filter circuit

Abstract

To provide a filter circuit capable of achieving desired characteristics while suppressing deterioration in characteristics of the filter circuit that are attained by a main resonance circuit.SOLUTION: A filter circuit 1 comprises two ports 3 and 4, a first resonance circuit 10, and a second resonance circuit 20. The first resonance circuit 10 is provided between the two ports 3 and 4 in the circuit configuration so as to be coupled with both the two ports 3 and 4. The second resonance circuit 20 is provided between the two ports 3 and 4 in the circuit configuration so as to be coupled with at least one of the two ports 3 and 4. The coupling between the second resonance circuit 20 and the two ports 3 and 4 is weaker than that between the first resonance circuit 10 and the two ports 3 and 4.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a filter circuit having two resonant circuits. [Background technology]

[0002] Bandpass filters are one of the electronic components used in communication devices, and are required to have low insertion loss in the passband and high insertion loss outside the passband.

[0003] Patent Document 1 describes a filter device that combines a bandpass filter and a band elimination filter (band rejection filter). In this filter device, the band rejection filter increases the insertion loss in a frequency range higher than the pass band. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-155836 Summary of the Invention [Problem to be solved by the invention]

[0005] Currently, communication services using fifth-generation mobile communication systems (hereinafter referred to as 5G) are beginning to be provided. 5G is expected to use frequency bands above 10 GHz, particularly the quasi-millimeter wave band of 10 to 30 GHz and the millimeter wave band of 30 to 300 GHz. Similar to the frequency bands used in mobile communication systems up to fourth generation, multiple standards with relatively close frequency bands exist in these frequency bands. Therefore, bandpass filters used in 5G are also required to have a sharp change in insertion loss in the frequency range close to the passband.

[0006] In the past, in bandpass filters, the number of resonators that make up the bandpass filter was increased to obtain a characteristic in which the insertion loss changes sharply in the frequency range close to the passband. However, when comparing resonators with the same Q value, the problem occurs that as the number of resonators increases, the insertion loss in the passband increases.

[0007] Here, in order to obtain a characteristic in which the insertion loss of a bandpass filter changes sharply in the frequency range close to the passband, it is considered to use a band elimination filter. In this case, the center frequency of the stopband of the band elimination filter must be set close to the passband. However, this causes a problem in that the insertion loss in the passband of the bandpass filter increases.

[0008] The above problem is not limited to filter circuits that include a bandpass filter and a band elimination filter, but applies to all filter circuits that use a slave resonant circuit to adjust the characteristics of a master resonant circuit.

[0009] The present invention has been made in view of the above problems, and its object is to provide a filter circuit comprising a main resonant circuit and a secondary resonant circuit, which is capable of realizing desired characteristics while suppressing deterioration of the characteristics of the filter circuit obtained by the main resonant circuit. [Means for solving the problem]

[0010] The filter circuit of the present invention includes two ports, a first resonant circuit including a plurality of first resonators, provided between the two ports in a circuit configuration, and coupled to both of the two ports, and a second resonant circuit including a plurality of second resonators, provided between the two ports in a circuit configuration, and coupled to at least one of the two ports. The coupling between the second resonant circuit and the two ports is weaker than the coupling between the first resonant circuit and the two ports.

[0011] The filter circuit of the present invention may further include two first capacitors that capacitively couple the first resonant circuit to the two ports, and at least one second capacitor that capacitively couples the second resonant circuit to the two ports. The capacitance of the at least one second capacitor may be smaller than the capacitance of each of the two first capacitors. Alternatively, the filter circuit of the present invention may further include at least one second capacitor that capacitively couples the second resonant circuit to the two ports, and the first resonant circuit may be directly connected to at least one of the two ports.

[0012] In the filter circuit of the present invention, the plurality of second resonators may include a first specific resonator and a second specific resonator. The first specific resonator may be coupled to one of the two ports. The second specific resonator may be coupled to the other of the two ports. The first specific resonator and the second specific resonator may be coupled to each other.

[0013] In the filter circuit of the present invention, each of the plurality of second resonators may be an open-ended resonator.

[0014] In the filter circuit of the present invention, the first resonant circuit may form a band-pass filter.

[0015] In the filter circuit of the present invention, the second resonant circuit may form a band elimination filter. [Effects of the Invention]

