High-frequency front-end circuit

Abstract

High-frequency front-end circuitry featuring the following characteristics: a demultiplex circuit (20) comprising a transmit filter (21, 21A, 212) configured such that a fundamental frequency band (ft0) of a transmit signal lies in a passband of the transmit filter (21, 21A, 212) and a receive filter (22) configured such that a fundamental frequency band (fr0) of a receive signal lies in a passband of the receive filter (22), wherein an end of the transmit filter (21, 21A, 212) and an end of the receive filter (22) are electrically connected via a common connection point provided between them; a power amplifier (PA) electrically connected to another end of the transmit filter (21, 21A, 212); and a phase adjustment circuit (30) which is electrically connected between the power amplifier (PA) and the transmit filter (21, 21A, 212), where, assuming that a Smith chart is divided into four quadrants by a first line indicating pure resistance and a second line connecting points of 90° phases on the outer circumference of the Smith chart to a reference impedance point, The phase adjustment circuit (30) performs a phase adjustment such that at the fundamental frequency (fr0) of the received signal, a quadrant in which a phase of the power amplifier (PA) is present, viewed from the transmit filter (21, 21A, 212), and a quadrant in which a phase is present, viewed from the power amplifier (PA) to the transmit filter (21, 21A, 212), are not in a conjugate relationship.

Description

Technical field

[0001] The present invention relates to a high-frequency front-end circuit that sends and receives high-frequency signals. State of the art

[0002] Several types of high-frequency front-end circuits have been presented so far. Some such high-frequency front-end circuits include duplexers that combine a transmit filter and a receive filter, as disclosed in patent document 1.

[0003] In a duplexer, one end of the transmit filter and one end of the receive filter are connected in a common terminal configuration, and this common terminal is connected to an antenna or antenna-side circuitry. Another end of the transmit filter is connected to a transmit circuit, and another end of the receive filter is connected to a receive circuit.

[0004] According to such a high-frequency front-end circuit, the transmit filter and the receive filter are connected, and in order to prevent a transmit signal from entering the receive filter side, an impedance at the fundamental frequency of the transmit signal is therefore set such that the receive filter side is open when viewed from the transmit filter side. List of mentioned documents Patent document

[0005] Patent document 1: Unexamined Japanese patent application with publication no. 2004-120295.

[0006] JP 2005-109889 A discloses a high-frequency module capable of improving harmonic characteristics and isolation characteristics. This high-frequency module comprises a branching filter circuit DIP for splitting multiple transmit and receive systems with different passbands into corresponding transmit and receive systems, a switching circuit SW connected to the branching filter circuit DIP to switch each transmit and receive system into a transmit and receive system, a semiconductor MMIC for harmonic amplification connected to the switching circuit SW to amplify a transmit signal in a passband of each transmit system, an output matching circuit PAMN connected to the semiconductor MMIC for harmonic amplification to perform impedance matching, and a coupler COP for monitoring an output of the semiconductor MMIC for harmonic amplification.The impedances that occur in the anteroposterior direction between the output matching circuit PAMN and the coupler COP at an n-fold frequency of the fundamental frequency and the fundamental frequency in the off state of the semiconductor element for harmonic amplification are not conjugate to each other.

[0007] The pocketbook of high-frequency technology, 4th edition, Berlin, Heidelberg, New York: Springer Verlag, 1986, pages C24-C29, ISBN 3 - 540 - 15393 - 4 by Meinke, Gundlach reveals definitions of the technical terms inversion diagram, impedance plane, admittance plane, transformation circuits, and the theory of transmission lines.

[0008] DE 10 2008 003 820 A1 discloses a frontend circuit for at least one FDD and at least one TDD mobile communication system, both of which use a common bandwidth, wherein a common transmission filter can optionally be inserted into the transmission path of the TDD or the FDD mobile communication system. Brief description of the invention Technical problem

[0009] However, it was discovered that the receiving sensitivity of the receiving circuit connected to the receiving filter decreases in such conventional high-frequency front-end circuits, even when isolation between the transmitting filter and the receiving filter is ensured, as described above.

[0010] Accordingly, it is an object of the present invention to create a high-frequency front-end circuit that is capable of preventing a decrease in receiver sensitivity. Solution to the problem

[0011] A high-frequency front-end circuit according to this invention comprises a demultiplexing circuit, a power amplifier, and a phase-adjusting circuit. The demultiplexing circuit includes a transmit filter configured such that a fundamental frequency band of a transmit signal lies within a passband of the transmit filter, and a receive filter configured such that a fundamental frequency band of a receive signal lies within a passband of the receive filter. In the demultiplexing circuit, one end of the transmit filter and one end of the receive filter are electrically connected via a common junction provided between them. The power amplifier is electrically connected to another end of the transmit filter. The phase-adjusting circuit is electrically connected between the power amplifier and the transmit filter.

