Variable Inductor

Abstract

This invention provides a variable inductor for high-frequency signals that allows for stepwise switching of inductance. [Solution] The device comprises a series circuit in which multiple inductors are connected in series, and one or more switches provided between at least one connection point among the connection points of the multiple inductors and a reference potential.

Description

Technical Field

[0001] The present invention relates to a variable inductor. Background Art

[0002] Patent Document 1 below discloses a multilayer circuit aimed at inexpensively implementing a configuration of a variable inductor that can be easily manufactured by an IC process, has low power consumption, does not generate parasitic capacitance, and can achieve a high Q value. This multilayer circuit includes a variable inductor that is provided with a plurality of switches at the input of a spiral inductor and changes inductance by switching the switches.

[0003] Further, Patent Document 2 below discloses an integrated circuit including a variable inductor. This integrated circuit is provided with an annular line around a spiral inductor, and includes a variable inductor that changes inductance by switching the connection of the annular path with a switch. Prior Art Documents Patent Documents

[0004] Patent Document 1 Japanese Unexamined Patent Publication No. 2007-142418 Patent Document 2 Japanese National Publication of International Patent Application No. 2007-507106 Summary of the Invention Problems to be Solved by the Invention

[0005] By the way, the variable inductor disclosed in Patent Document 1 requires a series switch on the RF signal line, and therefore has a problem that it is greatly affected by parasitic capacitance when processing high-frequency signals. Accordingly, the variable inductor of Patent Document 1 is poor in usability for processing high-frequency signals.

[0006] On the other hand, the variable inductor described in Patent Document 2 has a ring-shaped path around the spiral inductor, making it difficult to switch the inductance in steps. Therefore, the variable inductor described in Patent Document 2 is not suitable for high-frequency signals where stepwise switching of inductance is required.

[0007] This invention has been made in view of the above circumstances, and aims to provide a variable inductor for high-frequency signals that can switch its inductance in steps. [Means for solving the problem]

[0008] To achieve the above objective, the present invention employs a first solution relating to a variable inductor, comprising a series circuit in which a plurality of inductors are connected in series, and one or more switches provided between at least one of the connection points of the plurality of inductors and a reference potential.

[0009] In the present invention, as a second solution relating to a variable inductor, the first solution described above is provided with a transformer connected to one end of the series circuit for contactless transmission of two input signals.

[0010] In the present invention, as a third solution relating to a variable inductor, the second solution described above includes a pair of inductance variable units consisting of the series circuit and one or more switches, wherein the transformer includes a primary inductor to which one input signal is input at one end and the other input signal is input at the other end, and a secondary inductor to which a pair of secondary intermediate contacts are provided, with one of the inductance variable units connected to the first secondary intermediate contact and the other inductance variable unit connected to the second secondary intermediate contact, and a pair of output signals output from both ends.

[0011] In the present invention, as a fourth solution relating to a variable inductor, the primary inductor is provided with a bias primary contact to which a bias voltage is applied, in the third solution described above.

[0012] In the present invention, as a fifth solution relating to a variable inductor, the second solution described above includes a pair of inductance variable units consisting of the series circuit and one or more switches, the transformer includes a pair of primary-side intermediate contacts, one input signal is input to one end and the other input signal is input to the other end, one of the inductance variable units is electrically connected to the first primary-side intermediate contact and the other inductance variable unit is electrically connected to the second primary-side intermediate contact, and the transformer includes a primary inductor that outputs an output signal from both ends.

[0013] In the present invention, as a sixth solution relating to a variable inductor, the primary inductor is provided with a primary contact for biasing, as described in the fifth solution above.

[0014] In the present invention, as a seventh solution relating to a variable inductor, the transformer is provided with a primary inductor to which one input signal is input at one end and the other input signal is input at the other end, and a secondary inductor to which one end of the series circuit is connected and which outputs an output signal from one end.

[0015] In this invention, as an eighth solution relating to a variable inductor, the method of forming it as a multilayer board based on photolithography, as described in any of the first to seventh solutions above, is adopted. [Effects of the Invention]

[0016] According to the present invention, it is possible to provide a variable inductor for high-frequency signals that can switch the inductance in steps. [Brief explanation of the drawing]

[0017] [Figure 1] It is a circuit diagram showing the configuration of a variable inductor according to the first embodiment of the present invention. [Figure 2] It is a perspective view showing the outer shape of the variable inductor according to the first embodiment of the present invention. [Figure 3] It is a characteristic diagram showing the operation and performance of the variable inductor according to the first embodiment of the present invention. [Figure 4] It is a perspective view showing the outer shape of the variable inductor according to the second embodiment of the present invention. [Figure 5] It is a characteristic diagram showing the operation and performance of the variable inductor according to the second embodiment of the present invention. [Figure 6] It is a perspective view showing the outer shape of the variable inductor according to the third embodiment of the present invention. [Figure 7] It is a characteristic diagram showing the operation and performance of the variable inductor according to the third embodiment of the present invention. [Figure 8] It is a circuit diagram showing the configuration of a variable inductor according to the fourth embodiment of the present invention. [Figure 9] It is a perspective view showing the outer shape of the variable inductor according to the fourth embodiment of the present invention. [Figure 10] It is a characteristic diagram showing the operation and performance of the variable inductor according to the fourth embodiment of the present invention. [Figure 11] It is a circuit diagram showing the configuration of a variable inductor according to a modification of the present invention. MODE FOR CARRYING OUT THE INVENTION

[0018] Hereinafter, embodiments of the present invention will be described with reference to the drawings. [First Embodiment] First, the first embodiment of the present invention will be described with reference to FIGS. 1 to 3. As shown in FIG. 1, the variable inductor A1 according to the first embodiment includes a pair of input terminals Tin1, Tin2, a bias terminal Tdd, a pair of output terminals Tout1, Tout2, a transformer Tr, and a pair of inductance variable units D, D'.

[0019] As shown in the figure, the transformer Tr comprises four primary lines L11 to L14 and four secondary lines L21 to L24. In this transformer Tr, the four primary lines L11 to L14 together constitute a primary inductor. The four secondary lines L21 to L24 together constitute a secondary inductor.

[0020] Of the pair of inductance variable units D and D', one inductance variable unit D includes a first inductor L1, a second inductor L2, a third inductor L3, a fourth inductor L4, a first switch M1, a second switch M2, and a third switch M3, as shown in the figure.

