JP2023127164A - Electronic circuit and piezoelectric oscillator - Google Patents

Abstract

To obtain desired voltage-capacity characteristics by adding a peripheral circuit even in a case where a variable capacitance element with a small capacity variable ratio is used.SOLUTION: An electronic circuit comprises: a DC voltage source; a first variable capacitance element whose cathode is connected with the DC voltage source via a first resistor and whose anode is grounded; a second variable capacitance element whose cathode is connected with the DC voltage source via the first resistor and a second resistor and whose anode is grounded; and a transistor whose gate is applied with a predetermined voltage, whose drain is connected with a connection point between the first resistor and the second resistor, and whose source is connected with a connection point between the second resistor and the second variable capacitance element.SELECTED DRAWING: Figure 5

Description

The present invention relates to electronic circuits and piezoelectric oscillators.

Conventionally, a variable capacitance diode (varicap) as described in Patent Document 1, for example, has been known as a variable capacitance element.

Japanese Patent Application Publication No. 2005-183813

It is known that such a variable capacitance element has a small variable capacitance ratio. For example, when a piezoelectric oscillator is configured using a variable capacitance element with a small variable capacitance ratio, it becomes difficult to obtain an output signal in a wide frequency band. That is, when a piezoelectric oscillator is constructed using a variable capacitance element with a small variable capacitance ratio, there is a problem in that it is difficult to obtain desired voltage-frequency characteristics.

The present invention was made in view of the above-mentioned circumstances, and even when using a variable capacitance element with a small variable capacitance ratio, it is possible to obtain desired voltage-capacitance characteristics by adding a peripheral circuit. The purpose is to provide an electronic circuit that can be obtained.

An electronic circuit according to one aspect of the present invention includes a DC voltage source, a first variable capacitance element having a cathode connected to the DC voltage source via a first resistor and an anode grounded, and a cathode connected to the first resistor. and a second variable capacitance element connected to the DC voltage source via the first resistor and the second resistor, the anode of which is grounded; A transistor is connected to the connection point and has a source connected to the connection point between the second resistor and the second variable capacitance element.

In the electronic circuit according to one embodiment of the present invention, the transistor is an n-channel MOS-FET.

In the electronic circuit according to one aspect of the present invention, the first variable capacitance element and the second variable capacitance element are both variable capacitance diodes.

In the electronic circuit according to one aspect of the present invention, the first variable capacitance element and the second variable capacitance element have mutually equivalent electrical characteristics.

In the electronic circuit according to one aspect of the present invention, a voltage range applied by the DC voltage source is twice or more of a predetermined voltage applied to the gate of the transistor.

An electronic circuit according to one aspect of the present invention includes a DC voltage source, a first variable capacitance element whose cathode is connected to the DC voltage source via a first resistor, and whose anode is grounded; A predetermined voltage is applied to the gates of a plurality of second variable capacitance elements connected to the DC voltage source through a resistor and a corresponding second resistor among the plurality of second resistors, and whose anodes are grounded. , a drain is connected to a connection point between the first resistor and a corresponding second resistor among the plurality of second resistors, and a source is connected to a connection point between the corresponding second resistor among the plurality of second resistors and the plurality of the second resistors. A plurality of transistors are connected to connection points with corresponding second variable capacitance elements among the second variable capacitance elements.

In the electronic circuit according to one aspect of the present invention, voltages applied to the gates of each of the plurality of transistors are different from each other.

A piezoelectric oscillator according to one aspect of the present invention includes: a piezoelectric vibrator including a first terminal and a second terminal; a first variable capacitance element portion whose capacitance changes depending on a voltage applied to the first terminal; a second variable capacitance element portion whose capacitance changes depending on the voltage applied to the second terminal; a DC voltage source; one end connected to the first terminal and the other end connected to the DC voltage source. a first resistor, a transistor having a gate connected to the DC voltage source, a drain connected to a power source different from the DC voltage source, and a source connected to a second resistor; one end connected to the source of the transistor; , a second resistor whose other end is grounded, and a third resistor whose one end is connected to a connection point between the source of the transistor and the second resistor and whose other end is connected to the second terminal; 1 variable capacitance element section includes a first variable capacitance element whose cathode is connected to the first terminal and whose anode is grounded, and whose cathode is connected to the first terminal via a fourth resistor and whose anode is grounded. a second variable capacitance element; a second transistor having a gate applied with a predetermined voltage, a drain connected to the first terminal, and a source connected to a connection point between the fourth resistor and the second variable capacitance element; The second variable capacitance element section includes a third variable capacitance element having a cathode connected to the second terminal and an anode grounded, and a third variable capacitance element having a cathode connected to the second terminal via a fifth resistor. , a fourth variable capacitance element whose anode is grounded, a predetermined voltage is applied to the gate, the drain is connected to the second terminal, and the source is connected to the connection point between the fifth resistor and the fourth variable capacitance element. and a connected third transistor.

According to the present invention, even when a variable capacitance element with a small variable capacitance ratio is used, desired voltage-capacitance characteristics can be obtained by adding a peripheral circuit.

1 is a circuit diagram showing an example of a circuit configuration of a piezoelectric oscillator according to a first embodiment. FIG. 3 is a graph showing an example of voltage-capacitance characteristics of a variable capacitance element included in the piezoelectric oscillator according to the first embodiment. 3 is a graph showing an example of voltage-frequency characteristics at both ends of the piezoelectric vibrator of the piezoelectric oscillator according to the first embodiment. 3 is a graph showing an example of voltage-frequency characteristics of the piezoelectric oscillator according to the first embodiment. FIG. 2 is a circuit diagram showing an example of a circuit configuration of an electronic circuit according to a second embodiment. 7 is a graph showing an example of voltage-capacitance characteristics of an electronic circuit according to a second embodiment. FIG. 7 is a circuit diagram showing an example of a circuit configuration of an electronic circuit according to a third embodiment. 7 is a graph showing an example of voltage-capacitance characteristics of an electronic circuit according to a third embodiment. FIG. 7 is a circuit diagram showing an example of a circuit configuration of a piezoelectric oscillator according to a second embodiment. 1 is a circuit diagram showing an example of a circuit configuration of a piezoelectric oscillator according to a conventional technique. 2 is a graph showing an example of voltage-capacitance characteristics of a variable capacitance element included in a piezoelectric oscillator according to the prior art. 1 is a graph showing an example of voltage-frequency characteristics of a piezoelectric oscillator according to the prior art.

[Prior art]
First, a piezoelectric oscillator 9 according to the prior art will be described with reference to FIGS. 10 to 12. The piezoelectric oscillator 9 according to the prior art outputs a high frequency signal according to the applied voltage. As an example, the piezoelectric oscillator 9 may be a VCXO (Voltage Controlled Xtal Oscillator) that performs voltage control using a variable capacitance element (variable capacitance diode or varicap).

FIG. 10 is a circuit diagram showing an example of a circuit configuration of a piezoelectric oscillator according to the prior art. The circuit configuration of the piezoelectric oscillator 9 will be explained with reference to the same figure.
The piezoelectric oscillator 9 includes a piezoelectric vibrator 91, a DC power supply 92, a resistor 931, a resistor 932, an inverter 94, a resistor 95, a capacitor 96, a capacitor 97, a variable capacitor 98, and a variable capacitor 99. Equipped with.

