JP2000353918A - Piezoelectric oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact piezoelectric oscillator whose frequency control is simple. SOLUTION: This piezoelectric oscillator is provided with a piezoelectric oscillator 2, an amplifier 1, and a variable capacity element 3. In this case, the variable capacity element 3 is obtained as an MOS capacity element, and one terminal of the MOS capacity element is fixed to a V volt voltage, and the other terminal is constituted so that a control voltage can be applied in a range that a V volt is used as an intermediate value. Thus, it is possible to realize the piezoelectric oscillator for varying frequencies in a wide range without using any minus power source.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric oscillator,
In particular, the present invention relates to a piezoelectric oscillator using a MOS capacitance element.

[0002]

2. Description of the Related Art Oscillators using a piezoelectric vibrator represented by a crystal vibrator have been proposed in various circuit forms.
It has been put to practical use and is used in all electronic devices including signal sources for mobile phones and computers. On the other hand, in such an oscillator, a frequency adjustment at the time of manufacturing, a channel frequency adjustment function, or an AFC (automatic frequency
A variable capacitance element is indispensable in an oscillation circuit in order to achieve various purposes, such as realizing a frequency control function, further compensating for frequency temperature, and supporting a large number of channel frequencies.

As a circuit capable of satisfying such a function, for example, a circuit as shown in FIG. 6 is generally used. The oscillation circuit shown in the figure is a general circuit of a crystal oscillator using an inverter amplifier. Capacitors C1 and C2 are inserted between each output and ground, and the capacitors C1 and C2 are inserted.
Alternatively, a varicap diode D1 is connected as a variable capacitance element to one of the capacitors C2 (in this example, to the capacitor C1), and the cathode of the varicap diode D1 and the control terminal Vcont are connected with a resistor for DC blocking. R
It is configured to be connected via 2.

Since the operation of this oscillator circuit is well known, it will not be necessary to explain it again. However, to briefly explain, in this circuit, the control terminal Vcon
Varicap diode D according to the DC voltage applied to t
Since the capacitance value of 1 changes, various frequencies including AFC can be adjusted by controlling this control voltage as described above. On the other hand, in recent years, ICs have been desired for such oscillators in view of demands for miniaturization and power saving of various electronic devices. However, when a circuit including the varicap diode D1 as shown in FIG. 6 is formed into an IC, the diode must be formed by a process different from that of another semiconductor circuit, which hinders an inexpensive IC. Was.

That is, the varicap diode D1, which is a bipolar type semiconductor, must be formed in a separate step from the inverter amplifier 101, which is generally a C-MOS type semiconductor. As ICs became more complicated, ICs became more expensive. On the other hand, MOS type variable capacitance elements are known as variable capacitance elements suitable for IC,
Its utilization is expected. A crystal oscillator using such a MOS type variable capacitance element is disclosed in, for example,
155 “Quartz Crystal Unit with Frequency Adjustment Function” is disclosed. This is achieved by inserting a parallel circuit of a crystal unit 102 and a feedback resistor R1 between the input and output terminals of the inverter amplifier 101 as shown in FIG. The MOS type variable capacitance element 10 is connected to the input terminal of the amplifier 101.
3 as well as connecting the charge injection terminal TI of the MOS type variable capacitance element 103 to the control terminal Vcont.

Although the MOS type variable capacitance element 103 is merely an example, as shown in FIG.
It is known that a positive or negative voltage is applied to the ont with respect to an N-type substrate to flow a tunnel current in SiO ₂ to inject electrons into and out of the floating electrode 104. That is, for example, when a positive voltage is applied to the control terminal Vcont, electrons flow out of the floating electrode 104, so that the thickness of the depletion layer 105 adjacent to the floating electrode 104 is reduced, and the depletion layer capacitance is thereby increased. I do. Also, the control terminal Vcon
When a negative voltage is applied to t, the operation is the reverse of the above-described operation, and a description thereof will be omitted.

