JP2007318203A - Oscillator and capacity adjustment device - Google Patents

Abstract

The oscillation frequency is changed while avoiding the situation that the oscillation frequency is slowed down based on the change amount of the capacitance of the voltage controlled variable main capacitance element with respect to the control voltage due to the presence of the auxiliary capacitance element. .
An inverter element, a piezoelectric vibrator, a first capacitive element, a second capacitive element,
A voltage control variable main capacitance element; a plurality of auxiliary capacitance elements; and a plurality of voltage control variable sub capacitance elements, wherein the plurality of auxiliary capacitance elements and the plurality of voltage control variable sub capacitance elements are the voltage control variable main capacitance elements. The capacitance element can be connected or disconnected, and the change amount of the capacitance of the plurality of voltage controlled variable sub-capacitance elements with respect to the control voltage with respect to the capacitance of the plurality of auxiliary capacitance elements is substantially the same.
[Selection] Figure 1

Description

The present invention relates to an oscillation device that generates an oscillation signal having an oscillation frequency determined by a piezoelectric vibrator or the like such as a crystal vibrator, and a capacitance adjustment device used in the oscillation apparatus.

In the conventional oscillation device D10 described in the following Patent Document 1 as shown in FIG. 5, the varactor V is inherently dependent on the control voltage Vcnt applied from an external device (not shown).
10 by changing the capacitance of the quartz crystal X10, capacitors C10, and C20.
The oscillation frequency f (for example, around 26 MHz) approximate to the reference frequency fc (for example, 26 MHz) defined by, ie, the oscillation having the oscillation frequency f defined by the crystal resonator X10, the capacitors C10, C20, and the varactor V10. A signal OS10 is generated.

The oscillating device D10 is adjusted as shown in FIG. 5 in order to correct the deviation of the reference frequency fc caused by variations in characteristics of the crystal unit X10 and the like, that is, to adjust the reference frequency fc. A circuit A10 is included. The adjustment circuit A10 makes the capacitances different from each other (for example, 1 pF) in order to realize a capacitance (synthetic capacitance) necessary for adjusting the reference frequency fc.
, 2pF, 4pF,. . . ) Capacitors CB10, CB20, CB30,. . . , And switch voltages Vsw10, Vsw20, Vsw30,. . . Switches SW10, SW20, SW30,. . . Is provided.

More specifically, the capacitor CB10 and the switch SW10 are connected to the inverter element IN10.
In addition, the switch SW10 is connected to the ground potential GND in addition to the capacitor CB10 based on the switch voltage Vsw10 applied from the external device or another external device (not shown). The output terminal of the element IN10 and the ground potential GND
Connect in between or disconnect the connection. Other capacitors CB20, CB30,. . . And other switches SW20, 30,. . . Are provided in the same manner, and connect and disconnect similarly. In the oscillation device D10, for example, when it is desired to use the capacitance of the capacitor CB10 and the capacitance of the CB30 in order to correct the deviation of the reference frequency fc of the oscillation signal OS10, the switches SW10 and SW30 are connected, and the switch SW20 is changed. Set to the disconnected state.

In the conventional oscillation device D10, as one of the two extreme examples, the capacitor CB
10, CB20, CB30,. . . Are not used (disconnected), the capacitors CB10, CB20, CB30,... With respect to the capacity of the varactor V10, more precisely, the amount of change in the capacity of the varactor V10 with respect to the control voltage Vcnt. . . The ratio df (vertical axis) from the reference frequency fc due to the change in the capacity of the varactor V10 with respect to the reference frequency fc is substantially equal to zero. As shown by the dotted line, the control voltage Vcnt (horizontal axis) can react sensitively, in other words, the control voltage Vcn.
The oscillation frequency f can be changed with high sensitivity (sharp sensitivity) with respect to t (horizontal axis).

Japanese Patent Laying-Open No. 2005-27044

However, as another example, capacitors CB10, CB20, CB30,. . . Are used (connected), capacitors CB10, CB20, CB30,... With respect to the amount of change in capacitance of varactor V10 with respect to control voltage Vcnt. . . Since the ratio of the combined capacitance of the frequency becomes extremely large, the frequency deviation df with respect to the reference frequency fc as described above becomes insensitive to the control voltage Vcnt as shown by the solid line in FIG. There is a problem that the sensitivity of the change in the oscillation frequency f with respect to the control voltage Vcnt becomes dull.

