PIEZOELECTRIC OSCILLATOR

Abstract: In order to realize a small quartz oscillator having high frequency stability and capable of measuring DLD characteristics, in a piezo-oscillator comprising an oscillator circuit including a piezo-vibrator and an amplifier circuit, and a constant-voltage circuit, in which a power source and the oscillator circuit are connected through the constant-voltage circuit to supply a constant voltage to the oscillator circuit, depending on the said power source voltage, a function of the constant-voltage circuit is invalidated. With this structure, even after the piezo-vibrator and other electron circuits are integrally assembled, it is possible to adjust the drive level of the quartz vibrator and to measure the DLD characteristics by changing the power source voltage.

Description: TECHNICAL FIELD The present invention relates to a piezo-oscillator, and more particularly, to a small piezo-oscillator having excellent aging characteristics. BACKGROUND TECHNIQUE In recent years, as communications equipment is reduced in size, a reference signal source used for the equipment is required to be small in size, and a quartz oscillator shown in Figs. 5 for example has been proposed. Fig. 5(a) is a sectional view of a structure of a conventional quartz oscillator, and Fig. 5(b) is a circuit diagram of the conventional quartz oscillator. As shown in Fig. 5(a), the quartz oscillator 100 includes an integrated amplifier circuit 101, a quartz vibrator 102, a ceramic container 103 having a recess for accommodating the amplifier circuit 101 and the quartz vibrator 102 therein, and a metal lid 104. After the amplifier circuit 101 is mounted in on a bottom surface of the recess of the ceramic container 103, the quartz vibrator 102 is mounted such as to cover an upper surface of the amplifier circuit 101, and the ceramic container 103 is sealed by the lid 104 such as to cover these members. The quartz vibrator 102 and other electron parts are mounted in the common accommodation container in this manner, thereby realizing a compact quartz oscillator 100. However, with the above structure, it is impossible to check a drive level dependence characteristics (DLD characteristics, hereinafter) such as variation in oscillation frequency with respect to drive level variation of the quartz vibrator 102. That is, the DLD characteristics may be varied due to variation in producing procedure and producing conditions or the like. Since the DLD characteristics affects the stability of frequency and characteristics and reproducibility of the quartz vibrator 102, it is indispensable to check the vibrator after it was completed. A common method for checking the DLD characteristics of the quartz vibrator 102 is to change the drive level of the quartz vibrator 102 incorporated in the oscillator, and to check deviation of oscillation frequency with respect to variation of the drive level. In the case of the quartz oscillator 100, since the quartz vibrator 102 and the amplifier circuit 101 are accommodated in the same container, the quartz vibrator 102 alone can not be checked. It seems possible to control a voltage value of a power source Vcc to be supplied to the oscillator circuit of the quartz oscillator 100, thereby adjusting the amplification action of the amplifier circuit 101 to control the drive level of the quartz vibrator 102. However, since the quartz oscillator 100 output stable frequency signal even if the supplied power source voltage is varied, at least one of a constant-voltage circuit 105 and a constant-current circuit 106 is provided in the oscillator circuit as shown in Fig. 5(b) in many cases. Therefore, in the case of the quartz oscillator 100 having such a structure, even if the power source voltage value is controlled, since the drive level of the quartz vibrator 102 is not varied, there is a problem that DLD characteristics can not be checked. Document EP 0 724 331 discloses an oscillation circuit for generating a clock signal. A constant voltage generation circuit supplies a first voltage to the oscillation circuit until the clock signal is stabilized and the constant voltage generation circuit supplies a second voltage lower than the first voltage after the clock signal has been stabilized. The present invention has been accomplished to solve the above problems of the conventional constant-voltage oscillator, and it is an object of the invention to provided a small quartz oscillator in which the DLD characteristics can be measured after it is packaged even if a constant-voltage circuit or constant-current circuit is included in the circuit. DISCLOSURE OF THE INVENTION The object is achieved by providing a piezo-oscillator according to claim 1 or claim 4. The dependent claims refer to preferred embodiments of the invention. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a circuit diagram of an embodiment of a quartz oscillator based on the present invention; Fig. 2 is a circuit diagram of a control circuit of the quartz oscillator based on the invention; Fig. 3 is a circuit diagram of another embodiment of the of the quartz oscillator based on the invention; Fig. 4 is a circuit diagram of a control circuit of the quartz oscillator based on the invention; and Figs. 5 are views showing structure of a conventional quartz oscillator, wherein (a) is a side sectional view of the conventional quartz oscillator, and (b) is a circuit diagram of the conventional quartz oscillator. BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be explained in detail based on the illustrated embodiments. Fig. 1 is a circuit diagram of an embodiment of a quartz oscillator based on the present invention. A circuit shown in Fig. 1 has a structure in which an amplifier circuit 2 is cascaded to a typical Colpitts quartz oscillator 1. A power source Vcc, the amplifier circuit 2 and a constant-voltage circuit 3 are connected through a switch circuit 4. The switch circuit 4, a switch circuit 5 (which will be described later) included in the amplifier circuit 2 are connected to a control circuit 6 for controlling these switch circuits. In the oscillator circuit 1, a resistor R1 is connected between a ground and a base of a transistor Q1 that is an amplifier element. A capacitor C1 is connected between the base and an emitter, and a capacitor C2 between the emitter and the ground. A resistor R2 is connected in parallel to the capacitor C2. A resistor R3 is connected between the base of the transistor Q1 cascaded to the amplifier circuit 2 and a base of a transistor Q2. In the amplifier circuit 2, in addition to the above-explained connection relation, a power source line 7 and a collector of the transistor Q2 are connected through a resistor R4, and a constant-current circuit 8 and a resistor R5 are connected to the base of the transistor Q2, and the amplifier circuit 2 is structured such that any of them is connected to the power source line 7 by the switch circuit 5. The power source line 7 is structured such that the power source line 7 is connected any one of the constant-voltage circuit 3 and the power source Vcc by the switch circuit 4. Fig. 2 is a circuit diagram showing one example of the control circuit 6. Control of the switch circuit 4 is mainly explained. As shown in Fig. 2, the control circuit 6 includes a voltage comparing section 9. The control circuit 6 outputs a signal to the switch circuit 4 as a control signal, and controls a switch 10 and a switch 11 provided in the switch circuit 4. A positive terminal of the voltage comparing section 9 of the control circuit 6 is connected to the power source Vcc divided by a resistor R6 and a resistor R7 so as to supply voltage. A collector and a base of a transistor Q3 are connected, and a negative terminal of the voltage comparing section 9 is connected to the collector. As a result, the power source Vcc is supplied to the other negative terminal via a resistor R8. An emitter of a PNP transistor Q4 (transistor Q4, hereinafter) of the switch 10 connects to the power source Vcc. The emitter of the transistor Q4 connects to the base through a resistor R9, and the base connects to a collector of a transistor Q5 whose emitter is grounded. The base of the transistor Q5 is also grounded via a resistor R10, and connected to an output terminal of the comparing section 9 through a resistor R11. An emitter of a PNP transistor Q6 (transistor Q6, hereinafter) of the switch 11 connects to an output terminal of the constant-voltage circuit 3. A base of the transistor Q6 connects to an output terminal OP of the control circuit 6. The emitter is connected the base and the output terminal of the comparing section 9 via a resistor R12. The operation of the control circuit 6 will be explained. First, in the quartz oscillator, the power source voltage (Vcc) is usually set up in a prescribed range for oscillation, and the voltage at oscillation is defined as operation voltage (Vccd), and voltage higher than Vccd is defined as non-operation voltage (Vcch). A divided voltage ratio of the resistor R6 and the resistor R7 is set such that when the Vccd is maximum, voltage (voltage between the base and the emitter of the transistor Q3) of the positive terminal and voltage of the negative terminal of the comparator 12 become equal to each other. Therefore, an output signal of the comparing section 9 becomes LOW and outputs 0V when the Vcc is in the range of Vccd. At that time, an electric potential of the base of the transistor Q6 becomes lower than that of the emitter and thus, the transistor Q6 is actuated. Further, since the transistor Q5 is not actuated, the transistor Q4 is not actuated, thus the switch 10 is brought into OFF State. As a result, the constant-voltage circuit 3 and the power source line 7 are connected, and the constant-voltage circuit function is functioned. On the other hand, when the Vcc is equal to or higher than the Vcch, the output signal of the comparing section 9 becomes HI and outputs voltage Vh (voltage Vh>constant-voltage circuit output voltage). At that time, in the switch 11, since the electric potential of the base of the transistor Q6 becomes higher than that of the emitter, the transistor Q6 is not actuated. In addition, the transistor Q5 of the switch 10 is actuated so that the base of the transistor Q4 is grounded, the transistor Q4 is actuated. As a result, the power source Vcc and the power source line 7 are directly connected to each other and thus, the constant-voltage circuit function becomes invalid. The switch circuit 5 is operated in the same manner as the switch circuit 4. In the switch circuit 5, when the voltage is in the range of Vccd, the constant-current circuit 8 is connected to the power source line 7, and when the voltage is non-operation voltage Vcch, the resistor R5 is connected to the power source line 7. According to the above-explained operation, when the operation voltage is 5V ± 1V, if the voltage of the power source Vcc is 6V or higher, it is possible to invalidate the functions of the constant-voltage circuit 3 and the constant-current circuit 8. Therefore, it is possible to control the operation of the amplifier circuit by the voltage of the power source Vcc without affecting the oscillation when the quartz oscillator is used. Therefore, it is possible to control the drive level of the quartz oscillator and thus, the DLD characteristics can be checked after the package. Fig. 3 is a circuit diagram showing another embodiment of the quartz oscillator based on the present invention. Fig. 4 shows an example of circuit structure of the control circuit 6 shown in Fig. 3. The quartz oscillator circuit shown in Fig. 3 is different from that shown in Fig. 1 in that a frequency control voltage section AFC is connected to the positive terminal of the comparing section 9 as shown in Fig. 4 such that voltage of the frequency control voltage section AFC is supplied to the pos itive terminal, thereby controlling the switch circuit 4 and the switch circuit 5 by the voltage signal from the frequency control voltage section AFC. With this arrangement, it is possible to invalidate the functions of the constant-voltage circuit 3 and the constant-current circuit 8 even if the voltage is in a range of the operation voltage Vccd. Therefore, it is possible to control the drive level over a wider range. Similarly, in the examples shown in Figs. 1 and 2, it is possible to separately provide a switch control terminal, and to control a circuit that bypasses the constant-voltage circuit and the constant-current circuit irrespective of the power source voltage value. The present invention has been described while taking a case of the switch circuit constituted using the transistors, but the invention is not limited to this structure, and another switch circuit having a different structure may also be used if the switch circuit performs a switch operation. The present invention has been explained while taking the case of the oscillator using the quartz elements, the invention is not limited to this, and it is apparent that the invention may be applied to another piezo-oscillator other than quartz oscillator. In the piezo-oscillator based on the present invention, as explained above, it is possible to invalidate the control of the constant-voltage circuit and the constant-current circuit at operation voltage or higher even if the piezo-vibrator and the oscillator circuit including the constant-voltage circuit and the constant-current circuit are contained in the same container. Therefore, it is possible to control the drive level of the quartz vibrator and thus, there is effect that the DLD characteristics can be measured.

