Filter device, multiplexer and communication device

Abstract

The present application relates to filter device, multiplexer and communication device, provide the filter device of multi-band response with wide band and low loss passband, wide band stopband and narrow band and steep stopband. The filter (1) has: input and output terminal (100, 110);LC parallel resonant circuit (10) has inductor (L1) and capacitor (C1) connected in parallel with each other;And elastic wave series resonant circuit, have series arm resonator (s1, s2) connected in series with each other, LC parallel resonant circuit (10) and elastic wave series resonant circuit are connected in series between input and output terminal (100) and input and output terminal (110).

Description

Technical Field

[0001] This invention relates to filter devices, multiplexers, and communication devices. Background Technology

[0002] In the progress of multi-band front-end circuitry in mobile terminals, there is a demand for filter devices with wide bandwidth and low loss passband and narrow bandwidth and steep stopband.

[0003] Patent Document 1 discloses a filter having two Surface Wave Resonators connected in series. The stopband of the filter is defined according to the anti-resonance frequency of the two Surface Wave Resonators.

[0004] Patent Document 1: Japanese Patent Application Publication No. 2012-156881

[0005] However, the filter described in Patent Document 1 is difficult to simultaneously possess a wide-bandwidth and low-loss passband that ensures isolation between multiple communication frequency bands with various bandwidths, a wide-bandwidth stopband, and a narrow-bandwidth and steep stopband. Summary of the Invention

[0006] Therefore, the object of the present invention is to provide a multi-band corresponding filter device, multiplexer, and communication device that has a wide bandwidth and low loss passband, a wide bandwidth stopband, and a narrow bandwidth and steep stopband.

[0007] To achieve the above objectives, a filter device according to one aspect of the present invention includes: a first input / output terminal and a second input / output terminal; an LC parallel resonant circuit having a first inductor and a first capacitor connected in parallel; and an elastic wave series resonant circuit having a first elastic wave resonator and a second elastic wave resonator connected in series, wherein the LC parallel resonant circuit and the elastic wave series resonant circuit are connected in series between the first input / output terminal and the second input / output terminal.

[0008] According to the present invention, a multi-band corresponding filter device, multiplexer, and communication device can be provided, which have a wide bandwidth and low loss passband, a wide bandwidth stopband, and a narrow bandwidth and steep stopband. Attached Figure Description

[0009] Figure 1A This is a circuit diagram of the filter device according to Embodiment 1.

[0010] Figure 1B This is a graph showing the throughput characteristics of the filter device in Embodiment 1.

[0011] Figure 2A This is a circuit structure diagram of the elastic wave series resonant circuit in Implementation Method 1.

[0012] Figure 2B This is a graph showing the pass-through characteristics and impedance characteristics of a single unit in the elastic wave series resonant circuit of Embodiment 1.

[0013] Figure 3A This is a circuit structure diagram of the LC parallel resonant circuit in Implementation Method 1 and a Smith chart representing the impedance characteristics.

[0014] Figure 3B This is the equivalent circuit diagram of two series arm resonators in the specified frequency band of the filter device of Embodiment 1.

[0015] Figure 3C This is a graph showing the pass characteristics of the filter device in Embodiment 1 and the impedance characteristics of the two series arm resonators.

[0016] Figure 4A This is a graph comparing the pass-through and reflection characteristics near the second stopband of the filter device and the elastic wave series resonant circuit unit of Embodiment 1.

[0017] Figure 4B This is a graph comparing the pass-through characteristics near the first stopband of the filter device of Embodiment 1 and the elastic wave series resonant circuit unit.

[0018] Figure 5A This is the circuit structure of the resonant circuit of Variation 1 of Embodiment 1 and a graph showing the impedance characteristics of the resonant circuit.

[0019] Figure 5B This is the circuit structure of the resonant circuit of Variation 2 of Embodiment 1, and a graph showing the impedance characteristics of the resonant circuit.

[0020] Figure 5C This is the circuit structure of the resonant circuit of Variation 3 of Embodiment 1, and a graph showing the impedance characteristics of the resonant circuit.

[0021] Figure 5D This is the circuit structure of the resonant circuit of Variation 4 of Embodiment 1, and a graph showing the impedance characteristics of the resonant circuit.

[0022] Figure 6A This is a circuit diagram of the filter device in Embodiment 2.

[0023] Figure 6B It is a graph showing the pass characteristics, parallel connection circuit, and series connection circuit impedance characteristics of the filter device in Embodiment 2.

[0024] Figure 6CIt is a graph showing the pass-through characteristics near the second stopband of the filter device of Embodiment 2, and the impedance characteristics near the second stopband of the parallel connection circuit and the series connection circuit.

[0025] Figure 7A This is the circuit structure diagram of the multiplexer in Implementation Method 3.

[0026] Figure 7B This is a detailed circuit diagram of the multiplexer in Implementation Method 3.

[0027] Figure 7C This is a graph showing the throughput characteristics of the multiplexer in Implementation 3.

[0028] Figure 8 This is a circuit diagram of the communication device according to embodiment 4.

