JP5465891B2 - Crystal oscillation circuit - Google Patents

Description

  The present invention relates to a crystal oscillation circuit, and more particularly, to a crystal oscillation circuit that can reliably perform oscillation with a series arm of a crystal resonator when an extension coil is inserted.

[Conventional technology]
[General crystal oscillation circuit: Fig. 13]
A general crystal oscillation circuit will be described with reference to FIG. FIG. 13 is a circuit diagram of a general crystal oscillation circuit.
As shown in FIG. 13, a general crystal oscillation circuit includes a crystal resonator XL that oscillates a specific frequency, a transistor Q that has one end of the crystal resonator XL connected to the base, and amplifies the oscillated frequency, The oscillation circuit power supply is connected to the collector of the transistor Q via a resistor R2, the collector is connected to the base via a resistor R1, the collector is connected to the other end of the crystal resonator XL, and the other end is a capacitor C1. One end of the transistor Q is connected and the other end is grounded. The base of the transistor Q is connected to the other end of the capacitor C2, and the other end is grounded. The emitter of the transistor Q is grounded.

[Equivalent circuit: FIG. 14]
FIG. 14 shows an equivalent circuit of the circuit of FIG. FIG. 14 is an equivalent circuit diagram of a general crystal oscillation circuit.
As shown in FIG. 14A, the left side is a crystal unit XL, and the right side is an oscillation circuit (Oscillator) in which a load capacitance CL and a negative resistance -R are connected in series.

  FIG. 14B shows an equivalent circuit in which the crystal resonator is a four-element equivalent circuit in the equivalent circuit of FIG. As shown in FIG. 14B, the crystal resonator can be represented by a series connection (series arm) series resistance R1, a series capacity C1, a series inductance L1 and a parallel connection (parallel arm) parallel capacity C0. The oscillation circuit can be represented by a series connection of a load capacitance CL (= -Xc: reactance of the oscillation circuit) and a negative resistance -R.

Note that the capacitance C1 and the resistance R1 used in FIG. 13 and the series capacitance C1 and the series resistance R1 in FIG.
In the following description, CL is used as a load capacitance, XL is used as a reactance of the crystal resonator, and RL is used as a resonance resistance during load.

  When the crystal resonator is represented by RL + XL, the oscillation start condition is RL ≦ | −R |, and in the steady state of oscillation, RL = | −R |, and −R of the oscillation circuit decreases after the oscillation starts. As a result, the power loss due to the resonance resistance when the crystal resonator is loaded is always compensated, and the oscillation continues.

The oscillation frequency condition at this time is XL−Xc = 0.
When the resonance condition phenomenon (phase = 0 °), the oscillation circuit side is capacitive and the crystal resonator side is inductive.

[Crystal oscillation circuit with extension coil inserted: Fig. 15]
When an extension coil is inserted between the crystal unit XL and the base of the transistor Q (when an extension coil is inserted on the oscillation circuit side), the oscillation circuit side becomes inductive, and the parallel capacitance C0 and inductivity of the crystal unit The oscillation circuit side that has become may resonate.

A crystal oscillation circuit with an extension coil inserted will be described with reference to FIG. FIG. 15 is a circuit diagram of a crystal oscillation circuit in which an extension coil is inserted.
As shown in FIG. 15, the difference from FIG. 13 is that an extension coil is inserted between the crystal unit XL and the base of the transistor Q.

[Equivalent circuit: FIG. 16]
FIG. 16 is a diagram showing the equivalent circuit of FIG. 15 in the same manner as FIG. FIG. 16 is a diagram of an equivalent circuit of a crystal oscillation circuit in which an extension coil is inserted.
The left side of FIG. 16A is a crystal resonator, and the right side is an oscillation circuit in which an inductor L1 and a negative resistance -R are connected in series.

FIG. 16 (b) shows the equivalent circuit of FIG. 16 (a) as an equivalent circuit when the crystal unit is an equivalent constant circuit as in FIG. 14 (b). As shown in FIG. 16B, the crystal resonator can be represented by a series connection (series arm) series resistance R1, a series capacity C1, a series inductance L1 and a parallel connection (parallel arm) parallel capacity C0. The oscillation circuit can be represented by a series connection of a reactance + Xc of the oscillation circuit and a negative resistance -R.
The capacitance C1, resistance R1, and extension coil L1 used in FIG. 15 and the series capacitance C1, series resistance R1, and series inductance L1 in FIG. Values and inductance values are different.

