Piezoelectric oscillator

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

[Technical Field]

[0001] The present invention , pressure This relates to an electric oscillator. [Background technology]

[0002] Conventionally, a variable capacitance diode (varicap) as described in Patent Document 1, for example, has been known as a variable capacitance element. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-183813 Summary of the Invention [Problem to be solved by the invention]

[0004] Such variable capacitance elements are known to have a small capacitance variable ratio. For example, if a piezoelectric oscillator is configured using a variable capacitance element with a small capacitance variable ratio, it becomes difficult to obtain an output signal with a wide frequency band. In other words, if a piezoelectric oscillator is configured using a variable capacitance element with a small capacitance variable ratio, it becomes difficult to obtain the desired voltage-frequency characteristics.

[0005] The present invention has been made in view of the above-mentioned circumstances, and aims to provide an electronic circuit that can obtain desired voltage-capacitance characteristics by adding peripheral circuits, even when a variable capacitance element with a small capacitance variable ratio is used. [Means for solving the problem]

[0006] According to one aspect of the present invention The piezoelectric oscillator includes a piezoelectric vibrator having a first terminal and a second terminal, a first variable capacitance element unit whose capacitance changes in response to a voltage applied to the first terminal, a second variable capacitance element unit whose capacitance changes in response to a 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 supply different from the DC voltage source, and a source connected to the second resistor, a second resistor having one end connected to the source of the transistor and the other end grounded, and a third resistor having one end connected to a connection point between the source of the transistor and the second resistor and the other end connected to the second terminal, and the first variable capacitance element unit has a cathode connected to the first terminal. a second variable capacitance element having a cathode connected to the first terminal via a fourth resistor and an anode grounded; and a second transistor having a gate to which a predetermined voltage is applied, 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, wherein the second variable capacitance element section comprises a third variable capacitance element having a cathode connected to the second terminal and an anode grounded; a fourth variable capacitance element having a cathode connected to the second terminal via a fifth resistor and an anode grounded; and a third transistor having a gate to which a predetermined voltage is applied, 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. .

[0007] According to one aspect of the present invention Piezoelectric oscillator In the above, the transistor is an n-channel MOS-FET.

[0008] According to one aspect of the present invention Piezoelectric oscillator In the first variable capacitance element 、 the second variable capacitance element , the third variable capacitance element, and the fourth variable capacitance element are all variable capacitance diodes.

[0010] According to one aspect of the present invention Piezoelectric oscillator In the device, the range of the voltage applied by the DC voltage source is at least twice the predetermined voltage applied to the gate of the transistor. [Effects of the Invention]

[0014] According to the present invention, even when a variable capacitance element with a small capacitance variable ratio is used, the desired voltage-capacitance characteristics can be obtained by adding a peripheral circuit. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a circuit diagram showing an example of a circuit configuration of a piezoelectric oscillator according to a first embodiment. [Figure 2] 4 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. [Figure 3] 4 is a graph showing an example of voltage-frequency characteristics at both ends of a piezoelectric vibrator of the piezoelectric oscillator according to the first embodiment. [Figure 4] 4 is a graph showing an example of voltage-frequency characteristics of the piezoelectric oscillator according to the first embodiment. [Figure 5] FIG. 10 is a circuit diagram showing an example of a circuit configuration of an electronic circuit according to a second embodiment. [Figure 6] 10 is a graph showing an example of voltage-capacity characteristics of the electronic circuit according to the second embodiment. [Figure 7] FIG. 10 is a circuit diagram showing an example of a circuit configuration of an electronic circuit according to a third embodiment. [Figure 8] 10 is a graph showing an example of voltage-capacity characteristics of an electronic circuit according to a third embodiment. [Figure 9]FIG. 10 is a circuit diagram showing an example of a circuit configuration of a piezoelectric oscillator according to a second embodiment. [Figure 10] FIG. 1 is a circuit diagram showing an example of a circuit configuration of a piezoelectric oscillator according to a conventional technique. [Figure 11] 10 is a graph showing an example of voltage-capacitance characteristics of a variable capacitance element included in a piezoelectric oscillator according to a conventional technique. [Figure 12] 1 is a graph showing an example of voltage-frequency characteristics of a piezoelectric oscillator according to a conventional technique. DETAILED DESCRIPTION OF THE INVENTION

[0016] [Prior art] First, a conventional piezoelectric oscillator 9 will be described with reference to Fig. 10 to Fig. 12. The conventional piezoelectric oscillator 9 outputs a high-frequency signal according to an applied voltage. As an example, the piezoelectric oscillator 9 may be a VCXO (Voltage Controlled Crystal Oscillator) that controls voltage using a variable capacitance element (a variable capacitance diode or a varicap).

[0017] 10 is a circuit diagram showing an example of the circuit configuration of a conventional piezoelectric oscillator 9. The circuit configuration of the piezoelectric oscillator 9 will be described with reference to this diagram. 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 capacitance element 98 , and a variable capacitance element 99 .

[0018] The piezoelectric vibrator 91 oscillates when a predetermined voltage is applied. The piezoelectric vibrator 91 is, for example, a quartz crystal vibrator. The DC power supply 92 is a DC voltage source that outputs DC power. The DC power supply 92 applies a predetermined voltage across the piezoelectric vibrator 91. The DC power supply 92 applies a voltage of, for example, 0 [V (volts)] to 3.3 [V]. The resistor 931 is connected between the positive terminal of the DC power supply 92 and one end of the piezoelectric vibrator 91, and the resistor 932 is connected between the positive terminal of the DC power supply 92 and the other end of the piezoelectric vibrator 91. The inverter 94 is connected to one end of the piezoelectric vibrator 91 via a capacitor 96 and to the other end of the piezoelectric vibrator 91 via a capacitor 97. The resistor 95 is a feedback resistor connected between the input terminal and output terminal of the inverter 94. The cathode K of the variable capacitance element 98 is connected to the connection point of the piezoelectric vibrator 91, the resistor 932, and the capacitor 96. A cathode K of the variable capacitance element 99 is connected to the connection point of the piezoelectric vibrator 91, the resistor 931, and the capacitor 97. An anode A of the variable capacitance element 98 and the variable capacitance element 99 is grounded.

