JP2008312000A - Piezoelectric oscillator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric oscillator which allows fine adjustment of frequency variable characteristics and miniaturization. <P>SOLUTION: The voltage control type piezoelectric oscillator 10 having a piezoelectric vibrator 14 and an oscillation circuit 12 has: a first variable capacity diode 18 arranged so that control voltage is applied to the cathode side; and a second variable capacity diode 20 arranged so that the control voltage is similarly applied to the cathode side, and has: a first resistor 22 provided between the first variable capacity diode 18 and a control voltage input terminal 32; and a voltage division circuit 28 comprised of a second resistor 24 and a third resistor 26 provided between the cathode side of the first variable capacity diode 18 and the cathode side of the second variable capacity diode 20. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a piezoelectric oscillator, and more particularly to a voltage controlled oscillator (VCO).

  VCOs that can change the frequency variable characteristic by an external control voltage are generally widely used. In particular, a voltage controlled crystal oscillator (VCXO) employing a crystal having good temperature characteristics as an oscillation source has a wide range of use.

  In such a background, as disclosed in Patent Document 1, a circuit configuration is disclosed in which a value of a capacitance added to a feedback circuit is changed using a variable capacitance diode. However, in the circuit configuration disclosed in Patent Document 1, the adjustment width is determined by the combination of the junction capacitance of the variable capacitance diode and the applied voltage. For this reason, it has become impossible to cope with the recent increase in accuracy of frequency variable characteristics adjustment.

For this reason, various means for obtaining desired characteristics that cannot be handled by the conventional circuit configuration have been studied. For example, a technique disclosed in Patent Document 2 can be cited.
Japanese Utility Model Publication No. 62-61523 Japanese Patent Laid-Open No. 7-99411

If the circuit configuration is disclosed in the above-mentioned patent document, it is certainly considered that the oscillation characteristics can be adjusted. However, in the circuit configuration disclosed in Patent Document 2, a capacitor is used as the adjustment element, and thus there remains a problem that it is difficult to reduce the size of the circuit, to make an IC, or the like. The problem related to circuit miniaturization increases as the adjustment range of the frequency variable characteristic is subdivided. This is because it becomes necessary to individually make capacitors that match the adjustment range.
Accordingly, an object of the present invention is to provide a piezoelectric oscillator that solves the above-described problems and enables fine adjustment of frequency variable characteristics and miniaturization.

  In order to achieve the above object, a voltage controlled piezoelectric oscillator according to the present invention is a voltage controlled piezoelectric oscillator including a piezoelectric vibrator and an oscillation circuit, and is arranged such that a control voltage is applied to the cathode side. And a second variable capacitance diode arranged so that the control voltage is applied to the cathode side, and provided between the first variable capacitance diode and the control voltage input terminal. A voltage dividing circuit comprising a first resistor and a second resistor and a third resistor provided between the cathode side of the first variable capacitance diode and the cathode side of the second variable capacitance diode; Is provided. According to the voltage controlled piezoelectric oscillator having such a feature, the voltage applied to the cathode side of the variable capacitance diode can be adjusted by the voltage dividing circuit, so that the frequency variable characteristic can be finely adjusted. It becomes possible. In addition, since the circuit required for adjusting the frequency variable characteristic can be created only by the variable capacitance diode and the resistor, it is possible to reduce the size.

  In the voltage controlled piezoelectric oscillator having the above characteristics, the second variable capacitance diode may be arranged in series with the piezoelectric vibrator. According to such a configuration, even when the capacitance value of the variable capacitance diode changes with adjustment of the applied voltage by the voltage dividing circuit, the change in the frequency variable characteristic can be reduced. Therefore, the frequency variable characteristic can be adjusted with high accuracy.

の関係を満たすようにすると良い。このような関係を満たして抵抗値の調整を行うことにより、周波数可変特性全体をシフトさせることができる。 The second variable capacitance diode may be connected between one end side of the piezoelectric vibrator and the ground. According to such a configuration, when the capacitance value of the variable capacitance diode changes with adjustment of the applied voltage by the voltage dividing circuit, the amount of change in the frequency variable characteristic can be made relatively large. For this reason, the frequency variable characteristic can be adjusted in a wide range.
In the voltage-controlled piezoelectric oscillator having the above-described characteristics, the first resistor and the second resistor and the third resistor constituting the voltage dividing circuit include

It is better to satisfy the relationship. By satisfying such a relationship and adjusting the resistance value, the entire frequency variable characteristic can be shifted.

