A high-frequency front-end circuit includes first and second switching circuits, first, second, and third splitters, and first and second lines. The first line is connected to the second splitter. The second line is connected to the third splitter. An adjustment circuit is connected between the first and second lines. The frequency of a harmonic signal of a transmission signal transmitted through the first line has a frequency band that is close to or overlaps the frequency of a reception signal transmitted through the second line. The impedance of the adjustment circuit is set such that a harmonic signal transmitted from the adjustment circuit to the second line and a harmonic signal transmitted from the third splitter to the second line are not in same phase with each other at the connection point between the adjustment circuit and the second line.

BACKGROUND OF THE DISCLOSURE

Field of the Disclosure

The present disclosure relates to a high-frequency front-end circuit that has a separation function and is connected to an antenna that transmits and receives harmonic signals in a plurality of communication bands.

Description of the Related Art

Hitherto, various devices that transmit and receive harmonic signals in a plurality of communication bands by an antenna shared for these harmonic signals have been conceived. Such a device includes a high-frequency front-end circuit having a function to separate the harmonic signals to be transmitted and received by the antenna, per communication band.

As an existing high-frequency front-end circuit, a high-frequency switch module having a configuration to switch a communication band for transmission and reception by a switch, for example, as disclosed in Patent Document 1, has been put into practical use.

BRIEF SUMMARY OF THE DISCLOSURE

In the case where a switch is used as disclosed in Patent Document 1 and transmission and reception are simultaneously performed in a plurality of communication bands, a circuit configuration shown inFIG. 5is generally conceived. The case where transmission and reception are simultaneously performed in the plurality of communication bands includes the case where only transmission or only reception is performed in one communication band.FIG. 5is a circuit diagram of an existing high-frequency front-end circuit.

As shown inFIG. 5, an existing high-frequency front-end circuit10P includes a first splitter20, a first switching circuit31, a second switching circuit32, a second splitter41, and a third splitter42.

The first splitter20is connected to an antenna ANT, the first switching circuit31, and the second switching circuit32.

The first switching circuit31includes a common terminal P10and selection target terminals P11to P14. The selection target terminals P11to P14are selectively connected to the common terminal P10. The common terminal P10is connected to the first splitter20. The selection target terminals P11to P14are connected to respective circuits for individual communication bands. In the example inFIG. 5, the selection target terminal P12is connected to the second splitter41for a communication band A.

The second splitter41is connected to a first transmission signal input terminal Ptx1and a first reception signal output terminal Prx1.

The second switching circuit32includes a common terminal P20and selection target terminals P21to P24. The selection target terminals P21to P24are selectively connected to the common terminal P20. The common terminal P20is connected to the first splitter20. The selection target terminals P21to P24are connected to respective circuits for individual communication bands. In the example inFIG. 5, the selection target terminal P22is connected to the third splitter42for a communication band B.

The third splitter42is connected to a second transmission signal input terminal Ptx2and a second reception signal output terminal Prx2.

Here, in the case where transmission in the communication band A and reception in the communication band B are performed simultaneously, when the frequency of a harmonic signal of a transmission signal in the communication band A is close to or overlaps the frequency (fundamental frequency) of a reception signal in the communication band B, there is a possibility that the harmonic signal of the transmission signal in the communication band A inputted from the first transmission signal input terminal Ptx1sneaks around to the second reception signal output terminal Prx2.

When this phenomenon occurs, the reception sensitivity for the reception signal in the communication band B deteriorates.

Therefore, it is an object of the present disclosure to provide a high-frequency front-end circuit that is able to inhibit deterioration of reception sensitivity due to simultaneous transmission and reception.

A high-frequency front-end circuit of the present disclosure includes a first switching circuit for a low band, a second switching circuit for a high band, first, second, and third splitters, and first and second lines. A common terminal of the first switching circuit and a common terminal of the second switching circuit are connected to the first splitter. The second splitter is connected to a selection target terminal of the first switching circuit. The third splitter is connected to a selection target terminal of the second switching circuit. The first line is connected to the second splitter and is configured to transmit a transmission signal in a first communication band of the low band. The second line is connected to the third splitter and is configured to transmit a reception signal for a second communication band of the high band. An adjustment circuit is connected between the first line and the second line, and its impedance is set so as to satisfy the following condition. When a harmonic signal of the transmission signal in the first communication band has a frequency band that is close to or overlaps a fundamental frequency of the reception signal for the second communication band, the harmonic signal transmitted from the adjustment circuit to the second line and a harmonic signal transmitted from the third splitter to the second line are not in same phase with each other at a connection point between the adjustment circuit and the second line

With this configuration, the harmonic signal (a harmonic signal for cancellation) transmitted from the adjustment circuit to the second line and the harmonic signal (a harmonic signal to be cancelled) transmitted from the third splitter to the second line assuredly weaken each other.

