JP2011205713A - Colpitts oscillator circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a colpitts oscillator circuit which controls variation in a drive-level for oscillating a piezoelectric oscillator circuit with respect to change in an ambient temperature.SOLUTION: A series circuit including capacitors C1 and C2 as one part of a load capacitance is connected between a base and a ground of an oscillation transistor TR1, an emitter of the oscillation transistor TR1 is connected to a connection middle point of the series circuit, and an emitter resistor R1 is connected between the emitter and the ground. In addition, a series circuit including a resistor R2 and a thermistor TH1 is connected in parallel with the emitter resistor R1. A base bias circuit including resistors R3 and R4 is connected to the base of the oscillation transistor TR1, and a piezoelectric oscillator circuit X1 is connected between the base and the ground of the oscillation transistor TR1.

Description

The present invention relates to a Colpitts type oscillation circuit, and more particularly to a Colpitts type oscillation circuit that reduces the drive level (oscillator current flowing in a piezoelectric vibrator) of the oscillation circuit as much as possible and suppresses fluctuations of the drive level with respect to ambient temperature. .

Piezoelectric oscillators that supply stable frequency signals are widely used as reference oscillators for mobile communication mobile stations and base stations, and as reference clock sources for computers and the like. recent years,
With the demand for miniaturization and high performance of mobile communication devices and transmission communication devices, miniaturization and stabilization are strongly demanded for piezoelectric oscillators used in these devices. A piezoelectric vibrator used for a piezoelectric oscillator is an electromechanical vibrator, and it is known that a low drive level leads to high reliability with respect to secular change or the like.
On the other hand, as an oscillation circuit configuration of a piezoelectric oscillator, a Colpitts oscillation circuit having a transistor as an amplifier is generally used.

FIG. 6 is a circuit configuration diagram of a conventional Colpitts oscillation circuit disclosed in Patent Document 1. In FIG. The Colpitts-type oscillation circuit 101 includes a base of the oscillation transistor TR101 and a ground (GN
D), a series circuit of a capacitor C101 and a capacitor C102, which are part of the load capacitance, is connected, the midpoint of connection of this series circuit and the emitter of the oscillation transistor TR101 are connected, and an emitter is connected between the emitter and ground. A resistor R101 is connected. A base bias circuit including a resistor R102 and a resistor R103 is connected to the base of the oscillation transistor TR101, and the piezoelectric vibrator X1 is connected between the base of the oscillation transistor TR101 and the ground.
A series circuit of 01 and a capacitor Cv103 is connected. Also, the oscillation transistor T
A resistor R104 is connected between the collector of R101 and the power supply voltage (Vcc) line, a capacitor C104 is connected between the collector and the emitter, and an output signal is obtained from the collector via a DC cut capacitor C105. ing.
In the Colpitts type oscillation circuit 101 shown in FIG. 6, a capacitor C104 is connected between the collector and emitter of the oscillation transistor TR101. Oscillation transistor TR1
Since the phase of the emitter output and the collector output of 01 are shifted by 180 °, a negative feedback circuit is configured by connecting both output terminals with a capacitor C104. As a result of the output being suppressed by the negative feedback circuit, it is possible to rapidly decrease the drive level and increase the negative resistance value.

Next, FIG. 7 is another circuit configuration diagram of the Colpitts type oscillation circuit disclosed in Patent Document 2. In FIG. The Colpitts oscillation circuit shown in FIG. 7 has a configuration in which a transistor constituting the oscillation circuit and a transistor constituting the base-grounded amplifier circuit are connected in cascade.
The Colpitts type oscillation circuit 111 includes a base of the oscillation transistor TR111 and a ground (GND)
) Between the series circuit of the capacitor C111 and the capacitor C112, which are part of the load capacitance, and the connection midpoint of this series circuit and the emitter of the oscillation transistor TR111 are connected,
Further, an emitter resistor R111 is connected between the emitter and the ground. A series circuit of a piezoelectric vibrator X111 and a circuit network Z111 that performs temperature compensation of the piezoelectric vibrator is connected between the base of the oscillation transistor TR111 and the ground.
The collector of the oscillation transistor TR111 is connected to the emitter of the amplification transistor TR112, and a collector resistor R112 is connected between the collector of the amplification transistor TR112 and the power supply voltage (Vcc) line. Further, a parallel circuit of a resistor R113 and the thermistor TH111 from the power supply voltage line side as a base bias resistance of the oscillation transistor TR111 and the amplification transistor TR112 between the power supply voltage line and the ground, and a resistance R1
14, a resistor R115, and a resistor R116 are connected in series. And resistance R115
Is connected to the base of the oscillation transistor TR111, and the connection point of the resistors R114 and R115 is connected to the base of the amplification transistor TR112. Further, a capacitor C113 is provided between the base of the amplifying transistor TR112 and the ground.
Is connected. An output signal is obtained from the collector of the amplifying transistor TR112 via a DC cut capacitor C114.

