JP2011130083A - Variable filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a variable filter capable of achieving steep attenuation characteristics while suppressing the increase of insertion loss. <P>SOLUTION: A first variable resonator (10), a second variable resonator (20) and a third variable resonator (30), consisting of series circuits composed of capacitive elements (12, 22, 32) and inductors (11, 21, 31), respectively, at least one of each set of the capacitive element and the inductor being a variable element, as basic unit circuits, are provided between a first input/output terminal (1a) and a second input/output terminal (1b). The first variable resonator is connected in series between the two input/output terminals, the second variable resonator is connected to a point between the first input/output terminal and the first variable resonator at one end of the second variable resonator and is grounded at the other end, and the third variable resonator is connected to a point between the second input/output terminal and the first variable resonator at one end of the third variable resonator and is grounded at the other end. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a variable filter that can vary a bandwidth and a pass center frequency.

  FIG. 10 is a configuration diagram of a conventional variable bandpass filter. In this conventional variable bandpass filter, an LC resonance circuit including an inductor and a variable capacitance diode is connected between a first input / output terminal and a second input / output terminal. Then, the pass band of the input signal is made variable by applying a control voltage from the control voltage terminal (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 7-303019

However, the prior art has the following problems.
The conventional variable filter uses the LC resonance circuit only as a band pass filter. For this reason, when steep attenuation characteristics are obtained with a constant bandwidth, there is a problem that insertion loss at the pass center frequency increases.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to obtain a variable filter capable of realizing a steep attenuation characteristic while suppressing an increase in insertion loss.

  A variable filter according to the present invention includes a first variable resonator, a second variable resonator, and a third variable circuit, each of which includes a series circuit composed of a capacitor and an inductor, at least one of which is a variable element, as a basic unit circuit. The variable resonator is provided with a variable resonator between the first input / output terminal and the second input / output terminal, and the first variable resonator includes a first input / output terminal and a second input / output terminal. The second variable resonator has one end connected between the first input / output terminal and the first variable resonator, the other end is grounded, and the second variable resonator is connected in series. The variable resonator has one end connected between the second input / output terminal and the first variable resonator and the other end grounded.

  The variable filter according to the present invention includes a first variable resonator, a second variable resonator, and a parallel circuit composed of a capacitive element and an inductor, at least one of which is a variable element, as a basic unit circuit, and A variable filter including a third variable resonator between a first input / output terminal and a second input / output terminal, wherein the second variable resonator and the third variable resonator are connected in cascade. The first variable resonator is connected in series between the first input / output terminal and the second input / output terminal, and one end of the first variable resonator is between the second variable resonator and the third variable resonator. It is connected and the other end is grounded.

  According to the variable filter according to the present invention, by combining a variable resonator that operates as a band pass filter and a variable resonator that operates as a band rejection filter, a configuration that varies the resonance frequency of each variable resonator is provided. A variable filter capable of realizing a steep attenuation characteristic while suppressing an increase in insertion loss can be obtained.

It is a block diagram of the variable filter in Embodiment 1 of this invention. It is explanatory drawing which shows the example of the passage characteristic formed with the variable filter in Embodiment 1 of this invention. It is a block diagram of the variable filter in Embodiment 2 of this invention. It is a block diagram of the variable filter in Embodiment 3 of this invention. It is explanatory drawing which shows the example of the passage characteristic formed with the variable filter in Embodiment 3 of this invention. It is explanatory drawing which shows the example of the passage characteristic formed with the variable filter in Embodiment 4 of this invention. It is a block diagram of the variable filter in Embodiment 4 of this invention. It is a block diagram of the variable filter in Embodiment 6 of this invention. It is a block diagram of the variable filter in Embodiment 7 of this invention. It is a block diagram of the conventional variable bandpass filter.

  Hereinafter, preferred embodiments of the variable filter of the present invention will be described with reference to the drawings.

