JPS59178802A - Crystal oscillator - Google Patents

Abstract

PURPOSE:To improve the reproducibility of an oscillating state by inserting a buffer circuit comprising a resistor connected in series and a capacitor connected in parallel between a crystal oscillator and a tuning circuit so as to attain ease of adjusting operation as the entire crystal oscillator. CONSTITUTION:In adjusting the oscillating state, after a tuning frequency (f) of a tuning circuit 6 is set to a natural frequency F0 of the crystal oscillator 3 where an oscillating voltage characteristic Y (output level) shows a maximum value by changing an inductance L1 of a coil 5 and changing a capacitor C1 of a variable capacitor 2, the oscillating frequency almost decided by the natural frequency F0 of the crystal oscillator 3 has only to be adjusted minutely. Thus, it is not necessary to set the frequency to an intermediate frequency as a point C in the oscillating voltage characteristic X of a conventional crystal oscillator, then the adjusting operation as the entire crystal oscillator is simplified, allowing to decrease the time required for the adjustment. Further, the reproducibility of a setting value is improved by setting the tuning frequency to the frequency where the output level shows a maximum value in comparison with a conventional setting method where the tuning frequency is set to the intermediate value.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a crystal oscillator, and more particularly to a crystal oscillator that can be easily adjusted by a tuning circuit.

Some crystal oscillators include a tuning circuit in which a capacitor and a coil are connected in parallel, and the tuning frequency of this tuning circuit is adjusted to set the oscillation conditions of the crystal oscillator.

In this way, a crystal oscillator using a tuning circuit can easily oscillate at an overtone frequency twice or three times as much as the fundamental frequency of the crystal resonator. Furthermore, by varying the tuning frequency, it is possible to absorb deviations (variations) in the values of the coil and capacitor of the tuning circuit.

Among such crystal oscillators equipped with 31 gradient circuits, the basic circuit of a Colpitts type crystal oscillator is shown in FIG. However, the DC bias circuit is omitted in the figure.

In other words, 1 in the figure is a transistor (amplification element).
A variable capacitor 2 with a capacitance C1 is inserted between the base of the transistor 1 and the ground, a crystal resonator 3 is connected between the pace and the collector, and a capacitor 4 with a capacitance C2 and an inductance L1 are connected between the collector and the ground. A tuning circuit 6 constructed of a parallel circuit with a coil 5 that can vary the voltage is inserted, and its emitter is grounded.

The oscillation conditions for a Colpitts-type crystal oscillator with such a configuration are such that the crystal oscillator 3 exhibits inductive reactance,
In addition, the variable capacitor 2 and the tuning circuit 6 exhibit a g-1f reactance of a certain level or higher. Therefore, when the oscillation conditions are satisfied, the equivalent circuit of the crystal oscillator shown in FIG. 1 is obtained by replacing the tuning circuit 6 with a capacitor 7 having a capacitance c3 indicating capacitive reactance, as shown in FIG. Therefore, in order for the tuned circuit 6 to exhibit capacitive reactance, in the crystal oscillator configured in this way, the inductance L1 of the coil 5 of the tuned circuit 6 is varied to adjust the tuning 1 frequency f of the tuned circuit 6. A method of adjusting the oscillation state of a crystal oscillator by changing the oscillation state will be explained using FIG.

That is, FIG. 3 shows the level of the oscillation voltage υ appearing at the output terminal of the collector when the tuning frequency f of the tuning circuit 6 is changed.

Of course, the oscillation frequency is determined by the characteristics of the crystal resonator 3. First, the inductance L1 of the coil 5 is maximized and the power switch is turned on. That is, in FIG. 3, the frequency domain KaM is f×A. In this case, the tuning circuit 6 exhibits capacitance and reactance, but since the tuning frequency f is significantly lower than the natural frequency F0 of the crystal resonator 3, the impedance of the tuning circuit 6 is also low. Therefore, since the gain of transistor 1 is small and does not satisfy the oscillation condition, oscillation does not occur. Next, as the inductance L of the coil 6 is adjusted to gradually increase the tuning frequency f, the impedance increases, and oscillation occurs when the gain satisfies the oscillation condition f: (f=A). Then, it oscillates with the oscillation voltage and pressure of υ=a. When the tuning frequency f is further increased, the oscillation voltage τ increases as indicated by X in the figure. Then, the tuning frequency f is the resonance frequency Fr of the tuning circuit 6.
When K is reached, the tuning circuit 6 changes from capacitive reactance to inductive reactance, and the oscillation condition is no longer satisfied. Therefore, the oscillation voltage characteristic X suddenly drops to zero from the maximum value that resonates most with the oscillation frequency, and the oscillation stops. Therefore, the tuning frequency f is set from A to prit>
After setting the appropriate A in the song, change the capacitance C1 of the variable capacitor 2 to adjust the natural frequency F of the crystal camera 3. All you have to do is fine-tune the oscillation frequency, which is approximately determined by .

