodes 2 ′ and 3 ′ on both sides. The output impedance can be increased by reducing the number of electrode pairs of the central IDT electrode 31. Also in this embodiment, the electrode index of each comb-shaped electrode of the central IDT electrode 31 of the output side SAW filter is set equal. Also in this case, the phase of the center IDT electrode 31 of the SAW filter F2 is shifted by 180 °, so that the signal and ground connection of the IDT electrode 27 of the SAW filter F1 is reversed from the conventional one.
[0020]
FIGS. 9A, 9B and 9C respectively show the filter characteristics and two balanced outputs of an input unbalanced-output balanced cascaded dual-mode SAW filter manufactured using the electrode pattern of FIG. The phase difference characteristic and the amplitude difference characteristic between the terminals OUT1 and OUT2. It can be seen that both the phase difference characteristic and the amplitude characteristic are significantly improved as compared to the conventional characteristic shown in FIG. 21 with a phase difference error of 5 ° and an amplitude difference error of 1.4 dB.
[0021]
FIG. 10 shows a seventh embodiment of the present invention, which is an input unbalanced / output balanced cascaded double mode SAW filter having different input / output impedances. The input side SAW filter F1 shown in FIG. 3 is used as the input side SAW filter F1, and the output side SAW filter F2 shown in FIG. 8 is used as the output side SAW filter F2. The electrode index of each comb electrode of the IDT electrode 31 is the same, and the wide electrode fingers S1, S2 are moved to the outer IDT electrodes 36, 37 and 32, 33 forming the SAW filters F1, F2. Impedance matching is improved.
[0022]
FIG. 11A is an electrode pattern diagram showing the configuration of an input unbalanced / output balanced dual mode SAW filter according to the eighth embodiment of the present invention, in the propagation direction of the surface wave on the piezoelectric substrate. Three IDT electrodes 45, 46, and 47 are disposed close to each other along with reflectors 48a and 48b on both sides of the three IDT electrodes 45, 46, and 47 to form a primary-third-order longitudinally coupled double mode SAW filter. Then, the electrode fingers of the comb electrodes of the central IDT electrode 45 are made the same, and electrode fingers are added to the comb electrodes of one polarity of the IDT electrodes 46 and 47 on both sides, and the added electrodes An odd number of finger differences. This has the effect of making the phase difference between the IDT electrodes 46 and 47 on both sides different by 180 °. In the example of FIG. 11A, a case where electrode fingers 49 for 180 ° phase shift are added to the IDT electrode 47 is shown. As described above, the wide electrode fingers S1 and S2 are used to widen the band.
FIG. 11B shows an input unbalanced / output balanced cascaded dual mode SAW filter according to the ninth embodiment of the present invention, which is shown as an input side SAW filter F1 in FIG. The filter is configured using the SAW filter F1 on the input side and the SAW filter shown in FIG. 11A as the SAW filter F2 on the output side. Further, since the 180 ° phase shift electrode fingers 49 are provided on the outer IDT electrode 47, the conventional IDT electrode 43 can be used for the outer IDT electrode 43 of the SAW filter F1.
[0023]
FIG. 12 shows a ninth embodiment of the present invention, which is an input unbalanced / output balanced cascaded double mode SAW filter having different input / output impedances. As the input-side SAW filter F1, the outermost electrode fingers S1 and S2 of the center IDT electrode 101 of the input-side SAW filter F1 shown in FIG. 16 are separated, and the IDT electrodes 51 connected to the IDT electrodes 102 and 103 on both sides, respectively. 52, 53, and the output side SAW filter F2 shown in FIG. 11 as the output side SAW filter F2. Also in the case of this filter, the electrode indexes of the comb-shaped electrodes of the output IDT electrode 45 are the same, and the impedance matching of the filter may be good.
[0024]
FIG. 13 shows a tenth embodiment of the present invention, in which a SAW resonator R is connected in series to the input side of the cascaded double mode SAW filter of the input unbalanced-output balanced type shown in FIG. This is a filter with a polar configuration. The SAW resonator R is formed on the same piezoelectric substrate as the cascaded double mode SAW filter, and includes an IDT electrode 55 and reflectors 56a and 56b arranged on both sides thereof along the surface wave propagation direction. It is well known that the attenuation at a desired frequency can be increased by matching the anti-resonance frequency of the SAW resonator R to a frequency band that requires an increase in the attenuation. Also in this filter, the electrode index of each comb-shaped electrode of the output IDT electrode 1 'is set to the same number.
[0025]
FIG. 14 shows an eleventh embodiment according to the present invention, in which two input terminals between two SAW filters F1 and F2 of the input unbalanced / output balanced cascaded dual mode SAW filter shown in FIG. This is a polarized filter configured by connecting SAW resonators R1 and R2 in series. The SAW resonators R1 and R2 are formed on the same piezoelectric substrate as the cascaded double mode SAW filter, and their anti-resonance frequencies are matched to a frequency band that requires an increase in attenuation, thereby reducing the attenuation of a desired frequency. Can be increased. Also in this filter, the electrode index of each comb-shaped electrode of the output IDT electrode 1 'is set to the same number.