[0012] The phase adjustment circuit performs phase adjustment as follows. It is assumed that a Smith chart is divided into four quadrants by a first line representing pure resistance and a second line connecting points of 90° phase on the outer circumference of the Smith chart to a reference impedance point. The phase adjustment circuit acts such that, at the fundamental frequency of the received signal, a quadrant containing a phase of the power amplifier (as viewed from the transmitting filter) and a quadrant containing a phase (as viewed from the power amplifier towards the transmitting filter) are not conjugate.

[0013] With this configuration, it is easily possible to ensure an impedance mismatch between the power amplifier and the transmit filter at the fundamental frequency of the received signal. This prevents noise matched to the fundamental frequency of the received signal from entering the receive filter.

[0014] In addition, it is preferred that the high-frequency front-end circuit according to this invention has the following configuration. The phase adjustment circuit performs the phase adjustment such that, at the fundamental frequency of the received signal, a quadrant containing a phase of the power amplifier, viewed from the transmit filter, and a quadrant containing a phase, viewed from the power amplifier towards the transmit filter, are located on opposite sides, between which the second line is inserted.

[0015] According to this configuration, it is easily possible to ensure an even greater impedance mismatch between the power amplifier and the transmit filter at the fundamental frequency of the received signal.

[0016] In addition, it is preferred that the high-frequency front-end circuit according to this invention has the following configuration. The phase adjustment circuit performs the phase adjustment such that the impedance at the fundamental frequency of the transmitted signal approaches the reference impedance.

[0017] According to this configuration, transmission loss in the transmit signal can be further reduced, while ensuring impedance mismatch at the fundamental frequency of the received signal.

[0018] In addition, it is preferred that the high-frequency front-end circuit according to this invention has the following configuration. The phase-adjustment circuit comprises at least one attached electronic component that includes a reactance component.

[0019] According to this configuration, it is easily possible to change the configuration of the phase adjustment circuit, and thus the impedance mismatch between the transmit filter and the power amplifier at the fundamental frequency of the received signal can be implemented with more certainty.

[0020] In addition, the high-frequency front-end circuit according to this invention can have the following configuration. The phase adjustment circuit performs the phase adjustment according to the length of a transmission line that sends the transmit signal.

[0021] According to this configuration, the high-frequency front-end circuit can be implemented with a simple configuration, while ensuring an impedance mismatch between the transmit filter and the power amplifier at the fundamental frequency of the received signal.

[0022] In addition, the high-frequency front-end circuit according to this invention can have the following configuration. The high-frequency front-end circuit comprises a demultiplexing circuit, a power amplifier, and a phase-adjusting circuit. The demultiplexing circuit comprises a transmit filter configured such that a fundamental frequency band of a transmit signal lies within a passband of the transmit filter, and a receive filter configured such that a fundamental frequency band of a receive signal lies within a passband of the receive filter. In the demultiplexing circuit, one end of the transmit filter and one end of the receive filter are electrically connected via a common junction provided between the two. The power amplifier is electrically connected to another end of the transmit filter. The phase-adjusting circuit is included within the transmit filter.

[0023] The phase adjustment circuit performs phase adjustment as follows. It is assumed that a Smith chart is divided into four quadrants by a first line representing pure resistance and a second line connecting points of 90° phase on the outer circumference of the Smith chart to a reference impedance point. The phase adjustment circuit acts such that, at the fundamental frequency of the received signal, a quadrant containing a phase of the power amplifier (as viewed from the transmitting filter) and a quadrant containing a phase (as viewed from the power amplifier towards the transmitting filter) are not conjugate.

[0024] According to this configuration, the transmit filter also acts as the phase adjustment circuit, and the circuit configuration of the high-frequency front-end circuit can thus be simplified.

[0025] In addition, it is preferred that the high-frequency front-end circuit according to this invention has the following configuration. The transmit filter consists of a plurality of resonators. The phase adjustment circuit consists of a resonator connected to the power amplifier.

[0026] According to this configuration, a signal with the fundamental frequency of the received signal is reflected at one input end from the power amplifier towards the transmit filter and can therefore be more effectively prevented from entering the receive filter.