In the high-frequency front-end circuit of the present disclosure, the impedance of the adjustment circuit is preferably set such that the harmonic signal transmitted from the adjustment circuit to the second line and the harmonic signal transmitted from the third splitter to the second line are in opposite phase to each other at the connection point between the adjustment circuit and the second line.

With this configuration, the harmonic signal (the harmonic signal for cancellation) transmitted from the adjustment circuit to the second line and the harmonic signal (the harmonic signal to be cancelled) transmitted from the third splitter to the second line further assuredly weaken each other.

In the high-frequency front-end circuit of the present disclosure, the impedance of the adjustment circuit is preferably set such that the harmonic signal transmitted from the adjustment circuit to the second line and the harmonic signal transmitted from the third splitter to the second line have the same amplitude at the connection point between the adjustment circuit and the second line.

With this configuration, the harmonic signal (the harmonic signal for cancellation) transmitted from the adjustment circuit to the second line and the harmonic signal (the harmonic signal to be cancelled) transmitted from the third splitter to the second line assuredly cancel each other.

In the high-frequency front-end circuit of the present disclosure, the adjustment circuit may include a series circuit of a resistor and an inductor.

With this configuration, the amplitude is adjusted by the resistor, and the phase is adjusted by the inductor. Accordingly, it is possible to easily set the amplitude and the phase of the harmonic signal for cancellation.

In the high-frequency front-end circuit of the present disclosure, the adjustment circuit preferably includes a capacitor connected in parallel with the inductor.

With this configuration, it is possible to further assuredly set the phase of the adjustment circuit to a predetermined value.

In the high-frequency front-end circuit of the present disclosure, a parallel circuit of the inductor and the capacitor has a resonant frequency that is close to or overlaps a fundamental frequency of the transmission signal in the first communication band.

With this configuration, it is possible to more assuredly inhibit the transmission signal in the first communication band from leaking (being transmitted) via the adjustment circuit to the second line.

According to the present disclosure, it is possible to inhibit deterioration of reception sensitivity due to simultaneous transmission and reception.

DETAILED DESCRIPTION OF THE DISCLOSURE

A high-frequency front-end circuit according to a first embodiment of the present disclosure will be described with reference to the drawings.FIG. 1is a circuit diagram of the high-frequency front-end circuit according to the first embodiment of the present disclosure.

As shown inFIG. 1, the high-frequency front-end circuit10includes a first splitter20, a first switching circuit31, a second switching circuit32, a second splitter41, a third splitter42, and an adjustment circuit50.

The first splitter20is a so-called diplexer that roughly separates communication bands. The first splitter20is composed of a combination of a low pass filter21and a high pass filter22. The first splitter20includes a common terminal, a low frequency side terminal, and a high frequency side terminal. The low pass filter21is connected between the common terminal and the low frequency side terminal. The high pass filter22is connected between the common terminal and the high frequency side terminal.

The common terminal is connected to an external antenna ANT. The low frequency side terminal is connected to a common terminal P10of the first switching circuit31. The high frequency side terminal is connected to a common terminal P20of the second switching circuit32.

The first splitter20transmits a harmonic signal of a frequency band in a low band with low loss between the antenna ANT and the first switching circuit31via the low pass filter21. The first splitter20transmits a harmonic signal of a frequency band in a high band with low loss between the antenna ANT and the second switching circuit32via the high pass filter22.

The first switching circuit31includes the common terminal P10and selection target terminals P11to P14. The selection target terminals P11to P14are selectively connected to the common terminal P10.

Transmission/reception circuits for respective communication bands of the low band are connected to the selection target terminals P11to P14of the first switching circuit31, respectively. For example, as shown inFIG. 1, the second splitter41for a communication band A of the low band is connected to the selection target terminal P12. Although not shown, circuits similar to the circuit connected to the selection target terminal P12are connected to the selection target terminals P11, P13, and P14.

The second splitter41is a so-called duplexer that separates a transmission signal and a reception signal constituting one communication band. The second splitter41is composed of a combination of a low pass filter411and a high pass filter412. The second splitter41may be composed of two elastic wave filters having different pass bands, depending on the frequency band of the transmission signal and the reception signal.