[0021] Furthermore, in the pair of inductance variable sections D and D', the other inductance variable section D' includes, as shown in the figure, a fifth inductor L1', a sixth inductor L2', a seventh inductor L3', an eighth inductor L4', a fourth switch M1', a fifth switch M2', and a sixth switch M3'.

[0022] Of the pair of input terminals Tin1 and Tin2, one input terminal Tin1 is connected to one end of the first primary line L11 of the transformer Tr inside the variable inductor A1. The other input terminal Tin1, although not shown in the figure, is connected to one output terminal of a differential signal source outside the variable inductor A1. A non-inverting signal from the differential signal source is input to this one input terminal Tin1 as the first high-frequency input signal Vin1.

[0023] The other input terminal Tin2 is connected to the other end of the fourth primary line L14 of the transformer Tr inside the variable inductor A1. Furthermore, the other input terminal Tin2 is connected to the other output terminal of the differential signal source outside the variable inductor A1. An inverted signal from the differential signal source is input to this other input terminal Tin2 as a second high-frequency input signal Vin2.

[0024] The bias terminal Tdd is connected inside the variable inductor A1 to the other end of the second primary line L12 and one end of the third primary line L13 in the transformer Tr, i.e., to the primary contact c10 for bias. Furthermore, outside the variable inductor A1, this bias terminal Tdd is connected to the output terminal of the bias circuit. A predetermined bias voltage Vdd is applied to this bias terminal Tdd from an external bias power supply.

[0025] A predetermined bias voltage is applied to this bias terminal Tdd from the bias circuit. This bias voltage is supplied to one output terminal of the differential signal source via the first primary line L11 and the second primary line L12 of the transformer Tr and one input terminal Tin1. This bias voltage is also supplied to the other output terminal of the differential signal source via the third primary line L13 and the fourth primary line L14 of the transformer Tr and the other input terminal Tin2.

[0026] Of the pair of output terminals Tout1 and Tout2, one output terminal Tout1 is connected to one end of the first secondary line L21 of the transformer Tr inside the variable inductor A1. The other output terminal Tout1 is connected to the input terminal of the first downstream circuit outside the variable inductor A1. This one output terminal Tout1 outputs a non-inverting signal as the first high-frequency output signal Vout1 to the first downstream circuit.

[0027] The other output terminal Tout2 is connected to the other end of the fourth secondary line L24 of the transformer Tr inside the variable inductor A1. Furthermore, the other output terminal Tout2 is connected to the input terminal of the second downstream circuit outside the variable inductor A1. This one output terminal Tout1 outputs the inverted signal as a second high-frequency output signal Vout2 to the second downstream circuit.

[0028] In the variable inductor A1 according to the first embodiment, the transformer Tr is a magnetically coupled system consisting of four primary lines L11 to L14 and four secondary lines L21 to L24. That is, the transformer Tr transmits signals non-contactually from the primary circuit consisting of the four primary lines L11 to L14 to the secondary circuit consisting of the four secondary lines L21 to L24 by electromagnetically coupling the four primary lines L11 to L14 and the four secondary lines L21 to L24 with a predetermined coupling coefficient k.

[0029] The four primary lines L11 to L14 are connected in series as shown in the figure. That is, the first primary line L11 is a transmission line having a predetermined length (11th line length), with one end connected to one input terminal Tin1 and the other end connected to one end of the second primary line L12. Such a first primary line L11 has an inductance (11th inductance) corresponding to the 11th line length.

[0030] The second primary line L12 is a transmission line having a predetermined length (12th line length), with one end connected to the other end of the first primary line L11 and the other end connected to one end of the third primary line L13 and the bias terminal Tdd. Such a second primary line L12 has an inductance (12th inductance) corresponding to the 12th line length. The connection point between the other end of the second primary line L12 and one end of the third primary line L13 is the bias primary side contact c10 to which the bias voltage Vdd is applied.

[0031] The third primary line L13 is a transmission line having a predetermined length (13th line length), with one end connected to the other end of the second primary line L12 and the bias terminal Tdd, and the other end connected to one end of the fourth primary line L14. Such a third primary line L13 has an inductance (13th inductance) corresponding to the 13th line length.

[0032] The fourth primary line L14 is a transmission line having a predetermined length (14th line length), with one end connected to the other end of the third primary line L13 and the other end connected to the other input terminal Tin2. Such a fourth primary line L14 has an inductance (14th inductance) corresponding to the 14th line length.

[0033] The four secondary lines L21 to L24 are connected in series as shown in the figure. Specifically, the first secondary line L21 is a transmission line having a predetermined length (21st line length), with one end connected to one output terminal Tout1 and the other end connected to one end of the second secondary line L22. Such a first secondary line L21 has an inductance (21st inductance) corresponding to the 21st line length. The connection point between the other end of the first secondary line L21 and one end of the second secondary line L22 is the first secondary-side intermediate contact c21.

[0034] The second secondary line L22 is a transmission line having a predetermined length (22nd line length), with one end connected to the other end of the first secondary line L21 and the other end connected to one end of the third secondary line L23 and one end of one of the inductance variable units D. Such a second secondary line L22 has an inductance (22nd inductance) corresponding to the 22nd line length.

[0035] The third secondary line L23 is a transmission line having a predetermined length (23rd line length), with one end connected to the other end of the second secondary line L22 and the other end connected to one end of the fourth secondary line L24 and the other inductance variable section D'. Such a third secondary line L23 has an inductance (23rd inductance) corresponding to the 23rd line length. The connection point between the other end of the third secondary line L23 and one end of the fourth secondary line L24 is the second secondary side intermediate contact c22.

[0036] The fourth secondary line L24 is a transmission line having a predetermined length (24th line length), with one end connected to the other end of the third secondary line L23 and the other inductance variable section D', and the other end connected to the other output terminal Tout2. Such a fourth secondary line L24 has an inductance (24th inductance) corresponding to the 24th line length.

[0037] In this transformer Tr, the total inductance of the four primary lines L11 to L14 (primary inductance) and the total inductance of the four secondary lines L21 to L24 (secondary inductance) have a predetermined ratio. Furthermore, the 21st inductance and the 24th inductance are set to the same inductance, and the 22nd inductance and the 23rd inductance are set to the same inductance.

