N-pass filter

Abstract

An N-pass filter (1) is provided with N signal paths (P1-PN) and N signal paths (P41-P4N) connected in parallel between signal terminals (110 and 120), the signal path (PN) having a switch (1N) connected to the signal terminal (110), a switch (3N) connected to the signal terminal (120), and a base filter (5N) connected between the switches (1N and 3N), and the signal path (P4N) having a switch (4N) connected to the signal terminal (130). The base filter (5N) includes a series arm element having a reactance component, the switches (1N, 3N) modulate the input signal at a phase that is one cycle T in the signal paths (P1-PN), the switch (4N) modulates the input signal at a phase that is one cycle T in the signal paths (P41-P4N), and the phase of the drive signal of the switch (3N) and the phase of the drive signal of the switch (4N) are opposite.

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 disposed between an input terminal and an output terminal, and switches connected to both ends of the N basic filters sequentially switch the filters to have narrow-band filter characteristics.

[0003] Prior Art Literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 6-237149 Summary of the invention

[0006] Problem that the invention aims to solve

[0007] In the N-pass filter described in Patent Document 1, if an elastic wave filter, a filter including an inductor and a capacitor (LC filter), or a filter including a dielectric resonator (dielectric filter) is applied as a basic filter, an N-pass filter can be constructed in which a flat and low-loss passband frequency can be made variable by a switch driving frequency.

[0008] However, when an elastic wave filter, LC filter, or dielectric filter includes a series arm element whose impedance has an imaginary part (reactance component), the time response of the signal will be offset when switching due to the influence of the imaginary part. Therefore, when a filter including a series arm element with a reactance component is applied as a basic filter of an N-pass filter, all unnecessary response modes specified by k·Fck±Fb (Fck: switching drive frequency, Fb: basic filter center frequency, k: integer) will appear. As a result, the frequency variable range of the main response mode whose frequency does not overlap with the unnecessary response mode is greatly limited, making it difficult to realize an N-pass filter with a desired frequency variable width.

[0009] 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 which is constituted by a basic filter including series arm elements having a reactance component and has a wide frequency variable width.

[0010] Technical solutions to solve problems

[0011] In order to achieve the above-mentioned object, an N-pass filter involved in one embodiment of the present invention comprises: a first signal terminal, a second signal terminal and a third signal terminal; N (N is an integer greater than or equal to 3) first signal paths connected in parallel between the first signal terminal and the second signal terminal; and N second signal paths, the N first signal paths respectively having: a first modulator connected to the first signal terminal and modulating an input signal input from the first signal terminal or the second signal terminal; a second modulator connected to the second signal terminal and modulating the input signal; and a basic filter connected between the first modulator and the second modulator, the N second signal paths respectively modulating the input signal on the first signal path and a path connecting the node of the first signal terminal and the third signal terminal, and having a third modulator, the third modulator is connected to the third signal terminal and modulates an input signal input from the first signal terminal or the third signal terminal, the basic filter includes a series arm element having an inductive component, the first modulator and the second modulator are respectively driven by a driving signal that modulates the input signal with a phase that becomes one cycle T in N first signal paths, the third modulator is driven by a driving signal that modulates the input signal with a phase that becomes one cycle T in N second signal paths, and the phase of the driving signal driving the second modulator and the phase of the driving signal driving the third modulator are opposite phases.

[0012] Effects of the Invention

[0013] According to the present invention, it is possible to provide an N-pass filter which is composed of a basic filter including series arm elements having a reactance component and has a wide frequency variable width. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a circuit configuration diagram of an N-pass filter according to an embodiment.

[0015] Figure 2 2 is a timing chart showing a driving signal of the N-pass filter according to the embodiment.

[0016] Figure 3A It is a circuit configuration diagram of an N-pass filter according to Modification 1 of the embodiment.

[0017] Figure 3B It is a circuit configuration diagram of an N-pass filter according to Modification 2 of the embodiment.

[0018] Figure 3C It is a circuit configuration diagram of an N-pass filter according to Modification 3 of the embodiment.

[0019] Figure 4A 1 is a diagram showing an example of a circuit configuration of a basic filter according to an embodiment.

[0020] Figure 4B : is a graph showing an example of the transmission characteristic of a basic filter alone according to the embodiment.

[0021] Figure 5 : is a graph showing the pass characteristic of the N-pass filter according to the embodiment.

[0022] Fig. 6A It is a graph showing the pass characteristics of the N-pass filter according to the first modification of the embodiment.

[0023] Figure 6B Graphs showing pass characteristics of the N-pass filters in the vicinity of the main response mode according to Modification 1 and Comparative Example.

[0024] Fig. 7A 3 is a circuit configuration diagram of an N-pass filter according to a comparative example.

[0025] Figure 7B It is a graph showing the pass characteristics of an N-pass filter according to a comparative example.

[0026] Fig. 8A Graphs showing various response patterns when the base filter of the N-pass filter is a low-pass filter.

[0027] Figure 8B This is a graph showing the frequency variable range of the main response mode Fck when the basic filter of the N-pass filter according to Modification 1 is a low-pass filter.

[0028] Figure 8C : is a graph showing the frequency variable range in which the main response mode is 2Fck when the basic filter of the N-pass filter according to the embodiment is a low-pass filter.

[0029] Fig. 9A Graphs showing various response modes when the base filter of the N-pass filter is a band-pass filter.

[0030] Fig. 9B This is a graph showing a frequency variable range in which the main response mode is (Fck-Fb) when the base filter of the N-pass filter according to Modification 1 is a band-pass filter.

[0031] Fig. 9C This is a graph showing a frequency variable range in which the main response mode is (2Fck-Fb) when the base filter of the N-pass filter according to the embodiment is a band-pass filter.

[0032] Fig.10 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] In addition, in the following embodiments, the so-called "element A is configured in series between B and C" means that the signal input end of element A is connected to the wiring, electrode or terminal constituting B, and the signal output end of element A is connected to the wiring, electrode or terminal constituting C.

[0038] (Implementation Method)

[0039] [1. Circuit Configuration of N-pass Filters 1 and 1A]

[0040] 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 51 to 5N (N is an integer greater than or equal to 3), switches 11 to 1N (N is an integer greater than or equal to 3), switches 31 to 3N and switches 41 to 4N, a signal terminal 110 (a first signal terminal), a signal terminal 120 (a second signal terminal), a signal terminal 130 (a third signal terminal), and a signal output terminal 140.

[0041] The N-pass filter 1 includes N first signal paths including signal paths P1, P2, and PN. The signal paths P1 to PN are connected in parallel to each other between the signal terminal 110 and the signal terminal 120. In addition, the N-pass filter 1 includes N second signal paths including signal paths P41, P42, and P4N. The signal path P41 is a path connecting the node x1 on the signal path P1 and the signal terminal 130, the signal path P42 is a path connecting the node x2 on the signal path P2 and the signal terminal 130, and the signal path P4N is a path connecting the node xN on the signal path PN and the signal terminal 130. In other words, the N second signal paths are paths connecting the nodes on the first signal path and the signal terminal 130, respectively.

[0042] The switch 11 is an example of a first switch, and is connected to the signal terminal 110 and the basic filter 51. The switch 11 switches between connection and disconnection between the signal terminal 110 and the basic filter 51 by turning on and off according to the drive signal s1 based on the drive frequency Fck.

