BANDPASS FILTERS AND SPLIT FILTERS

Abstract

A bandpass filter (10, 20) having a first terminal (P11, P21) and a second terminal (P12, P22) and configured to selectively pass a signal of a frequency within a passband whose frequency is not less than a lower band cutoff frequency and not higher than an upper band cutoff frequency, characterized in that the bandpass filter (10, 20) additionally comprises an LC resonant circuit (11, 21) and a resonant circuit section (12, 22) arranged in series between the first terminal (P11, P21) and the second terminal (P12, P22); the resonant circuit section (12, 22) comprises at least one acoustic wave resonator (R1, R2) arranged in a path leading from the first terminal (P11, P21) to the second terminal (P21, P22); the resonant circuit section (12, 22) has a resonant frequency and at least one Antiresonance frequency; the resonance frequency lies within the passband;and at least one anti-resonance frequency lies outside the passband.

Description

BACKGROUND OF THE INVENTION 1. Field of the invention

[0001] The present invention relates to a bandpass filter and a branch filter comprising the bandpass filter. 2. Description of the related technology

[0002] Mobile communication systems based on the LTE standard have been used in practice in recent years, and the practical application of mobile communication systems based on the LTE-Advanced standard, which is a further development of the LTE standard, is also being investigated. "Carrier Aggregation" (CA) is a key technology of the LTE-Advanced standard. Carrier Aggregation uses multiple channels, referred to as "component carriers," simultaneously to enable broadband transmission.

[0003] A mobile communication device that can be operated according to CA uses multiple frequency bands simultaneously. Accordingly, such a mobile communication device requires a tap filter capable of simultaneously separating a multitude of signals in a multitude of frequency bands. A tap filter for the mutual separation of a first signal with a frequency within a first frequency band and a signal with a frequency within a second frequency band that lies above the first frequency band typically comprises a common terminal, a first signal terminal, a second signal terminal, a first filter arranged in a first signal path leading from the common terminal to the first signal terminal, and a second filter arranged in a second signal path leading from the common terminal to the second signal terminal.Examples of the first filter include a low-pass filter and a band-pass filter, and examples of the second filter include a high-pass filter and a band-pass filter.

[0004] A branch filter that uses a bandpass filter as the first or second filter has an advantage in its ability to increase attenuation outside the first frequency band in the first signal path and to increase attenuation outside the second frequency band in the second signal path.

[0005] Well-known bandpass filters include LC filters using inductance and capacitance, and acoustic wave filters using acoustic wave resonators. Acoustic wave resonators are resonators that utilize acoustic wave elements. These acoustic wave elements are elements that utilize acoustic waves. Acoustic wave elements include surface acoustic wave elements, which utilize surface acoustic waves, and volume acoustic wave elements, which utilize volume acoustic waves.

[0006] JP-2010-141859A discloses a diplexer comprising two bandpass filters, each formed from an LC filter.

[0007] JP-2015-115866A discloses a branch filter comprising two bandpass filters, each formed from an acoustic wave filter.

[0008] Mobile communication devices may require a tap filter to separate two signals in two relatively closely spaced frequency bands. Such a tap filter requires a filter with an insertion loss characteristic that changes abruptly in a frequency range near the cutoff frequency.

[0009] For LC filters, it is typically difficult to achieve an insertion loss characteristic that changes abruptly in a frequency range near the cutoff frequency.

[0010] On the other hand, although acoustic wave filters are suitable for achieving an insertion loss characteristic that changes abruptly in a frequency range near the cutoff frequency, they are not suitable for providing a wide passband.

[0011] Therefore, it was difficult in the conventional way to provide a tap filter suitable for separating two signals in two mutually relatively close frequency bands and to provide a bandpass filter suitable for such a tap filter. TASK AND PRESENTATION OF THE INVENTION

[0012] A first object of the present invention is to provide a bandpass filter which has an insertion loss characteristic which changes abruptly in a frequency range near the cutoff frequency.

[0013] A second object of the present invention is to provide a branching filter suitable for separating two signals in two relatively close frequency bands. A bandpass filter of the present invention is configured to selectively allow a signal of a frequency within a passband whose frequency is not lower than a lower band cutoff frequency and not higher than an upper band cutoff frequency to pass through.

[0014] The bandpass filter of the present invention comprises: a first terminal, a second terminal and an LC resonant circuit and a resonant circuit section arranged in series between the first terminal and the second terminal.

[0015] The resonant circuit section includes at least one acoustic wave resonator arranged in a path leading from the first terminal to the second terminal.

[0016] The resonant circuit section has a resonant frequency and at least one anti-resonant frequency. The resonant frequency lies within the passband. The at least one anti-resonant frequency lies outside the passband.

[0017] In the bandpass filter of the present invention, the at least one anti-resonance frequency can be higher than the upper band cutoff frequency. In this case, the resonant circuit section can comprise two acoustic wave resonators connected in series, as the at least one acoustic wave resonator.

[0018] In the bandpass filter of the present invention, the resonant circuit section can further comprise at least one inductor connected in parallel to the at least one acoustic wave resonator. The resonant circuit section can have, as the at least one anti-resonance frequency, an anti-resonance frequency lower than the lower band cutoff frequency and an anti-resonance frequency higher than the upper band cutoff frequency. In this case, the resonant circuit section can comprise, as the at least one acoustic wave resonator, two acoustic wave resonators connected in series, and as the at least one inductor, two inductors connected in parallel to the two acoustic wave resonators.

[0019] In the bandpass filter of the present invention, the LC resonant circuit can be an LC parallel resonant circuit which has a resonant frequency outside the passband.

[0020] A branch filter according to a first to third aspect of the present invention comprises a common terminal, a first signal terminal, a second signal terminal, a first filter, and a second filter. The first filter is arranged between the common terminal and the first signal terminal and is configured to selectively pass a signal of a frequency within a first passband. The second filter is arranged between the common terminal and the second signal terminal and is configured to selectively pass a signal of a frequency within a second passband above the first passband. In the branch filter according to the first aspect of the present invention, the first filter is a first bandpass filter. The first passband is a frequency band that is neither below a first lower band cutoff frequency nor above an upper band cutoff frequency.The first bandpass filter comprises a first LC resonant circuit and a first resonant circuit section between the common terminal and the first signal terminal, wherein the first LC resonant circuit and the first resonant circuit section are arranged in series in that order from the common terminal. The first resonant circuit section includes at least one acoustic wave resonator arranged in a path leading from the first LC resonant circuit to the first signal terminal. The first resonant circuit section has a resonant frequency within the first passband and at least one anti-resonant frequency higher than the first upper band cutoff frequency.

[0021] In the branch filter according to the first aspect of the present invention, the first resonant circuit section, as the at least one acoustic wave resonator, can comprise two acoustic wave resonators connected in series.

[0022] In the branch filter according to the first aspect of the present invention, the first LC resonant circuit can be a first LC parallel resonant circuit having a resonant frequency higher than the first upper band cutoff frequency.

