SWITCHING CIRCUIT AND HIGH FREQUENCY MODULE

Abstract

In a switching circuit, an inductance of an inductor of a shunt circuit is such that off capacitance of a second switching device that is in the off state when a first switching device is in the on state is used to define, in the shunt circuit, a series resonance circuit with a desired resonant frequency. Therefore, the frequency of an unnecessary signal to be attenuated is set to the resonant frequency of the series resonance circuit. Thus, the switching circuit achieves improved isolation characteristics with other circuits by attenuating the unnecessary signal.

Claims

1. A switching circuit comprising: a first terminal; a plurality of second terminals; first switching devices, each of the first switching devices being connected in series to a corresponding one of signal paths coupling the first terminal to a corresponding one of the plurality of second terminals; and shunt circuits, each of the shunt circuits being disposed between a corresponding one of the plurality of second terminals and a ground terminal; wherein each of the shunt circuits includes a second switching device and an inductor, the second switching device and the inductor being coupled to each other in series.

2. The switching circuit according to claim 1, wherein the inductors of the shunt circuits have inductances different from one another.

3. The switching circuit according to claim 2, further comprising: a third terminal; and third switching devices, each of the third switching devices being connected in series to a corresponding one of signal paths coupling the third terminal to a corresponding one of the plurality of second terminals.

4. The switching circuit according to claim 1, wherein each of the shunt circuits defines a series resonance circuit including a capacitance and the inductor, the capacitance being produced when the second switching device is in an off state, and the inductor of the series resonance circuit has an inductance value such that a resonant frequency of the series resonance circuit is equal or substantially equal to a frequency of a signal passing through one of the signal paths, the one of the signal paths being coupled to a different shunt circuit of the shunt circuits, the different shunt circuit being a shunt circuit in which the second switching device is in an on state.

5. The switching circuit according to claim 1, wherein each of the first switching devices and the second switches devices is one of a field-effect transistor, a circuit including a PIN diode, a bipolar transistor, and an electrostatic induction transistor.

6. The switching circuit according to claim 3, wherein each of the third switching devices is one of a field-effect transistor, a circuit including a PIN diode, a bipolar transistor, and an electrostatic induction transistor.

7. The switching circuit according to claim 1, wherein the inductor is a chip component.

8. A high frequency module comprising: the switching circuit according to claim 1; and a multi-layer substrate including a first principal surface on which the first, second, and third switching devices are mounted.

9. The high frequency module according to claim 8, wherein the inductor is a chip component mounted on the first principal surface of the multi-layer substrate or a wiring electrode in the multi-layer substrate.

10. The high frequency module according to claim 8, wherein the inductors of the shunt circuits have inductances different from one another.

11. The high frequency module according to claim 10, further comprising: a third terminal; and third switching devices, each of the third switching devices being connected in series to a corresponding one of signal paths coupling the third terminal to a corresponding one of the plurality of second terminals.

12. The high frequency module according to claim 8, wherein each of the shunt circuits defines a series resonance circuit including a capacitance and the inductor, the capacitance being produced when the second switching device is in an off state, and the inductor of the series resonance circuit has an inductance value such that a resonant frequency of the series resonance circuit is equal or substantially equal to a frequency of a signal passing through one of the signal paths, the one of the signal paths being coupled to a different shunt circuit of the shunt circuits, the different shunt circuit being a shunt circuit in which the second switching device is in an on state.

13. The high frequency module according to claim 8, wherein each of the first switching devices and the second switches devices is one of a field-effect transistor, a circuit including a PIN diode, a bipolar transistor, and an electrostatic induction transistor.

14. The high frequency module according to claim 11, wherein each of the third switching devices is one of a field-effect transistor, a circuit including a PIN diode, a bipolar transistor, and an electrostatic induction transistor.

15. The high frequency module according to claim 8, wherein the switching circuit is a switch IC.

16. The high frequency module according to claim 15, further comprising an antenna connected to the switch IC.

17. The high frequency module according to claim 16, wherein the antenna includes multi-band antennas or multiple single-band antennas.