[0026]
FIG. 15 shows a twelfth embodiment according to the present invention, which is a filter having a pole configuration in which a SAW resonator R is connected in series on the input side of the dual mode SAW filter shown in FIG. In this example as well, the attenuation of the desired frequency band can be increased, and the electrode index of each comb electrode of the output IDT electrode 11 is set to the same number.
[0027]
In the above description, the present invention has been described by taking the input unbalanced / output balanced cascaded dual mode SAW filter as an example. However, the present invention is not limited to this, and the dual mode SAW on the input side is not limited thereto. Needless to say, the present invention can also be applied to an input-output balanced cascaded double-mode SAW filter with a balanced filter and an input balanced-output unbalanced dual-mode SAW filter with an input / output switched.
Furthermore, with respect to the filter of the polar configuration, based on the input unbalanced-output balanced type cascaded double mode SAW filter shown in FIG. 1, an example in which a SAW resonator is connected in series on the input side thereof, and Although an example in which two SAW resonators are connected in series between filter stages has been described, the present invention is not limited to this, and the filters shown in FIGS. 3, 5, 7, 8, 10, 11 and 12 are also used. Needless to say, a SAW resonator can be connected in series to form a polarized filter. Further, the example in which two SAW resonators are connected in series between the stages of the filter has been described. However, the filters shown in FIGS. 5, 7, 11, and 12 connect one SAW resonator to each other. Needless to say, a filter having a pole configuration can be formed by providing resonators between filter stages and connecting them in series.
Also, as a piezoelectric substrate, 39 ° YX LiTaO_ThreeHowever, it is needless to say that the present invention can be applied to piezoelectric substrates such as lithium niobate, lithium tetraborate, and langasite.
[0028]
【The invention's effect】
  Since the present invention is configured as described above,In some embodimentsThis represents an excellent effect that the phase difference error and the amplitude error between the pair of balanced terminals can be greatly improved.In some embodiments,Since the impedance is improved, the passband characteristic is improved and the phase difference error and the amplitude error between the pair of balanced terminals can be greatly improved.In some embodiments,The phase difference error and the amplitude error between the pair of balanced terminals can be greatly improved, and the polarity of the outer IDT electrode can be changed, and there is an advantage that the degree of freedom is increased in the cascade connection.In some embodiments,The phase difference error and the amplitude error between the pair of balanced terminals can be greatly improved, the bandwidth can be expanded, and the polarity of the outer IDT electrode can be changed.In some embodiments,There is an excellent effect that the phase difference error and the amplitude error between the pair of balanced terminals can be greatly improved.In some embodiments,The phase difference error and the amplitude error of the balanced cascaded dual mode SAW filter having different input / output impedances can be greatly improved.In some embodiments,An excellent effect that phase difference error and amplitude error of balanced double SAW mode filters having different input / output impedances can be greatly improved, and an effect of shifting the phase of one electrode of the outer IDT electrode by 180 °. .In some embodiments,The input / output impedances of the cascaded dual mode SAW filter can be made different from each other to greatly improve the phase difference error and the amplitude error, and the comb electrode constituting the IDT electrode outside the first dual mode SAW filter can be used. It has an excellent effect of being able to change the polarity.In some embodiments,The phase difference error and the amplitude error can be greatly improved, and an excellent effect is achieved that a polar configuration can be achieved.In some embodiments,The phase difference error and the amplitude error can be greatly improved, and an excellent effect is achieved that a polar configuration can be achieved.
[Brief description of the drawings]
FIG. 1 is a plan view showing a configuration of an input unbalanced-output balanced cascaded dual mode SAW filter according to the present invention.
2 (a), (b), and (c) are filter characteristics of a cascaded double mode SAW filter that is prototyped using the electrode pattern of FIG. 1, respectively, and phase difference characteristics between two balanced output terminals; It is an amplitude difference characteristic.
FIG. 3 is a plan view showing the configuration of a cascaded double mode SAW filter of input unbalanced / output balanced type according to a second embodiment of the present invention.
FIG. 4 is a plan view showing the configuration of an input unbalanced / output balanced dual mode SAW filter to which 180 ° phase shift electrode fingers are added according to a third embodiment of the present invention.
FIG. 5 is a plan view showing the configuration of a cascaded double mode SAW filter of input unbalanced / output balanced type according to a fourth embodiment of the present invention.
6 (a), (b), and (c) are filter characteristics of a cascaded dual-mode SAW filter that is prototyped using the electrode pattern of FIG. 5, respectively, and phase difference characteristics between two balanced output terminals; It is an amplitude difference characteristic.
FIG. 7 is a plan view showing the configuration of a cascaded double mode SAW filter of input unbalanced-output balanced type according to a fifth embodiment of the present invention.
FIG. 8 is a plan view showing a configuration of an input unbalanced-output balanced cascaded double mode SAW filter having different input output impedances in a sixth embodiment of the present invention.
FIGS. 9A, 9B, and 9C are respectively a filter characteristic of a filter manufactured using the electrode pattern of FIG. 8, a phase difference characteristic between two balanced output terminals, and an amplitude difference characteristic.