[0027] In addition, a high-frequency front-end circuit according to this invention comprises a demultiplexing circuit, power amplifiers, and a phase-adjustment circuit. The demultiplexing circuit comprises a first transmit filter configured such that a fundamental frequency band of a first transmit signal lies within a passband of the first transmit filter, a second transmit filter configured such that a fundamental frequency band of a second transmit signal, which differs from the first transmit signal, lies within a passband of the second transmit filter, and a receive filter configured such that a fundamental frequency band of a first receive signal lies within a passband of the receive filter, with one end of the first transmit filter, one end of the second transmit filter, and one end of the third transmit filter being connected. The power amplifiers are each connected to a different end of the first transmit filter and a different end of the second transmit filter.The phase adjustment circuit is connected between the power amplifier and the second transmit filter, or is contained within the second transmit filter. A harmonic frequency of the second transmit signal and the fundamental frequency of the received signal are close to each other.

[0028] The phase adjustment circuit performs phase adjustment as follows. It is assumed that a Smith chart is divided into four quadrants by a first line representing pure resistance and a second line connecting points of 90° phase on the outer circumference of the Smith chart to a reference impedance point. The phase adjustment circuit acts such that, at the harmonic frequency of the second transmit signal, the quadrant containing the phase of the power amplifier (as viewed from the second transmit filter) and the quadrant containing the phase (as viewed from the power amplifier towards the second transmit filter) are not conjugate.

[0029] With this configuration, it is readily possible to ensure an impedance mismatch between the power amplifier and the second transmit filter at the harmonic frequency of the second transmit signal. This prevents a harmonic signal from the second transmit signal, which has a frequency close to the fundamental frequency of the received signal, from reaching the receive filter side. Advantageous effects of the invention

[0030] According to this invention, isolation between a transmitting side and a receiving side can be reliably ensured even for a receiving signal band, which makes it possible to prevent a decrease in receiving sensitivity. Brief description of the drawings Fig. Figure 1 is a block diagram illustrating a high-frequency front-end circuit according to a first embodiment of the present invention. Fig. Figure 2 is a Smith chart illustrating a principle of the high-frequency front-end circuit according to the first embodiment of the present invention. Fig. Figure 3 is an equivalent circuit diagram illustrating an example of a phase adjustment circuit according to the first embodiment of the present invention. Fig. Figure 4 is a curve illustrating receive sensitivity decay rate characteristics in a case where the high-frequency front-end circuit according to the first embodiment of the present invention is used, and in a case where the high-frequency front-end circuit according to the first embodiment of the present invention is not used. Fig. Figure 5 is an equivalent circuit diagram illustrating a different configuration of the phase setting circuit according to the first embodiment of the present invention. Fig. Figure 6 is a Smith chart illustrating a principle of another configuration of the high-frequency front-end circuit according to the first embodiment of the present invention. Fig. Figure 7 is a block diagram illustrating a front-end circuit according to a second embodiment of the present invention. Fig. Figure 8 is an equivalent circuit diagram illustrating a Tx filter equipped with a phase adjustment circuit according to the second embodiment of the present invention. Fig. Figure 9 is a block diagram illustrating a high-frequency front-end circuit according to a third embodiment of the present invention. Fig. Figure 10 is a Smith chart illustrating a principle of the high-frequency front-end circuit according to the third embodiment of the present invention. Description of the exemplary implementations

[0031] A high-frequency front-end circuit according to a first embodiment of the present invention is described with reference to the drawings. Fig. Figure 1 is a block diagram illustrating the high-frequency front-end circuit according to the first embodiment of the present invention.

[0032] As in Fig. As illustrated in Figure 1, a high-frequency front-end circuit 10 comprises a duplexer 20, a phase-adjustment circuit 30, and a power amplifier PA. The duplexer 20 comprises a Tx filter 21, which corresponds to a "transmit filter" according to the present invention, and an Rx filter 22, which corresponds to a "receive filter" according to the present invention.

[0033] One end of the Tx filter 21 and one end of the Rx filter 22 are connected to a common junction point. This junction point is connected to an antenna or an antenna-side circuit (not shown). This antenna transmits signals that have passed through the Tx filter 21 and receives signals from the outside.

[0034] The fundamental frequency of a transmitted signal of a predetermined communication standard lies within the passband of the Tx filter 21. The Tx filter 21 is configured to provide a predetermined attenuation with respect to the frequency of a received signal of the predetermined communication standard.

[0035] The fundamental frequency of the received signal of the predetermined communication standard lies within the passband of the Rx filter 22. Another end of the Rx filter 22 is connected to a low-noise amplifier LNA of a receiver circuit 90. An impedance matching circuit can be provided here for impedance matching at the frequency of the received signal between the Rx filter 22 and the low-noise amplifier LNA.

