JP2004159305A - Multilayered band pass filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact ceramic multilayered band pass filter capable of easily changing a frequency at an attenuation pole and reducing a height of the filter. <P>SOLUTION: In the multilayered band pass filter having two strip line resonator electrodes with short circuit ends on one side and open ends on the other side arranged in a filter or a module substrate formed by stacking a plurality of dielectric sheets or insulating sheets with conductor electrodes formed thereon, a U-shaped magnetic field coupling electrode pattern is arranged on a layer other than that for the resonator electrodes in a such a way that the U-shaped magnetic field coupling electrodes pattern faces the two strip line resonators, and both ends of the U-shaped magnetic field coupling electrodes pattern are short-circuited in a direction which is the same as a direction to which the resonator electrodes are short-circuited. <P>COPYRIGHT: (C)2004,JPO

Description

  The present invention relates to a high-frequency multilayer bandpass filter having an attenuation pole, and in particular, a resonator electrode pattern having a filter characteristic as an internal electrode inside a ceramic chip or a ceramic substrate and an input / output electrode pattern connected to an input / output circuit. And a band-pass filter having a structure suitable for reduction in height (thickness).

  2. Description of the Related Art In recent years, components used in wireless devices such as mobile phones and wireless LANs have been significantly reduced in size, performance, and functionality. With this trend, there is a strong demand for band-pass filters used in these wireless devices to be small, low-profile (thin) and high-performance. In addition, there is a strong demand for a reduction in height as well as a reduction in size. In addition, a high-frequency module has been commercialized in which a filter is formed as an inner layer on a ceramic substrate (LTCC substrate) fired at a low temperature, and the size of the module itself is also required to be reduced.

As prior arts of these ceramic laminated bandpass filters, for example, those disclosed in the following patent documents are known.
Japanese Patent No. 3208967 Japanese Patent No. 3191560 JP-A-7-313503 JP-A-8-316101

  However, in the case of the conventional ceramic laminated bandpass filter having the structure shown in FIGS. 10 and 11, when the distance between the upper and lower shield layers is reduced to reduce the height, the magnetic field coupling between the resonator electrode patterns is weakened. Therefore, there is a problem that it is difficult to make the attenuation pole near the pass band close to the pass band frequency and increase the attenuation near the pass band.

  The present invention has been made in view of the above circumstances, and has a structure that can easily change the frequency of an attenuation pole, obtain good bandpass characteristics, and can be reduced in height (thinned). It is an object of the present invention to provide a small ceramic laminated bandpass filter.

  The laminated bandpass filter of the present invention has a short-circuited end on one side and an open-ended end on a filter or module substrate formed by laminating a plurality of dielectric sheets or insulator sheets on which conductor electrodes are formed. In the laminated band-pass filter in which the two strip line resonator electrodes are arranged, the U-shaped magnetic field coupling electrode pattern is arranged so as to face the two strip line resonators. Are formed on a layer different from the layer on which the resonator electrodes are formed, and both ends of the U-shaped magnetic field coupling electrode pattern are short-circuited in the same direction as the direction in which the resonator electrode is short-circuited.

  Thereby, the distance between the magnetic field coupling electrode pattern and the resonator electrode pattern, that is, the thickness of the insulating layer between the magnetic field coupling electrode pattern and the resonator electrode pattern can be arbitrarily adjusted. Can be arbitrarily adjusted. Therefore, the magnetic field coupling between both patterns can be easily strengthened, sufficient magnetic field coupling strength can be obtained even if the height is reduced, the attenuation pole is brought closer to the pass band, and the attenuation near the pass band is increased. Design becomes possible. That is, even if the height between the upper and lower shield layers is reduced to 1 mm or less, a ceramic laminated bandpass filter having good attenuation characteristics and bandpass characteristics can be obtained.

  Here, the open end side of the resonator electrode pattern is a band-shaped pattern folded in a U-shape, and the short-circuited end side of the band-shaped pattern is connected to the ground electrode. The resonator electrode pattern is preferably a strip line type suitable for miniaturization and reduction in height. The length of the resonator electrode pattern is determined by the resonance frequency, but the band-shaped resonator electrode pattern is folded in a U-shape. As a result, the area occupied by the resonator can be reduced, and the size of the filter can be reduced.

