JP2015029238A - Duplexer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a variable frequency duplexer that can transmit/receive communication signals at low loss in each of a plurality of frequency bands, in a simple configuration.SOLUTION: A variable frequency duplexer 10 includes a transmission terminal Ptx, a reception terminal Prx and a common terminal Pcom. The transmission terminal Ptx and the reception terminal Prx are connected with first and second phase shift circuits 21, 22 having the same circuit configuration, respectively. An impedance compensation circuit 30 is connected between a junction A of the first and second phase shift circuits 21, 22 and the common terminal Pcom. The impedance compensation circuit 30 includes an inductor 301 connected between the junction A and the common terminal Pcom, and a capacitor 302 connected between a common terminal Pcom side of the inductor 301 and a ground. The capacitor 302 is a variable capacitance element, and a change in capacitance adjusts a characteristic of isolation between transmission and reception and reduces insertion losses in transmission and reception signals.

Description

  The present invention relates to a duplexer that includes a transmission terminal, a reception terminal, and a common terminal, a high-frequency signal input from the transmission terminal is output from the common terminal, and a high-frequency signal input from the common terminal is output from the reception terminal.

  2. Description of the Related Art Conventionally, an apparatus that transmits and receives a high-frequency signal wirelessly, such as a portable communication device, generally uses a common antenna for a transmission signal and a reception signal. In this case, a duplexer is often used to supply a transmission signal from the transmission circuit to the antenna and transmit a reception signal from the antenna to the reception circuit.

  For example, FIG. 22.7.2 of Non-Patent Document 1 describes that a duplexer is realized by using a circuit configuration of a divider (distributor). This duplexer uses a so-called Wilkinson divider configuration. In such a configuration, there are few circuit components of the duplexer, and transmission / reception with low loss becomes possible. In this case, since a distribution loss occurs, a duplexer having a filter configuration is used when the transmission frequency and the reception frequency are different.

22.7 A Tunable Integrated Duplexer with 50 dB Isolation in 40 nm CMOS, M.M. Mikhemar, H.M. Darabi, A .; Abidi, ISSCC 2009 / SESSION 22 / PA AND ANTENNA INTERFACE / 22.7

  On the other hand, there is a problem that the number of duplexers is increased as a result of the trend toward multibanding. In the conventional circuit configuration described above, when transmission / reception is performed in a single narrow frequency band, each communication signal, that is, a transmission signal and a reception signal can be transmitted with low loss, but a plurality of different frequency bands are used. It is difficult to transmit communication signals with low loss.

  For example, in order to transmit and receive a plurality of communication signals using different frequency bands with low loss, it is necessary to provide the above-described divider circuit configuration for each communication signal, which increases the size of the duplexer.

  Moreover, although it is described that the frequency to be transmitted can be varied by using the circuit configuration as shown in FIG. 22.7.3 of Non-Patent Document 1, the circuit configuration becomes complicated and a plurality of transmission attempts are made. The difference in loss between the frequency bands of communication signals becomes large and lacks practicality. Furthermore, when the impedance of the antenna connected to the common terminal changes due to the influence of a human body or the like, there is a problem that the isolation between the transmission signal and the reception signal deteriorates.

  An object of the present invention is to provide a duplexer that can transmit and receive a communication signal with low loss in each of a plurality of frequency bands and that can improve isolation between a transmission signal and a reception signal with a simpler circuit configuration than conventional ones.

  The present invention relates to a duplexer that includes a transmission terminal, a reception terminal, and a common terminal, outputs a transmission signal input from the transmission terminal from the common terminal, and outputs a reception signal input from the common terminal from the reception terminal. Have the following characteristics. The duplexer of the present invention includes a first phase shift circuit, a second phase shift circuit, an impedance compensation circuit, and a termination resistor. The first phase shift circuit includes a first inductor and a first capacitor connected between the transmission terminal and the common terminal. The second phase shift circuit is connected between the reception terminal and the common terminal, and includes a second inductor and a second capacitor. The impedance compensation circuit includes a first variable capacitor. The first variable capacitor is connected between a connection point of the first phase shift circuit and the second phase shift circuit and a transmission line or inductor connecting the common terminal and the ground. The termination resistor is connected between the transmission terminal and the reception terminal.