[0029] Explanation of reference numerals in the attached diagram: 1, 2, 2A, 3, 3A, 4, 4A, 62, 63, 64… Filters; 5, 5A… Multiplexers; 6… RF signal processing circuit (RFIC); 7… Baseband signal processing circuit (BBIC); 8… Antenna; 9… Communication device; 10… LC parallel resonant circuit; 20… Parallel connection circuit; 30… Series connection circuit; 52, 54… Switches; 72, 73, 74… Low-noise amplifiers; 100, 110, 120, 130… Input / output terminals; C1, C2, C7, C9, C1 0, C21… Capacitor, fa1, fa2, fa3, fa6, fa7, fa8, fa9, fa20, fa30… ​​Anti-resonant frequency, fa21… Secondary anti-resonant frequency, fr1, fr2, fr3, fr6, fr7, fr8, fr9, fr20, fr30… Resonant frequency, L1, L2, L3, L6, L8, L11, L21, L22, L23… Inductor, p11, p12, p13… Parallel arm resonator, s1, s2, s11, s12, s13… Series arm resonator. Detailed Implementation

[0030] Hereinafter, embodiments, examples, and variations of the present invention will be described in detail with reference to the accompanying drawings. Furthermore, the embodiments, examples, and variations described below are general or specific examples. The numerical values, shapes, materials, structural elements, configurations of structural elements, and connection methods shown in the following embodiments, examples, and variations are illustrative and not intended to limit the scope of the present invention. Structural elements in the following embodiments, examples, and variations not described in the independent claims can be described as any structural element.

[0031] Furthermore, in this disclosure, "consisting of circuit elements" includes not only the case where only the circuit element is included, but also the case where other circuit elements are included in addition to the circuit element. In other words, "consisting of circuit elements" does not exclude the case where other circuit elements are included.

[0032] (Implementation Method 1)

[0033] [1.1 Circuit structure and high-frequency characteristics of filter 1]

[0034] Figure 1A This is a circuit diagram of filter 1 according to embodiment 1. Filter 1 is an example of a filter device, as shown in the figure, and includes input and output terminals 100 and 110, an LC parallel resonant circuit 10, and series arm resonators s1 and s2.

[0035] Input / output terminal 100 is an example of a first input / output terminal, which is a terminal for inputting or outputting a high-frequency signal to or from the outside. Input / output terminal 110 is an example of a second input / output terminal, which is a terminal for outputting or inputting a high-frequency signal to or from the outside.

[0036] The LC parallel resonant circuit 10 has an inductor L1 (first inductor) and a capacitor C1 (first capacitor) connected in parallel.

[0037] Series arm resonator S1 is an example of a first elastic wave resonator, which uses surface acoustic waves (SAW). Series arm resonator S2 is an example of a second elastic wave resonator, which also uses surface acoustic waves. Series arm resonators S1 and S2 are connected in series, forming an elastic wave series resonant circuit.

[0038] The LC parallel resonant circuit 10 and the elastic wave series resonant circuit are connected in series between the input and output terminals 100 and 110. In other words, the input and output terminals 100, LC parallel resonant circuit 10, elastic wave series resonant circuit and input and output terminals 110 are arranged sequentially on the series arm path connecting the input and output terminals 100 and 110.

[0039] Furthermore, the number of series arm resonators constituting an elastic wave series resonant circuit can also be more than three.

[0040] Furthermore, it is preferable that no other circuit components are connected at the connection node between the series arm resonator s1 and the series arm resonator s2; preferably, the series arm resonator s1 and the series arm resonator s2 are directly connected. Additionally, it is preferable that no other circuit components are connected at the connection node between the LC parallel resonant circuit 10 and the series arm resonator s1; preferably, the LC parallel resonant circuit 10 and the series arm resonator s1 are directly connected.

[0041] Figure 1B This is a graph showing the pass-through characteristics of filter 1 according to embodiment 1. The graph shows the pass-through characteristics of filter 1 between input / output terminal 100 and input / output terminal 110.

[0042] LC parallel resonant circuit 10 is formed Figure 1B The diagram shows a wideband, low-loss first passband including passband a and passband b, and a wideband first stopband corresponding to the LC parallel resonant frequency of inductor L1 and capacitor C1. In this embodiment, the LC parallel resonant circuit 10 constitutes a high-pass filter. Alternatively, the LC parallel resonant circuit 10 can also be any one of a low-pass filter, a band-pass filter, and a band-stop filter.

[0043] On the other hand, the elastic wave series resonant circuit forms a narrow and steep second stopband corresponding to the anti-resonance frequency fa1 of the series arm resonator s1 and the anti-resonance frequency fa2 of the series arm resonator s2. Furthermore, the second stopband is included within the frequency range of the first passband.

[0044] Based on the above structure of filter 1, a multi-band filter device can be provided that combines a wide bandwidth and low loss passband, a wide bandwidth stopband, and a narrow bandwidth and steep stopband. Hereinafter, the detailed circuit structure and high-frequency characteristics of filter 1 according to this embodiment will be described.

[0045] Figure 2A This is a circuit diagram of the elastic wave series resonant circuit according to Embodiment 1. Additionally, Figure 2B This is a graph showing the transmission and impedance characteristics of a single unit in the elastic wave series resonant circuit of Embodiment 1. (See figure) Figure 2BAs shown, the impedance representing the resonant characteristics of the series arm resonator S1 has a near-zero minimum at the resonant frequency fr1 and a near-infinite maximum at the anti-resonant frequency fa1. Similarly, the impedance representing the resonant characteristics of the series arm resonator S2 has a near-zero minimum at the resonant frequency fr2 and a near-infinite maximum at the anti-resonant frequency fa2. Thus, the elastic wave series resonant circuit forms a low-loss passband near the resonant frequencies fr1 and fr2 where insertion loss is low, and a stopband at the anti-resonant frequencies fa1 and fa2 where insertion loss is extremely high. Furthermore, a passband is formed in the frequency band higher than this stopband. The series arm resonators S1 and S2 have a high resonant Q value due to the elastic wave resonator, thus enabling steep attenuation slopes at both ends of the stopband. In other words, the elastic wave series resonant circuit forms a band-stop filter with stopbands corresponding to the anti-resonant frequencies fa1 and fa2.