[0036] Another end of the Tx filter 21 is connected to an output end of the power amplifier PA, with the phase adjustment circuit 30 provided between them. Note that an input end of the power amplifier PA is connected to a transmit signal generation circuit (not shown).

[0037] The phase adjustment circuit 30 has a circuit configuration for performing impedance matching between the Tx filter 21 and the power amplifier PA in the fundamental frequency band of the transmitted signal. Furthermore, the phase adjustment circuit 30 has a circuit configuration based on the principle described below. Fig. Figure 2 is a Smith chart illustrating a principle of the high-frequency front-end circuit according to the first embodiment of the present invention.

[0038] As in Fig. As illustrated in Figure 2, according to the high-frequency front-end circuit 10 of the present invention, the Smith chart is divided into the four quadrants described below, and the phase adjustment is performed based on whether or not an impedance is present in one of the four quadrants. It should be noted that Fig. Figure 2 illustrates a normalized Smith chart. In other words, an impedance of 50 Ω in Fig. 2 is specified as impedance 1.

[0039] First, the method used to divide the Smith chart into quadrants is described. A Reiner resistance line in the Smith chart, or in other words, a line extending from the point of impedance 0 through the point of impedance 1 (a reference impedance point) to the point of impedance ∞ in Fig. The line extending from point 2 is used as the first line. Next, a line passing through two points at 90° phase on the outer circumference of the Smith chart and the point of impedance 1 (the reference impedance point) is used as the second line. The four regions into which the Smith chart is divided by the first and second lines, which are orthogonal to each other, are used as the first, second, third, and fourth quadrants. The first quadrant is a region exhibiting inductive reactance and high impedance, and the second quadrant is a region exhibiting inductive reactance and low impedance. The third quadrant is a region exhibiting capacitive reactance and low impedance, and the fourth quadrant is a region exhibiting capacitive reactance and high impedance.

[0040] In Fig. ZRX(fr0) specifies an impedance, viewed from the Tx filter 21 to the power amplifier PA, at the fundamental frequency of the received signal in a state where the phase-adjusting circuit 30 is not used. ZTX(fr0) specifies an impedance, viewed from the power amplifier PA to the Tx filter 21, at the fundamental frequency of the received signal in a state where the phase-adjusting circuit 30 is not used. ZTXc1(fr0) specifies a first impedance, viewed from the power amplifier PA to the Tx filter 21, at the fundamental frequency of the received signal in a state where the phase-adjusting circuit 30 is used. ZTXc2(fr0) specifies a second impedance, viewed from the power amplifier PA to the Tx filter 21, at the fundamental frequency of the received signal in a state where the phase-adjusting circuit 30 is used.ZTX(ft0) specifies an impedance, viewed from the power amplifier PA to the Tx filter 21, at the fundamental frequency of the transmitted signal in a state where the phase-adjusting circuit 30 is not used. ZTXc2(ft0) specifies an impedance, viewed from the power amplifier PA to the Tx filter 21, at the fundamental frequency of the transmitted signal in a state where the phase-adjusting circuit 30 is used.

[0041] As in Fig. As indicated in section 2, in the case of quadrants where the phase of the impedance ZRX (fr0), viewed from the Tx filter 21 to the power amplifier PA, and the phase of the impedance ZTX (fr0), viewed from the power amplifier PA to the Tx filter 21, are conjugate at the fundamental frequency of the received signal, the phase adjustment circuit 30 serves to shift the phase. Accordingly, as indicated by the impedance ZTXc1 (fr0), the impedance ZTXc2 (fr0), and so on, for the quadrant where the impedance ZRX (fr0) is present, the impedance can be shifted to a quadrant that is not conjugate with it.

[0042] The power amplifier PA and the Tx filter 21 therefore exhibit mismatched impedances at the fundamental frequency of the received signal. Consequently, noise with the same frequency as the fundamental frequency of the received signal is not fed into the Tx filter 21 by the power amplifier PA. As a result, this noise does not pass through the Tx filter 21 into the Rx filter 22, thus preventing a decrease in receiver sensitivity.

[0043] Furthermore, as in Fig. As specified in Figure 2, the phase adjustment circuit 30 is used to bring the impedance at the fundamental frequency of the transmitted signal closer to the reference impedance (50 Ω). This further reduces transmission loss of the transmitted signal, which in turn improves the transmission characteristics.

[0044] To achieve such a phase shift, the phase adjustment circuit 30 is equipped with a circuit configuration such as the one shown in Fig. 3 illustrated examples provided. Fig. Figure 3 is an equivalent circuit diagram illustrating an example of the phase adjustment circuit according to the first embodiment of the present invention.