In order to solve the above-described problems, an oscillation device according to the present invention is
(1) amplifier IN1;
(2) a piezoelectric vibrator X1 connected in parallel to the amplifier IN1, and
(3) a first capacitive element C1 connected to one of the input terminal and the output terminal of the amplifier IN1 and the fixed potential GND;
(4) A second capacitive element C2 and a voltage-controlled variable main capacitive element V1 provided in series between the other of the input terminal and the output terminal of the amplifier IN1 and the fixed potential GND, and the piezoelectric vibration The second capacitive element C2 for defining a reference frequency Fc serving as a reference in the range of the oscillation frequency F that the oscillation signal OS1 can take in cooperation with the child X1 and the first capacitive element C1;
And the voltage controlled variable main capacitive element V1 that receives the application of the control voltage Vcnt for changing the capacitance to vary the oscillation frequency F of the oscillation signal OS1,
(5) A plurality of auxiliary capacitive elements C, each of which can be connected or disconnected in parallel with the second capacitive element C2, and have different capacities to adjust the reference frequency Fc.
B1 to CB3,
(6) The oscillation frequency F of the oscillation signal OS1 by the voltage-controlled variable main capacitive element V1
Each voltage control variable sub-capacitance element VBi (i = 1, 2, 3,...)
Among the plurality of auxiliary capacitance elements CB1 to CB3, the auxiliary capacitance element CBi corresponding to the voltage controlled variable sub capacitance element Ci is connected in parallel to the voltage controlled variable main capacitance element V1 in conjunction with the connection or disconnection. And a plurality of voltage controlled variable sub-capacitance elements VB1 to VB3 whose capacitance changes upon application of the control voltage Vcnt, the plurality of voltage control variable sub-capacitance elements VB1. To VB3, one voltage controlled variable sub-capacitance element VBi
The ratio of the change amount of the capacitance of the one voltage controlled variable subcapacitance element VBi to the control voltage Vcnt with respect to the capacitance of the one auxiliary capacitance element CBi corresponding to is substantially the same.
A plurality of voltage-controlled variable sub-capacitance elements VB1 to VB3 having different capacitance variations with respect to the control voltage Vcnt.

According to the oscillation device according to the present invention described above, the plurality of voltage controlled variable sub-capacitance elements VB1 to VB1.
VB3 is a capacitance of the one voltage controlled variable subcapacitance element VBi with respect to the control voltage Vcnt with respect to the capacity of the one auxiliary capacitance element CBi between the plurality of voltage controlled variable subcapacitance elements VB1 to VB3. The change amounts of the capacitance with respect to the control voltage Vcnt are different from each other so that the ratio of the change amounts is substantially the same, and each voltage control variable subcapacitance element VBi is connected to the voltage control variable subcapacitance element VBi. Since the corresponding auxiliary capacitive element CBi can be connected to or disconnected from the voltage controlled variable main capacitive element in response to the connection or disconnection of the corresponding auxiliary capacitive element CBi, it is connected to the voltage controlled variable main capacitive element. One or more voltage-controlled variable sub-capacitance elements corresponding to at least one auxiliary capacitance element have a capacitance change amount of the voltage-controlled variable main capacitance element with respect to the control voltage Vcnt. Since the complement, unlike the conventional oscillator, the control voltage without slowing the sensitivity of the change in the oscillation frequency F against Vcnt, it is possible to vary the oscillation frequency F.

In the oscillation device according to the present invention, the control voltage Vcnt is based on the temperature change of the atmosphere in order to reduce the fluctuation of the oscillation frequency F due to the temperature change of the atmosphere of the oscillation device. The capacitance of the voltage controlled variable main capacitive element V1 is changed.