  With this configuration, it is possible to ensure isolation between the transmission terminal and the reception terminal in the transmission signal having the first frequency determined by the first and second phase shift circuits, the impedance compensation circuit, and the termination resistor. Furthermore, by adjusting the capacitance of the first variable capacitor of the impedance compensation circuit, it is possible to ensure isolation between the transmission terminal and the reception terminal even at a frequency different from the first frequency. At this time, since the impedance between the common terminal and the transmission terminal and the impedance between the common terminal and the reception terminal can also be adjusted by the impedance compensation circuit, the impedance is reduced not only at the first frequency but also at a plurality of frequencies. Loss transmission / reception becomes possible. That is, a frequency variable duplexer can be configured.

  The duplexer according to the present invention preferably further includes a second variable capacitor connected between the first variable capacitor of the impedance compensation circuit and the branch connection point remote from the first variable capacitor.

  In this configuration, by adjusting the capacitance of the second variable capacitor, transmission / reception can be performed with low loss even when the impedance of the antenna connected to the common terminal changes.

  The duplexer of the present invention preferably includes a capacitance adjustment circuit that monitors the transmission signal and the reception signal transmitted to the transmission terminal and the reception terminal and adjusts the capacitance of the second variable capacitor.

  In this configuration, since the leakage of the transmission signal to the reception terminal can be observed and fed back to the impedance compensation circuit, the S / N ratio of the reception circuit unit due to the leakage of the transmission signal to the reception circuit unit connected to the reception terminal can be reduced. Impedance can be optimized to suppress degradation.

  The duplexer of the present invention preferably includes a series circuit of an inductor and a capacitor connected between the connection point and the ground, and includes a trap circuit having a harmonic frequency of the transmission signal as a resonance frequency.

  In this configuration, it is possible to suppress the harmonics of the transmission signal from being output from the common terminal to the outside.

  According to the present invention, a communication signal can be transmitted and received with a low loss in each of a plurality of frequency bands, though the circuit configuration is simpler than in the past.

1 is a circuit diagram of a variable frequency duplexer according to a first embodiment of the present invention. It is a graph which shows the isolation characteristic between the transmission terminal and receiving terminal of the variable frequency duplexer which concerns on the 1st Embodiment of this invention. It is a graph which shows the insertion loss characteristic of the transmission signal and reception signal of the frequency variable duplexer which concerns on the 1st Embodiment of this invention. It is a circuit diagram of the frequency variable duplexer which concerns on the 2nd Embodiment of this invention. It is a figure which shows the change of the isolation characteristic between transmission / reception when the impedance of the external circuit connected to the common terminal Pcom changes. It is a circuit diagram of the frequency variable duplexer which concerns on the 3rd Embodiment of this invention. It is a circuit diagram of the variable frequency duplexer which concerns on the 4th Embodiment of this invention. It is a circuit diagram of the frequency variable duplexer which concerns on the 5th Embodiment of this invention.

  A frequency variable duplexer according to a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram of a variable frequency duplexer according to a first embodiment of the present invention. FIG. 2 is a graph showing isolation characteristics between the transmission terminal and the reception terminal of the variable frequency duplexer according to the first embodiment of the present invention. FIG. 3 is a graph showing insertion loss characteristics of a transmission signal and a reception signal of the variable frequency duplexer according to the first embodiment of the present invention.

  The variable frequency duplexer 10 includes a transmission terminal Ptx, a reception terminal Prx, and a common terminal Pcom. A first phase shift circuit 21 is connected to the transmission terminal Ptx, and a second phase shift circuit 22 is connected to the reception terminal Prx. The end of the first phase shift circuit 21 opposite to the side connected to the transmission terminal Ptx and the end of the second phase shift circuit 22 opposite to the side connected to the reception terminal Prx are connected at the connection point A. ing. An impedance compensation circuit 30 is connected between the connection point A and the common terminal Pcom. In addition, a midpoint between the transmission terminal Ptx and the first phase shift circuit 21 and a midpoint between the reception terminal Prx and the second phase shift circuit 22 are connected by a termination resistor 23.

