JP6305094B2 - Resonant circuit and oscillation circuit - Google Patents

Description

  The present invention relates to a resonance circuit and an oscillation circuit.

  Conventionally, by using a plurality of crystal resonators having different resonance frequencies, an anti-resonance circuit that can adjust an oscillation frequency in a frequency range wider than a frequency range that can be adjusted by a single crystal resonator is known (for example, (See Patent Document 1).

  FIG. 8 shows a configuration example of a conventional anti-resonance circuit 400. In FIG. 8, the anti-resonance circuit 400 is connected to the output resistor 440 and the load resistor 450 of the AC signal source 430.

  The anti-resonance circuit 400 includes a crystal resonator 411 and a crystal resonator 421 connected to different paths between the output resistor 440 and the load resistor 450. In the first path to which the crystal resonator 411 is connected, an attenuator 412, an inductor 413, and a capacitor 414 are provided in series. The crystal resonator 411 is connected to a connection point between the inductor 413 and the capacitor 414 and the ground. Similarly, an attenuator 422, an inductor 423, and a capacitor 424 are provided in series on the second path to which the crystal resonator 421 is connected. The crystal resonator 421 is connected to a connection point between the inductor 423 and the capacitor 424 and the ground.

  The crystal resonator 411 and the crystal resonator 421 have different resonance frequencies, and are connected to each other via a capacitor 414 and a capacitor 424. As a result, the anti-resonance circuit 400 resonates at a frequency between the resonance frequency of the crystal resonator 411 and the resonance frequency of the crystal resonator 421. By changing the attenuation rates of the attenuator 412 and the attenuator 422, the anti-resonance frequency of the anti-resonance circuit 400 changes.

JP 2007-295256 A

By the way, the resonance frequency of a resonator having a high Q such as a crystal resonator or a MEMS (Micro-Electro-Mechanical Systems) resonator is f _L = (1 / 2π) √ {(C ₁ + C _L ) / L ₁ C. ₁ C _L }. Here, C ₁ is the motional capacitance of the equivalent circuit of the resonator, the C _L load capacitor, L ₁ is a series inductance of the transducer.

In the oscillation circuit C ₁ is used a relatively small MEMS resonator, the frequency adjustment is performed by adjusting the bias voltage applied to the vibrator. However, when an oscillator having a very small C ₁ with respect to a capacitance value of the order of several pF that can be realized in an integrated circuit or individual components is used in the oscillation circuit, f _L == based on the relationship of C _L >> C ₁ Since (1 / 2π) √ (1 / L ₁ C ₁ ) can be approximated, the resonance frequency is determined based on L ₁ and C ₁ of the vibrator. Therefore, when the above vibrator is used in an oscillation circuit, the temperature characteristic of the resonance frequency of the vibrator is directly reflected in the temperature characteristic of the oscillation frequency.

  In particular, the temperature characteristic of the resonance frequency of the MEMS vibrator is about −30 ppm / ° C., and the frequency change range with respect to the temperature change is relatively large. Therefore, in an oscillation circuit using a MEMS vibrator, it is difficult to obtain a stable oscillation frequency by canceling the temperature change only by adjusting the bias voltage.

  In the anti-resonance circuit 400 shown in FIG. 8, the anti-resonance frequency can be changed in a wider frequency range than when the bias voltage of a single MEMS vibrator is adjusted. However, in the anti-resonance circuit 400, in order to make the Q value at the anti-resonance frequency large enough to be used in the oscillation circuit, the inductance values of the inductor 413 and the inductor 423 must be sufficiently large. It was. Specifically, in Patent Document 1, 27 μH is exemplified as the inductance values of the inductor 413 and the inductor 423.

  However, the inductance value of the inductor changes greatly according to the temperature change. It is also difficult to adjust the inductance value according to the variation of the vibrator. Therefore, an oscillation signal having a stable oscillation frequency cannot be obtained in a resonance circuit using an inductor. Furthermore, it has been difficult to incorporate an inductor having an inductance value on the order of μH in an integrated circuit. Therefore, an oscillation circuit that can obtain an oscillation signal having a stable oscillation frequency by using the conventional anti-resonance circuit 400 cannot be mass-produced at a low cost.