The piezoelectric vibrator 91 oscillates when a predetermined voltage is applied. The piezoelectric vibrator 91 is, for example, a crystal vibrator. The DC power supply 92 is a DC voltage source that outputs DC power. DC power supply 92 applies a predetermined voltage to both ends of piezoelectric vibrator 91 . The DC power supply 92 applies a voltage of, for example, 0 [V (volt)] to 3.3 [V]. A resistor 931 is connected between the positive terminal of the DC power source 92 and one end of the piezoelectric vibrator 91, and a resistor 932 is connected between the positive terminal of the DC power source 92 and the other end of the piezoelectric vibrator 91. Inverter 94 is connected to one end of piezoelectric vibrator 91 via capacitor 96 and to the other end of piezoelectric vibrator 91 via capacitor 97 . Resistor 95 is a feedback resistor connected between the input terminal and output terminal of inverter 94. A cathode K of the variable capacitance element 98 is connected to a connection point between the piezoelectric vibrator 91, the resistor 932, and the capacitor 96. A cathode K of the variable capacitance element 99 is connected to a connection point between the piezoelectric vibrator 91, the resistor 931, and the capacitor 97. Anodes A of variable capacitance element 98 and variable capacitance element 99 are grounded.

FIG. 11 is a graph showing an example of voltage-capacitance characteristics of a variable capacitance element included in a piezoelectric oscillator according to the prior art. An example of the voltage-capacitance characteristic of the variable capacitance element included in the piezoelectric oscillator 9 will be described with reference to the same figure. The figure shows an example of the voltage-capacitance characteristic of the variable capacitance element 98 or the variable capacitance element 99 included in the piezoelectric oscillator 9, with the horizontal axis representing the voltage applied to the variable capacitance element and the vertical axis representing the capacitance of the variable capacitance element. . In the following description, if the variable capacitance element 98 or the variable capacitance element 99 is not distinguished, they may be simply referred to as a variable capacitance element.

In FIG. 11, voltage-capacitance characteristics when the piezoelectric oscillator 9 uses two different variable capacitance elements are shown as a curve C61 and a curve C62, respectively. The variable capacitance element having the characteristics shown by the curve C61 and the variable capacitance element having the characteristics shown by the curve C62 have different impurity concentration distributions at the pn junction surface.
Specifically, in the voltage characteristic C∝V^-n of the junction capacitance, the curve C61 shows an example of the characteristic of a variable capacitance element using a step junction where n=1/2, and the curve C62 shows an example of the characteristic of a variable capacitance element using a step junction where n=1/2. An example of the characteristics of a variable capacitance element using a hyperstep junction, which is No. 2, is shown below.

As shown in curve C61, in a variable capacitance element using a stepped junction, the capacitance changes rapidly in the low voltage region, and the change in capacitance becomes small in the high voltage region (in the following explanation, the amount of change is (This is also referred to as ``reaching a plateau'' when the value decreases.) That is, in a variable capacitance element using a stepped junction, the change in capacitance with respect to a change in voltage differs depending on the voltage. In other words, a variable capacitance element using a stepped junction does not have linear voltage-capacitance characteristics.

On the other hand, as shown by curve C62, in a variable capacitance element using a hyperstep junction, the amount of change in capacitance is approximately constant regardless of whether the voltage is in a low voltage region or in a high voltage region. Here, the range in which the amount of change in capacitance is substantially constant is a range in which the amount of change in capacitance with respect to a change in voltage does not change depending on the voltage and can be considered to be constant. That is, in a variable capacitance element using a hyperstep junction, the amount of change in capacitance with respect to the amount of change in voltage does not depend on voltage. In other words, a variable capacitance element using a stepped junction has a linear voltage-capacitance characteristic.

Note that the horizontal axis shown in FIG. 11 may range from approximately 0 [V] to 3.3 [V], for example. Further, the vertical axis shown in FIG. 11 may range from 0 [pF (picofarad)] to 10 [pF], for example.

FIG. 12 is a graph showing an example of voltage-frequency characteristics of a piezoelectric oscillator according to the prior art. An example of the voltage-frequency characteristics of the piezoelectric oscillator 9 according to the prior art will be explained with reference to the same figure. The figure shows an example of the voltage-frequency characteristic of the piezoelectric oscillator 9, with the horizontal axis representing the voltage applied to the variable capacitance element and the vertical axis representing the oscillation frequency of the piezoelectric vibrator 91.
Note that the oscillation frequency is f=1/2π√LC∝1/√V^−n.
In the figure, the voltage-capacitance characteristic of a variable capacitance element using a step junction with n=1/2 is shown as curve C71, and the voltage-capacitance characteristic of a variable capacitance element using a hyperstep junction with n=2 is shown as curve C71. It is shown as curve C62.

As shown by curve C71, in the variable capacitance element using a step junction, the frequency changes rapidly in a low voltage region, and the frequency change becomes small in a high voltage region. That is, in a variable capacitance element using a stepped junction, the amount of change in frequency with respect to a change in voltage differs depending on the voltage. In other words, a variable capacitance element using a stepped junction does not have linear voltage-frequency characteristics.

On the other hand, as shown by curve C72, in the variable capacitance element using a hyperstep junction, the amount of change in frequency is approximately constant regardless of whether the voltage is in a low voltage region or in a high voltage region. Here, the range in which the amount of change in frequency is substantially constant is a range in which the amount of change in frequency with respect to the amount of change in voltage does not change depending on the voltage and can be considered to be constant. That is, in a variable capacitance element using a hyperstep junction, the amount of change in frequency with respect to the amount of change in voltage does not depend on the voltage. In other words, a variable capacitance element using a stepped junction has linear voltage-frequency characteristics.

[First embodiment]
A first embodiment will be described with reference to FIGS. 1 to 4.
In the first embodiment, even when a piezoelectric oscillator is configured using a variable capacitance element using a step junction having characteristics as shown by curve C61 or curve C71, desired voltage-frequency characteristics can be achieved. The purpose is to provide a piezoelectric oscillator 1 that can be obtained. In other words, it is an object of the present invention to provide a piezoelectric oscillator that can obtain desired voltage-frequency characteristics even when using a variable capacitance element with poor electrical characteristics.

FIG. 1 is a circuit diagram showing an example of a circuit configuration of a piezoelectric oscillator according to a first embodiment. An example of the circuit configuration of the piezoelectric oscillator 1 will be described with reference to the same figure. The piezoelectric oscillator 1 differs from the piezoelectric oscillator 9 according to the prior art in that different voltages are applied to the first variable capacitance element 18 and the second variable capacitance element 19, respectively.

Specifically, the piezoelectric oscillator 1 may be a VCXO that performs voltage control using a variable capacitance element. Although the piezoelectric oscillator 1 will be described as a VCXO in the following description, the piezoelectric oscillator 1 is not limited to this example. For example, the piezoelectric oscillator 1 may be an oscillator such as a VXO (Variable Xtal Oscillator).