[0007]

However, as described below, a MOS type variable capacitance element can basically change a capacitance value over a wide range only by using a positive power supply and a negative power supply. Thus, there is a disadvantage that a change in the capacitance value can hardly be obtained by any one of the single polarity power supplies. Hereinafter, this will be described in some detail. Figure 9 shows MO
FIG. 4 is a diagram illustrating an example of a relationship between a voltage between electrodes and a capacitance value of an S-type variable capacitance element. As is clear from the figure, in this case, the MOS type variable capacitance element has a voltage between terminals of -1.
The capacitance changes by about 80 pF within the range of 5V to + 0.5V. On the other hand, crystal oscillators, on the other hand, generally require a wide frequency variable range, but in order to perform high-precision frequency control, the capacitance value changes more slowly than the control voltage changes more steeply. Therefore, there is a demand for a variable capacitance element whose capacitance varies over a wide range of control voltages.

Therefore, in the case of a crystal oscillator as shown in FIG. 7, in order to obtain a wide range of variable capacitance using the MOS type variable capacitance element 103, it is necessary to apply both a positive voltage and a negative voltage to the control terminal Vcont. Since the control voltage source is required, there is a problem that the configuration of the system for controlling the frequency is complicated. The present invention has been made to solve the above problem, and a wide range of variable capacitance change can be obtained even by a single-polarity power supply of either the positive electrode or the negative electrode while using a MOS capacitance element suitable for IC. An object of the present invention is to provide a small-sized piezoelectric oscillator in which such frequency control is easy.

[0009]

According to a first aspect of the present invention, there is provided a piezoelectric vibrator comprising: a piezoelectric vibrator;
In an oscillator including an amplifier and a variable capacitance element, the variable capacitance element is a MOS capacitance element, and an AC voltage having an intermediate voltage of V volt is applied to one terminal of the MOS capacitance element, and the other terminal is connected to the other terminal. Is characterized in that a control voltage is applied in a range where the V volt is an intermediate value.

According to a second aspect of the present invention, there is provided an inverter piezoelectric oscillator in which a piezoelectric vibrator is connected between input and output terminals of an inverter amplifier, and divided capacitors C1 and C2 are connected between both ends of the piezoelectric vibrator and ground. By inserting a MOS capacitor in series with the piezoelectric vibrator, a bias voltage of V volt at the output terminal or the input terminal of the inverter amplifier is applied to one end of the MOS capacitor,
It is characterized in that the other end of the S-capacitance element is configured to supply a control voltage that changes in a range where V volt is an intermediate value.

According to a third aspect of the present invention, there is provided an inverter piezoelectric oscillator in which a piezoelectric vibrator is connected between input and output terminals of an inverter amplifier, and divided capacitors C1 and C2 are connected between both ends of the piezoelectric vibrator and ground. Then, two MOS capacitors are inserted on both sides of the piezoelectric vibrator, and an AC voltage having a V volt voltage as an intermediate voltage is applied to one end of the MOS capacitor, and the other end of the MOS capacitor is connected to V It is characterized in that it is configured to supply a control voltage that changes in a range where the volt is an intermediate value.