Claims: A piezo-oscillator comprising: an oscillator circuit (1) including a piezo-vibrator and an amplifier circuit (2), said piezo-vibrator having one of its terminals connected to an input terminal of said amplifier circuit (2) and having the other terminal grounded via a capacitive element (C2) so that said amplifier circuit (2) provides at its output a frequency based on the resonance frequency of said piezo-vibrator; a constant-voltage circuit (3) connected to a power source (Vcc); a frequency control voltage section (AFC) connected to said piezo-vibrator; a first switch circuit (4) for selectively connecting the output of either one of said power source (Vcc) and said constant-voltage circuit (3) to a power source line (7) of said amplifier circuit (2); a second switch circuit (5) connected to said power source line (7) of said amplifier circuit (2); a constant-current circuit (8) connected to said second switch circuit; and a resistance element (R5) connected to said second switch circuit; wherein said first switch circuit (4) connects said constant-voltage circuit (3) to said power source line of said amplifier circuit (2) when a voltage supplied to said frequency control voltage section (AFC) is equal to or lower than a predetermined value, and connects said power source (Vcc) to said power source line (7) of said amplifier circuit (2) when the voltage supplied to said frequency control voltage section (AFC) is higher than said predetermined value; and wherein said second switch circuit (5) connects said power source line (7) of said amplifier circuit (2) and said constant-voltage circuit (3) when said voltage supplied to said frequency control voltage section (AFC) is equal to or lower than said predetermined value, and connects said power source line (7) of said amplifier circuit (2) and said resistance element when the voltage supplied to said frequency control voltage section (AFC) is higher than said predetermined value. The piezo-oscillator of claim 1, wherein when the voltage supplied to said frequency control voltage section (AFC) is higher than said predetermined value, the voltage of said power source (Vcc) is controlled to change the voltage to be supplied to said amplifier circuit (2) to thereby change the drive level of said piezo-vibrator. The piezo-oscillator of claim 2, wherein it is possible to examine the drive level dependency characteristic of said piezo-vibrator by measuring a change in the resonance frequency of said piezo-vibrator caused by a change in the drive level of said piezo-vibrator. A piezo-oscillator comprising: an oscillator circuit (1) including a piezo-vibrator and an amplifier circuit (2), said piezo-vibrator having one of its terminals connected to an input terminal of said amplifier circuit (2) and having the other terminal grounded via a capacitive element so that said amplifier circuit (2) provides at its output a frequency based on the resonance frequency of said piezo-vibrator; a constant-voltage circuit (3) connected to a power source (Vcc); a first switch circuit (4) for selectively connecting the output of either one of said power source (Vcc) and said constant-voltage circuit (3) to a power source line (7) of said amplifier circuit (2); a second switch circuit (5) connected to said power source line (7) of said amplifier circuit (2); a constant-current circuit (8) connected to said second switch circuit; and a resistance element (R5) connected to said second switch circuit; wherein said first switch circuit (4) connects said constant-voltage circuit (3) to said power source line of said amplifier circuit (2) when a voltage supplied from said power source-(Vcc) is equal to or lower than a predetermined value, and connects said power source (Vcc) to said power source line (7) of said amplifier circuit (2) when the voltage supplied from said power source (Vcc) is higher than said predetermined value; and wherein said second switch circuit (5) connects said power source line (7) of said amplifier circuit to said constant-current circuit (8) when said voltage supplied from said power source (Vcc) is equal to or lower than said predetermined value, and connects said power source line (7) of said amplifier circuit (2) to said resistance element when the voltage supplied from said power source (Vcc) is higher than said predetermined value. The piezo-oscillator of claim 4, wherein when the voltage supplied from said power source (Vcc) is higher than said predetermined value, the voltage of said power source (Vcc) is controlled to change the voltage to be supplied to said amplifier circuit (2) to thereby change the drive level of said piezo-vibrator. The piezo-oscillator of claim 5, wherein it is possible to examine the drive level dependency characteristic of said piezo-vibrator by measuring a change in the resonance frequency of said piezo-vibrator caused by a change in the drive level of said piezo-vibrator.

Inventors: UCHIYAMA T, UCHIYAMA, T., UCHIYAMA, T., Toyo Communication Equip. Co., Ltd.
Applicants: TOYO COMMUNICATION EQUIP, TOYO COMMUNICATION EQUIPMENT CO. LTD.
Application year: 2000
Main classification: H03B5
IPC codes: H03B5