[0045] The phase adjustment circuit 30 comprises an inductor 301 and a capacitor 302. The inductor 301 is connected to the power amplifier PA and the Tx filter 21. The capacitor 302 is connected between the Tx filter 21 side of the inductor 301 and ground. The inductance of the inductor 301 and the capacitiveness of the capacitor 302 are set such that the Fig. The specified phase shift can be achieved.

[0046] It should be noted that the inductor 301, the capacitor 302, and so on can be implemented as electrode structures formed on a circuit board or as attached electronic components. If the inductor 301, the capacitor 302, and so on are implemented as electrode structures, the phase adjustment circuit 30 can be implemented with a simple configuration, and the high-frequency front-end circuit 10 can therefore also be implemented with a simple configuration. On the other hand, if the inductor 301, the capacitor 302, and so on are implemented as attached electronic components, the inductance, capacitance, and so on can be easily changed by replacing the attached electronic components, which makes it easy to adjust the inductance, capacitance, and so on. The desired phase shift amount can thus be achieved more precisely.

[0047] Fig. Figure 4 is a curve illustrating receive sensitivity decay rate characteristics in the case where the high-frequency front-end circuit according to the first embodiment of the present invention is used, and in the case where the high-frequency front-end circuit according to the first embodiment of the present invention is not used. The horizontal axis in Fig. Figure 4 represents a noise level generated by the power amplifier PA at the fundamental frequency of the received signal. The vertical axis in Fig. Figure 4 represents the receive sensitivity decrease rate. The solid line represents a case in which the phase adjustment circuit 30 is provided according to the present embodiment, whereas the dotted line represents a case in which the phase adjustment circuit 30 is not provided according to the present embodiment.

[0048] As in Fig. As indicated in 4, the rate of decrease in receive sensitivity can be reduced using the configuration according to the present embodiment.

[0049] It should be noted that the phase adjustment circuit may have the circuit configuration described below. Fig. Figure 5 is an equivalent circuit diagram illustrating another configuration of the phase adjustment circuit according to the first embodiment of the present invention. A phase adjustment circuit 30' comprises an inductor 303. The inductor 303 is connected between a connecting line that links the power amplifier PA to the Tx filter 21 and a ground.

[0050] As in Fig. As illustrated in Figure 6, with such a configuration the direction of the phase shift is opposite to that shown in Figure 6. Fig. 2 illustrated cases. Fig. Figure 6 is a Smith chart illustrating a principle of this other configuration of the high-frequency front-end circuit according to the first embodiment of the present invention. As shown in Fig. As indicated in Figure 6, in the case of quadrants where the phase of the impedance ZRX (fr0), viewed from the Tx filter 21 towards the power amplifier PA, is conjugate at the fundamental frequency of the received signal, and the phase of the impedance ZTX (fr0), viewed from the power amplifier PA towards the Tx filter 21, is conjugate at the fundamental frequency of the received signal, the phase is also shifted in this case. Accordingly, as indicated by an impedance ZTXc1' (fr0), for the quadrant where the impedance ZRX (fr0) is present, the impedance can be shifted to a quadrant that is not conjugate with it.

[0051] The rate of decrease in receiver sensitivity can also be reduced in the same way by performing such a phase shift.

[0052] It is desirable that the phase of the impedance, viewed from the Tx filter 21 to the power amplifier PA, and the phase of the impedance, viewed from the power amplifier PA to the Tx filter 21, at the fundamental frequency of the received signal, are in quadrants on the same side relative to the Reiner resistance line (the first line) and in quadrants opposite each other relative to the second line. Such a relationship makes it possible to increase the impedance mismatch between the Tx filter 21 and the power amplifier PA at the fundamental frequency of the received signal. Accordingly, it can be prevented with greater certainty that noise will not enter the Rx filter 22, and the rate of decrease in receive sensitivity can be reduced even further.

[0053] Next, a high-frequency front-end circuit according to a second embodiment of the present invention will be described with reference to the drawings. Fig. Figure 7 is a block diagram illustrating the high-frequency front-end circuit according to the second embodiment of the present invention. In a high-frequency front-end circuit 10A according to the present embodiment, the function of the phase-adjustment circuit 30, described in the first embodiment, is incorporated into the Tx filter, which is implemented as a Tx filter 21A equipped with a phase-adjustment circuit. The other configurations are the same as those of the high-frequency front-end circuit 10 according to the first embodiment. Therefore, only the differences from the high-frequency front-end circuit 10 according to the first embodiment are described in detail.