[0046] Furthermore, the stopband bandwidth and attenuation of the elastic wave series resonant circuit can be adjusted by making the anti-resonance frequencies of the series arm resonators s1 and s2 different.

[0047] Figure 3A (a) is a circuit diagram of the LC parallel resonant circuit 10 according to embodiment 1. Figure 3A (b) is a Smith chart showing the impedance characteristics of the LC parallel resonant circuit 10 in Embodiment 1. Figure 3A As shown in (b), the input and output impedances of the LC parallel resonant circuit 10 exhibit inductive behavior in the low-frequency band of 700-800MHz and capacitive behavior in the high-frequency band of 1000-1700MHz.

[0048] Figure 3B This is an equivalent circuit diagram of two series-arm resonators in the specified frequency band of filter 1 according to embodiment 1. Figure (a) shows the case where the LC parallel resonant circuit 10 is replaced by capacitor C10 in the 1000-1700MHz range. Here, the resonant frequency fr3 and the anti-resonant frequency fa3 of the series connection circuit of capacitor C10 and series-arm resonator s1 are defined.

[0049] Figure 3C This is a graph showing the pass-through characteristics of filter 1 according to embodiment 1 and the impedance characteristics of the two series-arm resonators. The graph shows the pass-through characteristics of filter 1, the impedance characteristics of the series connection circuit consisting of series-arm resonator s1 and capacitor C10, and the impedance characteristics of series-arm resonator s2.

[0050] As shown in the figure, the attenuation level of the second stopband of filter 1 is defined by the anti-resonant frequency fa3 of the series-connected circuit and the anti-resonant frequency fa2 of the series arm resonator s2. Here, the frequency difference between the resonant frequency fr3 of the series-connected circuit and the resonant frequency fr2 of the series arm resonator s2, and the anti-resonant frequency fa3 of the series-connected circuit and the anti-resonant frequency fa2 of the series arm resonator s2, i.e., the resonant bandwidth, defines the attenuation slope on the low-frequency side of the second stopband. The wider the resonant bandwidth, the gentler the attenuation slope; the narrower the resonant bandwidth, the steeper the attenuation slope.

[0051] In filter 1 of this embodiment, the resonant frequency fr3 of the series connection circuit in which capacitor C10 is connected in series with series arm resonator s1 is located on the high-frequency side compared with the resonant frequency fr1 of individual series arm resonator s1.

[0052] Figure 4A The filter 1 and the elastic wave series resonant circuit unit (in Implementation Method 1) are described. Figure 4A The graph compares the pass-through and reflection characteristics near the second stopband of the series resonator (s1+s2). Filter 1 is a circuit in which capacitor C10 is connected in series with an elastic wave series resonator. Therefore, the point where the reflection loss of filter 1 is extremely high (the resonant frequency of the series circuit consisting of the elastic wave series resonator and capacitor C10) is shifted to the high-frequency side compared to the point where the reflection loss of a single elastic wave series resonator is extremely high. On the other hand, the point where the reflection loss of filter 1 is extremely low (the anti-resonant frequency of the series circuit consisting of the elastic wave series resonator and capacitor C10) is at the same frequency as the point where the reflection loss of a single elastic wave series resonator is extremely high. Thus, in the pass-through characteristics of filter 1, the attenuation slope becomes steeper on the lower-frequency side compared to the second stopband. Therefore, the high-frequency end of the passband on the lower-frequency side compared to the second stopband (in... Figure 4A The insertion loss (0.07 dB) at 1.54 GHz is lower than that at the high-frequency end of the passband (at the lower frequency side) of the elastic wave series resonant circuit unit compared to the second stopband. Figure 4A The insertion loss (0.30dB) is small at 1.54GHz.

[0053] Figure 4B The filter 1 and the elastic wave series resonant circuit unit (in Implementation Method 1) are described. Figure 4BThe graph shows a comparison of the pass-through characteristics near the first stopband of the series arm resonators (s1+s2). As shown in the graph, in the single elastic wave series resonant circuit, no stopband is formed on the lower frequency side compared to the first passband (0.98dB@0.80GHz). In contrast, in filter 1, a wideband first stopband (15.46dB@0.80GHz) is formed on the lower frequency side compared to the first passband through the LC parallel resonant circuit 10.

[0054] As described above, the filter 1 according to this embodiment can form a wide-bandwidth first passband and a wide-bandwidth first stopband through the LC parallel resonant circuit 10, and can form a narrow-bandwidth and steep second stopband through the elastic wave series resonant circuit. Furthermore, by combining the elastic wave series resonant circuit and the LC parallel resonant circuit 10, the insertion loss at the high-frequency end of the first passband (passband a) near the second stopband can be reduced. In other words, the filter 1 of this embodiment can possess a wide-bandwidth and low-loss first passband, a wide-bandwidth first stopband, and a narrow-bandwidth and steep second stopband.

[0055] Furthermore, in this embodiment, by utilizing the capacitive nature of the impedance of the LC parallel resonant circuit 10 in the 1000-1700MHz range, the attenuation slope of the second stopband is made steep. Conversely, when the second stopband is located around 700-800MHz, the inductive nature of the impedance of the LC parallel resonant circuit 10 in the 700-800MHz range can also be utilized to widen the attenuation bandwidth of the second stopband.