The piezoelectric oscillator 1 includes a piezoelectric vibrator 11, a DC power supply 12, a first resistor 13, a transistor 21, a second resistor 22, a third resistor 23, an inverter 14, a resistor 15, a capacitor 16, It includes a capacitor 17, a first variable capacitance element 18, and a second variable capacitance element 19.

The piezoelectric oscillator 1 oscillates when a voltage is applied. The piezoelectric oscillator 1 is, for example, a crystal resonator. The piezoelectric vibrator 11 includes a first terminal 111 and a second terminal 112. The first terminal 111 is also written as XT, and the second terminal 112 is also written as XTN.

The DC power supply 12 is a DC voltage source that outputs DC power. The DC power supply 12 may be a constant voltage source capable of outputting a constant voltage regardless of the connected load. The DC power supply 12 includes a positive terminal 121 and a negative terminal 122, and the negative terminal 122 is grounded.

The first resistor 13 has one end connected to a connection point (hereinafter referred to as connection point P1) between the cathode K of the first variable capacitance element 18, the first terminal 111 of the piezoelectric vibrator 11, and the capacitor 16, and the other end. One end is connected to the positive terminal 121 of the DC power supply 12 .

The first variable capacitance element 18 may be a variable capacitance diode (varicap). The first variable capacitance element 18 includes an anode A and a cathode K. A cathode K of the first variable capacitance element 18 is connected to the first terminal 111 of the piezoelectric vibrator 11 at a connection point P1. Anode A of the first variable capacitance element 18 is grounded.

The second variable capacitance element 19 may be a variable capacitance diode (varicap). The second variable capacitance element 19 includes an anode A and a cathode K. A cathode K of the second variable capacitance element 19 is connected to the second terminal 112 of the piezoelectric vibrator 11 at a connection point P3. Anode A of the second variable capacitance element 19 is grounded.

Note that the first variable capacitance element 18 and the second variable capacitance element 19 may have mutually similar structures and thus may have mutually equivalent electrical characteristics. The electrical characteristics may be, for example, voltage-capacitance characteristics.
Note that the first variable capacitance element 18 and the second variable capacitance element 19 may have mutually different electrical characteristics by having mutually different structures.

The transistor 21 controls the voltage applied to the second variable capacitance element 19 according to the output voltage of the DC power supply 12. The transistor 21 may be, for example, an n-channel MOS-FET (Metal-Oxide-Semiconductor Field-Effect Transistor). The transistor 21 has a gate G connected to the connection point between the positive terminal of the DC power supply 12 and the first resistor 13, a drain D connected to the power supply 24, and a source S connected to the connection point between the second resistor 22 and the third resistor 23. It is connected to a connection point (hereinafter referred to as connection point P2). The power source 24 may be a different power source than the DC power source 12.

The second resistor 22 has one end connected to the source S of the transistor 21 and the other end grounded.
The third resistor 23 has one end connected to a connection point P2 between the source S of the transistor 21 and the second resistor 22, and the other end connected to the cathode K of the second variable capacitance element 19 and the second terminal 112 of the piezoelectric vibrator 11. (hereinafter referred to as connection point P3).

Inverter 14 includes an input terminal 141 and an output terminal 142. Input terminal 141 is connected to cathode K of first variable capacitance element 18 via capacitor 16 . The output terminal 142 is connected to the cathode K of the second variable capacitance element 19 via the capacitor 17. Resistor 15 is a feedback resistor connected in parallel with inverter 14 (that is, one end is connected to input terminal 141 and the other end is connected to output terminal 142).

Next, the electrical characteristics of the piezoelectric oscillator 1 will be explained with reference to FIGS. 2 to 4. Note that the graphs shown in FIGS. 2 to 4 are graphs showing results obtained by circuit simulation.

FIG. 2 is a graph showing an example of the voltage-capacitance characteristic of the variable capacitance element included in the piezoelectric oscillator according to the first embodiment. An example of the voltage-capacitance characteristics of the first variable capacitance element 18 and the second variable capacitance element 19 included in the piezoelectric oscillator 1 will be described with reference to the same figure. In the following description, when the first variable capacitance element 18 and the second variable capacitance element 19 are not distinguished, they may be simply referred to as variable capacitance elements.

Note that although the horizontal axis shown in FIG. 2 is shown in a range from 0 to 1, it may range from about 0 [V] to 3.3 [V], for example. Further, although the vertical axis shown in FIG. 2 is shown in a range from 0 to 2, it may be, for example, from 0 [pF] to 10 [pF].

A curve C21 shows the voltage-capacitance characteristic of the first variable capacitance element 18. A curve C22 shows the voltage-capacitance characteristic of the second variable capacitance element 19. A curve C23 shows the voltage-capacitance characteristic of the combined capacitance of the first variable capacitance element 18 and the second variable capacitance element 19.

The characteristics shown in the figure will be described with reference to an example in which the operating threshold voltage VTN of the transistor 21 (that is, the gate threshold voltage VGS(TH)) is 0.5.
Furthermore, both the first variable capacitance element 18 and the second variable capacitance element 19 are variable capacitance elements using step junctions.

The output voltage of the DC power supply 12 is applied to the first variable capacitance element 18 via the first resistor 13 . Therefore, the voltage-capacitance characteristic of the first variable capacitance element 18 shown by the curve C21 has the characteristic of a variable capacitance element using a step junction. That is, in the voltage-capacitance characteristic of the first variable capacitance element 18, the capacitance changes rapidly in a low voltage region, and the change in capacitance becomes small in a high voltage region. In other words, the curve C21 is not linear.

A voltage from a power supply 24 is applied to the second variable capacitance element 19 via a transistor 21 and a third resistor 23 . This is because the transistor 21 is off in a range where the output voltage of the DC power supply 12 is equal to or lower than the operating threshold voltage VTN of the transistor 21 (for example, from 0 to 0.5). A cathode K of the second variable capacitance element 19 is grounded via a second resistor 22 and a third resistor 23. Therefore, in a range where the output voltage of the DC power supply 12 is equal to or lower than the operating threshold voltage VTN of the transistor 21, the capacitance of the second variable capacitance element 19 has a maximum value (for example, 2.0).

When the output voltage of the DC power supply 12 exceeds the operating threshold voltage VTN of the transistor 21, the transistor 21 is turned on and the voltage of the power supply 24 is applied to the cathode K of the second variable capacitance element 19 via the third resistor 23. Therefore, in a range where the output voltage of the DC power supply 12 exceeds the operating threshold voltage VTN of the transistor 21, the capacitance of the second variable capacitance element 19 changes according to the output voltage of the DC power supply 12.

The combined capacitance of the first variable capacitance element 18 and the second variable capacitance element 19 is determined in a range where the output voltage of the DC power supply 12 is equal to or lower than the operating threshold voltage VTN of the transistor 21 (i.e., in a low voltage region), as shown in a curve C23. ), the capacitance of the first variable capacitance element 18 whose capacitance changes rapidly and the capacitance of the second variable capacitance element 19 whose capacitance is large and constant are combined.

In addition, the capacitance of the first variable capacitance element 18 reaches a peak in the range where the output voltage of the DC power supply 12 exceeds the operating threshold voltage VTN of the transistor 21 (that is, the high voltage region), and the capacitance of the first variable capacitance element 18 suddenly changes. The capacitance of the second variable capacitance element 19 is combined.

