JPS6238882B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a piezoelectric oscillator, and more particularly, to a piezoelectric oscillator that can reliably start oscillation.

As shown in FIG. 1, a conventional Colpitts-type piezoelectric oscillator is composed of an amplifying section consisting of an amplifying element 5, and a feedback section consisting of a feedback resistor 4, a piezoelectric vibrator 1, and phase rotation capacitors 2 and 3. There is. In FIG. 1, the product μβ of the amplification degree μ of the amplifying element 5 and the feedback amount β of the feedback section is calculated by the phase rotation capacitors 2 and 3 when the equivalent resistance CI of the piezoelectric vibrator 1 is constant.
It changes as shown in FIG. 2 depending on the composite capacitance value C of . In order to start oscillation, μβ must be greater than 1.

Now, the smaller the change in the equivalent resistance CI with respect to the change in the excitation level IQ of the piezoelectric vibrator 1, the better, but in reality, as shown in FIG. 3, there are many piezoelectric vibrators 1 that have a large equivalent resistance CI at the time of rising. Third
When using the piezoelectric vibrator 1 with the characteristics shown in the figure, if the combined capacitance value C of the phase rotation capacitors 2 and 3 is set so as to have an appropriate μβ with respect to the equivalent resistance CI in steady state, the result will be as shown in Figure 4. There is a drawback that μβ becomes smaller than 1 at the rising edge, making it impossible to start oscillation.

Furthermore, in order to ensure oscillation even when using the piezoelectric vibrator 1 having the characteristics shown in FIG. 3, it is necessary to reduce the combined capacitance C of the phase rotation capacitors 2 and 3 or the feedback resistor 4 in the circuit shown in FIG. Amplifying element 5
It is conceivable to set the amplification degree μ to be large so that μβ is larger than 1 with respect to the equivalent resistance CI at the time of rising. However, the piezoelectric vibrator 1
As shown in the figure, the equivalent resistance CI at rise is large and the equivalent resistance CI at steady state is small, so if μβ is set by the equivalent resistance CI at rise, μβ becomes too large at steady state, and the fifth This results in operation at a point where component sensitivity is large, such as point A on the characteristic curve of excitation level IQ and frequency change rate Δf/f in the figure, resulting in a disadvantage that frequency stability deteriorates. Furthermore, operating the piezoelectric vibrator 1 by increasing the excitation level IQ has the drawback of adversely affecting the aging of the frequency and generating unnecessary vibration modes.

As mentioned above, if a piezoelectric vibrator with the characteristics shown in FIG. 3 is used in the configuration shown in FIG. 1, it will have various drawbacks that are undesirable in terms of reliability as described above, so it is difficult to operate with high reliability. It was impossible to do so.

An object of the present invention is to provide a piezoelectric oscillator having a structure that eliminates the above-mentioned drawbacks and enables highly reliable operation by a piezoelectric vibrator having a large equivalent resistance at rise time as shown in FIG.

According to the present invention, in a piezoelectric oscillator having an amplifier section and a feedback section including a piezoelectric vibrator and a phase rotation capacitor, the piezoelectric oscillator is turned off in response to the oscillation output level at the time of starting oscillation, and the oscillation output level during steady operation is maintained. A series or parallel circuit of a switching element and an auxiliary capacitor that respond to the on state is connected to the phase rotation capacitor, and the composite phase rotation capacity of the auxiliary capacitor and the phase rotation capacitor when the switching element is in the off state is as follows. A piezoelectric oscillator is obtained which is characterized in that the piezoelectric oscillators are connected in such a connection relationship that the combined phase rotation capacitance is smaller than the above-mentioned combined phase rotation capacitance when the switching element is in the ON state.

According to the present invention, when starting oscillation of a piezoelectric vibrator having a large equivalent resistance at the time of rising as shown in FIG. 3, the switching element is turned off to reduce the composite phase rotation capacitance, thereby increasing μβ. By reliably starting oscillation, turning on the switching element during steady operation, and increasing the composite phase capacitance, it is possible to reduce μβ, reduce the excitation level, and operate at a point with small component sensitivity. It is possible to prevent frequency stability, deterioration of aging, and unnecessary vibration modes. In other words, it is possible to operate the piezoelectric vibrator with high reliability, which has a large equivalent resistance at the time of rising.