[0038] In the inductance variable section D, the first inductor L1 is a transmission line having a predetermined length (first line length), with one end connected to the other end of the first secondary line L21 and one end of the second secondary line L22 in the transformer Tr, i.e., the first output-side intermediate contact c21, and the other end connected to one end of the second inductor L2 and the drain terminal of the first switch M1. Such a first inductor L1 has an inductance (first inductance) corresponding to the first line length.

[0039] The second inductor L2 is a transmission line having a predetermined length (second line length), with one end connected to the other end of the first inductor L1 and the drain terminal of the first switch M1, and the other end connected to one end of the third inductor L3 and the drain terminal of the second switch M2. Such a second inductor L2 has an inductance (second inductance) corresponding to the second line length.

[0040] The third inductor L3 is a transmission line having a predetermined length (third line length), with one end connected to the other end of the second inductor L2 and the drain terminal of the second switch M2, and the other end connected to one end of the fourth inductor L4 and the drain terminal of the third switch M3. Such a third inductor L3 has an inductance (third inductance) corresponding to the third line length.

[0041] The fourth inductor L4 is a transmission line having a predetermined length (fourth line length), with one end connected to the other end of the third inductor L3 and the drain terminal of the third switch M3, and the other end grounded. Such a fourth inductor L4 has an inductance (fourth inductance) corresponding to the fourth line length.

[0042] The first switch M1 is an N-type MOS (Metal Oxide Semiconductor) transistor, as shown in the figure. The drain terminal of this first switch M1 is connected to the other end of the first inductor L1 and one end of the second inductor L2, and the source terminal is grounded. In other words, the first switch M1 is provided between the connection point of the first inductor L1 and the second inductor L2 and the reference potential (GND).

[0043] Furthermore, the gate terminal of the first switch M1 is connected to the first output terminal of a control circuit (not shown). In other words, the first switch M1 is controlled to be ON (conductive) / OFF (disconnected) based on a first control signal input from the control circuit.

[0044] The second switch M2 is an N-type MOS transistor, similar to the first switch M1. The drain terminal of this second switch M2 is connected to the other end of the second inductor L2 and one end of the third inductor L3, and the source terminal is grounded. In other words, the second switch M2 is located between the connection point of the second inductor L2 and the third inductor L3 and the reference potential (GND).

[0045] Furthermore, the gate terminal of the second switch M2 is connected to the second output terminal of a control circuit (not shown). In other words, the second switch M2 is controlled to be ON (conducting) / OFF (blocking) based on a second control signal input from the control circuit.

[0046] The third switch M3 is an N-type MOS transistor, similar to the first switch M1. The drain terminal of this third switch M3 is connected to the other end of the third inductor L3 and one end of the fourth inductor L4, and its source terminal is grounded. In other words, the third switch M3 is located between the connection point of the third inductor L3 and the fourth inductor L4 and the reference potential (GND).

[0047] Furthermore, the gate terminal of the third switch M3 is connected to the third output terminal of a control circuit (not shown). In other words, the third switch M3 is controlled to be ON (conductive) / OFF (disconnected) based on a third control signal input from the control circuit.

[0048] In other words, one of the inductance variable units D comprises a first series circuit in which four inductors L1 to L4 are connected in series, and three switches M1 to M3 provided between each of the connection points of the four inductors L1 to L4 and a reference potential (GND). Such one of the inductance variable units D corresponds to the variable inductor in the present invention.

[0049] In the other inductance variable section D', the fifth inductor L1' is a transmission line having a predetermined length (fifth line length), with one end connected to the other end of the third secondary line L23 and one end of the fourth secondary line L24 in the transformer Tr, i.e., the second output-side intermediate contact c22, and the other end connected to one end of the sixth inductor L2' and the drain terminal of the fifth switch M1'. Such a fifth inductor L1' has an inductance (fifth inductance) corresponding to the fifth line length.

[0050] The sixth inductor L2' is a transmission line having a predetermined length (sixth line length), with one end connected to the other end of the fifth inductor L1' and the drain terminal of the fourth switch M1', and the other end connected to one end of the seventh inductor L3' and the drain terminal of the fifth switch M2'. Such a sixth inductor L2' has an inductance (sixth inductance) corresponding to the sixth line length.

[0051] The seventh inductor L3' is a transmission line having a predetermined length (seventh line length), with one end connected to the other end of the sixth inductor L2' and the drain terminal of the fifth switch M2', and the other end connected to one end of the eighth inductor L4' and the drain terminal of the sixth switch M3'. Such a seventh inductor L3' has an inductance (seventh inductance) corresponding to the seventh line length.

[0052] The eighth inductor L4' is a transmission line having a predetermined length (eighth line length), with one end connected to the other end of the seventh inductor L3' and the drain terminal of the sixth switch M3', and the other end grounded. Such an eighth inductor L4' has an inductance (eighth inductance) corresponding to the eighth line length.

[0053] The fourth switch M1' is an N-type MOS transistor, similar to the first to third switches M1 to M3 described above. The drain terminal of this fourth switch M1' is connected to the other end of the fifth inductor L1' and one end of the sixth inductor L2', and its source terminal is grounded. In other words, the fourth switch M1' is located between the connection point of the fifth inductor L1' and the sixth inductor L2' and the reference potential (GND).

[0054] Furthermore, the gate terminal of the fourth switch M1' is connected to the fourth output terminal of a control circuit (not shown). In other words, the fourth switch M1' is controlled to be ON (conductive) / OFF (blocked) based on the fourth control signal input from the control circuit.

[0055] The fifth switch M2' is an N-type MOS transistor, similar to the fourth switch M1'. The drain terminal of this fifth switch M2' is connected to the other end of the sixth inductor L2' and one end of the seventh inductor L3', and its source terminal is grounded. In other words, the fifth switch M2' is located between the connection point of the sixth inductor L2' and the seventh inductor L3' and the reference potential (GND).

[0056] Furthermore, the gate terminal of the fifth switch M2' is connected to the fifth output terminal of a control circuit (not shown). In other words, the fifth switch M2' is controlled to be ON (conductive) / OFF (disconnected) based on the fifth control signal input from the control circuit.

[0057] The sixth switch M3' is an N-type MOS transistor, similar to the fourth switch M1'. The drain terminal of this sixth switch M3' is connected to the other end of the seventh inductor L3' and one end of the eighth inductor L4', and its source terminal is grounded. In other words, the sixth switch M3' is located between the connection point of the seventh inductor L3' and the eighth inductor L4' and the reference potential (GND).