Therefore, the combined capacitance of the first variable capacitance element 18 and the second variable capacitance element 19 changes even if the output voltage of the DC power supply 12 is lower than the operating threshold voltage VTN of the transistor 21, and the output voltage of the DC power supply 12 does not reach a plateau even if it exceeds the operating threshold voltage VTN of the transistor 21. Therefore, the combined capacitance of the first variable capacitance element 18 and the second variable capacitance element 19 has a nearly linear voltage-capacitance characteristic.

Note that the range of the voltage applied by the DC power supply 12 is larger than the operating threshold voltage VTN of the transistor 21. More preferably, the range of the voltage applied by the DC power supply 12 may be twice or more the operating threshold voltage VTN of the transistor 21.

FIG. 3 is a graph showing an example of voltage-frequency characteristics at both ends of the piezoelectric vibrator of the piezoelectric oscillator according to the first embodiment. An example of voltage-frequency characteristics at both ends of the piezoelectric vibrator 11 of the piezoelectric oscillator 1 will be described with reference to the same figure. A curve C31 shows the frequency characteristics of the voltage VXT at the first terminal 111. Curve C32 shows the frequency characteristics of voltage VXTN at second terminal 112.

Note that although the horizontal axis shown in FIG. 3 is shown in a range from 0 to 1, it may range from about 0 [V] to 3.3 [V], for example. Further, although the vertical axis shown in FIG. 3 is shown in a range from 0 to 1, it may be, for example, from 0 [MHz (megahertz)] to 8 [MHz].

As shown by the curve C31, as the voltage VXT at the first terminal 111 increases, the frequency also increases proportionally. On the other hand, as shown by the curve C32, the voltage VXTN at the second terminal 112 is 0 in the voltage range of 0 to 0.3, and the frequency increases proportionally from the point where the voltage exceeds 0.3. That is, voltage VXTN rises later than voltage VXT.

In other words, since the output voltage of the DC power supply 12 is directly applied to the first terminal 111 via the first resistor 13, when the output voltage of the DC power supply 12 increases, the voltage VXT also increases accordingly. On the other hand, voltage is not applied to the second terminal 112 until after the transistor 21 is turned on. Therefore, voltage VXTN rises later than voltage VXT by the operating threshold voltage VTN of transistor 21.

FIG. 4 is a graph showing an example of voltage-frequency characteristics of the piezoelectric oscillator according to the first embodiment. An example of the voltage-frequency characteristics of the piezoelectric oscillator 1 will be explained with reference to the same figure. Curve C4 shows the voltage-frequency characteristic of piezoelectric oscillator 1.

Note that although the horizontal axis shown in FIG. 4 is shown in a range from 0 to 1, it may range from about 0 [V] to 3.3 [V], for example. Further, although the vertical axis shown in FIG. 4 is shown in a range from 1 to 2, it may be, for example, from 8 [MHz] to 16 [MHz].

As shown in curve C4, the frequency changes sufficiently in the range where the output voltage of the DC power supply 12 is equal to or lower than the operating threshold voltage VTN of the transistor 21 (i.e., low voltage region), and the frequency changes sufficiently in the range where the output voltage of the DC power supply 12 is equal to or lower than the operating threshold voltage VTN of the transistor 21 (i.e., in the range where the voltage exceeds the operating threshold voltage VTN) The frequency changes sufficiently even in the high range region). That is, in the voltage-frequency characteristic of the piezoelectric oscillator 1, the frequency changes even in a low voltage region, and the amount of change in frequency does not reach a plateau even in a high voltage region.

[Summary of the first embodiment]
As explained above, the piezoelectric oscillator 1 according to the present embodiment includes the piezoelectric vibrator 11, the first variable capacitance element 18, the second variable capacitance element 19, the DC power supply (DC voltage source) 12, and the first It includes a resistor 13, a transistor 21, a second resistor 22, and a third resistor 23. By including the transistor 21, the piezoelectric oscillator 1 makes the voltage applied to the first variable capacitance element 18 and the voltage applied to the second variable capacitance element 19 different. Specifically, the piezoelectric oscillator 1 includes the transistor 21 and applies a voltage to the second variable capacitance element 19 later than the first variable capacitance element 18 . That is, the piezoelectric oscillator 1 secures the amount of change in capacitance by applying a voltage to the first variable capacitance element 18 in a low voltage region, and applies a voltage to the second variable capacitance element 19 in a high voltage region. By starting, the amount of change in capacity is secured.
Therefore, the piezoelectric oscillator 1 applies voltage to the second variable capacitance element 19 via the transistor 21 even when the voltage-capacitance characteristic of the first variable capacitance element 18 reaches a peak in a high voltage region. Thereby, the combined capacitance of the first variable capacitance element 18 and the second variable capacitance element 19 can be varied.

In other words, the piezoelectric oscillator 1 can obtain linear voltage-frequency characteristics even when using step junction first variable capacitance element 18 and second variable capacitance element 19 whose voltage-capacitance is not linear. I can do it.
Therefore, according to this embodiment, even when a piezoelectric oscillator is configured using a stepped junction variable capacitance element whose voltage-capacitance characteristics are not linear, desired voltage-frequency characteristics can be obtained.

Further, according to the embodiment described above, the transistor 21 is an n-channel type MOS-FET. Therefore, the piezoelectric oscillator 1 does not have a large power loss and has a small time delay unlike the case where bipolar transistors are used, so that desired voltage-frequency characteristics can be suitably obtained.

Further, according to the embodiment described above, both the first variable capacitance element 18 and the second variable capacitance element 19 are variable capacitance diodes (varicaps). Therefore, according to the present embodiment, a desired voltage-frequency characteristic can be obtained by using a step-junction variable capacitance diode whose voltage-capacitance characteristic is not a straight line, without spending a lot of money to develop a super-step junction variable capacitance diode. can be obtained.

Further, according to the embodiment described above, the first variable capacitance element 18 and the second variable capacitance element 19 have similar structures and thus have equivalent electrical characteristics. Therefore, according to this embodiment, the layout of structures can be easily performed.

Further, according to the embodiment described above, the range of the voltage applied by the DC power supply 12 is twice or more the operating threshold voltage VTN of the transistor 21. In other words, the DC power supply 12 can be varied to a voltage that is twice or more the operating threshold voltage VTN of the transistor 21. Therefore, according to the present embodiment, the capacitances of the second variable capacitance element 19 are combined at a voltage before the change in the capacitance of the first variable capacitance element 18 reaches a ceiling. Therefore, according to the piezoelectric oscillator 1, a linear voltage-capacitance characteristic can be obtained.

Note that in the above-described embodiment, a configuration in which the voltage VXTN rises later than the voltage VXT has been described, but the configuration may be such that the voltage VXT rises later than the voltage VXTN. In this case, the configuration may be such that the transistor 21, the second resistor 22, and the third resistor 23 are replaced with the first resistor 13.
By replacing the configurations of the transistor 21, the second resistor 22, and the third resistor 23 with the first resistor 13, the second variable capacitance element 19 can When the capacitance of the first variable capacitance element 18 changes and the output voltage of the DC power supply 12 exceeds the operating threshold voltage VTN of the transistor 21, the variable capacitances of the first variable capacitance element 18 are combined to obtain a linear voltage-capacitance characteristic. , and as a result voltage-frequency characteristics can be obtained.

