Patent ID: 12199589

DETAILED DESCRIPTION

Hereinafter, embodiments of the present disclosure and variations thereof will be described in detail with reference to the accompanying drawings. It should be noted that the following embodiments and modifications thereof are given by way of comprehensive or specific example only. The numerical values, shapes, materials, constituent elements, arrangement and connection forms of the constituent elements, and the like described in the following embodiments and modifications thereof are merely examples, and are not intended to limit the present disclosure. Among the constituent elements in the following embodiments and modifications thereof, constituent elements that are not described in the independent claims are described as arbitrary constituent elements.

In the present disclosure, “directly connected” means directly connected via a connection terminal and/or a wiring conductor without necessarily using other circuit elements. Meanwhile, the term “connected” includes not only a case of being directly connected via the connection terminal and/or the wiring conductor but also a case of being electrically connected using other circuit elements.

In the present disclosure, the phrase “constituted of a circuit element” includes not only a case where only the circuit element is included, but also a case where another circuit element is included in addition to the circuit element. That is, “constituted of a circuit element” does not exclude the inclusion of another circuit element.

First Embodiment

First, a description will be given of a first embodiment.

1.1 Transmission Characteristic of Filter Device10

FIG.1is a graph illustrating a transmission characteristic of a filter device10according to a first embodiment. InFIG.1, the horizontal axis represents a frequency, and the vertical axis represents an insertion loss. An insertion loss101indicates a frequency characteristic of the insertion loss in the filter device10according to the present embodiment. As illustrated inFIG.1, the filter device10has a pass band PB1, a stop band SB1, and a pass band PB2.

The pass band PB1is an example of a second pass band, and is located on a lower frequency side than the stop band SB1. The stop band SB1is an example of a first stop band, and is located between the pass band PB1and the pass band PB2. The pass band PB2is an example of a first pass band, and is located on a higher frequency side than the stop band SB1.

In the present embodiment, as an example, the filter device10having a stop band corresponding to a WiFi® 2.4 GHz band within the pass band corresponding to a middle high band (MHB) will be described. In this case, the pass band PB1corresponds to a communication band of equal to or higher than 1710 MHz and equal to or lower than 2370 MHz, the stop band SB1corresponds to a communication band of equal to or higher than 2402 MHz and equal to or lower than 2481.5 MHz, and the pass band PB2corresponds to a communication band of equal to or higher than 2510 MHz and equal to or lower than 2690 MHz.

The frequency and the insertion loss in marks m499, m500, m502, and m501shown inFIG.1are as follows.m499(2.200 GHz, 0.932 dB)m500(2.370 GHz, 1.769 dB)m502(2.510 GHz, 0.878 dB)m501(2.690 GHz, 1.044 dB)
1.2 Circuit Configuration of Filter Device10

Next, a circuit configuration of the filter device10according to the present embodiment having such a transmission characteristic will be described in detail with reference toFIG.2.

FIG.2is a circuit configuration diagram of the filter device10according to the first embodiment. As illustrated inFIG.2, the filter device10includes input/output terminals T1and T2, matching circuits11and16, resonance circuits12,14, and15, and a filter13.

The input/output terminal T1is an example of a first input/output terminal, and the input/output terminal T2is an example of a second input/output terminal. When the input/output terminal T1serves as an input terminal to which a high-frequency signal is input, the input/output terminal T2serves as an output terminal, and when the input/output terminal T2serves as the input terminal to which a high-frequency signal is input, the input/output terminal T1serves as the output terminal.

The matching circuit11is composed of an inductor L1. The matching circuit11performs impedance matching between circuit elements outside the filter device10and circuit elements in the filter device10, which are connected to each other via the input/output terminal T1. Note that the matching circuit11does not necessarily have to be constituted of a series inductor. For example, the matching circuit11may be constituted of a series inductor, a parallel inductor, a capacitor, or any combination thereof.

The inductor L1is directly connected to the input/output terminal T1. The inductor L1may be a substantially chip-shaped inductor mounted on a substrate, or may be an inductor constituted of a planar coil pattern formed in the substrate.

The resonance circuit12is an example of a third resonance circuit, and is constituted of a parallel arm resonator P1. The resonance characteristic of the resonance circuit12will be described later with reference toFIG.5A.

The parallel arm resonator P1is an example of a second parallel arm resonator, and is connected between a node N1on a path connecting the input/output terminals T1and T2, and the ground. The node N1is an example of a second node, and is disposed on a path connecting the inductor L1and the filter13.

