Resonant circuit and wave splitter

Abstract

A resonant circuit (30) comprises: a first resonator (11) having a first end (11a) and a second end (11b); a sub-circuit (40) connected in parallel to the first resonator (11); and a capacitor (C31). The sub-circuit (40) includes a first inductor (L31), a second inductor (L32), and a third inductor (L33). At least two inductors among the first inductor (L31), the second inductor (L32), and the third inductor (L33) are mutually connected. The capacitor (C31) is provided at a position that is between the first end (11a) of the first resonator (11) and the ground and is between the second end (11b) of the first resonator (11) and the ground.

Description

Resonance circuit and diplexer 【0001】 The present disclosure relates to a resonance circuit including a resonator and an inductor connected to the resonator, and a diplexer including this resonance circuit. 【0002】 In small mobile communication devices, a configuration is widely used in which an antenna commonly used in a plurality of applications having different systems and usage frequency bands is provided, and a plurality of signals transmitted and received by this antenna are separated using a diplexer. 【0003】 Generally, a diplexer that separates a first signal having a frequency within a first frequency band and a second signal having a frequency within a second frequency band higher than the first frequency band includes a common port, a first signal port, a second signal port, a first filter provided in a first signal path from the common port to the first signal port, and a second filter provided in a second signal path from the common port to the second signal port. As the first filter, for example, a low-pass filter is used. As the second filter, for example, a high-pass filter is used. These filters include, for example, an LC resonator configured using an inductor and a capacitor, or an elastic wave resonator configured using an elastic wave element. 【0004】 International Publication No. 2012 / 172909 discloses a diplexer including a low-pass filter, a high-pass filter, and an elastic wave trap filter. The high-pass filter and the elastic wave trap filter are connected in series. International Publication No. 2012 / 172909 discloses an elastic wave trap filter configured such that a plurality of parallel arms each have an elastic wave resonator, and an elastic wave trap filter configured such that a plurality of series arm resonators each composed of an elastic surface wave resonator are directly connected to each other and a plurality of parallel arms each have an elastic wave resonator. 【0005】 International Publication No. 2012 / 172909 【0006】Elastic wave resonators, such as those disclosed in International Publication No. 2012 / 172909, can form steep attenuation poles in the pass-through attenuation characteristics of a filter. Now, let's consider the case where an elastic wave resonator is used in a low-pass filter. The elastic wave elements constituting the elastic wave resonator are connected in series, for example, in a path from a common port to a first signal port. In this case, by setting the resonant frequency of the elastic wave element to a frequency within the passband of the low-pass filter, and setting the anti-resonant frequency of the elastic wave element to a frequency higher than the cutoff frequency of the low-pass filter but close to the cutoff frequency, it is possible to realize a pass-through attenuation characteristic in which the pass-through attenuation changes steeply near the cutoff frequency. On the other hand, there was a problem that the insertion loss increased in the frequency range of the low-pass filter's passband that is far from the cutoff frequency. 【0007】 The above problem applies not only to low-pass filters, but to resonant circuits in general that are used in filters with a relatively wide passband. 【0008】 One of the objectives of this disclosure is to provide a resonant circuit capable of achieving desired characteristics over a relatively wide frequency range, and a demultiplexer including this resonant circuit. 【0009】 A resonant circuit according to one embodiment of the present disclosure comprises a resonator having a first end and a second end, a subcircuit connected in parallel to the resonator, and a capacitor. The subcircuit includes a first inductor, a second inductor, and a third inductor. At least two of the first inductor, the second inductor, and the third inductor are connected to each other. The capacitor is provided between the first end of the resonator and ground, and between the second end of the resonator and ground. 【0010】A demultiplexer according to one embodiment of the present disclosure comprises a common port, a first signal port, a second signal port, a first filter provided between the common port and the first signal port and configured to selectively pass signals with frequencies within a first passband, and a second filter provided between the common port and the second signal port and configured to selectively pass signals with frequencies within a second passband. The first filter includes a resonant circuit. The resonant circuit includes a resonator having a first end and a second end, a subcircuit connected in parallel with the resonator, and a capacitor. The subcircuit includes a first inductor, a second inductor, and a third inductor. At least two of the first inductor, the second inductor, and the third inductor are connected to each other. The capacitor is provided between the first end of the resonator and ground, and between the second end of the resonator and ground. 