[Second embodiment]
First, a problem to be solved by the electronic circuit 3 according to the second embodiment will be explained. In the variable capacitance element described with reference to FIG. 11, whether it is a step junction or a superstep junction, the capacitance variable range when the voltage is varied from 0 to 1 is from 1.0 to 1.0. It is about 0.3, and the capacitance variable ratio is small. When using a variable capacitance element with a small variable capacitance ratio, even if the voltage applied to the variable capacitance element is increased, the capacitance cannot be lowered to a predetermined value or less, and the output frequency of the piezoelectric oscillator 1 cannot be lowered to a predetermined frequency or higher. It cannot be done. This characteristic in which the capacitance variable range reaches a ceiling is particularly noticeable in the case of stepped junctions.
The electronic circuit 3 according to the second embodiment obtains a sufficient variable capacitance ratio by adding a predetermined peripheral circuit to the variable capacitive element even when a variable capacitance element with a small variable capacitance ratio is used. The purpose is to

An electronic circuit 3 according to a second embodiment will be described with reference to FIGS. 5 and 6.
FIG. 5 is a circuit diagram showing an example of the circuit configuration of an electronic circuit according to the second embodiment. An example of the circuit configuration of the electronic circuit 3 will be described with reference to the figure.
The electronic circuit 3 includes a variable capacitance element (first variable capacitance element) 31, a transistor 32, a variable capacitance element (second variable capacitance element) 33, a resistor (second resistance) 34, a DC power supply 35, and a DC power supply 35. It includes a power source (DC voltage source) 36, a resistor (first resistor) 37, and a terminal 38.

The DC power supply 36 is a DC voltage source that outputs DC power. The DC power supply 36 may be a constant voltage source capable of outputting a constant voltage regardless of the connected load. The DC power supply 36 includes a positive terminal 361 and a negative terminal 362. The positive terminal 361 is connected to the resistor 37, and the negative terminal 362 is grounded.
The resistor 37 has one end connected to the positive terminal 361 of the DC power supply 36 and the other end connected to the cathode K of the variable capacitance element 31.

A cathode K of the variable capacitance element 31 is connected to a positive terminal 361 of the DC power supply 36 via a resistor 37. Anode A of variable capacitance element 31 is grounded.
A cathode K of the variable capacitance element 33 is connected to a positive terminal 361 of a DC power supply 36 via a resistor 37 and a resistor 34 . Further, the cathode K of the variable capacitance element 33 is connected to the source S of the transistor 32. Anode A of variable capacitance element 33 is grounded.
Note that both the variable capacitance element 31 and the variable capacitance element 33 may be variable capacitance diodes (varicaps).

Note that the variable capacitance element 31 and the variable capacitance element 33 may have mutually similar electrical characteristics by having similar structures. The electrical characteristics may be, for example, voltage-capacitance characteristics.

One end of the resistor 34 is connected to the connection point between the resistor 37 and the variable capacitance element 31, and the other end is connected to the connection point between the source S of the transistor 32 and the cathode K of the variable capacitance element 33. It is preferable that the resistance value of the resistor 34 is sufficiently larger than the resistance value of the resistor 37.

The transistor 32 is an n-channel type MOS-FET. A predetermined voltage is applied to the gate G of the transistor 32 by a DC power supply 35. The drain D of the transistor 32 is connected to the connection point between the resistor 37 and the resistor 34. A source S of the transistor 32 is connected to a connection point between the resistor 34 and the variable capacitance element 33.
The DC power supply 35 is a DC voltage source that outputs DC power. The DC power supply 35 applies a predetermined voltage to the gate G of the transistor 32.

FIG. 6 is a graph showing an example of voltage-capacitance characteristics of the electronic circuit according to the second embodiment. The electrical characteristics of the electronic circuit 3 will be explained with reference to the figure. The figure shows changes in the capacitance of the terminal 38 with respect to the ground point when the output voltage of the DC power supply 36 is varied. Note that the graph shown in FIG. 6 is a graph showing the results obtained by circuit simulation.
Although the horizontal axis is shown in a range from 0 to 1, it may range from about 0 [V] to 3.3 [V], for example. Further, although the vertical axis is shown in a range from 0 to 1.2, it may be, for example, from 0 [pF] to 12 [pF].
Further, in the example shown in the figure, an example will be described in which the operating threshold voltage VTN of the transistor 32 is 0.5.

The transistor 32 is on in a range where the output voltage of the DC power supply 36 is lower than or equal to the output voltage of the DC power supply 35 (that is, in a range where the voltage is from 0 to 0.5). In a range in which the output voltage of the DC power supply 36 exceeds the output voltage of the DC power supply 35 (that is, in a range where the voltage is between 0.5 and 1), the transistor 32 is off.

In a range where the output voltage of the DC power supply 36 is lower than the output voltage of the DC power supply 35 , the transistor 32 is on, so the output voltage of the DC power supply 36 is applied to the variable capacitance element 33 via the resistor 37 . Therefore, the capacitance of the electronic circuit 3 is the combined capacitance of the capacitance of the variable capacitance element 31 and the capacitance of the variable capacitance element 33.

Here, the resistance value of the resistor 34 is a sufficiently large resistance value so as not to affect the voltage-capacitance characteristics of the variable capacitance element 33. In the range where the output voltage of the DC power supply 36 exceeds the output voltage of the DC power supply 35, the transistor 32 is off, so the voltage-capacitance characteristic of the variable capacitance element 33 does not change. Therefore, the capacitance of the electronic circuit 3 depends on the capacitance of the variable capacitance element 31.

In other words, in the range where the output voltage of the DC power supply 36 exceeds the output voltage of the DC power supply 35, the amount of change in the combined capacitance of the variable capacitance element 31 and the variable capacitance element 33 reaches a ceiling, so the electronic circuit 3 By separating the variable capacitance element 33, the capacitance of the variable capacitance element 31 is made dominant, and a sufficient amount of change in capacitance is ensured.

Note that the range of the voltage applied by the DC power supply 36 is larger than the predetermined voltage applied to the gate G of the transistor 32 by the DC power supply 35. More preferably, the range of the voltage applied by the DC power supply 36 may be twice or more the predetermined voltage applied to the gate G of the transistor 32 by the DC power supply 35.

[Summary of second embodiment]
As described above, the electronic circuit 3 according to the present embodiment includes the DC power supply 36, the variable capacitance element 31, the variable capacitance element 33, and the transistor 32. By including the transistor 32, the electronic circuit 3 can apply voltage to the variable capacitance element 31 and apply voltage to the variable capacitance element 31 and the variable capacitance element 33 according to the output voltage of the DC power supply 36. Switch. More specifically, by including the transistor 32 , the electronic circuit 3 applies voltage to the variable capacitance element 33 later than to the variable capacitance element 31 . That is, the electronic circuit 3 secures the amount of change in capacitance by applying voltage to the variable capacitance element 31 and the variable capacitance element 33 in a region where the voltage is low, and disconnects the variable capacitance element 33 in a region where the voltage is high. to ensure the amount of change in capacity.