As the thermistor TH111, a thermistor TH111 having a characteristic that its resistance value decreases when the ambient temperature decreases and increases when the ambient temperature increases is used. Therefore, bias resistor R114
Since the parallel circuit (thermistor circuit) of the thermistor TH111 and the resistor R113 is provided between the power supply voltage line and the power supply voltage line, for example, when the ambient temperature rises, the resistance value of the thermistor TH111 rises and the power supply voltage line The base current flowing through the oscillation transistor TR111 and the amplification transistor TR112 is reduced. As a result, the base potentials of the oscillation transistor TR111 and the amplification transistor TR112 change so as to reduce the transistor characteristic variation with respect to changes in the ambient temperature, so that the Colpitts oscillation circuit 111 can obtain a stable oscillation output. It works as follows. That is, by controlling the base-emitter voltage by changing the base potential of the oscillation transistor TR111, the emitter current is adjusted, and the fluctuation of the negative resistance value of the Colpitts oscillation circuit due to the ambient temperature change is suppressed, Drive level temperature fluctuation is reduced.

JP 2004-48629 A JP 2003-152456 A

However, the Colpitts oscillation circuit disclosed in Patent Document 1 has a characteristic of reducing the drive level, but does not consider the influence of changes in ambient temperature. Therefore, in the conventional Colpitts type oscillation circuit, the oscillation output level fluctuates when the ambient temperature changes. as a result,
As the oscillation output level fluctuates, the drive level fluctuates and the drive level increases. When the drive level is increased from the set value, there is a problem that the secular change of the characteristic unique to the piezoelectric vibrator increases and the oscillation frequency fluctuates.
In the Colpitts type oscillation circuit shown in Patent Document 2, the emitter current of the oscillation transistor is adjusted by controlling the base potential. Therefore, the sensitivity to changes in ambient temperature is low, and the drive level excites the piezoelectric vibrator. The effect of suppressing the fluctuation was insufficient.
The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a Colpitts type oscillation circuit that suppresses fluctuations of a drive level for exciting a piezoelectric vibrator with respect to an ambient temperature change. .

SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

[Application Example 1] An oscillation transistor, a first capacitor connected between a base and an emitter of the oscillation transistor, a second capacitor connected between an emitter of the oscillation transistor and the ground, and the oscillation Colpitts oscillation circuit comprising: a piezoelectric vibrator connected between the base and ground of a transistor; and a first resistance circuit having a negative temperature coefficient of resistance connected between the emitter of the oscillation transistor and ground. It is characterized by.

According to the present invention, when the first resistance circuit including the temperature compensation circuit is connected between the emitter of the oscillation transistor and the ground, and the ambient temperature changes, the resistance value of the first resistance circuit is set. By changing it, the emitter current of the oscillation transistor is controlled. Therefore, when the ambient temperature changes, the fluctuation of the negative resistance value of the oscillation circuit can be suppressed, and the fluctuation of the drive level for exciting the piezoelectric vibrator can be reduced. As a result, the oscillation circuit can be operated at a low drive level as compared with the conventional Colpitts oscillation circuit, and the phase noise characteristics and aging characteristics of the Colpitts oscillation circuit can be improved.

Application Example 2 The first resistor circuit is characterized by the Colpitts oscillation circuit according to Application Example 1, which includes a parallel circuit of an emitter resistor and a first thermistor.

According to the present invention, since the first resistance circuit having a negative temperature coefficient is configured by a circuit including a thermistor, a desired characteristic can be easily selected by selecting a thermistor having a predetermined characteristic. Thus, the emitter current of the oscillation transistor can be controlled.

Application Example 3 The first resistor circuit is characterized by the Colpitts oscillation circuit according to Application Example 1 in which a series circuit of a first thermistor and a first resistor is connected in parallel to an emitter resistor.

According to the present invention as described above, the resistance is connected in series to the thermistor provided in the first resistance circuit, and the characteristics of the thermistor can be adjusted, so that the first resistance circuit having desired characteristics can be easily obtained. Since it can be configured, the emitter current of the oscillation transistor can be controlled.

