Patent Publication Number: US-2023163791-A1

Title: Radio-frequency circuit

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a continuation application of PCT International Application No. PCT/JP2021/022143 filed on Jun. 10, 2021, designating the United States of America, which is based on and claims priority of Japanese Patent Application No. 2020-124257 filed on Jul. 21, 2020. The entire disclosures of the above-identified applications, including the specifications, drawings, and claims are incorporated herein by reference in their entirety. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a radio-frequency circuit. 
     2. Description of the Related Art 
     5th Generation New Radio (5GNR) allows for the use of a communication band having a wider bandwidth. The efficient use of such a wide communication band is now being studied. For example, some countries or some regions are considering dividing a wide communication band into multiple sub-bands and allocating them to different mobile network operators (MNOs). They are also considering performing communication by simultaneously using multiple non-contiguous component carriers (CCs) in a wide communication band. This is called intra-band non-contiguous carrier aggregation. An example of the related art is disclosed in U.S. Patent Application Publication No. 2014/0111178. 
     SUMMARY 
     In the related art, however, it is difficult to efficiently use such a wide communication band. 
     In terms of this background, it is an aspect of the present disclosure to provide a radio-frequency circuit that can efficiently use a wide communication band. 
     A radio-frequency circuit according to an embodiment of the present disclosure includes a first switch and first, second, and third filters. The first switch is connected to an antenna connecting terminal. The first filter has a pass band corresponding to a first sub-band and is configured to connect to the antenna connecting terminal via the first switch. The first sub-band is included in a first band used for time division duplex (TDD) communication. The second filter has a pass band corresponding to a second sub-band included in the first band and is configured to connect to the antenna connecting terminal via the first switch. There is a gap between the first sub-band and the second sub-band. The third filter has a pass band corresponding to a third sub-band and is configured to connect to the antenna connecting terminal via the first switch. The third sub-band includes the first sub-band, the second sub-band, and the gap. 
     According to an embodiment of the present disclosure, it is possible to efficiently use a wider communication band. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a circuit diagram of a radio-frequency circuit and a communication apparatus according to a first embodiment; 
         FIG.  2    is a diagram for explaining the relationships among multiple sub-bands used in the first embodiment; 
         FIG.  3    is a circuit diagram of a radio-frequency circuit and a communication apparatus according to a first modified example; 
         FIG.  4    is a circuit diagram of a radio-frequency circuit and a communication apparatus according to a second modified example; 
         FIG.  5    is a circuit diagram of a radio-frequency circuit and a communication apparatus according to a third modified example; 
         FIG.  6    is a table illustrating some specific examples of multiple sub-bands; and 
         FIG.  7    is a circuit diagram of a radio-frequency circuit and a communication apparatus according to a second embodiment. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Embodiments of the disclosure will be described below in detail with reference to the accompanying drawings. All of the embodiments described below illustrate general or specific examples. Numerical values, configurations, materials, components, and positions and connection states of the components illustrated in the following embodiments are only examples and are not intended for limiting the disclosure. 
     The drawings are only schematically illustrated and are not necessarily precisely illustrated. For the sake of representation, the drawings may be illustrated in an exaggerated manner or with omissions, and the ratios of components in the drawings may be adjusted. The configurations, positional relationships, and ratios of components in the drawings may be different from those of the actual components. In the drawings, substantially identical components are designated by like reference numeral, and an explanation of such components will not be repeated or be merely simplified. 
     In this disclosure, “A connects to or is connected to B” includes, not only the meaning that A directly connects to or is directly connected to B using a connecting terminal and/or a wiring conductor, but also the meaning that A electrically connects to or is electrically connected to B via another circuit element. “Being connected between A and B” means that “connecting to or being connected to both A and B on a path which connects A and B”. 
     First Embodiment 
     [1.1 Circuit Configurations of Radio-Frequency Circuit  1  and Communication Apparatus  5 ] 
     The circuit configurations of a radio-frequency circuit  1  and a communication apparatus  5  according to a first embodiment will be described below with reference to  FIG.  1   .  FIG.  1    is a circuit diagram of the radio-frequency circuit  1  and the communication apparatus  5  according to the first embodiment. 
     [1.1.1 Circuit Configuration of Communication Apparatus  5 ] 
     The circuit configuration of the communication apparatus  5  will first be discussed. As illustrated in  FIG.  1   , the communication apparatus  5  according to the first embodiment includes a radio-frequency circuit  1 , an antenna  2 , a radio-frequency integrated circuit (RFIC)  3 , and a baseband integrated circuit (BBIC)  4 . 
     The radio-frequency circuit  1  conveys a radio-frequency signal between the antenna  2  and the RFIC  3 . The detailed circuit configuration of the radio-frequency circuit  1  will be discussed later. 
     The antenna  2  is connected to an antenna connecting terminal  100  of the radio-frequency circuit  1 . The antenna  2  sends a radio-frequency signal output from the radio-frequency circuit  1  and receives a radio-frequency signal from an external source and outputs it to the radio-frequency circuit  1 . 
     The RFIC  3  is an example of a signal processing circuit that processes a radio-frequency signal. The RFIC  3  will be explained below more specifically. The RFIC  3  performs signal processing, such as down-conversion, on a radio-frequency received signal which is received via components on a receive path of the radio-frequency circuit  1  and outputs the resulting received signal to the BBIC  4 . The RFIC  3  also performs signal processing, such as up-conversion, on a sending signal provided from the BBIC  4  and outputs the resulting radio-frequency sending signal to a sending path of the radio-frequency circuit  1 . The RFIC  3  includes a controller that controls components, such as switches and amplifiers, of the radio-frequency circuit  1 . All or some of the functions of the RFIC  3  as the controller may be installed in a source outside the RFIC  3 , such as in the BBIC  4  or the radio-frequency circuit  1 . 
     The BBIC  4  is a baseband signal processing circuit that performs signal processing by using an intermediate-frequency band, which is lower than a radio-frequency signal transmitted by the radio-frequency circuit  1 . Examples of signals to be processed by the BBIC  4  are image signals for displaying images and/or audio signals for performing communication via a speaker. 
     The antenna  2  and the BBIC  4  are optional, but not essential, components for the communication apparatus  5  of the first embodiment. 
     [1.1.2 Circuit Configuration of Radio-Frequency Circuit  1 ] 
     The circuit configuration of the radio-frequency circuit  1  will now be discussed below. As illustrated in  FIG.  1   , the radio-frequency circuit  1  includes a power amplifier  11 , a low-noise amplifier  21 , switches  51  and  52 , filters  61 ,  62 , and  63 , an antenna connecting terminal  100 , a radio-frequency input terminal  111 , and a radio-frequency output terminal  121 . 
     The antenna connecting terminal  100  connects to the antenna  2 . The radio-frequency input terminal  111  is a terminal for receiving a radio-frequency sending signal from a source that is external to (outside of) the radio-frequency circuit  1 . The radio-frequency output terminal  121  is a terminal for outputting a radio-frequency received signal to another device that is external to (outside of) the radio-frequency circuit  1 . 
     The power amplifier  11 , which can connect to the filters  61 ,  62 , and  63  via the switch  52 , amplifies a radio-frequency signal received by the radio-frequency input terminal  111  and supplies the amplified radio-frequency signal to the filters  61 ,  62 , and  63 . The power amplifier  11  can amplify first, second, and third sub-band sending signals received via the radio-frequency input terminal  111 . As the power amplifier  11 , a multistage amplifier and/or an amplifier that first converts a radio-frequency signal into a difference signal and then amplifies it may be used. However, the power amplifier  11  is not restricted to these types of amplifiers. 
     The low-noise amplifier  21  can connect to the filters  61 ,  62 , and  63  via the switch  52  and amplify a radio-frequency signal received by the antenna connecting terminal  100 . The low-noise amplifier  21  can amplify first, second, and third sub-band received signals received from the antenna connecting terminal  100  via the switch  51 , the filters  61 ,  62 , and  63 , and the switch  52 . A radio-frequency signal amplified by the low-noise amplifier  21  is output to the radio-frequency output terminal  121 . As the low-noise amplifier  21 , a multistage amplifier and/or an amplifier that first converts a radio-frequency signal into a difference signal and then amplifies it may be used. However, the low-noise amplifier  21  is not restricted to these types of amplifiers. 
     The filter  61 , which is an example of a first filter, has a pass band corresponding to the first sub-band. The filter  61  can thus allow the first sub-band signals to pass therethrough and attenuate the other frequency band signals. The filter  61  has two input/output terminals. One input/output terminal is connected to the switch  51  so that the filter  61  can connect to the antenna connecting terminal  100  via the switch  51 . The other input/output terminal is connected to the switch  52  so that the filter  61  can connect to the power amplifier  11  and the low-noise amplifier  21  via the switch  52 . 
     The filter  62 , which is an example of a second filter, has a pass band corresponding to the second sub-band. The filter  62  can thus allow the second sub-band signals to pass therethrough and attenuate the other frequency band signals. The filter  62  has two input/output terminals. One input/output terminal is connected to the switch  51  so that the filter  62  can connect to the antenna connecting terminal  100  via the switch  51 . The other input/output terminal is connected to the switch  52  so that the filter  62  can connect to the power amplifier  11  and the low-noise amplifier  21  via the switch  52 . 
     In the first embodiment, the filters  61  and  62  form one multiplexer  60 . That is, the filters  61  and  62  are integrated into one filter, which is connected to one terminal of the switch  51 . 
     The filter  63 , which is an example of a third filter, has a pass band corresponding to the third sub-band. The filter  63  can thus allow the third sub-band signals to pass therethrough and attenuate the other frequency band signals. The filter  63  has two input/output terminals. One input/output terminal is connected to the switch  51  so that the filter  63  can connect to the antenna connecting terminal  100  via the switch  51 . The other input/output terminal is connected to the switch  52  so that the filter  63  can connect to the power amplifier  11  and the low-noise amplifier  21  via the switch  52 . 
     Each of the filters  61 ,  62 , and  63  may be any one of a surface acoustic wave filter, a bulk acoustic wave (BAW) filter, an LC resonance filter, and a dielectric filter. For example, using acoustic wave filters as the filters  61  and  62  can improve isolation between the filters  61  and  62  whose pass bands have a relatively narrow gap. Using an LC resonance filter as the filter  63  can implement a filter having a relatively wide pass band with a small loss. 
     The relationships among the first sub-band, second sub-band, and third sub-band will be explained later with reference to  FIG.  2   . 
     The pass band corresponding to a frequency band means a pass band suitable for transmitting signals of this frequency band. Accordingly, a filter having a pass band corresponding to a certain frequency band allows signals of this frequency band to pass therethrough and attenuates signals of the other frequency bands which do not overlap the frequency band corresponding to the pass band. 
     The switch  51  is an example of a first switch. The switch  51  is connected between the antenna connecting terminal  100  and the filters  61 ,  62 , and  63 . The specific configuration of the switch  51  is as follows. The switch  51  has terminals  511 ,  512 , and  513 . The terminal  511  is connected to the antenna connecting terminal  100 . The terminal  512  is connected to the multiplexer  60 , that is, the filters  61  and  62 . The terminal  513  is connected to the filter  63 . 
     With this connection configuration, the switch  51  can connect the terminal  511  to one of the terminals  512  and  513  in response to a control signal from the RFIC  3 , for example. That is, the switch  51  can selectively connect the antenna  2  to the multiplexer  60  or to the filter  63 . The switch  51  is constituted by a single pole double throw (SPDT) switch circuit, for example, which is also known as an antenna switch. 
     The switch  52  is an example of a second switch. The switch  52  is connected between the filters  61 ,  62 , and  63  and each of the power amplifier  11  and the low-noise amplifier  21 . The specific configuration of the switch  52  is as follows. The switch  52  has terminals  521  through  525 . The terminals  521 ,  522 , and  523  are respectively connected to the filters  61 ,  62 , and  63 . The terminals  524  and  525  are respectively connected to the power amplifier  11  and the low-noise amplifier  21 . 
     With this connection configuration, the switch  52  can connect each of the terminals  521 ,  522 , and  523  to one of the terminals  524  and  525  in response to a control signal from the RFIC  3 , for example. That is, the switch  52  can selectively connect the filter  61  to the power amplifier  11  or to the low-noise amplifier  21 . The switch  52  can also selectively connect the filter  62  to the power amplifier  11  or to the low-noise amplifier  21 . The switch  52  can also selectively connect the filter  63  to the power amplifier  11  or to the low-noise amplifier  21 . The switch  52  can connect both of the terminals  521  and  522  to one of the terminals  524  and  525  at the same time. That is, the switch  52  can connect both of the filters  61  and  62  to the power amplifier  11  or to the low-noise amplifier  21  at the same time. The switch  52  is constituted by a multiple-connection switch circuit, for example. 
