JP6180846B2 - Crystal oscillator - Google Patents

Description

  The present invention relates to a crystal oscillator, and more particularly to a crystal oscillator that has a favorable aging characteristic and can be reduced in size at low cost.

[Description of Prior Art]
Conventionally, when trying to suppress the change in the output frequency (aging characteristics) due to the aging of the crystal oscillator, a highly stable material that has little change over time from the quartz crystal blank, electrode, support, sealing, and package to the crystal oscillator. Therefore, it is necessary to manufacture by a manufacturing method with little change with time.

  By the way, some crystal oscillators are required to be downsized and surface-mounted depending on the application, and some aging characteristics may not be good depending on the mounted crystal resonators in response to downsizing and surface mounting.

  A technique for correcting the aging characteristics in such a crystal oscillator is also known, but since it is realized by a circuit using a system IC, a ROM (Read Only Memory) or the like, it is expensive, has a large circuit scale, and is downsized. Hinder.

[Related technologies]
As techniques for improving the aging characteristics of the crystal oscillator, Japanese Patent Application Laid-Open No. 2001-308641 “Piezoelectric Oscillator” (Toyo Tsushinki Co., Ltd., Patent Document 1), Japanese Patent Application Laid-Open No. 2008-178040 “Oscillator” (Japan) Radio Industry Co., Ltd., Patent Document 2).

Patent Document 1 describes that in a piezoelectric oscillator, a limiter circuit has excellent aging characteristics by controlling the impedance between terminals of a load capacitor.
In Patent Document 2, a frequency selection circuit including an inductance and a varicap diode is provided in the feedback loop of the oscillator, and the negative resistance is adjusted in accordance with a change with time of the oscillator by controlling the capacitance of the varicap diode. Is described.

JP 2001-308641 A JP 2008-178040 A

  As described above, the conventional crystal oscillator has a problem that it is difficult to realize a crystal oscillator that has good aging characteristics and can be miniaturized at low cost.

  Note that Patent Document 1 and Patent Document 2 do not describe providing a capacitor having a capacitance loss characteristic that cancels the aging characteristic of the crystal resonator on the ground terminal side of the crystal resonator.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a crystal oscillator that is low-cost, has good aging characteristics, and can be miniaturized.

The present invention for solving the problems of the conventional example described above is a crystal oscillator including a transistor connected to one end of the crystal resonator and amplifying the output signal of the crystal resonator. the aging characteristics adjusting capacitor to obtain Bei deterioration characteristic is provided, at the other end of the crystal oscillator is only one end of the aging characteristic-adjusting capacitor is connected, the other end of the aging characteristic-adjusting capacitor is grounded, the aging characteristic adjustment The characteristics of the capacitor for use are adjusted so as to cancel out the aging characteristics of the crystal resonator whose oscillation frequency varies with time.

  According to the present invention, in the crystal oscillator, the aging characteristic adjusting capacitor is a varicap diode.

  Further, the present invention is characterized in that, in the crystal oscillator, the aging characteristic adjusting capacitor is composed of a plurality of capacitors connected in series, a plurality of capacitors connected in parallel, or a combination thereof.

  According to the present invention, in the crystal oscillator, any one of the plurality of capacitors is a varicap diode.

  According to the present invention, in the crystal oscillator, the aging characteristic adjusting capacitor is any one of a ceramic capacitor, an electrolytic capacitor, a tantalum capacitor, a mylar capacitor, and a film capacitor.

According to the crystal oscillator of the present invention, the crystal oscillator includes a crystal resonator and a transistor that is connected to one end of the crystal resonator and amplifies the output signal of the crystal resonator, and the capacitance decreases with time. the aging characteristics adjusting capacitor to obtain Bei characteristics provided, at the other end of the crystal oscillator is only one end of the aging characteristic-adjusting capacitor is connected, the other end of the aging characteristic-adjusting capacitor is grounded, aging characteristics adjusting capacitor The crystal oscillator is adjusted so as to cancel out the aging characteristics of the crystal oscillator whose oscillation frequency fluctuates with time, so the oscillation frequency of the crystal oscillator due to the capacity reduction characteristic of the capacitor for adjusting the aging characteristics The fluctuation compensates for the natural aging characteristics of the crystal unit and provides excellent aging characteristics. The effect of the crystal oscillator can be miniaturized can be realized at a low cost.