Application Example 4 Oscillation Transistor, First Capacitor Connected between Base and Emitter of Oscillation Transistor, Second Capacitor Connected between Emitter and Ground of Oscillation Transistor, and Oscillation Transistor A piezoelectric vibrator connected between the base and ground,
A Colpitts oscillation circuit including a second resistance circuit connected in series to the piezoelectric vibrator and having a negative temperature coefficient of resistance.

According to the present invention, since the second resistance circuit, which is a temperature compensation circuit, is connected in series with the piezoelectric vibrator, when the ambient temperature changes, the fluctuation of the drive level for exciting the piezoelectric vibrator is directly measured. Can be suppressed. As a result, the oscillation circuit can be operated at a low drive level as compared with the conventional Colpitts oscillation circuit, and the phase noise characteristics and aging characteristics of the Colpitts oscillation circuit can be improved.

Application Example 5 The second resistor circuit is characterized by the Colpitts oscillation circuit according to Application Example 4 in which a second resistor and a second thermistor are connected in parallel.

According to the present invention, since the second resistance circuit having a negative temperature coefficient is constituted by a circuit including a thermistor, a desired characteristic can be easily selected by selecting a thermistor having a predetermined characteristic. Therefore, the emitter current of the oscillation transistor can be controlled.

Application Example 6 The second resistor circuit is characterized by the Colpitts oscillation circuit according to Application Example 4 in which a series circuit of a second thermistor and a third resistor is connected in parallel to the second resistor.

According to the present invention, a resistor is connected in series to the thermistor provided in the second resistor circuit, and the characteristics of the thermistor can be adjusted, so that the second resistor circuit having a desired temperature characteristic can be easily obtained. Thus, the emitter current of the oscillation transistor can be controlled.

1 is a circuit configuration diagram showing a first embodiment of a Colpitts oscillation circuit according to the present invention. FIG. 5 is a diagram showing fluctuation characteristics of an oscillation frequency when a drive level for exciting a crystal resonator is changed in a Colpitts-type crystal oscillation circuit. It is the figure which showed the evaluation test result with respect to the temperature compensation of a Colpitts type oscillation circuit. FIG. 5 is a circuit configuration diagram showing a second embodiment of a Colpitts oscillator according to the present invention. FIG. 6 is a characteristic diagram showing a change in drive level of the Colpitts oscillation circuit with respect to an ambient temperature change. It is a circuit block diagram of the conventional Colpitts type | mold oscillation circuit. It is a circuit block diagram of the conventional Colpitts type | mold oscillation circuit.

FIG. 1 is a circuit configuration diagram showing a first embodiment of a Colpitts oscillation circuit according to the present invention.
In the Colpitts type oscillation circuit 1 shown in FIG. 1, a series circuit of a first capacitor C1 and a second capacitor C2 that are part of a load capacitance is connected between the base of the oscillation transistor TR1 and the ground (GND). The connection midpoint of this series circuit is connected to the emitter of the oscillation transistor TR1. An emitter resistor R1, a resistor (first resistor) R2 connected in parallel to the emitter resistor R1, and a thermistor (first resistor) are connected between the emitter of the oscillation transistor TR1 and the ground.
And a temperature compensation circuit (first resistance circuit) 11 composed of a series circuit of TH1. Furthermore, a base bias circuit including a resistor R3 and a resistor R4 is connected to the base of the oscillation transistor TR1, and the piezoelectric vibrator X1 is connected between the base of the oscillation transistor TR1 and the ground. Further, the collector of the oscillation transistor TR1 is connected to the power supply voltage (V
cc) line and an output signal is obtained from the emitter of the oscillation transistor TR1 through a DC cut capacitor C3.
The Colpitts oscillation circuit 1 according to the first embodiment configured as described above is characterized in that a temperature compensation circuit 11 including a series circuit of a resistor R2 and a thermistor TH1 is connected in parallel to the emitter resistor R1.

