N-pass filter

Abstract

An N-pass filter (1) is provided with N (N is an integer of 3 or more) signal paths (P1-PN) that are connected in parallel between an input / output terminal (110) and an input / output terminal (120). The signal path (PN) has: a switch (2N) that is connected to the input / output terminal (110) and modulates an input signal; a switch (3N) that is connected to the input / output terminal (120) and modulates the input signal at the same phase as the switch (2N); and a base filter (1N) connected between the switch (2N) and the switch (3N), the switch (2N) and the switch (3N) modulate the input signal at a phase of one cycle in the signal paths (P1-PN) and at a phase different for each signal path, and the base filters (11-1N) are band-pass filters configured only from passive elements.

Description

Technical Field

[0001] The present invention relates to an N-pass filter. Background Art

[0002] Patent document 1 discloses a frequency-variable N-pass filter. The N-pass filter includes N basic filters (original filters) arranged between an input terminal and an output terminal, and mixers connected to both ends of the N basic filters. With this structure, the N-pass filter becomes a filter with a variable passband, and can be used as a tuning filter used in a single superheterodyne receiver in a tuner circuit for receiving television signals or cable television signals.

[0003] Prior Art Literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 4-56524 Summary of the invention

[0006] Problem that the invention aims to solve

[0007] However, in the N-pass filter described in Patent Document 1, the basic filter is composed of active elements such as an operational amplifier. Therefore, when the N-pass filter is applied to the RF stage of a mobile phone, for example, in a high frequency region of 500 MHz or more, problems such as increased loss within the passband due to nonlinear characteristics of the active elements and insufficient attenuation outside the passband occur.

[0008] Therefore, the present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an N-pass filter having low loss within a passband and high attenuation outside the passband in a high frequency region.

[0009] Technical solutions to solve problems

[0010] In order to achieve the above-mentioned purpose, an N-pass filter involved in one embodiment of the present invention comprises: a first input / output terminal and a second input / output terminal; and N (N is an integer greater than or equal to 3) signal paths connected in parallel with each other between the first input / output terminal and the second input / output terminal, the N signal paths respectively comprising: a first modulator connected to the first input / output terminal and modulating an input signal input from the first input / output terminal or the second input / output terminal; a second modulator connected to the second input / output terminal and modulating the input signal with the same phase as that of the first modulator; and a basic filter connected between the first modulator and the second modulator, the first modulator and the second modulator modulating the input signal with a phase that forms a cycle in the N signal paths and with a phase that is different for each signal path, the basic filter being a bandpass filter composed only of passive elements.

[0011] Effects of the Invention

[0012] According to the present invention, it is possible to provide an N-pass filter having low loss within a pass band and high attenuation outside the pass band in a high frequency region. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a circuit configuration diagram of an N-pass filter according to an embodiment.

[0014] Figure 2 2 is a timing chart showing a driving signal of the N-pass filter according to the embodiment.

[0015] Figure 3 This is a diagram showing an example of a circuit configuration of a basic filter according to the first embodiment.

[0016] Figure 4A Graph showing the transmission characteristics of the basic filter alone according to the first embodiment near the passband.

[0017] Figure 4B This is a graph showing the broadband transmission characteristics including the attenuation band of the basic filter alone according to the first embodiment.

[0018] Figure 5 This is a graph showing an example of the pass characteristic of the N-pass filter according to the first embodiment.

[0019] Figure 6 This is a graph showing the pass characteristics when the drive frequency Fck of the N-pass filter according to the first embodiment is changed.

[0020] Figure 7 This is a diagram showing an example of a circuit configuration of a basic filter according to the second embodiment.

[0021] Fig. 8A 3 is a graph showing the resonance characteristics of the basic filter according to the second embodiment.

[0022] Figure 8B It is a graph showing the transmission characteristics of the basic filter alone according to the second embodiment near the passband.

[0023] Figure 8C This is a graph comparing the pass characteristics of the basic filters according to the first embodiment and the second embodiment.

[0024] Fig. 9 This is a graph showing the pass characteristics when the drive frequency Fck of the N-pass filter according to the second embodiment is changed.

[0025] Fig.10This is a diagram showing an example of a circuit configuration of a basic filter according to the third embodiment.

[0026] Fig.11 In the figure, (a) is a graph showing the pass characteristics of the basic filter alone according to the third embodiment near the pass band, and (b) is a graph showing the pass characteristics of the basic filter alone according to the second embodiment near the pass band.

[0027] Fig.12 This is a graph showing the pass characteristics when the drive frequency Fck of the N-pass filter according to the third embodiment is changed.

[0028] Fig.13 : is a graph showing the frequency variable range when the main response mode of the N-pass filter according to the embodiment is (Fck-Fb).

[0029] Fig.14 : is a graph showing the frequency variable range when the main response mode of the N-pass filter according to the embodiment is (−Fck+Fb).

[0030] Fig.15 : is a graph showing the frequency variable range when the main response mode of the N-pass filter according to the embodiment is (2Fck-Fb).

[0031] Fig.16 : is a graph showing the frequency variable range when the main response mode of the N-pass filter according to the embodiment is (Fck+Fb).

[0032] Fig.17 It is a circuit configuration diagram of a high-frequency module and a communication device according to an embodiment. DETAILED DESCRIPTION

[0033] Hereinafter, the embodiments of the present invention will be described in detail using the accompanying drawings. In addition, the embodiments described below all show general or specific examples. The numerical values, shapes, materials, constituent elements, configurations of constituent elements, and connection methods shown in the following embodiments are examples, and their purpose is not to limit the present invention. Among the constituent elements in the following embodiments, the constituent elements that are not recorded in the independent claims are described as arbitrary constituent elements. In addition, the sizes or size ratios of the constituent elements shown in the drawings may not be rigorous.

[0034] In addition, in the following embodiments, unless otherwise stated, the passband of the filter is defined as the frequency band between two frequencies that are 3 dB greater than the minimum value of the insertion loss in the passband. In addition, the center frequency of the filter is defined as the midpoint between the low-frequency end frequency and the high-frequency end frequency of the passband of the filter ((low-frequency end frequency + high-frequency end frequency) / 2).

[0035] In the following embodiments, the so-called "signal path" means a transmission line composed of wiring that propagates high-frequency signals, circuit elements and electrodes directly connected to the wiring, and terminals directly connected to the wiring or the electrode.

[0036] In addition, in the following embodiments, the so-called "connection" means not only the case of direct connection through a connection terminal and / or a wiring conductor, but also the case of electrical connection via other circuit elements. In addition, the so-called "connection between A and B" means connection with A and B on the path connecting A and B.

[0037] (Implementation Method)

[0038] [1. Circuit structure of N-pass filter 1]

[0039] Figure 1 1 is a circuit diagram of an N-pass filter 1 according to an embodiment. As shown in the figure, the N-pass filter 1 includes basic filters 11 to 1N (N is an integer greater than or equal to 3), switches 21 to 2N (N is an integer greater than or equal to 3), switches 31 to 3N (N is an integer greater than or equal to 3), and an input / output terminal 110 (a first input / output terminal) and an input / output terminal 120 (a second input / output terminal).