[0043] The switch 31 is an example of a second switch, and is connected to the signal terminal 120 and the basic filter 51. The switch 31 switches between connection and disconnection between the signal terminal 120 and the basic filter 51 by turning on and off according to the drive signal s31 based on the drive frequency Fck.

[0044] The switch 41 is an example of a third switch, and is connected to the signal terminal 130 and the basic filter 51. The switch 41 switches between connection and disconnection between the signal terminal 130 and the basic filter 51 by turning on and off according to a drive signal s41 based on the drive frequency Fck.

[0045] The basic filter 51 is connected between the switches 11 and 31 , and further connected between the switches 11 and 41 .

[0046] The switch 12 is an example of a first switch, and is connected to the signal terminal 110 and the basic filter 52. The switch 12 switches between connection and disconnection between the signal terminal 110 and the basic filter 52 by turning on and off according to the drive signal s2 based on the drive frequency Fck.

[0047] The switch 32 is an example of a second switch, and is connected to the signal terminal 120 and the basic filter 52. The switch 32 switches between connection and disconnection between the signal terminal 120 and the basic filter 52 by turning on and off according to the drive signal s32 based on the drive frequency Fck.

[0048] The switch 42 is an example of a third switch, and is connected to the signal terminal 130 and the basic filter 52. The switch 42 switches between connection and disconnection between the signal terminal 130 and the basic filter 52 by turning on and off according to a drive signal s42 based on the drive frequency Fck.

[0049] The basic filter 52 is connected between the switches 12 and 32 , and further, is connected between the switches 12 and 42 .

[0050] The switch 1N is an example of a first switch, and is connected to the signal terminal 110 and the basic filter 5N. The switch 1N switches between connection and disconnection between the signal terminal 110 and the basic filter 5N by turning on and off according to the drive signal sN based on the drive frequency Fck.

[0051] The switch 3N is an example of a second switch, and is connected to the signal terminal 120 and the basic filter 5N. The switch 3N switches between connection and disconnection between the signal terminal 120 and the basic filter 5N by turning on and off according to a drive signal s3N based on the drive frequency Fck.

[0052] The switch 4N is an example of a third switch, and is connected to the signal terminal 130 and the basic filter 5N. The switch 4N switches between connection and disconnection between the signal terminal 130 and the basic filter 5N by turning on and off according to a drive signal s4N based on the drive frequency Fck.

[0053] The basic filter 5N is connected between the switches 1N and 3N, and further connected between the switches 1N and 4N.

[0054] The switches 11 to 1N, 31 to 3N, and 41 to 4N are configured using, for example, CMOS (Complementary Metal Oxide Semiconductor).

[0055] The basic filter 51, the switches 11 and 31 form a signal path P1. The basic filter 52, the switches 12 and 32 form a signal path P2. The basic filter 5N, the switches 1N and 3N form a signal path PN.

[0056] Furthermore, the switch 41 forms a signal path P41, the switch 42 forms a signal path P42, and the switch 4N forms a signal path P4N.

[0057] Each of the basic filters 51 to 5N includes a series arm element having a reactance component (impedance having an imaginary part). The series arm element is a circuit element arranged in series in a path connecting the input end and the output end of the basic filter. Figure 4A and 4B for examples.

[0058] Figure 2 1 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 s8 supplied to the switches 11 to 1N (when N=8), the drive signals s31 to s38 supplied to the switches 31 to 3N (when N=8), and the drive signals s41 to s48 supplied to the switches 41 to 4N (when N=8) is shown. The drive signals s1 to s8, s31 to s38, and s41 to s48 are generated based on the drive frequency Fck (clock signal), and each switch becomes conductive (ON) at a high level (High), and each switch becomes non-conductive (OFF) at a low level (Low). More specifically, the period of the drive signals s1 to s8, the period of the drive signals s31 to s38, and the period of the drive signals s41 to s48 are T, respectively. Here, if the phase difference between the drive signal s1 and the drive signal s31, the phase difference between the drive signal s2 and the drive signal s32, and the phase difference between the drive signal s8 and the drive signal s38 are respectively set to α, the phase relationship between the drive signals can be expressed by Formula 1. In Formula 1, N is an integer of 1 to 8, and α is an arbitrary value.

[0059] The phase of the driving signal sN = (N-1) × 2π / 8

[0060] The phase of the driving signal s3N = (N-1) × 2π / 8 + α

[0061] The phase of the driving signal s4N = (N-1) × 2π / 8 + α + π (Formula 1)

[0062] The first switches (switches 11 to 1N) are driven by drive signals s1 to sN that modulate the input signal with a phase that becomes one cycle T in N first signal paths (signal paths P1 to PN). In addition, the second switches (switches 31 to 3N) are driven by drive signals s31 to s3N that modulate the input signal with a phase that becomes one cycle T in N first signal paths (signal paths P1 to PN). In addition, the third switches (switches 41 to 4N) are driven by drive signals s41 to s4N that modulate the input signal with a phase that becomes one cycle T in N second signal paths (signal paths P41 to P4N).

[0063] Each switch is operated according to the above-mentioned drive signal, whereby the N-pass filter 1 becomes a band-pass filter having a center frequency Frf defined by Expression 2.

[0064] Frf = k·Fck±Fb (Formula 2)

[0065] In Formula 2, Fb is the center frequency of the basic filter, and k is an integer. According to Formula 2, the N-pass filter 1 becomes a band-pass filter of a variable passband type by making the drive frequency Fck variable. In addition, the pass characteristic of the N-pass filter 1 becomes a plurality of passbands (and a plurality of attenuation bands) corresponding to the value of k. In addition, when the basic filter is a low-pass filter, Fb becomes 0.

[0066] Here, according to the phase relationship of Formula 1, at the frequency of (1 / T+Fb), the phase of the drive signal s3N driving the second switch (switches 31 to 3N) and the phase of the drive signal s4N driving the third switch (switches 41 to 4N) become opposite phases (the phase difference is π).

[0067] In addition, in the N-pass filter of the present invention, the phase difference between the drive signals s3N and s4N may not be strictly π (180°). In the N-pass filter of the present invention, the two signals are in opposite phases, which means that the phase difference between the two signals is within 180°±5%.

[0068] In the N-pass filter 1 according to the embodiment, the switches 11 to 1N may be each a first modulator that modulates an input signal input from the signal 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 signal terminal 110 or 120. In addition, the switches 41 to 4N may be each a third modulator that modulates an input signal input from the signal terminal 110 or 130. Specifically, the first modulator and the second modulator are each driven by a drive signal that modulates an input signal with a phase that becomes one cycle T in the N first signal paths. In addition, the third modulator is driven by a drive signal that modulates an input signal with a phase that becomes one cycle T in the N second signal paths. Switches 11 to 1N are each an example of a first modulator, switches 31 to 3N are each an example of a second modulator, and switches 41 to 4N are each an example of a third modulator. However, as the first modulator, the second modulator, and the third modulator, in addition to switches 11 to 1N, switches 31 to 3N, and switches 41 to 4N, mixers and the like can also be listed.

[0069] Here, in Figure 1In the N-pass filter 1 shown in FIG. 1 , if the transfer function of the basic filter is G, each frequency is ω, and each frequency of the driving signal is ω ck , then the transfer function T from the signal terminal 110 to the signal terminal 120 can be expressed by Equation 3.