  The first phase shift circuit 21 includes an inductor 211 and a capacitor 212. The inductor 211 is connected between the transmission terminal Ptx and the connection point A. The capacitor 212 is connected between the end of the inductor 211 on the transmission terminal Ptx side and the ground.

  The inductance of the inductor 211 and the capacitance of the capacitor 212, that is, the impedance of the first phase shift circuit are determined based on the frequency of the first communication signal including the first transmission signal and the first reception signal. Specifically, the first phase shift circuit is set to shift the phase of the first transmission signal input from the transmission terminal Ptx by ¼ of the wavelength of the first transmission signal.

  The second phase shift circuit 22 includes an inductor 221 and a capacitor 222. The inductor 221 is connected between the reception terminal Prx and the connection point A. The capacitor 222 is connected between the end of the inductor 221 on the receiving terminal Prx side and the ground.

  The inductance of the inductor 221 and the capacitance of the capacitor 222 are substantially the same as the inductance of the inductor 211 and the capacitance of the capacitor 212. That is, the second phase shift circuit is substantially the same as the first phase shift circuit.

  The impedance of the termination resistor 23 is set to approximately twice the characteristic impedance of the receiving circuit in the high frequency circuit, for example.

  The impedance compensation circuit 30 includes an inductor 301 and a capacitor 302. The capacitor 302 is a variable capacitance element. The inductor 301 is connected between the connection point A and the common terminal Pcom. The capacitor 302 is connected between the end of the inductor 301 on the common terminal Pcom side and the ground.

  Such a circuit configuration is a configuration in which an impedance compensation circuit 30 is connected between a connection point of a so-called Wilkinson divider and a common terminal Pcom.

  In such a circuit configuration, the first transmission signal and the first reception signal constituting the first communication signal are transmitted as follows.

  The first transmission signal input from the transmission terminal Ptx is transmitted to the common terminal Pcom via the first phase shift circuit 21, the connection point A, and the impedance compensation circuit 30.

  Further, considering the transmission path from the transmission terminal Ptx to the reception terminal Prx, the first transmission path that transmits the first phase shift circuit 21, the connection point A, and the second phase shift circuit 22, and the first transmission path that transmits the resistor 23. There are two transmission paths. The component that transmits the first transmission path in the first transmission signal has a half (half wavelength) phase of the wavelength. Accordingly, the component that transmits the first transmission path and the component that transmits the second transmission path in the first transmission signal have opposite phases. Thereby, the component transmitted through the first transmission path and the component transmitted through the second transmission line are canceled out, and the first transmission signal is not transmitted to the reception terminal Prx. That is, the isolation between the transmission terminal Ptx and the reception terminal Prx can be ensured at the frequency of the first transmission signal.

  Further, at the frequency of the first reception signal, the impedance when the first phase shift circuit 21 side is viewed from the connection point A and the impedance when the second phase shift circuit 22 side is viewed from the connection point A are connected to the reception terminal Prx. It is twice the impedance of the receiving circuit. Therefore, the impedance when the first and second phase shift circuits 21 and 22 are viewed from the connection point A matches the impedance of the receiving circuit. As a result, the first received signal that reaches the connection point A from the common terminal Pcom via the impedance compensation circuit 30 is transmitted to the first phase shift circuit 21 and the second phase shift circuit 22 with low loss.

  Since the first phase circuit 21 and the second phase shift circuit 22 have substantially the same circuit configuration, at both ends of the resistor 23, the component transmitted through the first phase shift circuit 21 in the first received signal and the first reception The phase of the component transmitted through the second phase shift circuit 22 in the signal is the same. Therefore, these components are not canceled out. As a result, the first reception signal is transmitted to the reception terminal Prx with low loss.