[0040] The switch 21 is an example of a first switch, and is connected to the input / output terminal 110 and the basic filter 11. The switch 21 switches between connection and disconnection between the input / output terminal 110 and the basic filter 11 by turning on and off according to the drive signal s1 based on the drive frequency Fck.

[0041] The switch 31 is an example of a second switch, and is connected to the input / output terminal 120 and the basic filter 11. The switch 31 switches on and off at the same timing as the switch 21 according to the drive signal s1 based on the drive frequency Fck, thereby switching the connection and disconnection between the input / output terminal 120 and the basic filter 11.

[0042] The switch 22 is an example of a first switch, and is connected to the input / output terminal 110 and the basic filter 12. The switch 22 switches between connection and disconnection between the input / output terminal 110 and the basic filter 12 by turning on and off according to the drive signal s2 based on the drive frequency Fck.

[0043] The switch 32 is an example of a second switch, and is connected to the input / output terminal 120 and the basic filter 12. The switch 32 performs an on / off operation at the same timing as the switch 22 according to the drive signal s2 based on the drive frequency Fck, thereby switching the connection and disconnection between the input / output terminal 120 and the basic filter 12.

[0044] The switch 2N is an example of a first switch, and is connected to the input / output terminal 110 and the basic filter 1N. The switch 2N is turned on and off by a drive signal sN based on a drive frequency Fck, thereby switching between connection and disconnection between the input / output terminal 110 and the basic filter 1N.

[0045] The switch 3N is an example of a second switch, and is connected to the input / output terminal 120 and the basic filter 1N. The switch 3N is turned on and off at the same timing as the switch 2N according to the drive signal sN based on the drive frequency Fck, thereby switching the connection and disconnection between the input / output terminal 120 and the basic filter 1N.

[0046] The basic filter 11 and the switches 21 and 31 form a signal path P1. The basic filter 12 and the switches 22 and 32 form a signal path P2. The basic filter 1N and the switches 2N and 3N form a signal path PN (N is an integer greater than or equal to 3).

[0047] The N-pass filter 1 includes N signal paths including signal paths P1 , P2 , and PN. The signal paths P1 to PN are connected in parallel to each other between the input / output terminal 110 and the input / output terminal 120 .

[0048] The basic filter 11 is connected between the switch 21 and the switch 31, and is a bandpass filter composed only of passive components. The basic filter 12 is connected between the switch 22 and the switch 32, and is a bandpass filter composed only of passive components. The basic filter 1N is connected between the switch 2N and the switch 3N, and is a bandpass filter composed only of passive components. In addition, the details of the circuit configuration of the basic filters 11 to 1N are illustrated in Examples 1 to 3.

[0049] Figure 21 is a timing diagram showing the drive signal of the N-pass filter 1 involved in the embodiment. In the same figure, an example of the drive signals s1 to sN supplied to the switches 21 to 2N and the switches 31 to 3N is shown. As shown in the figure, the drive signals s1 to sN are generated based on the clock signal CLK (drive frequency Fck). More specifically, when the period of the drive signals s1 to sN is set to T, the drive signals s1 to sN are respectively turned on during the period of T / N, and are delayed by T / N and turn on in sequence. As a result, the switches 21 to 2N are turned on at different timings for each signal path in the period T. In addition, the switches 31 to 3N are turned on at different timings for each signal path in the period T. That is, the basic filters 11 to 1N are connected to the input and output terminals 110 and 120 at different timings for each signal path in the period T.

[0050] According to the above configuration, the N-pass filter 1 becomes a band-pass filter having a center frequency Frf defined by the formula (1).

[0051] Frf = k × Fck ± Fb (Formula 1)

[0052] In Formula 1, Fb is the center frequency of the basic filter, and k is an integer. According to Formula 1, the N-pass filter 1 becomes a band-pass filter of variable passband type by making the driving frequency Fck variable. In addition, the pass characteristics of the N-pass filter 1 become a plurality of passbands (and a plurality of attenuation bands) corresponding to the value of k (integers from -∞ to +∞).

[0053] In addition, the N-pass filter 1 according to the present embodiment is not limited to the Figure 2 The driving signals s1 to sN shown in the figure are operated. The driving signals s1 to sN may not be turned on during the period of T / N, and may be shorter or longer than T / N. In other words, the periods during which the driving signals s1 to sN are turned on may not be strictly continuous, and may be slightly spaced apart. In addition, the periods during which the driving signals s1 to sN are turned on may be different or may be different.

[0054] According to the above structure of the N-pass filter 1, the basic filters 11 to 1N become bandpass filters composed only of passive elements, so compared with the case where the basic filter includes active elements such as semiconductor elements, saturation and nonlinear distortion caused by semiconductor elements can be suppressed. As a result, an N-pass filter 1 having low loss in the passband and high attenuation outside the passband in a high frequency region of 500 MHz or more, such as the RF stage used in a mobile phone, can be realized.

[0055] In the N-pass filter 1 according to the embodiment, the switches 21 to 2N may be each a first modulator that modulates an input signal input from the input / output terminal 110 or 120. In addition, the switches 31 to 3N may be each a second modulator that modulates an input signal input from the input / output terminal 110 or 120 with the same phase as the first modulator. Specifically, the first modulator and the second modulator may modulate an input signal input from the input / output terminal 110 or 120 with a phase that forms a cycle in N signal paths and with a phase that differs for each signal path. The switches 21 to 2N may be each an example of a first modulator, and the switches 31 to 3N may be each an example of a second modulator. However, as the first modulator and the second modulator, in addition to the switches 21 to 2N and the switches 31 to 3N, mixers and the like may also be cited.

[0056] [2. Circuit Configuration and Pass Characteristics of Basic Filters 11 to 1N According to Embodiment 1]

[0057] The N-pass filter 1 according to the first embodiment includes basic filters 11 to 1N (N is an integer greater than or equal to 3), switches 21 to 2N (N is an integer greater than or equal to 3), switches 31 to 3N (N is an integer greater than or equal to 3), and input / output terminals 110 and 120 .

[0058] Figure 3 1 is a diagram showing an example of a circuit configuration of basic filters 11 to 1N according to Embodiment 1. Figure 3 , an example of a circuit configuration of the basic filter 11 among the basic filters 11 to 1N is shown. The circuit configurations of the basic filters 12 to 1N are similar to those of the basic filters 11 to 1N. Figure 3 The circuit structure of the basic filter 11 shown is the same.

[0059] like Figure 3 As shown, the basic filter 11 includes capacitors 41, 42, and 43 and inductors 52 and 53. Each of the basic filters 11 to 1N according to the present embodiment is a bandpass filter composed only of passive elements, and includes an inductor and a capacitor.