[0019] 11 is a graph showing an example of the voltage-capacitance characteristic of a variable capacitance element included in a piezoelectric oscillator according to the prior art. An example of the voltage-capacitance characteristic of a variable capacitance element included in a piezoelectric oscillator 9 will be described with reference to the same figure. The figure shows an example of the voltage-capacitance characteristic of a variable capacitance element 98 or a 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, when there is no need to distinguish between the variable capacitance element 98 and the variable capacitance element 99, they may be simply referred to as variable capacitance elements.

[0020] 11 shows the voltage-capacitance characteristics as curves C61 and C62 when two different variable capacitance elements are used in piezoelectric oscillator 9. The variable capacitance element having the characteristics shown by curve C61 and the variable capacitance element having the characteristics shown by curve C62 have different impurity concentration distributions at the pn junction surface. Specifically, in the voltage characteristic C∝V^-n of the junction capacitance, curve C61 shows an example of the characteristics of a variable capacitance element using an abrupt junction where n=1 / 2, and curve C62 shows an example of the characteristics of a variable capacitance element using a hyperabrupt junction where n=2.

[0021] As shown by curve C61, a varactor using an abrupt junction changes capacitance rapidly in a low-voltage region and the change in capacitance becomes smaller in a high-voltage region (in the following description, the decrease in the amount of change is also referred to as "reaching a plateau"). That is, a varactor using an abrupt junction changes capacitance in response to a change in voltage differently depending on the voltage. In other words, a varactor using an abrupt junction does not have a linear voltage-capacitance characteristic.

[0022] On the other hand, as shown by curve C62, a varactor using a hyperabrupt junction has a substantially constant change in capacitance whether the voltage is low or high. Here, the range in which the change in capacitance is substantially constant refers to a range in which the change in capacitance with respect to a change in voltage does not change depending on the voltage and can be considered constant. In other words, a varactor using a hyperabrupt junction has a linear voltage-capacitance characteristic.

[0023] The horizontal axis shown in Fig. 11 may be, for example, from 0 [V] to 3.3 [V], and the vertical axis shown in Fig. 11 may be, for example, from 0 [pF (picofarad)] to 10 [pF].

[0024] 12 is a graph showing an example of the voltage-frequency characteristics of a piezoelectric oscillator according to the prior art. An example of the voltage-frequency characteristics of a piezoelectric oscillator 9 according to the prior art will be described with reference to the same figure. The figure shows an example of the voltage-frequency characteristics 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. The oscillation frequency is f=1 / 2π√LC∝1 / √V^-n. In the figure, the voltage-capacitance characteristics of a variable capacitance element using an abrupt junction where n=1 / 2 are shown as curve C71, and the voltage-capacitance characteristics of a variable capacitance element using a hyperabrupt junction where n=2 are shown as curve C62.

[0025] As shown by curve C71, a varactor using an abrupt junction changes frequency rapidly in the low voltage range and changes less in frequency in the high voltage range. That is, a varactor using an abrupt junction changes frequency by a different amount depending on the voltage. In other words, a varactor using an abrupt junction does not have a linear voltage-frequency characteristic.

[0026] On the other hand, as shown by curve C72, a varactor using a hyperabrupt junction has a substantially constant amount of frequency change whether the voltage is low or high. Here, the range in which the amount of frequency change is substantially constant refers to a range in which the amount of frequency change relative to the amount of voltage change does not change depending on the voltage and can be considered constant. In other words, a varactor using a hyperabrupt junction has a linear voltage-frequency characteristic.

[0027] [First embodiment] The first embodiment will be described with reference to FIGS. The first embodiment aims to provide a piezoelectric oscillator 1 that can obtain desired voltage-frequency characteristics even when the piezoelectric oscillator is configured using a variable capacitance element that uses an abrupt junction having the characteristics shown by curve C61 or curve C71. In other words, the first embodiment aims to provide a piezoelectric oscillator that can obtain desired voltage-frequency characteristics even when a variable capacitance element with poor electrical characteristics is used.

[0028] 1 is a circuit diagram showing an example of the circuit configuration of a piezoelectric oscillator according to a first embodiment. With reference to the diagram, an example of the circuit configuration of the piezoelectric oscillator 1 will be described. 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.

[0029] Specifically, the piezoelectric oscillator 1 may be a VCXO that performs voltage control using a variable capacitance element. In the following description, the piezoelectric oscillator 1 is described as a VCXO, but 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 Crystal Oscillator).

[0030] 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, a capacitor 17, a first variable capacitance element 18, and a second variable capacitance element 19.

[0031] The piezoelectric oscillator 1 oscillates when a voltage is applied. The piezoelectric oscillator 1 is, for example, a quartz crystal resonator. The piezoelectric resonator 11 includes a first terminal 111 and a second terminal 112. The first terminal 111 is also referred to as XT, and the second terminal 112 is also referred to as XTN.

[0032] 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 that can output a constant voltage regardless of the load connected to it. The DC power supply 12 has a positive terminal 121 and a negative terminal 122, and the negative terminal 122 is grounded.