     The provision (inclusion) of some of the circuit elements shown in  FIG.  1    in the radio-frequency circuit  1  may be omitted. For example, it is sufficient that the radio-frequency circuit  1  includes at least the switch  51  and the filters  61 ,  62 , and  63 . 
     [1.2 Relationships Among Sub-Bands] 
     Prior to an explanation of the relationships among the first sub-band, second sub-band, and third sub-band, the terms concerning frequency bands in the disclosure will be defined. 
     A “communication band” refers to a frequency band defined by a standards organization (such as 3rd Generation Partnership Project (3GPP) and Institute of Electrical and Electronics Engineers (IEEE)) for a communication system to be constructed using a radio access technology (RAT). In the first embodiment, as the communication system, a 5GNR system, long term evolution (LTE) system, and a wireless local area network (WLAN) system, for example, may be used. However, the communication system is not limited to these types of systems. In the present disclosure, the communication band may also simply be called a band. 
     A time division duplex (TDD) communication band refers to a communication band in which TDD is used as a duplex mode of communication and is synonymous with a communication band used for TDD communication. The duplex mode used in a communication band is defined by a standards organization in advance. 
     Based on the definitions of the above-described terms concerning frequency bands, the relationships among the first sub-band, second sub-band, and third sub-band will be explained below with reference to  FIG.  2   .  FIG.  2    is a diagram for explaining the relationships among multiple sub-bands used in the first embodiment. 
     As illustrated in  FIG.  2   , the third sub-band (f 3  min-f 3 max) is included in one TDD communication band (f 0 min-f 0 max), which is a continuous, relatively wide band. In the example in  FIG.  2   , the third sub-band coincides with the TDD communication band. The TDD communication band corresponds to a first band. 
     The first sub-band (f 1 min-f 1 max) and the second sub-band (f 2  min-f 2 max) are both included in the TDD communication band and are also included in the third sub-band. The lower limit frequency f 1 min of the first sub-band and the lower limit frequency f 2 min of the second sub-band are higher than or equal to the lower limit frequency f 0 min of the TDD communication band and the lower limit frequency f 3 min of the third sub-band. The upper limit frequency f 1 max of the first sub-band and the upper limit frequency of f 2 max of the second sub-band are lower than or equal to the upper limit frequency f 0 max of the TDD communication band and the upper limit frequency f 3 max of the third sub-band. 
     The second sub-band is located on the higher frequency side than the first sub-band and has a wider bandwidth than the first sub-band. There is a gap between the first sub-band and the second sub-band. That is, the first sub-band and the second sub-band are separated from each other and neither do they overlap nor are they adjacent to each other. More specifically, the lower limit frequency f 2 min of the second sub-band is higher than the upper limit frequency f 1 max of the first sub-band. 
     The first and second sub-bands may be allocated to a first mobile network operator (MNO) in a first region (such as Japan, USA, Europe, or China). At least part of the gap between the first sub-band and the second sub-band may be allocated to a second MNO, which is a different MNO from the first MNO, in the first region. That is, in the first region, the TDD communication band may be divided into multiple sub-bands, and among the multiple sub-bands, two sub-bands separated from each other (first sub-band and second sub-band) may be allocated to the first MNO, while one or more sub-bands included in the gap between these two sub-bands may be allocated to the second MNO. 
     In a second region, which is different from the first region, it is possible that the TDD communication band be not divided into multiple sub-bands and be allocated entirely to one MNO (third MNO, for example). Alternatively, the TDD communication band may be divided into multiple sub-bands whose frequency bands are different from those in the first region and be allocated to multiple MNOs. 
     Although the second sub-band is located on the higher frequency side than the first sub-band in  FIG.  2   , it may be located on the lower frequency side than the first sub-band. The bandwidth of the second sub-band is wider than that of the first sub-band. However, this is only an example. The bandwidth of the second sub-band may be narrower than or equal to that of the first sub-band. The third sub-band coincides with the TDD communication band in  FIG.  2   , but it may be wider than the TDD communication band. The first sub-band or the second sub-band may include a TDD communication band (second communication band), which is different from the above-described TDD communication band (first communication band). 
     [1.3 Advantages and Others] 
     As described above, a radio-frequency circuit  1  according to the first embodiment includes a switch  51  and filters  61 ,  62 , and  63 . The switch  51  is connected to an antenna connecting terminal  100 . The filter  61  has a pass band corresponding to a first sub-band which is included in a first band used for TDD communication, and can connect to the antenna connecting terminal  100  via the switch  51 . The filter  62  has a pass band corresponding to a second sub-band included in the first band and can connect to the antenna connecting terminal  100  via the switch  51 . There is a gap between the first sub-band and the second sub-band. The filter  63  has a pass band corresponding to a third sub-band and can connect to the antenna connecting terminal  100  via the switch  51 . The third sub-band includes the first sub-band, the second sub-band, and the gap. 
     With the above-described configuration, the radio-frequency circuit  1  includes the filter  61  having a pass band corresponding to the first sub-band and the filter  62  having a pass band corresponding to the second sub-band. Even when multiple sub-bands obtained by dividing the first band, which is a relatively wide band for TDD communication, are used, the radio-frequency circuit  1  can reduce interference between signals of the first and second sub-bands obtained by dividing the first band and those of the other sub-bands, thereby improving the quality of communication in the first and second sub-bands. In particular, the radio-frequency circuit  1  can make it less likely to cause the degradation of the receive sensitivity of signals of the first sub-band and/or the second sub-band, which would be caused by sub-band signals in the gap between the first sub-band and the second sub-band. As a result, the radio-frequency circuit  1  can implement simultaneous communication by using the non-contiguous first and second sub-bands within the first band (intra-band non-contiguous carrier aggregation). The radio-frequency circuit  1  also includes the filter  63  having a pass band corresponding to the third sub-band which includes the first sub-band, the second sub-band, and the gap therebetween. This enables the radio-frequency circuit  1  to transmit a signal of the third sub-band when the first band is not divided into multiple sub-bands, such as the first and second sub-bands. With the above-described configuration, even if the first band is divided into different sub-bands according to the countries or the regions, the radio-frequency circuit  1  is still applicable in such countries or regions. The radio-frequency circuit  1  can support communication in each of the first sub-band, the second sub-band, and the third sub-band including the gap between the first and second sub-bands and also improve the quality of communication in the first and second sub-bands. Hence, the radio-frequency circuit  1  is able to efficiently use a wide communication band. 