の関係を満たすようにしても良い。このような関係を満たして抵抗値の調整を行うことにより、周波数可変特性の傾きを調整することができる。 In the voltage controlled piezoelectric oscillator having the above-described characteristics, the voltage dividing ratio between the second resistor and the third resistor constituting the voltage dividing circuit is

The relationship may be satisfied. By satisfying such a relationship and adjusting the resistance value, the slope of the frequency variable characteristic can be adjusted.

  Further, in the voltage controlled piezoelectric oscillator having the above-described characteristics, each of the second resistor and the third resistor constituting the voltage dividing circuit is constituted by an array of resistor groups, and a changeover switch is provided. Control means for outputting a changeover signal to the changeover switch based on an input signal from the outside, and selectively determining a resistor having a desired resistance value as the second resistor and the third resistor. It is good to make it. With such a configuration, it is possible to adjust the voltage applied to the variable capacitance diode by the input of an external signal. Therefore, it is possible to perform characteristic adjustment according to the specification after the manufacture is completed.

  In the voltage controlled piezoelectric oscillator having such a configuration, the oscillation circuit can be a Colpitts oscillation circuit. Therefore, the frequency variable characteristic adjusting circuit can be incorporated without breaking the configuration of the conventional oscillation circuit. Further, as a configuration for obtaining a similar effect, the oscillation circuit can be an inverter oscillation circuit.

  Further, when an inverter type oscillation circuit is used, the oscillation circuit, the first variable capacitance diode, the second variable capacitance diode, the first resistor, and the voltage dividing circuit are integrated on one chip. It is desirable to make it. According to such a configuration, it is possible to obtain an optimum form for downsizing the voltage controlled piezoelectric oscillator.

  In the voltage controlled piezoelectric oscillator having the above configuration, a general-purpose CMOS oscillation circuit can be used as the inverter oscillation circuit. With such a configuration, it is possible to manufacture a voltage-controlled piezoelectric oscillator that is inexpensive and suitable for downsizing.

Hereinafter, embodiments of the voltage controlled piezoelectric oscillator of the present invention will be described in detail with reference to the drawings.
First, the circuit configuration according to the first embodiment of the voltage controlled piezoelectric oscillator will be described with reference to FIG. A voltage controlled piezoelectric oscillator (hereinafter simply referred to as a piezoelectric oscillator) 10 shown in FIG. 1 includes an oscillation circuit 12, a piezoelectric vibrator 14, and a frequency variable characteristic adjustment circuit 16.

  The oscillation circuit 12 shown in FIG. 1 is a well-known Colpitts type circuit. The piezoelectric vibrator 14 is not particularly limited as long as it has an element piece that exhibits a piezoelectric effect, such as a piezoelectric ceramic other than a single crystal element or a polycrystalline element as an element piece. In consideration of characteristics, it is desirable to select a crystal resonator, particularly an AT-cut crystal resonator.

  The frequency variable characteristic adjustment circuit 16 includes two variable capacitance diodes (a first variable capacitance diode 18 and a second variable capacitance diode 20) arranged in series with respect to the piezoelectric vibrator 14 in series at a high frequency, and a series. The first resistor 22 and the second resistor 24 are arranged in parallel, and the third resistor 26 and the fourth resistor 30 are arranged in parallel. In the oscillation characteristic adjusting circuit 16 having such an arrangement, the voltage dividing circuit 28 is configured by the second resistor 24 and the third resistor 26. The first variable capacitance diode 18 and the second variable capacitance diode 20 are configured such that the cathode sides are connected to each other. The voltage dividing circuit 28 is disposed between the first variable capacitance diode and the second variable capacitance diode. The frequency variable characteristic adjusting circuit 16 having such a configuration is disposed between the control voltage application terminal 32 and the piezoelectric vibrator 14. Therefore, the voltage applied to the control voltage application terminal 32 is applied to the cathode side terminals of the first variable capacitance diode 18 and the second variable capacitance diode 20.