  As described above, by using the configuration of the present embodiment, a low-loss duplexer can be configured for the first communication signal (the first transmission signal and the first reception signal) except for the distribution loss.

  Furthermore, if the configuration of the present embodiment is used, a low-loss duplexer can be realized for a communication signal using another frequency band whose frequency band is relatively close to that of the first communication signal. For example, when the first communication signal uses approximately 800 MHz, a low loss frequency variable transmission / reception duplexer (frequency variable duplexer) is realized even for communication signals using a frequency band from approximately 700 MHz to approximately 900 MHz. it can.

  In the case of a second communication signal (second transmission signal and second reception signal) that uses a frequency band different from that of the first communication signal (first transmission signal and first reception signal), the capacitance of the capacitor 302 of the impedance compensation circuit 30 is changed. Change. As described above, when the capacitance of the capacitor 302 is changed, the impedance of the transmission path for transmission from the transmission terminal Ptx to the reception terminal Prx via the first and second phase shift circuits 21 and 22 can be changed. Therefore, with respect to the second transmission signal, the amount of phase change from the transmission terminal Ptx to the end of the resistor 23 on the reception terminal Prx side via the first and second phase shift circuits 21 and 22 is determined. 2 The wavelength of the transmission signal can be approximately ½. Thereby, the isolation between the transmission terminal Ptx and the reception terminal Prx at the frequency of the second transmission signal can be ensured.

  The first phase circuit 21 and the second phase shift circuit 22 have the same circuit configuration, and the frequency of the first reception signal is close to the frequency of the second reception signal. The impedance when the first phase shift circuit 21 side is viewed from the side and the impedance when the second phase shift circuit 22 side is viewed from the connection point A can be approximately double the impedance of the reception circuit connected to the reception terminal Prx. . Therefore, the impedance of the first and second phase shift circuits 21 and 22 viewed from the connection point A substantially matches the impedance of the receiving circuit. At this time, the impedance viewed from the common terminal Pcom to the reception terminal Prx and the transmission terminal Ptx can be made closer to the impedance of the reception circuit by passing through the impedance compensation circuit 30. Thus, the second received signal input from the common terminal Pcom is transmitted to the first phase shift circuit 21 and the second phase shift circuit 22 with low loss.

  At both ends of the resistor 23, the phase of the component transmitted through the first phase shift circuit 21 in the second received signal and the component transmitted through the second phase shift circuit 22 in the second received signal are the same. Therefore, these components are not canceled out. Thereby, the second received signal is transmitted to the receiving terminal Prx with low loss.

  As described above, by using the configuration of the present embodiment, the transmission terminal Ptx and the transmission terminal Ptx can be used for communication signals of different types of frequencies by simply changing the capacitance of the impedance compensation circuit 30 using a single circuit configuration. Isolation between the reception terminals Prx can be ensured, and insertion loss between the common terminal Pcom, the transmission terminal Ptx, and the reception terminal Prx can be suppressed. As a result, it is possible to configure a frequency-variable and low-loss duplexer.

  FIG. 2 is a graph illustrating an example of isolation characteristics between the transmission terminal and the reception terminal of the variable frequency duplexer according to the first embodiment of the present invention. A characteristic curve represented by C = C1 in FIG. 2 is a characteristic curve when the capacitance of the capacitor 302 described above is a default value, that is, a value corresponding to the frequency f1 of the first transmission signal. A characteristic curve represented by C = C2 is a characteristic curve obtained by the capacitance of the capacitor 302 when the second transmission signal having the frequency f2 that is lower than the frequency f1 of the first transmission signal is used. A characteristic curve represented by C = C3 is a characteristic curve obtained by the capacitance of the capacitor 302 when a third transmission signal having a frequency f3 that is higher than the frequency f1 of the first transmission signal is used. The other characteristic curve indicates a case where the capacitor 302 has a predetermined value other than C1, C2, and C3.