18. A communication device comprising the high frequency module according to claim 8.

19. The communication device according to claim 18, wherein the communication device performs communication in multiple frequency bands and supports multiple communication systems.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] FIG. 1 is a sectional view of a high frequency module according to a first preferred embodiment of the present invention.

[0025] FIG. 2 is a diagram illustrating a high frequency circuit included in the high frequency module in FIG. 1.

[0026] FIG. 3 is a diagram illustrating a switching circuit included in the high frequency circuit in FIG. 2.

[0027] FIG. 4 is a diagram illustrating bandpass characteristics of the switching circuit in FIG. 3.

[0028] FIG. 5 is a diagram illustrating bandpass characteristics of a switching circuit of the related art.

[0029] FIG. 6 is a diagram illustrating a high frequency circuit included in a high frequency module according to a second preferred embodiment of the present invention.

[0030] FIG. 7 is a diagram illustrating a switching circuit included in the high frequency circuit in FIG. 6.

[0031] FIG. 8 is a diagram illustrating a switching circuit included in a high frequency module of the related art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Preferred Embodiment

[0032] A first preferred embodiment of the present invention will be described with reference to FIGS. 1 to 4. FIGS. 1 to 3 illustrate only a main configuration according to a preferred embodiment of the present invention. To simplify the description, the other configurations are not illustrated. Similarly to FIGS. 1 to 3, FIGS. 6 and 7 referred to in the description below also illustrate only a main configuration, and will not be described in the description thereof below.

[0033] A high frequency module 1 illustrated in FIGS. 1 and 2 is preferably mounted in a communication device (not illustrated) such as a cellular phone supporting the multi-mode and multi-bands in which multiple frequency bands are used to perform communication. Such a communication device supports multiple communication systems, such as the GSM standard, the W-CDMA standard, the LTE standard, and the Bluetooth standard. The high frequency module 1 includes a switching circuit that couples, through switching, an antenna A1 included in the communication device to multiple communication systems (not illustrated) used by the communication device.

[0034] The high frequency module 1 includes a multi-layer substrate 2 in which multiple (for example, five) insulating layers 2a to 2f are laminated, a switch IC 3 including a switching circuit 101, and circuit elements, such as inductors L1 to L4 and capacitors, which are preferably chip components 4 or wiring electrodes 5 provided in the multi-layer substrate 2.

[0035] The multi-layer substrate 2 preferably is a typical multi-layer substrate, such as an LTCC (low temperature co-fired ceramics) multi-layer substrate or a resin multi-layer substrate including a glass epoxy resin or the like. For example, the switch IC 3 and the chip components 4 to define matching circuits, various filter circuits, and the like are mounted on land electrodes 22 that are used to mount components and that are provided on a mounting surface 21 which is a first principal surface of the multi-layer substrate 2. The components and multiple external connecting terminals 24 which are provided on a second principal surface 23 of the multi-layer substrate 2 are electrically coupled to one another through the wiring electrode 5 included in the multi-layer substrate 2. The wiring electrodes 5 include in-plane conductors provided on the principal surfaces of the insulating layers, and via conductors connecting the in-plane conductors provided on the insulating layers. The electrodes, such as the land electrodes 22, the external connecting terminals 24, and the wiring electrodes 5, are preferably made of a conductive material containing Cu, Ag, or the like.

[0036] As illustrated in FIG. 2, the switch IC 3 includes a common terminal 31 (corresponding to a “first terminal”) coupled through a wiring electrode 5 to a common electrode ANT1a (external connecting terminal 24) provided on the multi-layer substrate 2, and multiple (in this preferred embodiment, four, for example) switching terminals 32a to 32d (corresponding to “second terminals”). The antenna A1 is coupled to the common electrode ANT1a. The switching terminals 32a to 32d support signals of different respective communication systems (not illustrated). To pass a signal of a desired communication system, the switch IC 3 couples, through switching, any of the switching terminals 32a to 32d to the common terminal 31. The configuration of the switching circuit 101 will be described in detail.