[0058] Furthermore, the gate terminal of the sixth switch M3' is connected to the sixth output terminal of a control circuit (not shown). In other words, the sixth switch M3' is controlled to be ON (conductive) / OFF (disconnected) based on the sixth control signal input from the control circuit.

[0059] In other words, the other inductance variable unit D' comprises a second series circuit in which four inductors L1' to L4' are connected in series, and three switches M1' to M3' are provided between each of the connection points of the four inductors L1' to L4' and a reference potential (GND). This one inductance variable unit D' corresponds to the variable inductor in the present invention, just like the one inductance variable unit D.

[0060] Here, the variable inductor A1 according to the first embodiment is formed as a multilayer board based on photolithography, as shown in Figure 2. That is, the variable inductor A1 is a high-frequency integrated circuit in which a pair of input terminals Tin1, Tin2, a bias terminal Tdd, a pair of output terminals Tout1, Tout2, a transformer Tr, and a pair of inductance variable parts D, D' are formed in a multilayer board by photolithography.

[0061] In this variable inductor A1, the branching positions P1 and P2 to the pair of inductance variable sections D and D' in the secondary inductor of the transformer Tr (four secondary lines L21 to L24) are located approximately midway between the bias terminal Tdd to which the bias voltage Vdd is applied and the input positions of the first high-frequency input signal Vin1 and the second high-frequency input signal Vin2 in the primary inductor of the transformer Tr (four primary lines L11 to L14).

[0062] For example, in a transformer (Tr), magnetic coupling with a coupling coefficient k is achieved by arranging the primary inductor constituting the primary circuit and the secondary inductor constituting the secondary circuit opposite each other with an insulator (dielectric) in between. This transformer (Tr) transmits the first high-frequency input signal Vin1 and the second high-frequency input signal Vin2, which are input to the primary circuit (primary inductor), to the secondary circuit (secondary inductor) of the transformer (Tr) without contact, based on the coupling coefficient k.

[0063] In other words, the transformer Tr induces a first high-frequency output signal Vout1 and a second high-frequency output signal Vout2 in the secondary circuit (secondary inductor) through magnetic coupling between the primary circuit (primary inductor) and the secondary circuit (secondary inductor), corresponding to the first high-frequency input signal Vin1 and the second high-frequency input signal Vin2.

[0064] Next, the operation and performance of the variable inductor A1 according to the first embodiment will be described in detail with reference to Figure 3.

[0065] In the variable inductor A1 according to the first embodiment, a pair of inductance variable units D and D', each connected to the secondary circuit of the transformer Tr, have their overall inductance variably set by turning on / off the first switch M1, the second switch M2 and the third switch M3, and the fourth switch M1', the fifth switch M2' and the sixth switch M3'. The pair of inductance variable units D and D' adjust the transmission characteristics (frequency characteristics) of the first high-frequency input signal Vin1 and the second high-frequency input signal Vin2 from the primary circuit to the secondary circuit.

[0066] In such a variable inductor A1, when the ON / OFF states of the three first switches M1, second switch M2, and third switch M3 in one inductance variable section D and the three fourth switches M1', fifth switch M2', and sixth switch M3' in the other inductance variable section D' are changed as shown in Figure 3(a), the input impedance Zin and output impedance Zout of the variable inductor A1 are set as shown in Figures 3(b) and (c).

[0067] In Figures 3(b) and (c), the white circles correspond to the top row of switch states in Figure 3(a). The black circles in Figures 3(b) and (c) correspond to the second row of switch states from the top in Figure 3(a), and the white squares correspond to the third row of switch states from the top in Figure 3(a). Furthermore, the black squares in Figures 3(b) and (c) correspond to the bottom row of switch states in Figure 3(a).

[0068] In other words, the input impedance Zin hardly changes even when the settings of the six switches M1, M2, M3, M1', M2', and M3' are changed, as shown in Figure 3(b). In contrast, the output impedance Zout shows a significant change when the settings of the six switches M1, M2, M3, M1', M2', and M3' are changed, as shown in Figure 3(c).

[0069] In a variable inductor A1 exhibiting these characteristics, the pair of inductance variable units D and D' are inductance variable circuits in which the circuit inductance changes based on the setting states of six switches: the first switch M1, the second switch M2, and the third switch M3, as well as the fourth switch M1', the fifth switch M2', and the sixth switch M3'. The pair of inductance variable units D and D' stepwise change the output impedance Zout of the variable inductor A1 by stepwise switching the circuit inductance.

[0070] In this embodiment, one of the inductance variable units D comprises a first series circuit in which four (or more) inductors L1 to L4 are connected in series, and three (or more) switches M1 to M3 provided between each of the connection points of the four (or more) inductors L1 to L4 and a reference potential (GND).

[0071] In this type of variable inductance section D, the three switches M1 to M3 are not connected in parallel with the four inductors L1 to L4, but rather are connected between each of the connection points of the four inductors L1 to L4 and the reference potential (GND).

[0072] In other words, the influence of the parasitic capacitance of the three (or more) switches M1 to M3 is extremely small for one of the inductance variable units D. Therefore, according to the first embodiment, it is possible to provide one of the inductance variable units D (variable inductor) for high-frequency signals that can switch the inductance in steps.

[0073] Furthermore, in this embodiment, the other inductance variable unit D' comprises a second series circuit in which four (or more) inductors L1' to L4' are connected in series, and three (or more) switches M1' to M3' are provided between each of the connection points of the four (or more) inductors L1' to L4' and the reference potential (GND).

[0074] In this other inductance variable section D', the three switches M1'~M3' are not connected in parallel with the four inductors L1'~L4', but rather are connected between each of the connection points of the four inductors L1'~L4' and the reference potential (GND).

[0075] In other words, the other inductance variable section D' is extremely less affected by the parasitic capacitance of the three (or more) switches M1' to M3'. Therefore, according to the first embodiment, it is possible to provide the other inductance variable section D' (variable inductor) for high-frequency signals that can switch the inductance in steps.

[0076] Furthermore, the variable inductor A1 according to the first embodiment further includes a transformer Tr connected to one end of the first and second series circuits for contactless transmission of the input signal. According to this first embodiment, the variable inductor A1 can function as a variable balun (variable transformer) capable of stepwise changing the output impedance Zout.