[0023] In the branching filter according to the second aspect of the present invention, the second filter is a second bandpass filter. The second passband is a frequency band that is neither below a second lower bandcut frequency nor above a second upper bandcut frequency. The second bandpass filter comprises a second LC resonant circuit and a second resonant circuit section between the common terminal and the second signal terminal. The first LC resonant circuit and the second resonant circuit section are arranged in series in that order from the common terminal. The second resonant circuit section comprises at least one acoustic wave resonator located in a path leading from the second LC resonant circuit to the second signal terminal, and at least one inductor arranged in parallel with the at least one acoustic wave resonator.The second resonant circuit section has a resonant frequency within the second passband, an anti-resonance frequency that is lower than the second lower band cutoff frequency, and an anti-resonance frequency that is higher than the second upper band cutoff frequency.

[0024] In the branch filter according to the second aspect of the present invention, the second resonant circuit section can comprise, as the at least one acoustic wave resonator, two acoustic wave resonators connected in series, and, as the at least one inductor, two inductors connected in parallel to the two acoustic wave resonators.

[0025] In the branch filter according to the second aspect of the present invention, the second LC resonant circuit can be a second LC parallel resonant circuit having a resonant frequency that is lower than the second lower band cutoff frequency.

[0026] In a branch filter according to the third aspect of the present invention, the first filter is a first bandpass filter. The first passband is a frequency band that is neither below a first lower band cutoff frequency nor above an upper band cutoff frequency. The first bandpass filter comprises a first LC resonant circuit and a first resonant circuit section between the common terminal and the first signal terminal, wherein the first LC resonant circuit and the first resonant circuit section are arranged in series in that order from the common terminal side. The first resonant circuit section comprises at least one first acoustic wave resonator arranged in a path leading from the first LC resonant circuit to the first signal terminal. The first resonant circuit section has a resonant frequency within the first passband and at least one anti-resonant frequency higher than the first upper band cutoff frequency.

[0027] In the branching filter according to the third aspect of the present invention, the second filter is a second bandpass filter. The second passband is a frequency band that is neither below a second lower bandcut frequency nor above a second upper bandcut frequency. The second bandpass filter comprises a second LC resonant circuit and a second resonant circuit section between the common terminal and the second signal terminal, wherein the second LC resonant circuit and the second resonant circuit section are arranged in series in that order from the common terminal side. The second resonant circuit section comprises at least one second acoustic wave resonator arranged in a path leading from the second LC resonant circuit to the second signal terminal, and at least one inductor arranged in parallel with the at least one second acoustic wave resonator.The second resonant circuit section has a resonant frequency within the second passband, an anti-resonance frequency that is lower than the lower band cutoff frequency, and an anti-resonance frequency that is higher than the upper band cutoff frequency.

[0028] In the branching filter according to the third aspect of the present invention, the first resonant circuit section can be the at least one first acoustic wave resonator, or two first acoustic wave resonators connected in series, and the second resonant circuit section can be the at least one second acoustic wave resonator, or two second acoustic wave resonators connected in series, and can be the at least one inductor, or two inductors connected in parallel with the two second acoustic wave resonators. In the branching filter according to the third aspect of the present invention, the first LC resonant circuit can be a first LC parallel resonant circuit having a resonant frequency higher than the first upper band cutoff frequency, and the second LC resonant circuit can be a second LC parallel resonant circuit having a resonant frequency lower than the second lower band cutoff frequency.

[0029] The bandpass filter of the present invention comprises a resonant circuit section that includes at least one acoustic wave resonator. The resonant frequency of the resonant circuit section lies within the passband, and the at least one anti-resonant frequency lies outside the passband. Due to this arrangement, the bandpass filter of the present invention provides an insertion loss characteristic that changes abruptly in a frequency range near the lower or upper band cutoff frequency.

[0030] In the branching filter according to the first aspect of the present invention, the first bandpass filter or the first filter corresponds to the bandpass filter of the present invention. The branching filter according to the first aspect of the present invention enables the first bandpass filter to provide an insertion loss characteristic that changes abruptly in a frequency range near the first upper band cutoff frequency.

[0031] In the branching filter according to the second aspect of the present invention, the second bandpass filter or the second filter corresponds to the bandpass filter of the present invention. The branching filter according to the second aspect of the present invention enables the second bandpass filter to provide an insertion loss characteristic that changes abruptly in a frequency range near the second lower band cutoff frequency.

[0032] In the branching filter according to the third aspect of the present invention, both the first bandpass filter or the first filter, and the second bandpass filter or the second filter, correspond to the bandpass filter of the present invention. The branching filter according to the third aspect of the present invention enables the first bandpass filter to provide an insertion loss characteristic that changes abruptly in a frequency range near the first upper band cutoff frequency, and enables the second bandpass filter to provide an insertion loss characteristic that changes abruptly in a frequency range near the second lower band cutoff frequency.

[0033] Thus, the first to third aspects of the present invention provide a branch filter suitable for separating two signals in two mutually relatively close frequency bands.

[0034] The tasks, features and advantages of the invention will become clearer from the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Fig. Figure 1 is a circuit diagram illustrating the configuration of a branch filter according to a first embodiment of the invention.

[0036] Fig. Figure 2 is a perspective view illustrating an example of the external appearance of the branch filter according to the first embodiment of the invention.

[0037] Fig. Figure 3 is a characteristic diagram illustrating an example of the properties of the branch filter according to the first embodiment of the invention.

[0038] Fig. Figure 4 is a characteristic diagram showing an enlarged view of part of the Fig. provides the 3 properties shown.

[0039] Fig. 5 is an explanatory diagram showing the impedance characteristic of a first acoustic wave resonator of the in Fig. 1 shows a branch filter.

[0040] Fig. Figure 6 is a characteristic diagram that illustrates the property of the first acoustic wave resonator of the in Fig. The branch filter shown in section 1 is shown.

[0041] Fig. Figure 7 is a circuit diagram that represents an equivalent circuit of a second resonant circuit section of the in Fig. The branch filter shown in section 1 is shown.

[0042] Fig. Figure 8 is an explanatory diagram showing the impedance characteristic of a second resonant circuit section of the in Fig. 1 shows a branch filter.

[0043] Fig. Figure 9 is a characteristic diagram that illustrates the property of the second resonant circuit of the in Fig. 1 shows a branch filter.

[0044] Fig. Figure 10 is a circuit diagram illustrating the configuration of a branch filter according to a second embodiment of the invention.

[0045] Fig. Figure 11 is a characteristic diagram illustrating an example of the properties of the branch filter according to the second embodiment of the invention.

[0046] Fig. Figure 12 is a circuit diagram illustrating the configuration of a branch filter according to a third embodiment of the invention.

[0047] Fig. Figure 13 is a characteristic diagram illustrating an example of the properties of the branch filter according to the third embodiment of the invention.