According to a fourth aspect of the present invention, in the inverter oscillator, a piezoelectric element is connected to an input / output terminal of the inverter amplifier, and divided capacitors C1 and C2 are connected between both ends of the piezoelectric element and ground. A MOS capacitance element is inserted between a vibrator and an input terminal of the inverter amplifier, or between the piezoelectric vibrator and an output terminal of the inverter amplifier, and a terminal of the MOS capacitance element on the side connected to the piezoelectric vibrator. A control voltage Vcont to the input terminal or the output terminal of the inverter amplifier.
When the voltage applied to one end of the S capacitance element is V, the voltage V is an intermediate voltage of the control voltage Vcont. According to a fifth aspect of the present invention, in the inverter oscillator in which a piezoelectric element is connected to an input / output terminal of the inverter amplifier, and divided capacitors C1 and C2 are connected between both ends of the piezoelectric element and ground, respectively, A MOS capacitor is inserted between the input terminal of the inverter amplifier or between the piezoelectric vibrator and the output terminal of the inverter amplifier, and a control voltage is applied to a terminal of the MOS capacitor connected to the piezoelectric vibrator. Vcont is applied, a DC circuit of a resistor and a capacitor is inserted and connected between a terminal on the inverter amplifier side of the MOS capacitor and an input or output terminal of the inverter amplifier, and further, the inverter amplifier of the MOS capacitor is connected. And a DC bias voltage is applied to the terminal on the side. According to a sixth aspect of the present invention, in addition to the fifth aspect, the amplitude level of the alternating current supplied to the MOS capacitance element is adjusted based on a resistance value of the DC circuit, and the inverter of the MOS capacitance element is adjusted. When a DC bias voltage supplied to a terminal on the amplifier side is V, the voltage V is an intermediate voltage of the control voltage Vcont.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on illustrated embodiments. FIG. 1 is a circuit diagram showing an embodiment of a voltage controlled crystal oscillator according to the present invention. In the crystal oscillator shown in FIG. 1, a feedback resistor R1 and a series circuit of a crystal oscillator 2 and a resistor R2 are inserted in parallel between input and output terminals of an inverter amplifier 1 having a power supply voltage of Vcc. 1, a capacitor C1 is inserted between one end of the crystal unit 2 and the ground, and a capacitor C2 is inserted between one end of the crystal unit 2 and the ground. MOS type variable capacitance element 3 is connected to capacitor C
3, and a connection point between the MOS type variable capacitance element 3 and the capacitor C3 and a control terminal Vcont are connected via a resistor R3.

Next, the operation of the crystal oscillator having such a configuration will be described. The operation of the inverter oscillating circuit is well known, and the description thereof is omitted. As is clear from the above description, the crystal oscillator shown in FIG. 1 is configured such that one terminal of the MOS type variable capacitance element 3 is connected to the input terminal of the inverter amplifier 1. One end of the variable capacitance element 3 has a threshold level voltage V = Vcc / 2 of the inverter amplifier 1.
Is applied.

Then, the control terminal Vcont is applied from 0V
When a DC control voltage in the range of Vcc is supplied, the voltage between the terminals of the MOS type variable capacitance element 3 is -Vcc / 2 to Vc based on the potential at the connection point with the input terminal of the inverter amplifier 1.
Since the voltage changes within the range of c / 2, as described with reference to FIG. 9, as a result, both the positive and negative voltages are applied to the MOS capacitor, so that the capacitance value changes over a wide range. That is, for example, when the inverter amplifier 1 operates with the power supply voltage Vcc = 5 V, the threshold voltage level Vref = 2.5 V of the inverter amplifier 1 is applied to one terminal of the MOS variable capacitance element 3. Further, at this time, when a control voltage (Vcont) in the range of 0 V to 5 V is supplied to the control terminal Vcont as a positive voltage, the terminal voltage Vcont-Vref of the MOS type variable capacitance element 3 is changed from -2.5 V to +2.5. Since the voltage is controlled in the range of 5 V, the capacitance value can be controlled over a wide range without using a minus power source as in the related art.

The oscillation circuit according to the present invention has the following effects in addition to the above effects. That is, in the above configuration, since the MOS type variable capacitance element 3 is inserted in the oscillation loop, the inverter amplifier 1
Side terminal has the threshold voltage level Vref
AC voltage which is an oscillation signal having an intermediate voltage of 2.5 V is applied. And, the amplitude level of the AC voltage is MO
There is a phenomenon that affects the capacitance variable sensitivity of the S-type variable capacitance element 3, and by actively utilizing this characteristic, the capacitance variable sensitivity of the MOS variable capacitance element 3 can be arbitrarily reduced.