[0054] The high-frequency front-end circuit 10A comprises a duplexer 20A and the power amplifier PA. The duplexer 20A includes the Tx filter 21A, equipped with a phase-adjustment circuit, and the Rx filter 22. One end of the Tx filter 21A and one end of the Rx filter 22 are connected. The other end of the Tx filter 21A is connected to the power amplifier PA.

[0055] The Tx filter 21A, equipped with a phase-adjustment circuit, is designed such that its passband includes the fundamental frequency of the transmitted signal, and such that an impedance mismatch with the power amplifier PA is achieved at the fundamental frequency of the received signal, as described above. In other words, the Tx filter 21A, equipped with a phase-adjustment circuit, is designed such that the phase of the impedance, viewed towards the power amplifier PA, at the fundamental frequency of the received signal, is at least not opposite to the phase of the impedance, viewed from the power amplifier PA towards the Tx filter 21A equipped with a phase-adjustment circuit.Furthermore, the Tx filter 21A equipped with a phase adjustment circuit can be set such that the phase of the impedance, viewed towards the power amplifier PA, is the same at the fundamental frequency of the received signal as the phase of the impedance, viewed from the power amplifier PA towards the Tx filter 21A equipped with a phase adjustment circuit.

[0056] In particular, the Tx-Filter 21A, which is equipped with a phase adjustment circuit, has the following circuit configuration. Fig. Figure 8A is an equivalent circuit diagram illustrating the Tx filter equipped with a phase-adjustment circuit according to the second embodiment of the present invention. The Tx filter 21A equipped with a phase-adjustment circuit comprises a plurality of resonators 21A1, 21A2, 21A3, and 21A4. Resonators 21A1 and 21A2 are connected in series, with resonator 21A1 being connected to the power amplifier PA and resonator 21A2 being connected to the Rx filter 22 via a connection point. Resonator 21A3 is connected between the power amplifier PA side of resonator 21A1 and ground. Resonator 21A4 is connected between a connecting line linking resonators 21A1 and 21A2 and ground.

[0057] Here, the impedance mismatch described above with respect to the fundamental frequency of the received signal is implemented by adjusting the characteristics of the resonator 21A3, which is closest to the power amplifier PA. By applying such a configuration, an impedance mismatch between the power amplifier PA and the Tx filter 21A, which is equipped with a phase adjustment circuit, can be implemented more effectively at the fundamental frequency of the received signal.

[0058] Providing such a configuration makes it possible to reduce the receive sensitivity degradation rate in the same way as in the first embodiment. Furthermore, the phase adjustment circuit and the Tx filter are integrated into the configuration of the present embodiment, which simplifies the circuit configuration of the high-frequency front-end circuit.

[0059] Next, a high-frequency front-end circuit according to a third embodiment of the present invention will be described with reference to the drawings. Fig. Figure 9 is a block diagram illustrating the high-frequency front-end circuit according to the third embodiment of the present invention. It should be noted that the present embodiment describes a case in which a third-order harmonic frequency of a second transmit signal is close to the fundamental frequency of a first receive signal, and in which carrier aggregation is performed, in which the second transmit signal is simultaneously transmitted and the first receive signal is received.

[0060] As in Fig. As illustrated in Figure 9, the high-frequency front-end circuit according to the present embodiment has a triplexer configuration instead of the duplexer configuration described in the first and second embodiments.

[0061] As in Fig. As illustrated in Figure 9, a high-frequency front-end circuit 10B comprises a triplexer 20B, a phase-adjustment circuit 30B, and power amplifiers PA1 and PA2. The triplexer 20B includes a Tx1 filter 211, corresponding to a "first transmit filter" according to the present invention, a Tx2 filter 212, corresponding to a "second transmit filter" according to the present invention, and an Rx1 filter 221, corresponding to a "first receive filter" according to the present invention.

[0062] One end of the Tx1 filter 211, one end of the Tx2 filter 212, and one end of the Rx1 filter 221 are connected. This connection point is connected to an antenna or an antenna-side circuit (not shown). This antenna transmits signals that have passed through the Tx1 filter 211 or the Tx2 filter 212 and receives signals from outside.

[0063] The Tx1 filter 211 is configured such that its passband contains the fundamental frequency of a first transmitted signal. The Tx1 filter 211 is configured to provide a predetermined attenuation with respect to the frequencies of the first received signal and the second transmitted signal.

[0064] The Tx2 filter 212 is configured such that its passband contains the fundamental frequency of the second transmitted signal. The Tx2 filter 211 is configured to provide a predetermined attenuation with respect to the frequencies of the first transmitted signal and the first received signal.

[0065] The Rx1 filter 221 is configured such that its passband contains the fundamental frequency of the first received signal. Another end of the Rx1 filter 221 is connected to the LNA of the receiving circuit 90. An impedance matching circuit can be provided here for impedance matching at the frequency of the received signal between the Rx1 filter 221 and the LNA.