     The radio-frequency circuit  1  according to the first embodiment may further include a switch  52 , a power amplifier  11 , and a low-noise amplifier  21 . The switch  52  is connected to the filters  61 ,  62 , and  63 . The power amplifier  11  can connect to the filters  61 ,  62 , and  63  via the switch  52 . The low-noise amplifier  21  can connect to the filters  61 ,  62 , and  63  via the switch  52 . 
     With this configuration, the radio-frequency circuit  1  can use the same power amplifier  11  and the same low-noise amplifier  21  for multiple sub-bands, thereby reducing the number of power amplifiers and the number of low-noise amplifiers. 
     In the radio-frequency circuit  1  according to the first embodiment, the filters  61  and  62  may form a multiplexer  60 . The switch  51  may include a terminal  511  connected to the antenna connecting terminal  100 , a terminal  512  connected to the multiplexer  60 , and a terminal  513  connected to the filter  63 . In the radio-frequency circuit  1  according to the first embodiment, the switch  51  may switch between a first connection state in which the terminals  511  and  512  are connected to each other and a second connection state in which the terminals  511  and  513  are connected to each other. 
     The two filters  61  and  62  are formed as the multiplexer  60  and can thus connect to the switch  51  only via one terminal. The radio-frequency circuit  1  thus requires only a minimal number of terminals of the switch  51 , thereby improving transmission characteristics of the switch  51 . 
     In the radio-frequency circuit  1  according to the first embodiment, the first sub-band or the second sub-band may include a second band used for TDD communication. The second band is a band different from the first band. 
     With this configuration, the radio-frequency circuit  1  does not require an additional circuit element to support communication using the second band. For example, if a communication band for LTE is used as the second band, the radio-frequency circuit  1  can support simultaneous communication using 5GNR and LTE (E-UTRAN New Radio-Dual Connectivity (EN-DC)). The modulation system for a 5GNR signal and that for an LTE signal are different. The radio-frequency circuit  1  may thus switch a dual signal of the power amplifier  11  between when a 5 GNR signal is amplified and when an LTE signal is amplified. In this case, the filter  63  may be omitted. 
     In the radio-frequency circuit  1  according to the first embodiment, the first sub-band and the second sub-band may be allocated to a first mobile network operator in a first region. At least part of the gap between the first sub-band and the second sub-band may be allocated to a second mobile network operator, which is different from the first mobile network operator, in the first region. 
     With this configuration, during the use of a communication service of the first mobile network operator in the first region, a radio-frequency signal of a sub-band allocated to the second mobile network operator is less likely to interfere with radio-frequency signals of the first and second sub-bands allocated to the first mobile network operator. The radio-frequency circuit  1  can thus improve the quality of the communication service of the first mobile network operator. 
     In the radio-frequency circuit  1  according to the first embodiment, the third sub-band may be allocated to a third mobile network operator in a second region, which is different from the first region. 
     With this configuration, when a communication service of the third mobile network operator is used in the second region, the radio-frequency circuit  1  can support communication using the third sub-band allocated to the third mobile network operator. The radio-frequency circuit  1  can thus support both of communication in the first region and that in the second region. 
     A communication apparatus  5  according to the first embodiment includes an RFIC  3  and the radio-frequency circuit  1 . The RFIC  3  processes a radio-frequency signal. The radio-frequency circuit  1  transmits the radio-frequency signal between the RFIC  3  and the antenna  2 . 
     The communication apparatus  5  can achieve advantages similar to those obtained by the radio-frequency circuit  1 . 
     First Modified Example 
     A first modified example of the first embodiment will now be described below. The first modified example is different from the first embodiment principally in that the first and second filters (filters  61  and  62 ) do not form a multiplexer and are individually connected to the antenna switch. The first modified example will be described below with reference to  FIG.  3    mainly by referring to the points different from the first embodiment. 
     [2.1 Circuit Configurations of Radio-Frequency Circuit  1 A and Communication Apparatus  5 A] 
     The circuit configurations of a radio-frequency circuit  1 A and a communication apparatus  5 A according to the first modified example will be discussed below with reference to  FIG.  3   .  FIG.  3    is a circuit diagram of the radio-frequency circuit  1 A and the communication apparatus  5 A according to the first modified example. The communication apparatus  5 A according to the first modified example includes the radio-frequency circuit  1 A, an antenna  2 , an RFIC  3 , and a BBIC  4 . The circuit configuration of the communication apparatus  5 A is similar to that of the communication apparatus  5  of the first embodiment and a detailed explanation thereof will be omitted. 
     [2.1.1. Circuit Configuration of Radio-Frequency Circuit  1 A] 
     As illustrated in  FIG.  3   , the radio-frequency circuit  1 A includes a power amplifier  11 , a low-noise amplifier  21 , switches  51 A and  52 , filters  61 A,  62 A, and  63 , an antenna connecting terminal  100 , a radio-frequency input terminal  111 , and a radio-frequency output terminal  121 . 
     The filter  61 A, which is an example of the first filter, has a pass band corresponding to the first sub-band. The filter  61 A can thus allow radio-frequency signals of the first sub-band to pass therethrough and attenuate radio-frequency signals of the other frequency bands. The filter  61 A has two input/output terminals. One input/output terminal is connected to the switch  51 A so that the filter  61 A can connect to the antenna connecting terminal  100  via the switch  51 A. The other input/output terminal is connected to the switch  52  so that the filter  61 A can connect to the power amplifier  11  and the low-noise amplifier  21  via the switch  52 . 