[0056] [1.2 Resonance Characteristics of the Modified Filter]

[0057] Figure 5A This is a circuit structure of the resonant circuit in Modification 1 of Embodiment 1, and a graph showing the impedance characteristics of the resonant circuit. In the filter 1 of Embodiment 1, there is a resonant circuit with an equivalent capacitor C10 connected in series with the series arm resonator s1. However, the filter in this modification has a resonant circuit where an inductor L6 (a third inductor) is connected in series with the series arm resonator s1 instead of the capacitor C10. Here, the resonant frequency fr6 and anti-resonant frequency fa6 of the resonant circuit of the inductor L6 and the series arm resonator s1 are defined. In the filter of this modification, the resonant frequency fr6 of the resonant circuit with the inductor L6 connected in series with the series arm resonator s1 is located on the lower frequency side compared to the resonant frequency fr1 of a single unit of the series arm resonator s1. Furthermore, the anti-resonant frequency fa6 of the resonant circuit with the inductor L6 connected in series with the series arm resonator s1 is the same as the anti-resonant frequency fa1 of a single unit of the series arm resonator s1. In other words, the resonant bandwidth of the above resonant circuit is wider than the resonant bandwidth of the series arm resonator s1.

[0058] Therefore, the filter of this modified example can expand the bandwidth of the second stopband.

[0059] Figure 5B This is a circuit structure of the resonant circuit in Modification 2 of Embodiment 1, and a graph showing the impedance characteristics of the resonant circuit. The filter in this modification is the same as filter 1 in Embodiment 1, having a resonant circuit in which a capacitor C7 (a third capacitor) is connected in series with the series arm resonator s1. Here, the resonant frequency fr7 and the anti-resonant frequency fa7 of the resonant circuit with capacitor C7 and series arm resonator s1 are defined. In the filter of this modification, the resonant frequency fr7 of the resonant circuit with capacitor C7 connected in series with series arm resonator s1 is located on the high-frequency side compared to the resonant frequency fr1 of a single unit of series arm resonator s1. Furthermore, the anti-resonant frequency fa7 of the resonant circuit with capacitor C7 connected in series with series arm resonator s1 is the same as the anti-resonant frequency fa1 of a single unit of series arm resonator s1. In other words, the resonant bandwidth of the above-described resonant circuit is narrower than the resonant bandwidth of the series arm resonator s1.

[0060] Therefore, the filter in this modified example can make the attenuation slope of the second stopband steep.

[0061] Figure 5C This is a circuit structure of the resonant circuit in Modification 3 of Embodiment 1, and a graph showing the impedance characteristics of the resonant circuit. In the filter 1 of Embodiment 1, there is a resonant circuit with an equivalent capacitor C10 connected in series with the series arm resonator s1. However, the filter in this modification has a resonant circuit in which an inductor L8 (fourth inductor) is connected in parallel with the series arm resonator s1 instead of the capacitor C10. Here, the resonant frequency fr8 and anti-resonant frequency fa8 of the resonant circuit of the inductor L8 and the series arm resonator s1 are defined. In the filter of this modification, the anti-resonant frequency fa8 of the resonant circuit with the inductor L8 connected in parallel with the series arm resonator s1 is located on the high-frequency side compared to the anti-resonant frequency fa1 of a single unit of the series arm resonator s1. Furthermore, the resonant frequency fr8 of the resonant circuit with the inductor L8 connected in parallel with the series arm resonator s1 is the same as the resonant frequency fr1 of a single unit of the series arm resonator s1. In other words, the resonant bandwidth of the above resonant circuit is wider than the resonant bandwidth of the series arm resonator s1.

[0062] Therefore, the filter of this modified example can expand the bandwidth of the second stopband.

[0063] Figure 5DThis is a circuit structure of the resonant circuit in Modification 4 of Embodiment 1, and a graph showing the impedance characteristics of the resonant circuit. In the filter 1 of Embodiment 1, there is a resonant circuit with an equivalent capacitor C10 connected in series with the series arm resonator s1. However, the filter in this modification has a resonant circuit where, instead of capacitor C10, a capacitor C9 (the fourth capacitor) is connected in parallel with the series arm resonator s1. Here, the resonant frequency fr9 and anti-resonant frequency fa9 of the resonant circuit with capacitor C9 and the series arm resonator s1 are defined. In the filter of this modification, the anti-resonant frequency fa9 of the resonant circuit with capacitor C9 connected in parallel with the series arm resonator s1 is located on the lower frequency side compared to the anti-resonant frequency fa1 of a single unit of the series arm resonator s1. Furthermore, the resonant frequency fr9 of the resonant circuit with capacitor C9 connected in parallel with the series arm resonator s1 is the same as the resonant frequency fr1 of a single unit of the series arm resonator s1. In other words, the resonant bandwidth of the above resonant circuit is narrower than the resonant bandwidth of the series arm resonator s1.

[0064] Therefore, the filter in this modified example can make the attenuation slope of the second stopband steep.

[0065] Furthermore, as a structure for adjusting the resonant bandwidth of the elastic wave series resonant circuit, the series arm resonators s1 and s2 can each utilize one of the following different elastic waves. That is, the elastic waves used by the series arm resonators s1 and s2 can be any one of the following:

[0066] (1) Love wave propagating in a LiNbO3 piezoelectric substrate with Y-cutting X propagation from -11° to 0°.

[0067] (2) Rayleigh wave propagating in a LiNbO3 piezoelectric substrate with X propagation at 126°~130° Y-cut.

[0068] (3) Leaky wave propagating in a LiTaO3 piezoelectric substrate with X propagation at 42° Y-cut.

[0069] At this time, the type of elastic wave used by the series arm resonator s1 is different from the type of elastic wave used by the series arm resonator s2. The order of the resonant bandwidth from narrowest to widest when using the above elastic waves is as follows: (2) above, (3) above, and (1) above.