The capacity adjusting device according to the present invention is:
(1) a capacitive element C2 having a fixed capacitance;
(2) A voltage controlled variable main capacitive element V1 connected in series with the capacitive element C2 and having a variable capacitance, and applying a control voltage Vcnt for changing the capacitance of the voltage controlled variable main capacitive element V1 Receiving said voltage controlled variable main capacitive element V1,
(3) A plurality of auxiliary capacitance elements CB1 to CB3, each of which can be connected or disconnected in parallel with the capacitance element C2, and have different capacitances;
(4) Each voltage controlled variable sub-capacitance element VBi (i = 1, 2, 3,...) Corresponds to the voltage controlled variable sub-capacitance element Ci among the plurality of auxiliary capacitance elements CB1 to CB3. In conjunction with the connection or disconnection of the auxiliary capacitive element CBi, the voltage-controlled variable main capacitive element V1
A plurality of voltage controlled variable subcapacitance elements VB1 to VB3 whose capacitances can be changed in response to application of the control voltage Vcnt, wherein the plurality of voltage controlled variable subcapacitors are connected. Between the elements VB1 to VB3, the capacitance of the one voltage controlled variable subcapacitance element VBi with respect to the control voltage Vcnt with respect to the capacity of one auxiliary capacitance element CBi corresponding to one voltage controlled variable subcapacitance element VBi. The plurality of voltage controlled variable sub-capacitance elements VB whose capacitance variations with respect to the control voltage Vcnt are different from each other so that the ratio of the variation is substantially the same.
1 to VB3.

According to the capacitance adjusting device according to the present invention described above, the plurality of voltage controlled variable sub-capacitance elements VB.
1 to VB3 of the one voltage controlled variable subcapacitance element VBi with respect to the control voltage Vcnt with respect to the capacitance of the one auxiliary capacitive element CBi between the plurality of voltage controlled variable subcapacitance elements VB1 to VB3. The control voltage Vcnt is set so that the ratio of capacitance change amounts is substantially the same.
And the voltage control variable subcapacitance elements VBi correspond to the connection or disconnection of the auxiliary capacitance elements CBi corresponding to the voltage control variable subcapacitance elements VBi. One or more voltage control variable corresponding to at least one auxiliary capacitance element connected to the voltage control variable main capacitance element can be connected to or disconnected from the voltage control variable main capacitance element. The sub-capacitance element complements the amount of change in the capacitance of the voltage-controlled variable main capacitance element with respect to the control voltage Vcnt, so that the control voltage Vcnt
The capacitance of the voltage controlled variable main capacitive element V1 can be varied without reducing the sensitivity of the capacitance change of the voltage controlled variable main capacitive element V1.

  Embodiments of an oscillation device according to the present invention will be described with reference to the drawings.

<Configuration and operation>
FIG. 1 shows the configuration of the oscillator according to the embodiment. As shown in FIG. 1, the oscillation device D1 of the embodiment includes an inverter element IN1, a crystal resonator X1, resistors R1 and R2, and a capacitor C.
1, C2 (first and second capacitive elements), a varactor V1 (voltage controlled variable main capacitive element), and an adjustment circuit A1.

The inverter element IN1 is one of amplifiers and is connected to a power supply potential Vcc (fixed potential) and a ground potential GND (other fixed potential) such as + 3V and + 5V, and is composed of, for example, a CMOS inverter element. ing.

The crystal resonator X1 is connected in parallel to the inverter element IN1, and capacitors C1, C
2 is used to define the reference frequency Fc of the oscillation signal OS1.

The resistor R1 is a so-called feedback resistor connected in parallel to the inverter element IN1,
Defines the bias of the oscillation device D1.

The resistor R2 defines a bias at the output end of the inverter element IN1, that is, one end (for example, the cathode side) of the varactor V1, based on the power supply potential Vcc.

The capacitor C1 is provided between the output terminal of the inverter element IN1 and the ground potential GND, and the capacitor C2 and the varactor V1 are provided in series between the output terminal of the inverter element IN1 and the ground potential GND. . The varactor V1 includes, for example, a MOS varactor and a PN varactor, and a control voltage V for changing the capacity of the varactor V1.
cnt is applied from an external control device (not shown).

The adjustment circuit A1 is provided at the output terminal of the inverter element IN1, and includes a plurality of auxiliary capacitors (auxiliary capacitance elements) CB1, CB2, CB3,. . . And the plurality of auxiliary capacitors C
B1, CB2, CB3,. . . A plurality of auxiliary varactors (voltage controlled variable sub-capacitance elements) VB1, VB2, VB3,. . . And the plurality of auxiliary capacitors CB1, CB2
, CB3,. . . And the plurality of auxiliary varactors VB1, VB2, VB3,. . . A plurality of switches SW 1, SW 2, SW 3,.
. . And the control voltage Vcnt to the auxiliary varactors VB1, VB2, VB3,. . . Resistors RB1, RB2, RB3,. . . And having.