【0011】 In the resonant circuit and demultiplexer of the present disclosure, the subcircuit includes a first inductor, a second inductor, and a third inductor, wherein at least two of the first, second, and third inductors are connected to each other. Capacitors are provided between the first end of the resonator and ground, and between the second end of the resonator and ground. This provides the effect that desired characteristics can be achieved over a relatively wide frequency range according to the present disclosure. 【0012】 This is a circuit diagram showing the circuit configuration of a demultiplexer according to the first embodiment of this disclosure. This is a perspective view showing a demultiplexer according to the first embodiment of this disclosure. This is a perspective view showing the first main body in the first embodiment of this disclosure. This is a perspective view showing the first main body in the first embodiment of this disclosure. This is a characteristic diagram showing an example of the pass-through attenuation characteristics of the embodiment model and the comparative example model. This is a circuit diagram showing the circuit configuration of a modified resonant circuit according to the first embodiment of this disclosure. This is a circuit diagram showing the circuit configuration of a resonant circuit according to the second embodiment of this disclosure. This is a circuit diagram showing the circuit configuration of a resonant circuit according to the third embodiment of this disclosure. 【0013】[First Embodiment] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. First, the circuit configuration of the demultiplexer 1 according to the first embodiment of the present disclosure will be described with reference to Figure 1. Figure 1 is a circuit diagram showing the circuit configuration of the demultiplexer 1. At least a part of the circuit shown in Figure 1 may be the actual circuit of the demultiplexer 1 or an equivalent circuit of the demultiplexer 1. 【0014】 The demultiplexer 1 according to this embodiment is configured to function as a diplexer. In the example shown in Figure 1, the demultiplexer 1 includes a common port 2, a first signal port 3, a second signal port 4, a first filter 10, and a second filter 20. The first filter 10 is provided between the common port 2 and the first signal port 3 in the circuit configuration. The second filter 20 is provided between the common port 2 and the second signal port 4 in the circuit configuration. In this application, the expression "in the circuit configuration" is used to refer to the arrangement on the circuit diagram, not the arrangement in the physical configuration. 【0015】 The first filter 10 has an input terminal 10a and an output terminal 10b. The input terminal 10a is connected to a common port 2. The output terminal 10b is connected to a first signal port 3. The first filter 10 is configured such that signals with frequencies within a first passband are selectively output from the output terminal 10b from the signals input to the input terminal 10a. In this embodiment, the first filter 10 is a low-pass filter. 【0016】 The second filter 20 has an input terminal 20a and an output terminal 20b. The input terminal 20a is connected to the common port 2. The output terminal 20b is connected to the second signal port 4. The second filter 20 is configured such that signals with frequencies within a second passband higher than the first passband are selectively output from the output terminal 20b. In this embodiment, the second filter 20 is a high-pass filter. 【0017】The first filter 10 includes an LC circuit 10A and a resonant circuit 30 according to this embodiment. The LC circuit 10A and the resonant circuit 30 may work together to form a low-pass filter. The LC circuit 10A is composed of at least one inductor and at least one capacitor. In this embodiment in particular, the LC circuit 10A is a low-pass filter circuit. In the example shown in Figure 1, the LC circuit 10A includes inductors L11, L12 and capacitors C11, C12. 【0018】 One end of inductor L11 is connected to common port 2. Capacitor C11 is connected in parallel with inductor L11. One end of inductor L12 is connected to the other end of inductor L11. One end of capacitor C12 is connected to the other end of inductor L12. The other end of capacitor C12 is connected to ground. 【0019】 The resonant circuit 30 includes a first resonator 11, a sub-circuit 40 connected in parallel to the first resonator 11, and a capacitor C31. The LC circuit 10A is provided between the input terminal 10a and the first resonator 11 in terms of circuit configuration. The first resonator 11 has a first terminal 11a and a second terminal 11b. The first terminal 11a of the first resonator 11 is connected to the other terminal of the inductor L11. The second terminal 11b of the first resonator 11 is connected to the first signal port 3. 【0020】 The first resonator 11 may include an elastic wave element. An elastic wave element is an element that utilizes elastic waves. The elastic wave element may be a surface acoustic wave element that utilizes surface acoustic waves, or a bulk elastic wave element that utilizes bulk elastic waves. There may be one or more elastic wave elements. In Figure 1, for convenience, the first resonator 11 is represented using one elastic wave element. 【0021】The subcircuit 40 includes a first inductor L31, a second inductor L32, and a third inductor L33. At least two of the first to third inductors L31 to L33 are connected to each other. In this embodiment in particular, any one of the first to third inductors L31 to L33 is connected to the other two inductors. In the example shown in Figure 1, each of the first to third inductors L31 to L33 is connected to one connection point. Capacitor C31 is provided between the subcircuit 40 and ground. 