Therefore, even if the voltage-capacitance characteristics of the electronic circuit 3 reach a peak in a high voltage region, the electronic circuit 3 can reduce the combined capacitance of the electronic circuit 3 by turning off the transistor 32, thereby reducing the capacitance. The variable range of can be increased.
Therefore, according to this embodiment, even when a variable capacitance element with a small variable capacitance ratio is used, desired voltage-capacitance characteristics can be obtained by adding peripheral circuits such as the transistor 32.

Further, according to the embodiment described above, the transistor 32 is an n-channel type MOS-FET. Therefore, the electronic circuit 3 does not have a large power loss and has a small time delay unlike the case where bipolar transistors are used, so that desired voltage-capacitance characteristics can be suitably obtained.

Further, according to the embodiment described above, both the variable capacitance element 31 and the variable capacitance element 33 are variable capacitance diodes (varicaps). Therefore, according to the present embodiment, it is possible to obtain desired voltage-capacitance characteristics using a variable capacitance diode with a small variable capacitance ratio, without spending money to develop a variable capacitance diode with a large variable capacitance ratio. can.

Further, according to the embodiment described above, the variable capacitance element 31 and the variable capacitance element 33 have similar structures and thus have equivalent electrical characteristics. Therefore, according to this embodiment, the layout of structures can be easily performed.

Further, according to the embodiment described above, the range of the voltage applied by the DC power supply 36 is more than twice the predetermined voltage applied to the gate G of the transistor 32 by the DC power supply 35. In other words, the DC power supply 36 can be varied to a voltage that is twice or more the voltage applied by the DC power supply 35. Therefore, according to the present embodiment, the capacitances of the variable capacitance elements 33 are combined at a voltage before the change in the capacitance of the variable capacitance elements 31 reaches a ceiling. Therefore, according to the electronic circuit 3, a large variable capacitance ratio can be obtained.

[Third embodiment]
A third embodiment will be described with reference to FIGS. 7 and 8. An electronic circuit 3A according to the third embodiment differs from the second embodiment in that it includes a plurality of transistors 32, variable capacitance elements 33, resistors 34, and DC power supplies 35.
In the figure, an example will be described in which n transistors 32 (n is a natural number of 2 or more), a variable capacitance element 33, a resistor 34, and a DC power supply 35 are provided.

FIG. 7 is a circuit diagram showing an example of the circuit configuration of an electronic circuit according to the third embodiment. An example of the circuit configuration of an electronic circuit 3A according to the third embodiment will be described with reference to the same figure. In the description of the electronic circuit 3A, the same components as the electronic circuit 3 may be given the same reference numerals and the description thereof may be omitted. The electronic circuit 3A includes a variable capacitance element (first variable capacitance element) 31, a DC power supply 36, and a resistor 37. The variable capacitance element 31, the DC power supply 36, and the resistor 37 are the same as those in the electronic circuit 3, so their explanations will be omitted.

The electronic circuit 3A includes a plurality of variable capacitance elements (second variable capacitance elements) 33. Specifically, the electronic circuit 3A includes a variable capacitance element 33-1, a variable capacitance element 33-2, . . . , a variable capacitance element 33-n.
Anode A of variable capacitance element 33 is grounded.
The cathode K of the variable capacitance element 33 is connected to the positive terminal 361 of the DC power supply 36 via a resistor (first resistor) 37 and a corresponding resistor 34 among the plurality of resistors (second resistors) 34. Specifically, the cathode K of the variable capacitance element 33-1 is connected to the DC power supply 36 via a resistor 37 and a corresponding resistor 34-1 among the plurality of resistors 34. Further, the cathode K of the variable capacitance element 33-2 is connected to the DC power supply 36 via a resistor 37 and a corresponding resistor 34-2 among the plurality of resistors 34. ..., and the cathode K of the variable capacitance element 33-n is connected to a DC power source 36 via a resistor 37 and a corresponding resistor 34-n among the plurality of resistors 34.

The electronic circuit 3A includes a plurality of transistors 32. Specifically, the electronic circuit 3A includes a transistor 32-1, a transistor 32-2, . . . , a transistor 32-n.
A predetermined voltage is applied to the gate G of the transistor 32 by a corresponding one of the plurality of DC power supplies 35 . Specifically, a predetermined voltage is applied to the gate G of the transistor 32-1 by a corresponding DC power supply 35-1 of the plurality of DC power supplies 35. Furthermore, a predetermined voltage is applied to the gate G of the transistor 32-2 by a corresponding DC power supply 35-2 among the plurality of DC power supplies 35. ..., and a predetermined voltage is applied to the gate G of the transistor 32-n by a corresponding DC power supply 35-n among the plurality of DC power supplies 35.

Here, it is preferable that the voltages applied to the gates G of each of the plurality of transistors 32 are different from each other. Specifically, the voltage applied to the gate G of the transistor 32-1 by the DC power supply 35-1, the voltage applied to the gate G of the transistor 32-2 by the DC power supply 35-2, ..., the DC power supply 35 -n is preferably different from the voltage applied to the gate G of the transistor 32-n.

A drain D of the transistor 32 is connected to a connection point between a resistor (first resistor) 37 and a corresponding one of the plurality of resistors (second resistors) 34. Specifically, the drain D of the transistor 32-1 is connected to the connection point between the resistor 37 and the corresponding resistor 34-1 among the plurality of resistors 34. Further, the drain D of the transistor 32-2 is connected to the connection point between the resistor 37 and the corresponding resistor 34-2 among the plurality of resistors 34. ..., and the drain D of the transistor 32-n is connected to the connection point between the resistor 37 and the corresponding resistor 34-n among the plurality of resistors 34.

The source S of the transistor 32 is connected to a connection point between a corresponding resistor 34 among the plurality of resistors (second resistors) 34 and a corresponding variable capacitance element 33 among the plurality of variable capacitance elements (second variable capacitance elements) 33. be done. Specifically, the source S of the transistor 32-1 is connected to a connection point between a corresponding resistor 34-1 among the plurality of resistors 34 and a corresponding variable capacitance element 33-1 among the plurality of variable capacitance elements 33. Ru. Further, the source S of the transistor 32-2 is connected to a connection point between a corresponding resistor 34-2 among the plurality of resistors 34 and a corresponding variable capacitance element 33-2 among the plurality of variable capacitance elements 33. ..., and the source S of the transistor 32-n is connected to the connection point between the corresponding resistor 34-n among the plurality of resistors 34 and the corresponding variable capacitance element 33-n among the plurality of variable capacitance elements 33. .

FIG. 8 is a graph showing an example of voltage-capacitance characteristics of the electronic circuit according to the third embodiment. The electrical characteristics of the electronic circuit 3A will be explained with reference to the figure. The figure shows changes in the capacitance of the terminal 38 with respect to the ground point when the output voltage of the DC power supply 36 is varied. Note that the graph shown in FIG. 8 is a graph showing the results obtained by circuit simulation.
Although the horizontal axis is shown in a range from 0 to 1, it may range from 0 [V] to about 3.3 [V], for example. Further, although the vertical axis is shown in a range from 0 to 1.2, it may be, for example, from 0 [pF] to 12 [pF].