The filter13is disposed on a path connecting the node N1and a node N2. The filter13is a high pass filter having pass bands including the pass bands PB1and PB2. The filter13may be any of a SAW filter, an acoustic wave filter using BAW, an FBAR filter, an LC filter, and a dielectric filter, and is not limited thereto.

The resonance circuit14is an example of a first resonance circuit, and is constituted of a parallel arm resonator P2. The resonance characteristic of the resonance circuit14will be described later with reference toFIG.5A.

The parallel arm resonator P2is an example of a first parallel arm resonator, and is connected between the node N2on a path connecting the filter13and a series arm resonator S1, and the ground. The node N2is an example of a first node.

The resonance circuit15is an example of a second resonance circuit, and is constituted of the series arm resonator S1and an inductor L2. The resonance characteristic of the resonance circuit15will be described later with reference toFIG.5A.

The series arm resonator S1is connected in series to the filter13. Further, the series arm resonator S1is directly connected to the inductor L2in series.

The inductor L2is an example of a first inductor, and is directly connected to the series arm resonator S1in series. The inductor L2is directly connected to the input/output terminal T2. The inductor L2may be a substantially chip-shaped inductor mounted on the substrate, or may be an inductor constituted of a planar coil pattern formed in the substrate.

The matching circuit16is constituted of the inductor L2. That is, the inductor L2is shared by the resonance circuit15and the matching circuit16. The matching circuit16performs impedance matching between the circuit elements outside the filter device10and the circuit elements in the filter device10, which are connected to each other via the input/output terminal T2.

Note that in one embodiment, the matching circuit11and the resonance circuit12are not necessarily essential components for the filter device according to the present disclosure. That is, in one embodiment, the inductor L1and the parallel arm resonator P1are not necessarily essential components for the filter device according to the present disclosure.

As the parallel arm resonators P1and P2, and the series arm resonator S1, an acoustic wave resonator can be used. More specifically, as the parallel arm resonators P1and P2and the series arm resonator S1, for example, a surface acoustic wave (SAW) resonator, a bulk acoustic wave (BAW) resonator, a film bulk acoustic resonator (FBAR), or the like can be used.

1.3 Transmission Characteristic of Filter Device10X

Here, a comparative example for explaining various characteristics of the filter device10according to the present embodiment will be described. First, a transmission characteristic of a filter device10X according to the comparative example will be described with reference toFIG.3.

FIG.3is a graph illustrating the transmission characteristic of the filter device10X according to the comparative example. InFIG.3, the horizontal axis represents the frequency, and the vertical axis represents the insertion loss. An insertion loss102indicates the frequency characteristic of the insertion loss in the filter device10X according to the comparative example. As illustrated inFIG.3, the filter device10X according to the comparative example has the pass band PB1, the stop band SB1, and the pass band PB2in ascending order of frequency, similarly to the filter device10according to the first embodiment.

The frequency and the insertion loss in marks m499, m500, m502, and m501illustrated inFIG.3are as follows.m499(2.200 GHz, 0.569 dB)m500(2.370 GHz, 2.102 dB)m502(2.510 GHz, 1.552 dB)m501(2.690 GHz, 0.560 dB)
1.4 Circuit Configuration of Filter Device10X

Next, a circuit configuration of the filter device10X according to the comparative example having such a transmission characteristic will be described mainly with reference toFIG.4, focusing on a difference from the filter device10according to the first embodiment.

FIG.4is a circuit configuration diagram of the filter device10X according to the comparative example. As illustrated inFIG.4, the filter device10X includes the input/output terminals T1and T2, the matching circuit11and a matching circuit16X, the resonance circuits12and14, and a resonance circuit15X, and the filter13.

The resonance circuit15X is constituted of a series arm resonator SIX. The series arm resonator SIX is arranged on a path connecting the node N1and the node N2, and is connected in series to the matching circuit11and the filter13.

The matching circuit16X is constituted of an inductor L2X which is directly connected to the input/output terminal T2. Here, the inductor L2X is not shared with the resonance circuit15X. The matching circuit16X performs impedance matching between the circuit elements outside the filter device10X and the circuit elements in the filter device10X, which are connected via the input/output terminal T2.

1.5 Comparison of Filter Device10with Filter Device10X

Next, various characteristics of the filter device10will be described while comparing the filter device10according to the first embodiment with the filter device10X according to the comparative example.

1.5.1 Resonance Characteristic and Transmission Characteristic

First, a resonance characteristic and the transmission characteristic will be described with reference toFIG.5AandFIG.5B.