【0022】 Furthermore, in the example shown in Figure 1, the first inductor L31 and the second inductor L32 are connected to each other. The third inductor L33 is connected to the connection point of the first inductor L31 and the second inductor L32, and the capacitor C31 is connected in series with the third inductor L33. However, as shown in Figure 1, when the first inductor L31 and the second inductor L32 are connected to each other, it is sufficient that one of the third inductor L33 and the capacitor C31 is connected to the connection point of the first inductor L31 and the second inductor L32, and the other of the third inductor L33 and the capacitor C31 is connected in series with the other of the third inductor L33 and the capacitor C31. Therefore, conversely to the example shown in Figure 1, the capacitor C31 may be connected to the connection point of the first inductor L31 and the second inductor L32, and the third inductor L33 may be connected in series with the capacitor C31. 【0023】 In the example shown in Figure 1, one end of the first inductor L31 is connected to the first end 11a of the first resonator 11. One end of the second inductor L32 is connected to the second end 11b of the first resonator 11. One end of the third inductor L33 is connected to the other end of the first inductor L31 and the other end of the second inductor L32. One end of the capacitor C31 is connected to the other end of the third inductor L33. The other end of the capacitor C31 is connected to ground. 【0024】At least one of the first to third inductors L31 to L33 may be an inductor element constructed using a laminated conductor, as described later. In this embodiment, in particular, each of the first and second inductors L31 and L32 is an inductor element. That is, each of the first and second inductors L31 and L32 is an intentionally provided inductor. 【0025】 The third inductor L33 may be an inductor element. Alternatively, the third inductor L33 may be a conductor having a specific inductance connected to each of the first and second inductors L31 and L32, or it may consist of a magnetic coupling between the first inductor L31 and the second inductor L32. 【0026】 The first end 11a and the second end 11b of the first resonator 11 are electrically connected by a subcircuit 40. In this embodiment in particular, the first end 11a and the second end 11b of the first resonator 11 are electrically connected by first and second inductors L31 and L32. The modes in which two elements are electrically connected include modes in which two elements are connected in series via a conductor and modes in which two elements are connected in series via an inductor. On the other hand, modes in which a capacitor exists between two elements, such as when two elements are connected via a capacitor, are not included in the modes in which two elements are electrically connected in series. 【0027】 Capacitor C31 is provided in the circuit configuration between the first end 11a of the first resonator 11 and ground, and between the second end 11b of the first resonator 11 and ground. In this embodiment, in particular, the first end 11a and the second end 11b of the first resonator 11 are not electrically connected to ground. That is, of the conductor in the path from the first end 11a of the first resonator 11 to ground, the portion connected to the first end 11a is not electrically connected to ground. Similarly, of the conductor in the path from the second end 11b of the first resonator 11 to ground, the portion connected to the second end 11b is not electrically connected to ground. 【0028】The second filter 20 includes inductors L21, L22, L23, capacitors C21, C22, C23, and a second resonator 21. The inductors L21 to L23, capacitors C21 to C23, and the second resonator 21 work together to form a high-pass filter. 【0029】 One end of capacitor C21 is connected to common port 2. One end of capacitor C22 is connected to the other end of capacitor C21. One end of inductor L21 is connected to the connection point between capacitors C21 and C22. One end of capacitor C23 is connected to the other end of inductor L21. The other end of capacitor C23 is connected to ground. 【0030】 One end of the second resonator 21 is connected to the other end of the capacitor C22. The other end of the second resonator 21 is connected to the second signal port 4. One end of the inductor L22 is connected to one end of the second resonator 21. One end of the inductor L23 is connected to the other end of the second resonator 21. The other ends of inductors L22 and L23 are connected to ground. 【0031】 Next, other components of the demultiplexer 1 will be described with reference to Figures 2 to 4. Figure 2 is a perspective view showing the demultiplexer 1. Figures 3 and 4 are perspective views showing the first main body 50. 【0032】 The demultiplexer 1 comprises a first body 50 and a second body 80 mounted on the first body 50. The first body 50 is composed of a laminate including a plurality of stacked dielectric layers and a plurality of conductors (a plurality of conductor layers and a plurality of through-holes). Each of the plurality of dielectric layers is composed of a dielectric material. As the dielectric material, for example, low-temperature co-fired ceramics (LTCC) are used. 【0033】The first body 50 may include a common port 2, a first signal port 3, and a second signal port 4. The first body 50 may further include a plurality of components of the first filter 10, excluding the first resonator 11, and at least one component of the second filter 20. In this embodiment in particular, the first body 50 includes inductors L11, L12, L21-L23, L31-L33 and capacitors C11, C12, C21-C23, C31. The inductors L11, L12, L31-L33 and capacitors C11, C12, C31 correspond to a plurality of components of the first filter 10, excluding the first resonator 11. The inductors L21-L23 and capacitors C21-C23 correspond to at least one component of the second filter 20. 