[0033] One end of the first resistor 13 is connected to the 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 is connected to the positive terminal 121 of the DC power supply 12.

[0034] First variable capacitance element 18 may be a variable capacitance diode (varicap). First variable capacitance element 18 has an anode A and a cathode K. Cathode K of first variable capacitance element 18 is connected to first terminal 111 of piezoelectric vibrator 11 at connection point P1. Anode A of first variable capacitance element 18 is grounded.

[0035] Second variable capacitance element 19 may be a variable capacitance diode (varicap). Second variable capacitance element 19 has an anode A and a cathode K. Cathode K of second variable capacitance element 19 is connected to second terminal 112 of piezoelectric vibrator 11 at connection point P3. Anode A of second variable capacitance element 19 is grounded.

[0036] First variable capacitance element 18 and second variable capacitance element 19 may have the same structure and therefore may have the same electrical characteristics, such as voltage-capacitance characteristics. First variable capacitance element 18 and second variable capacitance element 19 may have different structures and therefore different electrical characteristics.

[0037] Transistor 21 controls the voltage applied to second variable capacitance element 19 in accordance with the output voltage of DC power supply 12. Transistor 21 may be, for example, an n-channel MOS-FET (Metal-Oxide-Semiconductor Field-Effect Transistor). Transistor 21 has a gate G connected to a connection point between the positive terminal of DC power supply 12 and first resistor 13, a drain D connected to power supply 24, and a source S connected to a connection point between second resistor 22 and third resistor 23 (hereinafter referred to as connection point P2). Power supply 24 may be a power supply different from DC power supply 12.

[0038] One end of the second resistor 22 is connected to the source S of the transistor 21, and the other end is grounded. The third resistor 23 has one end connected to the connection point P2 between the source S of the transistor 21 and the second resistor 22, and the other end connected to the connection point between 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).

[0039] Inverter 14 has input terminal 141 and output terminal 142. Input terminal 141 is connected to cathode K of first variable capacitance element 18 via capacitor 16. Output terminal 142 is connected to cathode K of second variable capacitance element 19 via capacitor 17. Resistor 15 is a feedback resistor connected in parallel with inverter 14 (i.e., one end is connected to input terminal 141 and the other end is connected to output terminal 142).

[0040] Next, the electrical characteristics of the piezoelectric oscillator 1 will be described with reference to Figures 2 to 4. The graphs shown in Figures 2 to 4 are graphs showing the results obtained by circuit simulation.

[0041] 2 is a graph showing an example of the voltage-capacitance characteristics of the variable capacitance elements included in the piezoelectric oscillator according to the first embodiment. With reference to the same figure, 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. In the following description, when there is no need to distinguish between the first variable capacitance element 18 and the second variable capacitance element 19, they may be simply referred to as variable capacitance elements.

[0042] 2 is shown in a range from 0 to 1, but may be, for example, from 0 [V] to 3.3 [V]. Also, the vertical axis in FIG. 2 is shown in a range from 0 to 2, but may be, for example, from 0 [pF] to 10 [pF].

[0043] Curve C21 shows the voltage-capacitance characteristics for first variable capacitance element 18. Curve C22 shows the voltage-capacitance characteristics for second variable capacitance element 19. Curve C23 shows the voltage-capacitance characteristics for the combined capacitance of first variable capacitance element 18 and second variable capacitance element 19.

[0044] The characteristics shown in the figure will be described by taking an example in which the operating threshold voltage VTN (that is, the gate threshold voltage VGS(TH)) of the transistor 21 is 0.5. Moreover, first variable capacitance element 18 and second variable capacitance element 19 are both variable capacitance elements using abrupt junctions.

[0045] The output voltage of DC power supply 12 is applied to first variable capacitance element 18 via first resistor 13. Therefore, the voltage-capacitance characteristic of first variable capacitance element 18 shown by curve C21 has the characteristic of a variable capacitance element using an abrupt junction. That is, the voltage-capacitance characteristic of first variable capacitance element 18 exhibits a rapid change in capacitance in the low-voltage region and a small change in capacitance in the high-voltage region. In other words, curve C21 is not linear.

[0046] The voltage of power supply 24 is applied to second variable capacitance element 19 via transistor 21 and third resistor 23. When the output voltage of DC power supply 12 is in a range equal to or less than the operating threshold voltage VTN of transistor 21 (for example, from 0 to 0.5), transistor 21 is off. Cathode K of second variable capacitance element 19 is grounded via second resistor 22 and third resistor 23. Therefore, when the output voltage of DC power supply 12 is in a range equal to or less than the operating threshold voltage VTN of transistor 21, the capacitance of second variable capacitance element 19 becomes a maximum value (for example, 2.0).

[0047] When the output voltage of DC power supply 12 exceeds the operating threshold voltage VTN of transistor 21, transistor 21 turns on, and the voltage of power supply 24 is applied to cathode K of second variable capacitance element 19 via third resistor 23. Therefore, in the range where the output voltage of DC power supply 12 exceeds the operating threshold voltage VTN of transistor 21, the capacitance of second variable capacitance element 19 changes according to the output voltage of DC power supply 12.

[0048] The combined capacitance of first variable capacitance element 18 and second variable capacitance element 19 is a combination of the capacitance of first variable capacitance element 18, which changes rapidly in the range where the output voltage of DC power supply 12 is equal to or lower than the operating threshold voltage VTN of transistor 21 (i.e., the low voltage region), and the capacitance of second variable capacitance element 19, which has a large, constant capacitance, as shown in curve C23.