[0060] One end of the capacitor 41 is connected to the terminal 111, and the other end is connected to the terminal 112. The LC parallel resonant circuit composed of the capacitor 42 and the inductor 52 is connected between the node on the path connecting the terminal 111 and the capacitor 41 and the ground. The LC parallel resonant circuit composed of the capacitor 43 and the inductor 53 is connected between the node on the path connecting the terminal 112 and the capacitor 41 and the ground. According to the above connection structure, Figure 3The basic filter 11 shown is a π-type three-stage bandpass filter. The structure is such that the two LC parallel resonant circuits are coupled by a capacitor 41 instead of using a so-called series inductor. As a result, the maximum inductance value of the inductors 52 and 53 can be reduced to 0.63 nH, so that the basic filter 11 can be miniaturized.

[0061] Figure 4A Graph showing the pass characteristics of the basic filter 11 alone in the vicinity of the passband involved in Example 1. Figure 4B Graph showing the broadband pass characteristics including the attenuation band of the basic filter 11 alone according to the first embodiment. Figure 4A as well as Figure 4B As shown, the basic filter 11 is a bandpass filter having a center frequency of 960 MHz and a bandwidth of 120 MHz.

[0062] Figure 5 1 is a graph showing an example of the pass characteristics of the N-pass filter 1 involved in the first embodiment. In the N-pass filter 1 involved in the present embodiment, N=8, the center frequency Fb of the basic filter 11=979.49MHz, the drive frequency Fck=1200MHz, the drive signals s1 to s8 are rectangular pulses with a pulse width=(1 / 1200MHz) / 8, and the termination impedance of each of the basic filters 11 to 1N is set to 400Ω. In other words, the termination impedance of the N-pass filter 1 is set to 50Ω.

[0063] like Figure 5 As shown, in the frequency band range of DC to 3 GHz, the passband of the N-pass filter 1 appears at (Fck-Fb) (k=1), Fb (k=0), (2Fck-Fb) (k=2), (Fck+Fb) (k=1), (3Fck-Fb) (k=3). By setting the termination impedance of the basic filters 11 to 1N to 400Ω and the termination impedance of the N-pass filter 1 to 50Ω, each passband of the N-pass filter 1 can be made to have a flat pass characteristic.

[0064] In the N-pass filter 1 according to the present embodiment, the termination impedance at the input / output terminals 110 and 120 is set to Z 0 When the input and output impedances of the basic filters 11 to 1N are set to Zb, the reflection coefficient (Zb-N×Z 0 ) / (Zb+N×Z 0 ) satisfies the relationship in Formula 2.

[0065] (Zb-N×Z 0 ) / (Zb+N×Z 0 )<0.316 (Formula 2)

[0066] In the N-pass filter 1 of the present embodiment, the termination impedance at the terminals 111 and 112 of the basic filters 11 to 1N is designed to be 400Ω. 0 =50Ω, Zb=400Ω, and N=8 are substituted into Formula 2, and ideally, the reflection coefficient becomes 0.

[0067] In conventional N-pass filters, active elements are used as the basic filter, so the impedance is large and the terminal impedance can be regarded as almost an open circuit in many cases. Therefore, in the high frequency band of 500MHz or more, the mismatch loss with the external connection circuit becomes large.

[0068] In contrast, according to the N-pass filter 1 of the present embodiment, the reflection loss at the input / output terminals 110 and 120 can be reduced to less than 10 dB, thereby suppressing the mismatch loss with the external connection circuit connected to the input / output terminals 110 and 120. Therefore, the N-pass filter 1 can be applied to a high-frequency front-end circuit that transmits a high-frequency signal with low loss.

[0069] Figure 6 This is a graph showing the pass characteristics when the drive frequency Fck of the N-pass filter 1 involved in Example 1 is changed. In addition, the drive frequency Fck is changed in the range of 0.9 GHz to 1.5 GHz. As shown in the figure, the center frequency Fb (979.49 MHz) of the basic filter 11 to 1N and the drive frequency Fck (0.9 GHz to 1.5 GHz) are close, so the harmonic response (each response mode) is easy to overlap. In addition, if the harmonic response overlaps or approaches, the waveform of the pass characteristic is deformed, but no extreme loss degradation is seen.

[0070] According to the N-pass filter 1 of this embodiment, LC bandpass filters are used as basic filters 11 to 1N, and a low-loss transmission characteristic with large attenuation and suppressed waveform distortion can be obtained within a variable frequency range of a drive frequency Fck described later.

[0071] The basic filters 11 to 1N involved in this embodiment are composed of capacitors and inductors as passive elements. Therefore, even if the transmission signal is reflected by the antenna and an unnecessary signal is incident on the receiving circuit, compared with the N-pass filter having a basic filter using active elements, saturation and distortion caused by nonlinear characteristics will not occur, so an N-pass filter 1 with sufficient attenuation characteristics can be obtained.

[0072] [3. Circuit Configuration and Pass Characteristics of Basic Filters 11A to 1NA According to Embodiment 2]

[0073] The N-pass filter 1A according to the second embodiment includes basic filters 11A to 1NA (N is an integer greater than or equal to 3), switches 21 to 2N (N is an integer greater than or equal to 3), switches 31 to 3N (N is an integer greater than or equal to 3), and input / output terminals 110 and 120 .

[0074] Figure 7 1 is a diagram showing an example of a circuit configuration of basic filters 11A to 1NA according to Embodiment 2. Figure 7 , an example of the circuit configuration of the basic filter 11A among the basic filters 11A to 1NA is shown. The circuit configurations of the basic filters 12A to 1NA are similar to those of the basic filters 12A to 1NA. Figure 7 The circuit structure of the basic filter 11A shown is the same.

[0075] like Figure 7 As shown, basic filter 11A includes elastic wave resonators 61, 62, 63, 64, and 65 and capacitor 44. Basic filters 11A to 11NA according to the present embodiment are each a bandpass filter formed only of passive elements and include an elastic wave resonator.

[0076] Elastic wave resonators 61 to 63 are series arm resonators connected in series with each other between terminal 111 and terminal 112. Elastic wave resonator 64 is a parallel arm resonator connected between a node on a path connecting elastic wave resonators 61 and 62 and ground, and elastic wave resonator 65 is a parallel arm resonator connected between a node on a path connecting elastic wave resonators 62 and 63 and ground. One end of capacitor 44 is connected to a node on a path connecting elastic wave resonators 61 and 62, and the other end is connected to terminal 112. According to the above connection structure, Figure 7 The basic filter 11A shown is a ladder-type elastic wave bandpass filter.