Hereinafter, this will be described in detail. Here, in order to facilitate understanding, as shown in FIG. 2, the relationship between the terminal voltage and the capacitance value of the MOS type variable capacitance element is controlled at a control voltage of -0.5 V to +0.5 V around the terminal voltage 0 V. It is assumed that the capacitance value changes within the range. In FIG.
Is applied when a DC voltage Vref = 2.5 V equal to the threshold level is applied to one terminal of the MOS type variable capacitance element, and a positive DC control voltage centered at 2.5 V is applied to the other terminal. It shows the relationship between the inter-terminal voltage and the inter-terminal capacitance value, and a high capacitance variable sensitivity of about 80 pF / V can be obtained in an unsaturated region where the capacitance value changes linearly and greatly.

With respect to such a MOS type variable capacitance element,
Assume that the voltage Vref is a bias voltage of 2.5 V applied to the input terminal of the inverter amplifier 1 and is an oscillating AC voltage fed back to the input terminal of the inverter amplifier 1 with the bias voltage being the center voltage. First, when the amplitude level of the oscillation AC voltage is the AC voltage B which is much lower than the voltage width of the unsaturated region (F) as shown in FIG.
The capacitance value between the terminals changes in accordance with the voltage change in the positive half cycle and the negative half cycle of the AC voltage B, and as a result, it becomes almost the average value.

In this state, for example, the control voltage Vcont
Falls below the dotted line a in the figure, the minus half cycle of the AC voltage B reaches the saturation region (f), the amount of capacity change due to the minus half cycle decreases, and the capacity change accompanying the voltage change of the plus half cycle. Becomes dominant, the capacitance sensitivity between the terminals decreases as the AC signal B reaches the saturation region as shown by the dotted line A ′, and the control voltage Vcon
The range of t expands.

On the other hand, when the amplitude level of the oscillating AC voltage is the AC voltage C substantially equal to the width of the unsaturated voltage range as shown in FIG. Since the minus half cycle of the AC voltage C reaches the saturation region, the amount of capacitance change due to the minus half cycle in the region of the terminal voltage less than this becomes small,
Conversely, the same applies when Vcont is greater than 0 V,
As shown by the dotted line C ′, the capacitance sensitivity between the terminals has a wide range of variable capacitance characteristics.
F / V. In the above description, the AC voltage C
Has been described as an amplitude level substantially equal to the voltage width of the non-saturation range (F). However, if the amplitude level is about 50% or more of the non-saturation range, a sufficiently practical capacitance variable sensitivity can be obtained. is there. Further, the control of the amplitude level of the AC voltage can be easily performed by adjusting the resistor R2, for example.

FIG. 3 is a circuit diagram showing another embodiment of the crystal oscillator according to the present invention. 1 differs from the crystal oscillator shown in FIG. 1 in that a MOS type variable capacitance element 3 is inserted between the crystal resonator 2 and the capacitor C1 or between the crystal resonator 2 and the capacitor C2. FIG. 4A shows one terminal of the MOS variable capacitance element 3 connected to the output of the inverter amplifier 1 and FIG. 4B shows the other terminal connected to the input of the inverter amplifier. Is connected to the control terminal Vcont via the resistor R3. Further, as shown in FIG.
Insert a fixed or variable resistor Rc between point E and ground,
If the value of the resistor Rc can be set arbitrarily, the voltage at the point E can be controlled, whereby the voltage between the terminals of the MOS type variable capacitance element 3 is controlled and the frequency can be adjusted.

FIG. 4 is a circuit diagram showing still another embodiment of the crystal oscillator according to the present invention. The crystal oscillator shown in the figure is different from the crystal oscillator shown in FIGS. 1 and 3 in that a MOS type variable capacitance element 4 is provided between the crystal oscillator 2 and the capacitor C1, and the crystal oscillator 2 is provided between the crystal oscillator 2 and the capacitor C2. MOS type variable capacitance element 5
, One terminal of any of the MOS variable capacitance elements is connected to one of the input / output terminals of the inverter amplifier 1, and the other terminal is connected to the control terminal Vc.
It is located so as to be connected to ont via resistors R3 and R4. It is clear that a wider variable capacitance range can be obtained by such a configuration, and the operation will not be described again.