[0066] Another end of the Tx1 filter 211 is connected to an output of the power amplifier PA1. Note that an input of the power amplifier PA1 is connected to a transmit signal generation circuit (not shown).

[0067] Another end of the Tx2 filter 212 is connected to an output end of the power amplifier PA2, with the phase-adjustment circuit 30B provided between them. Note that an input end of the power amplifier PA2 is connected to a transmit signal generation circuit (not shown). The power amplifiers PA1 and PA2 can be integrated.

[0068] The phase adjustment circuit 30B features a circuit configuration for performing impedance matching between the Tx2 filter 212 and the power amplifier PA2 in the fundamental frequency band of the second transmit signal. Furthermore, the phase adjustment circuit 30B features a circuit configuration based on the principles described below. Fig. Figure 10 is a Smith chart illustrating a principle of the high-frequency front-end circuit according to the third embodiment of the present disclosure. The Smith chart shown in Fig. Figure 10 illustrates the same thing as the Smith chart shown in Fig. 2 is illustrated, and is divided into four quadrants according to the same concept as in Fig. 2 illustrated divided.

[0069] In Fig. 10 ZRX1 (fr0) specifies an impedance, viewed from the Tx2 filter 212 to the power amplifier PA2, at the fundamental frequency of the first received signal in a state where the phase-adjusting circuit 30B is not used. ZTX2 (ft3) specifies an impedance, viewed from the power amplifier PA2 to the Tx filter 212, at the third harmonic frequency of the second transmitted signal in a state where the phase-adjusting circuit 30B is not used. ZTX2c1 (ft3) specifies a first impedance, viewed from the power amplifier PA2 to the Tx filter 212, at the third harmonic frequency of the second transmitted signal in a state where the phase-adjusting circuit 30B is used.ZTX2c2 (ft3) specifies a second impedance, viewed from power amplifier PA2 to Tx filter 212, at the third harmonic frequency of the second transmit signal in a state where phase-adjusting circuit 30B is used. ZTX2 (ft0) specifies an impedance, viewed from power amplifier PA2 to Tx filter 212, at the fundamental frequency of the second transmit signal in a state where phase-adjusting circuit 30B is not used. ZTX2c2 (ft0) specifies an impedance, viewed from power amplifier PA2 to Tx filter 212, at the fundamental frequency of the second transmit signal in a state where phase-adjusting circuit 30B is used.

[0070] As in Fig. As indicated in section 10, in the case of quadrants where the phase of impedance ZRX1 (fr0), viewed from the Tx filter 212 to the power amplifier PA2, is conjugate at the fundamental frequency of the first received signal, and the phase of impedance ZTX2 (ft3), viewed from the power amplifier PA2 to the Tx filter 212, is conjugate at the third harmonic frequency of the second transmitted signal, the phase adjustment circuit 30B serves to shift the phase of impedance ZTX2 (ft3). Accordingly, as indicated by impedance ZTX2c1 (ft3), impedance ZTX2c2 (ft3), and so on, for the quadrant where impedance ZRX1 (ft0) is present, the impedance can be shifted to a quadrant that is not conjugate with it.

[0071] The power amplifier PA2 and the Tx filter 212 therefore exhibit mismatched impedances at the fundamental frequency of the first received signal, the third-order harmonic frequency of the second received signal, and so on. Consequently, a third-order harmonic signal of the second transmitted signal is not fed from the power amplifier PA2 into the Tx filter 212. As a result, the third-order harmonic signal of the second transmitted signal does not pass through the Tx filter 212 into the Rx1 filter 221, thus preventing a decrease in receive sensitivity relative to the first received signal, even when carrier aggregation is performed.

[0072] Furthermore, as in Fig.As specified in section 10, the phase adjustment circuit 30B is used to bring the impedance at the fundamental frequency of the second transmitted signal closer to the reference impedance (50 Ω). This further reduces transmission loss of the second transmitted signal, which in turn improves the transmission characteristics.

[0073] Although the foregoing describes a case in which the fundamental frequency of the first received signal and the third-order harmonic frequency of the second transmitted signal are brought closer together, the above configuration can also be applied in a case in which a different harmonic frequency of the second transmitted signal and the fundamental frequency of the first received signal are brought closer together.