[0070] [Mathematical formula 1]

[0071]

[0072] (Formula 3)

[0073] In addition, the frequency (k·ω ck +Δω) from the signal terminal 110 to the signal terminal 120 ka and the transfer function H from the signal terminal 110 to the signal terminal 130 kb It can be expressed by formula 4.

[0074] [Mathematical formula 2]

[0075]

[0076] (Formula 4)

[0077] According to Formula 4, when k is an even number (including 0), the transfer function H ka and H kb The values ​​become the same, and the signal transmitted from the signal terminal 110 to the signal terminal 120 and the signal transmitted from the signal terminal 110 to the signal terminal 130 become the same phase.

[0078] In addition, it can be seen that when k is an odd number, the transfer function H ka and H kb The positive and negative are reversed, and the signal transmitted from the signal terminal 110 to the signal terminal 120 and the signal transmitted from the signal terminal 110 to the signal terminal 130 are in opposite phases.

[0079] Therefore, if Figure 1 As shown, if the signal output from the signal terminal 120 and the signal output from the signal terminal 130 are added, when k is an odd number, H ka +H kb =0, which can suppress modes where k is an odd multiple.

[0080] When a filter including a series arm element having a reactance component is applied as a basic filter of an N-pass filter, all unnecessary response modes specified by k·Fck±Fb (Fck: switch drive frequency, Fb: basic filter center frequency, k: integer) appear. Therefore, the frequency variable range of the main response mode whose frequency does not overlap with the unnecessary response mode is greatly limited, and it is difficult to realize an N-pass filter with a desired frequency variable width.

[0081] In contrast, according to the configuration of the N-pass filter 1 according to the embodiment, the unwanted mode response when k is an odd multiple can be suppressed by adding the signals at the signal terminals 120 and 130. Therefore, the N-pass filter 1 composed of a basic filter including a series arm element having a reactance component can have a wide frequency variable width.

[0082] Furthermore, if the signal output from the signal terminal 130 is subtracted from the signal output from the signal terminal 120, when k is an even number (including 0), H ka -H kb = 0, which can suppress the mode where k is an even multiple (including 0). This can be achieved by Figure 3A The N-pass filter 1A shown is implemented.

[0083] Figure 3A 1 is a circuit diagram of an N-pass filter 1A according to a first modification of the embodiment. As shown in the figure, the N-pass filter 1A includes basic filters 51 to 5N (N is an integer greater than or equal to 3), switches 11 to 1N, switches 31 to 3N, and switches 41 to 4N, a signal terminal 110 (first signal terminal), a signal terminal 120 (second signal terminal), and a signal terminal 130 (third signal terminal), a balun 70, and a signal output terminal 140. The N-pass filter 1A according to this modification is different from the N-pass filter 1 according to the embodiment only in that the balun 70 is arranged between the signal terminals 120 and 130 and the signal output terminal 140. In the following, only the configuration of the N-pass filter 1A according to this modification that is different from the N-pass filter 1 according to the embodiment will be described.

[0084] The balun 70 is an example of a balun conversion element, and has a primary coil and a secondary coil that are electromagnetically coupled to each other. One of the balanced terminals of the primary coil is connected to the signal terminal 120, the other of the balanced terminals of the primary coil is connected to the signal terminal 130, the unbalanced terminal of the secondary coil is connected to the signal output terminal 140, and the other end of the secondary coil is grounded. According to this structure, the signal output from the signal terminal 120 and the signal output from the signal terminal 130 become two differential signals, and the signal after voltage synthesis is output to the signal output terminal 140. In addition, the balun conversion element is not limited to the balun, and may be a transformer, a semiconductor circuit, etc.

[0085] According to the configuration of the N-pass filter 1A according to the first modification, the unwanted mode response when k is an even multiple (including 0) can be suppressed by subtracting the signals at the signal terminals 120 and 130. Therefore, the N-pass filter 1A composed of a basic filter including a series arm element having a reactance component can have a wide frequency variable width.

[0086] In the N-pass filter 1 according to the embodiment and the N-pass filter 1A according to the modification 1, the signal terminal 110 is used as a signal input terminal to which an input signal is supplied, and the signal output terminal 140 is used as a signal output terminal to which an output signal is output, but the flow direction of the signal may be reversed. In other words, the signal output terminal 140 may be used as a signal input terminal to which an input signal is supplied, and the signal terminal 110 may be used as a signal output terminal to which an output signal is output.

[0087] Next, in the N-pass filter 1 according to the embodiment and the N-pass filter 1A according to the modification 1, a specific range of the phase difference between the drive signals s3N and s4N will be described.

[0088] For example, the following case is illustrated, that is, Figure 1 In the N-pass filter 1 according to the embodiment shown in the figure, (H 1a -H 1b ) is set as the master mode, and the adjacent (H 0a -H 0b ) and (H 2a -H 2b ) is set to disabled mode.

[0089] In this case, the range of the phase difference is preferably 174.261° to 185.739°. In Formula 4, if 180±5.739 (174.261° to 185.739°) is substituted for π, Formula 4 can be expressed as Formula 5.

[0090] [Mathematical formula 3]

[0091]

[0092] (Formula 5)

[0093] As shown in Formula 5, (H 0a -H 0b ) becomes 0, no response. In addition, it can be seen that in (H 2a -H 2b ) is different from the conventional N-pass filter (described later). Fig. 7A The N-pass filter 500 shown in FIG. 2a -H 2b ) compared to the unwanted mode, it can suppress 20dB (20log 10 ((0.0200-j0.1990) / 2)).

[0094] In addition, for example, the following case is exemplified. Figure 3A In the N-pass filter 1A according to the first modification shown in FIG. 2a +H 2b ) is set as the master mode, and the adjacent (H 1a +H 1b ) and (H 3a +H 3b ) is set to disabled mode.

[0095] In this case, the range of the phase difference is preferably 176.174° or more and 183.826° or less. It can be seen that in Formula 4, if π is replaced with 180±3.826 (176.174° or more and 183.826° or less), then (H 1a +H 1b ) is different from the conventional N-pass filter (described later). Fig. 7A The N-pass filter 500 shown in FIG. 1a +H 1b ) can suppress 29.5dB. 3a +H 3b ) is different from the conventional N-pass filter (described later). Fig. 7A The N-pass filter 500 shown in FIG. 1a +H 1b ) compared to the unwanted mode, it can suppress 20dB.

[0096] Here, the suppression level of 20 dB is equivalent to the minimum attenuation required for the receiving filter and the transmitting filter applied to the high frequency region above 500 MHz. If the attenuation of the transmitting filter and the receiving filter can be ensured to be above 20 dB, the signal leakage from the transmitting circuit to the receiving circuit can be reduced to below -40 dB by combining a circulator or a cancellation circuit with the transmitting filter and the receiving filter, and the degradation of the receiving sensitivity caused by the signal leakage can be reduced to an allowable value.

[0097] In the N-pass filter 1 according to the embodiment and the N-pass filter 1A according to the modification 1, in order to suppress the phase difference from shifting from the opposite phase, for example, a phase shift rotation circuit may be connected to the signal terminals 110 and 120. The phase shift rotation circuit may have a structure in which one end is connected to the signal terminal 110 or 120, the other end is grounded, a plurality of capacitors are connected in parallel to the one end and the other end, and a specific capacitor is connected by a switch.