The low pass filter411is connected between the selection target terminal P12of the first switching circuit31and a first reception signal output terminal Prx1. The low pass filter411is connected to the first reception signal output terminal Prx1via a first reception line LNrx1.

The high pass filter412is connected between the selection target terminal P12of the first switching circuit31and a first transmission signal input terminal Ptx1. The high pass filter412is connected to the first transmission signal input terminal Ptx1via a first transmission line (corresponding to a “first line” of the present disclosure) LNtx1.

The second switching circuit32includes the common terminal P20and selection target terminals P21to P24. The selection target terminals P21to P24are selectively connected to the common terminal P20.

Transmission/reception circuits for respective communication bands of the high band are connected to the selection target terminals P21to P24of the second switching circuit32, respectively. For example, as shown inFIG. 1, the third splitter42for a communication band B of the high band is connected to the selection target terminal P23. Although not shown, circuits similar to the circuit connected to the selection target terminal P23are connected to the selection target terminals P21, P22, and p24. The frequencies of the pass bands of the transmission/reception circuits connected to the respective selection target terminals P21to P24of the second switching circuit32are higher than the frequencies of the pass bands of the transmission/reception circuits connected to the respective selection target terminals P11to P14of the first switching circuit31.

The third splitter42is a so-called duplexer that separates a transmission signal and a reception signal constituting one communication band. The third splitter42is composed of a combination of a low pass filter421and a high pass filter422. The third splitter42may be composed of two elastic wave filters having different pass bands, depending on the frequency band of the transmission signal and the reception signal.

The low pass filter421is connected between the selection target terminal P23of the second switching circuit32and a second reception signal output terminal Prx2. The low pass filter421is connected to the second reception signal output terminal Prx2via a second reception line (corresponding to a “second line” of the present disclosure) LNrx2.

The high pass filter422is connected between the selection target terminal P22of the second switching circuit32and a second transmission signal input terminal Ptx2. The high pass filter422is connected to the second transmission signal input terminal Ptx2via a second transmission line LNtx2.

The adjustment circuit50is connected between the first transmission line LNtx1and the second reception line LNrx2.FIG. 2is a circuit diagram of the adjustment circuit according to the first embodiment of the present disclosure. InFIG. 2, lines representing respective signals for explaining the principle of cancellation of harmonic signals by using the adjustment circuit50are also shown.

The adjustment circuit50includes a resistor51and an inductor52. The resistor51and the inductor52are connected in series between the first transmission line LNtx1and the second reception line LNrx2. The connection point between the adjustment circuit50and the first transmission line LNtx1is PC1, and the connection point between the adjustment circuit50and the second reception line LNrx2is PC2.

With such a circuit configuration, the high-frequency front-end circuit10is able to achieve the following operation and advantageous effects.

Transmission in the communication band A of the low band and reception in the communication band B of the high band are simultaneously performed. That is, carrier aggregation for transmission in the communication band A and reception in the communication band B is performed. At this time, reception in the communication band A and transmission in the communication band B may not be performed.

In this case, in the first switching circuit31, the common terminal P10and the selection target terminal P12are connected to each other. In the second switching circuit32, the common terminal P20and the selection target terminal P23are connected to each other.

A transmission signal Stx1in the communication band A is inputted from the first transmission signal input terminal Ptx1and transmitted via the first transmission line LNtx1, the second splitter41, the first switching circuit31, and the first splitter20to the antenna ANT.

A reception signal Srx2in the communication band B is inputted from the antenna ANT (received by the antenna ANT) and transmitted via the first splitter20, the second switching circuit32, the third splitter42, and the second reception line LNrx2to the second reception signal output terminal Prx2.

Here, when the frequency of a harmonic signal of the transmission signal Stx1in the communication band A is close to or overlaps the frequency (fundamental frequency) of the reception signal Srx2in the communication band B, the harmonic signal of the transmission signal Stx1in the communication band A is transmitted via the third splitter42to the second reception line LNrx2. This is a harmonic signal Sd to be cancelled shown inFIG. 2.

This is due to, for example, a harmonic signal of the transmission signal Stx1in the communication band A leaking between the low pass filter21and the high pass filter22in the first splitter20and a harmonic signal of the transmission signal Stx1in the communication band A reflected by the antenna ANT, and the like.

In addition, a harmonic signal of the transmission signal Stx1in the communication band A is transmitted from the first transmission line LNtx1via the adjustment circuit50to the second reception line LNrx2. This is a harmonic signal Ss for cancellation shown inFIG. 2.