  Accordingly, the present invention has been made in view of these points, and a resonance circuit and an oscillation circuit that can be incorporated in an integrated circuit and can resonate at a frequency different from the resonance frequency of the vibrator are provided. The purpose is to provide.

  In the first embodiment of the present invention, a first vibrator, a second vibrator connected in series with the first vibrator, an inverting amplifier connected in series with each other in parallel with the first vibrator, and Provided is a resonance circuit including a capacitive element and a negative capacitance circuit provided between a node between a first vibrator and a second vibrator and a ground. The capacitance of the capacitive element is, for example, equal to the equivalent parallel capacitance of the first vibrator. Further, the negative capacitance circuit may be able to change the capacitance value.

  The resonance circuit may further include a first variable resistor provided in parallel with the first vibrator and a second variable resistor provided in parallel with the second vibrator. The oscillation circuit may further include a variable capacitance element between the first vibrator and the second vibrator.

  In a second embodiment of the present invention, a first vibrator, a second vibrator connected in series with the first vibrator, an inverting amplifier connected in series with each other in parallel with the first vibrator, and A capacitive element, a negative capacitance circuit provided between a node between the first vibrator and the second vibrator, and the ground, and a feedback that feeds back a signal output from the second vibrator to the first vibrator. And an oscillation circuit including the unit.

  According to the oscillation circuit of the present invention, there is an effect that it can be built in an integrated circuit and can be resonated at a frequency different from the resonance frequency of the vibrator.

1 shows a configuration example of an oscillator according to a first embodiment. 1 shows a simulation circuit using an equivalent circuit of a resonance circuit according to a first embodiment. An example of the frequency characteristic of the gain of the resonance circuit which concerns on 1st Embodiment is shown. An example of the frequency characteristic of the phase of the resonance circuit which concerns on 1st Embodiment is shown. The frequency characteristic of the gain of the resonance circuit which concerns on a comparative example is shown. The structural example of the resonance circuit which concerns on 2nd Embodiment is shown. The structural example of the resonance circuit which concerns on 3rd Embodiment is shown. An example of the frequency characteristic of the gain of the resonance circuit which concerns on 3rd Embodiment is shown. An example of the frequency characteristic of the phase of the resonance circuit which concerns on 3rd Embodiment is shown. The structural example of the oscillator which concerns on 4th Embodiment is shown. The structural example of the conventional oscillation circuit is shown.

<First Embodiment>
[Configuration of Oscillator 100]
FIG. 1 shows a configuration example of an oscillator 100 according to the first embodiment. The oscillator 100 includes a resonance circuit 1 and an amplifier circuit 2. The amplifier circuit 2 functions as a feedback unit that feeds back the signal output from the second vibrator 12 to the first vibrator 11. When the resonance circuit 1 and the amplifier circuit 2 form a loop, the oscillator 100 can generate an oscillation signal having a resonance frequency of the resonance circuit 1.

[Configuration of Resonant Circuit 1]
The resonance circuit 1 includes a first vibrator circuit 10, a second vibrator 12, and a negative capacitance circuit 15. The first oscillator circuit 10 includes a first oscillator 11, an inverting amplifier 13, and a capacitive element 14.
The first vibrator 11 and the second vibrator 12 are, for example, an AT cut crystal vibrator, an SC cut crystal vibrator, and a MEMS vibrator. The first vibrator 11 and the second vibrator 12 are connected in series.

The resonance frequency fr ₁ of the first vibrator 11 in the present embodiment is about 51.9 MHz, and the anti-resonance frequency fa ₁ is about 52.0 MHz. The resonance frequency fr ₂ of the second vibrator 12 is about 52.1 MHz, and the anti-resonance frequency fa ₂ is about 52.2 MHz. That is, the relationship between the resonance frequency and the anti-resonance frequency of the first vibrator 11 and the second vibrator 12 is fr ₁ <fa ₁ <fr ₂ <fa ₂ .