  Further, the open end side of the resonator electrode pattern is a wider stepped impedance resonator (SIR) than the short-circuit end side of the resonator electrode pattern, and the length of the resonator electrode pattern is increased by adopting this structure. The length can be reduced to １ ／ wavelength or less, and the size of the filter can be reduced.

  Further, the resonator electrode pattern and the input / output electrode pattern may be arranged in different layers and coupled by capacitive coupling. Further, this ceramic laminated band-pass filter may be used as a single chip component, or may be used as an electrode pattern for an inner layer on a high-frequency module substrate.

  ADVANTAGE OF THE INVENTION According to this invention, while favorable filter characteristics are obtained, the small ceramic laminated band-pass filter which has a low profile structure is provided.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In each of the drawings, the same reference numerals are given to electrodes or dielectric sheets having the same function, and redundant description is omitted.

  FIG. 1 is an external view of a ceramic multilayer bandpass filter according to one embodiment of the present invention. FIG. 2 is an exploded perspective view showing an example of an internal electrode pattern arranged on each green sheet of the ceramic multilayer band-pass filter according to the first embodiment of the present invention, and FIG. 3 shows an electrode pattern of a main part thereof. FIG. 4 is a plan view, and FIG. 4 is a cross-sectional view showing the stacked state.

  As shown in these figures, a plurality of green sheets S1, S2, S3, S4, S5,... Are stacked, pressed, cut into chips, and fired, whereby ceramic chips 5 are obtained. Here, the ceramic green sheet becomes a sintered body of the ceramic layer, and the internal electrode paste pattern formed by printing becomes a metal internal electrode layer. Next, on the outer surface of the sintered rectangular parallelepiped ceramic chip 5 or the like, a base electrode is formed by a printing method, sputtering, or the like, and Ni plating and Sn plating are performed thereon. 1 and 2 and ground electrodes 3 and 4 are formed.

  As shown in FIGS. 2 and 3, the green sheets S1, S3, S5, S7, and S9 are blank layers on which no internal electrode pattern is formed. On the green sheets S2 and S8, for example, H-shaped shield electrode patterns P21 and P81 are formed by screen printing with a silver-based (for example, silver, silver-palladium, etc.) paste, and become a shield layer after sintering. However, the shape of the shield electrode patterns P21 and P81 is not limited to a shape as long as it covers the resonator electrode patterns P41 and P42 of the green sheet S4. The shield electrode patterns P21 and P81 extend to the ends of the green sheets S2 and S8, and are electrically connected to the ground electrodes 3 and 4 provided on the outer surface of the chip 5. Although not shown, the interval (thickness) between the green sheets on which the internal electrode patterns are formed is adjusted by adjusting the required number of blank green sheets on which no internal electrodes are formed. Its thickness can be adjusted.

  A pair of resonator electrode patterns P41 and P42 are arranged in parallel on the green sheet S4 so as to face their open ends D and E, and the other sides (short-circuit ends) C and F of the resonator electrode patterns are connected to the ground electrode 3. Have been. That is, each of the resonator electrode patterns P41 and P42 is a band-shaped pattern whose open ends D and E are folded in a U-shape, and the short-circuited ends C and F of the band-shaped pattern are connected to the ground electrode 3 on one side of the strip line. It becomes a resonator and is adjusted to have a length of about a quarter wavelength (λ) at the pass band frequency. Further, since these two resonators are arranged so that the open ends D and E face each other, the coupling in the pass band is stronger in the electric field coupling than in the magnetic field coupling. One ends of the input / output electrode patterns P41a and P42a are connected to the resonator electrode patterns P41 and P42, and the other ends are connected to the input / output electrodes 1 and 2, respectively.

On the green sheet S6, a U-shaped band-shaped magnetic field coupling electrode pattern P61 is arranged. The magnetic field coupling electrode pattern P61 is arranged in parallel on another layer of the green sheet S6 so as to face the center of the pair of resonator electrode patterns P41 and P42 of the green sheet S4. Both ends of the U-shaped magnetic field coupling electrode pattern P61 extend to the end of the chip and are electrically connected to the ground electrode 3. By changing the dimension a and the pattern width w of the magnetic field coupling electrode pattern P61 and the interval t between the resonator electrode patterns (see FIGS. 3 and 4), the magnetic field coupling between the pair of resonator electrode patterns P41 and P42 is achieved. You can change the degree.
Further, the input / output electrode patterns P41a and P42a and the resonator electrode patterns P41 and P42 (or at least the resonator electrode patterns P41 and P42) are located between the upper and lower shield patterns P21 and P81 in the vertical cross section (see FIG. 4). It is desirable to adjust or set the thickness of the green sheets S3, S5, S7 so as to be located at approximately the middle of the distance.