【0034】 The second body 80 may include the first resonator 11. In this embodiment in particular, the second body 80 may further include the second resonator 21. 【0035】 The first body 50 has a bottom surface 50A and an upper surface 50B located at both ends of the stacking direction T of the multiple dielectric layers, and four side surfaces 50C to 50F connecting the bottom surface 50A and the upper surface 50B. Side surfaces 50C and 50D face opposite each other, and side surfaces 50E and 50F also face opposite each other. Side surfaces 50C to 50F are perpendicular to the bottom surface 50A and the upper surface 50B. 【0036】 Here, as shown in Figures 2 to 4, we define the X, Y, and Z directions. The X, Y, and Z directions are orthogonal to each other. In this embodiment, the Z direction is defined as one direction parallel to the stacking direction T. The Z direction is also one direction parallel to the direction in which the first body 50 and the second body 80 are aligned. 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. In addition, the expression "when viewed from the stacking direction T" means viewing the object from a position distant in the Z direction or the -Z direction, that is, viewing the object from a plan view from a position distant in a specific direction or a direction parallel to a specific direction. 【0037】As shown in Figures 3 and 4, the bottom surface 50A is located at the -Z end of the first body 50. The top surface 50B is located at the Z end of the first body 50. The top surface 50B is also the mounting surface for mounting the second body 80. Figure 3 shows the first body 50 as seen from the top surface 50B side. Figure 4 shows the first body 50 as seen from the bottom surface 50A side. 【0038】 Side 50C is located at the -X end of the first body 50. Side 50D is located at the X end of the first body 50. Side 50E is located at the -Y end of the first body 50. Side 50F is located at the Y end of the first body 50. 【0039】 The first body 50 further includes a plurality of electrodes 111, 112, 113, 114, 115, and 116 provided on the bottom surface 50A of the first body 50. Electrodes 111, 112, and 113 are arranged in this order in the X direction at a position closer to side surface 50E than to side surface 50F. Electrodes 114, 115, and 116 are arranged in this order in the -X direction at a position closer to side surface 50F than to side surface 50E. 【0040】 Electrode 112 corresponds to common port 2. Electrode 114 corresponds to first signal port 3. Electrode 116 corresponds to second signal port 4. Therefore, common port 2, first signal port 3, and second signal port 4 are located on the bottom surface 50A of the first main body 50. Electrodes 111, 113, and 115 are each connected to ground. 【0041】 The first body 50 further includes electrodes 121, 122, 123, and 124 provided on the upper surface 50B of the first body 50. The electrodes 121 to 124 are used for electrical connection between the first body 50 and the second body 80. Electrodes 121 and 122 are arranged in this order in the X direction. Electrodes 123 and 124 are positioned ahead of electrodes 121 and 122 in the Y direction and are arranged in this order in the X direction. 【0042】The second main body 80 further includes four electrodes 81, 82, 83, and 84. In a state where the second main body 80 is mounted on the first main body 50, the electrodes 81 to 84 respectively face the electrodes 121 to 124 of the first main body 50. The electrodes 81 to 84 are physically connected to the electrodes 121 to 124 by, for example, solder bumps 7. 【0043】 The size of the planar shape (shape as viewed from the stacking direction T) of the first main body 50 is different from the size of the planar shape of the second main body 80. In the example shown in FIG. 2, the planar shape of the first main body 50 is larger than the planar shape of the second main body 80. 【0044】 Also, in the example shown in FIG. 2, the second main body 80 is arranged so as to overlap the center of gravity of the upper surface 50B when viewed from the stacking direction T. The center of gravity of the second main body 80 when viewed from the stacking direction T may coincide with or may not coincide with the center of gravity of the upper surface 50B. 【0045】 The demultiplexer 1 may further include a sealing portion (not shown) for sealing the second main body 80. The sealing portion (not shown) covers at least a part of the periphery of the second main body 80 and the upper surface 50B of the first main body 50. The sealing portion may further cover the side surfaces 50C to 50F of the first main body 50. The sealing portion is made of, for example, resin. 【0046】 Next, the operations and effects of the resonance circuit 30 and the demultiplexer 1 according to the present embodiment will be described. In the present embodiment, the demultiplexer 1 includes a first filter 10 configured to selectively pass signals having frequencies within a first passband. The first filter 10 includes an LC circuit 10A and a resonance circuit 30 that cooperate to form a low-pass filter. The resonance circuit 30 includes a first resonator 11. 【0047】 The first resonator 11 may be configured such that its resonance frequency is a frequency within the first passband, and its anti-resonance frequency is higher than and close to the cut-off frequency of the first filter 10 (low-pass filter). Also, the first resonator 11 may include an elastic wave element. Thereby, it is possible to realize a passing attenuation characteristic in which the passing attenuation amount changes steeply in the vicinity of the cut-off frequency. 