[0048] Fig. Figure 14 is a characteristic diagram showing an enlarged view of part of the Fig. Provides the 13 properties shown. DETAILED DESCRIPTION OF THE PREFERRED EXECUTIONS [First embodiment]

[0049] Preferred embodiments of the present invention will now be described with reference to the drawings. First, the configuration of a branch filter according to a first embodiment of the invention will be described with reference to Fig. 1 shown. The branch filter 1 According to the first embodiment, it includes a common connection. 2 , a first signal connection 3 , a second signal connection 4 , a first filter 10 and a second filter 20 The first filter 10 is between the common connection 2 and the first signal connection 3 The second filter is arranged and designed to selectively allow a signal of a specific frequency within a first passband to pass through. 20 is between the common connection 2 and the second signal connection 4arranged and designed to selectively allow a signal of a frequency within a second passband above the first passband to pass through. In the first embodiment, the first filter 10 in particular a first bandpass filter and is the second filter 20 in particular a second bandpass filter. The first filter is described below. 10 also known as the first bandpass filter 10 designated and becomes the second filter 20 also known as the second bandpass filter 20 The first passband and the second passband are defined in mm with reference to Fig. 3 and Fig. 4 described. Fig. Figure 3 is a characteristic diagram that provides an example of the properties of the branch filter. 1 illustrated. Fig. Figure 4 is a characteristic diagram showing an enlarged view of part of the Fig. provides the 3 shown properties. Fig. 3 and Fig. In 4, the horizontal axis represents a frequency and the vertical axis represents damping. Fig. 3 and Fig. 4 shows the curve 51 the insertion loss characteristic of the first bandpass filter 10 and shows the curve 52 the insertion loss characteristic of the second bandpass filter 20 The in Fig. 3 and Fig. The four properties shown were determined by a simulation. Fig. 3 and Fig. In section 4, the symbol PB1 represents the first passband, and the symbol PB2 represents the second passband. The first passband, PB1, is a frequency band that does not extend below a first lower band cutoff frequency f. 1L and not above the first upper band cutoff frequency f 1H lies. The first lower band cutoff frequency f 1L and the first upper band cutoff frequency f 1Hare two frequencies at which the insertion loss characteristic of the first bandpass filter 10 an increase in attenuation of 3 dB compared to the minimum attenuation value. The first upper band cutoff frequency f 1H lies above the first lower band cutoff frequency f 1L The second passband PB2 is a frequency band that does not extend lower than a second lower band cutoff frequency f. 2L and not above a second upper band cutoff frequency f 2H lies. The second lower band cutoff frequency f 2L and the second upper band cutoff frequency f 2H are two frequencies at which the insertion loss characteristic of the second bandpass filter 20 an increase in attenuation of 3 dB compared to the minimum attenuation value. The second upper band cutoff frequency f 2H lies above the second lower band cutoff frequency f 2L The second lower band cutoff frequency f 2Llies above the first upper band cutoff frequency f 1H Now the configurations of the first and second bandpass filters will be shown. 10 and 20 in detail with reference to Fig. 1 described. The first bandpass filter 10 It includes a first connection P11 and a second connection P12. The first connection P11 is connected to the common connection. 2 connected. The second terminal P12 is connected to the first signal terminal. 3 connected. The first bandpass filter 10 It also includes a first LC resonant circuit. 11 and a first resonant circuit section 12 , which are arranged in series between the first terminal P11 and the second terminal P12. More precisely, the first LC resonant circuit 11 and the first resonant circuit section 12The components are arranged in series between the first terminal P11 and the second terminal P12, starting from the side of the first terminal P11, in that order. Accordingly, it can also be said that the first LC resonant circuit... 11 and the first resonant circuit section 12 between the common connection 2 and the first signal connection 3 are arranged and from the side of the common connection 2 are arranged in series in this order. The first LC resonant circuit 11 is a resonant circuit formed using an inductor and a capacitor. In the first embodiment, the first LC resonant circuit 11 in particular a first LC parallel resonant circuit including an inductor L11 and a capacitor C11, which are connected in parallel between the first terminal P11 and the second terminal P12, that is, between the common terminal2 and the first signal connection 3 , are arranged. The first resonant circuit section 12 It includes at least one first acoustic wave resonator arranged in a path leading from the first terminal P11 to the second terminal P12. More precisely, the at least one first acoustic wave resonator is arranged in a path leading from the first LC resonant circuit. 11 to the second connection P12, that is, in a path that leads from the first LC resonant circuit 11 to the first signal connection 3 leads to. In the first embodiment, the first resonant circuit section 12in particular, it is formed from a first acoustic wave resonator R1. The first acoustic wave resonator R1 is a resonator formed using an acoustic wave element. The acoustic wave element is an element that uses acoustic waves. The acoustic wave element used to form the first acoustic wave resonator R1 can be a surface acoustic wave element, which uses surface acoustic waves, or a volume acoustic wave element, which uses volume acoustic waves. The surface acoustic wave element uses surface acoustic waves, i.e., acoustic waves that propagate across the surface of a piezoelectric material, while the volume acoustic wave element uses volume acoustic waves, i.e., acoustic waves that propagate internally through a piezoelectric material. The first bandpass filter 10It also includes inductors L12 and L13 and capacitors C12, C13, and C14. Inductor L12 is connected between the first terminal P11 and the first LC resonant circuit. 11 The capacitor C12 is arranged between ground and the junction between inductor L12 and the first LC resonant circuit. 11 arranged. Capacitor C13 is located between the first LC resonant circuit. 11 and the first acoustic wave resonator R1. One end of the inductor L13 is connected to the junction between the capacitor C13 and the first acoustic wave resonator R1. One end of the capacitor C14 is connected to the other end of the inductor. 13 connected. The other end of capacitor C14 is connected to ground. The second bandpass filter 20 It includes a first connection P21 and a second connection P22. The first connection P21 is connected to the common connection. 2connected. The second terminal P22 is connected to the second signal terminal. 4 connected. The second bandpass filter 20 It also includes a second LC resonant circuit 21 and a second resonant circuit section 22 , which are arranged in series between the first terminal P21 and the second terminal P22. More precisely, the second LC resonant circuit 21 and the second resonant circuit section 22 The components are arranged in series between the first terminal P21 and the second terminal P22, starting from the side of the first terminal P21, in this order. Accordingly, it can also be said that the second LC resonant circuit... 21 and the second resonant circuit section 22 between the common connection 2 and the second signal connection 4 are arranged and from the side of the common connection 2are arranged in series in this order. The second LC resonant circuit 21 is a resonant circuit formed using an inductor and a capacitor. In the first embodiment, the second is an LC resonant circuit. 21 in particular a second LC parallel resonant circuit including an inductor L21 and a capacitor C21, which are connected in parallel between the first terminal P21 and the second terminal P22, that is, between the common terminal 2 and the second signal connection 4 , are arranged. The second resonant circuit section 22 It includes at least one second acoustic wave resonator arranged in a path leading from the first terminal P21 to the second terminal P22. More precisely, the at least one second acoustic wave resonator is arranged in a path leading from the second LC resonant circuit. 21to the second connection P22, that is, in a path that leads from the second LC resonant circuit 21 to the second signal connection 4 leads to the second resonant circuit section. 22 Furthermore, it includes at least one inductor connected in parallel with at least one second acoustic wave resonator. In the first embodiment, the second resonant circuit section consists of 22 in particular, consisting of a second acoustic wave resonator R2 and an inductor L2 connected in parallel with the second acoustic wave resonator R2. The second acoustic wave resonator R2 is formed using an acoustic wave element, just like the first acoustic wave resonator R1. The acoustic wave element used to form the second acoustic wave resonator R2 can be an acoustic surface wave element or an acoustic volume wave element. The second bandpass filter 20It also includes an inductor L22 and capacitors C22, C23, C24, and C25. Capacitor C22 is located between the first terminal P21 and the second LC resonant circuit. 21 The inductor L22 and the capacitor C23 are arranged in parallel between ground and the junction between capacitor C22 and the second LC resonant circuit. 21 The capacitor C24 is arranged between ground and the connection point between the second LC resonant circuit. 21 and the second resonant circuit section 22 The capacitor C25 is arranged between the second terminal P22 and ground. Now the path leading from the common terminal 2 to the first signal connection 3 leads, referred to as the first signal path, and is the path that leads from the common terminal. 2 to the second signal connection 4This leads to what is referred to as the second signal path. A first signal with a frequency within the first passband PB1 is selectively passed through the first signal path and not through the second signal path. A second signal with a frequency within the second passband PB2 is selectively passed through the second signal path and not through the first signal path. In this way, the branch filter separates the signals. 1 the first signal and the second signal from each other. Fig. Figure 2 is a perspective view that provides an example of the external appearance of the branch filter. 1 Illustrated. The branch filter 1 This example includes a stack 30 and the first and second acoustic wave resonators R1 and R2. The stack 30 It is shaped like a rectangular solid and has a periphery. The periphery of the stack 30It includes a top surface, a bottom surface, and four side surfaces. The stack 30 It includes dielectric layers and conductive layers stacked on top of each other. Other components of the branch filter 1 The first and second acoustic wave resonators R1 and R2 are constructed using the dielectric layers and the conductor layers of the stack. 30 The first and second acoustic wave resonators R1 and R2 are formed on the upper surface of the stack. 30 Assembled. The first and second acoustic wave resonators R1 and R2 can be combined into a pack, and the pack can be placed on the upper surface of the stack. 30 It should be mounted. Although this is not illustrated, there are three connections that lead to the common connection. 2 , the first signal connection 3 and the second signal connection 4correspond, and a connection to be connected to ground on the lower surface of the stack 30 arranged. The characteristics of the branch filter 1 will now be discussed with reference to Fig. 3 to Fig. Section 9 describes the characteristics of the first bandpass filter. 