JP2002223123A - Piezoelectric oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric oscillator having excellent power voltage characteristics where a stable oscillation operation function is obtained. SOLUTION: In the Colpitts piezoelectric oscillator provided with an oscillation circuit, which has a piezoelectric vibrator, an amplifier circuit and a varactor diode, a piezoelectric vibrator and a FET, a series circuit consisting of at least two resistors is inserted and connected between a source of the FET and ground, a connection midpoint of the series circuit and the source of the FET are connected via a capacitor and the connection midpoint of the series circuit and the gate of the FET are connected via a resistor. Thus, the drain current can be controlled without being affected by a level change in an oscillation signal and highly accurate drain current control is attained even when a low consumed current is selected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric oscillator, and more particularly, to a piezoelectric oscillator having excellent frequency stability against power supply voltage fluctuation.

[0002]

2. Description of the Related Art Heretofore, a crystal oscillator used in a communication device using a battery as a driving power source has a high frequency stability (hereinafter referred to as a power source voltage fluctuation characteristic) with respect to a change in power source voltage. That is, when the power supply voltage of the crystal oscillator fluctuates, the operation level of the amplifier circuit such as the oscillation transistor (the current flowing through the crystal oscillator or the current flowing through the amplifier) changes, and as a result, the oscillation frequency fluctuates. In order to solve such a problem, there is a crystal oscillator shown in FIG. That is, FIG. 4 is a circuit diagram showing a conventional crystal oscillator. A crystal oscillator 100 shown in the figure is a Colpitts type crystal oscillator, and an FE
A gate of T102 is connected, and a parallel circuit of a series circuit composed of capacitors 103 and 104 and a resistor 105 is inserted and connected between the gate and the ground.
4 is connected to the source of the FET 102, and this source is grounded via the resistor 106.
The drain of T102 is connected to the power supply voltage Vcc via the resistor 107.
Line and the output terminal O via the capacitor 108.
It is connected to a UT, and the other end of the crystal unit 101 is grounded via a capacitor 109.

The operation of the crystal oscillator 100 will be described below. Since the operation of the Colpitts oscillator is known, its description is omitted. Generally, in the FET, the value of the drain current ID can be determined by the value of the gate-source voltage VGS according to the transfer characteristic of the FET shown in FIG. 5, and when the voltage VGS, that is, the negative potential of the gate potential with respect to the source voltage increases, the drain current ID increases. It has the characteristic that the value of ID becomes small.

When the power supply voltage Vcc rises and the drain current ID increases, the crystal oscillator 100
06, the value of the voltage between the source and the ground, which is the voltage between both ends, rises. As a result, the value of the voltage VGS between the gate and the source, that is, the negative potential of the gate potential with respect to the source voltage becomes large. It works to reduce the drain current ID from the transfer characteristic. That is, since the gate of the FET is grounded by the resistor 105 and thus has zero potential, the higher the source potential, the higher the gate potential with respect to the source in the negative direction. Therefore, since the horizontal axis in FIG. 5 is moved to the left, the drain current ID becomes smaller. On the other hand, the operation in the case where the power supply voltage Vcc is reduced is the reverse of the above operation, and the description thereof is omitted.

The power supply voltage is obtained by the above-described negative feedback operation.
Even when Vcc fluctuates, the drain current ID is kept constant, so that the operating state of the crystal oscillator 100 is kept stable, and there is an effect that the fluctuation of the oscillation frequency is compressed.

[0006]

However, since the drain current ID is obtained by superimposing the oscillating signal, which is an AC current, on the DC current determined based on the setting of the bias circuit, not only the DC current but also the high-frequency signal is used. Since a negative feedback function acts on a certain oscillation signal, the gain of the amplifier is reduced.

That is, the gate-source voltage VGS of the FET 102 fluctuates according to the change in the ID of the drain current due to the oscillation signal, and the drain current is controlled so as to suppress the amplitude fluctuation of the oscillation signal. Therefore, there has been a problem that a required oscillation operation cannot be obtained, for example, a specified oscillation signal level is not output.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems of a piezoelectric oscillator. In an oscillation circuit using an FET, amplification of a high frequency signal is suppressed while maintaining an effect of suppressing an oscillation frequency fluctuation against a power supply voltage fluctuation. An object of the present invention is to provide a piezoelectric oscillator capable of obtaining a stable oscillation operation by preventing a decrease in gain.

[0009]

Means for Solving the Problems In order to solve the above-mentioned problems, the invention according to claim 1 according to the present invention comprises a piezoelectric vibrator and a piezoelectric vibrator.
In the Colpitts type piezoelectric oscillator having the ET, the piezoelectric vibrator is connected to the FET, and the FET is connected to the FET.
A series circuit composed of at least two resistors is inserted and connected between the source and the ground, and a connection point of the series circuit is connected to the FET.
Are connected via a capacitor, and the connection midpoint of the series circuit and the gate of the FET are connected via a resistor. According to a second aspect of the present invention, in addition to the first aspect, the other end of the piezoelectric vibrator, one end of which is grounded via a capacitor, is connected to the gate of the FET, and the other end is connected between the gate and the ground. A capacitor series circuit composed of two capacitors is inserted and connected, a connection midpoint of the capacitor series circuit is connected to the source of the FET, and a resistor series circuit composed of two resistors is inserted between the source and ground. A connection midpoint of the resistance series circuit and the source are connected via a capacitor, and a connection midpoint of the resistance series circuit and the gate are connected via an AC blocking resistor, and a drain of the FET is connected. And power supply voltage
The Vcc line is connected via a resistor.