[0077] Fig. 8A 1 is a graph showing the resonance characteristics of the basic filter 11A according to the second embodiment. In the basic filters 11A to 11NA according to the present embodiment, the elastic wave resonators 61 to 65 are resonators using surface acoustic waves, and as the substrate having piezoelectricity, for example, 40° Y-cut X-propagation LiTaO 3Single crystal substrate (hereinafter referred to as LT). The resonant frequency bandwidth ((antiresonant frequency - resonant frequency) / resonant frequency) of each of elastic wave resonators 61 to 65 is set to 4%, and the resonant frequency (and antiresonant frequency) of elastic wave resonators 61, 63, and 65 is set to 4% higher than the resonant frequency (and antiresonant frequency) of elastic wave resonators 62 and 64. In addition, the impedance of elastic wave resonators 61 and 65 is set to be 6 times higher than the impedance of elastic wave resonators 62 and 64, and the impedance of elastic wave resonator 63 is set to be 12 times higher than the impedance of elastic wave resonators 62 and 64. In addition, Fig. 8A , the impedance values ​​of elastic wave resonators 61 and 64 are shown as substantially equal impedance values. In addition, in order to improve the attenuation steepness near the passband of basic filters 11A to 1NA, capacitor 44 is arranged as a bridging capacitor between a node on the path connecting elastic wave resonators 61 and 62 and terminal 112. In addition, the termination impedance at terminals 111 and 112 of basic filters 11A to 1NA is designed to be 400Ω.

[0078] In the N-pass filter 1A according to the present embodiment, the termination impedance at the input / output terminals 110 and 120 is set to Z 0 When the input and output impedances of the basic filters 11A to 1NA are set to Zb, the reflection coefficient (Zb-N×Z 0 ) / (Zb+N×Z 0 ) satisfies the relationship in Formula 2.

[0079] This makes it possible to reduce the reflection loss at the input / output terminals 110 and 120 to less than 10 dB, thereby suppressing the mismatch loss with the external circuit connected to the input / output terminal 110 or 120. Therefore, the N-pass filter 1A can be applied to a high-frequency front-end circuit that transmits a high-frequency signal with low loss.

[0080] Figure 8B Graph showing the pass characteristics of the basic filter 11A alone in the vicinity of the passband involved in Example 2. Figure 8C Graph 1 is a graph comparing the pass characteristics of the basic filters involved in Example 1 and Example 2. Figure 8B As shown in FIG. 1 , the basic filter 11A becomes a bandpass filter with a center frequency of about 1 GHz and a bandwidth of about 30 MHz. Figure 8C As shown, the base filter 11A according to the second embodiment is a surface acoustic wave filter using an LT substrate, and therefore has a narrower passband width and a higher attenuation steepness near the passband than the base filter 11 according to the first embodiment.

[0081] Fig. 9Graph showing the pass characteristics when the driving frequency Fck of the N-pass filter 1A according to Example 2 is changed. In addition, the driving frequency Fck is changed in the range of 0.5 GHz to 9.5 GHz. As shown in the figure, in the frequency band range of DC to 20 GHz, the passband of the N-pass filter 1A appears at (k×Fck±Fb) (k=1, 2, 3).

[0082] According to the N-pass filter 1A involved in this embodiment, elastic wave resonators as passive elements are used as basic filters 11A~1NA, so within the variable frequency range of the drive frequency Fck described later, a low-loss transmission characteristic with large attenuation and suppressed waveform distortion can be obtained.

[0083] [4. Circuit Configuration and Pass Characteristics of Basic Filters 11B to 1NB According to Embodiment 3]

[0084] The N-pass filter 1B according to the third embodiment includes basic filters 11B to 1NB (N is an integer greater than or equal to 3), switches 21 to 2N (N is an integer greater than or equal to 3), switches 31 to 3N (N is an integer greater than or equal to 3), and input / output terminals 110 and 120 .

[0085] Fig.10 1 is a diagram showing an example of a circuit configuration of basic filters 11B to 1NB according to Embodiment 3. Fig.10 , an example of the circuit configuration of the basic filter 11B among the basic filters 11B to 1NB is shown. The circuit configuration of the basic filters 12B to 1NB is similar to Fig.10 The circuit structure of the basic filter 11B shown is the same.

[0086] like Fig.10 As shown, the basic filter 11B includes elastic wave resonators 66, 67, 68, 69, and 70. Each of the basic filters 11B to 11NB according to the present embodiment is a bandpass filter composed only of passive elements, and includes an elastic wave resonator.

[0087] Elastic wave resonators 66 to 68 are series arm resonators connected in series between terminals 111 and 112. Elastic wave resonator 69 is a parallel arm resonator connected between a node on a path connecting elastic wave resonators 66 and 67 and ground, and elastic wave resonator 70 is a parallel arm resonator connected between a node on a path connecting elastic wave resonators 67 and 68 and ground. According to the above connection structure, Fig.10 The basic filter 11B shown is a ladder-type elastic wave bandpass filter.

[0088] Fig.11(a) is a graph showing the transmission characteristics of the basic filter 11B alone according to the third embodiment. Fig.11 (b) is a graph showing the transmission characteristic of the basic filter 11A alone according to the second embodiment.

[0089] In the basic filters 11B to 1NB according to the present embodiment, the elastic wave resonators 66 to 70 are resonators using surface acoustic waves, and as the piezoelectric substrate, for example, 15° Y-cut X-propagation LiNbO 3 Single crystal substrate (hereinafter referred to as LN). The resonant frequency bandwidth ((antiresonant frequency - resonant frequency) / resonant frequency) of each of elastic wave resonators 66 to 70 is set to 10%, and the resonant frequency (and antiresonant frequency) of elastic wave resonators 66, 68, and 70 is set to be 12% higher on the high frequency side than the resonant frequency (and antiresonant frequency) of elastic wave resonators 67 and 69. In addition, the impedance of elastic wave resonators 66 and 70 is set to be 4.12 times higher than the impedance of elastic wave resonators 67 and 69, and the impedance of elastic wave resonator 68 is set to be 8.24 times higher than the impedance of elastic wave resonators 67 and 69. In addition, the termination impedance at terminals 111 and 112 of basic filters 11B to 1NB is designed to be 400Ω.

[0090] In the N-pass filter 1B according to the present embodiment, the termination impedance at the input / output terminals 110 and 120 is set to Z 0 When the input and output impedances of the basic filters 11B to 1NB are set to Zb, the reflection coefficient (Zb-N×Z 0 ) / (Zb+N×Z 0 ) satisfies the relationship in Formula 2.

[0091] This makes it possible to reduce the reflection loss at the input / output terminals 110 and 120 to less than 10 dB, thereby suppressing the mismatch loss with the external circuit connected to the input / output terminal 110 or 120. Therefore, the N-pass filter 1B can be applied to a high-frequency front-end circuit that transmits a high-frequency signal with low loss.

[0092] like Fig.11 As shown in (a) of FIG. 1 , the basic filter 11B becomes a bandpass filter having a center frequency of 100 MHz and a bandwidth of 10 MHz. Fig.11 As shown in (a) and (b), the basic filter 11B according to the third embodiment is a surface acoustic wave filter using an LN substrate, and therefore can obtain a pass characteristic with a wider relative bandwidth (passband / center frequency) than the basic filter 11A according to the second embodiment.