10 described. The first bandpass filter 10 the first LC resonant circuit 11 a resonance frequency f 1C outside the first passband PB1. In the present embodiment, the resonance frequency f 1C above the first upper band cutoff frequency f 1H The first section of the resonant circuit 12 , i.e., the first acoustic wave resonator R1, has a resonance frequency for and an antiresonance frequency f 1a on. The resonant frequency f 1ris a frequency at which the first acoustic wave resonator R1 exhibits a minimum impedance (maximum admittance). The antiresonance frequency f 1a is a frequency at which the first acoustic wave resonator R1 exhibits minimum admittance (maximum impedance). The antiresonance frequency f 1a lies above the resonance frequency f 1r . Fig. Figure 5 is a Smith chart showing the impedance characteristic of the first acoustic wave resonator R1. Fig. 5 gives the point f 1r the impedance of the first acoustic wave resonator R1 at the resonance frequency f 1r and the point f 1a the impedance of the first acoustic wave resonator R1 at the antiresonance frequency f 1a to. Fig. Figure 6 illustrates the reflection damping property of the first acoustic wave resonator R1. Fig. In 6, the horizontal axis represents a frequency and the vertical axis represents damping. Fig. 6 gives the point f 1r the reflection attenuation of the first acoustic wave resonator R1 at the resonance frequency f 1r and the point f 1a the reflection attenuation of the first acoustic wave resonator R1 at the antiresonance frequency f 1a on. As in Fig. 3 and Fig. As shown in section 4, the resonant frequency is f 1r of the first acoustic wave resonator R1 within the first passband PB1. The antiresonance frequency f 1a of the first acoustic wave resonator R1 lies above the upper band cutoff frequency f 1H The insertion loss characteristic 51 of the first bandpass filter 10 shows a first damping pole at the antiresonance frequency f 1a The resonant frequency f 1C of the first LC resonant circuit 11lies above the antiresonance frequency f 1a The insertion loss characteristic 51 of the first bandpass filter 10 shows a second damping pole at the resonance frequency f 1C The resonant frequency f 1r and the antiresonance frequency f 1a are relatively close together. Accordingly, adjusting the resonant frequency f leads to 1r and the antiresonance frequency f 1a as above, that the resonant frequency f 1r within the first passband PB1 and near the first upper band cutoff frequency f 1H is located, and leads to the antiresonance frequency f 1a outside the first passband PB1 and near the first upper band cutoff frequency f 1H is located. As in Fig. 3 and Fig. As shown in section 4, the first bandpass filter is... 10 consequently in a frequency region near the first upper band cutoff frequency f 1Ha small insertion loss at the resonance frequency f 1r , which lies within the first passband PB1, and a large insertion loss at the antiresonant frequency f 1a , which lies outside the first passband PB1, is ready. The first bandpass filter 10 Accordingly, it exhibits an insertion loss characteristic that shows a small insertion loss in the first passband PB1 and which is located in a frequency region near the first upper band cutoff frequency f 1H It changes abruptly. Then the characteristics of the second bandpass filter become apparent. 20 described. Regarding the second bandpass filter 20 the second LC resonant circuit 21 a resonance frequency f 2C outside the second passband PB2. In the present embodiment, the resonance frequency f 2C lower than the second lower band cutoff frequency f 2L The second resonant circuit section 22exhibits a resonance frequency f 2r and two antiresonance frequencies f 2aL and f 2aL on. The antiresonance frequency f 2aL is lower than the resonant frequency f 2r The antiresonance frequency f 2aH lies above the resonance frequency f 2r Reference is now made to Fig. 7 taken to describe the reason why the second resonant circuit section 22 a resonance frequency f 2r and two antiresonance frequencies f 2aL and f 2aH exhibits. Fig. Figure 7 is a circuit diagram that represents an equivalent circuit of the second resonant circuit section. 22 This circuit diagram ignores any resistive components in the second resonant circuit section. 22 As in Fig. As shown in Figure 7, the second acoustic wave resonator R2 can be represented as a circuit consisting of an inductor L1 and two capacitors C0 and C1. The second acoustic wave resonator R2 has a first end and a second end that are opposite each other in terms of the circuit configuration. One end of inductor L1 and one end of capacitor C0 are connected to the first end of the second acoustic wave resonator R2. One end of capacitor C1 is connected to the other end of inductor L1. 1 The two ends of capacitor C1 and capacitor C0 are connected to the other end of the second acoustic wave resonator R2. Inductor L2 is connected in parallel with the second acoustic wave resonator R2. If L1 denotes the inductance value of inductor L1, C0 denotes the capacitance value of capacitor C0, and C1 denotes the capacitance value of capacitor C1, Lm denotes the inductance value of inductor L2 and Z the impedance of the second resonant circuit section. 22 If it is called that, then the following applies: 1 / Z = (1 / jωL m ) + jωC0 + [1 / {jωL1 + (1 / jωC1)}] (1) where ω is an angular frequency and j is an imaginary unit. Rearranging equation (1) above yields equation (2) below. Z = jωL m (1–ω 2 L1C1) / {1 – ω 2 (L1C1 + L m C1 + L m C0) + ω 4 L1L m C1C0} (2) The resonance frequency f 2r of the second resonant circuit section 22 is obtained from the angular frequency ω where the numerator of equation (2) is 0 and can be expressed by equation (3) below. f 2r = 1 / {2π√(L1C1)} (3) If we determine the anti-resonance frequency of the second resonant circuit section 22To represent fa, the angular frequency ω is obtained where the denominator of equation (2) is 0, and can be expressed by equation (4) below. fa = (√X) / 2π (4) where X can be expressed by equation (5) below: X = {B ± √(B 2 – 4A)} / 2A (5) where A and B can each be expressed by equations (6) and (7) respectively: A = L1L m C1C0 (6) B = L1C1 + L m C1 + L m C0 (7). Equation (5) gives two solutions for X. Therefore, there are also two solutions for fa, which can be expressed by equation (4). The two solutions are the antiresonance frequencies f 2aL and f 2aH For example, if we have C0 = 1.26 pF, L m Assuming L1 = 1.9 nH, L1 = 91.87 nH and C1 = 0.0562 pF, then: f 2r = 2215.0 MHz; f 2aL = 2174.7 MHz; and f 2aH = 3313.1 MHz. Fig. Figure 8 is a Smith chart showing the impedance characteristic of the second resonant circuit section. 22 shows. In Fig. 8 gives the point f 2r the impedance of the second resonant circuit section 22 at the resonance frequency f 2r the point f 2aL the impedance of the second resonant circuit section 22 at the antiresonance frequency f 2aL and the point f 2aH the impedance of the second resonant circuit section 22 at the antiresonance frequency f 2aH to. Fig. Figure 9 illustrates the reflection damping property of the second resonant circuit section. 22 . In Fig. In 9, the horizontal axis represents a frequency and the vertical axis represents damping. Fig. 9 gives the point f 2r the reflection damping of the second resonant circuit section 22 at the resonance frequency f 2r the point f 2aLthe reflection damping of the second resonant circuit section 22 at the antiresonance frequency f 2aL and the point f 2aH the reflection damping of the second resonant circuit section 22 at the antiresonance frequency f 2aH on. As in Fig. 3 and Fig. As shown in section 4, the resonant frequency is f 2r of the second resonant circuit section 22 within the second passband PB2. The antiresonance frequency f 2aL of the second resonant circuit section 22 is lower than the second lower band cutoff frequency f 2L The antiresonance frequency f of the second resonant circuit section 22 lies above the second upper band cutoff frequency f 2H The insertion loss characteristic 52 of the second bandpass filter 20 shows a first damping pole at the antiresonance frequency f 2aL The resonant frequency f 2C of the second LC resonant circuit21 is lower than the antiresonance frequency f 2aL The insertion loss characteristic 52 of the second bandpass filter 20 shows a second damping pole at the resonance frequency f 2C The resonance frequency f2r and the antiresonance frequency f 2aL are relatively close together. Accordingly, adjusting the resonant frequency f leads to 2r and the antiresonance frequency f 2aL as above, that the resonant frequency f 2r within the second passband PB2 and near the second lower band cutoff frequency f 2L is located, and leads to the antiresonance frequency f 2aL outside the second passband PB2 and near the second lower band cutoff frequency f 2L is located. As in Fig. 3 and Fig. As shown in section 4, the second bandpass filter is... 20 consequently in a frequency range near the second lower band cutoff frequency f 2La small insertion loss at the resonance frequency f2r, which lies within the second passband PB2, and a large insertion loss at the antiresonance frequency f 2aL , which lies outside the second passband PB2, is ready. The second bandpass filter 20 Accordingly, it exhibits an insertion loss characteristic that shows a small insertion loss in the second passband PB2 and which is located in a frequency region near the second lower band cutoff frequency f 2L abruptly changes. As in Fig. Figure 3 shows the insertion loss characteristic. 52 of the second bandpass filter 20 a third attenuation pole at the antiresonance frequency f2aH. Consequently, the insertion loss characteristic of the second bandpass filter shows 20a large insertion loss in a frequency region above the second passband PB2. For a bandpass filter constructed using an LC filter without an acoustic wave resonator, any attempt to achieve an insertion loss characteristic that changes abruptly in a frequency region near the cutoff frequency would require a large number of stages or a large inductance to obtain a high Q value. This would lead to an increase in the size of the bandpass filter. In the present embodiment, the bandpass filter includes 10 the first acoustic wave resonator R1 and includes the second bandpass filter 20the second acoustic wave resonator R2. Compared to LC resonators, acoustic wave resonators are typically capable of delivering higher Q values. More precisely, typical LC resonators deliver Q values ​​in the range of 50 to 100, whereas acoustic wave resonators deliver Q values ​​of 200 or more. The first and second acoustic wave resonators R1 and R2 deliver Q values ​​of 200 or more, e.g., from 600 to 1000. Accordingly, the present embodiment achieves the insertion loss characteristic of the first and second bandpass filters described above. 10 and 20 without increasing the inductance or the number of stages. The present embodiment therefore represents the branch circuit. 1 A suitable filter designed to separate two signals in two relatively close frequency bands, and which can be reduced in size. This is the bandpass filter. 10of the branch circuit 1 According to the present embodiment, the first LC resonant circuit 11 and the first resonant circuit section 12 between the common connection 2 and the first signal connection 3 arranged and are located on the side of the common connection 2 from the series connection arranged in this order. The second bandpass filter 20 are the second LC resonant circuit 21 and the second resonant circuit section 22 between the common connection 2 and the second signal connection 4 arranged and are located on the side of the common connection 2 The filters are arranged in series in this order. Such a configuration offers advantages, as described below. The first bandpass filter 10requires impedance characteristic matching so that the reflection coefficient of the first signal path, as from the common terminal 2 seen, in the first passband PB1 has an absolute value of 0 or close to 0 and the reflection coefficient of the first signal path, as from the common terminal 2 seen, in the second passband PB2, has an absolute value of 1 or close to 1. The second bandpass filter 20 requires impedance characteristic matching so that the reflection coefficient of the second signal path, as from the common terminal 2 seen, in the second passband PB2 has an absolute value of 0 or close to 0, and the reflection coefficient of the second signal path, as seen from the common terminal 2seen in the first passband PB1, which has an absolute value of 1 or close to 1. Typically, acoustic wave resonators show a greater change in impedance with respect to frequency compared to LC resonant circuits. If the first resonant circuit section 12 between the first LC resonant circuit 11 and the connection point between the bandpass filters 10 and 20 is present and the second resonant circuit section 22 between the second LC resonant circuit 21 and the connection point between the bandpass filters 10 and 20 Given this, it will be correspondingly difficult to achieve the impedance characteristic adjustments described above in both of the bandpass filters. 10 and 20 to carry out. In the present embodiment, however, the first LC resonant circuit is located 11 between the first resonant circuit section 12and the connection point between the bandpass filters 10 and 20 and the second LC resonant circuit lies between the second resonant circuit section 22 and the connection point between the bandpass filters 10 and 20 This configuration makes it easy to perform the impedance characteristic matching described above on both bandpass filters. 10 and 20 To be carried out: In the present embodiment, the first bandpass filter can be 10 in a variety of different configurations, including, among others, the one in Fig. The configuration shown in 1 can be formed as long as the first LC resonant circuit 11 and the first resonant circuit section 12 are included and the intended properties of the first bandpass filter 10 can be achieved. Similarly, the second bandpass filter can be used. 20in a variety of different configurations, including, among others, the one in Fig. The configuration shown in 1 can be formed as long as the second LC resonant circuit 21 and the second resonant circuit section 22 are included and the intended properties of the second bandpass filter 20 This can be achieved. The branch filter of the present invention can be a bandpass filter or a highpass filter of any configuration instead of the second bandpass filter. 20 include. In this case, the branch filter at least provides the effect that the first bandpass filter 10 an insertion loss characteristic is achieved which shows a small insertion loss in the first passband PB1 and which is located in a frequency region near the first upper band cutoff frequency f 1HThe branch filter of the present invention can be a bandpass filter or a lowpass filter of any configuration instead of the first bandpass filter. 10 include. In this case, the branch filter at least provides the effect that the second bandpass filter 20 an insertion loss characteristic is achieved which shows a small insertion loss in the second passband PB2 and which changes abruptly in a frequency region near the second lower band cutoff frequency f2L. [Second embodiment]