[0016] In the filter circuit of the present invention, the coupling between the second resonant circuit and the two ports is weaker than the coupling between the first resonant circuit and the two ports, which makes it possible to realize a filter circuit that can achieve desired characteristics while suppressing degradation of the filter circuit characteristics obtained by the first resonant circuit. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a circuit diagram showing a circuit configuration of a filter circuit according to a first embodiment of the present invention. [Figure 2] 1 is a perspective view showing the appearance of a multilayer filter device including a filter circuit according to a first embodiment of the present invention. [Figure 3] 3 is an explanatory view showing a pattern-formed surface of a first dielectric layer in a laminate of the multilayer filter device according to the first embodiment of the present invention. FIG. [Figure 4] 3 is an explanatory diagram showing pattern-formed surfaces of the second to seventh dielectric layers in the laminate of the multilayer filter device according to the first embodiment of the present invention. FIG. [Figure 5] 3 is an explanatory view showing a pattern-formed surface of an eighth dielectric layer in the laminate of the multilayer filter device according to the first embodiment of the present invention. FIG. [Figure 6] 3 is an explanatory view showing a pattern-formed surface of a ninth dielectric layer in the laminate of the multilayer filter device according to the first embodiment of the present invention. FIG. [Figure 7] 3 is an explanatory view showing a pattern-formed surface of a tenth dielectric layer in the laminate of the multilayer filter device according to the first embodiment of the present invention. FIG. [Figure 8] 3 is an explanatory diagram showing pattern-forming surfaces of the eleventh to sixteenth dielectric layers in the laminate of the multilayer filter device according to the first embodiment of the present invention. FIG. [Figure 9] 3 is an explanatory view showing a terminal formation surface of a 16th dielectric layer in the laminate of the multilayer filter device according to the first embodiment of the present invention. FIG. [Figure 10] 1 is a perspective view showing the inside of a laminate of a multilayer filter device according to a first embodiment of the present invention. [Figure 11] FIG. 2 is a characteristic diagram showing an example of frequency characteristics of the filter circuit according to the first embodiment of the present invention. [Figure 12] FIG. 12 is a characteristic diagram showing an enlarged portion of the frequency characteristics shown in FIG. [Figure 13] FIG. 10 is a circuit diagram showing a circuit configuration of a filter circuit according to a second embodiment of the present invention. [Figure 14] 10 is an explanatory view showing a pattern-formed surface of a first dielectric layer in a laminate of a multilayer filter device according to a second embodiment of the present invention. FIG. [Figure 15] 10 is an explanatory view showing the pattern-forming surfaces of the second to seventh dielectric layers in the laminate of the multilayer filter device according to the second embodiment of the present invention. FIG. [Figure 16] FIG. 10 is an explanatory view showing a pattern-formed surface of an eighth dielectric layer in a laminate of a multilayer filter device according to a second embodiment of the present invention. [Figure 17] 10 is an explanatory view showing a pattern-formed surface of a ninth dielectric layer in a laminate of a multilayer filter device according to a second embodiment of the present invention. FIG. [Figure 18] 10 is an explanatory view showing a pattern-formed surface of a tenth dielectric layer in a laminate of a multilayer filter device according to a second embodiment of the present invention. FIG. [Figure 19] 10 is an explanatory diagram showing pattern-forming surfaces of the 11th to 16th dielectric layers in the laminate of the multilayer filter device according to the second embodiment of the present invention. FIG. [Figure 20] 10 is an explanatory view showing a terminal formation surface of a sixteenth dielectric layer in a laminate of a multilayer filter device according to a second embodiment of the present invention. FIG. [Figure 21] FIG. 10 is a perspective view showing the inside of a laminate of a multilayer filter device according to a second embodiment of the present invention. [Figure 22] FIG. 10 is a characteristic diagram showing an example of frequency characteristics of a filter circuit according to a second embodiment of the present invention. [Figure 23] FIG. 23 is a characteristic diagram showing an enlarged portion of the frequency characteristics shown in FIG. 22. [Figure 24] FIG. 10 is a circuit diagram showing a circuit configuration of a filter circuit according to a second embodiment of the present invention. [Figure 25] FIG. 10 is a circuit diagram showing a circuit configuration of a filter circuit according to a third embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0018] [First embodiment] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. First, an outline of the configuration of a filter circuit 1 according to a first embodiment of the present invention will be described with reference to Fig. 1. The filter circuit 1 includes two ports 3 and 4, a first resonant circuit 10, and a second resonant circuit 20. Each of the ports 3 and 4 is a port for inputting or outputting a signal.

[0019] In this embodiment, the first resonant circuit 10 constitutes a band-pass filter, and the second resonant circuit 20 constitutes a band elimination filter. In this embodiment, the first resonant circuit 10 is a main resonant circuit, and the second resonant circuit 20 is a secondary resonant circuit. The filter circuit 1 as a whole functions as a band-pass filter.

[0020] In terms of the circuit configuration, the first resonant circuit 10 is provided between the two ports 3 and 4. The first resonant circuit 10 is also coupled to both of the two ports 3 and 4. In this application, the expression "in terms of the circuit configuration" is used to refer to the arrangement on a circuit diagram, not the arrangement in a physical configuration.

[0021] The second resonant circuit 20 is provided between the two ports 3 and 4 in terms of the circuit configuration. The second resonant circuit 20 is coupled to at least one of the two ports 3 and 4. In particular, in this embodiment, the second resonant circuit 20 is coupled to both of the two ports 3 and 4. In this embodiment, the second resonant circuit 20 is provided in parallel to the first resonant circuit 10 between the two ports 3 and 4 in terms of the circuit configuration, and is not provided between the first resonant circuit 10 and port 3 or port 4.

[0022] The filter circuit 1 further includes two first capacitors C11 and C12 that capacitively couple the first resonant circuit 10 to the two ports 3 and 4. The first capacitor C11 capacitively couples the first resonant circuit 10 to the port 3. The first capacitor C12 capacitively couples the first resonant circuit 10 to the port 4.

[0023] The filter circuit 1 further includes at least one second capacitor that capacitively couples the second resonant circuit 20 with the two ports 3 and 4. In this embodiment, the filter circuit 1 particularly includes two second capacitors C21 and C22 as the at least one second capacitor. The second capacitor C21 capacitively couples the second resonant circuit 20 with the port 3. The second capacitor C22 capacitively couples the second resonant circuit 20 with the port 4.

[0024] The coupling between the second resonant circuit 20 and the two ports 3 and 4 is weaker than the coupling between the first resonant circuit 10 and the two ports 3 and 4. When the coupling between the resonant circuit and the ports is capacitive, as in this embodiment, the coupling becomes stronger as the capacitance of the capacitor that capacitively couples the resonant circuit and the ports increases. In other words, the coupling between the resonant circuit and the ports becomes weaker as the capacitance decreases.

[0025] In this embodiment, the capacitance of each of the second capacitors C21 and C22 is smaller than the capacitance of each of the first capacitors C11 and C12. As a result, the coupling between the second resonant circuit 20 and port 3 and between the second resonant circuit 20 and port 4 are weaker than the coupling between the first resonant circuit 10 and port 3 and between the first resonant circuit 10 and port 4. In one example, the capacitance of each of the second capacitors C21 and C22 is 0.03 pF, and the capacitance of each of the first capacitors C11 and C12 is 0.14 pF.

[0026] Next, an example of the configuration of the first and second resonant circuits 10, 20 will be described with reference to FIG. 1. First, the first resonant circuit 10 will be described. The first resonant circuit 10 includes a plurality of first resonators. In particular, in this embodiment, the first resonant circuit 10 includes, as the plurality of first resonators, two first resonators 11, 12 arranged in this order from the port 3 side in the circuit configuration. Each of the first resonators 11, 12 is a half-wavelength resonator with both ends open. The first resonators 11, 12 are magnetically coupled to each other.