FIG. 10 is a plan view showing a configuration of an input unbalanced-output balanced cascaded dual mode SAW filter having different input output impedances according to a seventh embodiment of the present invention.
11A is an input unbalanced-output balanced dual-mode SAW filter according to an eighth embodiment of the present invention, and FIG. 11B is an input according to the ninth embodiment using FIG. It is a top view which shows the structure of the filter which mutually made output impedance different.
FIG. 12 is a plan view showing the configuration of an input unbalanced-output balanced cascaded dual mode SAW filter having different input output impedances in the tenth embodiment of the present invention.
FIG. 13 is a plan view showing a configuration of an input unbalanced-output balanced type cascaded double mode SAW filter having a polar configuration in an eleventh embodiment according to the present invention.
FIG. 14 is a plan view showing a configuration of a cascaded double mode SAW filter of input unbalanced / output balanced type having a polar configuration in a twelfth embodiment according to the present invention.
FIG. 15 is a plan view showing a configuration of an input unbalanced-output balanced dual mode SAW filter having a polar configuration in a thirteenth embodiment according to the present invention;
16A is a conventional cascaded double mode SAW filter, and FIG. 16B is a conventional input unbalanced / output balanced cascaded dual mode SAW filter.
FIGS. 17A, 17B, and 17C are respectively a filter characteristic of a filter manufactured using the electrode pattern of FIG. 16B, a phase difference characteristic between two balanced terminals, and an amplitude difference characteristic. .
FIG. 18 is a circuit configuration for measuring the filter characteristics of a SAW filter.
FIG. 19 is a circuit configuration for measuring a phase difference characteristic and an amplitude difference characteristic between two balanced terminals of a SAW filter.
FIG. 20 is a plan view showing a configuration of a conventional input unbalanced / output balanced cascaded double mode SAW filter having different input output impedances.
FIGS. 21A, 21B, and 21C are respectively a filter characteristic of a filter manufactured using the electrode pattern of FIG. 20, a phase difference characteristic between two balanced terminals, and an amplitude difference characteristic.
[Explanation of symbols]
1, 2, 3, 1 ', 2', 3 ', 5, 6, 7, 11, 12, 13, 16, 17, 18, 21, 22, 23, 25, 26, 27, 31, 32, 33 , 35, 36, 37, 41, 42, 43, 51, 52, 53, 55, 57, 57 ', 60 .. IDT electrode
S1, S2 ... Electrode fingers for wide band
15. Electrode fingers
4a, 4b, 4'a, 4'b, 8a, 8b, 14a, 15b, 19a, 19b, 24a, 24b, 28a, 28b, 34a, 34b, 38a, 38b, 44a, 44b, 48a, 48b, 54a, 54b, 56a, 56b, 58a, 58b, 58'a, 58'b, 61a, 61b .. Grating reflector

Claims (8)

Three to three IDT electrodes comprising a central IDT electrode and IDT electrodes on both sides thereof are arranged close to each other along the propagation direction of the surface wave on the piezoelectric substrate, and a grating reflector is arranged on both sides thereof. In the longitudinally coupled double mode surface acoustic wave filter,
The electrode index of one comb electrode and the other comb electrode constituting the central IDT electrode is the same number,
Connecting the central IDT electrode to a balanced terminal;
Between the central IDT electrode and the IDT electrodes on both sides, a plurality of electrode fingers connected to one polarity comb electrode of the IDT electrodes on both sides are provided,
The balanced surface acoustic wave filter, wherein the number of the plurality of electrode fingers is different by an odd number between one and the other of the IDT electrodes on both sides. 2. The balanced elastic surface according to claim 1 , wherein among the plurality of electrode fingers, each electrode finger adjacent to the IDT electrodes on both sides is a wide electrode finger for widening a bandwidth. Wave filter.   3. The balanced surface acoustic wave filter according to claim 1, wherein one of the IDT electrodes on both sides has an odd number of electrode indexes than the other. Between the wide electrode fingers and the central IDT electrode, balanced according to claim 2, characterized in that a odd number of electrode fingers connected to one hand of the opposite sides of the IDT electrode Surface acoustic wave filter.   5. The balanced elastic according to claim 1, wherein among the electrode fingers connected to the IDT electrodes on both sides, an electrode finger adjacent to the central IDT electrode is grounded. 6. Surface wave filter.   6. A surface acoustic wave resonator in which an IDT electrode and grating reflectors are arranged on both sides thereof are connected in series to an unbalanced terminal of the balanced surface acoustic wave filter according to claim 1. A balanced surface acoustic wave filter.   7. The balanced surface acoustic wave filter according to claim 1, wherein at least one of the two primary-third-order longitudinally coupled double mode surface acoustic wave filters connected in cascade is the balanced surface acoustic wave filter according to claim 1. A balanced surface acoustic wave filter.   At least one surface acoustic wave resonator having an IDT electrode and grating reflectors disposed on both sides thereof is provided between two cascaded first-order third-order longitudinally coupled double-mode surface acoustic wave filters, which are connected in series. The balanced surface acoustic wave filter according to claim 7, which is connected.

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