FIG. 5 is a circuit diagram showing another embodiment of the crystal oscillator according to the present invention. The feature of the crystal oscillator shown in the figure is that the amplitude level of the AC voltage supplied to the MOS type variable capacitance element 3 and the DC bias voltage as the reference voltage can be separately adjusted. is there.

That is, as shown in the figure, in the crystal oscillator, the MOS type variable capacitance element 3 is inserted between the crystal unit 2 and the capacitor C1, or between the crystal unit 2 and the capacitor C2. A connection point between the crystal unit 2 and the MOS capacitor 3 is connected to the control terminal Vcont via the resistor R3, and the other terminal of the MOS capacitor 3 is connected between the power supply Vcc and the ground. Connected at the connection midpoint of the series circuit of the resistor R5 and the resistor R6.
(A), or to the input side of the inverter amplifier 1 as shown in (b) of FIG. .

With such a configuration, the MOS transistor is first obtained based on the relational expression of Vref (DC) = R6 × Vcc / (R5 + R6).
After setting the reference voltage value Vref of the DC bias of the type transformation element 3 and adjusting the reference capacitance value of the MOS type variable capacitance element 3, Vref (AC) = R5 × R6 × V0 / ((R5 + R6) × (R2 + R5 × R6 / (R
5 + R6))), only the value of resistor R2 is adjusted based on the
If the capacitance sensitivity of the MOS variable capacitance element 3 is adjusted by setting the amplitude of the AC voltage supplied to the variable capacitance element 3, even if the capacitance sensitivity is adjusted, the effect appears in the set value of the reference capacitance. As a result, the adjustment process of the crystal oscillator is simplified as a result. V0 is the inverter amplifier 1
Means the amplitude level of the AC component of the input / output voltage.

Although the present invention has been described using the configuration in which one terminal of the MOS type variable capacitance element applies the threshold voltage of the inverter amplifier 1, the present invention is not limited to this. Alternatively, a configuration in which a constant voltage is applied to one terminal of the MOS type variable capacitance element using a voltage generation circuit or the like may be employed.

Further, although the present invention has been described above by taking an oscillator using a quartz oscillator as an example, the present invention is not limited to this, and is applicable to an oscillator using a piezoelectric oscillator other than quartz. It is clear that this may be done.

[0028]

As described above, the piezoelectric oscillator according to the present invention is constructed as described above, so that the oscillating frequency can be widened without requiring a complicated system configuration for frequency control. This has the effect that control can be performed with high accuracy.

[Brief description of the drawings]

FIG. 1 shows a circuit diagram of an embodiment of a crystal oscillator according to the present invention.

FIG. 2 is a diagram illustrating a method for controlling the capacitance variable sensitivity of the crystal oscillator according to the present invention. (A) A case where the variable capacitance sensitivity is not controlled will be described. (B) A case where the variable capacitance sensitivity is controlled will be described.

FIG. 3 shows a circuit diagram of another embodiment of the crystal oscillator according to the present invention. (A) shows a circuit of another embodiment of a crystal oscillator according to the present invention. (B) shows a circuit of another embodiment of the crystal oscillator according to the present invention.

FIG. 4 shows a circuit diagram of another embodiment of the crystal oscillator according to the present invention.

FIG. 5 shows a circuit diagram of another embodiment of the crystal oscillator according to the present invention.

FIG. 6 is a circuit diagram of a conventional crystal oscillator.

FIG. 7 is a circuit diagram of a conventional crystal oscillator using a MOS variable capacitance element.

FIG. 8 is a sectional structural view of a MOS variable capacitance element.