[Characteristics of the oscillation circuit of FIG. 15: FIG. 17]
The characteristics of the oscillation circuit of FIG. 15 will be described with reference to FIG. FIG. 17 is a diagram showing gain and phase characteristics of a crystal oscillation circuit with an extension coil inserted.
In FIG. 17, the upper diagram shows gain characteristics with respect to frequency, with the horizontal axis representing frequency and the vertical axis representing gain. The lower diagram of FIG. 17 shows the phase characteristics with respect to the frequency, with the horizontal axis indicating the frequency and the vertical axis indicating the phase.

As shown in FIG. 17, the oscillation condition is to oscillate when the gain is 1 or more at the point of phase inversion (phase inversion 1 and 2).
Therefore, it oscillates at the point of phase reversal 2 (specifically, a high frequency around 1.2 GHz), and at a point other than the point of phase reversal 1 which is the originally assumed crystal oscillation point. A problem of oscillation will occur.

[Related technologies]
Incidentally, as a related prior art, there is "Crystal oscillation circuit" of Japanese Patent Laid-Open No. 04-137805 (Applicant: Juanatsu Co., Ltd.) (Patent Document 1).
In Patent Document 1, in a Colpitts type crystal oscillation circuit configured using a CMOS inverter M, a third capacitor Cx is connected in parallel to both ends of a crystal resonator XL.
This crystal oscillation circuit is designed to prevent a stable oscillation state at a frequency other than the target frequency.

Japanese Patent Laid-Open No. 04-137805

  However, since the crystal oscillation circuit of FIG. 15 uses an extension coil, the capacitance of the series arm (C1, L1, R1) of the crystal resonator and the impedance on the circuit side resonate, and the target crystal resonator There is a problem in that oscillation occurs at a frequency other than the series arm, and the original oscillation of the crystal unit is hindered.

  Further, although the prior art reference 1 realizes a stable oscillation state in the crystal oscillation circuit, in the crystal oscillation circuit when the extension coil is inserted, the oscillation in the series arm of the crystal resonator is surely performed. is not.

  The present invention has been made in view of the above circumstances, and in the case where the extension coil is inserted, the oscillation with the series arm of the crystal resonator is surely performed, and unnecessary oscillation other than the original oscillation frequency is suppressed. An object of the present invention is to provide a crystal oscillation circuit capable of performing

The present invention for solving the problems of the conventional example described above is a crystal oscillation circuit having a crystal resonator that oscillates a specific frequency and a transistor that amplifies the frequency oscillated by the crystal resonator. An extension coil is connected between one end of the child and the base of the transistor, a collector of the transistor is connected to the base via a first resistor, and an oscillation circuit power supply is connected to the collector via a second resistor, The collector is connected to the other end of the crystal unit, the other end is connected to one end of the first capacitor and the other end is grounded, and the other end is connected to one end of the second capacitor connected to the base of the transistor. There is grounded, the emitter of the transistor is grounded, is connected additional capacitor in parallel to the crystal oscillator, the additional capacitor equivalent circuit at the time of the crystal oscillator equivalent constant circuit Phase inversion is characterized that you have been set to occur only on certain oscillation frequency due to the series arm.

  The present invention is characterized in that, in the crystal oscillation circuit, the first capacitor is a variable capacitor.

  The present invention is characterized in that, in the crystal oscillation circuit, the second capacitor is a variable capacitor.

  The present invention is characterized in that, in the crystal oscillation circuit, both the first capacitor and the second capacitor are variable capacitors.

  The present invention includes a temperature compensation voltage generation circuit for detecting a temperature in the crystal oscillation circuit and generating a control voltage for the variable capacitor so that the oscillation frequency is constant according to the detected temperature fluctuation. Features.

The present invention is characterized in that, in the crystal oscillation circuit, the value of the additional capacitor is set to 0.4 pF to 1.0 pF .