FIG.5Ais a graph illustrating a resonance characteristic and the transmission characteristic of the filter device10according to the first embodiment.FIG.5Bis a graph illustrating a resonance characteristic and the transmission characteristic of the filter device10X according to the comparative example. InFIG.5AandFIG.5B, the horizontal axis represents the frequency. The left vertical axis represents an impedance corresponding to a resonance waveform. The right vertical axis represents the insertion loss.

InFIG.5A, resonance waveforms121,141, and151show resonance characteristics of the resonance circuits12,14, and15included in the filter device10according to the first embodiment, respectively. Similarly toFIG.1, the insertion loss101indicates the frequency characteristic of the insertion loss of the filter device10.

The resonance waveform121of the resonance circuit12has a resonance point121R and an anti-resonance point121A in the ascending order of the frequency. The resonance waveform141of the resonance circuit14has a resonance point141R and an anti-resonance point141A in the ascending order of the frequency. The resonance waveform151of the resonance circuit15has a resonance point (not illustrated for the lower frequency side than the frequency range of the graph), an anti-resonance point151A, and a sub-resonance point151S in the ascending order of the frequency.

The stop band SB1is formed along an attenuation pole corresponding to the resonance point121R, the anti-resonance point151A, and the resonance point141R. Here, among frequencies of the resonance point121R, the anti-resonance point151A, and the resonance point141R, the frequency of the resonance point121R is the lowest, and the frequency of the resonance point141R is the highest. That is, the resonance point121R forms an attenuation pole corresponding to the low frequency end of the stop band SB1, and the resonance point141R forms an attenuation pole corresponding to the high frequency end of the stop band SB1.

The frequency of the sub-resonance point151S (i.e., the sub-resonant frequency of the resonance circuit15) is higher than the frequency of the resonance point121R (i.e., the resonant frequency of the resonance circuit12), and is higher than the frequency of the resonance point141R (i.e., the resonant frequency of the resonance circuit14). Such a sub-resonant frequency makes it possible to improve the steepness of the attenuation characteristic at the high frequency end of the stop band SB1.

It should be noted that the frequency of the sub-resonance point151S can be within a range from 100% to 110% of the frequency of the resonance point141R, and can be within a range from 100% to 105% of the frequency of the resonance point141R. It was confirmed by an experiment that the steepness of the attenuation characteristic is remarkably improved at the high frequency end of the stop band SB1by such a sub-resonant frequency.

Also, the frequency of the sub-resonance point151S may be higher than the upper limit frequency (e.g., 2481.5 MHz) of the communication band (for example, WiFi® 2.4 GHz band) corresponding to the stop band SB1. For example, the frequency of the sub-resonance point151S may be included in the range of 100% to 110% (for example, 2481.5 MHz to 2729.7 MHz) of the upper limit frequency of the communication band corresponding to the stop band SB1, and in particular, may be included in the range of 100% to 105% (for example, 2481.5 MHz to 2605.6 MHz). It was confirmed by experiment that, even at such a sub-resonant frequency, the steepness of the attenuation characteristic at the high frequency end of the stop band SB1was remarkably improved.

InFIG.5B, resonant waveforms122,142, and152show resonance characteristics of the resonance circuits12,14, and15X included in the filter device10X according to the comparative example, respectively. Similarly toFIG.3, the insertion loss102indicates the frequency characteristic of the insertion loss of the filter device10X.

The resonance waveform122of the resonance circuit12has a resonance point122R and an anti-resonance point122A in the ascending order of the frequency. The resonance waveform142of the resonance circuit14has a resonance point142R and an anti-resonance point142A in the ascending order of the frequency. The resonance waveform152of the resonance circuit15X has a resonance point152R and an anti-resonance point152A in the ascending order of the frequency.

The stop band SB1is formed along the attenuation pole corresponding to the resonance point122R, the anti-resonance point152A, and the resonance point142R. In the filter device10X, the sub-resonance point of the resonance waveform152is not present at least in the frequency range of the graph.

In this manner, in the resonance waveforms151and152, there is a large difference in the presence or absence of the sub-resonance point. Due to the difference in the sub-resonance point, there is a difference in the transmission characteristic between the filter device10and the filter device10X at the low frequency end of the pass band PB2. Specifically, in the filter device10, the insertion loss at the low frequency end (m502) of the pass band PB2is 0.878 dB (refer toFIG.1), but in the filter device10X, the insertion loss at the low frequency end (m502) of the pass band PB2is 1.552 dB (refer toFIG.3). That is, in the filter device10, the insertion loss decreases at the low frequency end of the pass band PB2compared with the filter device10X.