[0098] [2. Circuit Configuration of N-pass Filters 1B and 1C]

[0099] Figure 3B This is a circuit structure diagram of an N-pass filter 1B involved in a variation 2 of the embodiment. As shown in the figure, the N-pass filter 1B includes basic filters 51 to 5N (N is an integer greater than or equal to 3), basic filters 61 to 6N, switches 11 to 1N, switches 21 to 2N, switches 31 to 3N and switches 41 to 4N, and a signal terminal 110 (first signal terminal), a signal terminal 120 (second signal terminal) and a signal terminal 130 (third signal terminal). The N-pass filter 1B involved in this variation is different from the N-pass filter 1 involved in the embodiment in that basic filters 61 to 6N and switches 21 to 2N are added. The following description of the N-pass filter 1B involved in this variation is centered on the structure that is different from the N-pass filter 1 involved in the embodiment. In addition, although in Figure 3B The signal output terminal 140 is not shown in the figure, but it can also be Figure 1 The signal terminal 120 and the signal terminal 130 are connected in the same manner. In addition, the structure may be as follows Figure 3A In this manner, the signal terminals 120 and 130 and the signal output terminal 140 are connected via the balun transformer 70 .

[0100] The N-pass filter 1B includes N first signal paths including signal paths P11, P12, and P1N, and the signal paths P11 to P1N are connected in parallel to each other between the signal terminal 110 and the signal terminal 120. In addition, the N-pass filter 1B includes N second signal paths including signal paths P21, P22, and P2N. The signal path P21 is a path connecting the node x1 on the signal path P11 and the signal terminal 130, the signal path P22 is a path connecting the node x1 on the signal path P12 and the signal terminal 130, and the signal path P2N is a path connecting the node x1 on the signal path P1N and the signal terminal 130. In other words, the N second signal paths are paths connecting nodes on the first signal path and the signal terminal 130.

[0101] The switch 21 is connected to the signal terminal 110 and the basic filter 61. The switch 21 switches between connection and disconnection between the signal terminal 110 and the basic filter 61 by turning on and off according to a drive signal s21 based on a drive frequency Fck.

[0102] The switch 41 is an example of a third switch, and is connected to the signal terminal 130 and the basic filter 61. The switch 41 switches between connection and disconnection between the signal terminal 130 and the basic filter 61 by turning on and off according to a drive signal s41 based on the drive frequency Fck.

[0103] The basic filter 61 is connected between the switches 21 and 41 .

[0104] The switch 22 is connected to the signal terminal 110 and the basic filter 62. The switch 22 switches between connection and disconnection between the signal terminal 110 and the basic filter 62 by turning on and off according to a drive signal s22 based on a drive frequency Fck.

[0105] The switch 42 is an example of a third switch, and is connected to the signal terminal 130 and the basic filter 62. The switch 42 switches between connection and disconnection between the signal terminal 130 and the basic filter 62 by turning on and off according to a drive signal s42 based on the drive frequency Fck.

[0106] The basic filter 62 is connected between the switches 22 and 42 .

[0107] The switch 2N is connected to the signal terminal 110 and the basic filter 6N. The switch 2N performs an on-off operation according to a drive signal s2N based on the drive frequency Fck, thereby switching between connection and disconnection between the signal terminal 110 and the basic filter 6N.

[0108] The switch 4N is an example of a third switch, and is connected to the signal terminal 130 and the basic filter 6N. The switch 4N switches between connection and disconnection between the signal terminal 130 and the basic filter 6N by turning on and off according to a drive signal s4N based on the drive frequency Fck.

[0109] The basic filter 6N is connected between the switches 2N and 4N.

[0110] The basic filter 51, the switches 11 and 31 form a signal path P11. The basic filter 52, the switches 12 and 32 form a signal path P12. The basic filter 5N, the switches 1N and 3N form a signal path P1N.

[0111] Furthermore, the basic filter 61, the switches 21 and 41 form a signal path P21. The basic filter 62, the switches 22 and 42 form a signal path P22. The basic filter 6N, the switches 2N and 4N form a signal path P2N.

[0112] Each of the basic filters 61 to 6N includes a series arm element having a reactance component (impedance having an imaginary part).

[0113] In the N-pass filter 1B involved in this variation, for example, if N=8, and the phase difference between the drive signal sN and the drive signal s3N and the phase difference between the drive signal s2N and the drive signal s4N are respectively set to α, then the phase relationship between the drive signals can be expressed by Formula 6.

[0114] The phase of the driving signal sN = (N-1) × 2π / 8

[0115] The phase of the driving signal s2N = (N-1) × 2π / 8

[0116] The phase of the driving signal s3N = (N-1) × 2π / 8 + α

[0117] The phase of the driving signal s4N = (N-1) × 2π / 8 + α + π (Equation 6)

[0118] Figure 3CThis is a circuit structure diagram of an N-pass filter 1C involved in a variant example 3 of the embodiment. As shown in the figure, the N-pass filter 1C includes basic filters 51 to 5N (N is an integer greater than 3), basic filters 61 to 6N, switches 11 to 1N, switches 31 to 3N and switches 41 to 4N, and a signal terminal 110 (first signal terminal), a signal terminal 120 (second signal terminal) and a signal terminal 130 (third signal terminal). The N-pass filter 1C involved in this variant example is different from the N-pass filter 1 involved in the embodiment in that basic filters 61 to 6N are added. The following description of the N-pass filter 1C involved in this variant example focuses on the structure that is different from the N-pass filter 1 involved in the embodiment. In addition, although in Figure 3C The signal output terminal 140 is not shown in the figure, but it can also be Figure 1 The signal terminal 120 and the signal terminal 130 are connected in the same manner. In addition, the structure may be as follows Figure 3A In this manner, the signal terminals 120 and 130 and the signal output terminal 140 are connected via the balun transformer 70 .

[0119] The N-pass filter 1C includes N first signal paths including signal paths P11, P12, and P1N, and the signal paths P11 to P1N are connected in parallel to each other between the signal terminal 110 and the signal terminal 120. In addition, the N-pass filter 1C includes N second signal paths including signal paths P21, P22, and P2N. The signal path P21 is a path connecting the node x1 on the signal path P11 and the signal terminal 130, the signal path P22 is a path connecting the node x2 on the signal path P12 and the signal terminal 130, and the signal path P2N is a path connecting the node xN on the signal path P1N and the signal terminal 130. In other words, the N second signal paths are paths connecting the nodes on the first signal path and the signal terminal 130.

[0120] The switch 41 is an example of a third switch, and is connected to the signal terminal 130 and the basic filter 61. The switch 41 switches between connection and disconnection between the signal terminal 130 and the basic filter 61 by turning on and off according to a drive signal s41 based on the drive frequency Fck.

[0121] The basic filter 61 is connected between the switches 11 and 41 .

[0122] The switch 42 is an example of a third switch, and is connected to the signal terminal 130 and the basic filter 62. The switch 42 switches between connection and disconnection between the signal terminal 130 and the basic filter 62 by turning on and off according to a drive signal s42 based on the drive frequency Fck.

[0123] The basic filter 62 is connected between the switches 12 and 42 .

[0124] The switch 4N is an example of a third switch, and is connected to the signal terminal 130 and the basic filter 6N. The switch 4N switches between connection and disconnection between the signal terminal 130 and the basic filter 6N by turning on and off according to a drive signal s4N based on the drive frequency Fck.