  As shown in FIG. 2, for the first transmission signal, an isolation of −30 dB or more is ensured in a frequency band having a width of approximately 60 MHz centered on the frequency f1 (approximately 800 MHz) of the first transmission signal. can do.

  Further, with respect to the second transmission signal, an isolation of −30 dB or more can be ensured in a frequency band having a width of about 50 MHz centered on the frequency f2 (about 720 MHz) of the second transmission signal.

  Further, with respect to the third transmission signal, an isolation of −30 dB or more can be ensured in a frequency band with a width of about 70 MHz centered on the frequency f3 (about 920 MHz) of the third transmission signal.

  Thus, by using the configuration of the present embodiment, it is possible to ensure isolation between the transmission terminal Ptx and the reception terminal Prx for a plurality of communication signals having different frequency bands.

  FIG. 3 is a graph showing insertion loss characteristics of a transmission signal and a reception signal of the variable frequency duplexer according to the first embodiment of the present invention. Also in FIG. 3, the characteristic curve represented by C = C2 is a characteristic curve obtained by the capacitance of the capacitor 302 when the second transmission signal having the frequency f2 which is lower than the frequency f1 of the first transmission signal is used. is there. A characteristic curve represented by C = C3 is a characteristic curve obtained by the capacitance of the capacitor 302 when a third transmission signal having a frequency f3 that is higher than the frequency f1 of the first transmission signal is used. The characteristic curve represented by Tx is the insertion loss of the transmission signal, and the characteristic curve represented by Rx is the insertion loss of the reception signal.

  As shown in FIG. 3, by using the configuration of the present embodiment, the insertion loss of the transmission signal and the frequency band BAND (f2) including the frequency f2 and the frequency band BAND (f3) including the frequency f3 are reduced. The insertion loss of the received signal can be reduced. That is, it can function as a low-loss variable frequency duplexer in both frequency bands BAND (f2) and BAND (f3).

  Next, a variable frequency duplexer according to a second embodiment of the present invention will be described with reference to the drawings. FIG. 4 is a circuit diagram of the variable frequency duplexer according to the first embodiment of the present invention.

  The frequency variable duplexer 10A of this embodiment is obtained by adding an impedance compensation capacitor 40 to the frequency variable duplexer 10 shown in the first embodiment, and other configurations are the same as those of the first embodiment. This is the same as the variable frequency duplexer 10 shown. Therefore, only different parts will be specifically described.

  The capacitor 40 is a variable capacitance element. The capacitor 40 is connected between the connection point A and the ground. In such a configuration, by changing the capacitance of the capacitor 40, it is possible to suppress deterioration of isolation between transmission and reception due to impedance change of an external circuit (specifically, for example, an antenna) connected to the common terminal Pcom. .

  FIG. 5 is a diagram illustrating a change in isolation characteristics between transmission and reception when the impedance of an external circuit connected to the common terminal Pcom changes. FIG. 5A shows a case where compensation by the capacitor 40 of the present embodiment is not performed, and FIG. 5B shows a case where compensation by the capacitor 40 of the present embodiment is performed. In FIG. 5, the element value of each element of the frequency variable duplexer 10A is determined so that each characteristic is optimized when the impedance is 50Ω. FIG. 5 shows a state where the impedance is discretely changed from 6.25Ω to 200Ω.

  As shown in FIG. 5A, if the configuration of the present embodiment is not used, the isolation characteristics change as the impedance of the external circuit connected to the common terminal Pcom changes. Then, as shown in FIG. 5A, the isolation at the frequency f4 that requires isolation deteriorates with the change in impedance.

  On the other hand, as shown in FIG. 5B, if the configuration of the present embodiment is used, that is, by adjusting the capacitance of the capacitor 40, the impedance of the external circuit connected to the common terminal Pcom is increased with the change in impedance. Although the isolation characteristics change, the isolation at the frequency f4 that requires isolation can be kept high. In addition, the frequency at which isolation is most obtained can be substantially maintained.

  Although FIG. 5 shows the case where the frequency f4 is approximately 860 MHz, the isolation characteristic can be similarly adjusted at other frequencies.