According to the present invention, there is provided a crystal oscillation circuit having a crystal resonator and a transistor, wherein an extension coil is connected between one end of the crystal resonator and the base of the transistor, and the collector of the transistor has a first resistance. And the collector is connected to the other end of the crystal resonator, and the other end is connected to one end of the first capacitor. the other end is grounded, the base of the transistor is grounded other end of the co Once the second capacitor is connected, the emitter of the transistor is grounded, additional capacitor is connected in parallel to the crystal oscillator, the additional capacitors, as a phase inversion by a series arm that is configured to occur only in a specific oscillation frequency of the equivalent circuit when the crystal oscillator equivalent constant circuit Runode, not reliably performed the oscillation of a crystal oscillator, there is an effect that it is possible to suppress an unnecessary oscillation in other than the original oscillation frequency.

  According to the present invention, since the above-described crystal oscillation circuit using the first capacitor or the second capacitor, or both the first capacitor and the second capacitor as variable capacitors, the oscillation frequency can be easily adjusted. There is.

  According to the present invention, the crystal oscillation circuit includes the temperature compensation voltage generation circuit that detects the temperature in the circuit and generates a control voltage for the variable capacitor so that the oscillation frequency becomes constant according to the detected temperature fluctuation. Therefore, there is an effect that the oscillation frequency can be stabilized.

1 is a circuit diagram of a crystal oscillation circuit according to an embodiment of the present invention. It is a figure of the equivalent circuit of the crystal oscillator based on embodiment of this invention. It is a figure which shows the gain and phase characteristic of the oscillation circuit which concern on embodiment. It is a figure which shows the gain characteristic and phase characteristic when capacity | capacitance Cx is added. It is a circuit diagram of the 2nd crystal oscillation circuit. It is a circuit diagram of the 3rd crystal oscillation circuit. It is a circuit diagram of the 4th crystal oscillation circuit. It is a circuit diagram of the 5th crystal oscillation circuit. It is a circuit diagram of the 6th crystal oscillation circuit. It is a circuit diagram of the 7th crystal oscillation circuit. It is a circuit diagram of the 8th crystal oscillation circuit. It is a circuit diagram of a ninth crystal oscillation circuit. It is a circuit diagram of a general crystal oscillation circuit. It is a figure of the equivalent circuit of a general crystal oscillation circuit. It is a circuit diagram of the crystal oscillation circuit which inserted the extension coil. It is a figure of the equivalent circuit of the crystal oscillation circuit which inserted the expansion | extension coil. It is a figure which shows the gain and phase characteristic of the crystal oscillation circuit of extension coil insertion.

Embodiments of the present invention will be described with reference to the drawings.
[Outline of the embodiment]
In the crystal oscillation circuit according to the embodiment of the present invention, an additional capacitor is connected in parallel to the crystal resonator in the configuration in which the extension coil is inserted between the output side of the crystal resonator and the base of the transistor. Therefore, it is possible to reliably oscillate with the series arm of the crystal resonator, and to suppress unnecessary oscillation other than the original oscillation frequency.

  Further, the crystal oscillation circuit according to the embodiment of the present invention uses a variable capacitor as a capacitor provided in the circuit, and can easily adjust the oscillation frequency.

  In addition, the crystal oscillation circuit according to the embodiment of the present invention includes a variable capacitor connected in series between the extension coil and the base of the transistor, and can easily adjust the oscillation frequency. .

  The crystal oscillation circuit according to the embodiment of the present invention is such that a capacitor provided in the circuit is a variable capacitor, and the variable capacitor is controlled by a temperature compensation voltage generation circuit. The oscillation frequency can be stabilized according to the change.

  In the crystal oscillation circuit according to the embodiment of the present invention, a variable capacitor is connected in series between the extension coil and the base of the transistor, and the variable capacitor is controlled by a temperature compensation voltage generation circuit. Yes, the oscillation frequency can be stabilized according to the temperature change in the circuit.

[This crystal oscillation circuit: Fig. 1]
A crystal oscillation circuit according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a circuit diagram of a crystal oscillation circuit according to an embodiment of the present invention.
As shown in FIG. 1, the crystal oscillation circuit (first crystal oscillation circuit) according to the embodiment of the present invention has a crystal oscillator XL that oscillates a specific frequency and a frequency oscillated by the crystal oscillator XL. The transistor Q to be amplified is connected to one end of the crystal unit XL and the other end is connected to the base of the transistor Q. The extension coil L1 is connected to the collector of the transistor Q via the resistor R2. The collector is connected to the base via the resistor R1, the collector is connected to the other end of the crystal unit XL, the other end is connected to one end of the capacitor C1, and the other end is grounded. When one end of the capacitor C2 is connected, the other end is grounded, the emitter of the transistor Q is grounded, and an additional capacitor (additional capacitor) Cx is connected in parallel with the crystal resonator XL.