Embodiment 1 FIG.
FIG. 1 is a configuration diagram of a variable filter according to Embodiment 1 of the present invention. The variable filter of FIG. 1 according to the first embodiment is configured by connecting three variable resonators 10, 20, and 30 between input / output terminals 1a and 1b. Here, the input / output terminal 1a is a first input / output terminal for inputting / outputting a signal, and the input / output terminal 1b is a second input / output terminal for inputting / outputting a signal.

  The first variable resonator 10 includes a series circuit including an inductor 11 and a variable capacitance diode 12 as a basic unit circuit. One end of the series circuit is connected to the first input / output terminal 1a, and the other end is connected to the second input / output terminal 1b.

  The second variable resonator 20 is configured with a series circuit including an inductor 21 and a variable capacitance diode 22 as a basic unit circuit. One end of the series circuit is connected to a connection portion between the first input / output terminal 1a and the variable resonator 10, and the other end is grounded.

  Further, the third variable resonator 30 includes a series circuit including an inductor 31 and a variable capacitance diode 32 as a basic unit circuit. One end of the series circuit is connected to a connection portion between the second input / output terminal 1b and the variable resonator 10, and the other end is grounded.

  As described above, the variable capacitance diodes 12, 22, and 32 are used for the three variable resonators 10, 20, and 30, respectively, and the resonance frequency can be varied by varying the respective capacitances. .

Next, the operation of the variable filter having the configuration of FIG. 1 will be described.
For example, a signal input from the first input / output terminal 1a passes through the variable resonators 10, 20, and 30 and is output from the second input / output terminal 1b. Here, the variable resonator 10 operates as a band pass filter. For this reason, the center frequency of the passing signal can be varied by changing the resonance frequency.

  On the other hand, with respect to the resonance frequency of the variable resonator 10, the resonance frequency of the variable resonator 20 is set to the low frequency side, and the resonance frequency of the variable resonator 30 is set to the high frequency side. Can be formed. By tuning and varying the resonance frequency for forming these attenuation poles with respect to the pass center frequency, the pass band width can be made constant.

FIG. 2 is an explanatory diagram showing an example of pass characteristics formed by the variable filter according to Embodiment 1 of the present invention. FIG. 2 shows the characteristics of two bands in which the center frequency is varied. Specifically, one has the center frequency set to f _ca and the attenuation poles set to f _la and f _ha , respectively, and the other sets the center frequency to f _cb and the attenuation poles to f _lb and f _{ha. hb} is set respectively. Further, the respective pass bandwidths are BWa and BWb.

  As shown in FIG. 2, by changing the resonance frequency of the variable resonator 10 that determines one pass band and the resonance frequencies of the two variable resonators 20 and 30 that determine two attenuation poles, respectively, In addition to having a steep attenuation characteristic in the vicinity, the pass band can be varied with a constant bandwidth. Furthermore, since it is a configuration that obtains a large amount of attenuation by the band rejection filter, the insertion loss at the pass center frequency can be kept low.

  As described above, according to the first embodiment, the variable resonator connected in series between the input and output terminals is operated as a bandpass filter, while one end is connected to the input and output terminals and the other end is grounded. Two variable resonators are operated as a band rejection filter. The resonance frequency of the band pass filter is set to the pass center frequency, and the resonance frequencies of the two band element filters are respectively set to the low frequency and high frequency of the pass center frequency. In this way, by providing a configuration that can vary the resonance frequency of each variable resonator, a variable that can realize a constant pass bandwidth and steep attenuation characteristics with low loss regardless of the pass center frequency. A filter can be obtained.

Embodiment 2. FIG.
The second embodiment is different from the first embodiment for realizing a variable filter that can realize a constant pass bandwidth and steep attenuation characteristics with low loss regardless of the pass center frequency. The configuration will be described.

  FIG. 3 is a configuration diagram of the variable filter according to the second embodiment of the present invention. The variable filter of FIG. 3 according to the second embodiment is configured by connecting three variable resonators 110, 120, and 130 between the input / output terminals 1a and 1b. Here, the input / output terminal 1a is a first input / output terminal for inputting / outputting a signal, and the input / output terminal 1b is a second input / output terminal for inputting / outputting a signal.