[0093] Fig.12Graph showing the pass characteristics when the driving frequency Fck of the N-pass filter 1B involved in Example 3 is changed. In addition, the driving frequency Fck is changed in the range of 0.4 GHz to 1.0 GHz. As shown in the figure, the pass band of the N-pass filter 1B appears at (k×Fck±Fb) in the frequency band range of DC to 1.0 GHz. Among them, in particular, the (Fck±Fb) (k=1) mode is separated from other harmonics, so the N-pass filter 1B becomes a waveform that roughly transfers the waveform of the basic filter 11B to 1NB. Therefore, in the mode with (Fck±Fb) (k=1) as the main response, the N-pass filter 1B can obtain a pass characteristic with a wide pass band compared to the N-pass filter 1A using a surface acoustic wave filter using an LT substrate, and a pass characteristic with a high attenuation steepness near the pass band compared to the N-pass filter 1 using an LC filter.

[0094] In addition, in addition to the surface acoustic wave filter using LT or LN as the piezoelectric substrate illustrated in Examples 2 and 3, the basic filter can also be (1) a thin film bulk acoustic wave filter using AlN, ScAlN, or (2) a bulk acoustic wave filter using piezoelectric single crystals such as quartz, lithium tantalate, lithium niobate, potassium niobate, or a sintered shaped piezoelectric body such as lead zirconate titanate or barium titanate.

[0095] Furthermore, as the basic filter, a longitudinal coupling filter using elastic wave resonators may be used in addition to a ladder filter using elastic wave resonators.

[0096] Furthermore, as the basic filter, in addition to the above-mentioned LC filter and elastic wave filter, a dielectric filter may be used.

[0097] [5. Frequency variable range when the main response mode is (Fck-Fb)]

[0098] In the N-pass filter 1 (including N-pass filters 1A and 1B) according to the embodiment, if there is an unwanted response overlapping the main response, an unwanted signal caused by the unwanted response is transmitted. In order to prevent the transmission of the unwanted signal, it is preferable that the main response and the unwanted response do not overlap in frequency.

[0099] Fig.13 1 is a graph showing a frequency variable range when the main response mode of the N-pass filter 1 according to the embodiment is (Fck-Fb). The graph shown in the same figure shows the relationship of Formula 1. In addition, the horizontal axis represents Fck normalized by Fb (=Fck / Fb), and the vertical axis represents Frf normalized by Fb (=Frf / Fb). As shown in the figure, by making the driving frequency Fck variable, the center frequency Frf of the N-pass filter 1 can be made variable.

[0100] In the N-path filter 1, when using any one of the modes of (k×Fck±Fb) (k is an integer) as the main response, other modes become useless responses. However, since there are infinitely many values of k, there are many useless response modes. Furthermore, in the N-path filter 1, a band-pass filter is used as the basic filter. Therefore, compared with the N-path filter that uses a low-pass filter as the basic filter, twice as many useless responses are generated. In addition, it can be assumed that if the drive frequency Fck is near 0, the useless response existing at negative frequencies moves to positive frequencies and overlaps with the main response. Therefore, when selecting one main response mode from many modes, it is preferable to select the condition where the main response mode does not overlap with the useless response mode.

[0101] In Fig.13 , as combinations of (Fck, Fb), response modes of (0, 1), (1, 1), (1, -1), (2, 1), (2, -1), (3, 1), (3, -1), (-1, 1), (-2, 1) are shown. Additionally, although not shown, there are many modes with k < -3 and k > 3 in the region where the drive frequency Fck is on the low-frequency side.

[0102] Here, when the main response mode is set to (Fck - Fb), the conditions where the Frf in the main response mode (Fck - Fb) does not overlap with the Frf of other useless response modes are shown by Range 1 (Equation 3) and Range 2 (Equation 4).

[0103] (Range 1)

[0104] Fck_min + Fb > Fck_max - Fb, and, Fck > 2Fb (Equation 3)

[0105] (Range 2)

[0106] 1Fb < Fck < 2Fb (Equation 4)

[0107] Here, Fck_min is the lower limit frequency of the drive frequency Fck in the main response mode, and Fck_max is the upper limit frequency of the drive frequency Fck in the main response mode.

[0108] As Fig.13 shown, in Range 1 and Range 2, even if the frequency is variable, the frequency of the main response mode does not overlap with the useless response mode. Thus, a large attenuation amount and a low-loss passband with suppressed waveform distortion can be obtained within a continuously variable frequency range.

[0109] For example, assume that the N-pass filter 1 is frequency-variable within the frequency range of 727 to 950 MHz, which is a downlink operating frequency band covering the frequency bands n5, n8, n12, n14, n18, n20, n28, and n29 for 5G-NR and the frequency bands B5, B8, B12, B13, B14, B17, B18, B19, B20, B26, B27, B28, B29, B67, B68, and B85 for 4G-LTE. In this case, (Fck-Fb) is selected as the main response mode. If Fb=300 MHz, Fck_min=1027 MHz, and Fck_max=1250 MHz are set, the drive frequency Fck becomes a frequency band that is easy to manufacture switches 21 to 2N and 31 to 3N using CMOS (Complementary Metal Oxide Semiconductor) technology. Furthermore, it is possible to construct an N-pass filter 1 in which the main response mode (Fck-Fb) is separated in frequency from the nearest unwanted response modes (Fck+Fb) and (Fb). In this case, the normalized Fck (=Fck / Fb) is in the range of 3.42 (=1027MHz / 300MHz) to 4.17 (=1250MHz / 300MHz), and the normalized Frf (=Frf / Fb) is in the range of 2.42 (=727MHz / 300MHz) to 3.17 (=950MHz / 300MHz).

[0110] In addition, the frequency band applied to the N-pass filter 1 means a frequency band predefined by a standardization organization (for example, 3GPP (registered trademark) (3rd Generation Partnership Project, 3rd Generation Partnership Project), IEEE (Institute of Electrical and Electronics Engineers, Institute of Electrical and Electronics Engineers), etc.) for a communication system constructed using a radio access technology (RAT: Radio Access Technology). In the present embodiment, as a communication system, for example, a 4G (4th Generation, fourth generation)-LTE (Long Term Evolution, long term evolution) system, a 5G (5th Generation, fifth generation)-NR (New Radio, new air interface) system, and a WLAN (Wireless Local Area Network, wireless local area network) system can be used, but it is not limited to these.

[0111] [6. Frequency variable range when the main response mode is (-Fck+Fb)]

[0112] Fig.14 It is a graph showing the frequency variable range when the main response mode of the N-way filter 1 involved in the embodiment is (-Fck + Fb). The graph shown in the figure represents the relationship of Equation 1. In addition, the horizontal axis represents Fck normalized by Fb (= Fck / Fb), and the vertical axis represents Frf normalized by Fb (= Frf / Fb). As shown in the figure, by varying the drive frequency Fck, the center frequency Frf of the N-way filter 1 can be varied.

[0113] In Fig.14 it shows the response modes of (1, -1), (2, -1), (3, -1), (-1, 1), (-2, 1), (-3, 1) as the combination of (Fck, Fb).

[0114] Here, when the main response mode is set to (-Fck + Fb), the condition that Frf in the main response mode (-Fck + Fb) does not overlap with Frf of other unwanted response modes is shown by Range 3 (Equation 5) and Range 4 (Equation 6).