     The filter  62 A, which is an example of the second filter, has a pass band corresponding to the second sub-band. The filter  62 A can thus allow radio-frequency signals of the second sub-band to pass therethrough and attenuate radio-frequency signals of the other frequency bands. The filter  62 A has two input/output terminals. One input/output terminal is connected to the switch  51 A so that the filter  62 A can connect to the antenna connecting terminal  100  via the switch  51 A. The other input/output terminal is connected to the switch  52  so that the filter  62 A can connect to the power amplifier  11  and the low-noise amplifier  21  via the switch  52 . 
     The filters  61 A and  62 A do not form a multiplexer. That is, the filters  61 A and  62 A are connected to different terminals of the switch  51 A. 
     The switch  51 A is an example of the first switch. The switch  51 A is connected between the antenna connecting terminal  100  and the filters  61 A,  62 A, and  63 . The specific configuration of the switch  51 A is as follows. The switch  51 A has terminals  511 A through  514 A. The terminal  511 A is connected to the antenna connecting terminal  100 . The terminals  512 A,  513 A, and  514 A are respectively connected to the filters  61 A,  62 A, and  63 . 
     With this connection configuration, the switch  51 A can connect the terminal  511 A to at least one of the terminals  512 A through  514 A in response to a control signal from the RFIC  3 , for example. That is, the switch  51 A can switch between the connection state of the antenna  2  to each of the filters  61 A,  62 A, and  63  and the disconnection state of the antenna  2  from each of the filters  61 A,  62 A, and  63 . The switch  51 A can connect the terminal  511 A to both of the terminals  512 A and  513 A at the same time. The switch  51 A is constituted by a multiple-connection switch circuit, for example, which is also known as an antenna switch. 
     [2.2 Advantages and Others] 
     As described above, in the radio-frequency circuit  1 A according to the first modified example, the switch  51 A may include a terminal  511 A connected to the antenna connecting terminal  100 , a terminal  512 A connected to the filter  61 A, a terminal  513 A connected to the filter  62 A, and a terminal  514 A connected to the filter  63 . In the radio-frequency circuit  1 A according to the first modified example, the switch  51 A may switch between a first connection state in which the terminal  511 A is connected to each of the terminals  512 A and  513 A and a second connection state in which the terminal  511 A is connected to the terminal  514 A. 
     With this configuration, the radio-frequency circuit  1 A can individually connect the filters  61 A and  62 A to the switch  51 A, thereby enhancing the isolation characteristics between the filters  61 A and  62 A. 
     Second Modified Example 
     A second modified example of the first embodiment will now be described below. The second modified example is different from the first embodiment principally in that a radio-frequency circuit includes a power amplifier and a low-noise amplifier for the first sub-band and those for the second and third sub-bands. The second modified example will be described below with reference to  FIG.  4    mainly by referring to the points different from the first embodiment. 
     [3.1 Circuit Configurations of Radio-Frequency Circuit  1 B and Communication Apparatus  5 B] 
     The circuit configurations of a radio-frequency circuit  1 B and a communication apparatus  5 B according to the second modified example will be discussed below with reference to  FIG.  4   .  FIG.  4    is a circuit diagram of the radio-frequency circuit  1 B and the communication apparatus  5 B according to the second modified example. The communication apparatus  5 B according to the second modified example includes the radio-frequency circuit  1 B, an antenna  2 , an RFIC  3 , and a BBIC  4 . The circuit configuration of the communication apparatus  5 B is similar to that of the communication apparatus  5  of the first embodiment and a detailed explanation thereof will be omitted. 
     [3.1.1. Circuit Configuration of Radio-Frequency Circuit  1 B] 
     As illustrated in  FIG.  4   , the radio-frequency circuit  1 B includes power amplifiers  11 B and  12 B, low-noise amplifiers  21 B and  22 B, switches  51 ,  52 B, and  53 B, filters  61 ,  62 , and  63 , an antenna connecting terminal  100 , radio-frequency input terminals  111 B and  112 B, and radio-frequency output terminals  121 B and  122 B. 
     The radio-frequency input terminals  111 B and  112 B are terminals for receiving radio-frequency sending signals from the outside of the radio-frequency circuit  1 B. More specifically, a first sub-band sending signal is input into the radio-frequency input terminal  111 B, while second and third sub-band sending signals are input into the radio-frequency input terminal  112 B. 
     The radio-frequency output terminals  121 B and  122 B are terminals for outputting radio-frequency received signals to the outside of the radio-frequency circuit  1 B. More specifically, a first sub-band received signal is output from the radio-frequency output terminal  121 B, while second and third sub-band received signals are output from the radio-frequency output terminal  122 B. 
     The power amplifier  11 B is an example of a first power amplifier. The power amplifier  11 B can connect to the filter  61  via the switch  52 B and amplify a radio-frequency signal received by the radio-frequency input terminal  111 B and transmit the amplified radio-frequency signal to the filter  61 . The power amplifier  11 B can amplify a first sub-band sending signal received via the radio-frequency input terminal  111 B. 
     The power amplifier  12 B is an example of a second power amplifier. The power amplifier  12 B can connect to the filters  62  and  63  via the switch  53 B and amplify a radio-frequency signal received by the radio-frequency input terminal  112 B and transmit the amplified radio-frequency signal to the filters  62  and  63 . The power amplifier  12 B can amplify second and third sub-band sending signals received via the radio-frequency input terminal  112 B. 
     The low-noise amplifier  21 B is an example of a first low-noise amplifier. The low-noise amplifier  21 B can connect to the filter  61  via the switch  52 B and amplify a radio-frequency signal received by the antenna connecting terminal  100 . The low-noise amplifier  21 B can amplify a first sub-band received signal received from the antenna connecting terminal  100  via the switch  51 , the filter  61 , and the switch  52 B. A radio-frequency signal amplified by the low-noise amplifier  21 B is output to the radio-frequency output terminal  121 B. 
     The low-noise amplifier  22 B is an example of a second low-noise amplifier. The low-noise amplifier  22 B can connect to the filters  62  and  63  via the switch  53 B and amplify a radio-frequency signal received by the antenna connecting terminal  100 . The low-noise amplifier  22 B can amplify a second sub-band received signal received from the antenna connecting terminal  100  via the switch  51 , the filter  62 , and the switch  53 B and can also amplify a third sub-band received signal received from the antenna connecting terminal  100  via the switch  51 , the filter  63 , and the switch  53 B. A radio-frequency signal amplified by the low-noise amplifier  22 B is output to the radio-frequency output terminal  122 B. 