[0125] The basic filter 6N is connected between switches 1N and 4N.

[0126] The basic filter 51, the switches 11 and 31 form a signal path P11. The basic filter 52, the switches 12 and 32 form a signal path P12. The basic filter 5N, the switches 1N and 3N form a signal path P1N.

[0127] Furthermore, the basic filter 61 and the switch 41 form a signal path P21. The basic filter 62 and the switch 42 form a signal path P22. The basic filter 6N and the switch 4N form a signal path P2N.

[0128] Each of the basic filters 61 to 6N includes a series arm element having a reactance component (impedance having an imaginary part).

[0129] In the N-pass filter 1C according to the present modification, for example, if N=8 and the phase difference between the drive signal sN and the drive signal s3N is α, the phase relationship between the drive signals can be expressed by Equation 1.

[0130] [3. Basic filter circuit structure and pass characteristics]

[0131] Figure 4A is a diagram showing an example of a circuit configuration of a basic filter 51 according to an embodiment. Figure 4A , an example of a circuit configuration of the basic filter 51 among the basic filters 51 to 5N is shown. The circuit configurations of the basic filters 52 to 5N are similar to those of Figure 4A The circuit structure of the basic filter 51 shown is the same.

[0132] like Figure 4A As shown, the basic filter 51 includes elastic wave resonators 511 , 512 , 513 , 514 , and 515 .

[0133] Elastic wave resonators 511 and 512 are series arm resonators connected in series between terminals 111 and 112. Elastic wave resonator 513 is a parallel arm resonator connected between terminal 111 and ground. Elastic wave resonator 515 is a parallel arm resonator connected between terminal 112 and ground. Elastic wave resonator 514 is a parallel arm resonator connected between a node on a path connecting elastic wave resonators 511 and 512 and ground.

[0134] Each of elastic wave resonators 511 and 512 is composed of three split resonators connected in series, and elastic wave resonator 514 is composed of two split resonators connected in parallel.

[0135] Each of the elastic wave resonators 511 and 512 is a series arm element having a reactance component (impedance having an imaginary part).

[0136] According to the above structure, Figure 4A The basic filter 51 shown is a ladder-type elastic wave bandpass filter. In the basic filters 51 to 5N involved in this embodiment, the elastic wave resonators 511 to 515 are resonators using surface acoustic waves, and as a substrate having piezoelectricity, for example, a -4° Y-cut X-propagation LiNbO3 single crystal substrate (hereinafter referred to as LN) is used. The resonant frequencies of the elastic wave resonators 511 and 512 are set to be higher than the resonant frequencies of the elastic wave resonators 513 to 514. In addition, in the N-pass filter 1, N=8 is set, and the termination impedance at the terminal 111 (signal terminal 110 side) of the basic filters 51 to 5N is designed to be 400Ω.

[0137] In the N-pass filter 1 , when the termination impedance at the signal terminal 110 is Z0 and the input and output impedances of the basic filters 51 to 5N are Zb, the reflection coefficient (Zb−N×Z0) / (Zb+N×Z0) preferably satisfies the relationship of Expression 7.

[0138] (Zb-N×Z0) / (Zb+N×Z0)<0.316 (Formula 7)

[0139] In the N-pass filter 1 , the termination impedance at the terminal 111 (signal terminal 110 side) of the basic filters 51 to 5N is designed to be 400Ω. If Z0=50Ω, Zb=400Ω, and N=8 are substituted into Formula 7, the reflection coefficient becomes 0 ideally.

[0140] In addition, if the impedance of the N-pass filter 1 on the signal terminal 110 side viewed from the signal terminal 120 is set to Z1, and the impedance of the N-pass filter 1 on the signal terminal 110 side viewed from the signal terminal 130 is set to Z2 (= Z1), then by setting the input and output impedance Zb1 of the terminal 112 (signal terminal 120 side) of the basic filter 51 to 5N to Z1×N / 2, and setting the input and output impedance Zb2 of the terminal 112 (signal terminal 130 side) of the basic filter 51 to 5N to Z2×N / 2, impedance matching at the signal terminals 120 and 130 can be achieved.

[0141] According to the N-pass filter 1 of the present embodiment, the reflection loss at the signal terminals 110, 120, and 130 can be reduced to less than 10 dB, thereby suppressing the mismatch loss with the external connection circuit connected to the signal terminals 110, 120, and 130. 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.

[0142] In the N-pass filter 1B according to the modification 2 and the N-pass filter 1C according to the modification 3, the number of basic filters is doubled compared to the N-pass filter 1 according to the embodiment. Therefore, the termination impedance of each basic filter at the signal terminal 110 is twice the input and output impedance Zb of the basic filters 51 to 5N of the N-pass filter 1.

[0143] Figure 4B : is a graph showing an example of the pass characteristic of the basic filter 51 alone according to the embodiment. As shown in the figure, the basic filter 51 is a bandpass filter having a center frequency of 305 MHz and a bandwidth of 10 MHz.

[0144] In addition, regarding the basic filters 51 to 5N, in addition to Figure 4A In addition to the elastic wave filter shown, a filter including an inductor and a capacitor (so-called LC filter) or a filter including a dielectric resonator (so-called dielectric filter) can also be applied. By applying an elastic wave filter, an LC filter, or a dielectric filter as a basic filter, an N-pass filter 1 can be configured in which a flat and low-loss passband frequency can be changed at the drive frequency Fck of each switch.

[0145] [4. Pass characteristics of N-pass filter]

[0146] Figure 5 1 is a graph showing the pass characteristics of the N-pass filter 1 according to the embodiment. Figure 1 In the N-pass filter 1 shown in FIG. 1 , the driving frequency Fck is set to 1020 MHz, and the basic filter is applied. Figure 4AThe SAW filter shown in the figure (center frequency Fb: 305MHz) is assumed to have N=8. Figure 5 In (a), the amplitude characteristics between the signal terminals 110 and 120 (solid line) and the amplitude characteristics between the signal terminals 110 and 130 (dashed line) are shown. Figure 5 (b) shows the phase characteristic (solid line) between the signal terminals 110 and 120 for the input signal and the phase characteristic (dashed line) between the signal terminals 110 and 130 for the input signal.

[0147] exist Figure 5 In the case of k=0 (even number), the response of 305MHz (=0×Fck+Fb) becomes the same amplitude and the same phase, and the response of 715MHz (=1×Fck-Fb) becomes the same amplitude and the opposite phase when k=1 (odd number). Figure 5 In (b), the phase between the signal terminals 110 and 120 at 715 MHz is -1229.8°, and the phase between the signal terminals 110 and 130 at 715 MHz is -1049.9°.

[0148] Therefore, according to Figure 1 In the circuit structure of the N-pass filter 1 shown in FIG. 1 , the signal of the signal terminal 120 and the signal of the signal terminal 130 are connected, so that the mode where k is an odd multiple can be suppressed. Figure 3A The circuit configuration of the N-pass filter 1A shown can suppress a mode in which k is an even multiple by subtracting the signal at the signal terminal 130 from the signal at the signal terminal 120 .

