JP2006157077A - Oscillator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an oscillator capable of obtaining a stable oscillating frequency without being affected by a phase characteristic of a crystal vibrator even if employing the crystal vibrator with a low Q value and large series resistance. <P>SOLUTION: The oscillator is configured such that a resonator 7 with a resonance frequency equal to an oscillating frequency is inserted to an oscillation loop of an oscillation circuit oscillated by a resonance circuit comprising a coil 3 and a capacitor 4. Further, the oscillator is configured such that the crystal vibrator is interposed between an emitter of a transistor of a common gate connection employed by a Colpitts oscillation circuit and a series connecting point of split capacitors in the resonance circuit comprising the coil 3 and the capacitor 4. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an oscillator that can oscillate stably and reliably using a crystal resonator having a high resonance frequency of 100 MHz or higher.

In a conventional crystal oscillation circuit, oscillation is performed using the phase characteristics of a crystal resonator.
In such an oscillation circuit, when the phase characteristic of the crystal resonator changes, the oscillation frequency also changes. Therefore, when a crystal resonator whose phase characteristic changes is used, a stable oscillation frequency cannot be obtained.

A crystal resonator having a high resonance frequency whose fundamental wave frequency exceeds 100 MHz often causes a problem called DLD unless designed well.
When DLD occurs, a jump phenomenon or a slope may increase in the frequency-current characteristics.

In addition, a jump phenomenon may occur in the series resistance-current characteristic, which causes a problem that the reliability of the crystal resonator is significantly impaired.
Furthermore, such a jump phenomenon and a large gradient of frequency change also appear in the frequency-phase characteristics of the crystal resonator.

  On the other hand, the Q value of a crystal resonator having a high resonance frequency such that the fundamental frequency exceeds 100 MHz is considerably lower than the Q value of a relatively low frequency crystal resonator having a fundamental frequency of about several tens of MHz. End up.

In addition, when a method using a spatial electrode method for frequency stabilization or a structure in which electrodes are not formed in the drive unit of the crystal piece and an electrode is arranged around it, the series resistance also decreases as the Q value decreases. To increase.
In addition, an oscillation circuit using such a crystal resonator is difficult to oscillate, and oscillation may stop due to a change in environmental conditions, for example, a temperature change.

  It is an object of the present invention to provide an oscillator that is not affected by the phase characteristics of a crystal resonator and that can obtain a stable oscillation frequency even when a crystal resonator having a low Q value and a large series resistance is used.

  A first aspect of the present invention is an oscillator characterized in that a resonator having a resonance frequency equal to the oscillation frequency is inserted in an oscillation loop of an oscillation circuit that oscillates in a resonance circuit composed of a coil and a capacitor. The resonator according to item 1, wherein the resonator is a crystal resonator.

  A third aspect of the present invention is the oscillator according to the first aspect, wherein the resonator is a SAW filter. A fourth aspect of the present invention is the oscillator according to the first aspect, wherein the oscillation frequency of the oscillation circuit is 100 MHz. An oscillator characterized by the above, and claim 5 according to claim 1, characterized in that the series connection point and the emitter of the split capacitor of the grounded Colpitts oscillation circuit that oscillates in the resonance circuit composed of the coil and the capacitor Is an oscillator characterized by interposing a quartz resonator between the two.

  The present invention can provide an oscillator that has a low Q value, a large series resistance, and can oscillate reliably even when a crystal resonator exhibiting a DLD is used, and can obtain a stable oscillation frequency.

Hereinafter, an embodiment of the present invention will be described in detail with reference to an example in which a crystal resonator is used as a resonator in a circuit diagram similar to the Colpitts oscillation circuit shown in FIG.
Reference numeral 1 denotes a PNP transistor whose emitter is grounded via a resistor 2.
The base is grounded E through a series resonance circuit of the coil 3 and the capacitor 4.

The base is grounded E through two divided capacitors 5 and 6 in series.
The series connection point of the divided capacitors 5 and 6 is connected to the emitter through the crystal resonator 7 and the capacitor 8 in series.
The emitter is connected to the oscillation output OUT via the capacitor 9.