[0049] Furthermore, in the range where the output voltage of DC power supply 12 exceeds the operating threshold voltage VTN of transistor 21 (i.e., in the high voltage region), the capacitance of first variable capacitance element 18, whose change in capacitance has plateaued, and the capacitance of second variable capacitance element 19, whose capacitance changes rapidly, are combined.

[0050] Therefore, the combined capacitance of first variable capacitance element 18 and second variable capacitance element 19 changes even when the output voltage of DC power supply 12 is equal to or lower than the operating threshold voltage VTN of transistor 21, and does not plateau even when the output voltage of DC power supply 12 exceeds the operating threshold voltage VTN of transistor 21. Therefore, the combined capacitance of first variable capacitance element 18 and second variable capacitance element 19 has a voltage-capacity characteristic that is nearly linear.

[0051] The range of 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 voltage applied by the DC power supply 12 may be twice or more the operating threshold voltage VTN of the transistor 21.

[0052] 3 is a graph showing an example of the voltage-frequency characteristics at both ends of the piezoelectric vibrator of the piezoelectric oscillator according to the first embodiment. An example of the 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. Curve C31 shows the frequency characteristics of the voltage VXT at the first terminal 111. Curve C32 shows the frequency characteristics of the voltage VXTN at the second terminal 112.

[0053] 3, the horizontal axis ranges from 0 to 1, but may be, for example, from 0 [V] to 3.3 [V]. Also, the vertical axis ranges from 0 to 1, but may be, for example, from 0 [MHz (megahertz)] to 8 [MHz].

[0054] As shown by curve C31, as the voltage VXT at the first terminal 111 increases, the frequency also increases proportionally. On the other hand, as shown by curve C32, the voltage VXTN at the second terminal 112 is 0 when the voltage is in the range of 0 to 0.3, and once the voltage exceeds 0.3, the frequency also increases proportionally. In other words, the voltage VXTN rises with a delay from the voltage VXT.

[0055] In other words, the output voltage of the DC power supply 12 is applied directly to the first terminal 111 via the first resistor 13, so when the output voltage of the DC power supply 12 increases, the voltage VXT also increases accordingly. On the other hand, no voltage is applied to the second terminal 112 until the transistor 21 is turned on. Therefore, the voltage VXTN rises later than the voltage VXT by the amount of the operating threshold voltage VTN of the transistor 21.

[0056] 4 is a graph showing an example of the 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 described with reference to the same figure. Curve C4 shows the voltage-frequency characteristics of the piezoelectric oscillator 1.

[0057] The horizontal axis in Fig. 4 ranges from 0 to 1, but may be, for example, from 0 [V] to 3.3 [V]. The vertical axis in Fig. 4 ranges from 1 to 2, but may be, for example, from 8 [MHz] to 16 [MHz].

[0058] As shown by 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 operation threshold voltage VTN of the transistor 21 (i.e., in the low-voltage range), and also changes sufficiently in the range where the output voltage exceeds the operation threshold voltage VTN (i.e., in the high-voltage range). That is, the voltage-frequency characteristics of the piezoelectric oscillator 1 show that the frequency changes even in the low-voltage range, and the amount of frequency change does not plateau even in the high-voltage range.

[0059] [Summary of the first embodiment] As described above, piezoelectric oscillator 1 according to this embodiment includes piezoelectric resonator 11, first variable capacitance element 18, second variable capacitance element 19, DC power supply (DC voltage source) 12, first resistor 13, transistor 21, second resistor 22, and third resistor 23. By including transistor 21, piezoelectric oscillator 1 differentiates the voltage applied to first variable capacitance element 18 from the voltage applied to second variable capacitance element 19. Specifically, by including transistor 21, piezoelectric oscillator 1 applies a voltage to second variable capacitance element 19 later than first variable capacitance element 18. That is, piezoelectric oscillator 1 ensures a change in capacitance by applying a voltage to first variable capacitance element 18 in a low-voltage range, and ensures a change in capacitance by starting to apply a voltage to second variable capacitance element 19 in a high-voltage range. Therefore, even if the voltage-capacitance characteristics of the first variable capacitance element 18 reach a plateau in a high voltage region, the piezoelectric oscillator 1 can vary the combined capacitance of the first variable capacitance element 18 and the second variable capacitance element 19 by applying a voltage to the second variable capacitance element 19 via the transistor 21.

[0060] In other words, the piezoelectric oscillator 1 can obtain linear voltage-frequency characteristics even when using the first variable capacitance element 18 and the second variable capacitance element 19, which are abrupt junctions in which the voltage-capacity relationship is not linear. Therefore, according to this embodiment, even when a piezoelectric oscillator is configured using a variable capacitance element with an abrupt junction whose voltage-capacitance characteristic is not linear, it is possible to obtain a desired voltage-frequency characteristic.

[0061] Furthermore, according to the above-described embodiment, the transistor 21 is an n-channel MOS-FET. Therefore, the piezoelectric oscillator 1 does not suffer from large power loss as in the case where a bipolar transistor is used, and the time delay is small, so that the desired voltage-frequency characteristics can be suitably obtained.

[0062] Furthermore, according to the above-described embodiment, first variable capacitance element 18 and second variable capacitance element 19 are both variable capacitance diodes (varicaps). Therefore, according to this embodiment, it is possible to obtain desired voltage-frequency characteristics by using a variable capacitance diode with an abrupt junction whose voltage-capacity characteristics are not linear, without having to spend a lot of money to develop a variable capacitance diode with a hyperabrupt junction.

[0063] Furthermore, according to the above-described embodiment, first variable capacitance element 18 and second variable capacitance element 19 have the same structure and therefore have equivalent electrical characteristics. Therefore, according to this embodiment, the layout of the structure can be easily performed.