     The switch  52 B is an example of the second switch and is connected between the filter  61  and each of the power amplifier  11 B and the low-noise amplifier  21 B. More specifically, the switch  52 B has terminals  521 B,  522 B, and  523 B. The terminal  521 B is connected to the filter  61 . The terminals  522 B and  523 B are respectively connected to the power amplifier  11 B and the low-noise amplifier  21 B. 
     With this connection configuration, the switch  52 B can connect the terminal  521 B to one of the terminals  522 B and  523 B in response to a control signal from the RFIC  3 , for example. That is, the switch  52 B can selectively connect the filter  61  to the power amplifier  11 B or to the low-noise amplifier  21 B. The switch  52 B is constituted by an SPDT switch circuit, for example. 
     The switch  53 B is an example of a third switch and is connected between the filters  62  and  63  and each of the power amplifier  12 B and the low-noise amplifier  22 B. More specifically, the switch  53 B has terminals  531 B through  534 B. The terminals  531 B and  532 B are respectively connected to the filters  62  and  63 . The terminals  533 B and  534 B are respectively connected to the power amplifier  12 B and the low-noise amplifier  22 B. 
     With this connection configuration, the switch  53 B can connect each of the terminals  531 B and  532 B to one of the terminals  533 B and  534 B in response to a control signal from the RFIC  3 , for example. That is, the switch  53 B can selectively connect the filter  62  to the power amplifier  12 B or to the low-noise amplifier  22 B. The switch  53 B can also selectively connect the filter  63  to the power amplifier  12 B or to the low-noise amplifier  22 B. The switch  53 B is constituted by two SPDT switch circuits, for example. 
     [3.2 Advantages and Others] 
     As described above, the radio-frequency circuit  1 B according to the second modified example includes switches  52 B and  53 B, power amplifiers  11 B and  12 B, and low-noise amplifiers  21 B and  22 B. The switch  52 B is connected to the filter  61 . The power amplifier  11 B can connect to the filter  61  via the switch  52 B. The low-noise amplifier  21 B can connect to the filter  61  via the switch  52 B. The switch  53 B is connected to the filters  62  and  63 . The power amplifier  12 B can connect to the filters  62  and  63  via the switch  53 B. The low-noise amplifier  22 B can connect to the filters  62  and  63  via the switch  53 B. 
     With this configuration, the radio-frequency circuit  1 B uses the same power amplifier  12 B and the same low-noise amplifier  22 B for amplifying the second and third sub-band signals, thereby reducing the number of power amplifiers and the number of low-noise amplifiers. The radio-frequency circuit  1 B uses different power amplifiers and different low-noise amplifiers for the first sub-band signals and the second sub-band signals. Hence, the performance required for a power amplifier and a low-noise amplifier to implement simultaneous communication of the first and second sub-bands becomes less demanding when different power amplifiers and different low-noise amplifiers are used than when the same power amplifier and the same low-noise amplifier are used. The radio-frequency circuit  1 B can also improve the quality of simultaneous communication using the first and second sub-bands. 
     In the radio-frequency circuit  1 B according to the second modified example, the bandwidth of the second sub-band may be wider than that of the first sub-band. 
     With this configuration, the same amplifier can be used for the second sub-band having a wider bandwidth than the first sub-band and for the third sub-band. The amplification characteristics in the second sub-band when the same amplifier is used for the second sub-band having a wider bandwidth and for the third sub-band are less likely to deteriorate than those in the first sub-band when the same amplifier is used for the first sub-band having a narrower bandwidth and for the third sub-band. It is thus possible to suppress the degradation of the amplification characteristics (such as a decline in the peak gain) caused by the use of the same amplifier for multiple sub-bands, as well as to reduce the number of amplifiers. 
     Third Modified Example 
     A third modified example of the first embodiment will now be described below. In the first embodiment and the first and second modified examples thereof, the third sub-band includes two sub-bands and a gap therebetween. However, the third sub-band may include three or more sub-bands and gaps therebetween. In the third modified example, the third sub-band also include a fourth sub-band. The third modified example will be described below with reference to  FIG.  5    mainly by referring to the points different from the first embodiment. 
     [4.1 Circuit Configurations of Radio-Frequency Circuit  1 C and Communication Apparatus  5 C] 
     The circuit configurations of a radio-frequency circuit  1 C and a communication apparatus  5 C according to the third modified example will be discussed below with reference to  FIG.  5   .  FIG.  5    is a circuit diagram of the radio-frequency circuit  1 C and the communication apparatus  5 C according to the third modified example. The communication apparatus  5 C according to the third modified example includes the radio-frequency circuit  1 C, an antenna  2 , an RFIC  3 , and a BBIC  4 . The circuit configuration of the communication apparatus  5 C is similar to that of the communication apparatus  5  of the first embodiment and a detailed explanation thereof will be omitted. 
     [4.1.1. Circuit Configuration of Radio-Frequency Circuit  1 C] 
     As illustrated in  FIG.  5   , the radio-frequency circuit  1 C includes a power amplifier  11 , a low-noise amplifier  21 , switches  51  and  52 C, filters  61 ,  62 ,  63 , and  64 C, an antenna connecting terminal  100 , a radio-frequency input terminal  111 , and a radio-frequency output terminal  121 . 
     The filter  64 C, which is an example of a fourth filter, has a pass band corresponding to the fourth sub-band. The filter  64 C can thus allow radio-frequency signals of the fourth sub-band to pass therethrough and attenuate radio-frequency signals of the other frequency bands. The filter  64 C has two input/output terminals. One input/output terminal is connected to the switch  51  so that the filter  64 C can connect to the antenna connecting terminal  100  via the switch  51 . The other input/output terminal is connected to the switch  52 C so that the filter  64 C can connect to the power amplifier  11  and the low-noise amplifier  21  via the switch  52 C. 
     In the third modified example, the filters  61 ,  62 , and  64 C form one multiplexer  60 C. That is, the filters  61 ,  62 , and  64 C are integrated into one filter, which is connected to one terminal of the switch  51 . 
     As in the first and second sub-bands, the fourth sub-band is included in the third sub-band. There is a gap between the fourth sub-band and the first sub-band. There is also a gap between the fourth sub-band and the second sub-band. 