  The first variable resonator 110 is configured with a parallel circuit including an inductor 111 and a variable capacitance diode 112 as a basic unit circuit. One end of the parallel circuit is connected between the variable resonator 120 and the variable resonator 130, and the other end is grounded.

  The second variable resonator 120 includes a parallel circuit including an inductor 121 and a variable capacitance diode 122 as a basic unit circuit. One end of the parallel circuit is connected to the first input / output terminal 1 a, and the other end is connected between the variable resonator 110 and the variable resonator 130.

  Further, the third variable resonator 130 includes a parallel circuit composed of an inductor 131 and a variable capacitance diode 132 as a basic unit circuit. One end of the parallel circuit is connected to the second input / output terminal 1 b, and the other end is connected between the variable resonator 110 and the variable resonator 120.

Next, the operation of the variable filter having the configuration of FIG. 3 will be described.
The variable resonator 110 is a shunt-connected LC parallel circuit, and is equivalent to the series-connected variable resonator 10 in FIG. The variable resonators 120 and 130 are LC parallel circuits connected in series, and are equivalent to the shunt-connected variable resonators 20 and 30 shown in FIG. Therefore, the circuit according to FIG. 3 is equivalent to the circuit of FIG. 1, and the operation is also the same as that of the circuit of FIG. 1 described in the first embodiment.

  As described above, according to the second embodiment, two variable resonators that are connected in series between input and output terminals are operated as a band rejection filter, while one variable variable resonator whose one end operates as a band element filter. A variable resonator connected between them and grounded at the other end is configured to operate as a bandpass filter. Then, by configuring such three variable resonators with a parallel circuit of an inductor and a variable capacitance diode, it is possible to obtain a circuit configuration equivalent to the circuit according to the first embodiment. The same effect can be obtained.

Embodiment 3 FIG.
In the third embodiment, the characteristics obtained in the first embodiment are further improved in the variable filter that can realize a constant pass bandwidth and a steep attenuation characteristic with low loss regardless of the pass center frequency. A circuit configuration for realizing the above will be described.

  FIG. 4 is a configuration diagram of the variable filter according to Embodiment 3 of the present invention. The configuration of the variable filter of FIG. 4 is different from the configuration of the variable filter of FIG. 1 in the first embodiment in that variable resonators 40 and 50 are newly provided. That is, in the first embodiment, two variable resonators that operate as a band rejection filter are provided. In the third embodiment, four variable resonators that operate as a band rejection filter are provided. Yes. Therefore, this different configuration will be mainly described below.

  The first to third variable resonators 10, 20, and 30 have the same configuration as in the first embodiment. The fourth variable resonator 40 includes a series circuit including an inductor 41 and a variable capacitance diode 42 as a basic unit circuit. One end of the series circuit is connected to a connection portion between the first input / output terminal 1a and the variable resonator 10, and the other end is grounded.

  The fifth variable resonator 50 includes a series circuit including an inductor 51 and a variable capacitance diode 52 as a basic unit circuit. One end of the series circuit is connected to a connection portion between the second input / output terminal 1b and the variable resonator 10, and the other end is grounded.

  As described above, the two newly added variable resonators 40 and 50 use the variable capacitance diodes 42 and 52, respectively, similarly to the three variable resonators 10, 20, and 30, respectively. The resonance frequency can be varied by varying the capacitance.

Next, the operation of the variable filter having the configuration of FIG. 4 will be described.
For example, a signal input from the first input / output terminal 1a passes through the variable resonators 10, 20, 30, 40, 50 and is output from the second input / output terminal 1b.