[0050] A branch filter according to a second embodiment of the invention is now described. Fig. Figure 10 is a circuit diagram illustrating the configuration of the branch filter according to the second embodiment. The branch filter 101According to the second embodiment, the device is designed to separate three signals with frequencies within three mutually distinct frequency bands. The three mutually distinct frequency bands are designated, from lowest to highest, as the lower band, the middle band, and the upper band. The branching filter 101 According to the second embodiment, it includes a common connection. 102 , a first signal connection 3 , and a third signal connection 5 The branch filter 101 It also includes a low-pass filter. 110 , a first bandpass filter 10 , a second bandpass filter 20 and a capacitor C40. The first and second bandpass filters 10 and 20 are designed in the same way as in the first embodiment. The low-pass filter 110 is between the common connection 102 and the third signal connection 5arranged. The low-pass filter 110 The circuit includes inductors L31 and L32 and capacitors C31, C32, and C33. Inductors L31 and L32 are connected in series between the common terminal. 102 and the third signal connection 5 The capacitor C31 is arranged between ground and the junction between inductors L31 and L32. The capacitor C32 is located between the third signal terminal. 5 and arranged to ground. Capacitor C33 is connected to the inductor. 32 Connected in parallel. One end of capacitor C40 is connected to the common terminal. 102 connected. The first connection P11 of the first bandpass filter 10 and the first connection P21 of the second bandpass filter 20 are connected to the other end of capacitor C40. The second terminal P12 of the first bandpass filter 10 is connected to the first signal connection 3connected. The second connection P22 of the second bandpass filter 20 is connected to the second signal port 4 tied together.