     The switch  52 C is an example of the second switch. The switch  52 C is connected between the filters  61 ,  62 ,  63 , and  64 C and each of the power amplifier  11  and the low-noise amplifier  21 . The specific configuration of the switch  52 C is as follows. The switch  52 C has terminals  521 C through  526 C. The terminals  521 C,  522 C,  523 C, and  524 C are respectively connected to the filters  61 ,  62 ,  64 C, and  63 . The terminals  525 C and  526 C are respectively connected to the power amplifier  11  and the low-noise amplifier  21 . 
     With this connection configuration, the switch  52 C can connect each of the terminals  521 C through  524 C to one of the terminals  525 C and  526 C in response to a control signal from the RFIC  3 , for example. That is, the switch  52 C can selectively connect the filter  61  to the power amplifier  11  or to the low-noise amplifier  21 . The switch  52 C can also selectively connect the filter  62  to the power amplifier  11  or to the low-noise amplifier  21 . The switch  52 C can also selectively connect the filter  63  to the power amplifier  11  or to the low-noise amplifier  21 . The switch  52 C can also selectively connect the filter  64 C to the power amplifier  11  or to the low-noise amplifier  21 . The switch  52 C can connect at least two of the terminals  521 C through  523 C to one of the terminals  525 C and  526 C at the same time. That is, the switch  52 C can connect at least two of the filters  61 ,  62 , and  64 C to the power amplifier  11  or to the low-noise amplifier  21  at the same time. The switch  52 C is constituted by a multiple-connection switch circuit, for example. 
     [4.2 Advantages and Others] 
     As described above, the radio-frequency circuit  1 C according to the third modified example may further include a filter  64 C. The filter  64 C has a pass band corresponding to a fourth sub-band included in the first band and can connect to the antenna connecting terminal  100  via the switch  51 . There is a gap between the fourth sub-band and each of the first sub-band and the second sub-band. The third sub-band may also include the fourth sub-band. 
     The radio-frequency circuit  1 C includes the filter  64 C having a pass band corresponding to the fourth sub-band. The radio-frequency circuit  1 C can thus support communication in each of the first sub-band, the second sub-band, the fourth sub-band, and the third sub-band including gaps therebetween and also improve the quality of communication in the first, second, and fourth sub-bands. 
     The third sub-band may include one or more sub-bands in addition to the first, second, and fourth sub-bands. In this case, the radio-frequency circuit  1 C may include one or more filters whose pass bands individually correspond to the additional sub-bands. 
     EXAMPLES 
     Examples of the individual sub-bands used in the above-described first embodiment and modified examples thereof will be explained below with reference to  FIG.  6   .  FIG.  6    is a table illustrating some specific examples of the sub-bands. The sub-bands illustrated in  FIG.  6    are only examples and do not limit sub-bands to which the above-described first embodiment and modified examples are applicable. 
     The table illustrated in  FIG.  6    shows nine specific examples that can be identified by No. 1 through No. 9. The nine specific examples will be individually explained below in this order. Hereinafter, three different MNOs will be called MNO1, MNO2, and MNO3. 
     [No. 1] 
     As the first sub-band, a frequency band of 3.7 to 3.8 gigahertz (GHz) is used. As the second sub-band, a frequency band of 4.0 to 4.1 GHz is used. As the third sub-band, a frequency band of 3.3 to 4.2 GHz is used. 
     The third sub-band includes band n77 for 5GNR, which is an example of the first band. In Japan, the first sub-band and the second sub-band are both allocated to MNO1, while one or more sub-bands included in the gap between the first and second sub-bands are allocated to MNO2 and/or MNO3. 
     [No. 2] 
     As the first sub-band, a frequency band of 3.44 to 3.52 GHz is used. As the second sub-band, a frequency band of 3.6 to 3.7 GHz is used. As the third sub-band, the frequency band of 3.3 to 4.2 GHz is used. 
     The third sub-band includes band n77 for 5GNR, which is an example of the first band. In Japan, the first sub-band and the second sub-band are both allocated to MNO2, while the gap between the first and second sub-bands is allocated to MNO1 and/or MNO3. 
     [No. 3] 
     As the first sub-band, the frequency band of 3.44 to 3.52 GHz is used. As the second sub-band, a frequency band of 3.55 to 3.70 GHz is used. As the third sub-band, the frequency band of 3.3 to 4.2 GHz is used. 
     The third sub-band includes band n77 for 5GNR, which is an example of the first band. The second sub-band includes band n48 for 5GNR or Band 48 for LTE, both of which are examples of a second band. In Japan, the first sub-band and part of the second sub-band are both allocated to MNO2, while the gap between the first and second sub-bands and the remaining part of the second sub-band are allocated to MNO1 and/or MNO3. 
     [No. 4] 
     As the first sub-band, a frequency band of 3.4 to 3.6 GHz is used. As the second sub-band, a frequency band of 3.9 to 4.0 GHz is used. As the third sub-band, the frequency band of 3.3 to 4.2 GHz is used. 
     The third sub-band includes band n77 for 5GNR, which is an example of the first band. In Japan, the first sub-band includes two frequency bands allocated to MNO3 and also includes two frequency bands allocated to MNO1 and MNO2. In Japan, the second sub-band is allocated to MNO3, while the gap between the first and second sub-bands is allocated to MNO1 and/or MNO2. 
     [No. 5] 
     As the first sub-band, a frequency band of 3.3 to 3.8 GHz is used. As the second sub-band, a frequency band of 3.9 to 4.0 GHz is used. As the third sub-band, the frequency band of 3.3 to 4.2 GHz is used. 
     The third sub-band includes band n77 for 5GNR, which is an example of the first band. The first sub-band includes band n78 for 5GNR, which is an example of the second band. In Japan, the first sub-band includes two frequency bands allocated to MNO3. In Japan, the second sub-band is allocated to MNO3, while the gap between the first and second sub-bands is allocated to MNO1 and/or MNO2. 
     [No. 6] 
     As the first sub-band, a frequency band of 3.40 to 3.44 GHz is used. As the second sub-band, a frequency band of 3.56 to 3.60 GHz is used. As the third sub-band, the frequency band of 3.3 to 4.2 GHz is used. As the fourth sub-band, a frequency band of 3.9 to 4.0 GHz is used. 