More precisely, the auxiliary capacitors CB1, CB2, CB3,. . . Are provided so as to be connected in parallel to or disconnected from the capacitor C2, and are connected in parallel to the varactor V1 in conjunction with the connection and the disconnection. Disconnected. Also, auxiliary varactors VB1, VB2, VB3,. . . Are provided so that they can be connected in parallel with the varactor V1 or can be disconnected. Auxiliary capacitors CB1, CB2, CB3,. . . And disconnecting the connection, and auxiliary varactors VB1, VB2, VB3,. . . The connection and disconnection of the
W1, SW2, SW3,. . . For example, the connection and disconnection of the auxiliary capacitor CB1 to the capacitor C2 and the connection and disconnection of the auxiliary capacitor CB1 to the varactor V1 are performed by the switch SW1 corresponding to the capacitor CB1 and the varactor V1. Based on the switch voltage Vsw1 output from the external storage device (not shown),
It is done in conjunction. Other auxiliary capacitors CB2, CB3,. . . , And other auxiliary varactors VB2, VB3,. . . Similarly, connection and disconnection for the other switches SW2, SW3,. . . , The switch voltages Vsw2, Vsw3,. .
. Is done.

Auxiliary capacitors CB1, CB2, CB3,. . . Have different capacities. More specifically, the capacities (synthetic capacities) presumed to be necessary for correcting the deviation of the reference frequency Fc caused by characteristic variations of the crystal unit X1 and the like are the auxiliary capacitors CB1 and CB2.
, CB3,. . . Auxiliary capacitors CB 1, CB 2, CB 3,. . . Each has a capacitance of 1 pF
, 2pF, 4pF,. . . It follows the power of 2. In the following, for ease of explanation and understanding, it is assumed that the auxiliary capacitors CB1 and CB3 are connected and the auxiliary capacitor CB2 is disconnected in order to correct the reference frequency Fc. .

Auxiliary varactors VB1, VB2, VB3,. . . Is composed of, for example, a MOS varactor and a PN varactor. The amount of change in the capacity of the varactor V1 with respect to the control voltage Vcnt, that is, the sensitivity to the control voltage Vcnt is, for example, a combination of the auxiliary capacitors CB1 and CB3 connected to the varactor V1. To compensate for the slowdown depending on the capacity, the control voltage V
The amount of change in capacitance with respect to cnt is different from each other. More specifically, the auxiliary varactors VB1, V
B2, VB3,. . . CV characteristics (auxiliary varactors VB1, VB with respect to the control voltage Vcnt
2, VB3,. . . Change amount of capacitance) is 1 pF / V, 2 pF / V, 4 pF / V,. . .
The ratio of the CV characteristic of the auxiliary varactor VB1 to the capacity of the auxiliary capacitor CB1,
The ratio of the CV characteristic of the auxiliary varactor VB2 to the capacity of the auxiliary capacitor CB2, the ratio of the CV characteristic of the auxiliary varactor VB3 to the capacity of the auxiliary capacitor CB3,. . . Of the auxiliary varactors VB1, VB2, VB3,. . . As with the capacity ratio, it follows a power of 2.

Switches SW1, SW2, SW3,. . . Are the auxiliary capacitors CB1, CB2, CB3,. . . Connection and disconnection, and auxiliary varactors VB1, VB2, VB3,. . . In order to execute connection and disconnection of the connection, for example, each is constituted by a MOS transistor.

Resistors RB1, RB2, RB3,. . . Are the end points (terminals) to which the control voltage Vcnt is applied and auxiliary varactors VB1, VB2, VB3,. . . And auxiliary capacitors CB1, CB2, CB3,. . . Are provided in parallel with each other.