  In addition, according to the present invention, since the aging characteristic adjusting capacitor is the above-described crystal oscillator that is a varicap diode, the capacitance of the aging characteristic adjusting capacitor can be finely adjusted even after mounting. As an optimum capacity according to the aging characteristics of the child, there is an effect that a crystal oscillator having excellent aging characteristics can be realized.

  Further, according to the present invention, the aging characteristic adjusting capacitor is the above-described crystal oscillator constituted by a plurality of capacitors connected in series, a plurality of capacitors connected in parallel, or a combination thereof. Accordingly, it is possible to optimize the capacity loss characteristic according to the above, and there is an effect that a crystal oscillator having an excellent aging characteristic can be realized.

It is a circuit diagram which shows the structure of the crystal oscillator which concerns on embodiment of this invention. It is a characteristic view which shows the example of the aging characteristic of a crystal oscillator. It is the characteristic view which showed the example of the secular change characteristic of a general capacitor | condenser. It is a circuit diagram which shows another example of a connection of the capacitor for adjustment. It is a characteristic view which shows an example of the resonant frequency offset amount with respect to load capacity.

Embodiments of the present invention will be described with reference to the drawings.
[Outline of the embodiment]
The crystal oscillator according to the embodiment of the present invention is provided with a capacitor whose capacitance decreases with time, between the crystal unit and the ground terminal, and the frequency change of the crystal unit caused by the capacitor is negative in the crystal unit. The crystal oscillator is adjusted to have a positive tendency characteristic that cancels the aging characteristic of the tendency, and a crystal oscillator having a good aging characteristic can be realized at low cost.

[Crystal Oscillator According to Embodiment: FIG. 1]
FIG. 1 is a circuit diagram showing a configuration of a crystal oscillator according to an embodiment of the present invention.
As shown in FIG. 1, the crystal oscillator (the present crystal oscillator) according to the embodiment of the present invention is a Colpitts oscillator, and includes a crystal resonator X and a transistor Tr that amplifies the oscillation frequency of the crystal resonator X. The one end of the crystal resonator is connected to one end of the transistor Tr.

A power supply voltage is applied to the collector of the transistor Tr via the resistor R1, and one end of the capacitor C3 is connected to the other end of the capacitor C3.
The emitter of the transistor Tr is grounded via the resistor R2, the base is grounded via the series-connected capacitors C1 and C2, and the point between the capacitors C1 and C2 is connected to the emitter of the transistor Tr. An output terminal is provided.

  Furthermore, the other end of the resistor R1 is connected to one end of the resistor R3, the other end of the resistor R3 is connected to a point between the crystal unit X and the base of the transistor Tr, and is connected to one end of the resistor R4. ing. The other end of the resistor R4 is grounded.

  As a feature of the present crystal oscillator, an aging characteristic adjusting capacitor (hereinafter referred to as an “adjusting capacitor”) C10 for adjusting the aging characteristic is connected to the other end of the crystal unit X, and the other of the adjusting capacitor C10. The end is grounded.

The adjustment capacitor C10 compensates for frequency changes due to the aging characteristics of the crystal unit X. That is, the adjustment capacitor 10 has a characteristic that causes a frequency change opposite to the aging characteristic of the crystal unit X.
Here, for the sake of simplicity of explanation, an example in which the adjustment capacitor 10 is configured by a single capacitor will be described. However, as will be described later, the adjustment capacitor 10 may be configured as a combination of a plurality of capacitors. is there.

[Aging characteristics of quartz crystal: Fig. 2]
Next, an example of aging characteristics of a crystal resonator used in a crystal oscillator will be described with reference to FIG. FIG. 2 is a characteristic diagram showing an example of the aging characteristic of the crystal resonator.
As shown in FIG. 2, the output frequency of the crystal resonator is determined from the set frequency value due to the mechanical stress being released by the operation over a long period of time or the generation of a small amount of outgas from the material inside the package. Cause a shift.