[0077] Furthermore, in the variable inductor A1 according to the first embodiment, a pair of inductance variable units D and D' are provided, each consisting of a first and second series circuit and six (or more) switches M1 to M3 and M1' to M3'. The transformer Tr includes four primary lines L11 to L14 (primary inductors) to which one input signal Vin1 is input to one end and the other input signal Vin2 is input to the other end, and a pair of secondary intermediate contacts c21 and c22, to which one inductance variable unit D is connected to the first secondary intermediate contact c21 and the other inductance variable unit D' is connected to the second secondary intermediate contact c22, and four secondary lines L21 to L24 (secondary inductors) that output first and second high-frequency output signals Vout1 and Vout2 from both ends.

[0078] According to this first embodiment, since it is equipped with a pair of inductance variable sections D and D', it is possible to provide a variable balun (variable transformer) for high-frequency signals that can switch the inductance in a stepwise and effective manner.

[0079] Furthermore, the variable inductor A1 according to the first embodiment is provided with a bias terminal Tdd connected to four primary lines L11 to L14 (primary inductors). According to this first embodiment, it is possible to supply a bias voltage to a differential signal source that generates one input signal Vin1 and the other input signal Vin2.

[0080] [Second Embodiment] Next, a second embodiment of the present invention will be described with reference to Figures 4 and 5. As shown in Figure 4, the variable inductor A2 according to this second embodiment is modified in which the branching positions P1 and P2 to the pair of inductance variable sections D and D' in the secondary inductor (four secondary lines L21 to L24) of the transformer Tr are changed compared to the variable inductor A1 according to the first embodiment (see Figure 2).

[0081] In other words, compared to the variable inductor A1 according to the first embodiment, the variable inductor A2 according to this second embodiment has a first branching position P1 connected to one inductance variable section D and a second branching position P2 connected to the other inductance variable section D' located closer to the input positions of the first high-frequency input signal Vin1 and the second high-frequency input signal Vin2 in the primary inductor (four primary lines L11 to L14) of the transformer Tr.

[0082] According to the variable inductor A2 of this second embodiment, as shown in Figure 5(a), when the ON / OFF states of the three first switches M1, second switch M2, and third switch M3 in one inductance variable unit D and the three fourth switches M1', fifth switch M2', and sixth switch M3' in the other inductance variable unit D' are changed, the input impedance Zin and output impedance Zout of the variable inductor A2 are set as shown in Figures 5(b) and (c).

[0083] In Figures 5(b) and (c), the white circles correspond to the top row of switch states in Figure 5(a). The black circles in Figures 5(b) and (c) correspond to the second row of switch states from the top in Figure 5(a), and the white squares correspond to the third row of switch states from the top in Figure 5(a). Furthermore, the black squares in Figures 5(b) and (c) correspond to the bottom row of switch states in Figure 5(a).

[0084] In other words, the input impedance Zin hardly changes even when the settings of the six first switches M1, second switch M2, third switch M3, and fourth switch M1', fifth switch M2', and sixth switch M3' are changed, as shown in Figure 5(b). In contrast, the output impedance Zout changes less than that of the variable inductor A1 according to the first embodiment when the settings of the six first switches M1, second switch M2, third switch M3, and fourth switch M1', fifth switch M2', and sixth switch M3' are changed, as the resistive component is suppressed.

[0085] According to this second embodiment, similar to the first embodiment, it is possible to provide variable inductance units D, D' and a variable balun (variable transformer), i.e., a variable inductor, for high-frequency signals that can switch the inductance in steps.

[0086] [Third Embodiment] Next, a third embodiment of the present invention will be described with reference to Figures 6 and 7. As shown in Figure 6, the variable inductor A3 according to this third embodiment is modified by changing the branching positions P1 and P2 to the pair of inductance variable sections D and D' in the secondary inductor (four secondary lines L21 to L24) of the transformer Tr compared to the variable inductors A1 and A2 according to the first and second embodiments (see Figures 2 and 4).

[0087] In other words, compared to the variable inductors A1 and A2 according to the first and second embodiments, the variable inductor A3 according to this third embodiment has a first branching position P1 connected to one inductance variable section D and a second branching position P2 connected to the other inductance variable section D' located further away from the input positions of the first high-frequency input signal Vin1 and the second high-frequency input signal Vin2 in the primary inductor (four primary lines L11 to L14) of the transformer Tr.

[0088] According to the variable inductor A3 of this third embodiment, as shown in Figure 7(a), when the ON / OFF states of the three first switches M1, second switch M2, and third switch M3 in one inductance variable unit D and the three fourth switches M1', fifth switch M2', and sixth switch M3' in the other inductance variable unit D' are changed, the input impedance Zin and output impedance Zout of the variable inductor A1 are set as shown in Figures 7(b) and (c).

[0089] In Figures 7(b) and (c), the white circles correspond to the top row of switch states in Figure 7(a). The black circles in Figures 7(b) and (c) correspond to the second row of switch states from the top in Figure 7(a), and the white squares correspond to the third row of switch states from the top in Figure 7(a). Furthermore, the black squares in Figures 7(b) and (c) correspond to the bottom row of switch states in Figure 7(a).

[0090] In other words, the input impedance Zin hardly changes even when the settings of the six first switches M1, second switch M2, third switch M3, and fourth switch M1', fifth switch M2', and sixth switch M3' are changed, as shown in Figure 7(b). In contrast, the output impedance Zout changes more significantly than that of the variable inductor A according to the first embodiment when the settings of the six first switches M1, second switch M2, third switch M3, and fourth switch M1', fifth switch M2', and sixth switch M3' are changed, due to an increase in the resistance component.

[0091] According to this third embodiment, similar to the first and second embodiments, it is possible to provide a pair of variable inductance units D, D' and a variable balun (variable transformer) capable of switching the inductance in steps as a variable inductor.

[0092] [Fourth Embodiment] Next, a fourth embodiment of the present invention will be described with reference to Figures 8-10. As shown in Figure 8, the variable inductor A4 according to the fourth embodiment has a pair of inductance variable units D and D' connected to the primary inductors (four primary lines L11 to L14) of the transformer Tr2 instead of the secondary inductors (four secondary lines L21 to L24).

[0093] Furthermore, this variable inductor A4 is connected to the primary inductors (four primary lines L11 to L14) of the pair of variable inductance units D and D' via a pair of coupling capacitors C and C'. In other words, this variable inductor A4 AC-connects the pair of variable inductance units D and D' to the primary inductors (four primary lines L11 to L14).