[0027] The first resonator 11 is coupled to port 3. The first resonator 11 has a first end 11a closest to port 3 and a second end 11b farthest from port 3. The first capacitor C11 is provided between the first end 11a of the first resonator 11 and port 3 in the circuit configuration.

[0028] The first resonator 12 is coupled to port 4. The first resonator 12 has a first end 12a closest to port 4 and a second end 12b farthest from port 4. The first capacitor C12 is provided in the circuit configuration between the first end 12a of the first resonator 12 and port 4.

[0029] The first resonant circuit 10 further includes a capacitor C13 that connects the second end 11b of the first resonator 11 and the second end 12b of the first resonator 12. The first resonator 11 and the first resonator 12 are magnetically coupled and capacitively coupled via the capacitor C13.

[0030] Next, the second resonant circuit 20 will be described. The second resonant circuit 20 includes a plurality of second resonators. In particular, in this embodiment, the second resonant circuit 20 includes, as the plurality of second resonators, two second resonators 21 and 22 arranged in this order from the port 3 side in the circuit configuration. Each of the second resonators 21 and 22 is a half-wavelength resonator with both ends open. The second resonators 21 and 22 are magnetically coupled to each other. The second resonators 21 and 22 correspond to the "first specific resonator" and the "second specific resonator" of the present invention, respectively.

[0031] The second resonator 21 is coupled to port 3. The second resonator 21 has a first end 21a closest to port 3 and a second end 21b farthest from port 3. The second capacitor C21 is provided between the first end 21a of the second resonator 21 and port 3 in terms of the circuit configuration.

[0032] The second resonator 22 is coupled to port 4. The second resonator 22 has a first end 22a closest to port 4 and a second end 22b farthest from port 4. A second capacitor C22 is provided in the circuit configuration between the first end 22a of the second resonator 22 and port 4.

[0033] Next, a description will be given of the configuration of a multilayer filter device (hereinafter simply referred to as a filter device) 2 in this embodiment. Fig. 2 is a perspective view showing the appearance of the filter device 2. The filter device 2 is a filter device including the filter circuit 1 shown in Fig. 1.

[0034] The filter device 2 includes the components of the filter circuit 1 described with reference to Fig. 1 and a laminate 50 for integrating the components of the filter circuit 1. The laminate 50 includes a plurality of laminated dielectric layers, and a plurality of conductor layers and a plurality of through holes formed in the plurality of dielectric layers.

[0035] The laminate 50 has a bottom surface 50A and a top surface 50B located at both ends in the stacking direction T of the multiple dielectric layers, and four side surfaces 50C to 50F connecting the bottom surface 50A and the top surface 50B. The side surfaces 50C and 50D face in opposite directions from each other, and the side surfaces 50E and 50F also face in opposite directions from each other. The side surfaces 50C to 50F are perpendicular to the top surface 50B and the bottom surface 50A.

[0036] Here, the X direction, Y direction, and Z direction are defined as shown in FIG. 2. The X direction, Y direction, and Z direction are perpendicular to each other. In this embodiment, a direction parallel to the stacking direction T is defined as the Z direction. Furthermore, the direction opposite to the X direction is defined as the −X direction, the direction opposite to the Y direction is defined as the −Y direction, and the direction opposite to the Z direction is defined as the −Z direction.

[0037] As shown in FIG. 2, the bottom surface 50A is located at the end of the stack 50 in the -Z direction. The top surface 50B is located at the end of the stack 50 in the Z direction. The side surface 50C is located at the end of the stack 50 in the -X direction. The side surface 50D is located at the end of the stack 50 in the X direction. The side surface 50E is located at the end of the stack 50 in the -Y direction. The side surface 50F is located at the end of the stack 50 in the Y direction.

[0038] The filter device 2 further includes terminals 511 and 661 and ground conductor layers 512 and 662. The terminal 511 and the ground conductor layer 512 are arranged on the bottom surface 50A. In particular, in this embodiment, the ground conductor layer 512 covers almost the entire bottom surface 50A. A gap is formed between the terminal 511 and the ground conductor layer 512.

[0039] Terminal 661 and ground conductor layer 662 are disposed on top surface 50B. In particular, in this embodiment, ground conductor layer 662 covers almost the entire top surface 50B. A gap is formed between terminal 661 and ground conductor layer 662.

[0040] Terminal 511 corresponds to port 3, and terminal 661 corresponds to port 4. Each of the ground conductor layers 512 and 662 is connected to ground.

[0041] Next, an example of the plurality of dielectric layers and the plurality of conductor layers constituting the laminate 50 will be described with reference to Figures 3 to 9. In this example, the laminate 50 has 16 laminated dielectric layers. Hereinafter, these 16 dielectric layers will be referred to as the first to sixteenth dielectric layers, in order from the bottom up. The first to sixteenth dielectric layers will be represented by reference numerals 51 to 66. In Figures 3 to 9, the plurality of circles represent the plurality of through holes.

[0042] 3 shows the pattern formation surface of the first dielectric layer 51. A terminal 511 and a ground conductor layer 512 are formed on the pattern formation surface of the dielectric layer 51. A specific through hole 51T1 connected to the terminal 511 is also formed in the dielectric layer 51. The multiple through holes formed in the dielectric layer 51 except for the specific through hole 51T1 are connected to the ground conductor layer 512.

[0043] 4 shows the pattern-forming surfaces of the second to seventh dielectric layers 52 to 57. A specific through-hole 52T1 is formed in each of the dielectric layers 52 to 57. The specific through-hole 51T1 formed in the dielectric layer 51 is connected to a specific through-hole 52T1 formed in the dielectric layer 52. Furthermore, in the dielectric layers 52 to 57, the specific through-holes 52T1 adjacent to each other above and below are connected to each other.

[0044] 5 shows the pattern-formed surface of the eighth dielectric layer 58. Conductor layers 581, 582, and 583 are formed on the pattern-formed surface of the dielectric layer 58. Also, a specific through-hole 58T1 is formed in the dielectric layer 58. A specific through-hole 52T1 formed in the dielectric layer 57 is connected to the specific through-hole 58T1.