[Equivalent circuit of crystal unit: Fig. 2]
Next, an equivalent circuit of the crystal unit in FIG. 1 will be described with reference to FIG. FIG. 2 is a diagram of an equivalent circuit of the crystal resonator according to the embodiment of the present invention.
As shown in FIG. 2, the equivalent circuit of the crystal unit is such that a coil L1, a capacitor C1, and a resistor R1 are connected in series as a series arm, and a capacitor C0 is connected in parallel to the series arm as a parallel arm. It is connected.

[Characteristics of the first crystal oscillation circuit: FIG. 3]
Next, the characteristics of the first crystal oscillation circuit will be described with reference to FIG. FIG. 3 is a diagram illustrating gain and phase characteristics of the oscillation circuit according to the embodiment.
As shown in FIG. 3, since the oscillation condition is that the gain is 1 or more at the point of phase inversion, oscillation occurs only at the point of phase inversion 1 and no oscillation occurs at other points.
This is because by providing the additional capacitor Cx, the phase characteristics are shifted to prevent resonance.

[Characteristics when capacitance Cx is added: Fig. 4]
The characteristics when a capacitor (capacitor) Cx is added to the input / output terminal of the crystal resonator XL as in the first crystal oscillation circuit will be described with reference to FIG. FIG. 4 is a diagram showing gain characteristics and phase characteristics when the capacitor Cx is added.
FIG. 4 shows gain characteristics and phase characteristics when the value of the capacitance (additional capacitor) Cx is changed from 0 to 1.0 pF.
The parallel arm capacitor C0 (C
para) is 0.5 pF.
When the frequency is around 640 MHz, phase inversion occurs due to the series arm (L1 R1 C1), and the original intended oscillation is performed.

When the value of the additional capacitor is 0 pF, the capacitor is not provided, and therefore, oscillation occurs at another phase inversion point as in the characteristics shown in FIG.
Even if an additional capacitor is provided, if it is a small value of 0 to 0.3 pF, there is still a phase inversion at another point, and oscillation occurs at another frequency.

  However, it can be seen that when the value of the additional capacitor Cx is in the range of 0.4 to 1.0 pF, phase inversion does not occur at another point and oscillation does not occur at another frequency. Accordingly, the value of the additional capacitor Cx is 0.4 pF or more, particularly 0.4 to 1.0 pF.

[Second to fifth crystal oscillation circuits: FIGS. 5 to 8]
Next, configurations of the second to fifth crystal oscillation circuits according to the embodiment of the present invention will be described with reference to FIGS. 5 is a circuit diagram of the second crystal oscillation circuit, FIG. 6 is a circuit diagram of the third crystal oscillation circuit, and FIG. 7 is a circuit diagram of the fourth crystal oscillation circuit. These are the circuit diagrams of the 5th crystal oscillation circuit.
In the second to fifth crystal oscillation circuits, an amplifier 1 and an output driver 2 including output terminals OUT1 and OUT2 are provided in an output stage.

As shown in FIG. 5, the second crystal oscillation circuit uses a capacitor C1 as a variable capacitor (variable capacitor) so that the oscillation frequency in the oscillation circuit can be adjusted.
As shown in FIG. 6, the third crystal oscillation circuit uses a capacitor C2 as a variable capacitor (variable capacitor) so that the oscillation frequency in the oscillation circuit can be adjusted.
As shown in FIG. 7, the fourth crystal oscillation circuit uses capacitors C1 and C2 as variable capacitors (variable capacitors) so that the oscillation frequency in the oscillation circuit can be adjusted.
Here, the variable capacitor uses a varicap diode that makes the frequency variable by an external voltage.

As shown in FIG. 8, the fifth crystal oscillation circuit has a configuration in which a variable capacitor C3 is connected in series between the extension coil L1 and the base of the transistor Q. By adjusting the capacitance of the variable capacitor C3, the oscillation frequency in the oscillation circuit can be adjusted.
Further, the oscillation frequency in the oscillation circuit may be adjustable by setting one of the capacitors C1 and C2 in the fifth crystal oscillation circuit or both of the capacitors C1 and C2 as variable capacitors (variable capacitors).