However, the crystal oscillator adjusted by the method described above has the following problems.

In other words, the frequency of the oscillation voltage at point C cannot be set at or near Fr1, which is the maximum value in the oscillation voltage characteristic X of the tuning frequency f of the actual crystal oscillator, and is sufficiently lower than the frequency Fr of the maximum oscillation voltage CK must be set.

This is based on the following reasons. In other words, ・3rd
This is the case when the oscillation voltage characteristic X multiplied by the tuning frequency f shown in the figure is gradually increased from A toward the body, but conversely, when the tuning frequency f is decreased from high to low, The oscillation start frequency and oscillation stop frequency must be different. In other words, with the tuning frequency f set at or near Fr!
6? .

If you turn on the tuning frequency f, it will not oscillate.
After lowering it to near point Fr to cause oscillation, it is necessary to move it again to point Fr. Therefore, for the above reasons, the tuning frequency f must be set not to the frequency F at which the oscillation voltage characteristic The adjustment operation for the oscillator as a whole becomes complicated, and the time required for adjustment is wasted (
There was a problem with making it big. Furthermore, since the frequency CK must be set at an intermediate position, the reproducibility of the set value of the tuning frequency f is low, and the oscillation state of the crystal oscillator is ip! l
There is a possibility that it differs depending on the equipment.

The present invention has been made based on the above circumstances, and its purpose is to change the tuning frequency to a frequency at which the oscillation output level shows a maximum value of 1.5 by adding a simple circuit. It is an object of the present invention to provide a crystal oscillator that can be set to 1, thereby facilitating adjustment operations and improving the reproducibility of oscillation states.

Embodiments of the present invention will be explained below with reference to the drawings.

41-1 is a basic circuit diagram of a crystal oscillator according to an embodiment of the present invention, and the same parts as in FIG. 1 are given the same reference numerals. Note that, like in FIG. 1, the surface current bias circuit is omitted.

In this embodiment, variable capacitors 2 are connected between the base and ground of the transistor 1, and between the base and the collector, respectively.
and a crystal resonator 3 are connected, and a tuning circuit 6 consisting of a parallel circuit of a capacitor 4 and a coil 5 is connected between the collector and ground. Furthermore, a buffer circuit 11 is inserted between the crystal resonator 3 and the tuning circuit 6 (in the embodiment, between the crystal resonator 3 and the collector). Further, the emitter of transistor 1 is grounded. the above·
The guffer circuit 11 includes a resistor 12 inserted between the crystal oscillator 3 and the collector, which controls the sum resistance R, and this resistor 12.
and a capacitor 13 having a capacitance C4 inserted between the connection point of the crystal camera 3 and the ground.

In the crystal oscillator configured in this way, the tuning circuit 6
When adjusting the oscillation state by changing the tuning frequency f by varying the coil 5, the relationship between the tuning frequency f and the oscillation voltage υ level becomes the oscillation voltage characteristic shown by Y in FIG.