Next, embodiments of the present invention will be described with reference to the drawings.

In the embodiment shown in FIG. 6, an oscillation circuit is constructed of a piezoelectric vibrator 1, phase rotation capacitors 2 and 3, an amplifying element 5, an auxiliary capacitor 6, a series circuit of a diode 7 as a switching element, and a feedback resistor 4. A rectifier 9 is connected to the oscillation output terminal OUT, and the rectified output is connected between the capacitor 6 and the diode 7 via a resistor 8.

At the moment when oscillation starts, the oscillation output amplitude is zero, so naturally the output of the rectifier 9 is also zero, and the diode 7 is in an off (non-conducting) state. Therefore, the phase rotation capacitor for the piezoelectric vibrator 1 is 2,
It becomes 3. When the oscillation output amplitude increases, a forward voltage can be applied to the diode 7 due to the function of the rectifier 9 (the function of extracting and smoothing the negative potential portion of the oscillation output amplitude). Then, the diode 7 becomes on (conducting) and the auxiliary capacitor 6
is connected in parallel with the phase rotation capacitor 3. As a result of the above, the composite phase rotation capacity at the time of oscillation startup can be reduced, and the composite phase rotation capacity at steady state can be increased.
can be made large, and μβ in steady state can be made small as shown in FIG. 7b, and even the piezoelectric vibrator 1 having the characteristics shown in FIG. 3 can be used at an excitation level with small component sensitivity.

FIG. 8 shows an embodiment in which the oscillation frequency is divided by a frequency divider 11 and then a rectified voltage is applied to the diode 7 via the rectifier coil 12 by the rectifier 9. In addition, in FIG. 8, 10 is a capacitor, and 13 and 14 are resistors.

Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments and includes many modifications. For example, in order to ensure that the diode 7 as a switching element is turned on and off, the diode 7 may be placed in a reverse bias state at the time of starting oscillation. Alternatively, a series circuit of auxiliary capacitor 6 and diode 7 may be connected in parallel to capacitor 2, or a circuit in which auxiliary capacitor 6 and diode 7 are connected in parallel may be connected in series to phase rotation capacitor 2 or 3. It's okay. Furthermore, as the switching element, not only a diode but also various other elements can be used.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram of a conventional Colpittz piezoelectric oscillator, and Figure 2 shows the phase rotation capacitance C and μ in Figure 1.
Figure 3 is a diagram showing an example of the characteristics between the excitation level IQ and equivalent resistance CI of a piezoelectric vibrator, and Figure 4 is a diagram showing a piezoelectric vibrator having the characteristics shown in Figure 1 and Figure 3. A diagram showing the characteristics of the oscillation level and μβ when using a vibrator. Figure 5 shows the excitation level of the piezoelectric vibrator.
A diagram showing an example of the characteristics of IQ and frequency change rate Δf/f, FIG. 6 is a circuit diagram showing an embodiment of the present invention,
Figure 7 shows the oscillation level and μ in the embodiment shown in Figure 6.
FIG. 8 is a circuit diagram showing another embodiment of the present invention. 1... Piezoelectric vibrator, 2 and 3... Phase rotation capacitor, 5... Amplifying element, 6... Auxiliary capacitor, 7... Diode which is a switching element,
9... Rectifier.

Claims (1)

[Claims] 1 A piezoelectric oscillator having an amplifying section and a feedback section including a piezoelectric vibrator and a phase rotation capacitor, the piezoelectric vibrator using a piezoelectric vibrator having a larger equivalent resistance at the time of starting oscillation than during steady operation as the piezoelectric vibrator. In an oscillator, a series or parallel circuit of a switching element and an auxiliary capacitor that is turned off in response to the oscillation output level at the start of oscillation and turned on in response to the oscillation output level during steady operation is connected to the phase rotation capacitor. The auxiliary capacitor and the phase rotation capacitor are connected in such a connection relationship that the combined phase rotation capacity of the auxiliary capacitor and the phase rotation capacitor when the switching element is in the off state is smaller than the combined phase rotation capacity when the switching element is in the on state. A piezoelectric oscillator characterized by: