JP5060416B2 - Oscillator - Google Patents

Description

  The present invention relates to an oscillator using a piezoelectric element, and more particularly to an oscillator that performs a plurality of fundamental wave oscillations.

Conventionally, as a solution for adapting an oscillator to a plurality of systems, there is a multi-channel oscillator. This is an indispensable technique for flexibly responding by switching the oscillation frequency according to the system requirements.
As an oscillator that oscillates at a plurality of frequencies, a dual mode crystal oscillation circuit (NDK) using overtone oscillation is known (for example, see Patent Document 1). Here, a first oscillating means for oscillating a third-order overtone vibration with respect to the fundamental wave vibration of the crystal oscillator, a second oscillating means for oscillating a fifth-order overtone with respect to the fundamental wave vibration of the crystal oscillator, By providing band limiting means for preventing interference of fifth-order overtone vibration between one of the first and second oscillation means and the crystal resonator, stable third-order and fifth-order overshoots are provided. Tone oscillation is realized.
JP 2007-274633 A

However, in the dual-mode crystal oscillation circuit described in Patent Document 1, a plurality of oscillation frequencies are obtained by applying a method of extracting overtones with a single piezoelectric element, so that the frequency interval can be freely set. Cannot be selected. Therefore, in order to select a frequency freely, it is necessary to have as many oscillators as necessary.
In general, as shown in FIG. 12, the oscillator includes an inverter circuit, an oscillation circuit including a feedback resistor connected in parallel to the inverter circuit, and a capacitive element connected between the input / output of the inverter circuit and the ground, A piezoelectric element having one end connected to the input end of the inverter circuit and the other end connected to the output end of the inverter circuit; and two electrical connections for electrically connecting one oscillation circuit and one piezoelectric element. An electrode is required.

  Therefore, when a plurality of (for example, N) oscillators are provided, a plurality of oscillation circuits and a plurality of piezoelectric elements are required as shown in FIG. In the example shown in FIG. 13, the outputs of the respective oscillators are bundled together via the coupling capacitors Cc1 to CcN, and a desired oscillation output can be taken out by turning on one of the N oscillation circuits. it can. However, when N oscillators are bundled in this way, the circuit area is N times that of the oscillator shown in FIG.

In addition, when there are a plurality of oscillators in which extension coils as shown in FIG. 14 are inserted, as shown in FIG. 15, the number of extension coils and electrodes corresponding to the number of outputs (N in this case) increases. The circuit scale is further increased as compared with the example of FIG.
Accordingly, an object of the present invention is to provide an oscillator that can freely select a plurality of oscillation frequencies without increasing the circuit scale.

In order to achieve the above object, an oscillator according to the present invention includes a piezoelectric element excited at a predetermined frequency, and an oscillation circuit that has an amplifier and drives the piezoelectric element by exciting current by flowing current through the piezoelectric element. An oscillator including a plurality of piezoelectric oscillation circuits each including an output of the plurality of oscillation circuits bundled into one output node, and one end of the plurality of piezoelectric elements is an input of the amplifier corresponding to each piezoelectric element. The other end of the plurality of piezoelectric elements is connected in common to the output node, and includes a selection circuit that selectively drives any one of the plurality of piezoelectric elements , An extension coil is connected between a common node in which the other ends of the plurality of piezoelectric elements are bundled together and the output node .

As described above, the outputs of the plurality of oscillation circuits are bundled into one output node, and the other ends of the piezoelectric elements having a necessary frequency are connected in common, and any one of the plurality of piezoelectric elements is selected by the selection circuit. By selecting and driving one, an oscillator with multiple inputs and one output can be realized. Thereby, a plurality of oscillations can be performed by one oscillator while suppressing an increase in circuit scale. Furthermore, since the extension coil is connected between the common node and the output node, the frequency sensitivity of the oscillator can be improved. Further, in the oscillator according to the invention, in the above, the selection circuit is configured by a switching element interposed between a current source and each amplifier, and the current source is controlled by controlling each switching element. From any one of the plurality of amplifiers, one of the plurality of piezoelectric elements is driven by supplying a current to any one of the plurality of amplifiers.
As a result, the selection circuit can be realized with a relatively simple circuit configuration.

The oscillator according to the present invention is characterized in that, in the above, the circuit portion excluding the piezoelectric element is configured by a one-chip IC.
Thereby, the circuit part excluding the piezoelectric element can be made into a complete IC. Furthermore, even when an extension coil is provided, by incorporating it in the IC chip, it can be prevented from being affected by parasitics compared to the case of being externally attached, and characteristics can be easily obtained. .

In addition, an electrode for electrically connecting an oscillation circuit inside the IC and a piezoelectric element outside the IC is required. However, even when a plurality of piezoelectric oscillation circuits are included by adopting a circuit configuration with multiple inputs and one output. An increase in the number of electrodes can be suppressed.
The oscillator according to the present invention further includes a capacitive element disposed between the input / output terminal of each amplifier and the ground, and at least one of the plurality of capacitive elements is a variable capacitive element. It is a feature.
Thereby, the capacitance value of the capacitive element can be adjusted, and the frequency output can be easily adjusted to the target frequency.

  As described above, the oscillator of the present invention has an effect that a plurality of fundamental wave oscillations can be freely selected without increasing the circuit scale and the number of parts.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing an oscillator according to the first embodiment of the present invention.
The oscillator according to the present embodiment includes piezoelectric oscillation circuits 11 and 12 including a combination of an oscillation circuit disposed inside the IC and a piezoelectric element disposed outside the IC.
In the figure, NM1 and NM2 are transistors functioning as inverters, and the gates of the transistors NM1 and NM2 are electrically connected to one ends of the piezoelectric elements X1 and X2 via electrodes EL1 and EL2, respectively.

  Further, SM1 and SM2 interposed between the transistors NM1 and NM2 and the current source are transistors that are turned on / off by receiving the selection signals SEL1 and SEL2, and the transistor SM1 (or SM2) is turned on. In this case, the oscillator current Idc is supplied to the transistor NM1 (or NM2) functioning as an inverter, and when it is OFF, the oscillator current Idc that is supplied to the transistor NM1 (or NM2) is cut off.

Further, R1 and R2 are resistors that determine the operating point of the oscillation circuit, and SW1 and SW2 connected in series to the resistors are switches that are turned on / off in conjunction with the transistors SM1 and SM2, respectively. C1 and C2 are capacitors on the input side of the oscillation circuit, and Cx is a capacitance on the output side of the oscillation circuit.
The outputs of the piezoelectric oscillation circuits 11 and 12 are bundled together at the output node N1 as shown in the figure, and the output node N1 and the common node N2 where the other ends of the piezoelectric elements X1 and X2 are bundled together are electrodes. It is configured to be electrically connected via EL3.

  When the control signal SEL is at the H level, the control signal SEL1 = H level and the control signal SEL = L level, the transistor SM1 and the switch SW1 are turned on, and the transistor SM2 and the switch SW2 are turned off. As a result, the current source Idc and the closed loop including the NM1, C1, Cx, and X1 of the piezoelectric oscillation circuit 11 constitute an oscillator, and the output of the piezoelectric oscillation circuit 11 becomes the final output OUT.

  On the other hand, when the control signal SEL is at the L level, the control signal SEL1 = L level and the control signal SEL = H level are set, the transistor SM2 and the switch SW2 are turned on, and the transistor SM1 and the switch SW1 are turned off. As a result, an oscillator is configured by the current source Idc and the closed loop including the NM2, C2, Cx, and X2 of the piezoelectric oscillation circuit 12, and the output of the piezoelectric oscillation circuit 12 becomes the final output OUT.

Thus, the piezoelectric element which operates by switching the selection signal SEL can be switched, and the oscillation frequency can be switched. In other words, by switching the closed loop by the selection signal SEL, it is possible to configure an oscillation circuit that can obtain two different oscillation frequencies with one circuit.
In other words, this oscillator has two inputs because it has two inverters, but has a circuit configuration of two inputs and one output that can be realized by bundling all outputs together.

FIG. 2 is a conceptual diagram of this embodiment. Here, an example in which N piezoelectric oscillation circuits are provided is shown.
As shown in FIG. 2, each piezoelectric oscillation circuit has an amplifier in which a feedback resistor is connected between the input terminal and the output terminal of the inverter circuit, and each output is bundled into one output node. One end of each piezoelectric element is connected to the input end of the corresponding inverter circuit, and the other end of each piezoelectric element is commonly connected to the output node.

At this time, by controlling so that any one of the N piezoelectric oscillation circuits operates by the control signals 1 to N, only one of the plurality of piezoelectric oscillation circuits can be selectively selected without colliding with each other. Can oscillate.
Incidentally, in order to obtain N different oscillation frequencies, when N oscillators having the configuration shown in FIG. 12 are provided, if N piezoelectric oscillation circuits are connected as they are, the configuration shown in FIG. 13 is obtained, and the circuit scale is simple. N times. Further, two electrodes are required to electrically connect a set of oscillation circuits and piezoelectric elements, and 2 × N electrodes are required when N piezoelectric oscillation circuits are provided.

Therefore, in the configuration shown in FIG. 13, since the number of outputs is the same as the number of inputs, a large chip area and mounting area are required in order to increase the number of channels. As described above, when a plurality of oscillators are bundled to cope with the increase in the number of channels, it is very difficult to suppress an increase in circuit scale.
On the other hand, in this embodiment, as shown in FIG. 2, the output of each oscillation circuit is bundled into one output node, and the other end of each piezoelectric element is connected to the output node in common, thereby outputting the output. The number is one. Therefore, even when N piezoelectric oscillation circuits are provided, the number of electrodes is (N + 1), and the circuit scale can be reduced as compared with the configuration shown in FIG.

As described above, in the first embodiment, the outputs of the plurality of oscillation circuits are bundled into one output node, and one end of each of the plurality of piezoelectric elements is connected to the input end of the amplifier corresponding to each piezoelectric element, and Since the other end of the piezoelectric element is commonly connected to the output node and any one of the plurality of piezoelectric elements is driven, a multi-input one-output oscillator can be realized.
At this time, by connecting a piezoelectric element having a desired frequency to the integrated oscillation circuit as described above, an oscillator capable of freely selecting fundamental wave oscillation can be obtained.

In addition, by constructing the circuit part excluding the piezoelectric element with a one-chip IC, an electrode for electrically connecting the oscillation circuit inside the IC and the piezoelectric element outside the IC is required. With the circuit configuration, even when N piezoelectric oscillation circuits are included, the number of electrodes can be limited to (N + 1), and an increase in circuit scale can be suppressed.
As described above, it is possible to freely select a plurality of oscillation frequencies with one oscillator while suppressing an increase in the circuit scale and the number of components.

In addition, a switching element (transistor) is interposed between the current source and the amplification transistor, and each switching element is controlled to supply current to only one of the plurality of amplifiers from the current source. Therefore, it is possible to realize a selection circuit that selects one of a plurality of piezoelectric elements with a relatively simple circuit configuration.
In the first embodiment, the 2-input 1-output oscillation circuit has been described. However, any number of inputs may be used. For example, the circuit configuration in the case of a 4-input 1-output oscillation circuit is as shown in FIG. In this case, the selection signals SEL1 to SEL4 are controlled such that any one of the piezoelectric oscillation circuits 11 to 14 is turned on. If SEL1 = H level, SEL2 = L level, SEL3 = L level, and SEL4 = L level, only the transistor SM1 and the switch SW1 are turned on, and the transistors SM2 to SM4 and the switches SW2 to SW4 are turned off. Only the oscillation circuit 11 can operate.

Next, a second embodiment of the present invention will be described.
In the second embodiment, an extension coil is added to the first embodiment described above.
FIG. 4 is a diagram illustrating an oscillator with two inputs and one output according to the second embodiment.
As shown in FIG. 4, in the oscillator according to the second embodiment, the extension coil Ls is inserted between the output node N1 of the oscillator and the common node N2 of the piezoelectric element in the oscillator of FIG. The configuration is the same as that of the oscillator shown in FIG.

The extension coil Ls is provided to improve the frequency sensitivity, and is assumed to be disposed outside the IC chip here.
Next, the function of the extension coil will be described in detail below.
FIG. 5 is an equivalent circuit for explaining the function of the extension coil. Assuming that the equivalent capacitance is Ct, the series impedance of CL1, CL2, and Ls is as follows.