[0149] Fig. 6A 1 is a graph showing the pass characteristics of the N-pass filter 1A according to Modification 1. In the same figure, the characteristics in the case where Figure 3A In the N-pass filter 1A shown in FIG. 1 , the driving frequency Fck is set to 1020 MHz, and the basic filter is applied. Figure 4A The surface acoustic wave filter shown in the figure (center frequency Fb: 305MHz), assume N=8. Fig. 6A As shown, in the N-pass filter 1A that can suppress modes in which k is an even multiple, the response modes of (0×Fck+Fb), (2×Fck±Fb), and (4×Fck±Fb) can be suppressed, and the response modes in which k is an odd multiple of (1×Fck±Fb), (3×Fck±Fb), and (5×Fck±Fb) are generated.

[0150] Figure 6BGraphs showing the pass characteristics of the N-pass filter 1A according to Modification Example 1 and the N-pass filter 500 according to the Comparative Example in the vicinity of the main response mode. In addition, the circuit configuration and the wideband pass characteristics of the N-pass filter 500 according to the Comparative Example will be described in detail. Fig. 7A as well as Figure 7B Shown in.

[0151] Fig. 7A : is a circuit diagram of an N-pass filter 500 according to a comparative example. Figure 7B Graph showing the pass characteristics of an N-pass filter 500 according to a comparative example. The N-pass filter 500 includes basic filters 51 to 5N (N is an integer greater than or equal to 3), switches 21 to 2N and switches 31 to 3N, and signal terminals 110 and 120. The N-pass filter 500 according to the comparative example is different from the N-pass filter 1 according to the embodiment in that the switches 21 to 2N and the switches 31 to 3N are turned on and off at the same timing, and the switches 41 to 4N are not added. The N-pass filter 500 according to the comparative example will be described below, centering on the structure that is different from the N-pass filter 1 according to the embodiment.

[0152] The switch 21 is connected to the signal terminal 110 and the basic filter 51. The switch 21 switches between connection and disconnection between the signal terminal 110 and the basic filter 51 by turning on and off according to the drive signal s1 based on the drive frequency Fck.

[0153] The switch 31 is connected to the signal terminal 120 and the basic filter 51. The switch 31 switches between connection and disconnection between the signal terminal 120 and the basic filter 51 by turning on and off at the same timing as the switch 21 according to the drive signal s1 based on the drive frequency Fck.

[0154] The switch 22 is connected to the signal terminal 110 and the basic filter 52. The switch 22 switches between connection and disconnection between the signal terminal 110 and the basic filter 52 by turning on and off according to the drive signal s2 based on the drive frequency Fck.

[0155] The switch 32 is connected to the signal terminal 120 and the basic filter 52. The switch 32 is turned on and off 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 signal terminal 120 and the basic filter 52.

[0156] The switch 2N is connected to the signal terminal 110 and the basic filter 5N. The switch 2N switches between connection and disconnection between the signal terminal 110 and the basic filter 5N by turning on and off according to the drive signal sN based on the drive frequency Fck.

[0157] The switch 3N is connected to the signal terminal 120 and the basic filter 5N. 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 signal terminal 120 and the basic filter 5N.

[0158] The basic filter 51, the switches 21 and 31 form a signal path P1. The basic filter 52, the switches 22 and 32 form a signal path P2. The basic filter 5N, the switches 2N and 3N form a signal path PN.

[0159] The N-pass filter 500 generates drive signals s1 to sN for driving switches 21 to 2N and switches 31 to 3N based on the 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 a period of T / N, and are sequentially turned on with a delay of T / N. Thus, switches 21 to 2N are turned on at different timings for each signal path in the period T. In addition, switches 31 to 3N are turned on at different timings for each signal path in the period T. That is, the basic filters 51 to 5N are connected to the signal terminals 110 and 120 at different timings for each signal path in the period T.

[0160] According to the above configuration, the N-pass filter 1 becomes a band-pass filter having a center frequency Frf defined by equation (2).

[0161] According to Formula 2, the N-pass filter 500 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 500 have a plurality of passbands (and a plurality of attenuation bands) corresponding to the value of k.

[0162] like Figure 7B As shown, in the N-pass filter 500 according to the comparative example, each response mode of (k·Fck±Fb) defined by Expression 2 occurs.

[0163] In addition, if Figure 6B As shown, the N-pass filter 1A according to the modification example 1 which suppresses the unwanted response can reduce the insertion loss in the passband in the main response mode (Fck-Fb) and increase the attenuation near the passband, compared with the N-pass filter 500 according to the comparative example which does not suppress the unwanted response.

[0164] [5. Frequency variable range of main response mode]

[0165] In the N-pass filter 1 (including the N-pass filter 1A) 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.

[0166] Hereinafter, the frequency variable range of the main response mode when a low-pass filter is applied as a basic filter and the frequency variable range of the main response mode when a band-pass filter is applied as a basic filter will be described.

[0167] Fig. 8A Graphs showing various response modes when the basic filters of N-pass filters 1 and 1A are low-pass filters. Fig. 8A In FIG. 1 , the relationship of Formula 2 is shown when the response mode is not suppressed. In addition, when the basic filter is a low-pass filter, Fb=0. Fig. 8A The horizontal axis represents Fck (=Fck / β) normalized by a constant β (>0), and the vertical axis represents Frf (=Frf / β) normalized by a constant β. As shown in the figure, by making the drive frequency Fck variable, the center frequency Frf of the N-pass filters 1 and 1A can be made variable. For example, when (1×Fck) is used as the main response mode, the variable frequency range of the center frequency Frf that does not generate an unnecessary response mode at the lower end of the variable frequency is greater than β and less than 2β when β≤Fck≤2β, for example, 0.5 GHz to 1 GHz. In addition, when (2×Fck) is used as the main response mode, the variable frequency range of the center frequency Frf that does not generate an unnecessary response mode at the lower end of the variable frequency is greater than 2β and less than 3β when β≤Fck≤1.5β.

[0168] Figure 8B Graph showing the frequency variable range when the main response mode is (1×Fck) in the case where the base filter of the N-pass filter 1A involved in the modification example 1 is a low-pass filter. In the N-pass filter 1A involved in the modification example 1, the response mode where k is an even multiple can be suppressed, so the number of useless response modes can be reduced. For example, when (1×Fck) is used as the main response mode, the (0×Fck) and (2×Fck) modes can be suppressed. Therefore, the variable frequency range of the center frequency Frf where no useless response mode is generated at the lower end of the variable frequency is greater than β and less than 3β when β≤Fck≤3β, for example, 0.5 GHz to 1.5 GHz, which is different from the case where the response mode where k is an even multiple is not suppressed. Fig. 8A Compared with the case of , a frequency variable width twice as large can be obtained.

[0169] Figure 8CIt is a graph showing the frequency variable range in which the main response mode is (2×Fck) when the basic filter of the N-way filter 1 involved in the embodiment is a low-pass filter. In the N-way filter 1 involved in the embodiment, the response modes with k being an odd multiple can be suppressed, so the number of useless response modes can be reduced. For example, when using (2×Fck) as the main response mode, the (1×Fck) and (3×Fck) modes can be suppressed. Therefore, the variable frequency range of the center frequency Frf where no useless response mode is generated at the lower end of the variable frequency is 2β or more and 4β or less when β≤Fck≤2β, and compared with the case where the response modes with k being an odd multiple are not suppressed, Fig. 8A a frequency variable width twice as large can be obtained.