[0064] Furthermore, according to the above-described embodiment, the range of voltage applied by DC power supply 12 is at least twice the operating threshold voltage VTN of transistor 21. In other words, DC power supply 12 can vary the voltage to at least twice the operating threshold voltage VTN of transistor 21. Therefore, according to this embodiment, the capacitance of second variable capacitance element 19 is combined at a voltage before the change in capacitance of first variable capacitance element 18 reaches its peak. Therefore, according to piezoelectric oscillator 1, a linear voltage-capacitance characteristic can be obtained.

[0065] In the above-described embodiment, the voltage VXTN rises later than the voltage VXT, but the voltage VXT may rise later than the voltage VXTN. In this case, the transistor 21, the second resistor 22, and the third resistor 23 may be replaced with the first resistor 13. By replacing the configuration of transistor 21, second resistor 22, and third resistor 23 with first resistor 13, the capacitance of second variable capacitance element 19 changes in the range where the output voltage of DC power supply 12 is equal to or less than the operating threshold voltage VTN of transistor 21, and the variable capacitance of first variable capacitance element 18 is combined in the range where the output voltage of DC power supply 12 exceeds the operating threshold voltage VTN of transistor 21, thereby making it possible to obtain linear voltage-capacitance characteristics and, ultimately, voltage-frequency characteristics.

[0066] [Second embodiment] First, the problem to be solved by the electronic circuit 3 according to the second embodiment will be described. The variable capacitance element described with reference to FIG. 11 has a small capacitance variable ratio, with a capacitance variable range of approximately 1.0 to 0.3 when the voltage is varied from 0 to 1, whether it is an abrupt junction or a hyperabrupt junction. When a variable capacitance element with a small capacitance variable ratio is used, the capacitance cannot be reduced below a predetermined value even if the voltage applied to the variable capacitance element is increased, and the output frequency of the piezoelectric oscillator 1 cannot be increased above a predetermined frequency. This characteristic of the capacitance variable range reaching a plateau is particularly noticeable in the case of an abrupt junction. The electronic circuit 3 according to the second embodiment aims to obtain a sufficient capacitance variable ratio by adding a predetermined peripheral circuit to the variable capacitance element, even when a variable capacitance element with a small capacitance variable ratio is used.

[0067] An electronic circuit 3 according to a second embodiment will be described with reference to FIGS. 5 is a circuit diagram showing an example of the circuit configuration of the electronic circuit according to the second embodiment. With reference to this diagram, an example of the circuit configuration of the electronic circuit 3 will be described. 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 resistor) 34, a DC power supply 35, a DC power supply (DC voltage source) 36, a resistor (first resistor) 37, and a terminal 38.

[0068] 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 that can output a constant voltage regardless of the load connected to it. The DC power supply 36 has a positive terminal 361 and a negative terminal 362. The positive terminal 361 is connected to a resistor 37, and the negative terminal 362 is grounded. One end of the resistor 37 is connected to the positive terminal 361 of the DC power supply 36 , and the other end is connected to the cathode K of the variable capacitance element 31 .

[0069] 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. An anode A of the variable capacitance element 31 is grounded. A cathode K of the variable capacitance element 33 is connected to a positive terminal 361 of the DC power supply 36 via resistors 37 and 34. The cathode K of the variable capacitance element 33 is also connected to a source S of the transistor 32. An anode A of the variable capacitance element 33 is grounded. The variable capacitance element 31 and the variable capacitance element 33 may both be variable capacitance diodes (varicaps).

[0070] The variable capacitance element 31 and the variable capacitance element 33 may have the same structure and therefore may have the same electrical characteristics, such as voltage-capacitance characteristics.

[0071] One end of resistor 34 is connected to the connection point between resistor 37 and variable capacitance element 31, and the other end is connected to the connection point between source S of transistor 32 and cathode K of variable capacitance element 33. It is preferable that the resistance value of resistor 34 is sufficiently larger than the resistance value of resistor 37.

[0072] The transistor 32 is an n-channel 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. The source S of the transistor 32 is connected to the 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.

[0073] 6 is a graph showing an example of the voltage-capacitance characteristics of the electronic circuit according to the second embodiment. The electrical characteristics of the electronic circuit 3 will be described with reference to the same figure. The same figure shows the change in capacitance of the terminal 38 with respect to the ground point when the output voltage of the DC power supply 36 is varied. The graph shown in FIG. 6 is a graph showing the results obtained by circuit simulation. The horizontal axis is shown in the range of 0 to 1, but may be, for example, 0 [V] to 3.3 [V]. The vertical axis is shown in the range of 0 to 1.2, but may be, for example, 0 [pF] to 12 [pF]. In the example shown in the figure, an example in which the operating threshold voltage VTN of the transistor 32 is 0.5 will be described.

[0074] When the output voltage of DC power supply 36 is equal to or less than the output voltage of DC power supply 35 (i.e., the voltage range is between 0 and 0.5), transistor 32 is on. When the output voltage of DC power supply 36 is greater than the output voltage of DC power supply 35 (i.e., the voltage range is between 0.5 and 1), transistor 32 is off.

[0075] In the range where the output voltage of DC power supply 36 is equal to or lower than the output voltage of DC power supply 35, transistor 32 is on, and therefore the output voltage of DC power supply 36 is applied to variable capacitance element 33 via resistor 37. Therefore, the capacitance of electronic circuit 3 is the combined capacitance of variable capacitance element 31 and variable capacitance element 33.