1 / (jω * Ct) = 1 / (jω * CL1) + 1 / (jω * CL2) + jω * Ls
1 / Ct = (1 / CL1 + 1 / CL2) −ω ² * Ls (1)
Here, ω is an angular frequency. If 1 / CL = 1 / CL1 + 1 / CL2, the following equation is derived from the above equation (1).
1 / Ct = 1 / CL-ω ² * Ls
= (1-ω ² * Ls * CL) / CL
∴ Ct = CL / (1-ω ² * Ls * CL) (2)
Moreover, when the series resonance frequency fs is used as the oscillation frequency f of the piezoelectric element,
f = fs * {1 + C1 / (2 * (C0 + Ct))}
= Fs * (1 + Δ) (3)
It is represented by Here, Δ = C1 / (2 * (C0 + Ct)) and fs = 1 / {2 * π * √ (L1 * C1)}.

The above equation (3) indicates the Ls dependency of the frequency sensitivity (variable range).
At this time, as apparent from the above equation (2),
ω ² * Ls * CL> 1
Ls> 1 / (ω ² * CL) (4)
In the extension coil that satisfies the above, Ct operates as a negative capacity. In this region, since Δ increases as shown in the above equation (3), the frequency variable range tends to increase. On the other hand, since Δ is small in the region where Ct is positive, the frequency variable range tends to be small even if there is an extension coil.

Thus, the frequency can be adjusted by inserting the extension coil Ls.
FIG. 6 is a conceptual diagram of this embodiment. Here, an example in which N piezoelectric oscillation circuits are provided is shown.
As shown in FIG. 6, each piezoelectric oscillation circuit has an amplifier in which a feedback resistor is connected between the input terminal and the output terminal of the inverter circuit, and each output is bundled into one output node. One end of each piezoelectric element is connected to the input terminal of the corresponding inverter circuit, and the other end of each piezoelectric element is bundled with one common node and connected to the output node via an extension coil.

At this time, by controlling so that any one of the N piezoelectric oscillation circuits operates by the control signals 1 to N, only one of the plurality of piezoelectric oscillation circuits can be selectively selected without colliding with each other. Can oscillate.
Incidentally, in order to obtain N different oscillation frequencies, when N oscillators having the configuration shown in FIG. 14 are provided, if N piezoelectric oscillation circuits are connected as they are, the configuration shown in FIG. 15 is obtained, and the circuit scale is simple. N times. In addition, two electrodes are required to electrically connect one set of oscillation circuit and the piezoelectric element, and further, an electrode for connecting an extension coil is also required. Therefore, N piezoelectric oscillation circuits 3 × N electrodes are required.

Thus, in the configuration shown in FIG. 15, the number of outputs is the same as the number of inputs. Therefore, when the extension coils are inserted, as many coils as the number of outputs are required. As a result, the circuit area greatly increases.
On the other hand, in this embodiment, as shown in FIG. 4, the output of each oscillation circuit is bundled into one output node, and the other end of each piezoelectric element is connected to the output node in common. Therefore, only one extension coil to be inserted is required, which is the same as the number of outputs, and there is no large increase in circuit scale. Further, by inserting the extension coil between the output node and the common node of the piezoelectric element, no electrode is added due to the insertion of the extension coil.

Thus, in the second embodiment, since the extension coil is inserted into the oscillator, the frequency sensitivity can be improved by adjusting the inductance value of the extension coil.
In addition, since the extension coil is inserted between the output node of the oscillator and the common node of the piezoelectric element, since one extension coil can be used in common in each oscillation circuit, there is an effect of reducing the number of parts, An increase in circuit scale can be suppressed.

  In the second embodiment, the 2-input 1-output oscillation circuit has been described. However, any number of inputs may be used. For example, the circuit configuration in the case of a 4-input 1-output oscillation circuit is as shown in FIG. In this case, the selection signals SEL1 to SEL4 are controlled such that any one of the piezoelectric oscillation circuits 11 to 14 is turned on. For example, when SEL1 = H level, SEL2 = L level, SEL3 = L level, and SEL4 = L level, only the transistor SM1 and the switch SW1 are turned on, and only the piezoelectric oscillation circuit 11 can be operated.