  As in the first embodiment, the variable resonator 10 has a resonance frequency set at the pass center frequency, and the variable resonator 20 has a resonance frequency set at a low frequency of the pass center frequency. In 30, the resonance frequency is set in a high range of the passing center frequency. Further, in the third embodiment, the resonance frequency of the added variable resonator 40 is set to the same frequency as that of the variable resonator 30, and the resonance frequency of the variable resonator 50 is set to the same frequency as that of the variable resonator 20. ing.

FIG. 5 is an explanatory diagram showing an example of pass characteristics formed by the variable filter according to Embodiment 3 of the present invention. FIG. 5 shows the characteristics of two bands in which the center frequency is varied, as in FIG. Specifically, one has the center frequency set to f _ca and the attenuation poles set to f _la and f _ha , respectively, and the other sets the center frequency to f _cb and the attenuation poles to f _lb and f _{ha. hb} is set respectively. Further, the respective pass bandwidths are BWa and BWb.

  As described above, in the third embodiment, by setting two variable resonators that form attenuation poles at the same resonance frequency, steep attenuation characteristics can be obtained as compared with the first embodiment. .

  As described above, according to the third embodiment, the number of resonators operated as a band rejection filter is increased as compared with the configuration of the first embodiment, so that a variable filter having a steeper attenuation characteristic can be obtained. realizable.

  In the third embodiment described above, considering the symmetry of the circuit, the resonance frequency of the variable resonator 40 is set to be the same as that of the variable resonator 30, and the resonance frequency of the variable resonator 50 is set to be the same as that of the variable resonator 20. is doing. However, the present invention is not limited to such a configuration, and the resonance frequency of the variable resonator 40 is set to be the same as that of the variable resonator 20, and the resonance frequency of the variable resonator 50 is set to be the same as that of the variable resonator 30. The same effect can be achieved.

  In the third embodiment described above, the case where two variable resonance circuits set to the same resonance frequency are used as the variable resonator forming the attenuation pole has been described. However, the present invention is not limited to such a configuration. By using three or more variable resonance circuits set to the same resonance frequency, the same or higher effect can be obtained.

Embodiment 4 FIG.
In the fourth embodiment, in the variable filter having the same configuration as that of the third embodiment, the resonance frequencies of the four variable resonators 20, 30, 40, and 50 that are operated as the band rejection filters that form the attenuation poles. Will be described in the case of setting them independently.

  In the fourth embodiment, the variable resonator 10 sets the resonance frequency to the pass center frequency. On the other hand, the variable resonators 20, 30, 40, and 50 operate as band-stop filters that form attenuation poles, and set their resonance frequencies independently.

FIG. 6 is an explanatory diagram showing an example of pass characteristics formed by the variable filter according to the fourth embodiment of the present invention. FIG. 6 shows the characteristics of two bands in which the center frequency is varied. Specifically, one has a center frequency set to f _ca and an attenuation pole set to f _la1, f _la2, f _ha1, and f _{ha2 ,} and the other has a center frequency set to f _cb , The attenuation poles are set to f _lb1 , f _lb2 , f _hb1 and f _hb2 respectively. Further, the respective pass bandwidths are BWa and BWb.

  As described above, in the fourth embodiment, a plurality of attenuation poles can be arbitrarily formed in the vicinity of the passing center frequency. As a result, good attenuation characteristics can be obtained over a wide band.

  As described above, according to the fourth embodiment, the number of resonators operated as a band rejection filter is increased as compared with the configuration of the first embodiment, and each resonance frequency is set independently. A plurality of attenuation poles can be formed, and a variable filter having good attenuation characteristics over a wide band can be realized.

  In the fourth embodiment described above, the case where four variable resonators forming the attenuation pole are used has been described. However, the present invention is not limited to such a configuration, and even if the number of variable resonators forming the attenuation pole is three or five or more, the same effect can be obtained.

Embodiment 5 FIG.
In the fifth embodiment, a case where the internal configuration of the variable resonator 10 in the third embodiment or the fourth embodiment is different will be described.