  The inverting amplifier 13 and the capacitive element 14 are connected in series with each other in parallel with the first vibrator 11. That is, the input terminal of the inverting amplifier 13 is connected to one end of the first vibrator 11, and the output terminal of the inverting amplifier 13 is connected to one end of the capacitive element 14. The other end of the capacitive element 14 is connected to a node between the first vibrator 11 and the second vibrator 12. The gain of the inverting amplifier 13 is preferably unity.

  The negative capacitance circuit 15 is provided between a node between the first vibrator 11 and the second vibrator 12 and the ground. The negative capacitance circuit 15 is a circuit having a property of discharging charges when a positive voltage is applied. For example, the negative capacitance circuit 15 includes a known circuit configured by combining an active element such as an operational amplifier or a plurality of transistors and a passive element such as a capacitor and a resistor.

  FIG. 2 shows a simulation circuit using an equivalent circuit of the resonance circuit 1 according to the first embodiment. In FIG. 2, the resonance circuit 1 is connected to an AC signal source 16 and a load resistor 17. The AC signal source 16 and the load resistor 17 are provided for simulating the operation when the resonance circuit 1 is used in the oscillator 100 shown in FIG.

  In the first vibrator 11, an equivalent parallel capacitor 111, an equivalent series capacitor 112, an equivalent series inductor 113, and an equivalent series resistor 114 connected in series with each other are connected in parallel. In the second vibrator 12, an equivalent parallel capacitor 121, an equivalent series capacitor 122, an equivalent series inductor 123, and an equivalent series resistor 124 connected in series with each other are connected in parallel.

  The capacitance of the capacitive element 14 is equal to the capacitance of the equivalent parallel capacitance 111 of the first vibrator 11. A signal output from the AC signal source 16 is input to the equivalent parallel capacitor 111 and input to the inverting amplifier 13. The signal input to the capacitive element 14 via the inverting amplifier 13 is in reverse phase to the signal input to the equivalent parallel capacitor 111. Therefore, the signal that has passed through the equivalent parallel capacitor 111 is canceled by the signal that has passed through the capacitive element 14 having the same capacitance value as the equivalent parallel capacitor 111.

  The capacitance values of the negative capacitance circuit 15 are, for example, opposite in sign to the capacitance values of the capacitive element 14, equivalent parallel capacitance 111, and equivalent parallel capacitance 121, and the capacitance values of the capacitive element 14, equivalent parallel capacitance 111, and equivalent parallel capacitance 121. Is equal to the sum of Since the negative capacitance circuit 15 is provided between the first vibrator 11 and the second vibrator 12, the effects of the equivalent parallel capacitor 111, the capacitor element 14, and the equivalent parallel capacitor 121 are canceled out. It becomes difficult to be influenced by the anti-resonance frequency of the first vibrator 11, and it becomes easy to oscillate between the resonance frequency of the first vibrator 11 and the resonance frequency of the second vibrator 12. As described above, even if the first vibrator circuit 10 is viewed from the node to which the negative capacitance circuit 15 is connected, that is, the connection point between the first vibrator circuit 10 and the second vibrator 12, the second vibrator 12, the resonance frequency of the first vibrator 11 can be reduced by making the capacitive element 14 of the first vibrator circuit 10, the equivalent parallel capacity 111, and the equivalent parallel capacity 121 of the second vibrator 12 invisible. And the resonance frequency of the second vibrator 12 can be established in the middle.

  Note that when the capacitance value of the negative capacitance circuit 15 becomes smaller than the sum of the capacitance values of the capacitive element 14, the equivalent parallel capacitance 111, and the equivalent parallel capacitance 121, the resonance frequency of the resonance circuit 1 becomes the resonance of the first vibrator 11. Approaching the frequency. Further, when the capacitance value of the negative capacitance circuit 15 becomes larger than the sum of the capacitance values of the capacitive element 14, the equivalent parallel capacitance 111, and the equivalent parallel capacitance 121, the resonance frequency of the resonance circuit 1 becomes the resonance of the second vibrator 12. Approaching the frequency. Therefore, the resonance frequency of the resonance circuit 1 can be changed by changing the capacitance value of the negative capacitance circuit 15. For example, if a variable capacitance element such as a varicap diode is used for the negative capacitance circuit 15, the resonance frequency of the resonance circuit 1 can be changed by changing the voltage applied to the variable capacitance element.