【0048】 Here, consider the case where the cutoff frequency of the first filter 10 is a relatively high frequency. In this case, the first passband becomes relatively wide. Depending on the configuration of the first resonator 11, the insertion loss in the relatively low frequency region of the first passband increases. 【0049】 In contrast, in the present embodiment, the resonance circuit 30 includes a sub-circuit 40 connected in parallel to the first resonator 11 and a capacitor C31. The sub-circuit 40 includes a connected first inductor L31, a second inductor L32, and a third inductor L33. At least two of the first inductor L31, the second inductor L32, and the third inductor L33 are connected to each other. The capacitor C31 is provided between the first end 11a of the first resonator 11 of the resonance circuit 30 and the ground, and between the second end 11b of the first resonator 11 and the ground. Thereby, according to the present embodiment, an increase in the insertion loss in the relatively low frequency region of the first passband can be suppressed. Thereby, according to the present embodiment, the insertion loss of the relatively wide first passband can be reduced. Hereinafter, this effect will be described with reference to the results of simulation. 【0050】 In the simulation, models of a comparative example and an example are used. The model of the comparative example is a model of the demultiplexer of the comparative example. The configuration of the demultiplexer of the comparative example is the same as the configuration of the demultiplexer 1 according to the present embodiment, except that the third inductor L33 and the capacitor C31 are not provided, and the other ends of the first and second inductors L31, L32 are connected to the ground. The model of the example is a model of the demultiplexer 1 according to the present embodiment. 【0051】In the simulation, the comparative example model and the example model were designed so that the cutoff frequency of the first filter 10 (low-pass filter) is 5 GHz and the cutoff frequency of the second filter 20 (high-pass filter) is 5.15 GHz. Then, for each of the comparative example model and the example model, the pass-through attenuation characteristics of the first filter 10 and the pass-through attenuation characteristics of the second filter 20 were determined. 【0052】 Figure 5 is a characteristic diagram showing the pass-through attenuation characteristics of the comparative example model and the embodiment model. In Figure 5, the horizontal axis represents frequency, and the vertical axis represents attenuation. Also in Figure 5, the curve denoted by reference numeral 91 shows the pass-through attenuation characteristics of the first filter 10 of the comparative example model. The curve denoted by reference numeral 92 shows the pass-through attenuation characteristics of the first filter 10 of the embodiment model. The curve denoted by reference numeral 93 shows the pass-through attenuation characteristics of the second filter 20 of the comparative example model. The curve denoted by reference numeral 94 shows the pass-through attenuation characteristics of the second filter 20 of the embodiment model. 【0053】 As indicated by reference numerals 91 and 92 in Figure 5, the first filter 10 is configured to form a plurality of attenuation poles on the high-frequency side of the first passband in the pass-through attenuation characteristics of the first filter 10. The plurality of attenuation poles include attenuation poles formed by the first resonator 11 and attenuation poles formed by a plurality of components of the first filter 10 excluding the first resonator 11. In this embodiment in particular, among the plurality of attenuation poles, the attenuation pole closest to the first passband is the attenuation pole formed by the first resonator 11. 【0054】 As indicated by reference numerals 93 and 94 in Figure 5, the second filter 20 is configured to form a plurality of attenuation poles on the low-frequency side of the second passband in the pass-through attenuation characteristics of the second filter 20. The plurality of attenuation poles include attenuation poles formed by the second resonator 21 and attenuation poles formed by a plurality of components of the second filter 20 excluding the second resonator 21. In this embodiment in particular, among the plurality of attenuation poles, the attenuation pole closest to the second passband is the attenuation pole formed by the second resonator 21. 【0055】Here, we focus on the attenuation in the relatively low frequency range within the first passband (for example, the frequency range of 2.5 GHz or less) of the pass-through attenuation characteristics (reference numerals 91 and 92) of the first filter 10. In this frequency range, the absolute value of the attenuation in the comparative example model increases as the frequency decreases. In contrast, in the embodiment model, the absolute value of the attenuation in the relatively low frequency range within the first passband is smaller compared to the comparative example model. As a result, in the embodiment model, the absolute value of the attenuation is smaller across the entire first passband. 【0056】 In the comparative example, the other ends of the first and second inductors L31 and L32 are electrically connected to ground. Therefore, in the comparative example, the path from the input terminal 10a to the output terminal 10b of the first filter 10 is electrically connected to ground. Consequently, in the comparative example, relatively low-frequency signals among the signals input to the first filter 10 flow to ground. 