Next, a third embodiment of the present invention will be described.
In the third embodiment, the capacitive elements C1, C2, and Cx in the first embodiment described above are variable capacitive elements.
FIG. 8 is a diagram showing an oscillator with two inputs and one output according to the third embodiment.
As shown in FIG. 8, in the oscillator according to the third embodiment, the capacitive element C1 is replaced with a variable capacitive element C1 ′ and the capacitive element C2 is replaced with a variable capacitive element C2 ′ in the oscillator shown in FIG. 1 except that the capacitive element Cx is replaced with a variable capacitive element Cx ′.

Here, the capacitance values of the variable capacitance elements C1 ′, C2 ′, Cx ′ can be changed according to the voltage level and the digital code.
With this configuration, as in the first embodiment described above, it is possible to configure an oscillation circuit having different oscillation frequencies in one circuit by switching the closed loop with the selection signal SEL. Further, since C1 ′, C2 ′ and Cx ′ constituting the oscillation circuit are variable capacitance elements, the frequency can be adjusted within the range indicated by the above expression (3) by changing the capacitance value of each capacitance element. Can do.
As described above, in the third embodiment, the capacitive element disposed between the input / output terminal of each amplifier and the ground is a variable capacitive element, so that it can be easily adjusted to the target frequency. .

Next, a fourth embodiment of the present invention will be described.
In the fourth embodiment, an extension coil is added to the third embodiment described above.
FIG. 9 is a diagram illustrating a two-input one-output oscillator according to the fourth embodiment.
As shown in FIG. 9, in the oscillator of the fourth embodiment, the extension coil Ls is inserted between the output node N1 of the oscillator and the common node N2 of the piezoelectric element in the oscillator of FIG. The configuration is the same as that of the oscillator shown in FIG.
The extension coil Ls is provided to improve the frequency sensitivity, and is assumed to be disposed outside the IC chip here.

  With such a configuration, as in the third embodiment described above, it is possible to configure an oscillation circuit with different oscillation frequencies in one circuit by switching the closed loop with the selection signal SEL. Further, since C1 ′, C2 ′ and Cx ′ constituting the oscillation circuit are variable capacitance elements, the frequency can be adjusted within the range indicated by the above expression (3) by changing the capacitance value of each capacitance element. Can do. In addition, by selecting the inductance value of the extension coil Ls so as to satisfy the expression (4), it is possible to take a wider frequency variable width than the circuit of the third embodiment described above.

  As shown in FIG. 9, when C1 ′, C2 ′, and Cx ′ constituting the oscillation circuit are variable capacitance elements, the capacitance value of each capacitance element can be easily adjusted to a target frequency. it can. For example, when a crystal or SAW device is applied as the piezoelectric element, the frequency can be adjusted in the same manner. However, since the Q value is high, the adjustment is performed in a very narrow band. In such a case, the above problem can be easily solved by inserting an extension coil.

Next, a fifth embodiment of the present invention will be described.
In the fifth embodiment, the extension coil Ls is arranged in the IC chip in the fourth embodiment described above.
FIG. 10 is a diagram illustrating a two-input one-output oscillator according to the fifth embodiment.
As shown in FIG. 10, the oscillator of the fifth embodiment is the same as the oscillator of FIG. 9 described above, in which the extension coil Ls is between the output node N1 of the oscillator and the common node N2 of the piezoelectric element, and the IC chip. Except for being inserted inside, it has the same configuration as the oscillator of FIG.

When the oscillation frequency f is a high frequency exceeding 1 GHz, the necessary extension coil has a size of less than 1 nH. In such a case, the desired performance can be achieved by incorporating it into the IC chip.
For example, when the oscillation frequency f = 2 GHz and CL = 10 pF, from the above equation (4),
Ls> 0.63 [nH]
Get. With such a numerical value, the extension coil Ls can be sufficiently incorporated.

By incorporating the extension coil in the IC chip, it is possible to prevent the influence of the parasitic effect as compared with the case where the extension coil is externally attached, and the characteristics can be easily obtained.
In the third to fifth embodiments, the case where the capacitors C1 ′, C2 ′, and Cx ′ are all configured by variable capacitors has been described. However, depending on the specifications, it is necessary to configure all the capacitors by variable capacitors. Absent.