[0037] As illustrated in FIG. 3, the switching circuit 101 includes multiple (in this preferred embodiment, four, for example) first switching devices 102a to 102d and multiple (in this preferred embodiment, four, for example) shunt circuits 103a to 103d. Each of the first switching devices 102a to 102d is coupled to the common terminal 31 at one end, and is coupled to a corresponding one of the switching terminals 32a to 32d at the other end. Thus, four signal paths SL1a to SL1d that couple the common terminal 31 to the respective switching terminals 32a to 32d are provided. Between each of the switching terminals 32a to 32d and a ground terminal (ground GND) included in the high frequency module 1, a corresponding one of the shunt circuits 103a to 103d is provided.

[0038] As illustrated in FIG. 3, each of the shunt circuits 103a to 103d includes a series circuit including a corresponding one of second switching devices 104a to 104d and a corresponding one of the inductors L1 to L4. Each of the second switching devices 104a to 104d is coupled, at one end, to a corresponding one of the switching terminals 32a to 32d (signal paths SL1a to SL1d). Each of the inductors L1 to L4 is coupled, at one end, to the other end of a corresponding one of the second switching devices 104a to 104d, and is coupled to the ground terminal (ground GND) at the other end. In this preferred embodiment, the second switching devices 104a to 104d are coupled through the land electrodes 22 to the inductors L1 to L4 that are chip components 4.

[0039] In this preferred embodiment, the first switching devices 102a to 102d and the second switching devices 104a to 104d are preferably field-effect transistors (FETs), for example. The FETs are provided on a semiconductor substrate as an integral unit so that the switch IC 3 is provided. The inductors of the shunt circuits may be mounted in the switch IC 3, or, as illustrated in FIG. 1, may be provided as chip components 4 on the multi-layer substrate 2 in such a manner as to be coupled to the switch IC 3 by using wiring electrodes 5 in the multi-layer substrate 2.

[0040] When a desired communication system is to be used, one of the first switching devices 102a to 102d is switched to the on state (in FIG. 3, the first switching device 102a is in the on state). Thus, the common terminal 31 is coupled to one of the switching terminals 32a to 32d through switching. As illustrated in FIG. 3, similarly to the switching circuit 500 of the related art described by referring to FIG. 8, when the first switching device 102a is switched to the on state, the second switching device 104a is switched to the off state. When the first switching devices 102b to 102d are switched to the off state, the second switching devices 104b to 104d are switched to the on state.

[0041] Referring to FIGS. 4 and 5, improvement of isolation characteristics among the switching terminals 32a to 32d (signal paths SL1a to SL1d) of the switching circuit 101 including the inductors L1 to L4 will be described. An example will be described under the assumption that the off capacitance Cf of the second switching device 104a is about 0.1 pF and that the inductance of the inductor L1 is set to 18 nH, for example. The horizontal axes in FIGS. 4 and 5 represent frequency (GHz), and the vertical axes represent bandpass characteristics (dB: signal level). FIG. 4 illustrates the signal level of a signal observed at the switching terminal 32a in the case where the first switching device 102a is in the on state when the common terminal 31 receives a high frequency signal. An exemplary case in which the first switching device 102a is in the on state will be described. However, when one of the first switching devices 102b to 102d is in the on state, an effect similar to an effect described below may also occur. Therefore, the description will not be made.

[0042] As illustrated in FIG. 3, when the first switching device 102a is in the on state, the off capacitance Cf of the second switching device 104a illustrated in FIG. 3 and the inductor L1 define an LC series resonance circuit so that, as illustrated in FIG. 4, an attenuation pole is provided in the bandpass characteristics between the common terminal 31 and the switching terminal 32a. The inductance of the inductor L1 is designed so that the frequency of the attenuation pole is equal to or close to the frequency of an unnecessary high frequency signal. Thus, especially when an unnecessary high frequency signal in a frequency band around the frequency band in which the attenuation pole is located is propagated to the signal path SL1a (switching terminal 32a) from the other signal paths SL1b to SL1d (switching terminals 32b to 32d), the unnecessary high frequency signal that has been propagated through the shunt circuit 103a may be directed to the ground terminal (ground GND). Thus, the isolation characteristics in the switching circuit 101 are improved.