1.5.2 Reflection Characteristic

Next, the reflection characteristic will be described with reference toFIG.6AandFIG.6B.

FIG.6Ais a graph illustrating a reflection characteristic of the filter device10according to the first embodiment.FIG.6Bis a graph illustrating a reflection characteristic of the filter device10X according to the comparative example. Return losses103and104inFIGS.6A and6Bshow the frequency characteristics of the return loss at the input/output terminal T1. InFIG.6AandFIG.6B, the horizontal axis represents the frequency, and the vertical axis represents the return loss.

Note that the frequency and the return loss in marks m507, m508, m510and m509inFIG.6Aare as follows.m507(2.200 GHz, 11.816 dB)m508(2.370 GHz, 7.621 dB)m510(2.510 GHz, 14.718 dB)m509(2.690 GHz, 9.786 dB)

On the other hand, the frequency and the return loss in marks m507, m508, m510and m509inFIG.6Bare as follows.m507(2.200 GHz, 17.579 dB)m508(2.370 GHz, 5.752 dB)m510(2.510 GHz, 7.695 dB)m509(2.690 GHz, 16.143 dB)

Referring toFIG.6AandFIG.6B, in the vicinity of the low frequency end of the pass band PB2under a large influence of the sub-resonance point151S (part A near 2.51 GHz), the return loss103of the filter device10is larger than the return loss104of the filter device10X. From this, it can be seen that in the filter device10, the return loss increases at the lower frequency end of the pass band PB2(reflection signal is reduced) as compared with the filter device10X, and the insertion loss is improved.

In addition, in the vicinity of the low frequency end of the pass band PB2, the return loss103inFIG.6Ais more steeply increased than the return loss104inFIG.6B. From this, it can be seen that, in the filter device10, a steeper attenuation characteristic than that of the filter device10X is realized at the low frequency end of the pass band PB2.

1.6 Effects

As described above, according to the filter device10of the present embodiment, the resonance circuit15including the series arm resonator S1and the inductor L2can have a sub-resonant frequency that is higher than the resonant frequency of the resonance circuit14constituted of the parallel arm resonator P2. Therefore, the filter device10can reduce the insertion loss of the pass band PB2located on the higher frequency side than the stop band SB1by the sub-resonance point151S of the resonance circuit15. As a result, the filter device10can realize a steeper attenuation characteristic than the filter device10X according to the comparative example at the low frequency end of the pass band PB2, that is, at the high frequency end of the stop band SB1.

Further, according to the filter device10of the present embodiment, the sub-resonant frequency of the resonance circuit15can be included in the range of 100% to 110% or 100% to 105% of the resonant frequency of the resonance circuit14. Thus, it is possible to prevent the sub-resonance point151S of the resonance circuit15from being excessively distant from the high frequency end of the stop band SB1and the low frequency end of the pass band PB2. As a result, a steeper attenuation characteristic can be realized at the high frequency end of the stop band SB1, and the insertion loss at the low frequency end of the pass band PB2can be effectively reduced.

In addition, according to the filter device10of the present embodiment, the inductor L2directly connected to the input/output terminal T2can be directly connected to the series arm resonator S1. Therefore, the inductor L2can be shared by the resonance circuit15and the matching circuit16, and the number of circuit elements can be reduced.

First Modification of First Embodiment

Next, a first modification of the first embodiment will be described. In this modification, a case where a filter included in the filter device is a high pass filter constituted of an acoustic wave resonator will be described.

FIG.7is a circuit configuration diagram of a filter device10A according to the first modification of the first embodiment. As illustrated inFIG.7, the filter device10A includes the input/output terminals T1and T2, the matching circuits11and16, the resonance circuits12,14and15, and a filter13A.

The filter13A is constituted of an acoustic wave resonator and is disposed on a path connecting the node N1and the node N2. The filter13A is a high pass filter having pass bands including the pass bands PB1and PB2. That is, the filter13A is a high pass filter having a cutoff frequency equal to or lower than the lower limit frequency (for example, 1710 MHz) of the pass band PB1.

Specifically, the filter13A includes series arm resonators S11and S12, and an inductor L11. The series arm resonators S11and S12are arranged on a path connecting the node N1and the node N2, and are connected in series to the inductor L1and the series arm resonator S1. Inductor L11is connected between the node N11on a path connecting the series arm resonator S11and the series arm resonator S12, and the ground.

As the series arm resonators S11and S12, similar to the parallel arm resonators P1and P2and the series arm resonators S1, the acoustic wave resonators can be used. For example, as the series arm resonators S11and S12, a SAW resonator, a BAW resonator, a FBAR, or the like can be used.