[0045] 6 shows the pattern formation surface of the ninth dielectric layer 59. Resonator conductor layers 591, 592, 593, and 594, conductor layers 595 and 596, and a ground conductor layer 597 are formed on the pattern formation surface of the dielectric layer 59. Each of the conductor layers 591 to 596 has a first end and a second end located opposite to each other.

[0046] Conductor layer 591 includes a portion extending from the first end in the Y direction and a portion extending from the second end in the X direction. Conductor layer 592 includes a portion extending from the first end in the Y direction and a portion extending from the second end in the -X direction. Conductor layer 593 includes a portion extending from the first end in the -Y direction and a portion extending from the second end in the X direction. Conductor layer 594 includes a portion extending from the first end in the -Y direction and a portion extending from the second end in the -X direction. Conductor layer 595 extends in the -X direction from the first end to the second end. Conductor layer 596 extends in the X direction from the first end to the second end.

[0047] Furthermore, a specific through hole 59T1 is formed in the dielectric layer 59. The specific through hole 59T1 is connected to a portion of the conductor layer 596 near a first end. The specific through hole 58T1 formed in the dielectric layer 58 is connected to a portion of the conductor layer 595 near a first end. Some of the multiple through holes formed in the dielectric layer 58 excluding the specific through hole 58T1 and some of the multiple through holes formed in the dielectric layer 59 excluding the specific through hole 59T1 are connected to the ground conductor layer 597.

[0048] A first end of conductor layer 591 is adjacent to, and spaced a predetermined distance from, a portion of conductor layer 595 near the second end. A first end of conductor layer 592 is adjacent to, and spaced a predetermined distance from, a portion of conductor layer 596 near the second end. A second end of conductor layer 591 and a second end of conductor layer 592 are adjacent to, and spaced a predetermined distance from, each other.

[0049] A first end of conductor layer 593 is adjacent to, with a predetermined gap therebetween, a portion of conductor layer 595 near the second end. A first end of conductor layer 594 is adjacent to, with a predetermined gap therebetween, a portion of conductor layer 596 near the second end. A second end of conductor layer 593 and a second end of conductor layer 594 are adjacent to, with a predetermined gap therebetween. The gap between the second end of conductor layer 593 and the second end of conductor layer 594 is larger than the gap between the second end of conductor layer 591 and the second end of conductor layer 592.

[0050] 7 shows the pattern-formed surface of the tenth dielectric layer 60. Conductor layers 601 and 602 are formed on the pattern-formed surface of the dielectric layer 60. Also, a specific through-hole 60T1 is formed in the dielectric layer 60. A specific through-hole 59T1 formed in the dielectric layer 59 is connected to another specific through-hole 60T1.

[0051] 8 shows the pattern-forming surfaces of the eleventh to sixteenth dielectric layers 61 to 66. A specific through-hole 61T1 is formed in each of the dielectric layers 61 to 66. The specific through-hole 60T1 formed in the dielectric layer 60 is connected to a specific through-hole 61T1 formed in the dielectric layer 61. Furthermore, in the dielectric layers 61 to 66, the specific through-holes 61T1 adjacent to each other above and below are connected to each other.

[0052] 9 shows the terminal formation surface, which is the surface opposite to the pattern formation surface of the 16th dielectric layer 66. A terminal 661 and a ground conductor layer 662 are formed on the terminal formation surface of the dielectric layer 66. A specific through-hole 61T1 formed in the dielectric layer 66 is connected to the terminal 661. The multiple through-holes formed in the dielectric layer 66 except for the specific through-hole 61T1 are connected to the ground conductor layer 662.

[0053] The laminate 50 shown in Figure 2 is constructed by stacking the first to sixteenth dielectric layers 51 to 66 so that the pattern-forming surface of the first dielectric layer 51 becomes the bottom surface 50A of the laminate 50 and the terminal-forming surface of the sixteenth dielectric layer 66 becomes the top surface 50B of the laminate 50.

[0054] FIG. 10 shows the inside of the laminate 50, which is formed by stacking the first through sixteenth dielectric layers 51 to 66. As shown in FIG. 10, the inside of the laminate 50 has the multiple conductor layers and multiple through holes shown in FIGS. 3 to 9 stacked therein. The conductor layer 595 is connected to the terminal 511 via specific through holes 51T1, 52T1, and 58T1. The conductor layer 596 is connected to the terminal 661 via specific through holes 59T1, 60T1, and 61T1. The ground conductor layers 512, 597, and 662 are connected to each other by multiple through holes excluding the specific through holes 51T1, 52T1, 58T1, 59T1, 60T1, and 61T1.

[0055] The following describes the correspondence between the components of the filter circuit 1 shown in Fig. 1 and the components inside the laminate 50 shown in Figs. 4 to 8. The first resonator 11 of the first resonant circuit 10 is formed by a resonator conductor layer 591. The first resonator 12 of the first resonant circuit 10 is formed by a resonator conductor layer 592. The second resonator 21 of the second resonant circuit 20 is formed by a resonator conductor layer 593. The second resonator 22 of the second resonant circuit 20 is formed by a resonator conductor layer 594.

[0056] The first capacitor C11 is formed by conductor layers 581, 591, and 595 and a dielectric layer 58 between these conductor layers. The first capacitor C12 is formed by conductor layers 582, 592, and 596 and a dielectric layer 58 between these conductor layers. The second capacitor C21 is formed by conductor layers 593, 595, and 601 and a dielectric layer 59 between these conductor layers. The second capacitor C22 is formed by conductor layers 594, 596, and 602 and a dielectric layer 59 between these conductor layers.

[0057] The capacitor C13 is composed of conductor layers 583, 591, and 592 and a dielectric layer 58 between these conductor layers.

[0058] Next, a brief description will be given of structural features of the filter device 2 according to the present embodiment. In the filter device 2, the conductor layers 591 to 594 for resonators are provided in a space surrounded by the conductor layers 512 and 662 for grounding and a plurality of through holes.

[0059] In the filter device 2, the area of each of the conductor layers 601 and 602 that form the second capacitors C21 and C22 is smaller than the area of each of the conductor layers 581 and 582 that form the first capacitors C11 and C12.