  FIG. 7 is a configuration diagram of the variable filter according to the fourth embodiment of the present invention. The variable filter shown in FIG. 7 is configured by continuously connecting two LC series circuits to the variable resonator 10 in the variable filter of FIG. Specifically, the variable resonator 10 according to the fifth embodiment includes a series circuit including an inductor 11a and a variable capacitance diode 12a, a series circuit including an inductor 11b and a variable capacitance diode 12b, and a variable capacitance diode 13. Has been.

  The basic operation of the variable filter according to the fifth embodiment is the same as that of the third embodiment or the fourth embodiment, and the variable resonator 10 has a resonance frequency set as the pass center frequency and is variable. The resonators 20, 30, 40, and 50 operate as band-stop filters that form attenuation poles.

  In the fifth embodiment, the variable resonator 10 that determines the passing center frequency has a two-stage configuration, so that narrower band characteristics can be obtained.

  As described above, according to the fifth embodiment, a variable filter having narrower band characteristics can be realized by configuring a variable resonator operated as a band-pass filter with a plurality of series circuits.

Embodiment 6 FIG.
In the sixth embodiment, the variable resonator 10 in the fourth embodiment is configured in a two-stage configuration, each variable resonator uses four variable capacitance diodes, and further controls for changing the capacitance of the variable capacitance diode. A configuration in which a bias circuit for applying a voltage is additionally described will be described.

FIG. 8 is a configuration diagram of the variable filter according to the sixth embodiment of the present invention.
The variable resonator 10 in FIG. 8 includes a series circuit including an inductor 11a and variable capacitance diodes 12a1, 12a2, 12a3, and 12a4, and a series circuit including an inductor 11b and variable capacitance diodes 12b1, 12b2, 12b3, and 12b4. And an inverter circuit composed of variable capacitance diodes 13a, 13b, 13c, and 13d.

  The variable resonator 20 is a series circuit including an inductor 21 and variable capacitance diodes 22a, 22b, 22c, and 22d. The variable resonator 30 is a series circuit including an inductor 31 and variable capacitance diodes 32a, 32b, 32c, and 32d. The variable resonator 40 is a series circuit including an inductor 41 and variable capacitance diodes 42a, 42b, 42c, and 42d. Furthermore, the variable resonator 50 is a series circuit including an inductor 51 and variable capacitance diodes 52a, 52b, 52c, and 52d.

  The resistor 3a has one end connected between the variable capacitance diodes 12a1 and 12a2, and the other end connected to the control voltage terminal 2a. The resistor 3b has one end connected between the variable capacitance diodes 12b1 and 12b2, and the other end connected to the control voltage terminal 2a.

  The resistor 3c has one end connected between the variable capacitance diodes 13c and 13d and the other end connected to the control voltage terminal 2b. The resistor 3d has one end connected between the variable capacitance diodes 22a and 22b and the other end connected to the control voltage terminal 2c. The resistor 3e has one end connected between the variable capacitance diodes 32c and 32d and the other end connected to the control voltage terminal 2c.

  The resistor 3f has one end connected between the variable capacitance diodes 42a and 42b, and the other end connected to the control voltage terminal 2d. The resistor 3g has one end connected between the variable capacitance diodes 52c and 52d and the other end connected to the control voltage terminal 2d.

  One end of the resistor 3h is connected between the connection of the variable capacitance diodes 12a2, 12b1, and 13a, and the other end is grounded. One end of the resistor 3i is connected between the inductors 11a, 21 and 41 and the other end is grounded. One end of the resistor 3j is connected between the inductors 11b, 31, and 51, and the other end is grounded.

  Capacitor 4a has one end connected to input / output terminal 1a and the other end connected between the connections of inductors 11a, 21 and 41. Capacitor 4b has one end connected to input / output terminal 1b and the other end connected between the connections of inductors 11b, 31, and 51.