  As described above, by using the configuration of this embodiment, it is possible to obtain the same effect as that of the above-described first embodiment, and to further suppress the influence of the impedance change of the external circuit connected to the common terminal Pcom, thereby reducing the loss. Thus, a duplexer with high isolation between transmission and reception can be stably realized.

  Next, a variable frequency duplexer according to a third embodiment of the present invention will be described with reference to the drawings. FIG. 6 is a circuit diagram of a variable frequency duplexer according to the third embodiment of the present invention.

  The frequency variable duplexer 10B according to the present embodiment is different from the frequency variable duplexer 10A according to the second embodiment in order to compensate isolation degradation between transmission and reception due to a change in impedance at the antenna end, separately from the frequency variable. A capacitance adjustment circuit for adjusting the capacitance of the capacitor 40 is added, and the other configuration is the same as that of the frequency variable duplexer 10A shown in the second embodiment. Therefore, only portions different from the frequency variable duplexer 10A according to the second embodiment will be specifically described.

  In the variable frequency duplexer 10B, a capacitor 51 having a very small capacity for monitoring leakage of a transmission signal to the reception end is connected to a transmission line connecting the transmission terminal Ptx and the resistor 23. In addition, a minute-capacitance capacitor 52 is connected to the transmission line connecting the reception terminal Prx and the resistor 23 for extracting a monitor signal of the transmission signal for comparison with the transmission signal leaked to the reception end. . The monitor signal extraction capacitors 51 and 52 are connected to the capacitance adjustment circuit 50. With this configuration, the capacitance adjustment circuit 50 can compensate for isolation between transmission and reception from the level of the transmission signal output from the transmission terminal Ptx and the level of the transmission signal leaking to the reception terminal Prx.

  The capacitance adjustment circuit 50 determines the amount of isolation deterioration between the transmission terminal Ptx and the reception terminal Prx from the level of the transmission signal leaking to the reception terminal Prx with reference to the level of the transmission signal output from the transmission terminal Ptx. Estimate and detect. The capacitance adjustment circuit 50 adjusts the capacitance of the capacitor 40 based on the detected isolation deterioration amount so that the isolation becomes high.

  With such a configuration, the isolation between the transmission terminal Ptx and the reception terminal Prx can be observed over time, and the isolation between the transmission terminal Ptx and the reception terminal Prx is increased in substantially real time. Can be adjusted. As a result, a duplexer with low loss and high isolation between transmission and reception can be realized more stably. Further, it is possible to suppress the deterioration of the S / N ratio of the receiving circuit unit due to the leakage of the transmission signal to the receiving circuit unit connected to the receiving terminal.

  Next, a variable frequency duplexer according to a fourth embodiment of the present invention will be described with reference to the drawings. FIG. 7 is a circuit diagram of a variable frequency duplexer according to the fourth embodiment of the present invention.

  The variable frequency duplexer 10C according to the present embodiment is obtained by further adding a capacitor 60 to the variable frequency duplexer 10A shown in the second embodiment, and the other configuration is the duplexer shown in the second embodiment. This is the same as the variable frequency 10A. Therefore, only portions different from the frequency variable duplexer 10A according to the second embodiment will be specifically described.

  The capacitor 60 is a variable capacitance element. The capacitor 60 is connected in parallel to the inductor 301 of the impedance compensation circuit 30. In such a configuration, by adjusting the capacitance of the capacitor 60, it is possible to suppress the influence on the isolation between transmission and reception due to the impedance change of the external circuit connected to the common terminal Pcom together with the capacitor 40 described above. At this time, since the capacitor 60 is connected in series between the connection point A and the common terminal Pcom, the impedance is changed along a different locus from the capacitor 40 connected between the connection point A and the ground. Can do. Therefore, the impedance can be compensated for the desired frequency with higher accuracy.

  The capacitor 60 can also be used as a part of the impedance compensation circuit 30, and by adjusting the capacitance of the capacitor 60 as appropriate, the frequency between which transmission and reception can be kept high and transmission and reception with lower loss can be achieved. A variable duplexer can be realized.