[0115] (Range 3)

[0116] 0.5Fb < Fck < 0.66Fb (Equation 5)

[0117] (Range 4)

[0118] 0.67Fb < Fck < 1Fb (Equation 6)

[0119] As Fig.14 shown, in Range 3 and Range 4, even if the frequency is variable, the frequency of the main response mode does not overlap with the unwanted response mode. Therefore, a large attenuation amount and a low-loss passband with suppressed waveform distortion can be obtained in a continuously variable frequency range.

[0120] For example, when the N-way filter 1 is frequency variable in the frequency range of 727 to 950 MHz, selecting (-Fck + Fb) as the main response mode, if Fb = 2000 MHz and Fck is set in the range of 1273 MHz to 1050 MHz, the basic filters 11 to 1N can be constructed in a high frequency range. Therefore, when an LC filter or a surface acoustic wave filter is used as the basic filter, the N-way filter 1 can be miniaturized.

[0121] [7. Frequency Variable Range when the Main Response Mode is (2Fck - Fb)]

[0122] Fig.15It is a graph showing the frequency variable range when the main response mode of the N-channel filter 1 involved in the embodiment is (2Fck - Fb). The graph shown in the figure represents the relationship of Equation 1. In addition, the horizontal axis represents Fck normalized by Fb (= Fck / Fb), and the vertical axis represents Frf normalized by Fb (= Frf / Fb). As shown in the figure, by varying the drive frequency Fck, the center frequency Frf of the N-channel filter 1 can be varied.

[0123] In Fig.15 it shows the response modes of (0, 1), (1, 1), (1, -1), (2, 1), (2, -1), (3, 1), (3, -1), (-1, 1), (-2, 1) as the combinations of (Fck, Fb).

[0124] Here, when the main response mode is set to (2Fck - Fb), the condition that Frf in the main response mode (2Fck - Fb) does not overlap with Frf of other unwanted response modes is shown by Range 5 (Equation 7).

[0125] (Range 5)

[0126] Fck > 1Fb, and 2Fck_max - Fb < Fck_min + Fb (Equation 7)

[0127] Here, Fck_min is the lower limit frequency of the drive frequency Fck in the main response mode, and Fck_max is the upper limit frequency of the drive frequency Fck in the main response mode.

[0128] As Fig.15 shown, in Range 5, even if the frequency is variable, the frequency of the main response mode does not overlap with the unwanted response mode. Therefore, a large attenuation amount and a low-loss passband with suppressed waveform distortion can be obtained within a continuous variable frequency range.

[0129] For example, when the N-channel filter 1 is frequency variable in the frequency range of 727 to 950 MHz, if (2Fck - Fb) is selected as the main response mode, and Fb = 500 MHz and Fck is set in the range of 613.5 MHz to 725 MHz, an N-channel filter 1 with the main response mode of (2Fck - Fb) can be constructed where the frequency is sufficiently separated from (Fck + Fb) and (Fb) which are the closest unwanted response modes.

[0130] [8. Frequency Variable Range when the Main Response Mode is (Fck + Fb)]

[0131] Fig.16It is a graph showing the frequency variable range when the main response mode of the N-way filter 1 involved in the embodiment is (Fck + Fb). The graph shown in the figure represents the relationship of Equation 1. In addition, the horizontal axis represents Fck normalized by Fb (= Fck / Fb), and the vertical axis represents Frf normalized by Fb (= Frf / Fb). As shown in the figure, by varying the drive frequency Fck, the center frequency Frf of the N-way filter 1 can be varied.

[0132] In Fig.16 it shows the response modes of (0, 1), (1, 1), (1, -1), (2, 1), (2, -1), (3, 1), (3, -1), (-1, 1), (-2, 1) as the combinations of (Fck, Fb).

[0133] Here, when the main response mode is set to (Fck + Fb), the condition that Frf in the main response mode (Fck + Fb) does not overlap with Frf of other unwanted response modes is shown by Range 6 (Equation 8).

[0134] (Range 6)

[0135] Fck > 2Fb, and,

[0136] Fck_max + Fb < 2Fck_min - Fb, and,

[0137] Fck_max - Fb < Fck_min + Fb (Equation 8)

[0138] Here, Fck_min is the lower limit frequency of the drive frequency Fck in the main response mode, and Fck_max is the upper limit frequency of the drive frequency Fck in the main response mode.

[0139] As Fig.16 shown, in Range 6, even if the frequency is variable, the frequency of the main response mode does not overlap with the unwanted response mode. Therefore, a large attenuation amount and a low-loss passband with suppressed waveform distortion can be obtained within a continuous variable frequency range.

[0140] In addition, in the N-way filter 1 involved in the embodiment, (k × Fck + Fb) (k is an integer) can also be used as the main response mode. In the case of this main response mode (k × Fck + Fb), Frf is the sum of the drive frequency Fck (an integer multiple of) and the center frequency Fb of the basic filters 11 to 1N. Therefore, compared with the N-way filter using a low-pass filter as the basic filter, the drive frequency Fck can be reduced.

[0141] Accordingly, in an N-pass filter 1 that uses a high-frequency band above 10 GHz as a passband, when a semiconductor switch is used as a modulator, there is a problem that there is no surplus in the circuit that generates the response frequency of the switch and the signal that drives the switch. However, according to this structure, the driving frequency Fck can be reduced and the burden on the semiconductor switch and the driving signal generating circuit can be alleviated.

[0142] [9. Circuit Configuration of High-Frequency Module 5 and Communication Device 10 According to Embodiment]

[0143] Fig.17 1 is a circuit diagram of a high-frequency module 5 and a communication device 10 according to the embodiment. As shown in the figure, the communication device 10 includes a high-frequency module 5 , an RF signal processing circuit (RFIC) 6 , and an antenna 7 .

[0144] The high frequency module 5 transmits a high frequency signal between the antenna 7 and the RFIC 6. The antenna 7 is connected to the antenna connection terminal 100 of the high frequency module 5, transmits the high frequency signal output from the high frequency module 5, and receives a high frequency signal from the outside and outputs it to the high frequency module 5.

[0145] RFIC6 is an example of a signal processing circuit that processes a high-frequency signal. Specifically, RFIC6 performs signal processing on a high-frequency reception signal input via the reception path of the high-frequency module 5 by down-conversion, etc., and outputs the reception signal generated by the signal processing to a baseband signal processing circuit (BBIC: not shown). In addition, RFIC6 performs signal processing on a transmission signal input from the BBIC by up-conversion, etc., and outputs the high-frequency transmission signal generated by the signal processing to the transmission path of the high-frequency module 5. In addition, RFIC6 has a control unit that controls the N-pass filters 1, 2 and amplifiers of the high-frequency module 5. In addition, part or all of the functions of the control unit of RFIC6 can also be installed outside RFIC6, for example, it can also be installed on the BBIC or the high-frequency module 5.

[0146] In addition, in the communication device 10 according to the present embodiment, the antenna 7 is not an essential component.