Here, the impedance of the adjustment circuit50, that is, the resistance value R of the resistor51, and the inductance L of the inductor52are set as described next.

(Resistance Value R of Resistor51)

The resistance value R of the resistor51is set such that the amplitude of the harmonic signal Sd to be cancelled is substantially equal to the amplitude of the harmonic signal Ss for cancellation. Particularly, the resistance value R of the resistor51is preferably set such that the amplitude of the harmonic signal Sd to be cancelled is equal to the amplitude of the harmonic signal Ss for cancellation.

(Inductance L of Inductor52)

The inductance L of the inductor52is set such that the harmonic signal Sd to be cancelled and the harmonic signal Ss for cancellation are not in same phase with each other at the connection point PC2. Particularly, the inductance L of the inductor52is preferably set such that the harmonic signal Sd to be cancelled and the harmonic signal Ss for cancellation are in opposite phase to each other at the connection point PC2.

Due to such a configuration, the harmonic signal Sd to be cancelled and the harmonic signal Ss for cancellation weaken each other, whereby it is possible to suppress the harmonic signal to be transmitted to the second reception signal output terminal Prx2. Particularly, since the amplitude of the harmonic signal Sd to be cancelled and the amplitude of the harmonic signal Ss for cancellation are equal to each other, and the harmonic signal Sd to be cancelled and the harmonic signal Ss for cancellation are in opposite phase to each other at the connection point PC2, it is possible to cancel the harmonic signal Sd to be cancelled and the harmonic signal Ss for cancellation. Accordingly, it is possible to eliminate the harmonic signal to be transmitted to the second reception signal output terminal Prx2.

Due to such a configuration, it is possible to inhibit deterioration of the reception sensitivity at the second reception signal output terminal Prx2for the reception signal Srx2in the communication band B.

The resistor51and the inductor52may be components mounted on a circuit board or may be conductor patterns formed on a circuit board. However, when mounting components are used as the resistor51and the inductor52, the resistor51and the inductor52are easily replaceable. Therefore, it is possible to easily perform an operation of setting the adjustment circuit50to the desired impedance, and it is possible to easily change or adjust the adjustment circuit50even after circuit formation.

Next, a high-frequency front-end circuit according to a second embodiment will be described with reference to the drawing.FIG. 3is a circuit diagram of an adjustment circuit of the high-frequency front-end circuit according to the second embodiment of the present disclosure.

The high-frequency front-end circuit according to the present embodiment is different from the high-frequency front-end circuit10according to the first embodiment in the configuration of an adjustment circuit50A.

The adjustment circuit50A includes a resistor51, an inductor52, and a capacitor53.

The resistor51and the inductor52are connected in series between the first transmission line LNtx1and the second reception line LNrx2. The capacitor53is connected in parallel with the inductor52.

Therefore, the adjustment circuit50A is composed of a parallel resonant circuit of the inductor52and the capacitor53and a series circuit of the inductor52and the resistor51.

The resistance value R of the resistor51is set in the same principle as in the first embodiment.

The inductance L of the inductor52and the capacitance C of the capacitor53are set as follows.

The inductance L of the inductor52and the capacitance C of the capacitor53are set such that the harmonic signal Sd to be cancelled and the harmonic signal Ss for cancellation are not in same phase with each other at the connection point PC2. Particularly, the inductance L of the inductor52and the capacitance C of the capacitor53are preferably set such that the harmonic signal Sd to be cancelled and the harmonic signal Ss for cancellation are in opposite phase to each other at the connection point PC2.

Furthermore, the resonant frequency fr of the parallel resonant circuit of the inductor52and the capacitor53is substantially equal to the frequency ftx1of the transmission signal Stx1in the communication band A.

Due to such a configuration, it is possible to inhibit the above-described harmonic signal of the transmission signal Stx1in the communication band A from leaking to the second reception signal output terminal Prx2, and it is possible to inhibit the transmission signal Stx1from leaking to the second reception signal output terminal Prx2.

Accordingly, it is possible to inhibit deterioration of the reception sensitivity in the communication band B, and it is possible to inhibit breakage of a subsequent circuit due to flow of the transmission signal Stx1thereinto.

Even when the resonant frequency fr is not equal to the frequency ftx1of the transmission signal Stx1, at least if a phase shift by which the above-described harmonic signals weaken each other is achieved, it is only necessary to set the inductance L of the inductor52and the capacitance C of the capacitor53as appropriate. In this case, a wider phase shift becomes possible by using the inductor52and the capacitor53than by using only the inductor52. Therefore, it is possible to assuredly set a desired phase shift amount.