  As shown in FIG. 4, the coupling degree of the magnetic field coupling between the resonator electrode patterns P41, P42 and the magnetic field coupling electrode pattern P61 is greatly affected by the distance t between these patterns. The adjustment of the interval t can be performed by changing the number or thickness of the green sheets S5 inserted between the green sheets S4 and S6. Specifically, when the interval t is reduced, the magnetic field coupling between the resonator electrode pattern and the magnetic field coupling electrode pattern increases, and as a result, the magnetic field coupling between the pair of resonator electrodes increases, and the attenuation pole frequency increases. On the contrary, if the interval t is increased, the magnetic field coupling between the pair of resonator electrodes is reduced, and the attenuation pole frequency can be reduced.

  When the height of the ceramic laminated band-pass filter is reduced, the distance between the shield electrode patterns P21 and P61 is reduced, and the magnetic field coupling at the short-circuited portion between the resonator electrode patterns P41 and P42 is weakened. This makes it difficult to control the resonance frequency of the attenuation pole due to capacitive coupling occurring between the open ends of the two resonator electrodes and magnetic field coupling occurring between the short ends. However, in the case of this embodiment, even if the height is reduced, the distance t between the magnetic field coupling electrode pattern P61 and the resonator electrode patterns P41, P42 provided on a different layer from the resonator electrode patterns P41, P42 can be easily reduced. Therefore, the attenuation pole frequency can be made closer to the pass band, and the attenuation near the pass band can be increased. For this reason, even if the height is reduced by the presence of the magnetic field coupling electrode pattern P61, it is easy to make the attenuation pole generated on the lower side of the pass band due to the magnetic field coupling and the electrostatic coupling close to the pass band. Therefore, it is possible to realize a band-pass filter having a good band-pass characteristic having a steep attenuation characteristic on the lower side of the pass band.

  FIG. 5 shows an example of an internal electrode pattern arranged on each green sheet of the multilayer bandpass filter according to the second embodiment of the present invention. This is an embodiment in which the input / output electrode pattern is formed on a layer different from the layer on which the resonator electrode pattern is formed. That is, the input / output electrode patterns P541 and P542 are formed on the green sheet S54, and the pair of open ends of the input / output electrode patterns P541 and P542 are formed on the green sheet S55. P551 and P552 are arranged so as to face open ends, and both are capacitively coupled.

  The other points are the same as the second embodiment and the first embodiment. That is, a pair of U-shaped resonator electrode patterns P551 and P552 on the green sheet S55 are formed in parallel so that the pair of open ends face each other. A U-shaped magnetic field coupling electrode pattern P571 is formed on the green sheet S57 so as to face the center of the pair of resonator electrode patterns P551 and P552 of the green sheet S55. Both ends of the magnetic field coupling electrode pattern P571 extend to the ends of the green sheet S57 and are electrically connected to the ground electrode 3. Here, the thickness of the green sheets S53, S56, and S58 is set such that the resonator electrode patterns P551 and P552 are located at approximately the middle of the distance between the upper and lower shield electrode patterns P521 and P591 in a longitudinal sectional view. It is desirable to adjust or set and arrange. For this reason, even when the height is reduced, it is easy to bring the attenuation pole generated on the lower side of the pass band due to the magnetic field coupling and the capacitive coupling between the resonator electrodes closer to the pass band, and the steep attenuation on the lower side of the pass band. Similarly, a band-pass filter having good band-pass characteristics having characteristics can be realized.

  FIG. 6 is an exploded perspective view showing an example of internal electrode patterns arranged on each green sheet of the ceramic multilayer bandpass filter according to the third embodiment of the present invention. The third embodiment of the present invention is a bandpass filter using an SIR (Stepped Impedance Resonator) type resonator, and FIG. 7A is a plan view showing an electrode pattern of a main part thereof, and FIG. () Is a cross-sectional view showing the state of lamination.