     The third sub-band includes band n77 for 5GNR, which is an example of the first band. In Japan, the first sub-band, the second sub-band, and the fourth sub-band are all allocated to MNO3, while the gap between the first and second sub-bands and the gap between the second and fourth sub-bands are allocated to MNO2 and/or MNO3. 
     [No. 7] 
     As the first sub-band, the frequency band of 3.40 to 3.44 GHz is used. As the second sub-band, the frequency band of 3.56 to 3.60 GHz is used. As the third sub-band, a frequency band of 3.3 to 3.8 GHz is used. 
     The third sub-band includes band n78 for 5GNR, which is an example of the first band. In Japan, the first sub-band and the second sub-band are both allocated to MNO3, while the gap between the first and second sub-bands is allocated to MNO2 and/or MNO3. 
     [No. 8] 
     As the first sub-band, a frequency band of 5.15 to 5.35 GHz is used. As the second sub-band, a frequency band of 5.470 to 5.925 GHz is used. As the third sub-band, a frequency band of 5.150 to 5.925 GHz is used. 
     [No. 9] 
     As the first sub-band, a frequency band of 5.925 to 6.425 GHz is used. As the second sub-band, a frequency band of 6.525 to 7.125 GHz is used. As the third sub-band, a frequency band of 5.925 to 7.125 GHz is used. 
     Second Embodiment 
     A second embodiment will now be described below. The second embodiment is different from the first embodiment mainly in that frequency bands included in a frequency range (frequency range 2 (FR2)) of millimeter-wave bands are used as the first through third sub-bands. The second embodiment will be described below with reference to  FIG.  7    mainly by referring to the points different from the first embodiment. 
     [4.1 Circuit Configurations of Radio-Frequency Circuit  1 D and Communication Apparatus  5 D] 
       FIG.  7    is a circuit diagram of a radio-frequency circuit  1 D and a communication apparatus  5 D according to the second embodiment. As illustrated in  FIG.  7   , the communication apparatus  5 D includes the radio-frequency circuit  1 D, an antenna  2 , a power amplifier  13 , a low-noise amplifier  23 , switches  54  and  55 , a phase shifter  71 , and a BBIC  4 . The communication apparatus  5 D of the second embodiment is different from the communication apparatus  5  of the first embodiment in that the switches  54  and  55 , power amplifier  13 , low-noise amplifier  23 , and phase shifter  71  are added. The configuration of the radio-frequency circuit  1 D is also different from that of the radio-frequency circuit  1 . 
     The switch  54  is a switch circuit that selectively connects to the power amplifier  13  or to the low-noise amplifier  23 . Likewise, the switch  55  is a switch circuit that selectively connects to the power amplifier  13  or to the low-noise amplifier  23 . That is, the switches  54  and  55  are switch circuits that allow a sending signal to be sent from the antenna  2  or a received signal received by the antenna  2  to flow through the communication apparatus  5 D. 
     The power amplifier  13  is connected between the switches  54  and  55  and amplifies sending signals of the first, second, and third sub-bands. The low-noise amplifier  23  is connected between the switches  54  and  55  and amplifies received signals of the first, second, and third sub-bands. 
     The phase shifter  71  is connected between the switch  55  and the antenna connecting terminal  100  of the radio-frequency circuit  1 D and shifts the phase of sending signals of the first, second, and third sub-bands and that of received signals of the first, second, and third sub-bands. 
     The radio-frequency circuit  1 D includes a power amplifier  11 , a low-noise amplifier  21 , switches  51  and  52 , filters  61 ,  62 , and  63 , mixers  81  and  82 , an antenna connecting terminal  100 , a radio-frequency input terminal  111 , and a radio-frequency output terminal  121 . 
     The mixer  81  is connected between a terminal  524  of the switch  52  and the output terminal of the power amplifier  11  and converts an intermediate-frequency sending signal to a millimeter-wave sending signal. 
     The mixer  82  is connected between a terminal  525  of the switch  52  and the input terminal of the low-noise amplifier  21  and converts a millimeter-wave received signal to an intermediate-frequency received signal. 
     In the second embodiment, as the filters  61 ,  62 , and  63 , a distributed-element circuit or a stub may be used. 
     In the second embodiment, as the first band, 5GNR n257, n258, n259, n260, or n262, for example, may be used. However, the first band is not limited to these bands. 
     Other Modified Examples 
     The radio-frequency circuits and communication apparatuses have been discussed above through illustration of the embodiments and modified examples. However, the invention is not restricted to the above-described embodiments and modified examples. Other embodiments implemented by combining certain components in the above-described embodiments and modified examples, and other modified examples obtained by making various modifications to the above-described embodiments by those skilled in the art without departing from the scope and spirit of the invention are also encompassed in the invention. Various devices integrating the above-described radio-frequency circuits and communication apparatuses are also encompassed in the invention. 
     For example, in the circuit configurations of the radio-frequency circuits and communication apparatuses according to the embodiments and modified examples, another circuit element and another wiring may be inserted onto a path connecting circuit elements and/or a path connecting signal paths illustrated in the drawings. For example, in the above-described embodiments, a filter may be inserted between the antenna connecting terminal  100  and the switch  51 . A matching circuit may be inserted between the antenna connecting terminal  100  and the filters  61 ,  62 , and  63  and/or between the filters  61 ,  62 , and  63  and each of the power amplifier  11  and the low-noise amplifier  21 . 
     In the above-described embodiments and modified examples, TDD communication bands for 5GNR or LTE are used. In addition to or instead of 5GNR or LTE, a communication band for another radio access technology (RAT) may be used. For example, a communication band for a WLAN may be used as a TDD communication band. Additionally, a millimeter-wave band of 7 GHz or higher may be used as a TDD communication band. In this case, a distributed-element filter may be used as a filter. 
     In the above-described embodiments and modified examples, the same power amplifier and the same low-noise amplifier are used for two or three sub-bands. However, this is only an example. For instance, a power amplifier and a low-noise amplifier may be provided for each sub-band. For example, in  FIG.  1   , the filter  61  may connect to a first power amplifier and a first low-noise amplifier via a switch; the filter  62  may connect to a second power amplifier and a second low-noise amplifier via a switch; and the filter  63  may connect to a third power amplifier and a third low-noise amplifier via a switch. 
     The present invention can be widely used for a communication apparatus, such as a cellular phone, as a radio-frequency circuit provided in a front-end portion.