【0057】 In contrast, in this embodiment, the capacitor C31 is provided between the first end 11a and the second end 11b of the first resonator 11 and ground, and the path from the input end 10a to the output end 10b of the first filter 10 is not electrically connected to ground. As a result, according to this embodiment, it is possible to suppress the flow of relatively low-frequency signals to ground. Consequently, according to this embodiment, it is possible to suppress the increase in insertion loss in the relatively low-frequency region of the first passband, and to reduce the insertion loss across the entire first passband. 【0058】Furthermore, focusing on the high-frequency region of the first passband in the pass-through attenuation characteristics (reference numerals 91, 92) of the first filter 10, the absolute value of the attenuation is sufficiently large in both the comparative example model and the embodiment model. As a result, the absolute value of the reflection attenuation of the first filter 10 in this frequency region becomes sufficiently small. This frequency region overlaps with the second passband of the second filter 20. As can be seen from the pass-through attenuation characteristics (reference numerals 93, 94) of the second filter 20, there is almost no difference in the frequency attenuation in the second passband between the comparative example model and the embodiment model. According to this embodiment, the insertion loss in the second passband can be sufficiently reduced. 【0059】 Next, other features of this embodiment will be described. As mentioned above, in the pass-through attenuation characteristics of the first filter 10, among the multiple attenuation poles formed on the high-frequency side of the first passband, the attenuation pole closest to the first passband may be the attenuation pole formed by the first resonator 11. In this case, the resonant circuit 30 may be configured such that no attenuation pole is formed on the high-frequency side of the first passband by the components of the resonant circuit 30 other than the first resonator 11. Specifically, for example, the resonant circuit 30 may be configured such that the resonant frequencies of the first and second inductors L31 and L32 are smaller than the resonant frequencies of the third inductor L33 and capacitor C31. 【0060】[Modified Version] Next, a modified version of the resonant circuit 30 according to this embodiment will be described with reference to Figure 6. Figure 6 is a circuit diagram showing the circuit configuration of a modified version of the resonant circuit 30. In the modified version, the resonant circuit 30 includes a sub-circuit 140 instead of the sub-circuit 40 shown in Figure 1. The sub-circuit 140 includes a first inductor L41, a second inductor L42, and a third inductor L43. Any one of the first to third inductors L41 to L43 is connected to the other two inductors. In particular, in the modified version, one end of the first inductor L41 and one end of the third inductor L43 are connected to each other, one end of the second inductor L42 and the other end of the third inductor L43 are connected to each other, and the other end of the first inductor L41 and the other end of the second inductor L42 are connected to each other. 【0061】 Furthermore, one end of the first inductor L41 and one end of the third inductor L43 are connected to the first end 11a of the first resonator 11. One end of the second inductor L42 and the other end of the third inductor L43 are connected to the second end 11b of the first resonator 11. 【0062】 Capacitor C31 is located between the sub-circuit 140 and ground. Capacitor C31 is connected to the other end of the first inductor L41 and the other end of the second inductor L42. 【0063】 [Second Embodiment] Next, a second embodiment of the present disclosure will be described with reference to Figure 7. Figure 7 is a circuit diagram showing the circuit configuration of a resonant circuit 30 according to this embodiment. In this embodiment, the resonant circuit 30 includes at least one matching element. In the example shown in Figure 7, the resonant circuit 30 includes, as at least one matching element, a matching inductor L34 connected to the first end 11a of the first resonator 11 and a matching inductor L35 connected to the second end 11b of the first resonator 11. 【0064】Although not shown in the figures, the resonant circuit 30 according to this embodiment may be provided between the LC circuit 10A of the first filter 10 and the first signal port 3, similar to the first embodiment. In this case, the matching inductor L34 is provided between the first resonator 11 and the LC circuit 10A, and the matching inductor L35 is provided between the first resonator 11 and the first signal port 3. The matching inductors L34 and L35 may be used, for example, to adjust the reflection attenuation characteristics of the first filter 10. 【0065】 Other configurations, operations, and effects in this embodiment are the same as those in the first embodiment. 【0066】 [Third Embodiment] Next, a third embodiment of the present disclosure will be described with reference to Figure 8. Figure 8 is a circuit diagram showing the circuit configuration of the resonant circuit 30 according to this embodiment. The configuration of the resonant circuit 30 according to this embodiment differs from the second embodiment in the following respects. In this embodiment, the resonant circuit 30 includes matching capacitors C32 and C33 instead of the matching inductors L34 and L35 in the second embodiment. One end of the matching capacitor C32 is connected to the first end 11a of the first resonator 11. One end of the matching capacitor C33 is connected to the second end 11b of the first resonator 11. The other ends of the matching capacitors C32 and C33 are connected to ground. 