"effect"
In the oscillation device D1 having the above-described configuration, a switch voltage that defines “connection” in order to correct a deviation of the reference frequency Fc of the oscillation signal OS1 due to variations in characteristics of the crystal resonator X1 and the like. Vsw1, Vsw3, and switch voltage V that defines “disconnection”
According to sw2, the auxiliary capacitors CB1 (1pF) and CB3 (4pF) are connected in parallel with the capacitor C2 by the switches SW1 and SW3, and the auxiliary capacitor CB2 (2pF) is not connected in parallel with the capacitor C2 by the switch SW2. That is, the connection is disconnected. In conjunction with the connection and disconnection, the auxiliary varactor VB1 is connected in parallel with the varactor V1.
(1 pF / V), auxiliary varactor VB3 (4 pF / V) is connected, and auxiliary varactor V
B2 (2 pF / V) is disconnected. Auxiliary varactor V connected in parallel to varactor V1
B1 and the auxiliary varactor VB3 are connected in parallel to the capacitor C2 by changing the capacitance according to the control voltage Vcnt, respectively, with respect to changing the oscillation frequency F by changing the capacitance of the varactor V1 based on the control voltage Vcnt. That is, due to the presence of the combined capacitance of the auxiliary capacitor CB1 and the auxiliary capacitor CB3 connected in parallel to the varactor V1, the amount of change in the capacitance of the varactor V1 corresponding to the control voltage Vcnt, that is, the sensitivity of the varactor V1 decreases. Can be reduced. In other words, it is assumed that all the auxiliary capacitors CB1, CB2, CB3,. . . Are connected, as shown by the solid line in FIG. 2, all the auxiliary capacitors CB1, CB2, CB3,. . . As in the case where the varactor V1 is connected (illustrated by a dotted line), the oscillation frequency F can be changed without reducing the sensitivity of the varactor V1 to the control voltage Vcnt.

In other words, in the variable adjustment device B1 including the varactor V1, the capacitor C2, and the adjustment circuit A1, the auxiliary capacitors CB1, CB2, CB3,... In parallel with the capacitor C2, that is, in parallel with the varactor V1. . . Is connected, the capacity of the varactor V1 can be changed without reducing the sensitivity of the capacity change of the varactor V1 with respect to the control voltage Vcnt.

<Modification 1>
FIG. 3 shows a configuration of the oscillation device of the first modification. In the oscillation device D1 of the first modification, as shown in FIG. 3, the configuration on the input side and the configuration on the output side of the inverter element IN1 in the oscillation device D1 of the embodiment shown in FIG. 1 are interchanged. More specifically, the oscillation device D of Modification 1
1, the capacitor C1, which is the input side configuration of the oscillation device D1 of the embodiment, is provided on the output side of the inverter element IN1, and on the other hand, the varactor is the configuration of the output side of the oscillation device D1 of the embodiment. V1, capacitor C2, resistor R2, and adjustment circuit A1 are provided on the input side of the inverter element IN. The effect similar to that of the oscillation device D1 of the above-described embodiment can be obtained also by the oscillation device D1 of the modification 1 having such a configuration.

<Modification 2>
FIG. 4 shows the configuration of the oscillator according to the second modification. As shown in FIG. 4, the oscillation device D <b> 2 of the modification 2 includes the adjustment circuit A <b> 1, similarly to the oscillation device D <b> 1 of the embodiment and the modification 1, and on the other hand, the oscillation device of the embodiment and the modification 1 Unlike D1, it has a bipolar transistor TR1, a crystal resonator XC1, resistors RC1 to RC5, and capacitors CC1 and CC2. Specifically, in the oscillation device D2 of Modification 2, the crystal resonator XC1, the voltage control variable main capacitance element V1, and the capacitor C2 are connected in series between the base of the transistor TR1 and the ground potential GND, and the transistor TR1. A resistor RC1 is connected between the emitter of the transistor TR1 and the ground potential GND, and a capacitor CC1 is connected between the base and emitter of the transistor TR1,
A capacitor CC2 is connected in parallel with the resistor RC1, a resistor RC2 is connected between the base of the transistor TR1 and the ground potential GND, and a resistor RC3 is connected between the collector of the transistor TR1 and the power supply potential Vcc. One end of the crystal resonator XC1 (
Corresponds to the base of transistor TR1. ) And a power supply potential Vcc, and a resistor RC4 is connected between the other end of the crystal unit XC1 and the power supply potential Vcc.
The adjustment circuit A1 is provided at the other end of the crystal unit XC1.

Also by the oscillation device D2 of the second modification having the above-described configuration, the same effect as that of the oscillation device D1 of the above-described embodiment and the first modification can be obtained.