  By configuring the frequency variable characteristic adjusting circuit 16 in such a configuration, the voltage applied from the control voltage application terminal 32 is on the cathode side with respect to both the first variable capacitance diode 18 and the second variable capacitance diode 20. Will be applied. Since the variable capacitance diode causes a capacitance change according to the so-called reverse bias voltage, when the cathode side voltage is higher than the anode side voltage, the combined feedback static voltage is applied according to the applied voltage from the control voltage application terminal 32. The capacitance changes (see FIG. 2). For this reason, a change is caused in the frequency variable characteristic of the piezoelectric vibrator 14. The first resistor 22 is a voltage applied to both the first variable capacitance diode 18 and the second variable capacitance diode 20, and the second resistor 24 and the third resistor 26 are the second variable capacitance. Each voltage applied to the diode 20 is adjusted.

Ｒ１〜Ｒ３が、数式５の関係を満足する場合、Ｒ１はＲ２とＲ３の和に対して十分に小さいため、第１の可変容量ダイオード１８に印加される電圧は、第２の抵抗（Ｒ２）２４と第３の抵抗（Ｒ３）２６の分圧比に影響されることが無く、制御電圧入力端子３２に入力された電圧がそのまま印加されることとなる。このため、第１の可変容量ダイオード１８により調整される周波数可変特性への影響はほとんど無い。 Here, in the piezoelectric oscillator 10 according to the present embodiment, when the resistance value of the first resistor 22 is R1, the resistance value of the second resistor 24 is R2, and the resistance value of the third resistor 26 is R3, It is set so that the relationship between R1, R2, and R3 satisfies the relationship of Equation 5, or the relationship between R2 and R3 satisfies the relationship of Equation 6.

When R1 to R3 satisfy the relationship of Expression 5, since R1 is sufficiently small with respect to the sum of R2 and R3, the voltage applied to the first variable capacitance diode 18 is the second resistance (R2). The voltage input to the control voltage input terminal 32 is applied as it is without being affected by the voltage dividing ratio between the voltage 24 and the third resistor (R3) 26. For this reason, there is almost no influence on the frequency variable characteristic adjusted by the first variable capacitance diode 18.

  On the other hand, by changing the ratio of the second resistor (R2) 24 and the third resistor (R3) 26, that is, the voltage dividing ratio, the voltage applied to the second variable capacitance diode 20 changes. Then, by finely adjusting the voltage dividing ratio by adjusting the resistance value, the applied voltage to the second variable capacitance diode 20 can be finely adjusted, and the frequency variable characteristics can be finely adjusted.

  Further, when the relationship between the second resistor (R2) 24 and the third resistor (R3) 26 satisfies the relationship of Equation 6, even if the relationship of Equation 5 is not satisfied, the voltage dividing ratio Does not affect the variable characteristics adjusted by the first variable capacitance diode 18.

As described above, according to the frequency variable characteristic adjusting circuit 16 according to the present embodiment, the frequency variable characteristic can be finely adjusted by selecting the second resistor (R2) 24 and the third resistor (R3) 26. Although it is possible, there is a difference in the change of the frequency variable characteristic between the case where the mathematical formula 5 is satisfied and the sum of R2 and R3 is changed and the case where the mathematical formula 6 is satisfied. For example, when Expression 5 is satisfied and the sum of R2 and R3 is changed, the change in the frequency variable characteristic is as shown in FIG. FIG. 3 is a graph showing an example of frequency variable characteristics when either R2 or R3 is constant and the other is changed.
On the other hand, when the voltage dividing ratio by R2 and R3 is changed while satisfying Expression 6, the graph showing the change of the frequency change characteristic shows a form as shown in FIG.

  As described above, according to the piezoelectric oscillator 10 according to the present embodiment, the first resistor (R1) 22 to the third resistor (R3) 26 are finely adjusted so as to satisfy the relationship of Equation 5 and Equation 6. It is possible to finely adjust the shift amount of the entire frequency variable characteristic (FIG. 3) and the slope of the frequency variable characteristic (FIG. 4). Therefore, it is possible to adjust the frequency variable characteristic desired as the characteristic of the piezoelectric oscillator 10 from the respective viewpoints such as the total shift amount and the inclination, and the high accuracy with respect to the desired frequency variable characteristic. It is possible to make adjustments.

  In the piezoelectric oscillator 10 having the above-described configuration, the second resistor (R2) 24 and the third resistor (R3) 26 are configured in an array of a plurality of resistors having individual resistance values, that is, as resistor groups 24a and 26a. You may make it do (refer FIG. 5). Selection of the resistance value from each of the resistance groups 24a and 26a constituting the second resistor (R2) and the third resistor (R3) may be performed by a switching method based on a selection signal input from the outside. Specifically, as shown in FIG. 5, an external input terminal group 40 and a switching signal output unit 42 may be provided. Here, the switching signal output unit 42 stores information on a correspondence list between the pattern of the input signal and the combination of the resistors in the resistor groups 24a and 26a, and when the signal is input, A combination switching signal corresponding to the pattern is output.