FIG. 9 shows a relationship between a voltage between terminals of a MOS type variable capacitance element and a capacitance value.

[Description of Signs] 1, 101 inverter amplifier, 2, 102 crystal oscillator,
3, 4, 5103 MOS variable capacitance elements, R1, R2,
R3, R4, R5, R6 resistance, C1, C2, C3, C4
Capacitor, 104 floating electrode, 105 depletion layer, Vcc power supply, Vcont control terminal

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5J079 AA04 BA12 BA17 BA44 BA47 DA14 FA14 FA17 FA21 FB03 GA04 GA09 GB04 KA01 KA05

Claims (6)

[Claims] In an oscillator including a piezoelectric vibrator, an amplifier, and a variable capacitance element, the variable capacitance element is a MOS capacitance element, and one terminal of the MOS capacitance element is connected to a V volt voltage at an intermediate level. And a control voltage is applied to the other terminal in a range having the V volt as an intermediate value. 2. An inverter piezoelectric oscillator in which a piezoelectric vibrator is connected between input and output terminals of an inverter amplifier, and divided capacitors C1 and C2 are connected between both ends of the piezoelectric vibrator and ground, respectively. Is inserted in series with the MOS capacitor, a bias voltage of V volt at the output terminal or the input terminal of the inverter amplifier is applied to one end of the MOS capacitor, and the other terminal of the MOS capacitor is connected to V volt. A piezoelectric oscillator configured to supply a control voltage that changes within a range of an intermediate value. 3. An inverter piezoelectric oscillator in which a piezoelectric vibrator is connected between input and output terminals of an inverter amplifier, and divided capacitors C1 and C2 are connected between both ends of the piezoelectric vibrator and ground, respectively. , Two MOS capacitance elements are inserted on both sides of the MOS capacitance element, an AC voltage having a V volt voltage as an intermediate voltage is applied to one end of the MOS capacitance element, and the other end of the MOS capacitance element has a V volt as an intermediate value. A piezoelectric oscillator configured to supply a control voltage that changes in a range. 4. An inverter oscillator in which a piezoelectric element is provided at an input / output terminal of an inverter amplifier, and divided capacitors C1 and C2 are connected between both ends of the piezoelectric element and ground.
A MOS capacitor is inserted between the piezoelectric vibrator and the input terminal of the inverter amplifier, or between the piezoelectric vibrator and the output terminal of the inverter amplifier, and
The control voltage Vcont is applied to the terminal of the OS capacitive element connected to the piezoelectric vibrator.
Is applied, and the voltage applied to one end of the MOS capacitor is a DC bias voltage at the input terminal or the output terminal of the inverter amplifier, and the voltage V is the control voltage.
A piezoelectric oscillator having an intermediate voltage of Vcont. 5. An inverter oscillator in which a piezoelectric element is connected to an input / output terminal of an inverter amplifier, and divided capacitors C1 and C2 are connected between both ends of the piezoelectric element and ground.
A MOS capacitor is inserted between the piezoelectric vibrator and the input terminal of the inverter amplifier, or between the piezoelectric vibrator and the output terminal of the inverter amplifier, and
The control voltage Vcont is applied to the terminal of the OS capacitive element connected to the piezoelectric vibrator.
And a DC circuit of a resistor and a capacitor is inserted and connected between the terminal of the MOS capacitance element on the side of the inverter amplifier and the input or output terminal of the inverter amplifier. Wherein a DC bias voltage is applied to the terminals of the piezoelectric oscillator. 6. The method according to claim 6, wherein the amplitude level of the alternating current supplied to the MOS capacitance element is adjusted based on the resistance value of the DC circuit, and the DC bias voltage supplied to the terminal of the MOS capacitance element on the inverter amplifier side is adjusted. 7. The piezoelectric oscillator according to claim 6, wherein when V is V, the voltage V is an intermediate voltage of the control voltage Vcont.