[0051] The low-pass filter 110 It selectively allows signals with frequencies within the lower band to pass through. The first bandpass filter 100 It selectively allows signals with frequencies within the middle band and signals with frequencies within the upper band to pass through. The second bandpass filter 20 It selectively allows signals with frequencies within the upper band to pass through. Now the path leading from the common terminal is... 102 via the low-pass filter 110 to the third signal connection 5 This path is referred to as the lower band path. The path leading from the common connection 102 via capacitor C40 and the first bandpass filter 10 to the first signal connection 3The path leading from the common junction is called the middle band path. 102 via capacitor C40 and the second bandpass filter 20 to the second signal connection 4 The path that leads to the lower band is called the upper band path. Signals with frequencies within the lower band are selectively passed through the lower band path. Signals with frequencies within the middle band are selectively passed through the middle band path. Signals with frequencies within the upper band are selectively passed through the upper band path. The connection point between the first bandpass filter 10 and the second bandpass filter 20 is referred to as terminal P2. In the second embodiment, terminal P2 corresponds to the common terminal of the present invention. Fig. Figure 11 is a characteristic diagram that provides an example of the properties of the branch filter. 101 illustrated. In Fig. In 11, the horizontal axis represents a frequency and the vertical axis represents damping. Fig. 11 shows the curve 60 The insertion loss characteristic of the path of the lower band is shown by the curve. 61 the insertion loss characteristic of the path of the middle band and shows the curve 62 the insertion loss characteristic of the upper band path. The in Fig. The 11 properties shown were determined by simulation. The remainder of the configuration, operation, and effects of the second embodiment is similar to those of the first embodiment. [Third embodiment]