Next, the operation of the variable filter having the configuration of FIG. 8 will be described.
The basic operation of the variable filter according to the sixth embodiment is the same as that of the third embodiment or the fourth embodiment, and the variable resonator 10 has a resonance frequency set as a pass center frequency and is variable. The resonators 20, 30, 40, and 50 operate as band-stop filters that form attenuation poles. However, in the configuration of FIG. 8 in the sixth embodiment, since the variable resonator 10 of FIG. 4 is configured by a two-stage filter, a narrow band pass characteristic can be obtained.

  Further, each variable resonator uses four variable capacitance diodes, and a circuit is configured by connecting them in parallel and in series. As a result, it is possible to disperse the voltage applied to each variable capacitance diode by the input signal and the current flowing to each variable capacitance diode, and to obtain higher power durability characteristics.

  Further, by using a plurality of variable capacitance diodes used for each resonator, the control voltage corresponding to the desired capacitance can be changed. For this reason, it is possible to change the change ratio of the variable filter with respect to the control voltage as well as improving the power durability.

  As described above, according to the sixth embodiment, four variable capacitance diodes that are components of each variable resonator are connected in series and parallel. As a result, it is possible to realize a variable filter having higher power handling characteristics with respect to the input signal. Furthermore, by using a configuration in which a plurality of variable capacitance diodes are used for each variable resonator, the control voltage corresponding to the desired capacitance can be changed. As a result, it is possible to realize a variable filter having a function of changing the change ratio of the variable filter with respect to the control voltage as well as improving the power durability.

  In the sixth embodiment, the case where four variable capacitance diodes are used for each resonator has been described. However, the present invention is not limited to such a configuration, and the same effect can be obtained when a series resonant circuit is configured by using two, three, or five or more variable capacitance diodes. it can.

Embodiment 7 FIG.
In the seventh embodiment, the variable resonator configured as the basic unit circuit in the series circuit of the inductor and the variable capacitance diode in the first embodiment is replaced with the parallel circuit of the inductor and the variable capacitance diode as the basic unit circuit. The case will be described.

  FIG. 9 is a configuration diagram of the variable filter according to the seventh embodiment of the present invention. Each variable resonator 10a, 20a, 30a in FIG. 9 includes a parallel circuit composed of inductors 11, 21, 31 and variable capacitance diodes 12, 22, 32, respectively.

Next, the operation of the variable filter having the configuration of FIG. 9 will be described.
For example, a signal input from the first input / output terminal 1a passes through the variable resonators 10a, 20a, 30a and is output from the second input / output terminal 1b. Here, the variable resonator 10a operates as a band rejection filter. For this reason, the center frequency which blocks | prevents a passage signal can be varied by changing the resonance frequency.

  On the other hand, with respect to the resonance frequency of the variable resonator 10a, the resonance frequency of the variable resonator 20a is set to the low frequency side, and the resonance frequency of the variable resonator 30a is set to the high frequency side so that both resonance frequencies pass. A band can be formed. As described above, the variable filter according to the seventh embodiment is operated as a variable band rejection filter, unlike the first to sixth embodiments.

  In the seventh embodiment, a steep stop band can be realized by forming a pass band by the variable resonators 20a and 30a in the vicinity of the band stop frequency by the variable resonator 10a. Further, the stop bandwidth can be made constant by tuning and varying the resonance frequency of each of the variable resonators 10a, 20a, and 30a.

  As described above, according to the seventh embodiment, the variable resonator connected in series between the input and output terminals is operated as a band element filter, while one end is connected to the input and output terminals and the other end is grounded. Two variable resonators are operated as a band pass filter. By providing such a configuration, it is possible to form a pass band by two band pass filters in the vicinity of a band stop frequency by the band element filter. As a result, it is possible to realize a variable filter that can make the stop band width constant while realizing a steep stop band.

  In the above-described seventh embodiment, the case where the series circuit including the capacitive element and the inductor in FIG. 1 is replaced with the parallel circuit including the capacitive element and the inductor has been described. However, the present invention is not limited to this. Absent. As in the seventh embodiment, the series circuit in FIGS. 4, 7, and 8 can be replaced with a parallel circuit, and the parallel circuit in FIG. 3 can be replaced with a series circuit.

