JP4145695B2 - Piezoelectric oscillator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a piezoelectric oscillator, and more particularly, to a circuit configuration for reducing power consumption of a piezoelectric oscillator.
[0002]
[Prior art]
In recent years, mobile communication devices such as mobile phones and portable information terminal devices have been widely used. As an oscillation circuit built in a semiconductor integrated circuit used for such mobile communication, there is an inverter oscillation circuit as disclosed in Japanese Patent Application Laid-Open No. 2000-299612. FIG. 3 is an example of a conventional inverter oscillation circuit. This circuit is grounded via the capacitor C11 from the output terminal 11 of the signal inverting amplifier 10 whose input and output are connected by a high resistance R11, and the signal inverting amplifier 10 via the piezoelectric vibrator Xtal and the frequency adjusting capacitor C14. The input terminal 12 is connected, and the input terminal 12 is grounded via the capacitor C12. The output signal is extracted through a series circuit of a resistor R12 and a capacitor C13. In addition, it is common to use a CMOS inverter having a sufficient driving capability to start up the piezoelectric oscillation in a shorter time. For this reason, the piezoelectric oscillation circuit normally consumes unnecessary power in association with the operation of the CMOS inverter having a high driving capability in spite of not requiring a large driving capability in the steady oscillation state after starting. As a result, there has been a problem that the battery life of the mobile communication device has been shortened. In addition, since the piezoelectric element is strongly excited more than necessary in a steady oscillation state, mechanical stress generated in the piezoelectric element is large, and an excellent aging characteristic as a piezoelectric oscillator may not be obtained.
[Patent Document 1]
JP 2000-299612 A
[Problems to be solved by the invention]
As described above, in the conventional circuit of FIG. 3, as described above, it is difficult to reduce the current consumption, and it is difficult to suppress the vibrator current because the output is extracted in synchronization with the oscillation output by the parallel resonance circuit. Met.
The present invention has been made in view of the above problems, and an object thereof is to provide a piezoelectric oscillator in which the current of the piezoelectric vibrator is reduced with a simple circuit configuration.
[0004]
[Means for Solving the Problems]
In order to solve the above problems, the present invention provides a piezoelectric vibrator having a piezoelectric element excited at a predetermined frequency, and a signal inverting amplifier for exciting the piezoelectric element by passing a current through the piezoelectric element. A grounded output terminal of the signal inverting amplifier having a high resistance connected between the input and output through a circuit in which a capacitor and a parallel tuning circuit are connected in series, and the capacitor and the parallel tuning. The connection point of the circuit is grounded via a diode clamp circuit, and the connection point is connected to the input terminal of the signal inverting amplifier via two series-connected capacitors. The connection point is grounded via the piezoelectric vibrator and the frequency adjusting element. The conventional Hartley-type inverter oscillation circuit makes it easy to start oscillation by increasing the negative resistance by setting a constant close to series resonance in order to increase the load capacity. However, since the current flowing through the piezoelectric vibrator is determined by the level between the input and output of the inverter, the current suppression effect is low in an inverter having a high gain. Accordingly, the present invention solves this problem by grounding the clamp circuit from the output of the inverter via a capacitor.
According to this invention, since the clamp circuit is grounded from the output of the inverter via the capacitor, both ends of the piezoelectric vibrator are clamped, and the impedance of the inverter is drastically reduced to lower the oscillation gain. The effect of suppressing the current flowing through the child can be enhanced.
[0005]
According to a second aspect of the present invention, the diode clamp circuit is formed by connecting two diodes in parallel so that their polarities are different from each other.
The oscillation waveform is basically an alternating current. Therefore, it is necessary to clamp each waveform of both poles. Therefore, it can be realized by connecting the diodes in opposite polarities in parallel.
According to this invention, since clamping is performed at both poles of the oscillation waveform, the clamping amount is large and the clamping can be performed with a good balance.
According to a third aspect of the present invention, when viewed from the connection point of the two capacitors, a series resonance circuit is constituted by one of the two capacitors and the parallel tuning circuit.
When the series resonant circuit resonates at the oscillation frequency, the impedance is minimized and the circuit current is maximized. As a result, the negative resistance can be increased and the oscillation can be easily started.
According to this invention, since the series resonance circuit is formed in the loop of the piezoelectric vibrator, the negative resistance can be increased and the oscillation can be easily started.
According to a fourth aspect of the present invention, the piezoelectric vibrator is a quartz crystal vibrator.
According to this invention, it is possible to realize an inexpensive and high frequency stability oscillator by using a crystal resonator as the piezoelectric resonator.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings. However, the components, types, combinations, shapes, relative arrangements, and the like described in this embodiment are merely illustrative examples and not intended to limit the scope of the present invention only unless otherwise specified. . In the following embodiments, a crystal oscillator is described as an example of a piezoelectric oscillator (vibrator), but the present invention is applicable to general piezoelectric oscillators other than crystals.