[0010]

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 crystal oscillator according to the present invention. In the crystal oscillator 1 shown in FIG. 1, one end of a crystal oscillator 2 is connected to the gate of an FET 3, the other end of the crystal oscillator 2 is grounded via a capacitor 4, and furthermore, a connection between the gate of the FET 3 and the ground is provided. , A series circuit composed of a capacitance 5 and a capacitance 6 which bear a part of a load capacitance is inserted and connected, a connection point of the series circuit is connected to a source of the FET 3, and a resistor 7 is connected between the source and the ground. A series circuit including the resistor 8 is inserted and connected. Further, the connection point of the series circuit and the gate of the FET 3 are connected via a resistor 9, the resistor 7 and a bypass capacitor 10 are connected in parallel, and the power supply voltage Vcc line and the drain of the FET 3 are connected via a resistor 11. And the drain and output terminal OU
The circuit shown in this embodiment is a series circuit in which a source resistor inserted between a source and ground is divided into two resistors 7 and 8,
The feature is that a bypass capacitance 10 is loaded on the source-side resistor 7.

The operation of the crystal oscillator 1 will be described below. Since the operation of the Colpitts type crystal oscillator is known, the description is omitted. In the circuit of FIG.
When the power supply voltage Vcc rises above the reference value, the voltage between the terminals of the resistor 7 increases on the basis of the increase in the drain current ID accompanying this, so that the gate-source voltage of the FET 3 increases and the gate negative potential with respect to the source. Becomes larger, and the drain current I is increased based on the transfer characteristics of the FET shown in FIG.
It works to suppress the increase in D.

On the other hand, when the power supply voltage Vcc is lower than the reference value, the negative potential between the gate and the source is reduced and the drain current ID is suppressed. The description of the operation, which is the reverse operation when the power supply voltage Vcc rises above the reference value, will be omitted. on the other hand,
In response to the change in the drain current ID based on the change in the amplitude of the oscillation signal, the oscillation signal that is an AC signal
, The voltage between the terminals of the resistor 7 is kept at a constant value without being affected by the voltage, and the gate-source voltage VGS is not affected by the amplitude change of the oscillation signal. With respect to the oscillation signal, the resistor 8 acts as a load to form an oscillation loop via the capacitor 9 and the capacitor 5, so that the amplification degree for oscillation can be secured.

Therefore, the control of the drain current by the gate-source voltage VGS is limited to the control of the DC voltage change due to the fluctuation of the power supply voltage Vcc or the like. When the crystal oscillator 1 is of a low current consumption type, the source resistor is separated into a resistor 7 and a resistor 8 so that the resistor 7 for determining the set value of the gate-source voltage VGS has a low resistance value. Can be used, whereby the value of the gate-source voltage VGS can be set in a high voltage region where the rate of change of the drain current ID is large, and the degree of freedom in design can be ensured. Further, as another embodiment based on the present invention, a crystal oscillator having a configuration as shown in FIG. 2 may be used. That is, the crystal oscillator 1 shown in FIG.
Is characterized in that a connection midpoint between the resistors 7 and 8 is connected to a connection midpoint between the capacitors 5 and 6.
Even with such a configuration, the functions described above can be obtained. When an AC feedback function is required, a crystal oscillator having a configuration as shown in FIG. 3 may be used. That is,
FIG. 3 is a circuit diagram of a crystal oscillator according to another embodiment of the present invention. The feature of the crystal oscillator 1 shown in the figure is that the resistor 9 is configured to be grounded. In such a configuration, the level of the AC signal fed back by the value of the resistor 8 can be set according to the required feedback function, so that an excessive feedback function does not occur as compared with the conventional case.

Further, although the present invention has been described using a quartz oscillator, the present invention is not limited to this, and can be applied to an oscillator using a piezoelectric oscillator other than quartz.

[0015]

As described above, according to the first aspect of the present invention, there is provided a Colpitts type piezoelectric oscillator including a piezoelectric vibrator and an FET, wherein at least two resistors are connected between a source and a ground of the FET. A circuit is inserted and connected, a connection point of the series circuit is connected to a source of the FET via a capacitor, and a connection point of the series circuit is connected to a gate of the FET via a resistor. Therefore, the drain current can be controlled without being affected by the level change of the oscillation signal, and the drain current can be controlled with high accuracy even at a low current consumption setting. is there.

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

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

FIG. 4 is a circuit diagram of a conventional crystal oscillator.

FIG. 5 is a diagram showing a transfer characteristic of an FET.

[Description of Signs] 1, 100 crystal oscillator, 2, 101 crystal oscillator, 3, 1
02FET, 4, 5, 6, 10, 12, 103, 10
4, 108, 109 capacity, 7, 8, 9, 11, 105,
106, 107 resistance

Claims (2)

[Claims] 1. A Colpitts-type piezoelectric oscillator comprising a piezoelectric vibrator and an FET, wherein the piezoelectric vibrator is connected to the FET and a series circuit comprising at least two resistors between a source and a ground of the FET. The connection midpoint of the series circuit and the source of the FET are connected via a capacitor, and the connection midpoint of the series circuit and the gate of the FET are connected via a resistor. Piezo oscillator. 2. The other end of a piezoelectric vibrator, one end of which is grounded via a capacitor, is connected to the gate of an FET, and a capacitor series circuit composed of two capacitors is inserted and connected between the gate and the ground. Connecting the connection midpoint of the capacitance series circuit to the source of the FET, inserting and connecting a resistance series circuit composed of two resistors between the source and the ground, The source is connected via a capacitor, the connection midpoint of the resistor series circuit and the gate are connected via an AC blocking resistor, and the drain of the FET is connected to a power supply voltage.
2. The piezoelectric oscillator according to claim 1, wherein the piezoelectric oscillator is connected to a Vcc line via a resistor.