[0052] A branch filter according to a third embodiment of the invention is now described. Fig. Figure 12 is a circuit diagram illustrating the configuration of the branch filter according to the third embodiment. The branch filter 201 According to the third embodiment, the device is designed to separate three signals with frequencies within three frequency bands, i.e., the lower band, the middle band, and the upper band, as in the second embodiment. The branching filter according to the third embodiment includes a first bandpass filter. 210 instead of the first bandpass filter 10 the second embodiment and a second bandpass filter 220 instead of the second bandpass filter 20 of the second embodiment. The low-pass filter 110 It selectively allows signals with frequencies within the lower band to pass through. The first bandpass filter 100It selectively allows signals with frequencies within the middle band and signals with frequencies within the upper band to pass through. The second bandpass filter 220 It selectively allows signals with frequencies within the upper band to pass through. Now the path leading from the common terminal is... 102 via the low-pass filter 110 to the third signal connection 5 This path is referred to as the lower band path. The path leading from the common connection 102 via capacitor C40 and the first bandpass filter 210 to the first signal connection 3 The path leading from the common junction is called the middle band path. 102 via capacitor C40 and the second bandpass filter 220 to the second signal connection 4The path that leads to the lower band is called the upper band path. Signals with frequencies within the lower band are selectively passed through the lower band path. Signals with frequencies within the middle band are selectively passed through the middle band path. Signals with frequencies within the upper band are selectively passed through the upper band path. The connection point between the first bandpass filter 210 and the second bandpass filter 220 is referred to as terminal P2. In the third embodiment, terminal P2 corresponds to the common terminal of the present invention. The first bandpass filter 210 includes a first resonant circuit section 212 instead of the first resonant circuit section 12 of the first bandpass filter 10 of the first embodiment. The first resonant circuit section 212It includes two first acoustic wave resonators, R11 and R12, connected in series. The acoustic wave resonators R11 and R12 are in the path leading from the first LC resonant circuit. 11 to the second terminal P12, i.e. the path leading from the first LC resonant circuit 11 to the first signal connection 3 leads, arranged and are from the side of the first LC resonant circuit 11 The acoustic wave resonators R11 and R12 are arranged in the order of R11 and R12. These resonators are formed using acoustic wave elements. The acoustic wave elements used to form the acoustic wave resonators R11 and R12 can be surface acoustic wave elements or volume acoustic wave elements. The first resonant circuit section 212It also includes an inductor L14. The inductor L14 is arranged between ground and the junction between the acoustic wave resonators R11 and R12. The second bandpass filter 220 includes a second resonant circuit section 222 instead of the second resonant circuit section 22 of the second bandpass filter 20 of the first embodiment. The second resonant circuit section 222 It includes two second acoustic wave resonators, R21 and R22, connected in series. The acoustic wave resonators R21 and R22 are in the path leading from the second LC resonant circuit. 21 to the second terminal P22, i.e. the path leading from the second LC resonant circuit 21 to the second signal connection 4 leads, arranged and are from the side of the second LC resonant circuit 21arranged in the order of R21 and R22. The acoustic wave resonators R21 and R22 are resonators formed using acoustic wave elements. The acoustic wave elements used to form the acoustic wave resonators R21 and R22 can be acoustic surface wave elements or acoustic volume wave elements. The second resonant circuit section 222 It also includes an inductor L24, which is connected in parallel with the acoustic wave resonator R21, and an inductor L25, which is connected in parallel with the acoustic wave resonator R22. The second bandpass filter 220 It also includes a capacitor C25. The capacitor C25 is located between ground and the junction between the acoustic wave resonators R21 and R22. Fig. Figure 13 is a characteristic diagram that provides an example of the properties of the branch filter. 201 illustrated. Fig. Figure 14 is a characteristic diagram showing an enlarged view of part of the Fig. Provides 13 of the properties shown. In Fig. 13 and Fig. In figure 14, the horizontal axis represents a frequency and the vertical axis represents damping. Fig. 13 shows the curve 70 The insertion loss characteristic of the path of the lower band is shown by the curve. 71 the insertion loss characteristic of the path of the middle band and shows the curve 72 the insertion loss characteristic of the upper band path. The in Fig. 13 and Fig. The 14 properties shown were determined by a simulation. The first resonant circuit section 212 exhibits a resonance frequency f 1r within the first passband PB1 and two antiresonance frequencies f 1a1 and f 1a2 , which are above the first upper band cutoff frequency f 1Hlie, on. The antiresonance frequency f 1a1 is the antiresonance frequency of the acoustic wave resonator R11. The antiresonance frequency f 1a2 is the antiresonance frequency of the acoustic wave resonator R12. As in Fig. Figure 14 shows the insertion loss characteristic. 71 of the path of the middle band two damping poles at the two antiresonance frequencies f 1a1 and f 1a2 The first section of the resonant circuit 212 preferably includes an element for changing the impedance between the acoustic wave resonators R11 and R12, such that the acoustic wave resonators R11 and R12 have mutually different anti-resonance frequencies. The in Fig. The inductor L14 shown in Figure 12 is preferably used as the element for changing the impedance. The second resonant circuit section 222 exhibits a resonance frequency f2r within the second passband PB2 and two antiresonance frequencies f 2a1and f 2a2 , which are lower than the second lower band cutoff frequency f2L. The antiresonance frequency f 2a1 is one of the antiresonance frequencies of a circuit consisting of the acoustic wave resonator R21 and the inductor L24. The antiresonance frequency f 2a2 is one of the anti-resonance frequencies of a circuit consisting of the acoustic wave resonator R22 and the inductor L25. As in Fig. Figure 14 shows the insertion loss characteristic. 72 of the upper band path two damping poles at the two antiresonance frequencies f 2a1 and f 2a2 The third embodiment allows the first bandpass filter to 210 provides an insertion loss characteristic that is present in a frequency region near the first upper band cutoff frequency f 1H The insertion loss characteristic of the first bandpass filter changes more abruptly than this. 10the second embodiment. The third embodiment also allows the second bandpass filter to 220 provides an insertion loss characteristic that changes more abruptly in a frequency region near the second lower band cutoff frequency f2L than the insertion loss characteristic of the second bandpass filter. 20the second embodiment. The remainder of the configuration, operation, and effects of the third embodiment are similar to those of the first or second embodiment. The present invention is not limited to the preceding embodiments, and various modifications can be made to it. For example, the features of the first and second bandpass filters in the present invention are not limited to those illustrated in the preceding embodiments and can be freely designed, provided the requirements of the appended claims are met. Obviously, many modifications and variations of the present invention are possible in light of the above teachings. Accordingly, it is understood that the invention, within the scope of protection of the appended claims and equivalents thereof, can be practiced in preferred embodiments other than those preceding them. QUOTES INCLUDED IN THE DESCRIPTION

[0053] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0054] JP 2010-141859 A

[0006] JP 2015-115866 A

[0007]