[0147] Next, the circuit structure of the high frequency module 5 is described. Fig.17 As shown, the high-frequency module 5 includes N-pass filters 1 and 2 , a power amplifier 4 , a low-noise amplifier 3 , an antenna connection terminal 100 , a high-frequency input terminal 101 , and a high-frequency output terminal 102 .

[0148] The antenna connection terminal 100 is connected to the antenna 7. The high frequency input terminal 101 is connected to the RFIC 6 and is a terminal for receiving a high frequency transmission signal from the RFIC 6. The high frequency output terminal 102 is connected to the RFIC 6 and is a terminal for outputting a high frequency reception signal to the RFIC 6.

[0149] The N-pass filter 1 is any one of the N-pass filter 1 according to the first embodiment, the N-pass filter 1A according to the second embodiment, and the N-pass filter 1B according to the third embodiment, and is a filter for reception connected between the antenna connection terminal 100 and the low noise amplifier 3. The N-pass filter 1 makes the passband and the attenuation band variable according to the drive signals s1 to sN output from the RFIC 6. Thus, the N-pass filter 1 can selectively pass high-frequency signals of multiple frequency bands.

[0150] The N-pass filter 2 is any one of the N-pass filter 1 involved in the first embodiment, the N-pass filter 1A involved in the second embodiment, and the N-pass filter 1B involved in the third embodiment, and is a transmission filter connected between the antenna connection terminal 100 and the power amplifier 4. The N-pass filter 2 makes the passband and the attenuation band variable according to the drive signals s1 to sN output from the RFIC 6. Thus, the N-pass filter 2 can selectively pass high-frequency signals of multiple frequency bands.

[0151] The drive circuit that outputs the drive signals s1 to sN may be included in the control unit of the RFIC 6 , or in the high-frequency module 5 , or may be configured as a semiconductor IC (Integrated Circuit) independently of the high-frequency module 5 and the RFIC 6 .

[0152] The low noise amplifier 3 is connected between the N-pass filter 1 and the high frequency output terminal 102 , and amplifies the reception signal input from the antenna connection terminal 100 .

[0153] The power amplifier 4 is connected between the N-pass filter 2 and the high-frequency input terminal 101 , and amplifies the transmission signal input from the high-frequency input terminal 101 .

[0154] According to the above configuration, it is not necessary to arrange filters corresponding to a plurality of frequency bands respectively, but only one N-pass filter corresponding to the plurality of frequency bands needs to be arranged, so that the high-frequency module 5 and the communication device 10 can be miniaturized.

[0155] In addition, the high frequency module 5 and the communication device 10 may also include Fig.17 In addition to the circuit elements shown, impedance matching elements, switches, etc. are also included.

[0156] The high frequency module 5 may also include a plurality of power amplifiers and a switch for switching the connection between any one of the plurality of power amplifiers and the N-pass filter 2. The high frequency module 5 may also include a plurality of low noise amplifiers and a switch for switching the connection between any one of the plurality of low noise amplifiers and the N-pass filter 1.

[0157] (Other Implementations)

[0158] The N-pass filter according to the present invention is described by enumerating the embodiments above, but the present invention is not limited to the above embodiments. Various modifications that can be obtained by implementing various modifications that can be thought of by a person skilled in the art to the above embodiments within the scope of the present invention, and various devices in which the N-pass filter according to the present invention is built-in are also included in the present invention.

[0159] Furthermore, for example, in the N-pass filter according to the above-described embodiment, matching elements such as inductors and capacitors and switch circuits may be connected between the components.

[0160] The following describes the characteristics of the N-pass filter described in the above-mentioned embodiments.

[0161] <1>

[0162] An N-pass filter having:

[0163] a first input / output terminal and a second input / output terminal; and

[0164] N (N is an integer greater than or equal to 3) signal paths are connected in parallel with each other between the first input / output terminal and the second input / output terminal.

[0165] The N signal paths respectively have:

[0166] a first modulator connected to the first input / output terminal and modulating an input signal input from the first input / output terminal or the second input / output terminal;

[0167] a second modulator connected to the second input / output terminal and modulating the input signal with the same phase as that of the first modulator; and

[0168] A basic filter connected between the first modulator and the second modulator,

[0169] The first modulator and the second modulator modulate the input signal with a phase that forms a cycle in the N signal paths and with a phase that is different for each of the signal paths.

[0170] The basic filter is a bandpass filter composed only of passive elements.

[0171] <2>

[0172] according to <1> The N-pass filter, wherein

[0173] The first modulator is a first switch that switches connection and disconnection between the first input / output terminal and the basic filter according to a drive signal.

[0174] The second modulator is a second switch that switches connection and non-connection between the second input / output terminal and the basic filter at the same timing as the first switch according to the drive signal.

[0175] <3>

[0176] according to <1> or <2> The N-pass filter, wherein

[0177] The driving frequencies of the first modulator and the second modulator are set to Fck, the center frequency in the passband of the basic filter monomer is set to Fb, the center frequency in the passband of the main response mode of the N-pass filter is set to Fck-Fb, the maximum driving frequency that can use the main response mode is set to Fck_max, and the minimum driving frequency that can use the main response mode is set to Fck_min. In this case, the following relationship is satisfied:

[0178] Fck_min+Fb>Fck_max-Fb, and

[0179] Fck>2Fb.

[0180] <4>

[0181] according to <1> or <2> The N-pass filter, wherein

[0182] The driving frequencies of the first modulator and the second modulator are set to Fck, the center frequency in the passband of the basic filter monomer is set to Fb, and the center frequency in the passband of the main response mode of the N-pass filter is set to Fck-Fb. In this case, the following relationship is satisfied:

[0183] 1Fb <Fck<2Fb。

[0184] <5>

[0185] according to <1> or <2> The N-pass filter, wherein

[0186] The driving frequencies of the first modulator and the second modulator are set to Fck, the center frequency in the passband of the basic filter monomer is set to Fb, and the center frequency in the passband of the main response mode of the N-pass filter is set to -Fck+Fb. In this case, the following relationship is satisfied:

[0187] 0.5Fb <Fck<0.66Fb。

[0188] <6>

[0189] according to <1> or <2> The N-pass filter, wherein

[0190] The driving frequencies of the first modulator and the second modulator are set to Fck, the center frequency in the passband of the basic filter monomer is set to Fb, and the center frequency in the passband of the main response mode of the N-pass filter is set to -Fck+Fb. In this case, the following relationship is satisfied:

[0191] 0.67Fb <Fck<1Fb。

[0192] <7>

[0193] according to <1> or <2> The N-pass filter, wherein

[0194] The driving frequencies of the first modulator and the second modulator are set to Fck, the center frequency in the passband of the basic filter monomer is set to Fb, and the center frequency in the passband of the main response mode of the N-pass filter is set to 2Fck-Fb. In this case, the following relationship is satisfied:

[0195] Fck>1Fb, and

[0196] 2Fck_max-Fb <Fck_min+Fb。

[0197] <8>

[0198] according to <1> or <2> The N-pass filter, wherein

[0199] The driving frequencies of the first modulator and the second modulator are set to Fck, the center frequency in the passband of the basic filter monomer is set to Fb, and the center frequency in the passband of the main response mode of the N-pass filter is set to Fck+Fb. In this case, the following relationship is satisfied:

[0200] Fck>2Fb, and

[0201] Fck_max+Fb<2Fck_min-Fb, and

[0202] Fck_max-Fb <Fck_min+Fb。

[0203] <9>

[0204] according to <1> ~ <8> An N-pass filter as described in any one of claims 1 to 5, wherein

[0205] The basic filter includes an inductor and a capacitor.