  Next, a variable frequency duplexer according to a fifth embodiment of the present invention will be described with reference to the drawings. FIG. 8 is a circuit diagram of a variable frequency duplexer according to the fifth embodiment of the present invention.

  The frequency variable duplexer 10D according to the present embodiment is obtained by adding a trap circuit to the frequency variable duplexer 10A illustrated in the second embodiment, and other configurations are the frequency variable duplexers illustrated in the second embodiment. Same as duplexer 10A. Therefore, only portions different from the frequency variable duplexer 10A according to the second embodiment will be specifically described.

  The frequency variable duplexer 10 </ b> D includes a trap circuit 70. The trap circuit 70 includes an inductor 701 and a capacitor 702, and the inductor 701 and the capacitor 702 are connected in series. The trap circuit 70 is connected between the connection point A and the ground. In other words, the inductor 701 and the capacitor 702 are connected in series between the connection point A and the ground. The inductance of the inductor 701 and the capacitance of the capacitor 702 are set such that the frequency of the second harmonic of the transmission signal becomes the resonance frequency. For example, the frequency of the second harmonic of the first transmission signal in the first communication signal is set to be the resonance frequency.

  With such a configuration, the second harmonic signal of the transmission signal input from the transmission terminal Ptx is guided to the ground via the trap circuit 70.

  Since the frequency variable duplexer according to the embodiment of the present invention is based on the Wilkinson divider, the second harmonic signal may be transmitted without any loss. However, by providing the trap circuit 70 shown in the configuration of the present embodiment, the second harmonic signal of the transmission signal is not transmitted to the common terminal Pcom and is not output from the common terminal Pcom to the outside.

  In the configuration of the present embodiment, an example is shown in which a trap circuit that traps a second harmonic signal of one type of transmission signal is used. However, you may add the trap circuit with respect to the 2nd harmonic signal of all the transmission signals transmitted with the duplexer 10D. Further, a variable frequency type trap circuit may be formed by using a variable capacitance element as a capacitor constituting the trap circuit.

  Note that the circuit configurations shown in the above-described embodiments can be appropriately combined as necessary.

10, 10A, 10B, 10C, 10D: frequency variable duplexer 21: first phase shift circuit 22: second phase shift circuit 23: termination resistor 30: impedance compensation circuit 40: capacitor (variable capacitance element)
50: Capacitance adjustment circuit 51, 52: Capacitor for taking out monitor signal 60: Capacitor (variable capacitance element)
70: Trap circuit 211, 221, 301, 701: Inductor 212, 222, 702: Capacitor 302: Capacitor (variable capacitance element)

Claims (4)

A duplexer that includes a transmission terminal, a reception terminal, and a common terminal, outputs a transmission signal input from the transmission terminal from the common terminal, and outputs a reception signal input from the common terminal from the reception terminal,
A first phase shift circuit including a first inductor and a first capacitor connected between the transmission terminal and the common terminal;
A second phase shift circuit including a second inductor and a second capacitor connected between the receiving terminal and the common terminal;
An impedance compensation circuit comprising at least a first variable capacitor connected between a connection point between the first phase shift circuit and the second phase shift circuit, a transmission line connecting the common terminal, and a ground;
A terminating resistor connected between the transmitting terminal and the receiving terminal;
Duplexer with   The duplexer according to claim 1, further comprising a second variable capacitor connected between a branch connection point remote from the first variable capacitor of the impedance compensation circuit and the ground.   The duplexer according to claim 2, further comprising a capacitance adjustment circuit that monitors the transmission signal and the reception signal transmitted to the transmission terminal and the reception terminal and adjusts the capacitance of the second variable capacitor. It consists of a series circuit of an inductor and a capacitor connected between the connection point and the ground, and includes a trap circuit having a harmonic frequency of the transmission signal as a resonance frequency.
The duplexer according to any one of claims 1 to 3.

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