【0067】 Although not shown in the figures, the resonant circuit 30 according to this embodiment may be provided between the LC circuit 10A of the first filter 10 and the first signal port 3, similar to the first embodiment. In this case, the matching capacitor C32 is provided between the first resonator 11 and the LC circuit 10A, and the matching capacitor C33 is provided between the first resonator 11 and the first signal port 3. The matching capacitors C32 and C33 may be used, for example, to adjust the reflection attenuation characteristics of the first filter 10. 【0068】 Other configurations, operations, and effects in this embodiment are the same as those in the first or second embodiment. 【0069】This disclosure is not limited to the embodiments described above, and various modifications are possible. For example, the resonant circuit of this disclosure may be used not only as a low-pass filter but also as other filters such as a band-pass filter. 【0070】 Furthermore, a capacitor may be provided between the first end 11a of the first resonator 11 and the first inductor L31, and another capacitor may be provided between the second end 11b of the first resonator 11 and the second inductor L32. In this case, capacitor C31 may or may not be provided. 【0071】 As described above, a resonant circuit according to one embodiment of the present disclosure comprises a resonator having a first end and a second end, a subcircuit connected in parallel to the resonator, and a capacitor. The subcircuit includes a first inductor, a second inductor, and a third inductor. At least two of the first inductor, the second inductor, and the third inductor are connected to each other. The capacitor is provided between the first end of the resonator and ground, and between the second end of the resonator and ground. 【0072】 In a resonant circuit according to one embodiment of the present disclosure, any one of the first inductor, second inductor, and third inductor may be connected to the other two inductors. A capacitor may be provided between the sub-circuit and ground. 【0073】 Furthermore, in a resonant circuit according to one embodiment of the present disclosure, the first inductor and the second inductor may be connected to each other. One of the third inductor and the capacitor may be connected to the connection point of the first inductor and the second inductor. The other of the third inductor and the capacitor may be connected in series with the one of the third inductor and the capacitor. One end of the first inductor may be connected to the first end of the resonator. One end of the second inductor may be connected to the second end of the resonator. 【0074】Furthermore, in a resonant circuit according to one embodiment of the present disclosure, at least one of the first inductor, second inductor, and third inductor may be configured using an inductor element. 【0075】 Furthermore, in a resonant circuit according to one embodiment of the present disclosure, the resonator may include an elastic wave element. 【0076】 Furthermore, the resonant circuit according to one embodiment of the present disclosure may further include at least one matching element connected to at least one of the first and second ends of the resonator. 【0077】 Furthermore, a resonant circuit according to one embodiment of the present disclosure may cooperate with an LC circuit including at least one inductor and at least one capacitor to form a low-pass filter that selectively passes signals with frequencies within the passband. The low-pass filter may be configured to form a plurality of attenuation poles on the high-frequency side of the passband in the pass-through attenuation characteristics of the low-pass filter. The resonator may be configured to form the attenuation pole closest to the passband among the plurality of attenuation poles. The low-pass filter may have an input terminal and an output terminal. The LC circuit may be a low-pass filter circuit and may also be provided between the input terminal and the resonator. 【0078】A demultiplexer according to one embodiment of the present disclosure comprises a common port, a first signal port, a second signal port, a first filter provided between the common port and the first signal port and configured to selectively pass signals with frequencies within a first passband, and a second filter provided between the common port and the second signal port and configured to selectively pass signals with frequencies within a second passband. The first filter includes a resonant circuit. The resonant circuit includes a resonator having a first end and a second end, a subcircuit connected in parallel with the resonator, and a capacitor. The subcircuit includes a first inductor, a second inductor, and a third inductor. At least two of the first inductor, the second inductor, and the third inductor are connected to each other. The capacitor is provided between the first end of the resonator and ground, and between the second end of the resonator and ground. 【0079】 Furthermore, in a demultiplexer according to one embodiment of the present disclosure, the second passband may be higher than the first passband. 【0080】 Furthermore, a demultiplexer according to one embodiment of the present disclosure may further comprise a first body and a second body mounted on the first body. The first body may include a common port, a first signal port, and a second signal port. The second body may include a resonator. The first body may further comprise a plurality of components of a first filter excluding the resonator and at least one component of a second filter. 【0081】 This application claims priority to Japanese Patent Application No. 2024-214143, filed on 9 December 2024, which is incorporated herein by reference in its entirety.