[0060] Next, the operation and effect of the filter circuit 1 according to this embodiment will be described. As described above, in this embodiment, the coupling between the second resonant circuit 20 and the two ports 3 and 4 is weaker than the coupling between the first resonant circuit 10 and the two ports 3 and 4. As a result, according to this embodiment, the second resonant circuit 20 can be incorporated into the filter circuit 1 while suppressing the effect of the second resonant circuit 20.

[0061] In particular, in this embodiment, the first resonant circuit 10 constitutes a band-pass filter, and the second resonant circuit 20 constitutes a band-elimination filter. Specifically, the effect of the second resonant circuit 20 is to increase the insertion loss in a frequency range near the center frequency of the stop band of the band-elimination filter formed by the second resonant circuit 20 in the frequency characteristics of the insertion loss of the filter circuit 1 (frequency characteristics of the insertion loss of the band-pass filter). Therefore, according to this embodiment, the second resonant circuit 20 can be incorporated into the filter circuit 1 while reducing the insertion loss in the above frequency range to a necessary level. Therefore, according to this embodiment, by setting the center frequency of the stop band of the band-elimination filter formed by the second resonant circuit 20 to a frequency close to the pass band of the band-pass filter formed by the first resonant circuit 10, it is possible to obtain a characteristic in which the insertion loss changes sharply in a frequency range close to the pass band of the filter circuit 1 while suppressing an increase in the insertion loss in the pass band of the filter circuit 1.

[0062] Increasing the number of resonators constituting the bandpass filter can also achieve a characteristic in which the insertion loss changes sharply in the frequency range close to the passband. However, when comparing resonators with the same Q value, the problem arises that the insertion loss in the passband increases as the number of resonators increases.

[0063] In contrast, in this embodiment, the first resonant circuit 10 includes only two resonators. According to this embodiment, it is possible to obtain a characteristic in which the insertion loss changes sharply in a frequency range close to the pass band without increasing the number of resonators constituting the bandpass filter. As a result, according to this embodiment, it is possible to suppress an increase in the insertion loss in the pass band. Furthermore, according to this embodiment, it is possible to reduce the size of the filter circuit 1 and the filter device 2.

[0064] The center frequency of the stopband of the band elimination filter formed by the second resonant circuit 20 may be in the frequency range on the lower side of the passband of the bandpass filter formed by the first resonant circuit 10, or may be in the frequency range on the higher side of the passband.

[0065] Next, an example of the frequency characteristics of the filter circuit 1 according to this embodiment will be shown. 11 1 is a characteristic diagram showing an example of the frequency characteristics of the filter circuit 1. 12 The figure 11 1 is a characteristic diagram showing a part of the frequency characteristics shown in FIG. 1, specifically, an enlarged frequency region near the passband. 11 and Figure 12 In the figure, the horizontal axis indicates frequency and the vertical axis indicates attenuation. 11 and Figure 12 9, the curve labeled 91 indicates the insertion loss, and the curve labeled 92 indicates the return loss.

[0066] figure 11 and Figure 12In the example shown in FIG. 1, the center frequency of the stop band of the band elimination filter formed by the second resonant circuit 20 is in the frequency range on the lower side of the pass band of the band pass filter formed by the first resonant circuit 10. 11 and Figure 12 As shown in Fig. 1, this embodiment provides a characteristic in which the insertion loss (attenuation) changes sharply in the frequency range close to the passband. Furthermore, the magnitude of the insertion loss (absolute value of the attenuation) in the passband is sufficiently small.

[0067] [Second embodiment] Next, a second embodiment of the present invention will be described. First, differences between the filter circuit 1 according to this embodiment and the first embodiment will be briefly described with reference to Fig. 13. Fig. 13 is a circuit diagram showing the circuit configuration of the filter circuit 1 according to this embodiment.

[0068] In this embodiment, each of the first resonators 11 and 12 of the first resonant circuit 10 is a quarter-wave resonator with one end shorted and the other end open. The second end 11b of the first resonator 11 and the second end 12b of the first resonator 12 are each connected to ground. In Fig. 13, symbol L11 denotes the inductance component of the line connecting the first resonators 11 and 12 to ground.

[0069] Next, a filter device 2 according to the present embodiment will be described with reference to Figs. 14 to 20. The configuration of the filter device 2 according to the present embodiment is the same as that of the filter device 2 according to the first embodiment, except for the plurality of dielectric layers constituting the laminate 50. In the present embodiment, the laminate 50 has 16 laminated dielectric layers 71 to 86, instead of the dielectric layers 51 to 66 according to the first embodiment. Hereinafter, these 16 dielectric layers 71 to 86 will be referred to as the first to sixteenth dielectric layers 71 to 86, in order from the bottom up. In Figs. 14 to 20, the plurality of circles represent the plurality of through holes.

[0070] 14 shows the pattern formation surface of the first dielectric layer 71. A terminal 511 and a ground conductor layer 512 are formed on the pattern formation surface of the dielectric layer 71. A specific through hole 71T1 connected to the terminal 511 is also formed in the dielectric layer 71. The multiple through holes formed in the dielectric layer 71, excluding the specific through hole 71T1, are connected to the ground conductor layer 512. The multiple through holes connected to the ground conductor layer 512 include specific through holes 71T2 and 71T3.

[0071] 15 shows the pattern-forming surfaces of the second to seventh dielectric layers 72 to 77. Specific through holes 72T1, 72T2, and 72T3 are formed in each of the dielectric layers 72 to 77. Specific through holes 71T1 to 71T3 formed in the dielectric layer 71 are connected to specific through holes 72T1 to 72T3 formed in the dielectric layer 72, respectively. Furthermore, in the dielectric layers 72 to 77, adjacent through holes with the same reference numerals are connected to each other.

[0072] 16 shows the pattern-formed surface of the eighth dielectric layer 78. Conductor layers 781 and 782 are formed on the pattern-formed surface of the dielectric layer 78. Specific through-holes 78T1, 78T2, and 78T3 are also formed in the dielectric layer 78. Specific through-holes 72T1 to 72T3 formed in the dielectric layer 77 are connected to specific through-holes 78T1 to 78T3, respectively.