Here, the influence of the drive level for exciting the piezoelectric vibrator on the oscillation characteristics of the oscillation circuit will be described.
FIG. 2 is a diagram showing fluctuation characteristics of the oscillation frequency when the drive level for exciting the crystal resonator is changed in the Colpitts-type crystal oscillation circuit.
In FIG. 2, the horizontal axis represents the drive level (mA) for exciting the crystal resonator, and the vertical axis represents the fluctuation (ppm) of the oscillation frequency of the oscillation circuit. FIG. 2 shows characteristics of a Colpitts oscillation circuit using an AT-cut fundamental wave crystal resonator as an example of a piezoelectric resonator, and the oscillation frequency is 52 MHz.
And the case of 230 MHz are shown.
According to FIG. 2, when the oscillation frequency is relatively low, such as 52 MHz, there is almost no fluctuation in the oscillation frequency even if the drive level is changed. However, when the oscillation frequency becomes high, such as 230 MHz, the drive level is reduced. When the frequency is increased, the oscillation frequency is greatly changed in the increasing direction.
Therefore, when the Colpitts type oscillation circuit is used in a high frequency band, it is important to excite the crystal resonator at a low drive level in order to improve the phase noise characteristic and the aging characteristic of the oscillation circuit.
A general Colpitts oscillation circuit has a characteristic that the negative resistance value decreases as the ambient temperature rises, and the negative resistance value increases as the ambient temperature falls. For this reason, in many cases, the circuit is designed so that the negative resistance value is as large as possible so that the oscillation circuit operates stably even if the ambient temperature rises and the negative resistance value decreases.
As a result, when the ambient temperature becomes low, the negative resistance value of the oscillation circuit increases, causing a phenomenon that the negative resistance value becomes larger than necessary, and accordingly, the drive level for exciting the piezoelectric vibrator also increases. The evil that occurs occurs.
Therefore, in order to stably operate the Colpitts type oscillation circuit, it is necessary to lower the drive level for exciting the piezoelectric vibrator and to reduce the fluctuation with respect to the change in the ambient temperature.

Next, the contents described above will be described using mathematical expressions.
The Colpitts type oscillation circuit represented by the mathematical formula shows a case of a basic circuit before performing temperature compensation, and a resistance R2 serving as a temperature compensation circuit and a thermistor TH1 are added to the emitter resistance of the oscillation transistor.
This shows a case where the series circuits are not connected in parallel.
First, the negative resistance Rn of the oscillating circuit is obtained by Expression (1), where gm is the mutual conductance of the oscillating transistor TR1.

また、相互コンダクタンスｇｍは、式（２）で求められる。

Further, the mutual conductance gm is obtained by Expression (2).

式（２）に示すように、相互コンダクタンスｇｍは、周囲温度が上昇すると減少すると
いう特性を有している。
次に、ドライブレベルＩｓは、式（３）により求めることができる。

As shown in Expression (2), the mutual conductance gm has a characteristic of decreasing as the ambient temperature increases.
Next, the drive level Is can be obtained by equation (3).

式（３）において、発振回路中の損失であるＲｅは周囲温度の上昇により増加するので
、式（３）に示すように、ドライブレベルＩｓは、周囲温度が上昇すると減少する。

In Expression (3), Re, which is a loss in the oscillation circuit, increases as the ambient temperature increases. As shown in Expression (3), the drive level Is decreases as the ambient temperature increases.

From the above results, it can be seen that in order to ensure a drive level with little fluctuation even when the ambient temperature changes, it is only necessary to adjust the emitter current Ie corresponding to the change when the ambient temperature changes. That is, for example, when the ambient temperature rises, if the emitter current Ie is changed to increase accordingly, the fluctuation of the drive level Is is suppressed.
Therefore, in the Colpitts oscillation circuit 1 of the first embodiment, the oscillation transistor T
A temperature compensation circuit composed of a series circuit of a resistor R2 and a thermistor TH1 was connected in parallel with the emitter resistor R1 of R1. The thermistor TH1 used in the Colpitts oscillator 1 of the first embodiment has a characteristic that the resistance value has a negative temperature coefficient.
As a result, since the resistance value of the thermistor TH1 decreases as the ambient temperature rises, the emitter current of the oscillation transistor TR1 increases, while when the ambient temperature falls, the thermistor T
Since the resistance value of H1 increases, the emitter current of the oscillation transistor TR1 can be decreased. Accordingly, it is possible to suppress the fluctuation of the negative resistance value with respect to the change of the ambient temperature and reduce the fluctuation of the drive level for exciting the piezoelectric vibrator.
The resistor R2 connected in series with the thermistor TH1 is for adjusting the characteristics of the thermistor TH1, but only the thermistor TH1 may be connected in parallel to the emitter resistor R1 without connecting the resistor R2. .