Claims

[1] A bandpass filter ( 10 , 20 ), which has a first terminal (P11, P21) and a second terminal (P12, P22) and is configured to selectively pass a signal of a frequency within a passband whose frequency is not less than a lower band cutoff frequency and not higher than an upper band cutoff frequency, characterized by that the bandpass filter ( 10 , 20 ) additionally an LC resonant circuit ( 11 , 21 ) and a resonant circuit section ( 12 , 22 ) includes, which are arranged in series between the first terminal (P11, P21) and the second terminal (P12, P22); the resonant circuit section ( 12 , 22 ) comprises at least one acoustic wave resonator (R1, R2) arranged in a path leading from the first terminal (P11, P21) to the second terminal (P21, P22); the resonant circuit section (12 , 22 ) has a resonant frequency and at least one anti-resonant frequency; The resonant frequency lies within the passband; and at least one anti-resonance frequency lies outside the passband. [2] Bandpass filter according to claim 1, wherein the at least one anti-resonance frequency is higher than the upper band cutoff frequency. [3] Bandpass filter according to claim 2, wherein the resonant circuit section ( 212 , 222 ) as comprising at least one acoustic wave resonator, two acoustic wave resonators (R11, R12, R21, R22) connected in series. [4] Bandpass filter according to claim 1, wherein the resonant circuit section ( 22 ) additionally includes at least one inductor (L2) connected in parallel to the at least one acoustic wave resonator (R2), and the resonant circuit section ( 22), than which has at least one anti-resonance frequency, an anti-resonance frequency that is lower than the lower band cutoff frequency, and an anti-resonance frequency that is higher than the upper band cutoff frequency. [5] Bandpass filter according to claim 4, wherein the resonant circuit section ( 222 ), as comprising at least one acoustic wave resonator, two acoustic wave resonators (R21, R22) connected in series, and comprising at least one inductor and two inductors (L24, L25) connected in parallel to the two acoustic wave resonators (R21, R22). [6] Bandpass filter according to any one of claims 1 to 5, wherein the LC resonant circuit ( 11 , 21 ) an LC parallel resonant circuit ( 11 , 21 ) is one that has a resonant frequency outside the passband. [7] Branch filter comprising: a common connection ( 2 ); a first signal connection ( 3 ); a second signal connection ( 4 ); a first filter ( 10 ), which is between the common connection ( 2 ) and the first signal connection ( 3 ) is arranged and designed to selectively pass a signal of a frequency within a first passband and a second filter ( 20 ), which is between the common connection ( 2 ) and the second signal connection ( 4 ) is arranged and designed to selectively pass a signal of a frequency within a second passband above the first passband, characterized by that the first filter ( 10 ) a first bandpass filter ( 10 ) is; the first passband is a frequency band that is neither below a first lower band cutoff frequency nor above an upper band cutoff frequency; the first bandpass filter ( 10 ) includes a first LC resonant circuit ( 11 ) and a first resonant circuit section ( 12 ), which are arranged in series in this order starting from the common connection side; the first resonant circuit section ( 12 ) comprises at least one acoustic wave resonator (R) located in a path extending from the first LC resonant circuit ( 11 ) to the first signal connection ( 3 ) leads, is arranged; and the first resonant circuit section ( 12 ) has a resonant frequency within the first passband and at least one antiresonant frequency that is higher than the first upper band cutoff frequency. [8] Branch filter according to claim 7, wherein the first resonant circuit section ( 212 ), as comprising at least one acoustic wave resonator, two acoustic wave resonators (R11, R12) connected in series. [9] Branch filter according to claim 7 or 8, wherein the first LC resonant circuit ( 11 ) a first LC parallel resonant circuit ( 11 ) is, which has a resonant frequency that is higher than the first upper band cutoff frequency. [10] Branch filter comprising: a common connection ( 2 ); a first signal connection ( 3 ); a second signal connection ( 4 ); a first filter ( 10 ), which is between the common connection ( 2 ) and the first signal connection ( 3 ) is arranged and configured to selectively pass a signal of a frequency within a first passband; and a second filter ( 20 ), which is between the common connection ( 2 ) and the second signal connection ( 4) is arranged and designed to selectively pass a signal of a frequency within a second passband above the first passband, characterized by that the second filter ( 20 ) a second bandpass filter ( 20 ) is; the second passband is a frequency band that is neither below a second lower band cutoff frequency nor above a second upper band cutoff frequency; the second bandpass filter ( 20 ) includes a second LC resonant circuit ( 21 ) and a second resonant circuit section ( 22 ) between the common connection ( 2 ) and the second signal connection ( 4 ), where the second LC resonant circuit ( 21 ) and the second resonant circuit section ( 22 ) are arranged in series in this order starting from the common connection side; the second resonant circuit section ( 22) comprises at least one acoustic wave resonator (R) arranged in a path extending from the second LC resonant circuit ( 21 ) to the second signal connection ( 4 ) leads to, and at least one inductor (L2) arranged in parallel to the at least one acoustic wave resonator (R2), and the second resonant circuit section ( 22 ) has a resonant frequency within the second passband, an anti-resonant frequency that is lower than the second lower band cutoff frequency, and an anti-resonant frequency that is higher than the second upper band cutoff frequency. [11] Branch filter according to claim 10, wherein the second resonant circuit section ( 222), comprising at least one acoustic wave resonator, two acoustic wave resonators (R21, R22) connected in series, and, comprising at least one inductor, two inductors (L24, L25) connected in parallel (R21, R22) to the two acoustic wave resonators. [12] Branch filter according to claim 10 or 11, wherein the second LC resonant circuit ( 21 ) a second LC parallel resonant circuit ( 21 ) is, which has a resonant frequency that is lower than the second lower band cutoff frequency. [13] Branch filter comprising: a common connection ( 2 ); a first signal connection ( 3 ); a second signal connection ( 4 ); a first filter ( 10 ), which is between the common connection ( 2 ) and the first signal connection ( 3) is arranged and configured to selectively pass a signal of a frequency within a first passband; and a second filter ( 20 ), which is between the common connection ( 2 ) and the second signal connection ( 4 ) is arranged and designed to selectively pass a signal of a frequency within a second passband above the first passband, characterized by that the first filter ( 10 ) a first bandpass filter ( 10 ) is; the first passband is a frequency band that is neither below a first lower band cutoff frequency nor above an upper band cutoff frequency; the first bandpass filter ( 10 ) a first LC resonant circuit ( 11 ) and a first resonant circuit section ( 12 ) comprises, where the first LC resonant circuit ( 11 ) and the first resonant circuit section ( 12) are arranged in series in this order starting from the common connection side; the first resonant circuit section ( 12 ) at least one acoustic wave resonator (R) arranged in a path extending from the first LC resonant circuit ( 11 ) to the first signal connection ( 3 ) leads; and the first resonant circuit section ( 12 ) has a resonance frequency within the first passband and at least one anti-resonance frequency that is higher than the first upper band cutoff frequency. the second filter ( 20 ) a second bandpass filter ( 20 ) is; the second passband is a frequency band that is neither below a second lower band cutoff frequency nor above a second upper band cutoff frequency; the second bandpass filter ( 20 ) includes a second LC resonant circuit ( 21 ) and a second resonant circuit section ( 22 ), where the first LC resonant circuit ( 21 ) and the second resonant circuit section ( 22 ) are arranged in series in this order starting from the common connection side; the second resonant circuit section ( 22 ) at least a second acoustic wave resonator (R) arranged in a path extending from the second LC resonant circuit ( 21 ) to the second signal connection ( 4 ) leads, and includes at least one inductor (L2) arranged in parallel to at least one second acoustic wave resonator (R2), and the second resonant circuit section ( 22 ) a resonance frequency within the second passband, an anti-resonance frequency that is lower than the second lower band cutoff frequency, and an anti-resonance frequency that is higher than the second upper band cutoff frequency. [14] Branch filter according to claim 13, wherein the first resonant circuit section ( 212 ), than at least one first acoustic wave resonator, two first acoustic wave resonators (R11, R12) connected in series, and the second resonant circuit section ( 222 ), as comprising at least one second acoustic wave resonator, two second acoustic wave resonators (R21, R22) connected in series, and, as comprising at least one inductor, two inductors (L24, L25) connected in parallel (R21, R22) to the two second acoustic wave resonators. [15] Branch filter according to claim 13 or 14, wherein the first LC resonant circuit ( 11 ) a first LC parallel resonant circuit ( 11 ) is, which has a resonant frequency that is higher than the first upper band cutoff frequency, and the second LC resonant circuit ( 21 ) a second LC parallel resonant circuit ( 21) is, which has a resonant frequency that is lower than the second lower band cutoff frequency.

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