2A shows aging characteristics due to mechanical stress dissipation, and FIG. 2B shows aging characteristics due to outgas generation in the package.
The aging characteristic (C) of the entire crystal unit is expressed as the sum of the characteristics of (A) and (B), and a change over time over a long period (for example, several years) is generally a negative fluctuation that falls below the set frequency. Become.

[Capacitor aging characteristics: Fig. 3]
Next, aging characteristics of a general capacitor will be described with reference to FIG. FIG. 3 is a characteristic diagram showing an example of the aging characteristics of a general capacitor.
As shown in FIG. 3, the capacitor has a “capacity drop” in which the capacitance decreases with time.
In this crystal oscillator, the aging characteristic of the crystal oscillator is compensated by using the capacity loss characteristic of the capacitor to improve the aging characteristic of the crystal oscillator.

[Characteristics for adjusting aging characteristics]
Here, the characteristics of the aging characteristic adjusting capacitor C10 of the present crystal oscillator will be described.
The adjustment capacitor C10 is a capacitor that causes a loss of capacitance, and is provided between the crystal unit X and the ground terminal as shown in FIG.
When the capacitance of the adjustment capacitor C10 decreases with time, the load capacity of the crystal unit decreases. This is a factor that causes the oscillation frequency of the crystal unit X to vary to the plus side.

[Relationship between load capacitance change and frequency offset: Fig. 5]
The relationship between the change in load capacitance and the oscillation frequency offset is shown in FIG. FIG. 5 is a characteristic diagram showing an example of the resonance frequency offset amount with respect to the load capacitance.
As shown in FIG. 5, as the load capacity (C _L ) decreases, the frequency offset amount (Δf / f) increases. That is, the decrease in the load capacity causes the oscillation frequency to fluctuate to the plus side.

Therefore, in this crystal oscillator, the aging characteristic of the crystal unit X is measured in advance, and a capacitor loss characteristic (capacity loss characteristic) curve that can satisfactorily cancel the aging characteristic is determined (calculated) accordingly. Then, a capacitor having such a capacity loss characteristic is selected and connected to the crystal unit X as the adjustment capacitor C10.
As a result, the aging characteristics of the crystal unit X and the adjustment capacitor C10 cancel each other, the fluctuation of the oscillation frequency of the crystal unit X due to secular change can be suppressed, and the aging characteristic of the crystal unit can be improved. is there.

As the adjustment capacitor C10, a general-purpose product such as a ceramic capacitor, an electrolytic capacitor, a tantalum capacitor, a mylar capacitor, or a film capacitor can be used. Appropriate capacitors should be selected in consideration of mounting or lead type.
As a result, it is possible to realize a crystal oscillator that does not require a large package, has good aging characteristics, and can be miniaturized at low cost.

[Application example: Fig. 4]
An application example of the present crystal oscillator will be described with reference to FIG. FIG. 4 is a circuit diagram showing another connection example of the adjustment capacitor. 4 shows a configuration from the crystal unit X to the ground terminal, and the other configurations are the same as those in FIG.
FIG. 4A shows a configuration in which a varicap diode D1 is provided as the adjustment capacitor C10.
By using the varicap diode D1 as a capacitor, the initial capacitance can be adjusted even after mounting. Further, the varicap diode D1 causes a loss of capacitance due to a change with time, and the aging characteristic of the crystal unit X can be offset by using a varicap diode having an appropriate loss of capacitance characteristic.

In addition, when a good aging characteristic cannot be obtained with only one capacitor, a plurality of capacitors may be used as an aging characteristic adjusting capacitor.
4B and 4C are examples in which a plurality of capacitors are provided as aging characteristic adjusting capacitors. FIG. 4B shows a configuration in which capacitors C11 and C12 are connected in series. FIG. 4C shows capacitors C13 and C14. A configuration connected in parallel is shown.
Furthermore, it is good also as a structure which combined the serial connection and the parallel connection using three or more capacitors.