  With such a configuration, when a signal is input to the external input terminal group 40, the switching signal output unit 42 outputs a switching signal corresponding to the input signal pattern, and each resistor group 24a, 26a Each resistor that matches the signal pattern is selected. In the case of the example shown in FIG. 5, since the external input terminal group 40 is configured by four terminals, a combination of 4 bits, that is, 16 patterns of resistors can be selected.

  Here, as a method for setting the resistance value, it is possible to adopt a means of cutting the pattern with a laser or the like and reducing the resistance value until a desired resistance value is obtained. However, in this case, when the initial resistance value is too high, an oscillation failure occurs, and when the resistance value is reduced too much, it cannot be restored. On the other hand, the method of selecting a desired resistance value by switching has an advantage in that fine adjustment by selection switching for obtaining a desired resistance value is possible. In addition, if the resistor is built, unlike the capacitor, it can be integrated, which is suitable for downsizing the circuit.

  Next, a second embodiment according to the piezoelectric oscillator of the present invention will be described with reference to FIG. The piezoelectric oscillator according to the present embodiment is also configured based on a piezoelectric vibrator, an oscillation circuit, and an oscillation characteristic adjustment circuit. Accordingly, parts having the same function are denoted by reference numerals added with 100, and detailed description thereof is omitted.

  The piezoelectric oscillator 110 according to the present embodiment is characterized in that a circuit using an inverter 112a is configured as the oscillation circuit 112, and the above-described frequency variable characteristic adjusting circuit 116 is disposed therein.

  The oscillation circuit 112 according to the present embodiment is a feedback circuit that includes an inverter 112a, a resistor 112b, and capacitors 112c and 112d as main components, and is controlled by the frequency variable characteristic adjustment circuit 116 according to the first embodiment described above. The frequency variable characteristic of the piezoelectric oscillator 110 is changed by changing the combined feedback capacitance.

  In the piezoelectric oscillator 110 according to the present embodiment, the oscillation circuit 112 and the frequency variable characteristic adjustment circuit 116 can be integrated as a one-chip IC, and the piezoelectric oscillator 110 has a particularly advantageous configuration for making the piezoelectric oscillator 110 smaller and thinner. It can be said that there is. Other characteristics are the same as those of the piezoelectric oscillator 10 according to the first embodiment.

  Next, a third embodiment according to the piezoelectric oscillator of the present invention will be described with reference to FIG. The piezoelectric oscillator according to the present embodiment is also configured based on a piezoelectric vibrator, an oscillation circuit, and an oscillation characteristic adjustment circuit. Therefore, components having the same functions are denoted by reference numerals obtained by adding 200 to the reference numerals according to the first embodiment, and detailed descriptions thereof are omitted.

  The circuit configuration of the piezoelectric oscillator 210 according to this embodiment is substantially the same as that of the piezoelectric oscillator 110 according to the second embodiment described above, but in this embodiment, a general-purpose CMOS inverter is used as the oscillation circuit 212. The frequency variable characteristic adjusting circuit 216 and the piezoelectric vibrator 214 are connected to the oscillation circuit 212.

  In the piezoelectric oscillator 210 having such a configuration, a general-purpose IC chip constituting a CMOS inverter can be used, and the frequency variable characteristic adjusting circuit 216 itself can be easily configured. It can be said that the configuration is suitable for the above. Other characteristics are the same as those of the piezoelectric oscillator 110 according to the second embodiment described above.

  Next, another embodiment according to the piezoelectric oscillator of the present invention will be described with reference to FIGS. The piezoelectric oscillators shown in FIGS. 8 and 9 differ from the piezoelectric oscillators according to the first to third embodiments only in the configuration of the frequency variable characteristic adjusting circuit. Therefore, components having similar functions are denoted by reference numerals added with the drawings 300 (the form shown in FIG. 8) and 400 (the form shown in FIG. 9), and the detailed description thereof is omitted. .

  First, the piezoelectric oscillator 310 of the form shown in FIG. 8 corresponds to the piezoelectric oscillator 10 according to the first embodiment. The difference from FIG. 1 is that the second variable capacitance diode 320 disposed in the frequency variable characteristic adjustment circuit 316 is disposed so as to be connected between one end of the piezoelectric vibrator 314 and the ground. .

By arranging the variable capacitance diodes 318 and 320 in such a manner, the shift amount of the entire frequency variable characteristic can be greatly changed.
Moreover, the piezoelectric oscillator 410 of the form shown in FIG. 9 corresponds to the piezoelectric oscillator 110 according to the second embodiment. 6 differs from the piezoelectric oscillator 310 shown in FIG. 8 in the connection position of the second variable capacitance diode 420 in the frequency variable characteristic adjustment circuit 416. Even a piezoelectric oscillator having such a configuration can be a voltage-controlled piezoelectric oscillator according to the present invention.

It is a figure which shows the structure of the voltage control type piezoelectric oscillator which concerns on 1st Embodiment. It is a graph which shows the characteristic of the capacity | capacitance change of a variable capacitance diode. 10 is a graph showing changes in frequency variable characteristics corresponding to Equation 5. 10 is a graph showing changes in frequency variable characteristics corresponding to Equation 6. It is a figure which shows the example in the case of arraying the resistance which comprises a voltage dividing circuit. It is a figure which shows the structure of the voltage control type piezoelectric oscillator which concerns on 2nd Embodiment. It is a figure which shows the structure of the voltage control type piezoelectric oscillator which concerns on 3rd Embodiment. It is a figure which shows the modification of the voltage control type piezoelectric oscillator which concerns on 1st Embodiment. It is a figure which shows the modification of the voltage control type piezoelectric oscillator which concerns on 2nd Embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ......... Voltage control type piezoelectric oscillator (piezoelectric oscillator), 12 ......... oscillation circuit, 14 ......... piezoelectric vibrator, 16 ... frequency variable characteristic adjustment circuit, 18 ......... first variable capacitance diode, 20 ......... Second variable capacitance diode, 22 ......... First resistor (R1), 24 ......... Second resistor (R2), 26 ......... Third resistor (R3), 28 ... ... voltage dividing circuit, 30 ... fourth resistor, 32 ... control voltage application terminal.

Claims (10)

In a voltage controlled piezoelectric oscillator including a piezoelectric vibrator and an oscillation circuit,
A first variable capacitance diode arranged so that the control voltage is applied to the cathode side, and a second variable capacitance diode similarly arranged so that the control voltage is applied to the cathode side,
A first resistor provided between the first variable capacitance diode and a control voltage input terminal;
A voltage dividing circuit comprising a second resistor and a third resistor provided between the cathode side of the first variable capacitance diode and the cathode side of the second variable capacitance diode is provided. A voltage-controlled piezoelectric oscillator.   2. The voltage controlled piezoelectric oscillator according to claim 1, wherein the second variable capacitance diode is connected in series to the piezoelectric vibrator.   2. The voltage controlled piezoelectric oscillator according to claim 1, wherein the second variable capacitance diode is connected between one end of the piezoelectric vibrator and a ground. The first resistor and the second resistor and the third resistor constituting the voltage dividing circuit are

The voltage-controlled piezoelectric oscillator according to claim 1, wherein the relationship is satisfied. The voltage dividing ratio between the second resistor and the third resistor constituting the voltage dividing circuit is

The voltage-controlled piezoelectric oscillator according to claim 1, wherein the relationship is satisfied.   The second resistor and the third resistor constituting the voltage dividing circuit are each constituted by an array of resistor groups, and a switching signal is sent to the changeover switch based on a changeover switch and an external input signal. 6. A control means for outputting a signal, wherein the second resistor and the resistor having a desired resistance value are selectively defined as the second resistor and the third resistor. The voltage-controlled piezoelectric oscillator described.   7. The voltage controlled piezoelectric oscillator according to claim 1, wherein the oscillation circuit is a Colpitts type oscillation circuit.   7. The voltage controlled piezoelectric oscillator according to claim 1, wherein the oscillation circuit is an inverter oscillation circuit.   9. The voltage according to claim 8, wherein the oscillation circuit, the first variable capacitance diode, the second variable capacitance diode, the first resistor, and the voltage dividing circuit are integrated on one chip. Control type piezoelectric oscillator.   9. The voltage controlled oscillator according to claim 8, wherein a general-purpose CMOS oscillation circuit is used as the inverter oscillation circuit.

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