Next, a high-frequency front-end circuit according to a third embodiment of the present disclosure will be described with reference to the drawing.FIG. 4is a circuit diagram of the high-frequency front-end circuit according to the third embodiment of the present disclosure.

The high-frequency front-end circuit10C according to the present embodiment is different from the high-frequency front-end circuit10according to the first embodiment in the configuration of a first splitter20C due to addition of a third switching circuit33, a fourth splitter43, and an adjustment circuit50C.

The first splitter20C separates three frequency bands. For example, the first splitter20C separates a low band, a middle band, and a high band. The first splitter20C is connected to the first switching circuit31, the second switching circuit32, and the third switching circuit33.

The third switching circuit33includes a common terminal P30and selection target terminals P31to P34. The selection target terminals P31to P34are selectively connected to the common terminal P30.

Transmission/reception circuits for respective communication bands of the middle band are connected to the selection target terminals P31to P34of the second switching circuit32, respectively. For example, as shown inFIG. 4, the fourth splitter43for a communication band C of the middle band is connected to the selection target terminal P33. Although not shown, circuits similar to the circuit connected to the selection target terminal P33are connected to the selection target terminals P31, P32, and P34.

The fourth splitter43is a so-called duplexer that separates a transmission signal and a reception signal constituting one communication band. The fourth splitter43is composed of a combination of a low pass filter431and a high pass filter432. The fourth splitter43may be composed of two elastic wave filters having different pass bands, depending on the frequency band of the transmission signal and the reception signal.

The low pass filter431is connected between the selection target terminal P33of the third switching circuit33and a third reception signal output terminal Prx3. The low pass filter431is connected to the third reception signal output terminal Prx3via a third reception line LNrx3.

The high pass filter432is connected between the selection target terminal P33of the third switching circuit33and a third transmission signal input terminal Ptx3. The high pass filter432is connected to the third transmission signal input terminal Ptx3via a third transmission line LNtx3.

The adjustment circuit50C is connected between the first transmission line LNtx1and the third reception line LNrx3.

The impedance of the adjustment circuit50C is set such that: the amplitude of a harmonic signal of a transmission signal in the communication band A from the fourth splitter43is substantially equal to (particularly equal to) the amplitude of a harmonic signal of the transmission signal in the communication band A from the adjustment circuit50C; and the amplitude of the harmonic signal of the transmission signal in the communication band A from the fourth splitter43and the amplitude of the harmonic signal of the transmission signal in the communication band A from the adjustment circuit50C are not in same phase with (are particularly in opposite phase to) each other at the connection point between the adjustment circuit50C and the third reception line LNrx3.

Due to such a configuration, even when carrier aggregation for transmission in the communication band A and reception in the communication band C is performed or even when the frequency of the harmonic signal of the transmission signal in the communication band A is close to or overlaps the frequency of a reception signal in the communication band C, it is possible to inhibit deterioration of the reception sensitivity for the reception signal.

As described above, in the present embodiment, even when the harmonic frequency of a transmission signal in one communication band is close to or overlaps the frequencies of reception signals in a plurality of other communication bands, it is possible to inhibit deterioration of the reception sensitivity for the reception signals.

By applying the configuration of the present embodiment, it is possible to connect an adjustment circuit between the second transmission line LNtx2and the third reception line LNrx3and inhibit the harmonic signal of the transmission signal inputted from the second transmission signal input terminal Ptx2from leaking to the third reception signal output terminal Prx3.

In the above-described embodiments, a specific circuit configuration of each splitter has not been described, but in the case of a circuit obtained by combining an inductor and a capacitor, it is possible to reduce the shape of the inductor of the adjustment circuit by intentionally coupling the splitter to the inductor or the capacitor of the adjustment circuit. Accordingly, it is possible to reduce the size of the adjustment circuit, and it is possible to reduce the size of the high-frequency front-end circuit. At this time, by adjusting the coupling amount, it is possible to adjust the characteristics of a filter forming each splitter, and make the splitter have desired characteristics without using an additional inductor or capacitor.10,10C high-frequency front-end circuit20,20C first splitter21low pass filter22high pass filter31first switching circuit32second switching circuit33third switching circuit41second splitter42third splitter43fourth splitter50,50A,50C adjustment circuit51resistor52inductor53capacitor411low pass filter412high pass filter421low pass filter422high pass filter431low pass filter432high pass filter