  By finely adjusting the capacitance loss characteristics by changing the characteristics and connection method of each capacitor that makes up the adjustment capacitor, the secular change in output frequency due to multiple capacitors is close to the reversal characteristics of the aging characteristics of the crystal unit X Thus, the aging characteristic of the crystal oscillator X can be effectively canceled and the aging characteristic of the crystal oscillator can be improved.

Further, although not shown in the figure, a varicap diode and a capacitor may be used in combination as an adjustment capacitor. A configuration in which a varicap diode and a capacitor are connected in series on the ground terminal side of the crystal unit or in parallel It is also possible to adopt a configuration connected to the above or a combination thereof.
In any case, it is possible to improve the aging characteristics of the crystal oscillator by providing an adjustment capacitor adjusted to have a capacity loss characteristic that effectively compensates the aging characteristics of the crystal resonator X used. It can be done.

[Effect of the embodiment]
The crystal oscillator according to the embodiment of the present invention is a Colpitts oscillator provided with a crystal resonator X and a transistor Tr, and has a capacitance between the crystal resonator X and the ground terminal due to a change with time. An aging characteristic adjustment capacitor C10 that decreases (causes loss of capacitance) is provided, and by optimizing the capacitance loss characteristic of the aging characteristic adjustment capacitor C10, the aging characteristic in the negative direction of the crystal unit X is used for aging characteristic adjustment. Efficiently cancels out the positive aging characteristic due to the decrease in the load capacity of the capacitor C10 to improve the aging characteristic of the output frequency of the crystal oscillator, and can be realized at a low cost without impeding the downsizing. There is.

  Further, according to the present crystal oscillator, since the aging characteristic adjusting capacitor C10 is a crystal oscillator composed of the varicap diode D1, the capacitance can be finely adjusted even after mounting, and the crystal oscillator X As an optimum capacity loss characteristic according to the aging characteristic, there is an effect that the aging characteristic of the crystal unit X can be canceled well and a crystal oscillator having a good aging characteristic can be realized.

  In addition, according to the present crystal oscillator, the capacitor for adjusting the aging characteristic is realized by a series connection or a parallel connection of a plurality of capacitors, or a combination thereof. Fine adjustment can be performed, and the aging characteristics of the oscillator can be improved.

  Furthermore, according to the present crystal oscillator, since any one of the plurality of capacitors is a varicap diode, the capacity loss characteristic can be finely adjusted according to the aging characteristic of the crystal unit X, and the aging characteristic of the oscillator is good. There is an effect that can be made.

  INDUSTRIAL APPLICABILITY The present invention is suitable for a crystal oscillator that has good aging characteristics and can be downsized at low cost.

  X ... crystal resonator, Tr ... transistor, C1-C3 ... capacitor, C10-C14 ... capacitor for adjusting aging characteristics, R1-R4 ... resistor, D1 ... varicap diode

Claims (5)

A crystal oscillator comprising a crystal resonator and a transistor connected to one end of the crystal resonator and amplifying an output signal of the crystal resonator,
It provided the aging characteristics adjusting capacitor to obtain Bei characteristics that capacity is reduced by aging,
Only one end of the aging characteristic adjustment capacitor is connected to the other end of the crystal resonator, and the other end of the aging characteristic adjustment capacitor is grounded.
The crystal oscillator, wherein the characteristic of the capacitor for adjusting the aging characteristic is adjusted so as to cancel out the aging characteristic of the crystal resonator whose oscillation frequency fluctuates due to a change with time.   2. The crystal oscillator according to claim 1, wherein the aging characteristic adjusting capacitor is a varicap diode.   2. The crystal oscillator according to claim 1, wherein the aging characteristic adjusting capacitor is composed of a plurality of capacitors connected in series, a plurality of capacitors connected in parallel, or a combination thereof.   4. The crystal oscillator according to claim 3, wherein any one of the plurality of capacitors is a varicap diode.   5. The crystal oscillator according to claim 1, wherein the aging characteristic adjusting capacitor is any one of a ceramic capacitor, an electrolytic capacitor, a tantalum capacitor, a mylar capacitor, and a film capacitor.

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