Next, an evaluation test was performed on the characteristics of the Colpitts type oscillation circuit before temperature compensation and after temperature compensation according to the first embodiment. FIG. 3 is a diagram showing the evaluation test results.
In FIG. 3, the characteristics of the basic circuit of the Colpitts oscillation circuit before temperature compensation, the characteristics of the Colpitts oscillation circuit of the first embodiment, and Patent Document 2 (conventional second example) are described. The characteristics of the Colpitts oscillation circuit are shown. The Colpitts oscillation circuit here is
This is an oscillation circuit using an AT cut crystal resonator, and the oscillation frequency is 311 MHz.
As can be seen from the evaluation test results shown in FIG. 3, in the Colpitts oscillation circuit according to the first embodiment, the emitter current Ie increases as the ambient temperature increases, and accordingly, the amount of change in the negative resistance Rn increases. is decreasing. When the temperature compensation is performed for the change in the ambient temperature, the drive level Is has a fluctuation value within 0.14 mA, and the fluctuation value before the temperature compensation is 0.4.
This is a significant improvement compared to 7 mA.
On the other hand, the Colpitts oscillation circuit according to the second conventional example is low in sensitivity to changes in ambient temperature because the emitter current Ie of the oscillation transistor is adjusted by controlling the base potential. The fluctuation value of the level Is is 0.30 mA, and it can be seen that the degree of improvement is low compared to the case where the temperature compensation according to the first embodiment is performed.

Next, a second embodiment of the Colpitts oscillator according to the present invention will be described.
FIG. 4 is a circuit configuration diagram of a Colpitts oscillation circuit according to the second embodiment.
In the Colpitts type oscillation circuit 2 shown in FIG. 4, a series circuit of a first capacitor C1 and a second capacitor C2 which are part of a load capacitance is connected between the base of the oscillation transistor TR1 and the ground (GND). The connection midpoint of this series circuit is connected to the emitter of the oscillation transistor TR1, and an emitter resistor R1 is connected between the emitter and ground. Then, a base bias circuit including a resistor R3 and a resistor R4 is connected to the base of the oscillation transistor TR1. In order to directly adjust the drive level for exciting the piezoelectric vibrator X1 and the piezoelectric vibrator X1 between the base of the oscillation transistor TR1 and the ground, a resistor (second resistor) R5,
A resistor (third resistor) R6 and a thermistor (second thermistor) T connected in parallel to the resistor R5
A temperature compensation circuit (second resistance circuit) 12 composed of a series circuit of H2 is connected in series. The collector of the oscillation transistor TR1 is connected to the power supply voltage (Vcc) line, and an output signal is obtained from the emitter of the oscillation transistor TR1 through the DC cut capacitor C3.
The Colpitts oscillation circuit 2 according to the second embodiment configured as described above includes the piezoelectric vibrator X
In order to adjust the drive level that excites 1, the resistor R5, the resistor R6, and the thermistor TH2
The temperature compensation circuit 12 is characterized in that it is inserted and connected in series between the piezoelectric vibrator X1 and the ground.

Next, the operation of the temperature compensation circuit in the second embodiment will be described.
As described in the first embodiment, in the Colpitts oscillation circuit, when the ambient temperature rises, the negative resistance value of the oscillation circuit decreases and the drive level for exciting the piezoelectric vibrator X1 also decreases. When the ambient temperature falls, the negative resistance value of the oscillation circuit increases and the drive level for exciting the piezoelectric vibrator X1 also increases.
Therefore, a resistance circuit composed of the resistor R5, the resistor R6, and the thermistor TH2 is inserted and connected in series with the piezoelectric vibrator X1 as a temperature compensation circuit, and the drive level for exciting the piezoelectric vibrator X1 when the ambient temperature changes is adjusted. I did it.
The thermistor TH2 used in the Colpitts oscillator 2 of the second embodiment has a characteristic that the resistance value has a negative temperature coefficient.
Accordingly, the temperature compensation circuit functions in a direction in which the drive level for exciting the piezoelectric vibrator X1 increases because the resistance value decreases as the ambient temperature rises and the resistance value of the thermistor TH2 decreases. The temperature compensation circuit functions to decrease the drive level for exciting the piezoelectric vibrator X1 because the resistance value increases as the resistance value of the thermistor TH2 increases as the ambient temperature decreases.
As a result, by operating the temperature compensation circuit in this way, the drive level for exciting the piezoelectric vibrator X1 can be directly controlled, and even if the ambient temperature changes, fluctuations in the drive level can be reduced. If a temperature compensation circuit is inserted in series with the piezoelectric vibrator X1, the loss of the oscillation circuit increases. Therefore, it is necessary to sufficiently secure the negative resistance value of the oscillation circuit.
In the temperature compensation circuit, the resistor R6 connected in series with the thermistor TH2 is:
Although it is for adjusting the characteristics of the thermistor TH2, it may be deleted and only the thermistor TH2 may be connected in parallel to the resistor R5.