[0074] Accordingly, applying the configuration of the present embodiment makes it possible to reduce the rate of decrease in the received signal's sensitivity, even when the harmonic frequency of the transmitted signal, for which carrier aggregation is performed, is brought closer to the fundamental frequency of the received signal. Reference symbol list 10, 10A, 10B High-frequency front-end circuit 20, 20A Duplexer 20B Triplexer 21 Tx filters 211 Tx1 filter 212 Tx2 filter 22 Rx filters 221 Rx1 filter 21A Tx filter equipped with a phase adjustment circuit 30, 30', 30B Phase adjustment circuit 90 Receiving circuit 21A1, 21A2, 21A3, 21A4 resonator 301, 303 Inductor 302 Capacitor PA, PA1, PA2 Power Amplifiers

Claims

[1] High-frequency front-end circuit having the following features: a demultiplex circuit (20) comprising a transmit filter (21, 21A, 212) configured such that a fundamental frequency band (ft0) of a transmit signal lies in a passband of the transmit filter (21, 21A, 212) and a receive filter (22) configured such that a fundamental frequency band (fr0) of a receive signal lies in a passband of the receive filter (22), wherein an end of the transmit filter (21, 21A, 212) and an end of the receive filter (22) are electrically connected via a common connection point provided between them; a power amplifier (PA) electrically connected to another end of the transmit filter (21, 21A, 212); and a phase adjustment circuit (30) which is electrically connected between the power amplifier (PA) and the transmit filter (21, 21A, 212), where, assuming that a Smith chart is divided into four quadrants by a first line indicating pure resistance and a second line connecting points of 90° phases on the outer circumference of the Smith chart to a reference impedance point, The phase adjustment circuit (30) performs a phase adjustment such that at the fundamental frequency (fr0) of the received signal, a quadrant in which a phase of the power amplifier (PA) is present, viewed from the transmit filter (21, 21A, 212), and a quadrant in which a phase is present, viewed from the power amplifier (PA) to the transmit filter (21, 21A, 212), are not in a conjugate relationship. [2] High-frequency front-end circuit according to claim 1, wherein the phase adjustment circuit (30) performs the phase adjustment such that at the fundamental frequency (fr0) of the received signal, a quadrant in which a phase of the power amplifier (PA) is present, viewed from the transmit filter (21, 21A, 212), and a quadrant in which a phase is present, viewed from the power amplifier (PA) towards the transmit filter (21, 21A, 212), are located on opposite sides, between which the second line is inserted. [3] High-frequency front-end circuit according to claim 1 or 2, wherein the phase adjustment circuit (30) performs the phase adjustment such that an impedance at the fundamental frequency (ft0) of the transmit signal approaches the reference impedance. [4] High-frequency front-end circuit according to any one of claims 1 to 3, wherein the phase adjustment circuit (30) comprises at least one attached electronic component with a reactance component. [5] High-frequency front-end circuit according to any one of claims 1 to 4, wherein the phase adjustment circuit (30) performs the phase adjustment according to the length of a transmission line that sends the transmit signal. [6] High-frequency front-end circuit according to any one of claims 1 to 4 wherein the phase adjustment circuit is included in the transmit filter (21A). [7] High-frequency front-end circuit according to claim 6, where the transmitting filter (21A) consists of a plurality of resonators (21A1-21A4); and The phase adjustment circuit consists of a resonator connected to the power amplifier. [8] A high-frequency front-end circuit that has the following features: a demultiplex circuit (20) comprising a first transmit filter (211) configured such that a fundamental frequency band of a first transmit signal lies in a passband of the first transmit filter (211), a second transmit filter (212) configured such that a fundamental frequency band of a second transmit signal, which differs from the first transmit signal, lies in a passband of the second transmit filter (212), and a receive filter (221) configured such that a fundamental frequency band of a first receive signal lies in a passband of the receive filter (221), wherein an end of the first transmit filter (211), an end of the second transmit filter (212), and an end of the receive filter (221) are electrically connected via a common connection point provided between them; Power amplifiers, each electrically connected to a different end of the first transmit filter (211) and a different end of the second transmit filter (212); and a phase adjustment circuit (30) which is connected between the power amplifier (PA2) and the second transmit filter (212) or is contained in the second transmit filter (212), where a harmonic frequency of the second transmitted signal and the fundamental frequency of the received signal are close to each other; and where a Smith chart is assumed to be divided into four quadrants by a first line indicating pure resistance and a second line connecting points of 90° phases on the outer circumference of the Smith chart to a reference impedance point, wherein the phase adjustment circuit (30) performs the phase adjustment such that at the harmonic frequency of the second transmit signal, a quadrant in which a phase of the power amplifier is present, viewed from the second transmit filter (212), and a quadrant in which a phase is present, viewed from the power amplifier to the second transmit filter (212), are not in a conjugate relationship.

Images