As described above, according to the filter device10A of this modification, a filter constituted of the acoustic wave resonator can be used as the filter13A. Therefore, a steep attenuation characteristic can be realized even at the low frequency end of the pass band PB1.

Second Modification of First Embodiment

Next, a second modification of the first embodiment will be described. In this modification, a case where the filter included in the filter device is an LC high pass filter will be described.

FIG.8is a circuit configuration diagram of a filter device10B according to a second modification of the first embodiment. As illustrated inFIG.8, the filter device10B includes the input/output terminals T1and T2, the matching circuits11and16, the resonance circuits12,14, and15, and a filter13B.

The filter13B is an LC filter disposed on a path connecting the node N1and the node N2. The filter13B is a high pass filter having pass bands including the pass bands PB1and PB2. That is, the filter13B is a high pass filter having a cutoff frequency equal to or lower than the lower limit frequency (for example, 1710 MHz) of the pass band PB1.

Specifically, the filter13B includes a capacitor C11and an inductor L12. The capacitor C11is disposed on a path connecting the node N1and the node N2, and is connected in series to the inductor L1and the series arm resonator S1. The inductor L12is connected between the node N12on a path connecting the capacitor C11and the series arm resonator S1, and the ground.

As described above, according to the filter device10B of this modification, an LC filter can be used as the filter13B. Therefore, the filter13B can easily realize a broadband pass band including the pass band PB1and the pass band PB2.

Second Embodiment

Next, a description will be given of a second embodiment. the present embodiment differs from the first embodiment in that the inductor is connected in parallel to the parallel arm resonator P1in order to improve the transmission characteristic in a high frequency region of the pass band PB2. Hereinafter, the present embodiment will be described in detail with reference to the drawings, focusing on differences from the first embodiment described above.

2.1 Circuit Configuration of Filter Device10C

First, a circuit configuration of a filter device10C according to the present embodiment will be described with reference toFIG.9.

FIG.9is a circuit configuration diagram of the filter device10C according to the second embodiment. As illustrated inFIG.9, the filter device10C includes the input/output terminals T1and T2, the matching circuits11and16, a resonance circuit12C and the resonance circuits14and15, and the filter13.

The resonance circuit12C is an example of a third resonance circuit, and is constituted of the parallel arm resonator P1and an inductor L3. The resonance characteristic of the resonance circuit12C will be described later with reference toFIG.11.

The inductor L3is an example of a second inductor, and is connected in parallel to the parallel arm resonator P1. Specifically, the inductor L3is connected between a node N3on a path connecting the inductor L1and the node N1, and the ground.

2.2 Transmission Characteristic of Filter Device10C

Next, a transmission characteristic of the filter device10C according to the present embodiment will be described with reference toFIG.10.

FIG.10is a graph illustrating the transmission characteristic of the filter device10C according to the second embodiment. InFIG.10, the horizontal axis represents the frequency, and the vertical axis represents the insertion loss. An insertion loss101C indicates the frequency characteristic of the insertion loss in the filter device10C. As illustrated inFIG.10, the filter device10C has the pass band PB1, the stop band SB1, and the pass band PB2in ascending order of frequency, similarly to the filter device10according to the first embodiment.

The frequency and the insertion loss in marks m499, m500, m502and m501illustrated inFIG.10are as follows.m499(2.200 GHz, 0.730 dB)m500(2.370 GHz, 1.715 dB)m502(2.510 GHz, 0.705 dB)m501(2.690 GHz, 0.813 dB)

ComparingFIG.10andFIG.1, it can be seen that in the filter device10C according to the present embodiment, the insertion loss is decreased in the pass band PB2(m502, m501).

2.3 Resonance Characteristic of Filter Device10C

Next, the resonance characteristic of the filter device10C according to the present embodiment will be described with reference toFIG.11.

FIG.11is a graph illustrating a resonance characteristic and a transmission characteristic of the filter device10C according to the second embodiment. InFIG.11, the horizontal axis represents the frequency. The left vertical axis represents an impedance corresponding to a resonance waveform. The right vertical axis represents an insertion loss.

A resonance waveform121C and the resonance waveforms141and151respectively show resonance characteristics of the resonance circuits12C,14, and15included in the filter device10C according to the present embodiment. Similarly toFIG.10, the insertion loss101C indicates the frequency characteristic of the insertion loss of the filter device10C.

The resonance waveform121C of the resonance circuit12C has a resonance point121CR and an anti-resonance point121CA in the ascending order of the frequency.