The collector is connected to the power source Vcc, and bias resistors 10 and 11 are interposed between the power source Vcc and the base and between the base and the ground E, respectively.
Note that the oscillation frequency of the Colpitts oscillation circuit determined by the circuit constant of the series resonance circuit of the coil 3 and the capacitor 4 and the resonance frequency of the crystal resonator 7 are approximately matched.

With such a configuration, when the series connection point of the split capacitors 5 and 6 is directly connected to the emitter, it is a well-known emitter-grounded Colpitts oscillation circuit, and the oscillation frequency is a circuit of a series resonance circuit of the coil 3 and the capacitor 4. Determined by a constant.
The frequency stability of such an oscillating circuit is, for example, as shown in the graph of FIG. 2 and is 10.6 ppm.

Then, a crystal resonator 7 and a capacitor 8 are inserted in series between the series connection point of the split capacitors 5 and 6 that are the oscillation loop of the oscillation circuit and the emitter.
Therefore, the oscillation frequency of the Colpitts oscillation circuit is regulated by the resonance frequency of the crystal resonator 7, and a stable oscillation frequency can be obtained.

FIG. 3 is a graph showing the frequency stability of such an oscillation circuit, which is 0.2 ppm, and the stability is remarkably improved.
Further, in this case, since the crystal resonator 7 only regulates the oscillation frequency, it is hardly affected by the DLD, Q value, and phase characteristics.

FIG. 4 is a graph showing the frequency stability of an oscillator in which a crystal resonator that generates DLD is used in the oscillation circuit shown in FIG. 1, and shows very good frequency stability.
The present invention is not limited to the above embodiment. For example, when the oscillation frequency is controlled from the outside, the same members as those in FIG. That's fine.

That is, a varicap diode 12 is inserted between the crystal resonator 7 and the capacitor 8, a control voltage VC is applied to the cathode side from the outside, and the anode is grounded E via the return resistor 13.
In this way, the oscillation frequency can be changed according to the control voltage.

  In such a case, a change in oscillation frequency with respect to a change in temperature, that is, a frequency-temperature characteristic is measured in advance, and a compensation voltage that maintains a constant oscillation frequency according to this characteristic is given as the control voltage VC. It can operate as an oscillator.

  Further, in the embodiment shown in FIG. 1, a description has been given of the case where a crystal resonator is used as a resonator. However, since the resonator only needs to obtain a resonance characteristic at a target frequency, for example, a SAW (surface acoustic wave) filter, MCF (monolithic). Of course, a crystal filter or the like can also be used.

It is a circuit diagram of the oscillator of one embodiment of the present invention. It is a graph which shows the frequency stability of a Colpitts oscillation circuit. It is a graph which shows the frequency stability of the oscillator of one embodiment of this invention. It is a graph which shows the frequency stability at the time of using the crystal oscillator which produces DLD for the oscillator of one embodiment of this invention. It is a circuit diagram of the oscillator of the other embodiment of this invention.

Explanation of symbols

1 Transistor 3 Coil (resonance circuit)
4 Capacitor (resonant circuit)
5, 6 Split capacitor 7 Crystal resonator (resonator)
E Ground Vcc Power supply OUT Oscillation output VC Control voltage

Claims (5)

An oscillator comprising a resonator having a resonance frequency equal to the oscillation frequency inserted in an oscillation loop of an oscillation circuit that oscillates in a resonance circuit composed of a coil and a capacitor. 2. The oscillator according to claim 1, wherein the resonator is a crystal resonator. 2. An oscillator according to claim 1, wherein the resonator is a SAW filter. 2. The oscillator according to claim 1, wherein the oscillation frequency of the oscillation circuit is 100 MHz or more. 2. The crystal resonator according to claim 1, wherein a crystal resonator is interposed between the series connection point of the split capacitor of the Colpitts oscillation circuit grounded in the emitter that oscillates in a resonance circuit including a coil and a capacitor, and the emitter. Oscillator.

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