[0170] Fig. 9A It is a graph showing each response mode when the basic filters of the N-way filters 1 and 1A are band-pass filters. In Fig. 9A it, the relationship of Equation 2 in the case where the response mode is not suppressed is shown. Fig. 9A The horizontal axis of it represents Fck (=Fck / Fb) normalized by the center frequency Fb of the basic filter, and the vertical axis represents Frf (=Frf / Fb) normalized by the center frequency Fb. As shown in the figure, by varying the drive frequency Fck, the center frequencies Frf of the N-way filters 1 and 1A can be varied. For example, when using (1×Fck+Fb) as the main response mode, the frequency range of the drive frequency Fck where no useless response mode is generated at the lower end and the upper end of the variable frequency becomes as shown in Equation 8.

[0171] Fck>2Fb, and,

[0172] Fck_max+Fb<2Fck_min-Fb, and,

[0173] Fck_max-Fb<Fck_min+Fb (Equation 8)

[0174] In addition, for example, when using (1×Fck-Fb) as the main response mode, the frequency range of the drive frequency Fck where no useless response mode is generated at the lower end and the upper end of the variable frequency becomes as shown in Equation 9.

[0175] Fck_min+Fb>Fck_max-Fb, and, Fck>2Fb

[0176] Or,

[0177] 1Fb<Fck<2Fb (Equation 9)

[0178] In addition, Fck_min is the driving frequency of the switch at the lower limit of the frequency variable range of the main response mode, and Fck_max is the driving frequency of the switch at the upper limit of the frequency variable range of the main response mode.

[0179] Fig. 9B It is a graph showing the frequency variable ranges of the main response modes (1×Fck - Fb) and (1×Fck + Fb) when the basic filter of the N-path filter 1A related to Modification 1 is a band-pass filter. In the N-path filter 1A related to Modification 1, response modes with k being an even multiple can be suppressed. Therefore, for example, when using (1×Fck - Fb) as the main response mode, the (0×Fck + Fb) mode can be suppressed. Thus, the frequency range of the driving frequency Fck where no unwanted response modes are generated at the lower and upper ends of the variable frequency becomes as shown in Equation 10.

[0180] Fck > Fb, and,

[0181] Fck_max < 2Fck_min + 2Fb (Equation 10)

[0182] That is to say, by suppressing response modes with k being an even multiple, the number of unwanted response modes can be reduced. Compared with the case where response modes are not suppressed Fig. 9A and the frequency range defined by Equation 9, the frequency variable range of the center frequency Frf of the N-path filter 1A can be widened.

[0183] In addition, for example, when using (1×Fck + Fb) as the main response mode, the (0×Fck + Fb) and (2×Fck - Fb) modes can be suppressed. Therefore, the frequency range of the driving frequency Fck where no unwanted response modes are generated at the lower and upper ends of the variable frequency becomes as shown in Equation 11.

[0184] Fck > Fb, and,

[0185] 2Fck_min - Fb < Fck_max + Fb, and,

[0186] Fck_min + Fb < Fck_max - Fb (Equation 11)

[0187] That is to say, by suppressing response modes with k being an even multiple, the number of unwanted response modes can be reduced. Compared with the case where response modes are not suppressed Fig. 9A and the frequency range defined by Equation 8, the frequency variable range of the center frequency Frf of the N-path filter 1A can be widened.

[0188] Fig. 9C1 is a graph showing a frequency variable range in which the main response modes are (2×Fck-Fb) and (2×Fck+Fb) when the base filter of the N-pass filter 1 according to the embodiment is a bandpass filter. In the N-pass filter 1 according to the embodiment, it is possible to suppress the response mode in which k is an odd multiple, so for example, when (2×Fck-Fb) is used as the main response mode, the (1×Fck+Fb) mode can be suppressed. Therefore, the frequency range of the driving frequency Fck in which the unnecessary response mode does not occur at the lower end and the upper end of the variable frequency becomes as shown in Formula 12.

[0189] 0.5×Fb <Fck<Fb

[0190] or,

[0191] Fck>Fb, and 2Fck_min+Fb>2Fck_max-Fb (Equation 12)

[0192] That is, by suppressing the response modes that are odd multiples of k, the number of useless response modes can be reduced, which is equivalent to not suppressing the response modes. Fig. 9A The frequency variable range of the center frequency Frf of the N-pass filter 1 can be widened compared with the predetermined frequency range.

[0193] In addition, for example, when (2×Fck+Fb) is used as the main response mode, the (3×Fck+Fb) and (1×Fck-Fb) modes can be suppressed, so the frequency range of the driving frequency Fck that does not generate the unnecessary response mode at the lower end and the upper end of the variable frequency becomes as shown in Formula 13.

[0194] Fck>Fb, and 4Fck_min-Fb>2Fck_max+Fb (Equation 13)

[0195] That is, by suppressing the response modes that are odd multiples of k, the number of useless response modes can be reduced, which is equivalent to not suppressing the response modes. Fig. 9A The frequency variable range of the center frequency Frf of the N-pass filter 1 can be widened compared with the predetermined frequency range.

[0196] [6. Circuit Configuration of High-Frequency Module 5 and Communication Device 10 According to Embodiment]

[0197] Fig.10 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 .

[0198] 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.

[0199] 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.

[0200] In addition, in the communication device 10 according to the present embodiment, the antenna 7 is not an essential component.

[0201] Next, the circuit structure of the high frequency module 5 is described. Fig.10 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 .

[0202] 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.

[0203] The N-pass filter 1 is any one of the N-pass filter 1 of the embodiment, the N-pass filter 1A of the modification 1, the N-pass filter 1B of the modification 2, and the N-pass filter 1C of the modification 3, and is a reception filter 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, s21 to s2N, s31 to s3N, and s41 to s4N output from the RFIC 6. Thus, the N-pass filter 1 can selectively pass high-frequency signals of multiple frequency bands.

[0204] The N-pass filter 2 is any one of the N-pass filter 1 of the embodiment, the N-pass filter 1A of the modification 1, the N-pass filter 1B of the modification 2, and the N-pass filter 1C of the modification 3, 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, s21 to s2N, s31 to s3N, and s41 to s4N output from the RFIC 6. Thus, the N-pass filter 2 can selectively pass high-frequency signals of multiple frequency bands.

[0205] In addition, the driving circuit that outputs driving signals s1 to sN, s21 to s2N, s31 to s3N and s41 to s4N can be included in the control unit of RFIC6, and can also be included in the high-frequency module 5. In addition, it can also be configured independently from the high-frequency module 5 and RFIC6 as a semiconductor IC (Integrated Circuit).

[0206] 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 .

[0207] 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 .

[0208] 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.

[0209] In addition, the high frequency module 5 and the communication device 10 may also include Fig.10 In addition to the circuit elements shown, impedance matching elements, switches, etc. are also included.

[0210] 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.

[0211] (Other Implementations)

[0212] 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.

[0213] 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.

[0214] The following describes the characteristics of the N-pass filter described in the above-mentioned embodiments.