[0043] As described above, in the present preferred embodiment, the off capacitance of the second switching device 104a that is in the off state when the first switching device 102a is in the on state is used to attenuate an unnecessary signal, improving the isolation characteristics of the switching circuit 101.

[0044] The inductors L1 to L4 of the shunt circuits 103a to 103d may have inductances different from one another. In this case, LC series resonance circuits to which resonant frequencies different from one another are set are provided in the shunt circuits 103a to 103d. Therefore, the frequency band of a signal to be attenuated may be set for each of the signal paths SL1a to SL1d.

[0045] The inductors L1 to L4 are provided for the multi-layer substrate 2. Therefore, it is not necessary to mount inductors in the switch IC 3, resulting in reduction of the switch IC 3 in size. In addition, the inductances of the inductors L1 to L4 may be easily adjusted just by replacing chip components, achieving a wider range of choices in design of the switching circuit 101.

Second Preferred Embodiment

[0046] Referring to FIGS. 6 and 7, a second preferred embodiment of the present invention will be described. The high frequency module 1 according to this preferred embodiment is different from that according to the first preferred embodiment described above in that, as illustrated in FIG. 6, a common terminal 33 (corresponding to a “third terminal” of the present invention) coupled to an antenna A2 is further included in a switch IC 3a. In the description below, points different from those in the first preferred embodiment will be mainly described. The other configurations and operations are similar to those in the first preferred embodiment described above, and are designated with identical reference characters. Thus, the other configurations and operations will not be described.

[0047] As illustrated in FIG. 6, the switch IC 3a includes the common terminal 31 coupled to a common electrode ANT1 (external connecting terminal 24) through a wiring electrode 5, the common terminal 33 coupled to a common electrode ANT2 (external connecting terminal 24) through a wiring electrode 5, and the multiple switching terminals 32a to 32d. The antenna A1 is coupled to the common electrode ANT1, and the antenna A2 is coupled to the common electrode ANT2. The switch IC 3 couples one of the common terminals 31 and 33 to one of the switching terminals 32a to 32d through switching. The configuration of a switching circuit 101a will be described in detail.

[0048] As illustrated in FIG. 7, the switching circuit 101a is structured so that the switching circuit 101 in FIG. 3 further includes multiple (in this preferred embodiment, four, for example) third switching devices 106a to 106d. Each of the third switching devices 106a to 106d is coupled to the common terminal at one end, and is coupled to a corresponding one of the switching terminals 32a to 32d at the other end. Thus, each of the third switching devices 106a to 106d is connected in series to a corresponding one of four signal paths SL2a to SL2d that couple the common terminal 33 to the respective switching terminals 32a to 32d. In the present preferred embodiment in FIG. 7, the common terminal 31 is coupled to the switching terminal 32a, and the common terminal 33 is coupled to the switching terminal 32d.

[0049] Similarly to the first switching devices 102a to 102d and the second switching devices 104a to 104d, the third switching devices 106a to 106d preferably are field-effect transistors (FETs), and include the first and second switching devices as an integral unit on a semiconductor substrate, thus defining the switch IC 3. The inductors of the shunt circuits may be mounted in the switch IC 3, or may be provided as chip components 4 on the multi-layer substrate 2 as illustrated in FIG. 1 so as to couple to the switch IC 3 by using wiring electrodes 5 in the multi-layer substrate 2.