[0070] Accordingly, the degree of freedom in adjusting the attenuation bandwidth and attenuation slope of the second stopband is increased.

[0071] (Implementation Method 2)

[0072] In this embodiment, the structure of a filter in which circuit elements such as inductors and capacitors are added to the elastic wave series resonant circuit of filter 1 in order to realize the cellular frequency band of fourth-generation mobile communication system (4G) and fifth-generation mobile communication system (5G) as well as the passband and stopband corresponding to GPS (Global Positioning System, registered trademark) will be described.

[0073] Figure 6A This is a circuit diagram of filter 2 according to Embodiment 2. Filter 2 is an example of a filter device, as shown in the diagram, and includes input / output terminals 100 and 110, an LC parallel resonant circuit 10, a parallel connection circuit 20, and a series connection circuit 30. Compared with filter 1 in Embodiment 1, filter 2 of this embodiment differs in that inductors or capacitors are connected to the series arm resonators s1 and s2. Hereinafter, regarding filter 2 of this embodiment, descriptions of points similar to filter 1 in Embodiment 1 will be omitted, and descriptions will focus on the differences.

[0074] The parallel connection circuit 20 includes a series arm resonator s1 and an inductor L2. The series arm resonator s1 and the inductor L2 are connected in parallel. Furthermore, the resonant frequency fr20 and the anti-resonant frequency fa20 of the parallel connection circuit 20 are defined. The parallel connection circuit 20 has... Figure 5C The resonant circuit shown has the same resonant characteristics, but its anti-resonant frequency fa20 is located on the high-frequency side compared to the anti-resonant frequency fa1 of the series arm resonator s1. Furthermore, the resonant frequency fr20 is the same as the resonant frequency fr1 of the series arm resonator s1. In other words, the resonant bandwidth of the parallel connection circuit 20 is wider than that of the series arm resonator s1.

[0075] The series connection circuit 30 includes a series arm resonator s2 and a capacitor C2. The series arm resonator s2 is connected in series with the capacitor C2. Furthermore, the resonant frequency fr30 and the anti-resonant frequency fa30 of the series connection circuit 30 are defined. The series connection circuit 30 has... Figure 5B The resonant circuit shown has the same resonant characteristics, with the resonant frequency fr30 located at a higher frequency compared to the resonant frequency fr1 of the individual unit of the series arm resonator s1. Furthermore, the anti-resonant frequency fa30 is the same as the anti-resonant frequency fa1 of the individual unit of the series arm resonator s1. In other words, the resonant bandwidth of the series connection circuit 30 is narrower than that of the series arm resonator s1.

[0076] Figure 6B It is a graph showing the pass characteristics of filter 2 in embodiment 2 and the impedance characteristics of parallel connection circuit 20 and series connection circuit 30.

[0077] LC parallel resonant circuit 10 is formed Figure 6B The diagram shows a wideband, low-loss first passband including passband a and passband b, and a wideband first stopband corresponding to the LC parallel resonant frequency of inductor L1 and capacitor C1. Furthermore, in this embodiment, passband a corresponds, for example, to 1427.9-1510.9 MHz, and passband b corresponds, for example, to 1710-2690 MHz. The frequency band resulting from combining passbands a and b corresponds, for example, to the frequency band resulting from combining the mid-low frequency band, mid-frequency band, and high frequency band in a cellular frequency band. Additionally, the first stopband corresponds, for example, to the low-frequency band (699-915 MHz) in a cellular frequency band.

[0078] On the other hand, the parallel connection circuit 20 and the series connection circuit 30 form a narrow and steep second stopband corresponding to the anti-resonant frequencies fa20 and fa30. Furthermore, in this embodiment, the second stopband corresponds, for example, to the GPS frequency band (1559-1608MHz).

[0079] Figure 6C This is a graph showing the pass-through characteristics near the second stopband of the filter 2 in Embodiment 2, and the impedance characteristics near the second stopband of the parallel connection circuit 20 and the series connection circuit 30.

[0080] As shown in the figure, the attenuation level of the second stopband of filter 2 is defined by the anti-resonant frequency fa20 of the parallel connection circuit 20 and the anti-resonant frequency fa30 of the series connection circuit 30. Here, the frequency difference between the resonant frequencies fr30 and fr20 and the anti-resonant frequencies fa30 and fa20, i.e., the resonant bandwidth, defines the attenuation slope on the low-frequency side of the second stopband. In other words, the wider the resonant bandwidth, the gentler the attenuation slope; the narrower the resonant bandwidth, the steeper the attenuation slope.

[0081] In filter 2 of this embodiment, the second stopband is expanded by a parallel connection circuit 20 with a relatively wide resonant bandwidth, and the attenuation slope of the low-frequency side of the second stopband is made steep by a series connection circuit 30 with a relatively narrow resonant bandwidth.

[0082] Furthermore, the secondary anti-resonant frequency fa21 generated by the parallel connection circuit 20 is included in the first stopband. Therefore, compared with the filter 1 of Embodiment 1, which only utilizes the LC parallel resonant circuit 10 to form the first stopband, the filter 2 of this embodiment can ensure a greater amount of attenuation in the first stopband.

[0083] As described above, the filter 2 according to this embodiment can have a wide-bandwidth and low-loss first passband (a band that combines the mid-low frequency band, mid-frequency band and high frequency band in the cellular band), a wide-bandwidth and high-attenuation first stopband (low frequency band in the cellular band), and a narrow-bandwidth and steep second stopband (GPS band).

[0084] (Implementation Method 3)

[0085] In this embodiment, the structure of a multiplexer including filter 1 of embodiment 1 or filter 2 of embodiment 2 will be described.

[0086] Figure 7A This is a circuit diagram of the multiplexer 5 in Embodiment 3. As shown in the figure, the multiplexer 5 includes filters 2, 3 and 4, and input / output terminals 100, 110, 120 and 130.

[0087] Input / output terminal 100 is a common terminal for connecting filters 2, 3 and 4.

[0088] Filter 2 is the filter 2 of Embodiment 2, and is connected to the input / output terminal 100. Filter 2 includes an LC parallel resonant circuit 10 (high-pass filter: HPF), a parallel connection circuit 20, and a series connection circuit 30 (band-stop filter: BRF). Thus, filter 2 has a wide-bandwidth and low-loss first passband (the band combining the mid-low frequency band, mid-frequency band, and high-frequency band in the cellular band), a wide-bandwidth and high-attenuation first stopband (the low-frequency band in the cellular band), and a narrow-bandwidth and steep second stopband (GPS band).

[0089] Filter 3 is an example of a second filter and is connected to input / output terminal 100. Filter 3 is, for example, a bandpass filter having multiple elastic wave resonators and a passband that includes a narrow frequency band of a second stopband.

[0090] Filter 4 is an example of the first filter and is connected to the input / output terminal 100. Filter 4 is, for example, a low-pass LC filter consisting of an inductor and a capacitor, having a wide passband including a first stopband.

[0091] Furthermore, the multiplexer 5 can replace the filter 2, and the filter 1 of embodiment 1 can be used instead.

[0092] Figure 7B This is a detailed circuit diagram of the multiplexer 5A in Embodiment 3. The multiplexer 5A is an embodiment of the multiplexer 5 in Embodiment 3. As shown in the figure, the multiplexer 5A includes filters 2A, 3A, and 4A, and input / output terminals 100, 110, 120, and 130.

[0093] Filter 2A, relative to filter 2, also has an inductor L3 connected between capacitor C2 and input / output terminal 110.

[0094] Filter 3A includes series arm resonators s11, s12, and s13, parallel arm resonators p11, p12, and p13, and an inductor L11. The series arm resonators s11, s12, and s13 are connected in series in the path connecting input / output terminal 100 and input / output terminal 120. The parallel arm resonators p11, p12, and p13 are respectively connected between the aforementioned path and the ground wire. The inductor L11 is connected between the parallel arm resonator p13 and the input / output terminal 120. Thus, filter 3A constitutes a trapezoidal filter that uses a narrow second stopband (GPS band) as its passband.

[0095] Filter 4A includes inductors L21, L22, and L23, and capacitor C21. Inductors L21 and L22 are connected in series in the path connecting input / output terminal 100 and input / output terminal 130. The series connection circuit of inductor L23 and capacitor C21 is connected between the connection node of inductors L21 and L22 and ground. Thus, filter 4A constitutes a low-pass LC filter with a wide first stopband (low frequency band) as the passband.

[0096] Figure 7C This is a graph showing the throughput characteristics of the multiplexer 5A in Embodiment 3. The graph shows the throughput characteristics between input / output terminals 100-110 of filter 2A, between input / output terminals 100-120 of filter 3A, and between input / output terminals 100-130 of filter 4A, with filters 2A, 3A, and 4A all connected to input / output terminals 100.

[0097] like Figure 7C As shown, filter 2A possesses a wide-bandwidth and low-loss first passband (the band combining the mid-low frequency, mid-frequency, and high-frequency bands in the cellular band), a wide-bandwidth and high-attenuation first stopband (the low-frequency band in the cellular band), and a narrow-bandwidth and steep second stopband (the GPS band). Due to the transmission characteristics of filter 2A, filter 3A ensures low loss in the narrow-band passband, and filter 4A ensures low loss in the wide-band passband. In other words, due to the transmission characteristics of filter 2A, the isolation between filters 2A, 3A, and 4A is improved, and the low loss of filters 2A, 3A, and 4A is ensured.

[0098] (Implementation Method 4)

[0099] In this embodiment, the structure of the communication device including the multiplexer 5 of embodiment 3 will be described.

[0100] Figure 8This is a circuit diagram of the communication device 9 according to Embodiment 4. As shown in the figure, the communication device 9 includes a multiplexer 5, an RF signal processing circuit (RFIC) 6, a baseband signal processing circuit (BBIC) 7, an antenna 8, switches 52 and 54, filters 62, 63 and 64, and low-noise amplifiers 72, 73 and 74.

[0101] RFIC6 is an RF signal processing circuit that processes the high-frequency signals transmitted and received by antenna 8. Specifically, RFIC6 processes the received signal input via multiplexer 5 through down-conversion or the like, and outputs the resulting received signal to BBIC7. Additionally, RFIC6 processes the transmit signal input from BBIC7 through up-conversion or the like, and outputs the resulting transmit signal to multiplexer 5.

[0102] BBIC7 is a circuit that performs signal processing using an intermediate frequency band that is lower than the high-frequency signal transmitted in multiplexer 5. The signal processed by BBIC7 can be used, for example, as an image signal for image display or as an audio signal for communication via a speaker.

[0103] Switch 52 has a common terminal and multiple selection terminals. The common terminal of switch 52 is connected to the input / output terminal 110. The multiple selection terminals of switch 52 are respectively connected to the receiving path for receiving signals that belong to any one of the communication frequency bands in the cellular frequency band, including the low-to-mid frequency band, the mid-frequency band, and the high-frequency band. In this connection structure, switch 52 switches the connection of filter 2 to each receiving path.