Next, a sixth embodiment of the present invention will be described.
In the sixth embodiment, the oscillator in the first to fifth embodiments described above is applied as a sensor oscillator.
FIG. 11 is a diagram illustrating a sensor oscillator with two inputs and one output according to the sixth embodiment. Here, description will be made by applying the configuration of the oscillator shown in FIG.

Here, it is assumed that X1 and X2 are piezoelectric elements with uniform sensitivity. Sensitivity means the amount of change in output relative to input, and need not be the same resonance frequency.
In this embodiment, the piezoelectric element X1 is mounted so as to block the external environment, and the piezoelectric element X2 is mounted so as to be exposed to the external environment by opening a window or the like, so that the piezoelectric element X1 functions as a reference oscillator. The piezoelectric element X2 is caused to function as a sensor oscillator.

  In the circuit shown in FIG. 11, when the selection signal SEL is switched and operated at regular intervals, the operation is switched between oscillation on the reference element side and oscillation on the sensor element side. Since the reference oscillator side is cut off from the external environment, stable oscillation is continued, but the sensor oscillator side has an oscillation frequency affected by the external environment. This frequency response occurs because the resonance frequency fluctuates in accordance with the mass of a substance attached to the surface of the piezoelectric element.

By utilizing this property, not only a physical sensor such as a mass sensor or a stress sensor but also a chemical sensor typified by a gas sensor can be used by forming a reaction film on a piezoelectric element. Thus, a sensor circuit can be easily constructed.
In FIG. 11, the configuration of the oscillator according to the first embodiment has been described. However, the configurations of the oscillators according to the second to fifth embodiments can be applied according to specifications desired to be achieved.

1 is a diagram illustrating an oscillator according to a first embodiment. It is a key map of a 1st embodiment. It is a figure which shows another example (4 inputs 1 output) in 1st Embodiment. It is a figure which shows the oscillator which concerns on 2nd Embodiment. It is an equivalent circuit for demonstrating the function of an extending | stretching coil. It is a conceptual diagram of 2nd Embodiment. It is a figure which shows another example (4 inputs 1 output) in 2nd Embodiment. It is a figure which shows the oscillator which concerns on 3rd Embodiment. It is a figure which shows the oscillator which concerns on 4th Embodiment. It is a figure which shows the oscillator which concerns on 5th Embodiment. It is a figure which shows the oscillator which concerns on 6th Embodiment. It is a figure which shows the conventional oscillator (no expansion | extension coil). It is a figure which shows the example which has N oscillators (no expansion | extension coil). It is a figure which shows the conventional oscillator (with extension coil). It is a figure showing an example with N oscillators (with extension coils).

Explanation of symbols

11-14 Piezoelectric oscillation circuit 21,22 Piezoelectric oscillation circuit C1-C4, Cx capacitive element C1 ′, C2 ′, Cx ′ Variable capacitive element EL1-EL3 Electrode NM1-NM4 Amplifying transistor SM1-SM4 Selection transistor SW1-SW4 selection Switches X1 to X4 Piezoelectric elements

Claims (4)

An oscillator including a plurality of piezoelectric oscillation circuits each including a piezoelectric element excited at a predetermined frequency, and an oscillation circuit that includes an amplifier and drives the piezoelectric element by exciting a current through the piezoelectric element,
The outputs of the plurality of oscillation circuits are bundled into one output node,
One end of each of the plurality of piezoelectric elements is connected to an input end of the amplifier corresponding to each piezoelectric element, and the other end of the plurality of piezoelectric elements is connected to the output node in common.
A selection circuit that selectively drives any one of the plurality of piezoelectric elements ;
An extension coil is connected between a common node in which the other ends of the plurality of piezoelectric elements are bundled together and the output node .   The selection circuit includes a switching element interposed between a current source and each amplifier, and controls each switching element to change any one of the plurality of amplifiers from the current source. The oscillator according to claim 1, wherein any one of the plurality of piezoelectric elements is driven by supplying a current. 3. The oscillator according to claim 1, wherein the circuit portion excluding the piezoelectric element is configured by a one-chip IC. Comprising a capacitive element arranged respectively between the ground and the output terminal of each amplifier, any one of the claims 1-3, characterized in that at least one of said plurality of capacitive elements is a variable capacitance element The oscillator according to item.

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