  FIG. 3A shows an example of the frequency characteristic of the gain of the resonance circuit 1 according to the first embodiment. The broken line in FIG. 3A is the frequency characteristic of the gain of the first vibrator circuit 10. 3A is a frequency characteristic of the gain of the second vibrator 12. Further, the solid line in FIG. 3A is the frequency characteristic of the gain of the resonance circuit 1. FIG. 3B shows an example of the frequency characteristic of the phase of the resonance circuit 1 according to the first embodiment. The broken line in FIG. 3B is the phase of the first vibrator circuit 10. Also, the one-dot chain line in FIG. 3B is the phase of the second vibrator 12. The solid line in FIG. 3B is the phase of the resonance circuit 1.

  As shown in FIG. 3A, in the frequency characteristic of the gain of the first vibrator circuit 10, there is a peak with a large gain in the vicinity of 51.9 MHz which is the resonance frequency of the first vibrator 11. In the frequency characteristics of the gain of the second vibrator 12, there is a peak with a large gain in the vicinity of 52.1 MHz which is the resonance frequency of the second vibrator 12. In the frequency characteristic of the gain of the resonance circuit 1, there is a peak with a large gain in the vicinity of 52.0 MHz between the resonance frequency of the first vibrator 11 and the resonance frequency of the second vibrator 12. Thus, in the resonance circuit 1, it can be seen that the frequency between the resonance frequency of the first vibrator 11 and the resonance frequency of the second vibrator 12 is the resonance frequency. Further, as shown in FIG. 3B, the phases of the first vibrator 11, the second vibrator 12, and the resonance circuit 1 are changed by 180 degrees at frequencies corresponding to the respective gain peaks.

In the frequency characteristics of the gains of the second vibrator 12 and the resonance circuit 1, a peak with a small gain occurs in the vicinity of 52.2 MHz which is the anti-resonance frequency of the second vibrator 12. On the other hand, as indicated by the broken line in FIG. This is because the inverting amplifier 13 and the capacitive element 14 are provided in parallel with the first vibrator 11 for the following reason, so that the anti-resonance frequency of the first vibrator circuit 10 becomes the resonance frequency of the second vibrator 12. This is because it is higher than fr ₂ .

The anti-resonance frequency fa ₁ of the first vibrator 11 is represented by fa ₁ = fr ₁ · (1 / 2π) √ {1 + C ₁ / C ₀ }. Here, C ₀ is the capacitance value of the equivalent parallel capacitance 111 of the first vibrator 11, and C ₁ is the capacitance value of the equivalent series capacitance 112 of the first vibrator 11. As can be seen from the above equation, the smaller the capacitance value of the equivalent parallel capacitance 111 of the first vibrator 11 is, the higher the anti-resonance frequency fa ₁ tends to be.

In the first oscillator circuit 10 according to the present embodiment, since the inverting amplifier 13 and the capacitive element 14 are provided, C ₀ is canceled out, so that the anti-resonance frequency fa ₁ of the first oscillator circuit 10 is the second oscillator. 12 becomes larger than the resonance frequency fr ₂ of. As a result, in the resonant circuit 1, the oscillation conditions are satisfied in all frequency range between the resonance frequency fr ₂ of the resonance frequency fr ₁ and the second vibrator 12 of the first vibrator 11, the resonant circuit 1 The resonance frequency can be changed in a wide frequency range.