[0073] 17 shows the pattern formation surface of the ninth dielectric layer 79. Resonator conductor layers 791, 792, 793, and 794, conductor layers 795 and 796, and a ground conductor layer 797 are formed on the pattern formation surface of the dielectric layer 79. Each of the conductor layers 791 to 796 has a first end and a second end located opposite to each other.

[0074] Each of the conductor layers 791 and 795 extends in the −X direction from the first end to the second end, each of the conductor layers 792 and 796 extends in the X direction from the first end to the second end, and each of the conductor layers 793 and 794 extends in the −Y direction from the first end to the second end.

[0075] Furthermore, specific through holes 79T1, 79T2, and 79T3 are formed in the dielectric layer 79. The specific through hole 79T1 is connected to a portion of the conductor layer 796 near a first end. The specific through hole 78T1 formed in the dielectric layer 78 is connected to a portion of the conductor layer 795 near a first end. The specific through holes 78T2 and 78T3 formed in the dielectric layer 78 and the specific through holes 79T2 and 79T3 are connected to the ground conductor layer 797.

[0076] A portion of conductor layer 791 near its first end is adjacent to, and spaced a predetermined distance from, a portion of conductor layer 795 near its second end. A portion of conductor layer 792 near its first end is adjacent to, and spaced a predetermined distance from, a portion of conductor layer 796 near its second end. The second ends of each of conductor layers 791 and 792 are connected to a ground conductor layer 797. In FIG. 17 , the boundaries between conductor layers 791 and 792 and ground conductor layer 797 are indicated by dotted lines.

[0077] A first end of conductor layer 793 is adjacent to, and spaced apart from, a portion of conductor layer 795 near the second end. A first end of conductor layer 794 is adjacent to, and spaced apart from, a portion of conductor layer 796 near the second end.

[0078] 18 shows the pattern-formed surface of the tenth dielectric layer 80. Conductor layers 801 and 802 are formed on the pattern-formed surface of the dielectric layer 80. Specific through-holes 80T1, 80T2, and 80T3 are also formed in the dielectric layer 80. Specific through-holes 79T1 to 79T3 formed in the dielectric layer 79 are connected to specific through-holes 80T1 to 80T3, respectively.

[0079] 19 shows the pattern-forming surfaces of the eleventh to sixteenth dielectric layers 81 to 86. Specific through-holes 81T1, 81T2, and 81T3 are formed in each of the dielectric layers 81 to 86. Specific through-holes 80T1 to 80T3 formed in the dielectric layer 80 are connected to specific through-holes 81T1 to 81T3 formed in the dielectric layer 81, respectively. Furthermore, in the dielectric layers 81 to 86, vertically adjacent through-holes with the same reference numerals are connected to each other.

[0080] 20 shows the terminal formation surface, which is the surface opposite to the pattern formation surface of the 16th dielectric layer 86. A terminal 861 and a ground conductor layer 862 are formed on the terminal formation surface of the dielectric layer 86. A specific through hole 81T1 formed in the dielectric layer 86 is connected to the terminal 661. The multiple through holes (excluding the specific through hole 81T1) formed in the dielectric layer 86, including specific through holes 81T2 and 81T3 formed in the dielectric layer 86, are connected to the ground conductor layer 662.

[0081] In this embodiment, the laminate 50 is constructed by stacking the first to sixteenth dielectric layers 71 to 86 so that the pattern forming surface of the first dielectric layer 71 becomes the bottom surface 50A of the laminate 50 and the terminal forming surface of the sixteenth dielectric layer 86 becomes the top surface 50B of the laminate 50.

[0082] FIG. 21 shows the inside of the laminate 50, which is formed by stacking the first through sixteenth dielectric layers 71-86. As shown in FIG. 21, the inside of the laminate 50 has the multiple conductor layers and multiple through holes shown in FIGS. 14-20 stacked therein. The conductor layer 795 is connected to the terminal 511 via specific through holes 71T1, 72T1, and 78T1. The conductor layer 796 is connected to the terminal 661 via specific through holes 79T1, 80T1, and 81T1. The ground conductor layers 512, 662, and 797 are connected to each other by multiple through holes excluding the specific through holes 51T1, 52T1, 58T1, 59T1, 60T1, and 61T1. In particular, the ground conductor layer 797 is connected to the ground conductor layer 512 via specific through holes 71T2, 71T3, 72T2, 72T3, 78T2, and 78T3, and is connected to the ground conductor layer 662 via specific through holes 79T2, 79T3, 80T2, 80T3, 81T2, and 81T3.

[0083] The following describes the correspondence between the components of the filter circuit 1 shown in Fig. 13 and the internal components of the laminate 50 shown in Figs. 15 to 19. The first resonator 11 of the first resonant circuit 10 is formed by a resonator conductor layer 791. The first resonator 12 of the first resonant circuit 10 is formed by a resonator conductor layer 792. The second resonator 21 of the second resonant circuit 20 is formed by a resonator conductor layer 793. The second resonator 22 of the second resonant circuit 20 is formed by a resonator conductor layer 794.

[0084] The first capacitor C11 is composed of conductor layers 781, 791, and 795 and a dielectric layer 78 between these conductor layers. The first capacitor C12 is composed of conductor layers 782, 792, and 796 and a dielectric layer 78 between these conductor layers. The second capacitor C21 is composed of conductor layers 793, 795, and 801 and a dielectric layer 79 between these conductor layers. The second capacitor C22 is composed of conductor layers 794, 796, and 802 and a dielectric layer 79 between these conductor layers.

[0085] Next, a brief description will be given of structural features of the filter device 2 according to the present embodiment. In the filter device 2, the conductor layers 791 to 794 for resonators are provided in a space surrounded by the conductor layers 512 and 662 for grounding and a plurality of through holes.

[0086] In the filter device 2, the area of each of the conductor layers 801 and 802 that form the second capacitors C21 and C22 is smaller than the area of each of the conductor layers 781 and 782 that form the first capacitors C11 and C12.