Further, in the example shown in FIG. 8, an example will be described in which n=3, that is, an example in which three transistors 32, three variable capacitance elements 33, three resistors 34, and three DC power supplies 35 are provided.
As an example, the explanation will be made assuming that the voltage applied by the DC power supply 35-1 is 0.3, the voltage applied by the DC power supply 35-2 is 0.5, and the voltage applied by the DC power supply 35-3 is 0.75. .

In the range where the output voltage of the DC power supply 36 is lower than the output voltage of the DC power supply 35-1 (that is, the voltage range is from 0 to 0.3), the transistors 32-1, 32-2, and 32-3 are Both are on.
In a range where the output voltage of the DC power supply 36 is equal to or lower than the output voltage of the DC power supply 35-1, the transistors 32-1, 32-2, and 32-3 are all on, so the variable capacitance elements 33-1, A voltage is applied to both variable capacitance element 33-2 and variable capacitance element 33-3. Therefore, the capacitance of the electronic circuit 3A is the combined capacitance of the variable capacitance element 31, variable capacitance element 33-1, variable capacitance element 33-2, and variable capacitance element 33-3.

In the range where the output voltage of the DC power supply 36 exceeds the output voltage of the DC power supply 35-1 and is below the output voltage of the DC power supply 35-2 (that is, the voltage range is from 0.3 to 0.5), the transistor 32 -1 is off, and transistor 32-2 and transistor 32-3 are on.
In the range where the output voltage of the DC power supply 36 exceeds the output voltage of the DC power supply 35-1 and is lower than or equal to the output voltage of the DC power supply 35-2, the transistor 32-1 is off, and the transistors 32-2 and 32-3 are turned off. is on, voltage is applied to variable capacitance element 33-2 and variable capacitance element 33-3. In other words, variable capacitance element 33-1 is disconnected. Therefore, the capacitance of the electronic circuit 3A is the combined capacitance of the variable capacitance element 31, the variable capacitance element 33-2, and the variable capacitance element 33-3.

In the range in which the output voltage of the DC power supply 36 exceeds the output voltage of the DC power supply 35-2 and is below the output voltage of the DC power supply 35-3 (that is, in the range where the voltage is from 0.5 to 0.75), the transistor 32 -1 and transistor 32-2 are off and transistor 32-3 is on.
In the range where the output voltage of the DC power supply 36 exceeds the output voltage of the DC power supply 35-2 and is lower than or equal to the output voltage of the DC power supply 35-3, the transistors 32-1 and 32-2 are off, and the transistor 32-3 is off. is on, so a voltage is applied to the variable capacitance element 33-3. In other words, variable capacitance element 33-1 and variable capacitance element 33-2 are separated. Therefore, the capacitance of the electronic circuit 3A is the combined capacitance of the variable capacitance element 31 and the variable capacitance element 33-3.

In the range where the output voltage of the DC power supply 36 exceeds the output voltage of the DC power supply 35-3 (that is, the voltage range is from 0.75 to 1), the transistors 32-1, 32-2, and 32-3 Both are off.
In the range where the output voltage of the DC power supply 36 exceeds the output voltage of the DC power supply 35-3, the transistors 32-1, 32-2, and 32-3 are all off, so the variable capacitance elements 33-1, No voltage is applied to either the transistor 32-2 or the variable capacitance element 33-3. In other words, variable capacitance element 33-1, variable capacitance element 33-2, and variable capacitance element 33-3 are separated. Therefore, the capacitance of the electronic circuit 3A is that of the variable capacitance element 31.

That is, according to the present embodiment, the variable capacitance element 33 to which voltage is applied among the plurality of variable capacitance elements 33 changes according to the output voltage of the DC power supply 36. In other words, as the output voltage of the DC power supply 36 increases, the plurality of variable capacitance elements 33 are sequentially separated, and thus the combined capacitance changes. Therefore, the combined capacitance of the electronic circuit 3A changes depending on the output voltage of the DC power supply 36. Therefore, according to the electronic circuit 3A, the capacitance variable range can be expanded.

[Summary of third embodiment]
As described above, the electronic circuit 3A according to the present embodiment includes a plurality of transistors 32, a variable capacitance element 33, a resistor 34, and a DC power supply 35 in addition to the variable capacitance element 31, the DC power supply 36, and the resistor 37. The conduction state of the plurality of transistors 32 is switched according to the output voltage of the DC power supply 36.
That is, according to the present embodiment, the variable capacitance element 33 to which voltage is applied among the plurality of variable capacitance elements 33 changes according to the output voltage of the DC power supply 36. In other words, as the output voltage of the DC power supply 36 increases, the variable capacitance element 33 is disconnected, so the combined capacitance changes. Therefore, the combined capacitance of the electronic circuit 3A changes depending on the output voltage of the DC power supply 36. Therefore, according to the electronic circuit 3A, the capacitance variable range is widened and a large variable capacitance ratio can be obtained.

Further, according to the embodiment described above, the voltages applied to the gates G of each of the plurality of transistors 32 are different from each other. Therefore, as the output voltage of the DC power supply 36 increases, the plurality of variable capacitance elements 33 are sequentially disconnected. Therefore, the combined capacitance of the electronic circuit 3A changes depending on the output voltage of the DC power supply 36. Therefore, according to the electronic circuit 3A, a large variable capacitance ratio can be obtained.

[Fourth embodiment]
A fourth embodiment will be described with reference to FIG. A piezoelectric oscillator 5 according to the fourth embodiment is obtained by applying the electronic circuit 3 to the piezoelectric oscillator 1. Specifically, the piezoelectric oscillator 5 is different from the piezoelectric oscillator 1 in that it includes a first variable capacitor section 51 and a second variable capacitor section 52 instead of the first variable capacitor 18 and the second variable capacitor 19. is different. In the description of the piezoelectric oscillator 5, the description of the same configuration as the piezoelectric oscillator 1 may be omitted.

FIG. 9 is a circuit diagram showing an example of a circuit configuration of a piezoelectric oscillator according to the second embodiment. An example of the circuit configuration of the piezoelectric oscillator 5 will be described with reference to the same figure.
The piezoelectric oscillator 5 includes a piezoelectric vibrator 11, a first variable capacitance element section 51, a second variable capacitance element section 52, a DC power supply (DC voltage source) 12, a transistor 21, a first resistor 13, and a first variable capacitance element section 51. 2 resistor 22 and a third resistor 23.

The capacitance of the first variable capacitance element section 51 changes depending on the voltage applied to the first terminal 111 of the piezoelectric vibrator 11 by the DC power supply 12 .
The first variable capacitance element section 51 includes a variable capacitance element (first variable capacitance element) 511, a transistor (second transistor) 512, a variable capacitance element (second variable capacitance element) 513, and a resistor (fourth resistance). 514 and a DC power supply 515.
A cathode K of the variable capacitance element 511 is connected to the first terminal 111 of the piezoelectric vibrator 11 . Anode A of variable capacitance element 511 is grounded.
A cathode K of the variable capacitance element 513 is connected to the first terminal 111 of the piezoelectric vibrator 11 via a resistor 514. Anode A of variable capacitance element 513 is grounded.
A predetermined voltage is applied to the gate G of the transistor 512 by a DC power supply 515. A drain D of the transistor 512 is connected to the first terminal 111 of the piezoelectric vibrator 11 . A source S of the transistor 512 is connected to a connection point between the resistor 514 and the variable capacitance element 513.
One end of the resistor 514 is connected to the first terminal 111 of the piezoelectric vibrator 11, and the other end is connected to a connection point between the cathode K of the variable capacitance element 513 and the source S of the transistor 512.
The DC power supply 515 applies a predetermined voltage to the gate G of the transistor 512.