[0076] Here, the resistance value of resistor 34 is large enough not to affect the voltage-capacitance characteristics of variable capacitance element 33. In the range where the output voltage of DC power supply 36 exceeds the output voltage of DC power supply 35, transistor 32 is off, and therefore the voltage-capacitance characteristics of variable capacitance element 33 do not change. Therefore, the capacitance of electronic circuit 3 depends on the capacitance of variable capacitance element 31.

[0077] In other words, in the range where the output voltage of DC power supply 36 exceeds the output voltage of DC power supply 35, the amount of change in the combined capacitance of variable capacitance element 31 and variable capacitance element 33 reaches a plateau, and therefore, by disconnecting variable capacitance element 33, electronic circuit 3 makes the capacitance of variable capacitance element 31 dominant and ensures a sufficient amount of change in capacitance.

[0078] The range of the voltage applied by the DC power supply 36 is larger than the predetermined voltage applied by the DC power supply 35 to the gate G of the transistor 32. More preferably, the range of the voltage applied by the DC power supply 36 may be at least twice the predetermined voltage applied by the DC power supply 35 to the gate G of the transistor 32.

[0079] [Summary of the second embodiment] As described above, the electronic circuit 3 according to this embodiment includes a DC power supply 36, a variable capacitance element 31, a variable capacitance element 33, and a transistor 32. By including the transistor 32, the electronic circuit 3 switches between applying a voltage to the variable capacitance element 31 and applying a voltage to both the variable capacitance element 31 and the variable capacitance element 33, depending on the output voltage of the DC power supply 36. More specifically, by including the transistor 32, the electronic circuit 3 applies a voltage to the variable capacitance element 33 later than to the variable capacitance element 31. That is, in a low-voltage region, the electronic circuit 3 ensures a change in capacitance by applying a voltage to the variable capacitance element 31 and the variable capacitance element 33, and in a high-voltage region, the electronic circuit 3 ensures a change in capacitance by disconnecting the variable capacitance element 33.

[0080] Therefore, even if the voltage-capacitance characteristics of the electronic circuit 3 reach a plateau in a high voltage region, the electronic circuit 3 can reduce the combined capacitance of the electronic circuit 3 and increase the variable range of the capacitance by turning off the transistor 32. Therefore, according to this embodiment, even when a variable capacitance element with a small capacitance variable ratio is used, by adding peripheral circuits such as the transistor 32, it is possible to obtain desired voltage-capacitance characteristics.

[0081] Furthermore, according to the above-described embodiment, the transistor 32 is an n-channel MOS-FET. Therefore, the electronic circuit 3 does not suffer from large power loss as in the case of using a bipolar transistor, and the time delay is small, so that the desired voltage-capacity characteristics can be suitably obtained.

[0082] Furthermore, according to the above-described embodiment, both the variable capacitance element 31 and the variable capacitance element 33 are variable capacitance diodes (varicaps). Therefore, according to this embodiment, it is possible to obtain desired voltage-capacitance characteristics using a variable capacitance diode with a small variable capacitance ratio, without having to spend a lot of money to develop a variable capacitance diode with a large variable capacitance ratio.

[0083] Furthermore, according to the above-described embodiment, the variable capacitance element 31 and the variable capacitance element 33 have the same structure and therefore have the same electrical characteristics. Therefore, according to this embodiment, the layout of the structure can be easily performed.

[0084] Furthermore, according to the above-described embodiment, the range of the voltage applied by the DC power supply 36 is at least 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 vary the voltage to at least twice the voltage applied by the DC power supply 35. Therefore, according to this embodiment, the capacitance of the variable capacitance element 33 is combined at a voltage before the change in capacitance of the variable capacitance element 31 reaches its peak. Therefore, according to the electronic circuit 3, a large variable capacitance ratio can be obtained.

[0085] [Third embodiment] The third embodiment will be described with reference to Figures 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 same figure, an example in which n (n is a natural number of 2 or more) transistors 32, a variable capacitance element 33, a resistor 34, and a DC power supply 35 are provided will be described.

[0086] 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, components similar to those in the electronic circuit 3 will be assigned the same reference numerals and description thereof will be omitted in some cases. 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 similar to those in the electronic circuit 3, and therefore description thereof will be omitted.

[0087] 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. The anode A of the 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 of the multiple resistors (second resistors) 34. Specifically, the cathode K of the variable capacitance element 33-1 is connected to the DC power supply 36 via the resistor 37 and a resistor 34-1 that is a corresponding resistor of the multiple resistors 34. The cathode K of the variable capacitance element 33-2 is connected to the DC power supply 36 via the resistor 37 and a resistor 34-2 that is a corresponding resistor of the multiple resistors 34. ...The cathode K of the variable capacitance element 33-n is connected to the DC power supply 36 via the resistor 37 and a resistor 34-n that is a corresponding resistor of the multiple resistors 34.

[0088] 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 multiple DC power supplies 35. Specifically, a predetermined voltage is applied to the gate G of the transistor 32-1 by a corresponding one of the multiple DC power supplies 35-1. A predetermined voltage is applied to the gate G of the transistor 32-2 by a corresponding one of the multiple DC power supplies 35. ...A predetermined voltage is applied to the gate G of the transistor 32-n by a corresponding one of the multiple DC power supplies 35-n.

[0089] Here, it is preferable that the voltages applied to the gate G of each of the plurality of transistors 32 are different from one another. Specifically, it is preferable that the voltage applied to the gate G of transistor 32-1 by DC power supply 35-1, the voltage applied to the gate G of transistor 32-2 by DC power supply 35-2, ..., the voltage applied to the gate G of transistor 32-n by DC power supply 35-n are different from one another.