[0087] The specific through holes 71T2, 71T3, 72T2, 72T3, 78T2, 78T3, 79T2, 79T3, 80T2, 80T3, 81T2, and 81T3 are electrically connected to the ground conductor layers 512, 662, and 797. The ground conductor layers 512, 662, and 797 are electrically connected to the ground. Hereinafter, the specific through holes 71T2, 71T3, 72T2, 72T3, 78T2, 78T3, 79T2, 79T3, 80T2, 80T3, 81T2, and 81T3 will be referred to as the multiple specific through holes connected to the ground.

[0088] The plurality of specific through holes connected to ground include two through holes aligned along a direction perpendicular to the stacking direction T. Specifically, these two through holes are a pair of specific through holes 71T2 and 71T3, a pair of specific through holes 72T2 and 72T3, a pair of specific through holes 78T2 and 78T3, a pair of specific through holes 79T2 and 79T3, a pair of specific through holes 80T2 and 80T3, and a pair of specific through holes 81T2 and 81T3. The two specific through holes included in these pairs are aligned along a direction perpendicular to at least one of the directions in which a resonator conductor layer 791 (described later) extends and the directions in which a resonator conductor layer 792 extends. In this embodiment, the two specific through holes included in these pairs are aligned along a direction parallel to the Y direction.

[0089] The resonator conductor layer 791 extends in a first direction away from the plurality of specific through holes connected to ground. The resonator conductor layer 791 extends in a second direction away from the plurality of specific through holes connected to ground. In this embodiment, in particular, each of the resonator conductor layers 791 and 792 is electrically connected to the plurality of specific through holes connected to ground.

[0090] The first and second directions are directions perpendicular to the stacking direction T. In this embodiment, the first direction is the X direction and the second direction is the −X direction. Therefore, the first direction and the second direction are opposite to each other.

[0091] Each of the resonator conductor layers 793, 794 includes a narrow portion and two wide portions located on both sides of the narrow portion. The second resonators 21, 22 formed by the resonator conductor layers 793, 794 are both stepped impedance resonators.

[0092] Next, the unique functions and effects of the filter device 2 according to this embodiment will be described. In this embodiment, as described above, each of the resonator conductor layers 791, 792 extends in a direction away from the specific through-holes connected to ground. Therefore, in this embodiment, if the resonator conductor layers 791, 792 or the specific through-holes connected thereto are misaligned in a direction parallel to the X-direction due to manufacturing variations, one of the resonator conductor layers 791, 792 becomes longer and the other becomes shorter. This allows the present embodiment to offset changes in the resonator characteristics caused by changes in the length of the resonator conductor layers. As a result, the present embodiment allows the changes in the characteristics of the first resonator circuit 10, i.e., the bandpass filter, caused by manufacturing variations to be suppressed.

[0093] Furthermore, in this embodiment, as described above, the plurality of specific through holes connected to ground include two through holes aligned along a direction orthogonal to the stacking direction T and orthogonal to at least one of the extending directions of the resonator conductor layer 791 and the resonator conductor layer 792. In this embodiment, the two through holes are aligned along a direction orthogonal to both the extending direction of the resonator conductor layer 791 and the extending direction of the resonator conductor layer 792. Therefore, even if the resonator conductor layers 791 and 792 or the plurality of connected specific through holes are misaligned in a direction parallel to the Y direction, the lengths of the resonator conductor layers 791 and 792 hardly change. This also makes it possible, according to this embodiment, to suppress changes in the characteristics of the first resonator circuit 10, i.e., the bandpass filter, due to manufacturing variations.

[0094] The above-described effects of the present embodiment will be described below with reference to the results of a simulation. In the simulation, a model of an example and a model of a comparative example were used. Both the model of the example and the model of the comparative example are bandpass filter models including a ground conductor layer and two resonator conductor layers extending from the ground conductor layer.

[0095] In the model of the example, similar to the filter device 2 of the present embodiment, the two resonator conductor layers are arranged to sandwich the ground conductor layer and extend in opposite directions. In the model of the comparative example, the two resonator conductor layers extend in the same direction from the ground conductor layer. In the simulation, the longitudinal direction (direction parallel to the extending direction) of the resonator conductor layers was set to the same direction in the model of the example and the model of the comparative example. In the simulation, the length of each of the two resonator conductor layers in the model of the example was set to 700 μm, and the length of each of the two resonator conductor layers in the model of the comparative example was set to 855 μm.

[0096] In the simulation, the shift amount of the lower cutoff frequency, which is the lower limit of the passband, and the shift amount of the upper cutoff frequency, which is the upper limit of the passband, were calculated when two resonator conductor layers were shifted by 15 μm in the longitudinal direction of the resonator conductor layers. In the model of the example, when two resonator conductor layers were shifted by 15 μm in the longitudinal direction of the resonator conductor layers, one of the two resonator conductor layers became shorter by 15 μm and the other became longer by 15 μm. In the model of the comparative example, when two resonator conductor layers were shifted by 15 μm in the longitudinal direction of the resonator conductor layers, both of the two resonator conductor layers became shorter or longer by 15 μm. In the simulation, the two resonator conductor layers were shifted so that both of the two resonator conductor layers became longer.

[0097] When the two resonator conductor layers are shifted as described above, the deviation of the lower cutoff frequency in the comparative example model is 0.80% and the deviation of the upper cutoff frequency is 1.25%. Furthermore, the deviation of the lower cutoff frequency in the example model is 0.11% and the deviation of the upper cutoff frequency is 0.11%. As can be seen from the simulation results, this embodiment can suppress variations in the lower cutoff frequency and the upper cutoff frequency due to manufacturing variations.

[0098] Next, an example of the frequency characteristics of the filter circuit 1 according to this embodiment will be shown. Fig. 22 is a characteristic diagram showing an example of the frequency characteristics of the filter circuit 1. Fig. 23 is a characteristic diagram showing an enlarged view of a portion of the frequency characteristics shown in Fig. 22, specifically, a frequency region near the pass band. In Figs. 22 and 23, the horizontal axis represents frequency and the vertical axis represents attenuation. In Figs. 22 and 23, the curve labeled 93 represents insertion loss, and the curve labeled 94 represents return loss.