[0094] Such a variable inductor A4 comprises a pair of input terminals Tin1, Tin2, a bias terminal Tdd, a pair of output terminals Tout1, Tout2, a transformer Tr2, a pair of coupling capacitors C, C', and a pair of inductance variable units D, D'. Below, we will describe the components that differ from those of the variable inductors A1 to A3 according to the first to third embodiments, namely the transformer Tr2 and the pair of coupling capacitors C, C'.

[0095] Transformer Tr2, like transformer Tr in the first to third embodiments, has four primary lines L11 to L14 and four secondary lines L21 to L24 that are magnetically coupled. However, the other end of the first primary line L11 and one end of the second primary line L12 are connected to one end of one coupling capacitor C, and the other end of the third primary line L13 and one end of the fourth primary line L14 are connected to one end of the other coupling capacitor C'.

[0096] Here, in transformer Tr2, the connection point between the other end of the first primary line L11 and one end of the second primary line L12 is the first primary-side intermediate contact c11, and the connection point between the other end of the third primary line L13 and one end of the fourth primary line L14 is the second primary-side intermediate contact c12. One inductance variable unit D is connected to the first primary-side intermediate contact c11 in transformer Tr2, and the other inductance variable unit D' is connected to the second primary-side intermediate contact c12 in transformer Tr2.

[0097] Of the pair of coupling capacitors C and C', one coupling capacitor C is a two-terminal element having a predetermined capacitance (first capacitance). One end of the coupling capacitor C is connected to the other end of the first primary line L11 and one end of the second primary line L12, i.e., the first primary-side intermediate contact c11, and the other end is connected to one end of the first inductor L1 in one of the inductance variable units D.

[0098] The other coupling capacitor C' is a two-terminal element having a predetermined capacitance (second capacitance). One end of the other coupling capacitor C' is connected to the other end of the third primary line L13 and one end of the fourth primary line L14, i.e., the second primary-side intermediate contact c12, and the other end is connected to one end of the fifth inductor L1' in the other inductance variable section D'.

[0099] The variable inductor A4 configured in this way is formed as a multilayer board based on photolithography, as shown in Figure 9. That is, the variable inductor A4 is a high-frequency integrated circuit in which a pair of input terminals Tin1, Tin2, a bias terminal Tdd, a pair of output terminals Tout1, Tout2, a transformer Tr2, and a pair of inductance variable sections D, D' are formed within a multilayer board by photolithography.

[0100] In this variable inductor A4, branch positions P3 and P4 to a pair of inductance variable sections D and D' in the primary inductor (four primary lines L11 to L14) of transformer Tr2 are located approximately midway between the bias terminal Tdd to which the bias voltage Vdd is applied and the input positions of the first high-frequency input signal Vin1 and the second high-frequency input signal Vin2 in the primary inductor (four primary lines L11 to L14) of transformer Tr.

[0101] Transformer Tr2 achieves magnetic coupling with a coupling coefficient k by arranging the primary inductors (four primary lines L11~L14) that constitute the primary circuit and the secondary inductors (four secondary lines L21~L24) that constitute the secondary circuit opposite each other with an insulator (dielectric) in between. Based on the coupling coefficient k, transformer Tr2 non-contact transmits the first high-frequency input signal Vin1 and the second high-frequency input signal Vin2, which are input to the primary circuit (primary inductor), to the secondary circuit (secondary inductor) of transformer Tr2.

[0102] In other words, the transformer Tr2 induces a first high-frequency output signal Vout1 and a second high-frequency output signal Vout2 in the secondary circuit (secondary inductor) through magnetic coupling between the primary circuit (primary inductor) and the secondary circuit (secondary inductor), corresponding to the first high-frequency input signal Vin1 and the second high-frequency input signal Vin2.

[0103] Furthermore, in this variable inductor A4, the pair of inductance variable units D and D', each connected to the primary circuit (primary inductor) of the transformer Tr2, adjust the transmission characteristics (frequency characteristics) of the first high-frequency input signal Vin1 and the second high-frequency input signal Vin2 from the primary circuit to the secondary circuit by switching the first switch M1, the second switch M2, and the third switch M3, as well as the fourth switch M1', the fifth switch M2', and the sixth switch M3' ON / OFF.

[0104] In such a variable inductor A4, as shown in Figure 10(a), when the ON / OFF states of the three first switches M1, second switch M2, and third switch M3 in one inductance variable section D, and the three fourth switches M1', fifth switch M2', and sixth switch M3' in the other inductance variable section D' are changed, the input impedance Zin and output impedance Zout of the variable inductor A4 are different from those of the variable inductors A1 to A3 according to the first to third embodiments, as shown in Figures 10(b) and (c).

[0105] In Figures 10(b) and (c), the white circles correspond to the top row of switch states in Figure 10(a). The black circles in Figures 10(b) and (c) correspond to the second row of switch states from the top in Figure 10(a), and the white squares correspond to the third row of switch states from the top in Figure 10(a). Furthermore, the black squares in Figures 10(b) and (c) correspond to the bottom row of switch states in Figure 10(a).

[0106] In other words, the input impedance Zin of the variable inductor A4 according to the fourth embodiment shows a significant change when the settings of the six first switches M1, second switch M2, third switch M3, and fourth switch M1', fifth switch M2', and sixth switch M3' are changed, as shown in Figure 10(b).

[0107] Furthermore, the output impedance Zout of this variable inductor A4 hardly changes even when the settings of the six switches M1, M2, and M3, as well as the fourth switch M1', fifth switch M2', and sixth switch M3' are changed, as shown in Figure 10(c).

[0108] The variable inductor A4 according to the fourth embodiment includes a pair of inductance variable units D and D' consisting of a first and second series circuit and six (or more) switches M1 to M3 and M1' to M3', and the transformer Tr2 includes a pair of primary-side intermediate contacts c11 and c12, to which one input signal Vin1 is input to one end and the other input signal Vin2 is input to the other end, with one inductance variable unit D connected to the first primary-side intermediate contact c11 and the other inductance variable unit D' connected to the second primary-side intermediate contact c12, and four primary lines L21 to L24 (secondary inductors) that output first and second high-frequency output signals Vout1 and Vout2 from both ends.