[Comparative example]
FIG. 3C shows gain frequency characteristics in a circuit in which the inverting amplifier 13, the capacitive element 14, and the negative capacitance circuit 15 are removed from the resonance circuit 1 as a comparative example. The broken line in FIG. 3C is the frequency characteristic of the gain of the first vibrator 11. Also, the one-dot chain line in FIG. 3C is the frequency characteristic of the gain of the second vibrator 12. Also, the solid line in FIG. 3C shows the frequency characteristics of the gain in the circuit of the comparative example in which the first vibrator 11 and the second vibrator 12 are connected in series.

As shown in FIG. 3C, in the circuit in which the inverting amplifier 13, the capacitive element 14, and the negative capacitance circuit 15 are deleted from the resonance circuit 1, the resonance frequency fr ₁ of the first vibrator 11 and the resonance frequency of the second vibrator 12. since there is the antiresonant frequency fa ₁ of the first vibrator 11 between fr _2, the frequency is changed between the resonance frequency fr ₂ of the resonance frequency fr ₁ and the second vibrator 12 of the first oscillator 11 intoxicated to, the resonance frequency fr ₁ of the first oscillator 11 at every frequency range between the resonance frequency fr ₂ of the second vibrator 12 is not satisfied oscillation condition is not only satisfied the oscillation condition in a narrow frequency range .

[Effect in the first embodiment]
As described above, according to the resonance circuit 1 according to the first embodiment, the first vibrator 11, the second vibrator 12 connected in series with the first vibrator 11, and the first vibrator 11 in parallel. And an inverting amplifier and a capacitive element connected in series with each other, and a negative capacitance circuit 15 provided between the node between the first vibrator 11 and the second vibrator 12 and the ground. , it is possible to set the resonance frequency to a frequency between the resonance frequency fr ₂ of the resonance frequency fr ₁ and the second vibrator 12 of the first oscillator 11.

<Second Embodiment>
[Equipped with variable resistance in parallel with the vibrator]
FIG. 4 shows a configuration example of the resonance circuit 1 according to the second embodiment. The resonant circuit 1 is different from the resonant circuit 1 shown in FIG. 2 in that it further includes a first variable resistor 18 and a second variable resistor 19, and is the same in other points.

  The first variable resistor 18 is provided in parallel with the first vibrator 11. The second variable resistor 19 is provided in parallel with the second vibrator 12. The current flowing through the first vibrator 11 is adjusted by adjusting the resistance value of the first variable resistor 18. Further, the current flowing through the second vibrator 12 is adjusted by adjusting the resistance value of the second variable resistor 19.

  For example, when the resistance value of the first variable resistor 18 is relatively large with respect to the equivalent series resistor 114 and the resistance value of the second variable resistor 19 is relatively small with respect to the equivalent series resistor 124, it is output from the AC signal source 16. The passed current passes through the first vibrator circuit 10. A relatively large proportion of the current that has passed through the first vibrator circuit 10 passes through the second variable resistor 19. Accordingly, in this case, the resonance circuit 1 is hardly affected by the second vibrator 12, and among the signals that have passed through the first vibrator circuit 10, signals having a frequency that is away from the resonance frequency of the second vibrator 12 are also included. Not attenuated. As a result, the resonance frequency of the resonance circuit 1 is closer to the resonance frequency of the first vibrator circuit 10 than the resonance frequency of the second vibrator 12.

  On the other hand, when the resistance value of the first variable resistor 18 is relatively small with respect to the equivalent series resistor 114 and the resistance value of the second variable resistor 19 is relatively large with respect to the equivalent series resistor 124, it is output from the AC signal source 16. The current passes through the first variable resistor 18 with almost no influence of the first vibrator circuit 10. A relatively large proportion of the current that has passed through the first variable resistor 18 passes through the second vibrator 12. Therefore, in this case, the resonance circuit 1 is hardly affected by the first vibrator circuit 10, and a signal having a frequency away from the resonance frequency of the first vibrator circuit 10 is not attenuated to the second vibrator 12. Entered. As a result, the resonance frequency of the resonance circuit 1 is closer to the resonance frequency of the second vibrator 12 than the resonance frequency of the first vibrator circuit 10.