  The green sheets S61, S63, S65, S67, and S69 are blank layers on which no internal electrode pattern is formed. On the green sheets S62 and S68, the shield electrode patterns P621 and P681 are formed by screen printing of a silver-based or copper-based thick film paste to be a shield layer. Input / output electrode patterns P641a and P642a and resonator electrode patterns P641 and P642 are formed on the green sheet S64. The resonator electrode patterns P641 and P642 are formed by cascading first transmission line patterns P641b and P642b which are narrow and have high characteristic impedance and second transmission line patterns P641c and P642c which are wider and have lower characteristic impedance than the first transmission line pattern. Things. The total line length is adjusted so as to resonate near the center frequency of the multilayer bandpass filter, and short-circuit ends I and L at one end thereof are exposed to the chip-side end face and connected to the ground electrode 3. The other ends J and K are wide open ends, and the open ends J and K are arranged so as to face each other to form a pair of resonator electrode patterns. The U-shaped band-shaped magnetic field coupling electrode pattern P661 is disposed on the green sheet S66, which is a separate layer, so as to face the center of each of the resonator electrode patterns P641 and P642.

  FIG. 8A shows an equivalent circuit of the ceramic multilayer band-pass filter according to the first to third embodiments of the present invention. Cp represents the distributed capacitance of the resonator electrode pattern as a lumped-constant capacitance, and Lp represents the distributed inductance of the resonator electrode pattern as a lumped-constant inductance. The resonator electrode is adjusted so that its length resonates near the center frequency of the passband, and Cp and Lp constitute a resonance circuit. Cm represents an equivalent capacitance generated by electric field coupling caused by the open ends of the pair of resonator electrodes facing each other, and M represents magnetic field coupling between the resonator electrode and the magnetic field coupling electrode by a lumped constant inductance. is there. An attenuation pole is generated outside the pass band by M due to magnetic field coupling and Cm due to electric field coupling, and the frequency of the attenuation pole is determined by M and Cm. Here, the input / output electrodes are taken out from the middle of the equivalent inductance Lp. However, in the case of the second embodiment, input and output are capacitively coupled.

  FIG. 8B shows an equivalent circuit of the conventional ceramic multilayer band-pass filter shown in FIGS. Cp represents the distributed capacitance of the resonator electrode pattern as a lumped-constant capacitance, and Lp represents the distributed inductance of the resonator electrode pattern as a lumped-constant inductance. The resonator electrode is adjusted so that its length resonates near the center frequency of the passband, and Cp and Lp constitute a resonance circuit. Further, Cm indicates an equivalent capacitance generated by electric field coupling when the open ends of the pair of resonator electrodes face each other, and M indicates magnetic field coupling between the pair of resonator electrodes by a lumped constant inductance. An attenuation pole is generated outside the pass band by M due to magnetic field coupling and Cm due to electric field coupling, and the frequency of the attenuation pole is determined by M and Cm.

  In this band-pass filter, the resonator electrode pattern is formed such that the capacitive coupling generated at the open ends J and K of the resonator electrode pattern is stronger than the magnetic field coupling generated at the short-circuit sides I and L at a frequency near the pass band. Are placed. As a result, the coupling in the pass band becomes capacitive, and an attenuation pole due to magnetic coupling and capacitive coupling is formed on the lower side of the pass band. The degree of coupling between the two resonator electrode patterns is determined by the distance d32 between the open ends and the distance d31 between the short-circuit ends (see FIG. 7). When the distance d32 is reduced, the capacitive coupling becomes stronger, and when the distance d31 is reduced, the magnetic field coupling M becomes stronger. The degree of coupling is substantially determined by the difference between the degree of capacitive coupling and the degree of magnetic field coupling. The input / output impedance matching of the filter is substantially determined by the position b3 of the input / output lead electrode from the resonator electrode pattern. Further, an attenuation pole is generated outside the pass band by the magnetic field coupling M and the electrostatic coupling Cm, and the frequency of the attenuation pole is substantially determined by a relational expression based on the magnetic field coupling M and the electrostatic coupling Cm.