[0109] According to this fourth embodiment, since it includes a pair of inductance variable sections D and D', it is possible to provide a variable balun (variable transformer) for high-frequency signals that can switch the inductance in a stepwise and effective manner.

[0110] Furthermore, in the variable inductor A4 according to the fourth embodiment, the four primary lines L11 to L14 (primary inductors) are equipped with bias primary side contacts c10, and capacitors C and C' are provided between the first primary side intermediate contact c11 and one inductance variable unit D, and between the second primary side intermediate contact c12 and the other inductance variable unit D', respectively. According to this fourth embodiment, a bias voltage can be supplied to the differential signal source that generates one input signal Vin1 and the other input signal Vin2.

[0111] It should be noted that the present invention is not limited to the embodiments described above, and the following modifications are possible, for example. (1) In the above embodiment, variable inductors A1 to A4 have been described, each comprising transformers Tr and Tr2 connected to one end of a first series circuit in one inductance variable unit D and a second series circuit in the other inductance variable unit D', respectively, and which transmit a pair of input signals Vin1 and Vin2 non-contact and output a pair of output signals Vout1 and Vout2. However, the present invention is not limited thereto.

[0112] For example, transformers Tr and Tr2 may be omitted if necessary. That is, one of the inductance variable units D is not affected by the parasitic capacitance of the first to third switches M1 to M3 because the first to third switches M1 to M3 are not connected in parallel to the first to fourth inductors L1 to L4. Therefore, one of the inductance variable units D has sufficient performance as a variable inductor for high-frequency signals that can switch the inductance in steps.

[0113] The other inductance variable section D' is not affected by the parasitic capacitance of the 4th to 6th switches M1' to M3' because the 4th to 6th switches M1' to M3' are not connected in parallel to the 5th to 8th inductors L1' to L4'. Therefore, the other inductance variable section D' has sufficient performance as a variable inductor for high-frequency signals that can switch the inductance in steps.

[0114] (2) In the above embodiment, a variable inductor A1 to A4 having a pair of inductance variable units D and D' has been described, but the present invention is not limited thereto. As shown in Figure 11, a circuit configuration having a single inductance variable unit Da may also be adopted.

[0115] As shown in the figure, the variable inductor Aa in this modified example comprises a pair of input terminals T1a and T2a, an output terminal T3a, a transformer Tra, and an inductance variable unit Da. Of the pair of input terminals T1a and T2a, one input terminal T1a is connected to one end of the first primary line L1a of the transformer Tra inside the variable inductor Aa. The other input terminal T1a, although not shown, is connected to one output terminal of a predetermined differential signal source outside the variable inductor Aa. A non-inverting signal from the differential signal source is input to this one input terminal T1a as a first high-frequency input signal Vin1.

[0116] The other input terminal T2a is connected to the other end of the second primary line L1b in the transformer Tra, inside the variable inductor Aa. Furthermore, the other input terminal T2a is connected to the other output terminal of the differential signal source, outside the variable inductor Aa. An inverted signal from the differential signal source is input to this other input terminal T2a as the second high-frequency input signal Vin2.

[0117] The output terminal T3a is connected inside the variable inductor Aa to one end of the first secondary transmission line L2a in the transformer Tra. Furthermore, outside the variable inductor Aa, this output terminal T3a is connected to the input terminal of the subsequent circuit. This output terminal T3a outputs a non-inverting signal as a high-frequency output signal Vout to the subsequent circuit.

[0118] The transformer Tra comprises two primary lines L1a and L1b and two secondary lines L2a and L2b. In this transformer Tra, the first primary line L1a and the second primary line L1b are connected in series and together constitute a primary inductor. Similarly, the first secondary line L2a and the second secondary line L2b are connected in series and together constitute a secondary inductor. In such a transformer Tra, the primary inductor and the secondary inductor are magnetically coupled with a predetermined coupling coefficient.

[0119] The first primary line L1a is a transmission line having a predetermined length (first a line length), with one end connected to one input terminal T1a and the other end connected to one end of the second primary line L1b. Such a first primary line L1a has an inductance (first a inductance) corresponding to the first a line length.

[0120] The second primary line L1b is a transmission line having a predetermined length (first b line length), with one end connected to the other end of the first primary line L1a and the other end connected to the other input terminal T2a. Such a second primary line L1b has an inductance (first b inductance) corresponding to the first b line length.

[0121] The first secondary line L2a is a transmission line having a predetermined length (secondary line length), with one end connected to the output terminal T3a and the other end connected to one end of the second secondary line L2b. Such a first secondary line L2a has an inductance (secondary inductance) corresponding to the secondary line length.

[0122] The second secondary line L2b is a transmission line having a predetermined length (second b line length), with one end connected to the other end of the first secondary line L2a and the other end grounded. Such a second secondary line L2b has an inductance (second b inductance) corresponding to the second b line length. The connection point between the other end of the first secondary line L2a and one end of the second secondary line L2b is the secondary side intermediate contact ca, to which one end of the series circuit in the inductance variable section Da is connected.

[0123] In other words, the transformer Tra comprises a primary inductor (two primary lines L1a, L1b) to which one input signal Vin1 is input at one end and the other input signal Vin2 is input at the other end, and a secondary inductor (two secondary lines L2a, L2b) to which one end of the series circuit in the inductance variable section Da is connected, and which outputs an output signal Vout from one end.

[0124] In this transformer, the total inductance of the two primary lines L1a and L1b (primary inductance) and the total inductance of the two secondary lines L2a and L2b (secondary inductance) have a predetermined ratio. Furthermore, the inductance of 2a and 2b are set to the same inductance.

[0125] As shown in the figure, the variable inductance unit Da comprises a first inductor L1a, a second inductor L2a, a third inductor L3a, a first switch M1a, and a second switch M2a. One end of this variable inductance unit Da is connected to the secondary side intermediate contact ca of the transformer Tra.

[0126] In this inductance variable section Da, the first inductor L1a is a transmission line having a predetermined length (first a line length), with one end connected to the other end of the first secondary line L2a and one end of the second secondary line L2b in the transformer Tra, i.e., the output-side intermediate contact ca, and the other end connected to one end of the second inductor L2a and the drain terminal of the first switch M1a. Such a first inductor L1a has an inductance (first a inductance) corresponding to the first a line length.