[0104] Switch 54 has a common terminal and multiple selection terminals. The common terminal of switch 54 is connected to the input / output terminal 130. The multiple selection terminals of switch 54 are respectively connected to the receiving path for receiving signals that belong to the low-frequency band of the cellular frequency band. In this connection structure, switch 54 switches the connection of filter 4 to each receiving path.

[0105] Filter 62 is configured in the receiving path for transmitting received signals belonging to any one of the communication frequency bands in the cellular band, including the low-frequency band, mid-frequency band, and high-frequency band. Filter 63 is configured in the receiving path for transmitting received signals in the GPS band. Filter 64 is configured in the receiving path for transmitting received signals belonging to the low-frequency band in the cellular band.

[0106] Low-noise amplifier 72 is capable of low-noise amplification of received signals from any of the mid-low frequency, mid-frequency, and high-frequency communication bands within the cellular frequency band, and is connected between the output terminal of filter 62 and RFIC 6. Low-noise amplifier 73 is capable of low-noise amplification of received signals from the GPS frequency band and is connected between the output terminal of filter 63 and RFIC 6. Low-noise amplifier 74 is capable of low-noise amplification of received signals from the low-frequency communication band within the cellular frequency band and is connected between the output terminal of filter 64 and RFIC 6.

[0107] Antenna 8 is connected to input / output terminal 100, radiates high-frequency signals output from multiplexer 5, and receives high-frequency signals from the outside and outputs them to multiplexer 5.

[0108] In addition, a transmission path for transmitting signals belonging to any one of the communication frequency bands in the cellular band, such as the low-frequency band, mid-low-frequency band, mid-frequency band, and high-frequency band, can be added between the multiplexer 5 and RFIC6.

[0109] Furthermore, in the communication device 9 of this embodiment, the antenna 8, BBIC 7, switches 52 and 54, filters 62 to 64, and low-noise amplifiers 72 to 74 are not essential structural elements.

[0110] Based on the above structure, a communication device 9 is provided that can perform demultiplexing, multiplexing, or both demultiplexing and multiplexing on high-frequency signals of any one of the communication bands belonging to the mid-low frequency band, mid frequency band, and high frequency band in the cellular frequency band, high-frequency signals of the GPS frequency band, and high-frequency signals of the communication band belonging to the low frequency band in the cellular frequency band with high isolation and low loss.

[0111] (Effect)

[0112] As described above, the filter 1 of Embodiment 1 includes: input and output terminals 100 and 110, an LC parallel resonant circuit 10 having an inductor L1 and a capacitor C1 connected in parallel, and an elastic wave series resonant circuit having series arm resonators s1 and s2 connected in series. The LC parallel resonant circuit 10 and the elastic wave series resonant circuit are connected in series between the input and output terminals 100 and 110.

[0113] According to the above structure, a wide-band first passband and a wide-band first stopband can be formed by the LC parallel resonant circuit 10, a narrow-band and steep second stopband can be formed by the elastic wave series resonant circuit, and the insertion loss at the end of the first passband near the second stopband can be reduced by the combined circuit of the elastic wave series resonant circuit and the LC parallel resonant circuit 10.

[0114] Alternatively, in filter 1, the LC parallel resonant circuit 10 may have a first passband and a first stopband corresponding to the LC parallel resonant frequency, and the elastic wave series resonant circuit may have a second stopband corresponding to the anti-resonant frequency fa1 of the series arm resonator s1 and the anti-resonant frequency fa2 of the series arm resonator s2, and the second stopband may be included in the frequency range of the first passband.

[0115] Accordingly, a narrow and steep second stopband can be formed within the first passband.

[0116] Alternatively, in filter 1, the anti-resonance frequency fa1 of the series arm resonator s1 may be different from the anti-resonance frequency fa2 of the series arm resonator s2.

[0117] Accordingly, the attenuation bandwidth of the second stopband can be adjusted in accordance with the frequency difference between the anti-resonance frequency fa1 and the anti-resonance frequency fa2.

[0118] Alternatively, filter 1 may also include an inductor L6 connected in series with either the series arm resonator s1 or s2.

[0119] Therefore, the bandwidth of the second stopband can be expanded.

[0120] Alternatively, filter 1 may also include an inductor L8 connected in parallel with the series arm resonator s1 or s2.

[0121] Therefore, the bandwidth of the second stopband can be expanded.

[0122] Alternatively, filter 1 may also include a capacitor C7 connected in series with either the series arm resonator s1 or s2.

[0123] Therefore, the attenuation slope of the second stopband can be made steeper.

[0124] Alternatively, filter 1 may also include a capacitor C9 connected in parallel with either the series arm resonator s1 or s2.

[0125] Therefore, the attenuation slope of the second stopband can be made steeper.

[0126] Alternatively, in filter 1, the series arm resonators s1 and s2 can each utilize one of the following different methods:

[0127] (1) Laffer waves propagating in a LiNbO3 piezoelectric substrate with Y-cutting X propagation from -11° to 0°.

[0128] (2) Rayleigh waves propagating in a LiNbO3 piezoelectric substrate with X propagation at 126°–130° Y-cutting.

[0129] (3) Leakage wave propagating in a LiTaO3 piezoelectric substrate with X propagation at 42° Y-cut.

[0130] Accordingly, since the resonant bandwidth can be adjusted in the order of (2), (3), and (1) above, the degree of freedom in adjusting the attenuation bandwidth and attenuation slope of the second stopband is increased.

[0131] Alternatively, in filter 2 of embodiment 2, the first passband may include a frequency band of 1427.9MHz-1510.9MHz and a frequency band of 1710MHz-2690MHz, the first stopband may include a frequency band of 699MHz-915MHz, and the second stopband may include a frequency band of 1559MHz-1608MHz.