Claims

1. A resonant circuit comprising: a resonator having a first end and a second end; a sub-circuit connected in parallel to the resonator; and a capacitor, wherein the sub-circuit includes a first inductor, a second inductor, and a third inductor, and at least two of the first inductor, the second inductor, and the third inductor are connected to each other; and the capacitor is provided between the first end of the resonator and ground, and between the second end of the resonator and ground.

2. The resonant circuit according to claim 1, characterized in that any one of the first inductor, the second inductor, and the third inductor is connected to the other two inductors, and the capacitor is provided between the sub-circuit and the ground.

3. The resonant circuit according to claim 1, characterized in that the first inductor and the second inductor are connected to each other, one of the third inductor and the capacitor is connected to the connection point of the first inductor and the second inductor, the other of the third inductor and the capacitor is connected in series with the one, one end of the first inductor is connected to the first end of the resonator, and one end of the second inductor is connected to the second end of the resonator.

4. The resonant circuit according to claim 1, characterized in that at least one of the first inductor, the second inductor, and the third inductor is configured using an inductor element.

5. The resonant circuit according to claim 1, characterized in that the resonator includes an elastic wave element.

6. The resonant circuit according to claim 1, further comprising at least one matching element connected to at least one of the first and second ends of the resonator.

7. The resonant circuit according to claim 1, characterized in that it works in cooperation with an LC circuit including at least one inductor and at least one capacitor to form a low-pass filter that selectively passes signals with frequencies within a passband.

8. The resonant circuit according to claim 7, characterized in that the low-pass filter is configured to form a plurality of attenuation poles on the high-frequency side of the passband in the pass-through attenuation characteristics of the low-pass filter, and the resonator is configured to form the attenuation pole closest to the passband among the plurality of attenuation poles.

9. The resonant circuit according to claim 7, characterized in that the low-pass filter has an input terminal and an output terminal, and the LC circuit is a low-pass filter circuit and is provided between the input terminal and the resonator.

10. A demultiplexer comprising: a common port; a first signal port; a second signal port; a first filter provided between the common port and the first signal port and configured to selectively pass signals with frequencies within a first passband; and a second filter provided between the common port and the second signal port and configured to selectively pass signals with frequencies within a second passband, wherein the first filter includes a resonant circuit; the resonant circuit includes: a resonator having a first end and a second end; a sub-circuit connected in parallel to the resonator; and a capacitor; the sub-circuit includes a first inductor, a second inductor, and a third inductor; at least two of the first inductor, the second inductor, and the third inductor are connected to each other; and the capacitor is provided between the first end of the resonator and ground, and between the second end of the resonator and ground.

11. The demultiplexer according to claim 10, characterized in that the second passband is higher than the first passband.

12. The demultiplexer according to claim 10, further comprising a first body and a second body mounted on the first body, wherein the first body includes the common port, the first signal port and the second signal port, and the second body includes the resonator.

13. The demultiplexer according to claim 12, characterized in that the first body further includes a plurality of components of the first filter excluding the resonator and at least one component of the second filter.

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