[0090] The drain D of the transistor 32 is connected to the connection point between the resistor (first resistor) 37 and a corresponding resistor 34 among 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 a corresponding resistor 34-1 among the plurality of resistors 34. The drain D of the transistor 32-2 is connected to the connection point between the resistor 37 and a corresponding resistor 34-2 among the plurality of resistors 34. ...The drain D of the transistor 32-n is connected to the connection point between the resistor 37 and a corresponding resistor 34-n among the plurality of resistors 34.

[0091] The source S of the transistor 32 is connected to the connection point between a corresponding resistor 34 of the plurality of resistors (second resistors) 34 and a corresponding variable capacitance element 33 of the plurality of variable capacitance elements (second variable capacitance elements) 33. Specifically, the source S of the transistor 32-1 is connected to the connection point between a corresponding resistor 34-1 of the plurality of resistors 34 and a corresponding variable capacitance element 33-1 of the plurality of variable capacitance elements 33. The source S of the transistor 32-2 is connected to the connection point between a corresponding resistor 34-2 of the plurality of resistors 34 and a corresponding variable capacitance element 33-2 of the plurality of variable capacitance elements 33. ...The source S of the transistor 32-n is connected to the connection point between a corresponding resistor 34-n of the plurality of resistors 34 and a corresponding variable capacitance element 33-n of the plurality of variable capacitance elements 33.

[0092] 8 is a graph showing an example of the voltage-capacitance characteristics of the electronic circuit according to the third embodiment. The electrical characteristics of the electronic circuit 3A will be described with reference to the same figure. The same figure shows the change in capacitance of the terminal 38 with respect to the ground point when the output voltage of the DC power supply 36 is varied. The graph shown in FIG. 8 is a graph showing the results obtained by circuit simulation. The horizontal axis is shown in the range of 0 to 1, but it may be, for example, 0 [V] to 3.3 [V]. Also, the vertical axis is shown in the range of 0 to 1.2, but it may be, for example, 0 [pF] to 12 [pF].

[0093] In the example shown in FIG. 8, 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 will be described. As an example, 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.

[0094] In the range in which 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 (that is, the range in which the voltage is from 0 to 0.3), the transistors 32-1, 32-2, and 32-3 are all on. In the range where the output voltage of DC power supply 36 is equal to or lower than the output voltage of DC power supply 35-1, transistors 32-1, 32-2, and 32-3 are all on, and therefore voltage is applied to variable capacitance elements 33-1, 33-2, and 33-3. Therefore, the capacitance of electronic circuit 3A is the combined capacitance of variable capacitance elements 31, 33-1, 33-2, and 33-3.

[0095] In the range where the output voltage of DC power supply 36 exceeds the output voltage of DC power supply 35-1 and is equal to or less than the output voltage of DC power supply 35-2 (i.e., the range where the voltage is 0.3 to 0.5), transistor 32-1 is off and transistors 32-2 and 32-3 are on. When the output voltage of DC power supply 36 exceeds the output voltage of DC power supply 35-1 but is equal to or lower than the output voltage of DC power supply 35-2, transistor 32-1 is off and transistors 32-2 and 32-3 are on, so that voltage is applied to variable capacitance elements 33-2 and 33-3. In other words, variable capacitance element 33-1 is disconnected. Therefore, the capacitance of electronic circuit 3A is the combined capacitance of variable capacitance elements 31, 33-2, and 33-3.

[0096] In the range where the output voltage of DC power supply 36 exceeds the output voltage of DC power supply 35-2 and is equal to or less than the output voltage of DC power supply 35-3 (i.e., the range where the voltage is from 0.5 to 0.75), transistors 32-1 and 32-2 are off and transistor 32-3 is on. When the output voltage of DC power supply 36 exceeds the output voltage of DC power supply 35-2 but is equal to or lower than the output voltage of DC power supply 35-3, transistors 32-1 and 32-2 are off and transistor 32-3 is on, so that a voltage is applied to variable capacitance element 33-3. In other words, variable capacitance elements 33-1 and 33-2 are disconnected. Therefore, the capacitance of electronic circuit 3A is the combined capacitance of variable capacitance elements 31 and 33-3.

[0097] In the range in which the output voltage of the DC power supply 36 exceeds the output voltage of the DC power supply 35-3 (that is, the range in which the voltage is from 0.75 to 1), the transistors 32-1, 32-2, and 32-3 are all off. In the range where the output voltage of DC power supply 36 exceeds the output voltage of DC power supply 35-3, transistors 32-1, 32-2, and 32-3 are all off, and therefore no voltage is applied to variable capacitance element 33-1, 32-2, or 33-3. In other words, variable capacitance element 33-1, variable capacitance element 33-2, and variable capacitance element 33-3 are disconnected. Therefore, the capacitance of electronic circuit 3A becomes variable capacitance element 31.

[0098] That is, according to this embodiment, the variable capacitance element 33 to which voltage is applied, among the plurality of variable capacitance elements 33, varies in accordance with 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 disconnected, and the combined capacitance changes. Therefore, the combined capacitance of the electronic circuit 3A varies in accordance with the output voltage of the DC power supply 36. Therefore, the electronic circuit 3A can widen the variable capacitance range.

[0099] [Summary of the third embodiment] As described above, the electronic circuit 3A according to this embodiment includes, in addition to the variable capacitance element 31, the DC power supply 36, and the resistor 37, a plurality of transistors 32, the variable capacitance element 33, the resistor 34, and the DC power supply 35. The conductive states of the plurality of transistors 32 are switched in accordance with the output voltage of the DC power supply 36. That is, according to this embodiment, the variable capacitance element 33 to which voltage is applied, among the plurality of variable capacitance elements 33, varies in accordance with 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 elements 33 are increasingly disconnected, and the combined capacitance changes. Therefore, the combined capacitance of the electronic circuit 3A varies in accordance with the output voltage of the DC power supply 36. Therefore, according to the electronic circuit 3A, the variable capacitance range is widened, and a large variable capacitance ratio can be obtained.