FIG. 1 is a circuit diagram of an inverter oscillation circuit with a clamp circuit according to an embodiment of the present invention. In addition, the circuit element value shown as an example with the circuit element code | symbol below is a design condition at the time of confirming the oscillator electrical characteristic mentioned later. In this inverter oscillation circuit, a parallel tuning circuit in which a capacitor C2 and an inductor L1 are connected in parallel through a capacitor C1 is connected in series from an output terminal 2 of the inverter 1 whose input and output are connected by a high resistance R1, and this is grounded. The diodes D1 and D2 are connected in parallel so as to have different polarities from the connection point of series connection, and are grounded. Further, it is connected to the input terminal 3 of the inverter 1 via the capacitors C3 and C4, and is grounded via the piezoelectric vibrator Xtal and the frequency adjusting capacitor C7 from the connection point of the capacitors C3 and C4 connected in series. In this circuit, the output is taken out through a series circuit of a resistor R2 and a capacitor C6.
[0007]
Next, the operation of this embodiment will be described. Since the oscillation operation is a well-known technique, a detailed description thereof will be omitted here. First, when the power supply VCC5V is input to the inverter 1, vibration starts according to the natural frequency of the piezoelectric element Xtal, and a high level voltage is generated at the output terminal 2 of the inverter 1. The AC component of the voltage passes through the capacitor C1 and is input to the parallel tuning circuits L1, C2 and the clamp diodes D1, D2. In the clamp diodes D1 and D2, when the voltage is positive, the diode D2 conducts, and when the voltage is negative, the diode D1 conducts, and the forward voltage of each diode is a predetermined voltage (about 0.7V) from the characteristics of the diode. It doesn't go up any more. Therefore, when the feedback signal to be supplied from the output terminal 2 of the inverter 1 to the piezoelectric element Xtal exceeds a certain excitation level, the diodes D1 and D2 are turned on, and the excitation level becomes larger than ± 0.7 Vp-p. There is no. As a result, the impedance between the input and output of the inverter 1 is drastically lowered and the oscillation gain is drastically lowered, so that the current flowing through the piezoelectric element X can be significantly suppressed.
The constants of the oscillation circuit of this embodiment are as follows: R1: 100 kΩ, R2: 10 kΩ, C1: 100 pF, C2: 180 pF, C3: 30 pF, C4: 6 pF, C6: 10000 pF, C7: 100 pF, L1: 1 μH, D1 , D2: 1SS315, Xtal: At-cut 1st 10 MHz, inverter 1: TC7SU04F.
[0008]
FIG. 2 is a diagram showing the relationship between the negative resistance value of the inverter oscillation circuit with a clamp circuit of FIG. 1 and the input level of the oscillator. The horizontal axis is the input level (mV) of the oscillator (inverter circuit), and the vertical axis is the negative resistance (Ω). Reference numeral 15 in FIG. 2 is a characteristic of the circuit of the present invention, and reference numeral 16 is a characteristic of the conventional circuit. As is clear from this figure, the characteristic of the conventional circuit of reference numeral 16 is that the negative resistance is substantially constant at a large value and is not greatly affected by the input level of the oscillator. On the other hand, it can be seen that the present invention of reference numeral 15 exhibits the characteristic that the negative resistance decreases when the input level of the oscillator is 300 mV or more, thereby suppressing the vibrator current. Thus, by suppressing the amplitude by the clamp circuit, the negative resistance is drastically reduced, and as a result, the vibrator current is suppressed.
Although the embodiment of the present invention has been described above, the present invention is characterized in that a vibrator is inserted between the input of the inverter oscillation circuit and the ground, and the configuration of the clamp circuit and the configuration of the inverter circuit have been described in the present embodiment. The present invention is not limited to this, and other forms and circuit configurations do not depart from the spirit of the present invention.
[0009]
【The invention's effect】
As described above, according to the first aspect of the present invention, the clamp circuit is grounded from the output of the inverter through the capacitor to clamp both ends of the piezoelectric vibrator, and the impedance of the inverter is drastically reduced to thereby reduce the oscillation gain. Therefore, the effect of suppressing the current flowing through the piezoelectric vibrator can be enhanced.
Further, in the second aspect, since clamping is performed at both poles of the oscillation waveform, the clamping amount is large and the clamping can be performed with a good balance.
According to the third aspect of the present invention, since clamping is performed with one pole of the oscillation waveform, the decrease in the oscillation gain is somewhat reduced, but the cost is reduced by reducing the component cost.
According to the fourth aspect of the present invention, an inexpensive and high frequency stability oscillator can be realized by using a crystal resonator as the piezoelectric resonator.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of an inverter oscillation circuit with a clamp according to an embodiment of the present invention.
2 is a diagram illustrating a relationship between a negative resistance value of the inverter oscillation circuit with a clamp circuit of FIG. 1 and an input level of the oscillator according to the present invention. FIG.
FIG. 3 is an implementation circuit diagram of a conventional inverter oscillation circuit.
[Explanation of symbols]
Xtal Piezoelectric element C1, C2, C3, C4, C6, C7 Capacitor D1, D2 Diode 1 Inverter R1 Feedback resistor R2 Fixed resistor

Claims (4)

A piezoelectric oscillator comprising: a piezoelectric vibrator including a piezoelectric element excited at a predetermined frequency; and a signal inverting amplifier for exciting the piezoelectric element by passing a current through the piezoelectric element,
The output terminal of the signal inverting amplifier connected between the input and output with a high resistance is grounded through a circuit in which a capacitor and a parallel tuning circuit are connected in series, and the connection point of the capacitor and the parallel tuning circuit is connected through a diode clamp circuit. And connecting the connection point to the input terminal of the signal inverting amplifier via two series-connected capacitors, and connecting the connection point of the two capacitors connected in series to the piezoelectric vibrator and the frequency adjusting element. Piezoelectric oscillator characterized by being grounded via 2. The piezoelectric oscillator according to claim 1, wherein the diode clamp circuit includes two diodes connected in parallel so as to have different polarities. 2. The piezoelectric oscillator according to claim 1, wherein when viewed from a connection point of the two capacitors, a series resonance circuit is configured by one of the two capacitors and the parallel tuning circuit. The piezoelectric oscillator according to claim 1, wherein the piezoelectric vibrator is a crystal vibrator.

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