[0127] The second inductor L2a is a transmission line having a predetermined length (second a line length), with one end connected to the other end of the first inductor L1a and the drain terminal of the first switch M1a, and the other end connected to one end of the third inductor L3a and the drain terminal of the second switch M2a. Such a second inductor L2a has an inductance (second a inductance) corresponding to the second a line length.

[0128] The third inductor L3a is a transmission line having a predetermined length (third a line length), with one end connected to the other end of the second inductor L2a and the drain terminal of the second switch M2a, and the other end grounded. Such a third inductor L3a has an inductance (third a inductance) corresponding to the third a line length.

[0129] The first switch M1a is an N-type MOS (Metal Oxide Semiconductor) transistor, as shown in the figure. The drain terminal of this first switch M1a is connected to the other end of the first inductor L1a and one end of the second inductor L2a, and the source terminal is grounded. In other words, the first switch M1a is provided between the connection point of the first inductor L1a and the second inductor L2a and the reference potential (GND).

[0130] Furthermore, the gate terminal of the first switch M1a is connected to the first output terminal of a control circuit (not shown). In other words, the first switch M1a is controlled to be ON (conductive) / OFF (disconnected) based on a first control signal input from the control circuit.

[0131] The second switch M2a is an N-type MOS transistor, similar to the first switch M1a. The drain terminal of this second switch M2a is connected to the other end of the second inductor L2a and one end of the third inductor L3a, and its source terminal is grounded. In other words, the second switch M2a is located between the connection point of the second inductor L2a and the third inductor L3a and the reference potential (GND).

[0132] Furthermore, the gate terminal of the second switch M2a is connected to the second output terminal of a control circuit (not shown). In other words, the second switch M2a is controlled to be ON (conductive) / OFF (disconnected) based on a second control signal input from the control circuit.

[0133] In other words, the inductance variable section Da comprises a series circuit in which three inductors L1a to L3a are connected in series, and two switches M1a and M2a provided between each of the connection points of the three inductors L1a to L3a and the reference potential (GND).

[0134] In the variable inductor Aa configured in this way, the inductance variable section Da is not provided with two switches M1a and M2a in parallel with the three inductors L1a to L3a, but rather is provided between each of the connection points of the three inductors L1a to L3a and the reference potential (GND).

[0135] In other words, the inductance variable section Da is extremely unaffected by the parasitic capacitance of the two (or more) switches M1a and M2a. Therefore, this modified example makes it possible to provide an inductance variable section Da (variable inductor) for high-frequency signals that can switch the inductance in steps.

[0136] Furthermore, the variable inductor Aa in this modified configuration is equipped with a transformer Tra connected to one end of a series circuit for contactless transmission of the input signal. Therefore, this variable inductor Aa can function as a variable balun (variable transformer) capable of stepwise changing the output impedance Zout.

[0137] (3) In the above embodiment, a switch was provided between all connection points in the series circuit and the reference potential (GND), but the present invention is not limited thereto. That is, the switch only needs to be provided between at least one of the multiple connection points in the series circuit and the reference potential (GND). Also, in the case of a series circuit with one connection point, the switch only needs to be provided between this one connection point and the reference potential (GND). Note that the reference potential in the present invention is not limited to GND, which is the ground potential.

[0138] (4) In the fourth embodiment described above, capacitors C and C' are provided between the first primary intermediate contact c11 and one inductance variable unit D, and between the second primary intermediate contact c12 and the other inductance variable unit D', respectively. However, the present invention is not limited thereto. That is, the two capacitors C and C' may be omitted as needed.

[0139] For example, by replacing the six first switches M1, second switches M2 and M3, as well as the fourth switch M1', fifth switch M2' and sixth switch M3', with P-type MOS transistors, the two capacitors C and C' can be omitted. [Explanation of Symbols]

[0140] A1~A4, Aa... Variable inductor, c10... Primary bias contact, c11, c12... Primary intermediate contact, c21, c22... Secondary intermediate contact, C, C'... Capacitor, D, D'... Variable inductance section, L11~L14... Primary line, L21~L24... Secondary line, L1... First inductor, L2... Second inductor, L3... Third inductor, L4... Fourth inductor, L1'... Fifth inductor, L2'... Sixth inductor, L3'... Seventh inductor, L4'... Eighth inductor, M1... First switch, M2... Second switch, M3... Third switch, M1'... Fourth switch, M2'... Fifth switch, M3'... Sixth switch, Tin1, Tin2... Input terminal, Tdd... Bias terminal, Tout1, Tout2... Output terminal, Tr, Tr2... Transformer

Claims

1. A series circuit in which multiple inductors are connected in series, One or more switches are provided between at least one of the connection points of the multiple inductors and the reference potential. A variable inductor characterized by having the following features.

2. The variable inductor according to claim 1, characterized in that it is connected to one end of the series circuit and includes a transformer for non-contact transmission of two input signals.

3. The system comprises a series circuit and a pair of inductance variable units consisting of one or more switches, The aforementioned transformer A primary inductor to which one input signal is input at one end and the other input signal is input at the other end, A secondary inductor comprising a pair of secondary intermediate contacts, wherein one of the inductance variable units is connected to the first secondary intermediate contact, and the other inductance variable unit is connected to the second secondary intermediate contact, and a pair of output signals are output from both ends. The variable inductor according to claim 2, characterized by comprising:

4. The variable inductor according to claim 3, characterized in that the primary inductor is provided with a bias primary contact to which a bias voltage is applied.

5. The system comprises a series circuit and a pair of inductance variable units consisting of one or more switches, The aforementioned transformer A primary inductor comprising a pair of primary-side intermediate contacts, wherein one input signal is input to one end and the other input signal is input to the other end, one of the inductance variable units is electrically connected to the first primary-side intermediate contact, and the other of the inductance variable units is electrically connected to the second primary-side intermediate contact, A secondary inductor that outputs an output signal from both ends The variable inductor according to claim 2, characterized by comprising:

6. The variable inductor according to claim 5, characterized in that the primary inductor is provided with a primary contact for biasing.

7. The aforementioned transformer A primary inductor to which one input signal is input at one end and the other input signal is input at the other end, The series circuit is equipped with a secondary intermediate contact to which one end is connected, and a secondary inductor that outputs an output signal from one end. The variable inductor according to claim 2, characterized by comprising:

8. A variable inductor according to any one of claims 1 to 7, characterized in that it is formed as a multilayer board based on photolithography.

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