[0206] <10>

[0207] according to <9> The N-pass filter, wherein

[0208] The driving frequencies of the first modulator and the second modulator are set to Fck, and the center frequency in the passband of the basic filter unit is set to Fb. In this case, the center frequency in the passband of the main response mode of the N-pass filter is k×Fck+Fb (k is an integer).

[0209] <11>

[0210] according to <1> ~ <8> An N-pass filter as described in any one of claims 1 to 5, wherein

[0211] The basic filter is an elastic wave filter.

[0212] <12>

[0213] according to <1> ~ <11> An N-pass filter as described in any one of claims 1 to 5, wherein

[0214] The termination impedance of the N-pass filter is set to Z 0 ,

[0215] The input and output impedance of the basic filter is set to Zb. In this case, the following relationship is satisfied:

[0216] (Zb-N×Z 0 ) / (Zb+N×Z 0 )<0.316.

[0217] Industrial Applicability

[0218] The present invention can be widely used in communication devices such as mobile phones as a low-loss and high-attenuation filter applicable to multi-band and multi-mode frequency standards.

[0219] Description of Reference Numerals

[0220] 1, 2, 1A, 1B: N-pass filter;

[0221] 3: Low noise amplifier;

[0222] 4: Power amplifier;

[0223] 5: High frequency module;

[0224] 6: RF signal processing circuit (RFIC);

[0225] 7: Antenna;

[0226] 10: Communication device;

[0227] 11, 11A, 11B, 12, 12A, 12B, 1N, 1NA, 1NB: basic filters;

[0228] 21, 22, 2N, 31, 32, 3N: switch;

[0229] 41, 42, 43, 44: capacitors;

[0230] 52, 53: Inductor;

[0231] 61, 62, 63, 64, 65, 66, 67, 68, 69, 70: elastic wave resonators;

[0232] 100: Antenna connection terminal;

[0233] 101: High frequency input terminal;

[0234] 102: high frequency output terminal;

[0235] 110, 120: input and output terminals;

[0236] 111, 112: terminal;

[0237] P1, P2, PN: signal path;

[0238] s1, s2, sN: driving signals.

Claims

1. An N-pass filter, comprising: a first input / output terminal and a second input / output terminal; and N signal paths are connected in parallel with each other between the first input / output terminal and the second input / output terminal, wherein: N is an integer greater than or equal to 3, The N signal paths respectively have: a first modulator connected to the first input / output terminal and modulating an input signal input from the first input / output terminal or the second input / output terminal; a second modulator connected to the second input / output terminal and modulating the input signal with the same phase as the first modulator; and A basic filter connected between the first modulator and the second modulator, The first modulator and the second modulator modulate the input signal with a phase that forms a cycle in the N signal paths and with a phase that is different for each of the signal paths. The basic filter is a bandpass filter composed only of passive elements.

2. The N-pass filter according to claim 1, wherein: The first modulator is a first switch that switches connection and disconnection between the first input / output terminal and the basic filter according to a drive signal. The second modulator is a second switch that switches connection and non-connection between the second input / output terminal and the basic filter at the same timing as the first switch according to the drive signal.

3. The N-pass filter according to claim 1 or 2, wherein: The driving frequencies of the first modulator and the second modulator are set to Fck, the center frequency in the passband of the basic filter unit is set to Fb, the center frequency in the passband of the main response mode of the N-pass filter is set to (Fck-Fb), the maximum driving frequency that can use the main response mode is set to Fck_max, and the minimum driving frequency that can use the main response mode is set to Fck_min. In this case, the following relationship is satisfied: Fck_min+Fb>Fck_max-Fb, and Fck>2Fb.

4. The N-pass filter according to claim 1 or 2, wherein: The driving frequencies of the first modulator and the second modulator are set to Fck, the center frequency in the passband of the basic filter unit is set to Fb, and the center frequency in the passband of the main response mode of the N-pass filter is set to (Fck-Fb). In this case, the following relationship is satisfied: 1Fb <Fck<2Fb。 5. The N-pass filter according to claim 1 or 2, wherein: The driving frequencies of the first modulator and the second modulator are set to Fck, the center frequency in the passband of the basic filter unit is set to Fb, and the center frequency in the passband of the main response mode of the N-pass filter is set to (-Fck+Fb). In this case, the following relationship is satisfied: 0.5Fb <Fck<0.66Fb。 6. The N-pass filter according to claim 1 or 2, wherein: The driving frequencies of the first modulator and the second modulator are set to Fck, the center frequency in the passband of the basic filter unit is set to Fb, and the center frequency in the passband of the main response mode of the N-pass filter is set to (-Fck+Fb). In this case, the following relationship is satisfied: 0.67Fb <Fck<1Fb。 7. The N-pass filter according to claim 1 or 2, wherein: The driving frequencies of the first modulator and the second modulator are set to Fck, the center frequency in the passband of the basic filter unit is set to Fb, and the center frequency in the passband of the main response mode of the N-pass filter is set to (2Fck-Fb). In this case, the following relationship is satisfied: Fck>1Fb, and 2Fck_max-Fb <Fck_min+Fb。 8. The N-pass filter according to claim 1 or 2, wherein: The driving frequencies of the first modulator and the second modulator are set to Fck, the center frequency in the passband of the basic filter unit is set to Fb, and the center frequency in the passband of the main response mode of the N-pass filter is set to (Fck+Fb). In this case, the following relationship is satisfied: Fck>2Fb, and Fck_max+Fb<2Fck_min-Fb, and Fck_max-Fb <Fck_min+Fb。 9. The N-pass filter according to any one of claims 1 to 8, wherein: The basic filter includes an inductor and a capacitor.

10. The N-pass filter according to claim 9, wherein: The driving frequencies of the first modulator and the second modulator are set to Fck, and the center frequency in the passband of the basic filter monomer is set to Fb. In this case, the center frequency in the passband of the main response mode of the N-pass filter is (k×Fck+Fb), where k is an integer.

11. The N-pass filter according to any one of claims 1 to 8, wherein: The basic filter is an elastic wave filter.

12. The N-pass filter according to any one of claims 1 to 11, wherein: The termination impedance of the N-pass filter is set to Z0, The input and output impedance of the basic filter is set to Zb. In this case, the following relationship is satisfied: (Zb-N×Z0) / (Zb+N×Z0)<0.316.

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