The capacitance of the second variable capacitance element section 52 changes depending on the voltage applied to the second terminal 112 of the piezoelectric vibrator 11 by the DC power supply 12.
The second variable capacitance element section 52 includes a variable capacitance element (third variable capacitance element) 521, a transistor (third transistor) 522, a variable capacitance element (fourth variable capacitance element) 523, and a resistor (fifth resistor). 524 and a DC power supply 525.
A cathode K of the variable capacitance element 521 is connected to the second terminal 112 of the piezoelectric vibrator 11. Anode A of variable capacitance element 521 is grounded.
A cathode K of the variable capacitance element 513 is connected to the second terminal 112 of the piezoelectric vibrator 11 via a resistor 524. Anode A of variable capacitance element 523 is grounded.
A predetermined voltage is applied to the gate G of the transistor 522 by a DC power supply 525. A drain D of the transistor 522 is connected to the second terminal 112 of the piezoelectric vibrator 11. A source S of the transistor 522 is connected to a connection point between the resistor 524 and the variable capacitance element 523.
One end of the resistor 524 is connected to the second terminal 112 of the piezoelectric vibrator 11, and the other end is connected to a connection point between the cathode K of the variable capacitance element 523 and the source S of the transistor 522.
The DC power supply 525 applies a predetermined voltage to the gate G of the transistor 522.

[Summary of the fourth embodiment]
As explained above, in the piezoelectric oscillator 5 according to the present embodiment, the first variable capacitance element section 51 and the second variable capacitance element 19 are replaced with the first variable capacitance element 18 and the second variable capacitance element 19 in the configuration of the piezoelectric oscillator 1. A capacitive element section 52 is provided. Therefore, according to the piezoelectric oscillator 5, by providing the transistor 21, different voltages can be applied to the first terminal 111 and the second terminal 112 of the piezoelectric vibrator 11, respectively, and a linear voltage-capacitance characteristic can be obtained. Further, according to the piezoelectric oscillator 5, by including the first variable capacitance element section 51 and the second variable capacitance element section 52, the capacitance variable range is widened and a large variable capacitance ratio can be obtained.

Although the mode for implementing the present invention has been described above using embodiments, the present invention is not limited to these embodiments in any way, and various modifications and substitutions can be made without departing from the spirit of the present invention. can be added.

DESCRIPTION OF SYMBOLS 1... Piezoelectric oscillator, 11... Piezoelectric vibrator, 111... First terminal, 112... Second terminal, 12... DC power supply, 13... First resistor, 14... Inverter, 141... Input terminal, 142... Output terminal, 15... Resistor, 16... Capacitor, 17... Capacitor, 18... First variable capacitance element, 19... Second variable capacitance element, 21... Transistor, 22... Second resistor, 23... Third resistor, 24... Power supply, P1, P2, P3... Connection point, 3... Electronic circuit, 31... Variable capacitance element, 32... Transistor, 33... Variable capacitance element, 34... Resistor, 35... DC power supply, 36... DC power supply, 37... Resistor, 38... Terminal, 5... Piezoelectric oscillator, 51... First variable capacitance element section, 511... Variable capacitance element, 512... Transistor, 513... Variable capacitance element, 514... Resistor, 515... DC power supply, 52... Second variable capacitance element section, 521... Variable capacitance Element, 522...Transistor, 523...Variable capacitance element, 524...Resistor, 525...DC power supply

Claims (8)

a DC voltage source;
a first variable capacitance element whose cathode is connected to the DC voltage source via a first resistor and whose anode is grounded;
a second variable capacitance element whose cathode is connected to the DC voltage source via the first resistor and second resistor and whose anode is grounded;
a transistor having a gate to which a predetermined voltage is applied, a drain connected to a connection point between the first resistor and the second resistor, and a source connected to a connection point between the second resistor and the second variable capacitance element; An electronic circuit comprising and . The electronic circuit according to claim 1, wherein the transistor is an n-channel MOS-FET. The electronic circuit according to claim 1 or 2, wherein the first variable capacitance element and the second variable capacitance element are both variable capacitance diodes. The electronic circuit according to any one of claims 1 to 3, wherein the first variable capacitance element and the second variable capacitance element have mutually equivalent electrical characteristics. The electronic circuit according to any one of claims 1 to 4, wherein the voltage range applied by the DC voltage source is twice or more of a predetermined voltage applied to the gate of the transistor. a DC voltage source;
a first variable capacitance element whose cathode is connected to the DC voltage source via a first resistor and whose anode is grounded;
a plurality of second variable capacitance elements whose cathodes are connected to the DC voltage source via the first resistor and the corresponding second resistor among the plurality of second resistors, and whose anodes are grounded;
A predetermined voltage is applied to a gate, a drain is connected to a connection point between the first resistor and a corresponding one of the plurality of second resistors, and a source is connected to a corresponding one of the plurality of second resistors. An electronic circuit comprising: a plurality of transistors connected to a connection point between the second resistor and a corresponding one of the plurality of second variable capacitance elements. The electronic circuit according to claim 5, wherein voltages applied to the gates of each of the plurality of transistors are different from each other. a piezoelectric vibrator including a first terminal and a second terminal;
a first variable capacitance element portion whose capacitance changes depending on the voltage applied to the first terminal;
a second variable capacitance element portion whose capacitance changes depending on the voltage applied to the second terminal;
a DC voltage source;
a first resistor having one end connected to the first terminal and the other end connected to the DC voltage source;
a transistor having a gate connected to the DC voltage source, a drain connected to a power source different from the DC voltage source, and a source connected to a second resistor;
a second resistor whose one end is connected to the source of the transistor and whose other end is grounded;
a third resistor, one end of which is connected to a connection point between the source of the transistor and the second resistor, and the other end of which is connected to the second terminal;
The first variable capacitance element section is
a first variable capacitance element whose cathode is connected to the first terminal and whose anode is grounded;
a second variable capacitance element whose cathode is connected to the first terminal via a fourth resistor and whose anode is grounded;
a second transistor having a gate applied with a predetermined voltage, a drain connected to the first terminal, and a source connected to a connection point between the fourth resistor and the second variable capacitance element;
The second variable capacitance element section is
a third variable capacitance element whose cathode is connected to the second terminal and whose anode is grounded;
a fourth variable capacitance element whose cathode is connected to the second terminal via a fifth resistor and whose anode is grounded;
A piezoelectric oscillator comprising: a third transistor having a gate applied with a predetermined voltage, a drain connected to the second terminal, and a source connected to a connection point between the fifth resistor and the fourth variable capacitance element.

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