[0050] One of the first switching devices 102a to 102d is switched to the on state (in FIG. 7, the first switching device 102a is in the on state). Thus, the common terminal 31 is coupled to one of the switching terminals 32a to 32d through switching. A signal of a desired communication system may be passed between the switching terminal and the common terminal 31. One of the third switching devices 106a to 106d is switched to the on state (in FIG. 7, the third switching device 106d is in the on state). Thus, the common terminal 33 is coupled to one of the switching terminals 32a to 32d through switching. A signal of a desired communication system may be passed between the switching terminal and the common terminal 33.

[0051] As illustrated in FIG. 7, similarly to the first preferred embodiment described above, when the first switching device 102a and the third switching device 106d are switched to the on state, the second switching devices 104a and 104d are switched to the off state. When the first switching devices 102b and 102c and the third switching devices 106b and 106c are switched to the off state, the second switching devices 104b and 104c are switched to the on state. That is, for each of the switching terminals 32a to 32d, in the case where one of a corresponding one of the first switching devices 102a to 102d and a corresponding one of the third switching devices 106a to 106d coupled to the switching terminal is switched to the on state, the second switching device coupled to the switching terminal coupled to the switching device that is in the on state is switched to the off state. In contrast, for each of the switching terminals 32a to 32d, in the case where both of a corresponding one of the first switching devices 102a to 102d and a corresponding one of the third switching devices 106a to 106d connected to the switching terminal are switched to the off state, the second switching device coupled to the switching terminal coupled to the first and third switching devices that are in the off state is switched to the on state.

[0052] Both of a corresponding one of the first switching devices 102a to 102d and a corresponding one of third switching devices 106a to 106d coupled to each of the switching terminals 32a to 32d are not switched to the on state. That is, the on/off state of each of the first switching devices 102a to 102d and the third switching devices 106a to 106d is controlled so that the communication system coupled to each of the switching terminals 32a to 32d is not coupled to the antennas A1 and A2 at the same time.

[0053] As described above, in this preferred embodiment, the inductances of the inductors L1 to L4 of the shunt circuit 103a are adequately set. Thus, desired attenuation poles are provided in the bandpass characteristics of each of the signal paths SL1a to SL1d coupling the common terminal 31 to the switching terminals 32a to 32d and the bandpass characteristics of each of the signal paths SL2a to SL2d coupling the common terminal 33 to the switching terminals 32a to 32d. Accordingly, similarly to the first preferred embodiment described above, the isolation characteristics among the switching terminals 32a to 32d (signal paths SL1a to SL1d, SL2a to SL2d) in the switching circuit 101a are improved.

[0054] The present invention is not limited to the preferred embodiments described above. Without departing from the gist, in addition to the above-described preferred embodiments, various changes may be made, and the configurations described above may be combined with each other in any manner. For example, the number of the switching terminals 32a to 32d, the number of the first switching devices 102a to 102d, and the number of the third switching devices 106a to 106d are not limited to the numbers described above. In accordance with the number of the communication systems handled by the communication device and the number of antennas A1 and A2, a necessary number of circuit elements such as switching devices may be included. In addition, a switching terminal that is not coupled to a shunt circuit may be further included. Further, a pair of first and second terminals may define a switching circuit. In this case, any of the first and second terminals may be coupled to an antenna.

[0055] In the above-described preferred embodiments, the switching devices 102a to 102d, 104a to 104d, and 106a to 106d may be field-effect transistors, for example. Alternatively, each of the switching devices 102a to 102d, 104a to 104d, and 106a to 106d may be a circuit including a PIN diode, or various switching devices, such as a bipolar transistor and an electrostatic induction transistor, for example.

[0056] An antenna coupled to the switch IC 3 or 3a is not limited to the multi-band antennas A1 and A2 described above, and may be multiple single-band antennas supporting the respective bands used in communication. In addition, the number of antennas coupled to a switch IC and the number of communication systems coupled to the switch IC may be appropriately set to adequate numbers in accordance with the configuration of a communication device in which the high frequency module 1 is mounted.

[0057] Preferred embodiments of the present invention may be widely applied to a switching circuit including a first switching device connected in series to a signal path and a second switching device shunt-connected to the signal path, and a high frequency module including the switching circuit.

[0058] While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.