[0100] Furthermore, according to the above-described embodiment, the voltages applied to the gates G of the plurality of transistors 32 are different from one another. 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 according to the output voltage of the DC power supply 36. Therefore, the electronic circuit 3A can obtain a large variable capacitance ratio.

[0101] [Fourth embodiment] A fourth embodiment will be described with reference to Fig. 9. A piezoelectric oscillator 5 according to the fourth embodiment is obtained by applying an electronic circuit 3 to the piezoelectric oscillator 1. Specifically, the piezoelectric oscillator 5 differs from the piezoelectric oscillator 1 in that it includes a first variable capacitance element section 51 and a second variable capacitance element section 52 instead of the first variable capacitance element 18 and the second variable capacitance element 19. In the description of the piezoelectric oscillator 5, a description of the same configuration as the piezoelectric oscillator 1 may be omitted.

[0102] 9 is a circuit diagram showing an example of the circuit configuration of a piezoelectric oscillator according to the second embodiment. With reference to this diagram, an example of the circuit configuration of the piezoelectric oscillator 5 will be described. The piezoelectric oscillator 5 includes a piezoelectric vibrator 11, a first variable capacitance element unit 51, a second variable capacitance element unit 52, a DC power supply (DC voltage source) 12, a transistor 21, a first resistor 13, a second resistor 22, and a third resistor 23.

[0103] The capacitance of first variable capacitance element unit 51 changes in response to the voltage applied to first terminal 111 of piezoelectric vibrator 11 by DC power supply 12 . First variable capacitance element section 51 includes variable capacitance element (first variable capacitance element) 511, transistor (second transistor) 512, variable capacitance element (second variable capacitance element) 513, resistor (fourth resistor) 514, and DC power supply 515. The cathode K of the variable capacitance element 511 is connected to the first terminal 111 of the piezoelectric vibrator 11. The anode A of the 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. An anode A of the 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. The drain D of the transistor 512 is connected to the first terminal 111 of the piezoelectric vibrator 11. The source S of the transistor 512 is connected to the 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 the connection point between the cathode K of the variable capacitance element 513 and the source S of the transistor 512 . A DC power supply 515 applies a predetermined voltage to the gate G of the transistor 512 .

[0104] The capacitance of second variable capacitance element section 52 changes in response to the voltage applied to second terminal 112 of piezoelectric vibrator 11 by DC power supply 12 . Second variable capacitance element section 52 includes variable capacitance element (third variable capacitance element) 521, transistor (third transistor) 522, variable capacitance element (fourth variable capacitance element) 523, resistor (fifth resistor) 524, and DC power supply 525. The cathode K of the variable capacitance element 521 is connected to the second terminal 112 of the piezoelectric vibrator 11. The anode A of the variable capacitance element 521 is grounded. The cathode K of the variable capacitance element 513 is connected to the second terminal 112 of the piezoelectric vibrator 11 via a resistor 524. The anode A of the 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. The drain D of the transistor 522 is connected to the second terminal 112 of the piezoelectric vibrator 11. The source S of the transistor 522 is connected to the 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 the 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 .

[0105] [Summary of the Fourth Embodiment] As described above, the piezoelectric oscillator 5 according to this embodiment includes the first variable capacitance element section 51 and the second variable capacitance element section 52 instead of the first variable capacitance element 18 and the second variable capacitance element 19 in the configuration of the piezoelectric oscillator 1. Therefore, according to the piezoelectric oscillator 5, by including the transistor 21, different voltages can be applied to the first terminal 111 and the second terminal 112 of the piezoelectric vibrator 11, respectively, to obtain a linear voltage-capacitance characteristic. Furthermore, 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.

[0106] The above describes the form for carrying out the present invention using an embodiment, but the present invention is not limited to such an embodiment, and various modifications and substitutions can be made within the scope that does not deviate from the spirit of the present invention. [Explanation of symbols]

[0107] 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 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

1. A piezoelectric vibrator having a first terminal and a second terminal; a first variable capacitance element portion whose capacitance changes in response to a voltage applied to the first terminal; a second variable capacitance element portion whose capacitance changes in response to a 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 supply different from the DC voltage source, and a source connected to a second resistor; a second resistor having one end connected to the source of the transistor and the other end grounded; a third resistor having one end connected to the connection point between the source of the transistor and the second resistor and the other end connected to the second terminal; Equipped with The first variable capacitance element unit is a first variable capacitance element having a cathode connected to the first terminal and an anode grounded; a second variable capacitance element having a cathode connected to the first terminal via a fourth resistor and an anode grounded; a second transistor having a gate to which a predetermined voltage is applied, 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 unit is a third variable capacitance element having a cathode connected to the second terminal and an anode grounded; a fourth variable capacitance element having a cathode connected to the second terminal via a fifth resistor and an anode grounded; a third transistor having a gate to which a predetermined voltage is applied, 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; Piezoelectric oscillator.

2. The transistor is an n-channel MOS-FET.

2. The piezoelectric oscillator according to claim 1.

3. The first variable capacitance element, the second variable capacitance element, the third variable capacitance element, and the fourth variable capacitance element are all variable capacitance diodes.

3. The piezoelectric oscillator according to claim 1.

4. The range of the voltage applied by the DC voltage source is at least twice the predetermined voltage applied to the gate of the transistor. The piezoelectric oscillator according to any one of claims 1 to 3.

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