That is, like the crystal oscillator shown in Figure 1, when the tuning frequency f is gradually increased from the lowest value, oscillation starts at a frequency that satisfies the oscillation condition (f = D), and the oscillation % of τ = d.
Oscillates at 5 pressure. Then, when the tuning frequency f is further increased, the oscillation voltage υ gradually increases as indicated by Y in the figure. Then, when the tuning frequency f reaches the resonance frequency FrK of the tuning circuit 6, the 49% circuit 6 converts into an inductive reactance, and the oscillation attempts to stop. However, crystal oscillator 3
Since a buffer circuit 1 consisting of a resistor 12 connected in series and a capacitor 13 connected in parallel is inserted between the tuning circuit 6 and the tuning circuit 6, the tuning circuit 6 is Since the impedance when looking at the oscillation shows capacitance, even if the tuning frequency f becomes larger than the resonant frequency Fr, the oscillation does not stop and continues. Then, when the tuning frequency f reaches the natural frequency F0 of the crystal resonator 3, the oscillation voltage characteristic Y (output level) shows an extremely high value. After that, when the tuning frequency f is further increased, the tuning frequency f becomes distant from the resonant frequency Fr, so the oscillation voltage τ
As a result, the oscillation condition no longer holds true at a certain frequency (f=G), and oscillation stops. In addition, crystal oscillator 3
Since the contact 12 is inserted between the collector 1 and the transistor 1, the level of the oscillation voltage τ appearing on the collector side is lower by the resistance loss compared to the conventional example shown in FIG. Therefore, the oscillation start frequency is also higher than the oscillation start frequency A of the conventional example.

Therefore, by changing the inductance L1 of the coil 6, the tuning frequency f of the tuning circuit 6 is set to the natural frequency F of the crystal resonator 3 at which the oscillation voltage characteristic Y (output level) exhibits the maximum value.

After setting, the capacitance CI of the variable capacitor 2 is changed to obtain the natural frequency F of the crystal resonator 3. All you have to do is fine-tune the oscillation frequency, which is approximately determined by .

In this way, when adjusting the oscillation state, it is sufficient to set the tuning frequency f of the tuning circuit 6 to the frequency at which the oscillation voltage characteristic Y (output level) shows the maximum value. There is no need to set the frequency to an intermediate frequency like the 0 point in . Therefore, the adjustment operation for the entire crystal oscillator is simple, and the time required for adjustment can be shortened. In addition, setting the tuning frequency to the frequency at which the output level reaches its maximum value can improve the reproducibility of the set value compared to the conventional setting method of setting it to an intermediate value, so the oscillation state of the crystal oscillator can be adjusted. It is easy to adjust to the same condition every time.

Furthermore, since the tuning frequency is set so that the output level is maximized, the output oscillation voltage value can be set precisely. For example, in the embodiment, although the oscillation voltage characteristics are reduced due to the provision of the resistor 12,
Since the maximum value e of the oscillation voltage characteristic is utilized, it is possible to obtain a higher output level than the conventional intermediate value C.

As explained above, according to the present invention, by inserting a buffer circuit consisting of a resistor connected in series and a capacitor connected in parallel between the crystal resonator and the tuning circuit, the tuning frequency can be adjusted to the output voltage of the oscillation. Since it is possible to set the frequency to the maximum value, it is possible to easily adjust the crystal oscillator as a whole, and to improve the reproducibility of the oscillation state.

[Brief explanation of the drawing]

Fig. 1 is a basic circuit diagram showing a conventional crystal oscillator, Fig. 2 is an equivalent circuit diagram of the same crystal oscillator, and Fig. 3 is a characteristic diagram showing the operation of a crystal oscillator according to an embodiment of the present invention. is a basic circuit diagram showing the same crystal oscillator. 1...Transostor (amplification element), 2...Capacitor, 3...Crystal resonator, 4...Capacitor, 5
... Coil, 6... Tuning circuit, 7... Capacitor, 11... Buffer circuit, 12... Resistor, 13...
・Capacitor. Applicant's agent Patent attorney Takeshi Suzue Figure 1
Fig. 2 Fig. 3 Fig.

Claims (2)

[Claims] (1) A capacitor and a tuning circuit are connected between the input end and the ground of the amplification element and between the output end and the ground, respectively.
and a crystal oscillator in which a first terminal of a crystal resonator is connected to an input terminal of the amplifying element, and a second terminal of the crystal resonator is connected to an output terminal of the amplifying element; between the second terminal of the tuning circuit and the output terminal of the amplifying element to which the tuning circuit is connected, a device is provided that allows the oscillation to continue even if the tuning frequency of the tuning circuit becomes higher than the resonant frequency of the tuning circuit. A crystal oscillator characterized by the insertion of a buffer circuit. (2) The buffer circuit is characterized in that a resistor is inserted between the tuning circuit and the crystal resonator, and a capacitor is inserted between the connection point of the resistor and the crystal resonator and the ground. A crystal oscillator according to paragraph (1) of the patent claim.