[0215] <1>

[0216] An N-pass filter having:

[0217] A first signal terminal, a second signal terminal, and a third signal terminal;

[0218] N (N is an integer greater than or equal to 3) first signal paths connected in parallel to each other between the first signal terminal and the second signal terminal; and

[0219] The N second signal paths,

[0220] The N first signal paths respectively have:

[0221] a first modulator connected to the first signal terminal and modulating an input signal input from the first signal terminal or the second signal terminal;

[0222] a second modulator connected to the second signal terminal and modulating the input signal; and

[0223] A basic filter connected between the first modulator and the second modulator,

[0224] The N second signal paths are paths connecting nodes on the first signal path and the third signal terminal, respectively, and have a third modulator connected to the third signal terminal and modulating an input signal input from the first signal terminal or the third signal terminal.

[0225] The basic filter comprises series arm elements having a reactive component,

[0226] The first modulator and the second modulator are each driven by a drive signal that modulates the input signal with a phase that becomes one period T in the N first signal paths.

[0227] The third modulator is driven by a drive signal that modulates the input signal with a phase that becomes one period T in the N second signal paths.

[0228] When the passband frequency of the basic filter is set to Fb, at a frequency of (1 / T+Fb), the phase of the drive signal driving the second modulator and the phase of the drive signal driving the third modulator are opposite to each other.

[0229] <2>

[0230] according to <1> The N-pass filter, wherein

[0231] At a frequency of (1 / T+Fb), a difference between a phase of a driving signal driving the second modulator and a phase of a driving signal driving the third modulator is greater than or equal to 174.261° and less than or equal to 185.739°.

[0232] <3>

[0233] according to <1> or <2> The N-pass filter, wherein

[0234] The first modulator is a first switch that switches connection and disconnection between the first signal terminal and the basic filter according to a driving signal.

[0235] The second modulator is a second switch that switches connection and disconnection between the second signal terminal and the basic filter according to a driving signal.

[0236] The third modulator is a third switch that switches connection and disconnection between the third signal terminal and the basic filter according to a drive signal.

[0237] <4>

[0238] according to <1> ~ <3> An N-pass filter as described in any one of claims 1 to 5, wherein

[0239] It also has a signal input terminal and a signal output terminal.

[0240] The signal input terminal is the first signal terminal,

[0241] The signal output terminal is a terminal to which the second signal terminal and the third signal terminal are connected.

[0242] <5>

[0243] according to <1> ~ <3> An N-pass filter as described in any one of claims 1 to 5, wherein

[0244] Also available:

[0245] signal input terminals and signal output terminals; and

[0246] A balanced-unbalanced transformation element has two balanced terminals and one unbalanced terminal.

[0247] The signal input terminal is the first signal terminal,

[0248] One of the two balanced terminals is connected to the second signal terminal.

[0249] The other of the two balanced terminals is connected to the third signal terminal.

[0250] The signal output terminal is connected to the unbalanced terminal.

[0251] <6>

[0252] according to <1> ~ <5> An N-pass filter as described in any one of claims 1 to 5, wherein

[0253] The basic filter is any one of an elastic wave filter, a filter including an inductor and a capacitor, and a filter including a dielectric resonator.

[0254] <7>

[0255] according to <1> ~ <6> An N-pass filter as described in any one of claims 1 to 5, wherein

[0256] The termination impedance at the first signal terminal of the N-pass filter is set to Z0,

[0257] The input and output impedance of the first signal terminal of the basic filter is assumed to be Zb. In this case, the following relationship is satisfied:

[0258] (Zb-N×Z0) / (Zb+N×Z0)<0.316.

[0259] Industrial Applicability

[0260] 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.

[0261] Description of Reference Numerals

[0262] 1, 2, 1A, 1B, 1C, 500: N-pass filter;

[0263] 3: Low noise amplifier;

[0264] 4: Power amplifier;

[0265] 5: High frequency module;

[0266] 6: RF signal processing circuit (RFIC);

[0267] 7: Antenna;

[0268] 10: Communication device;

[0269] 11, 12, 1N, 21, 22, 2N, 31, 32, 3N, 41, 42, 4N: switch;

[0270] 51, 52, 5N, 61, 62, 6N: basic filters;

[0271] 70: Balanced-unbalanced transformer;

[0272] 100: Antenna connection terminal;

[0273] 101: High frequency input terminal;

[0274] 102: high frequency output terminal;

[0275] 110, 120, 130: signal terminal;

[0276] 111, 112: terminal;

[0277] 140: signal output terminal;

[0278] 511, 512, 513, 514, 515: elastic wave resonator;

[0279] P1, P2, PN, P11, P12, P1N, P21, P22, P2N, P41, P42, P4N: signal path;

[0280] s1, s2, sN, s21, s22, s2N, s31, s32, s3N, s41, s42, s4N: driving signals;

[0281] x1, x2, xN: nodes.

Claims

1. An N-pass filter, comprising: A first signal terminal, a second signal terminal, and a third signal terminal; N first signal paths are connected in parallel with each other between the first signal terminal and the second signal terminal, wherein: N is an integer greater than 3; and The N second signal paths, The N first signal paths respectively have: a first modulator connected to the first signal terminal and modulating an input signal input from the first signal terminal or the second signal terminal; a second modulator connected to the second signal terminal and modulating the input signal; and A basic filter connected between the first modulator and the second modulator, The N second signal paths are paths connecting nodes on the first signal path and the third signal terminal, respectively, and have a third modulator connected to the third signal terminal and modulating an input signal input from the first signal terminal or the third signal terminal. The basic filter comprises series arm elements having a reactive component, The first modulator and the second modulator are each driven by a drive signal that modulates the input signal with a phase that becomes one period T in the N first signal paths. The third modulator is driven by a drive signal that modulates the input signal with a phase that becomes one period T in the N second signal paths. The phase of the driving signal for driving the second modulator and the phase of the driving signal for driving the third modulator are opposite to each other.

2. The N-pass filter according to claim 1, wherein: A difference between a phase of a driving signal for driving the second modulator and a phase of a driving signal for driving the third modulator is greater than or equal to 174.261° and less than or equal to 185.739°.

3. The N-pass filter according to claim 1 or 2, wherein: The first modulator is a first switch that switches connection and disconnection between the first signal terminal and the basic filter according to a driving signal. The second modulator is a second switch that switches connection and disconnection between the second signal terminal and the basic filter according to a driving signal. The third modulator is a third switch that switches connection and disconnection between the third signal terminal and the basic filter according to a drive signal.

4. The N-pass filter according to any one of claims 1 to 3, wherein: It also has a signal input terminal and a signal output terminal. The signal input terminal is the first signal terminal, The signal output terminal is a terminal to which the second signal terminal and the third signal terminal are connected.

5. The N-pass filter according to any one of claims 1 to 3, wherein: Also available: signal input terminals and signal output terminals; and A balanced-unbalanced transformation element has two balanced terminals and one unbalanced terminal. The signal input terminal is the first signal terminal, One of the two balanced terminals is connected to the second signal terminal. The other of the two balanced terminals is connected to the third signal terminal. The signal output terminal is connected to the unbalanced terminal.

6. The N-pass filter according to any one of claims 1 to 5, wherein: The basic filter is any one of an elastic wave filter, a filter including an inductor and a capacitor, and a filter including a dielectric resonator.

7. The N-pass filter according to any one of claims 1 to 6, wherein: The termination impedance at the first signal terminal of the N-pass filter is set to Z0, The input and output impedance of the first signal terminal of the basic filter is assumed to be Zb. In this case, the following relationship is satisfied: (Zb-N×Z0) / (Zb+N×Z0)<0.316.

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