InFIG.11, the anti-resonance point121CA is moved to the higher frequency side than the anti-resonance point121A inFIG.5A. As a result, the frequency of the anti-resonance point121CA (i.e., the anti-resonant frequency of the resonance circuit12C) is higher than the frequency of the resonance point141R (i.e., the resonant frequency of the resonance circuit14), and is included in the pass band PB2.

2.4 Reflection Characteristic of Filter Device10C

Next, a reflection characteristic of the filter device10C according to the present embodiment will be described with reference toFIG.12.

FIG.12is a graph illustrating a reflection characteristic of the filter device10C according to the second embodiment. InFIG.12, a return loss103C indicates a frequency characteristic of a return loss at the input/output terminal T1. InFIG.12, the horizontal axis represents the frequency, and the vertical axis represents the return loss.

The frequency and the return loss in the marks m507, m508, m510and m509shown inFIG.12are as follows.m507(2.200 GHz, 16.477 dB)m508(2.370 GHz, 7.912 dB)m510(2.510 GHz, 30.853 dB)m509(2.690 GHz, 11.887 dB)

ComparingFIG.12andFIG.6A, the return loss103C inFIG.12is larger than the return loss103inFIG.6Ain the high frequency region (part B) of the pass band PB2where the influence of the anti-resonance point121CA is large. That is, since the anti-resonance point121CA has moved into the pass band PB2, it can be seen that in the filter device10C according to the present embodiment, the return loss is increased (reflection signal is reduced) in the high frequency region of the pass band PB2, and the insertion loss is reduced in comparison with the filter device10according to the first embodiment.

2.5 Effects

As described above, according to the filter device10C of the present embodiment, the inductor L3connected in parallel to the parallel arm resonator P1can be provided. Thus, the anti-resonant frequency of the resonance circuit12C constituted of the parallel arm resonator P1and the inductor L3can be made higher than the resonant frequency of the resonance circuit14, and can be moved into the pass band PB2. As a result, the insertion loss in the pass band PB2can be decreased.

Third Embodiment

Next, a description will be given of a third embodiment. In the present embodiment, a description will be given of a multiplexer and a communication device using a filter device in which the filter device10A according to the first modification of the first embodiment and the filter device10C according to the second embodiment are combined with each other.

3.1 Circuit Configuration of Filter Device10D

First, a circuit configuration of a filter device10D according to the present embodiment will be described with reference toFIG.13.

FIG.13is a circuit configuration diagram of the filter device10D according to the third embodiment. As illustrated inFIG.13, the filter device10D includes the input/output terminals T1and T2, the matching circuits11and16, the resonance circuits12C,14, and15, and the filter13A.

3.2 Transmission Characteristic of Filter Device10D

Next, a transmission characteristic of the filter device10D according to the present embodiment will be described with reference toFIG.14.

FIG.14is a graph illustrating the transmission characteristic of the filter device10D according to the third embodiment. InFIG.14, the horizontal axis represents the frequency, and the left vertical axis and the right vertical axis represent the insertion loss. An insertion loss101D indicates the frequency characteristic of the insertion loss in the filter device10D, and corresponds to the left vertical axis. An insertion loss101Dx is an enlarged view in the vicinity of 0 dB of the insertion loss101D, and corresponds to the right vertical axis.

As illustrated inFIG.14, the filter device10D has a stop band SB2, a stop band SB3, the pass band PB1, the stop band SB1, and the pass band PB2in the ascending order of the frequency. The stop band SB2corresponds to a communication band of equal to or higher than 1428 MHz and equal to or lower than 1511 MHz, and is mainly formed by the series arm resonator S11. The stop band SB3corresponds to a communication band of equal to or higher than 1559 MHz and equal to or lower than 1608 MHz, and is mainly formed by the series arm resonator S12.

The frequency and the insertion loss in marks m559, m560, m561and m562illustrated inFIG.14are as follows.m559(1.710 GHz, 1.130 dB)m560(2.370 GHz, 1.001 dB)m561(2.510 GHz, 0.965 dB)m562(2.690 GHz, 0.587 dB)
3.3 Circuit Configuration of Multiplexer1and Communication Device5

Next, the circuit configuration of a multiplexer1and a communication device5including the filter device10D configured as described above will be described.FIG.15is a circuit configuration diagram of the communication device5including the multiplexer1according to the third embodiment.

As illustrated inFIG.15, the communication device5includes the multiplexer1, an antenna element2, an RF signal processing circuit (RFIC)3, a baseband signal processing circuit (BBIC)4, and reception low noise amplifiers40to44.

The RFIC3is an RF signal processing circuit for processing a high-frequency signal transmitted and received by the antenna element2. Specifically, the RFIC3performs signal processing on a high-frequency reception signal input via a reception path of the multiplexer1by down-converting or the like, and outputs the reception signal generated by the signal processing to the BBIC4.

The BBIC4is a circuit that performs signal processing by using an intermediate frequency band having a lower frequency than that of the high-frequency signal propagating through the multiplexer1. The signal processed in the BBIC4is used, for example, as an image signal for image display, or as a voice signal for communication via a speaker.

The antenna element2is connected to a common terminal20of the multiplexer1, receives a high-frequency signal from the outside, and outputs the high-frequency signal to the multiplexer1.

Each of the reception low noise amplifiers40to44amplifies the high-frequency signal input from output terminals30to34of the multiplexer1with low noise. Each of the reception low noise amplifiers40to44is, for example, a low noise amplifier. The high-frequency signal amplified by the reception low noise amplifiers40to44is output to the RFIC3.

In one embodiment, the antenna element2and the BBIC4are not necessarily essential components for the communication device according to the present disclosure.

Next, the circuit configuration of the multiplexer1will be described.

As illustrated inFIG.15, the multiplexer1includes the common terminal20, the filter device10D and filter devices21to24each connected to the common terminal20, and the output terminals30to34.

The common terminal20is connected to the antenna element2. The filter device10D is disposed on a path connecting the common terminal20and the output terminal30, and passes a high-frequency signal of the MHB (equal to or higher than 1710 MHz and equal to or lower than 2370 MHz and equal to or higher than 2510 MHz and equal to or lower than 2690 MHz) out of the high-frequency signals input from the common terminal20. A BAW resonator, for example, is used as the resonator of the filter device10D.

The filter device21is disposed on a path connecting the common terminal20and the output terminal31, and passes a high-frequency signal of the WiFi® 2.4 GHz band (equal to or higher than 2402 MHz and equal to or lower than 2481.5 MHz) out of the high-frequency signals input from the common terminal20. That is, the filter device21is a band pass filter having a pass band corresponding to the WiFi® 2.4 GHz band. For example, an acoustic wave filter using a BAW resonator is used as the filter device21.

The filter device22is disposed on a path connecting the common terminal20and the output terminal32, and passes a high-frequency signal of a global positioning system (GPS) band (equal to or higher than 1559 MHz and equal to or lower than 1608 MHz) out of the high-frequency signals input from the common terminal20. That is, the filter device22is a band pass filter having a pass band corresponding to the GPS band. For example, an acoustic wave filter using a BAW resonator is used as the filter device22.

The filter device23is disposed on a path connecting the common terminal20and the output terminal33, and passes a high-frequency signal of a middle low band (MLB) (equal to or higher than 1428 MHz and equal to or lower than 1511 MHz) out of the high-frequency signals input from the common terminal20. That is, the filter device23is a band pass filter having a pass band corresponding to the MLB. An FBAR filter, for example, is used as the filter device23.

The filter device24is disposed on a path connecting the common terminal20and the output terminal34, and passes a high-frequency signal of a low band (LB) (equal to or higher than 690 MHz and equal to or lower than 960 MHz) out of the high-frequency signals input from the common terminal20. That is, the filter device24is a low pass filter having a pass band corresponding to the LB. For example, an LC filter is used as the filter device24.

Note that the filter devices21to24may be any one of a SAW filter, an acoustic wave filter using a BAW, an FBAR filter, an LC filter, and a dielectric filter, and is not limited thereto.

3.4 Transmission Characteristic of Multiplexer1

Next, a transmission characteristic of the multiplexer1configured as described above will be described.FIG.16is a graph illustrating the transmission characteristic of the multiplexer1according to the third embodiment. InFIG.16, the horizontal axis represents the frequency, and the vertical axis represents the insertion loss.

FromFIG.16, it can be seen that the multiplexer1forms pass bands corresponding to a plurality of communication bands (LB, MLB, GPS, MHB, and WiFi® 2.4 GHz).

3.5 Effects

As described above, according to the multiplexer1of the present embodiment, by using the filter device10D having the stop band corresponding to the WiFi® 2.4 GHz band within the pass band corresponding to the MHB, the high-frequency signals of a plurality of communication bands including the MHB and WiFi® 2.4 GHz bands can be divided into the respective communication bands.

Other Embodiments

Although the filter device and the multiplexer according to the embodiment of the present disclosure have been described with reference to the embodiments and modifications thereof, the filter device and the multiplexer according to the present disclosure are not limited to the above embodiments and modifications thereof. Further another embodiment realized by combining arbitrary constituent elements in the above embodiments and modifications thereof, modifications obtained by carrying out various variations that will occur to those skilled in the art without necessarily departing from the gist of the present disclosure with respect to the above embodiments and modifications thereof, and various apparatuses including the filter device and the multiplexer are also included in the present disclosure.

For example, in the filter device, the multiplexer and the communication device according to the embodiments and the modifications thereof, another circuit element and another wiring may be inserted between the circuit elements disclosed in the drawings and the paths connecting the signal paths. For example, the multiplexer1according to the third embodiment may be provided with one or more switches for switching between the conduction and non-conduction between the common terminal20and each filter device on a path connecting the common terminal20and the filter devices10D and21to24.

In the above embodiments and modifications thereof, the inductor L2directly connected to the series arm resonator S1in series is directly connected to the input/output terminal T2and shared by the resonance circuit15and the matching circuit16, but the present disclosure is not limited to this configuration. For example, the filter device may include an inductor directly connected to the series arm resonator S1in series, separately from the inductor L2constituting the matching circuit16. Such a filter device10E will be described with reference toFIG.17.

FIG.17is a circuit configuration diagram of the filter device10E according to another embodiment. As illustrated inFIG.17, the filter device10E includes the input/output terminals T1and T2, the matching circuit11and a matching circuit16E, the resonance circuits12and14, and a resonance circuit15E, and the filter13.

The resonance circuit15E is an example of the second resonance circuit, and is constituted of the series arm resonator S1and an inductor L21.

The series arm resonator S1and the inductor L21are arranged on a path connecting the node N1and the node N2. The series arm resonator S1is directly connected to the inductor L21in series.

The matching circuit16E is constituted of an inductor L22which is directly connected to the input/output terminal T2. Here, the inductor L22of the matching circuit16E is not included in the resonance circuit15E. The matching circuit16E performs impedance matching between the circuit elements outside the filter device10E and the circuit elements in the filter device10E, which are connected to each other via the input/output terminal T2.

Even when the filter device10E is configured as described above, the sub-resonant frequency of the resonance circuit15E can be made higher than the resonant frequency of the resonance circuit14E, so that a steep attenuation characteristic can be achieved at the high frequency end of the stop band SB1. In one embodiment, in the filter device10E, the inductor L1, the parallel arm resonator P1, and the inductor L22are not necessarily essential components for the filter device according to the present disclosure.

In each of the above embodiments and modifications thereof, the filter included in the filter device is a high pass filter, but the present disclosure is not limited thereto. The filter may be a low pass filter or a band pass filter.

Although the communication band corresponding to the pass band and/or the stop band of the filter device has been specifically described in the above embodiments and modifications thereof, these communication bands are illustrative and not limited thereto.

In each of the above embodiments and modifications thereof, the filter device forms a narrow-band stop band within a broadband pass band, but is not limited thereto. For example, the filter device may form a stop band at the low frequency end of the pass band of the LC high pass filter or LC band pass filter. In this case, the filter device can improve the attenuation characteristic at the low frequency end of the broadband pass band.

In the third embodiment, although the multiplexer is used in a reception circuit, the multiplexer may be used in a transmission circuit. In this case, the communication device may include a transmission power amplifier instead of the reception low noise amplifier. Also, the multiplexer may be used in the transmission/reception circuit. In this case, the communication device may include both of the reception low noise amplifier and the transmission power amplifier.

In the above third embodiment, the multiplexer includes five filter devices, but the number of filter devices is not limited to this. The multiplexer may include any one of the filter devices according to the above embodiments and modifications thereof, and other one or more filter devices, and the number of other one or more filter devices is not particularly limited.

In the third embodiment, a plurality of reception low noise amplifiers is connected to the filter device in a one-to-one manner, but the present disclosure is not limited thereto. One common reception low noise amplifier may be connected to some filter devices. In this case, the communication device may include a switch for switching between the conduction and the non-conduction of the reception low noise amplifier shared with each of the filter devices.

INDUSTRIAL APPLICABILITY

The present disclosure can be applied to a filter device and a multiplexer which are arranged in a multiband supported front end unit, and can be widely used for communication devices such as a cellular phone including the filter device and the multiplexer.

While embodiments of the disclosure have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without necessarily departing from the scope and spirit of the disclosure. The scope of the disclosure, therefore, is to be determined solely by the following claims.