  In the first to seventh embodiments described above, the variable capacitance diode is used as the variable capacitance element. However, an FET (Field Effect Transistor) or a mechanical capacitance variable means may be used as the variable capacitance. The effect of can be produced.

  In the first to seventh embodiments described above, the variable element is used as the variable element. However, the capacitor element may be fixed and a variable inductor may be used as the variable element. Can play.

  Further, as the inductors in the first to seventh embodiments described above, spiral inductors, meander inductors, and helical inductors may be used, and MIM capacitors and interdigital capacitors may be used as capacitors. Can play.

  1a, 1b input / output terminals, 2a, 2b, 2c, 2d control voltage terminals, 3a, 3b, 3c, 3d, 3e, 3f, 3g, 3h, 3i, 3j resistors, 4a, 4b capacitors (capacitance elements), 10, 10a variable resonator, 11, 11a, 11b inductor, 12, 12a, 12a1, 12a2, 12a3, 12a4, 12b, 12b1, 12b2, 12b3, 12b4 variable capacitance diode, 13, 13a, 13b, 13c, 13d variable capacitance diode, 20, 20a Variable resonator, 21 Inductor, 22, 22a, 22b, 22c, 22d Variable capacitance diode, 30, 30a Variable resonator, 31 Inductor, 32, 32a, 32b, 32c, 32d Variable capacitance diode, 40 Variable resonator 41 Inductors 42, 42a, 42b, 42c, 4 d Variable capacitance diode, 50 Variable resonator, 51 Inductor, 52, 52a, 52b, 52c, 52d Variable capacitance diode, 110 Variable resonator, 111 Inductor, 112 Variable capacitance diode, 120 Variable resonator, 121 Inductor, 122 Variable capacitance Diode, 130 variable resonator, 131 inductor, 132 variable capacitance diode.

Claims (6)

A first variable resonator, a second variable resonator, and a third variable resonator, each of which includes a series circuit composed of a capacitive element and an inductor, at least one of which is a variable element, as a basic unit circuit, are connected to the first variable resonator. A variable filter provided between the input / output terminal and the second input / output terminal,
The first variable resonator is connected in series between the first input / output terminal and the second input / output terminal,
One end of the second variable resonator is connected between the first input / output terminal and the first variable resonator, and the other end is grounded.
One end of the third variable resonator is connected between the second input / output terminal and the first variable resonator, and the other end is grounded. The variable filter according to claim 1,
A series circuit including a capacitive element and an inductor, at least one of which is a variable element, is configured as a basic unit circuit, and one end thereof is the first input / output terminal or the second input / output terminal and the first variable resonator. A variable filter, further comprising at least one variable resonator connected between and the other end of which is grounded. A first variable resonator, a second variable resonator, and a third variable resonator, each of which includes a parallel circuit including a capacitive element and an inductor, at least one of which is a variable element, as a basic unit circuit, are connected to the first variable resonator. A variable filter provided between the input / output terminal and the second input / output terminal,
The second variable resonator and the third variable resonator are cascade-connected to each other and connected in series between the first input / output terminal and the second input / output terminal,
The variable filter, wherein one end of the first variable resonator is connected between the second variable resonator and the third variable resonator, and the other end is grounded. The variable filter according to any one of claims 1 to 3,
The first variable resonator is configured by connecting two or more basic unit circuits in cascade. The variable filter according to any one of claims 1 to 4,
At least one of the plurality of variable resonators constituting the variable filter is characterized in that the variable element used in the basic unit circuit includes a plurality of variable elements connected in series and parallel. . The variable filter according to any one of claims 1 to 5,
Replacing a variable resonator consisting of a series circuit consisting of a capacitive element and an inductor with a parallel circuit consisting of a capacitive element and an inductor, and replacing a variable resonator consisting of a parallel circuit consisting of a capacitive element and an inductor in series A variable filter characterized by being replaced with a circuit.

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