  As described above, when the coupling of the pass band is capacitive, an attenuation pole is formed on the lower side than the pass band, and the attenuation pole frequency is adjusted by adjusting the strength of the magnetic field coupling and the electrostatic coupling, It is possible to increase the amount of attenuation near the pass band and obtain excellent attenuation characteristics. In order to increase the attenuation in the vicinity of the pass band, it is necessary to increase the magnetic field coupling to bring the attenuation pole close to the vicinity of the pass band. Therefore, in the prior art, the distance f between the resonator electrodes in FIG. No. However, if the distance between the upper and lower shield electrodes is shortened to reduce the height, the magnetic field becomes extremely weak, and the distance f needs to be considerably reduced, which is limited by the limitations of the manufacturing process.

  In the present invention, a magnetic field coupling electrode is added on a layer different from the resonator electrode pattern, and a magnetic field coupling electrode pattern P661 is formed on the green sheet S66. This magnetic field coupling electrode pattern has a U-shape and is formed at a position facing the center of the two resonator electrode patterns P641 and P642 as shown in FIG. Further, both ends of the magnetic field coupling electrode pattern P661 are exposed at the chip end and are connected to the ground electrode 3. As shown in FIG. 7, the line width w3 of the magnetic field coupling electrode pattern P661 is narrower than the width of the resonator electrode patterns P641 and P642. It is.

  In the band-pass filter of FIG. 6, the resonator electrode pattern is arranged such that the electrostatic coupling generated on the open end side of the resonator electrode is stronger than the magnetic field coupling generated on the short-circuit side at a frequency near the pass band. . Thereby, the coupling in the pass band is capacitive, and an attenuation pole due to the magnetic coupling M and the capacitance (electric field) coupling Cm is formed on the lower side of the pass band.

  Next, a method for adjusting the magnetic field coupling M and the electric field coupling Cm in the bandpass filter of the present invention will be described. The electric field coupling Cm is adjusted by changing the distance d32 between the open ends of the resonator electrode pattern (FIG. 7), similarly to the conventional bandpass filter. If the distance d32 is reduced, the electric field coupling becomes stronger, and if it is increased, the electric field coupling becomes weaker. Although not shown, when further increasing the electric field coupling, a capacitive coupling electrode pattern may be provided on another layer so as to face the open end electrode surface of the resonator electrode pattern.

  The adjustment of the magnetic field coupling M is performed by changing the interlayer distance t3 (FIG. 7B) between the magnetic field coupling electrode pattern P661 and the resonator electrode patterns P641 and P642. When t3 is reduced, the magnetic field coupling is increased, and when t3 is increased, it is reduced. The adjustment of the magnetic field coupling M is significantly different from that of the conventional bandpass filter, and is a feature of the bandpass filter of the present invention. That is, the magnetic field coupling electrode pattern is provided on a different layer from the resonator electrode pattern, and the interlayer distance t3 is adjusted. With this configuration, even if the distance between the shield electrodes is shortened due to the low profile, it is possible to strengthen the magnetic field coupling by adjusting t3, so that the magnetic field coupling M and the electrostatic coupling Cm occur. It becomes easy to bring the low-frequency side attenuation pole close to the vicinity of the pass band, and it is possible to design a band-pass filter having excellent low-frequency side attenuation characteristics even when the height is reduced.

  FIG. 9A shows a comparison of characteristics between the band-pass filter of the present invention and a conventional band-pass filter. The height of both bandpass filters and the distance between the shield electrodes are the same. As can be seen from the figure, in the band-pass filter of the present invention, the attenuation pole approaches the vicinity of the pass band, and the attenuation characteristics near the pass band are excellent. Further, in order to reduce the height, in the conventional type, the attenuation pole is further away from the pass band, and it is difficult to increase the amount of attenuation near the pass band. Adjusting t3 makes it possible to easily bring the attenuation pole frequency closer to the pass band.

  Regarding the multilayer bandpass filter of the first embodiment of the present invention, three types of green sheets (t = 270 μm, 320 μm, 420 μm) having different thicknesses are used as the green sheet S5, and resonance is performed by changing the interlayer distance t. FIG. 9B shows transmission characteristics by electromagnetic field simulation when the coupling degree of the magnetic field coupling M between the device electrode patterns P41 and P42 and the magnetic field coupling electrode pattern P61 is changed. According to this result, it can be seen that when the interlayer distance t decreases, the attenuation pole frequency approaches the frequency of the pass band, and the frequency characteristics near the pass band are improved.