[0132] Accordingly, filter 2 can have a wide-bandwidth and low-loss first passband (the band that combines the low-frequency, mid-frequency and high-frequency bands in the cellular band), a wide-bandwidth and high-attenuation first stopband (the low-frequency band in the cellular band), and a narrow-bandwidth and steep second stopband (GPS band).

[0133] In addition, the multiplexer 5 of embodiment 3 includes: a filter 2 connected to the input / output terminal 100, a filter 4 connected to the input / output terminal 100 and having a passband including a first stopband, and a filter 3 connected to the input / output terminal 100 and having a passband including a second stopband. The filter 4 is an LC filter and the filter 3 is an elastic wave filter.

[0134] Accordingly, filter 2 combines a wide-bandwidth, low-loss first passband, a wide-bandwidth, high-attenuation first stopband, and a narrow-bandwidth, steep second stopband. Therefore, filter 3 ensures low-loss performance in the narrow-bandpass, and filter 4 ensures low-loss performance in the wide-bandpass. This improves the isolation between filters 2, 3, and 4, ensuring low-loss performance for each filter.

[0135] In addition, the communication device 9 includes: an RFIC 6 for processing high-frequency signals transmitted and received by the antenna 8, and a multiplexer 5 for transmitting high-frequency signals between the antenna 8 and the RFIC 6.

[0136] Accordingly, a communication device 9 is provided that can perform demultiplexing, multiplexing, or both demultiplexing and multiplexing on high-frequency signals of any one of the communication bands belonging to the mid-low frequency band, mid frequency band, and high frequency band in the cellular frequency band, high-frequency signals of the GPS frequency band, and high-frequency signals of the communication band belonging to the low frequency band in the cellular frequency band with high isolation and low loss.

[0137] (Other implementation methods)

[0138] The filter device, multiplexer, and communication device of the present invention have been described above through examples, embodiments, and modifications. However, the filter device, multiplexer, and communication device of the present invention are not limited to the above-described embodiments, embodiments, and modifications. Other embodiments implemented by combining any structural elements of the above-described embodiments, embodiments, and modifications; modifications obtained by implementing various modifications of the above-described embodiments, embodiments, and modifications that can be conceived by those skilled in the art without departing from the spirit of the present invention; and various devices that incorporate the above-described filter device, multiplexer, and communication device are also included in the present invention.

[0139] For example, in the filter devices, multiplexers, and communication devices described in the above embodiments, examples, and variations, other circuit elements and wiring may be inserted between the paths connecting the circuit elements and signal paths disclosed in the accompanying drawings.

[0140] This invention can be used in filter devices, multiplexers, and communication devices configured in front-ends corresponding to multiple frequency bands, and can be widely used in communication devices such as mobile phones equipped with such filter devices, multiplexers, and communication devices.

Claims

1. A filter device comprising: a first input-output terminal and a second input-output terminal; an LC parallel resonant circuit having a first inductor and a first capacitor connected in parallel to each other; and an elastic wave series resonant circuit having a first elastic wave resonator and a second elastic wave resonator connected in series to each other, the LC parallel resonant circuit and the elastic wave series resonant circuit being connected in series between the first input-output terminal and the second input-output terminal, the LC parallel resonant circuit having a first passband and a first stopband corresponding to an LC parallel resonant frequency, the elastic wave series resonant circuit having a second stopband corresponding to an anti-resonance frequency of the first elastic wave resonator and an anti-resonance frequency of the second elastic wave resonator, the second stopband being included in a frequency range of the first passband.

2. The filter device according to claim 1, wherein the anti-resonance frequency of the first elastic wave resonator and the anti-resonance frequency of the second elastic wave resonator are different.

3. The filter device according to claim 1 or 2, further comprising a third inductor connected in series to the first elastic wave resonator or the second elastic wave resonator.

4. The filter device according to claim 1 or 2, further comprising a fourth inductor connected in parallel to the first elastic wave resonator or the second elastic wave resonator.

5. The filter device according to claim 1 or 2, further comprising a third capacitor connected in series to the first elastic wave resonator or the second elastic wave resonator.

6. The filter device according to claim 1 or 2, further comprising a fourth capacitor connected in parallel to the first elastic wave resonator or the second elastic wave resonator.

7. The filter device according to claim 1 or 2, wherein the first elastic wave resonator and the second elastic wave resonator respectively propagate one of the following different from each other: (1) a Love wave propagating in a -11° to 0° Y-cut X-propagation LiNbO3 piezoelectric substrate, (2) a Rayleigh wave propagating in a 126° to 130° Y-cut X-propagation LiNbO3 piezoelectric substrate, and (3) a Leaky wave propagating in a 42° Y-cut X-propagation LiTaO3 piezoelectric substrate.

8. The filter device according to claim 1 or 2, wherein the first passband includes a frequency band of 1427.9 MHz to 1510.9 MHz and a frequency band of 1710 MHz to 2690 MHz, the first stopband includes a frequency band of 699 MHz to 915 MHz, and the second stopband includes a frequency band of 1559 MHz to 1608 MHz.

9. A multiplexer comprising: the filter device according to any one of claims 1 to 8 connected to a common terminal; a first filter connected to the common terminal and having a passband including the first stopband; and a second filter connected to the common terminal and having a passband including the second stopband. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ The first filter described above is an LC filter, The second filter described above is an elastic wave filter.

10. A communication device comprising: RF signal processing circuitry that processes high-frequency signals transmitted and received by an antenna; and The multiplexer of claim 9, which transmits the high-frequency signals between the antenna and the RF signal processing circuitry.

Images