FIGS. 5A and 5B are characteristic diagrams showing fluctuations of the drive level of the Colpitts oscillation circuit with respect to changes in the ambient temperature. FIG. 5A shows numerical data, and FIG. 5B shows a graph. In FIG.
The comparison results of the basic circuit of the Colpitts type oscillation circuit, the Colpitts type oscillation circuit of the second example of the conventional example, and the Colpitts type oscillation circuit according to the first and second embodiments of the present invention are shown.
The Colpitts type oscillation circuit in this case is an oscillation circuit using an AT cut crystal resonator,
The oscillation frequency is 311 MHz. In (b), the horizontal axis indicates the ambient temperature (° C.), and the vertical axis indicates the drive level (mA).
As shown in the numerical data, in the basic circuit, the drive level fluctuates by 0.47 mA when the ambient temperature changes, but in the Colpitts oscillation circuit 1 according to the first embodiment, the drive level fluctuates by 0. .14 mA, Colpitts oscillation circuit 2 according to the second embodiment
Then, it can be seen that the fluctuation of the drive level is 0.22 mA, which is greatly improved.
In the conventional oscillation circuit according to the second example, the fluctuation of the drive level is 0.30 mA.
It can be seen that the degree of improvement is lower than that of the Colpitts type oscillation circuit of the present embodiment.
Next, as shown in FIG. 5B, the Colpitts oscillation circuit according to the first and second embodiments has a slight drive level variation in the entire ambient temperature range.
On the other hand, it can be seen that the Colpitts type oscillation circuit according to the second conventional example has a small improvement compared to the temperature characteristics of the oscillation circuit that has performed temperature compensation according to the first and second embodiments.
In this embodiment, the case where a thermistor is used in the temperature compensation circuit has been described as an example. However, this is merely an example, and the resistance value changes with a negative temperature coefficient due to ambient temperature fluctuations. It is also possible to use a resistor or the like.
The configuration of the Colpitts oscillation circuit of this embodiment is merely an example, and the oscillation circuit includes at least an oscillation transistor, a capacitor connected between the base and emitter of the transistor, and an emitter of the transistor and the ground. Any Colpitts type oscillation circuit having a connected capacitor and a piezoelectric vibrator connected between the base of the transistor and the ground is applicable.

1, 2, Colpitts type oscillation circuit, C1, C2, C3, capacitor, R1, R2, R3,
R4, R5, R6 ... resistors, TH1, TH2 ... thermistors, TR1 ... transistors, X1 ...
Piezoelectric vibrator.

Claims (6)

An oscillation transistor; a first capacitor connected between a base and an emitter of the oscillation transistor; a second capacitor connected between an emitter of the oscillation transistor and a ground; and a base-ground of the oscillation transistor A Colpitts oscillation circuit comprising: a piezoelectric vibrator connected in between; and a first resistance circuit having a negative temperature coefficient of resistance value connected between the emitter of the oscillation transistor and ground. . 2. The Colpitts oscillation circuit according to claim 1, wherein the first resistance circuit includes a parallel circuit of an emitter resistor and a first thermistor. 2. The Colpitts oscillation circuit according to claim 1, wherein the first resistor circuit includes an emitter resistor and a series circuit of a first thermistor and a first resistor connected in parallel. 3. A first transistor connected between an oscillation transistor and a base-emitter of the oscillation transistor;
A capacitor, a second capacitor connected between the emitter and ground of the oscillation transistor, a piezoelectric vibrator connected between the base of the oscillation transistor and ground, and a resistance value connected in series to the piezoelectric vibrator. A Colpitts oscillation circuit comprising: a second resistance circuit having a negative temperature coefficient. 5. The Colpitts oscillation circuit according to claim 4, wherein the second resistor circuit includes a second resistor and a second thermistor connected in parallel. 5. The Colpitts oscillation circuit according to claim 4, wherein the second resistor circuit includes a second resistor and a series circuit of a second thermistor and a third resistor connected in parallel.

Images