  Although three embodiments of the above-described ceramic multilayer band-pass filter have been described, the present invention is not limited to the above-described embodiments. Applicable to modules. As described above, it goes without saying that various modifications can be made without departing from the spirit of the present invention.

It is an outline view of a ceramic lamination type bandpass filter. FIG. 3 is an exploded perspective view showing an example of internal electrode patterns arranged on each green sheet of the ceramic multilayer bandpass filter according to the first embodiment of the present invention. FIG. 2 is a plan view showing a relative position of a magnetic field coupling electrode pattern with respect to a resonator electrode pattern and an input / output electrode pattern of the ceramic multilayer bandpass filter according to the first embodiment of the present invention. FIG. 4 is a cross-sectional view taken along line AA shown in FIG. 3 of the multilayer ceramic bandpass filter according to the first embodiment of the present invention. It is an exploded perspective view showing an example of an internal electrode pattern arranged in each green sheet of a ceramic lamination type bandpass filter which is a 2nd example of the present invention. It is an exploded perspective view showing an example of an internal electrode pattern arranged in each green sheet of a ceramic lamination type bandpass filter which is a 3rd example of the present invention. FIG. 7A is a plan view showing a relative position of a magnetic field coupling electrode pattern with respect to a resonator electrode pattern and an input / output electrode pattern of a ceramic multilayer bandpass filter according to a third embodiment of the present invention. FIG. 2 is a sectional view taken along line HH shown in FIG. It is an equivalent circuit diagram of (a) 1st Example of this invention, and (b) the ceramic laminated bandpass filter of the prior art example. It is a transmission characteristic diagram of the ceramic laminated bandpass filter of the first embodiment of the present invention and the conventional example, (a) is the transmission characteristic of the first embodiment (dotted line) and the transmission characteristic of the conventional example (solid line), (B) shows the transmission characteristics when the green sheet thickness is changed according to the first embodiment of the present invention. It is an exploded perspective view showing an example of an internal electrode pattern arranged in each green sheet of a conventional example. It is a top view which shows the resonator electrode pattern and input / output electrode pattern of the conventional example.

Explanation of reference numerals

1, 2 I / O electrodes 3, 4 Ground electrode 5 Ceramic chips S1-S9, S51-S60, S61-S69 Green sheets S101-S107 Green sheets P21, P81, P521, P591, P621, P681 Shield pattern P1021, P1061 Shield pattern P41, P42, P551, P552 Resonator electrode patterns P641, P642, P1041, P1042 Resonator electrode patterns P41a, P42a, P541, P542 Input / output electrode patterns P641a, P642a, P1041a, P1042a Input / output electrode patterns P61, P571, P661 Magnetic field Coupling electrode pattern

Claims (6)

In a filter or module substrate formed by laminating a plurality of dielectric sheets or insulator sheets on which conductor electrodes are formed, two strip line resonators each having a short-circuited end on one side and an open end on the other. In a multilayer bandpass filter in which electrodes are arranged,
The U-shaped magnetic field coupling electrode is disposed on a layer different from the layer on which the resonator electrodes are formed so that the U-shaped magnetic field coupling electrode pattern faces the two strip line resonators. The both ends of the pattern are short-circuited in the same direction as the direction in which the resonator electrode is short-circuited.   2. The multilayer bandpass filter according to claim 1, wherein the distance between the upper and lower shield electrodes of the stripline type resonator electrode is as low as 1 mm or less.   2. The multilayer filter according to claim 1, wherein in the band-pass filter, the resonator electrode pattern has a U shape, and the open end sides of the U shape resonator electrode pattern face each other. 3. Bandpass filter.   2. The bandpass filter according to claim 1, wherein the open end side of the resonator electrode pattern is a wide SIR (stepped Impedance Resonator) with respect to the short-circuit end side of the resonator electrode pattern. 3. Stacked bandpass filter.   5. The multilayer bandpass filter according to claim 1, wherein an input / output electrode pattern is taken out of the resonator electrode pattern.   The input / output electrode pattern is formed on a layer different from the resonator electrode so as to face a part of the resonator electrode pattern, and is taken out by capacitive coupling. 5. The multilayer bandpass filter according to item 4.

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