<Modification 3>
The oscillation frequency F of the oscillation signal OS1 in the oscillation device D1 of the embodiment and the modification 1
However, when it fluctuates due to the environment in which the oscillation device D1 is placed, that is, due to the temperature change of the atmosphere, the control voltage Vcnt is based on the temperature change of the atmosphere. By defining the amount (degree) of change of the capacitance, it is possible to realize that the oscillation frequency F of the oscillation signal OS1 is kept constant regardless of the temperature change, that is, temperature compensation is performed. .

The figure which shows the structure of the oscillation apparatus of an Example. The figure which shows the sensitivity of the oscillation apparatus of an Example. The figure which shows the structure of the oscillation apparatus of the modification 1. FIG. The figure which shows the structure of the oscillation apparatus of the modification 2. The figure which shows the structure of the conventional oscillation apparatus. The figure which shows the sensitivity of the conventional oscillation apparatus.

Explanation of symbols

D1 ... Oscillator, IN1 ... Inverter element, X1 ... Piezoelectric vibrator, V1 ... Voltage control variable main capacitance element, C1, C2 ... Capacitor, A1 ... Adjustment circuit, CB1, CB2, CB3 ... Auxiliary capacitor, VB1, VB2, VB3 ... auxiliary varactor, SW1, SW2, SW3 ... switch.

Claims (3)

(1) an amplifier;
(2) a piezoelectric vibrator connected in parallel to the amplifier;
(3) a first capacitive element connected between one of an input terminal and an output terminal of the amplifier and a fixed potential;
(4) A second capacitive element and a voltage-controlled variable main capacitive element provided in series with each other between the other of the input end and the output end of the amplifier and the fixed potential, wherein the piezoelectric vibrator and the first A second capacitive element for defining a reference frequency that is a reference for a range of oscillation frequencies that can be taken by the oscillation signal in cooperation with the first capacitive element, and a capacitor for varying the oscillation frequency of the oscillation signal. The voltage-controlled variable main capacitance element that receives the application of a control voltage for changing;
(5) A plurality of auxiliary capacitance elements, each auxiliary capacitance element being connectable or disconnectable in parallel with the second capacitance element, and having different capacitances to adjust the reference frequency;
(6) In order to complement the variation of the oscillation frequency of the oscillation signal by the voltage-controlled variable main capacitance element, each voltage-controlled variable sub-capacitance element is the voltage-controlled variable sub-capacitance among the plurality of auxiliary capacitance elements. In conjunction with the connection or disconnection of the auxiliary capacitance element corresponding to the element, the voltage control variable main capacitance element can be connected in parallel or disconnected, and the capacitance is received by the application of the control voltage. A plurality of voltage-controlled variable sub-capacitance elements that change, and the capacitance of one auxiliary capacitance element corresponding to one voltage-controlled variable sub-capacitance element between the plurality of voltage-control variable sub-capacitance elements, The plurality of voltage controlled variable subcapacitors having different capacitance changes relative to the control voltage such that a ratio of a capacitance change amount of the one voltage controlled variable subcapacitance element to the control voltage is substantially the same. Element and Oscillating apparatus comprising a. The control voltage changes the capacitance of the voltage controlled variable main capacitance element based on the temperature change of the atmosphere in order to reduce the fluctuation of the oscillation frequency due to the temperature change of the atmosphere of the oscillation device. The oscillation device according to claim 1. (1) a capacitive element having a fixed capacitance;
(2) A voltage controlled variable main capacitive element connected in series with the capacitive element and having a variable capacitance, wherein the voltage control receives a control voltage applied to change the capacitance of the voltage controlled variable main capacitive element. A variable main capacitance element;
(3) Each auxiliary capacitive element can be connected or disconnected in parallel with the capacitive element,
A plurality of auxiliary capacitive elements having different capacitances;
(4) Each voltage control variable sub-capacitance element is connected to the connection or disconnection of the auxiliary capacitance element corresponding to the voltage control variable sub-capacitance element among the plurality of auxiliary capacitance elements. A plurality of voltage-controlled variable sub-capacitors that can be connected in parallel to or disconnected from the variable main-capacitance element, and whose capacitance changes upon application of the control voltage, the plurality of voltage-controlled variable sub-capacitors The ratio of the change amount of the capacitance of the one voltage-controlled variable sub-capacitance element to the control voltage for the capacitance of one auxiliary capacitance element corresponding to one voltage-controlled variable sub-capacitance element is substantially between the elements. And a plurality of voltage-controlled variable sub-capacitance elements having different capacitance variations with respect to the control voltage.

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