  By changing the resistance values of the first variable resistor 18 and the second variable resistor 19, the respective frequency components of the signal input to the resonance circuit 1 pass through the first vibrator circuit 10 and the second vibrator 12. The amount of attenuation in between changes. The resonance circuit 1 resonates at a frequency at which the amount of attenuation while passing through the first vibrator circuit 10 and the second vibrator 12 is the smallest.

[Effects of Second Embodiment]
As described above, according to the resonance circuit 1 according to the second embodiment, by further including the first variable resistor 18 and the second variable resistor 19, the resonance frequency of the resonance circuit 1 is set to the resonance of the first vibrator 11. It is possible to adjust between the frequency and the resonance frequency of the second vibrator 12. That is, in the resonance circuit 1 according to the second embodiment, the peak frequency in the frequency characteristic of the resonance circuit 1 indicated by the solid line in FIG. 3A is set according to the values of the first variable resistor 18 and the second variable resistor 19. it can be varied between the resonant frequency fr ₂ of the resonance frequency fr ₁ and the second vibrator 12 of the first oscillator 11.

<Third Embodiment>
[A variable capacitance element is provided between the first vibrator 11 and the second vibrator 12]
FIG. 5 shows a configuration example of the resonance circuit 1 according to the third embodiment. The resonance circuit 1 according to the third embodiment is different from the resonance circuit 1 shown in FIG. 4 in that the variable capacitance element 20 is further provided, and is the same in other points. FIG. 6A shows an example of the frequency characteristic of the gain of the resonance circuit 1 according to the third embodiment. FIG. 6B shows an example of the frequency characteristic of the phase of the resonance circuit 1 according to the third embodiment.

  The variable capacitance element 20 is provided between the first vibrator 11 and the second vibrator 12. The variable capacitance element 20 is, for example, a varicap diode or an element group configured by series connection of an FET and a resistor. By changing the capacitance value of the variable capacitance element 20, the resonance frequency of the resonance circuit 1 can be changed.

  A broken line in FIG. 6A represents a frequency characteristic of gain in the resonance circuit 1 in which the second variable resistor 19 is short-circuited in a state where the capacitance value of the variable capacitance element 20 is sufficiently large. In this state, the frequency characteristic of the first vibrator 11 strongly influences the frequency characteristic of the resonance circuit 1, so that the resonance frequency of the resonance circuit 1 is close to the resonance frequency of the first vibrator 11. By reducing the capacitance value of the variable capacitance element 20 in a state where the second variable resistor 19 is short-circuited, the resonance frequency of the resonance circuit 1 increases and changes to the frequency characteristic indicated by the solid line.

  Further, the resistance value of the second variable resistor 19 and the capacitance value of the variable capacitance element 20 are sufficiently increased so that the resonance frequency of the first vibrator 11 and the resonance frequency of the second vibrator 12 are in the vicinity of the center. When the capacitance value of the variable capacitor 20 is decreased after the resonance frequency of the resonance circuit 1 is set, the frequency characteristic of the second vibrator 12 has a strong influence on the frequency characteristic of the resonance circuit 1. As a result, the frequency characteristic of the resonance circuit 1 approaches the frequency characteristic of the second vibrator 12 as indicated by a one-dot chain line in FIG. 6A.

[Effect in the third embodiment]
As described above, according to the resonance circuit 1 according to the third embodiment, the resonance frequency of the resonance circuit 1 can be further freely changed by further including the variable capacitance element 20.

<Fourth Embodiment>
FIG. 7 shows a configuration example of an oscillator 200 according to the fourth embodiment. The resonance circuit 1 in the oscillator 200 shown in FIG. 7 includes a third vibrator 21, a negative capacitance circuit 22, an inverting amplifier 23, and a capacitive element 24, so that the resonance circuit in the oscillator 100 shown in FIG. Unlike the circuit 1, it is the same in other points.

  The resonance frequency of the third vibrator 21 is higher than the resonance frequency of the second vibrator 12. The capacitance value of the negative capacitance circuit 22 is opposite in sign to the inter-terminal capacitance of the second vibrator 12, the inter-terminal capacitance of the third vibrator 21, and the capacitive element 24, and is equal to the sum of these capacitance values. The inverting amplifier 23 and the capacitive element 24 cancel the inter-terminal capacitance of the second vibrator 12.