[0099] 22 and 23, the center frequency of the stopband of the band elimination filter formed by the second resonant circuit 20 exists in a frequency range on the lower side of the passband of the bandpass filter formed by the first resonant circuit 10. As shown in Fig. 22 and 23, according to this embodiment, it is possible to obtain a characteristic in which the insertion loss (attenuation) changes sharply in a frequency range close to the passband. Moreover, the magnitude of the insertion loss (absolute value of attenuation) in the passband is sufficiently small.

[0100] Other configurations, actions, and effects of this embodiment are the same as those of the first embodiment.

[0101] [Third embodiment] Next, a third embodiment of the present invention will be described with reference to Fig. 24. Fig. 24 is a circuit diagram showing the circuit configuration of a filter circuit 1 according to this embodiment.

[0102] The configuration of the filter circuit 1 according to this embodiment differs from that of the first embodiment in the following respects. In this embodiment, the first capacitors C11 and C12 of the first embodiment are not provided. Therefore, the first resonant circuit 10 is directly connected to each of the ports 3 and 4. Specifically, the first end 11a of the first resonator 11 of the first resonant circuit 10 is directly connected to the port 3, and the first end 12a of the first resonator 12 of the first resonant circuit 10 is directly connected to the port 4.

[0103] As described in the first embodiment, when the coupling between the resonant circuit and the port is capacitive, the coupling becomes stronger as the capacitance of the capacitor that capacitively couples the resonant circuit and the port increases. Here, when the resonant circuit and the port are directly connected, in the high frequency range, the coupling is essentially the same as when the resonant circuit and the port are capacitively coupled with an infinite capacitance. Therefore, in this embodiment, the coupling between the first resonant circuit 10 and the port 3 and between the first resonant circuit 10 and the port 4 are stronger than in the first embodiment. Furthermore, the coupling between the first resonant circuit 10 and the two ports 3 and 4 is stronger than the coupling between the second resonant circuit 20 and the single port 3 and 4.

[0104] The configuration of the first resonant circuit 10 may be the same as that of the second embodiment. The other configurations, actions, and effects of this embodiment are the same as those of the first or second embodiment.

[0105] [Fourth embodiment] Next, a fourth embodiment of the present invention will be described with reference to Fig. 25. Fig. 25 is a circuit diagram showing the circuit configuration of a filter circuit 1 according to this embodiment.

[0106] The configuration of the filter circuit 1 according to this embodiment differs from that of the first embodiment in the following respects. In this embodiment, the second resonators 21 and 22 of the second resonant circuit 20 are not magnetically coupled to each other. This configuration can be achieved, for example, by increasing the distance between the two resonator conductor layers that constitute the second resonators 21 and 22.

[0107] In this embodiment, one of the second resonators 21 and 22 may not be provided. For example, when only the second resonator 21 is provided, the second resonant circuit 20 is coupled only to port 3. When only the second resonator 22 is provided, the second resonant circuit 20 is coupled only to port 4.

[0108] The configuration of the first resonant circuit 10 may be the same as that of the second embodiment. Also, as in the third embodiment, the first resonant circuit 10 may be directly connected to each of the ports 3 and 4. Other configurations, actions, and effects of this embodiment are the same as those of any of the first to third embodiments.

[0109] The present invention is not limited to the above-described embodiments and can be modified in various ways. For example, the number and configuration of each of the first and second resonators are not limited to those described in the embodiments, and may be any number that satisfies the scope of the claims. The number of each of the first and second resonators may be three or more.

[0110] Furthermore, the first resonant circuit 10 is not limited to a band-pass filter, and may also constitute other filters such as a low-pass filter or a high-pass filter. [Explanation of symbols]

[0111] 1...filter circuit, 2...filter device, 3, 4...port, 10...first resonant circuit, 11, 12...first resonator, 20...second resonant circuit, 21, 22...second resonator, 50...laminated body, 51-66...dielectric layer, 511, 661...terminal, 512, 662...ground conductor layer, C11, C12...first capacitor, C13...capacitor, C21, C22...second capacitor.

Claims

1. Two ports and a first resonant circuit including a plurality of first resonators, the first resonant circuit being arranged between the two ports in a circuit configuration and coupled to both of the two ports; a second resonant circuit including a plurality of second resonators, the second resonant circuit being arranged between the two ports in a circuit configuration and coupled to at least one of the two ports; a laminate including a plurality of laminated dielectric layers, and a plurality of conductor layers and a plurality of through holes formed in the plurality of dielectric layers, for integrating the two ports, the first resonant circuit, and the second resonant circuit; components of the first resonant circuit and components of the second resonant circuit are configured using the plurality of conductor layers; A filter circuit, characterized in that the coupling between the second resonant circuit and the two ports is weaker than the coupling between the first resonant circuit and the two ports.

2. two first capacitors for capacitively coupling the first resonant circuit and the two ports; at least one second capacitor for capacitively coupling the second resonant circuit and the two ports; 2. The filter circuit according to claim 1, wherein the capacitance of said at least one second capacitor is smaller than the capacitance of each of said two first capacitors.

3. further comprising at least one second capacitor for capacitively coupling the second resonant circuit and the two ports; 2. The filter circuit according to claim 1, wherein the first resonant circuit is directly connected to at least one of the two ports.

4. the plurality of second resonators include a first specific resonator and a second specific resonator; the first particular resonator is coupled to one of the two ports; 4. The filter circuit according to claim 1, wherein the second specific resonator is coupled to the other of the two ports.

5. 5. The filter circuit according to claim 4, wherein the first specific resonator and the second specific resonator are coupled to each other.

6. 6. The filter circuit according to claim 1, wherein each of the plurality of second resonators is an open-ended resonator.

7. 7. The filter circuit according to claim 1, wherein the first resonant circuit constitutes a band-pass filter.

8. Two ports; a first resonant circuit including a plurality of first resonators, the first resonant circuit being arranged between the two ports in a circuit configuration and coupled to both of the two ports; a second resonant circuit including a plurality of second resonators, the second resonant circuit being arranged between the two ports in a circuit configuration and coupled to at least one of the two ports; Coupling between the second resonant circuit and the two ports is weaker than coupling between the first resonant circuit and the two ports; The filter circuit is characterized in that the second resonant circuit constitutes a band elimination filter.

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