  7 includes the negative capacitance circuit 22, the inverting amplifier 23, and the capacitive element 24, the anti-resonance frequency of the first vibrator 11 and the anti-resonance frequency of the second vibrator 12 can be reduced. Since it becomes higher than the resonance frequency of the third vibrator 21, the oscillator 200 oscillates at a frequency between the resonance frequency of the first vibrator 11 and the resonance frequency of the third vibrator 21. By changing the capacitance value of the negative capacitance circuit 22, the oscillation frequency of the oscillator 200 can be changed between the resonance frequency of the first vibrator 11 and the resonance frequency of the third vibrator 21. As in the second embodiment, a variable resistor is provided in parallel with the third vibrator 21 to change the resistance value of the variable resistor, or in the same manner as in the third embodiment, The oscillation frequency of the oscillator 200 can also be changed by providing a variable capacitance element between the third vibrator 21 and changing the capacitance value of the variable capacitance element.

[Effects of the fourth embodiment]
As described above, according to the oscillator 200 according to the fourth embodiment, the third embodiment 21, the negative capacitance circuit 22, the inverting amplifier 23, and the capacitive element 24 are further provided, and thus the above-described embodiment. The oscillation frequency can be changed in a wider frequency range than that.

  As mentioned above, although this invention was demonstrated using embodiment, the technical scope of this invention is not limited to the range as described in the said embodiment. It will be apparent to those skilled in the art that various modifications or improvements can be added to the above embodiment. It is apparent from the scope of the claims that the embodiments added with such changes or improvements can be included in the technical scope of the present invention.

For example, in the first embodiment, the inverting amplifier 13 and the capacitive element 14 are connected in series to the first vibrator 11 in parallel. However, the inverting amplifier 13 and the capacitive element 14 are connected to the second vibrator 12 in parallel. An equivalent circuit may be connected.
In the fourth embodiment, the configuration in which the oscillator 200 includes three vibrators has been described. However, the oscillator 200 may include more vibrators.

DESCRIPTION OF SYMBOLS 1 ... Resonance circuit, 2 ... Amplifier circuit, 11 ... 1st vibrator, 12 ... 2nd vibrator, 13 ... Inverting amplifier, 14 ... Capacitance element, 15 ... Negative capacitance circuit, 16 ... AC signal source, 17 ... load resistance, 18 ... first variable resistor, 19 ... second variable resistor, 20 ... variable capacitance element, 21 ... 3rd vibrator, 22 ... Negative capacitance circuit, 23 ... Inverting amplifier, 24 ... Capacitance element, 200 ... Oscillator

Claims (6)

A first vibrator;
A second vibrator connected in series with the first vibrator and having a resonance frequency different from that of the first vibrator;
An inverting amplifier and a capacitive element connected in series with each other in parallel with the first vibrator;
A negative capacitance circuit provided between a node between the first vibrator and the second vibrator and the ground;
A resonant circuit comprising: The capacitance of the capacitive element is equal to the equivalent parallel capacitance of the first vibrator,
The resonant circuit according to claim 1. The negative capacitance circuit can change a capacitance value.
The resonance circuit according to claim 1 or 2. A first variable resistor provided in parallel with the first vibrator;
A second variable resistor provided in parallel with the second vibrator;
The resonance circuit according to any one of claims 1 to 3, further comprising:   5. The resonant circuit according to claim 1, further comprising a variable capacitance element between the first vibrator and the second vibrator. A first vibrator;
A second vibrator connected in series with the first vibrator and having a resonance frequency different from that of the first vibrator;
An inverting amplifier and a capacitive element connected in series with each other in parallel with the first vibrator;
A negative capacitance circuit provided between a node between the first vibrator and the second vibrator and the ground;
A feedback unit that feeds back a signal output from the second vibrator to the first vibrator;
An oscillation circuit comprising:

Images