[Sixth to ninth crystal oscillation circuits: FIGS. 9 to 12]
Next, configurations of the sixth to ninth crystal oscillation circuits according to the embodiment of the present invention will be described with reference to FIGS. 9 is a circuit diagram of the sixth crystal oscillation circuit, FIG. 10 is a circuit diagram of the seventh crystal oscillation circuit, and FIG. 11 is a circuit diagram of the eighth crystal oscillation circuit. These are circuit diagrams of a ninth crystal oscillation circuit.
The sixth to ninth crystal oscillation circuits are provided with an amplifier 1 and an output driver 2 including output terminals OUT1 and OUT2 at an output stage.

The sixth to ninth crystal oscillation circuits include a temperature compensation voltage generation circuit 3 inside the circuit.
The temperature compensation voltage generation circuit 3 detects the temperature in the circuit and controls the variable capacitor so that the oscillation frequency becomes constant according to the detected temperature.
Specifically, if the temperature detected by the temperature compensation voltage generation circuit 3 varies by Δt, the normal frequency varies by Δf, so the variable capacitor is controlled to suppress the variation of Δf.

As shown in FIG. 9, in the sixth crystal oscillation circuit, the capacitor C1 is a variable capacitor (variable capacitor), and the capacitance of the variable capacitor is controlled by the temperature compensation voltage generation circuit 3 to stabilize the oscillation frequency in the oscillation circuit. It aims to make it easier.
In the seventh crystal oscillation circuit, as shown in FIG. 10, the capacitor C2 is a variable capacitor (variable capacitor), and the temperature of the variable capacitor is controlled by the temperature compensation voltage generation circuit 3 to stabilize the oscillation frequency in the oscillation circuit. It aims to make it easier.
As shown in FIG. 11, the eighth crystal oscillation circuit uses capacitors C1 and C2 as variable capacitors (variable capacitors), and controls the capacitances of the two variable capacitors by the temperature compensation voltage generation circuit 3, so that the oscillation circuit includes This is intended to stabilize the oscillation frequency.
Here, the variable capacitor uses a varicap diode that makes the frequency variable by an external voltage.

As shown in FIG. 12, the ninth crystal oscillation circuit has a configuration in which a variable capacitor C3 is connected in series between the extension coil L1 and the base of the transistor Q. The capacitance of the variable capacitor C3 is controlled by the temperature compensation voltage generation circuit 3 to stabilize the oscillation frequency in the oscillation circuit.
Further, one of the capacitors C1 and C2 or both of the capacitors C1 and C2 in the ninth crystal oscillation circuit is made a variable capacitor (variable capacitor), and the capacitance of these variable capacitors is controlled by the temperature compensation voltage generation circuit 3 to oscillate. The oscillation frequency in the circuit may be adjustable.

[Effect of the embodiment]
According to the first crystal oscillation circuit, in the configuration in which the extension coil L1 is inserted between the output side of the crystal unit XL and the base of the transistor Q, the additional capacitor Cx is connected in parallel to the crystal unit XL. Thus, there is an effect that the oscillation with the series arm in the crystal resonator can be reliably performed, and unnecessary oscillations other than the original oscillation frequency can be suppressed.
In particular, the load capacitance Cx is effectively 0.4 pF or more.

  According to the second to fourth crystal oscillation circuits, the capacitor in the circuit is a variable capacitor, and there is an effect that the oscillation frequency can be easily adjusted.

  According to the fifth crystal oscillation circuit, the variable capacitor is connected in series between the extension coil L1 and the base of the transistor Q, and the oscillation frequency can be easily adjusted.

  According to the sixth to eighth crystal oscillation circuits, the capacitor in the circuit is a variable capacitor, and the variable capacitor is controlled by the temperature compensation voltage generation circuit 3, and oscillates according to the temperature change in the circuit. This has the effect of stabilizing the frequency.

  According to the ninth crystal oscillation circuit, a variable capacitor is connected in series between the extension coil L1 and the base of the transistor Q, and the variable capacitor is controlled by the temperature compensation voltage generation circuit 3. There is an effect that the oscillation frequency can be stabilized according to the temperature change in the circuit.

  The present invention is suitable for a crystal oscillation circuit capable of surely oscillating with a series arm of a crystal resonator when an extension coil is inserted.

  DESCRIPTION OF SYMBOLS 1 ... Amplifier, 2 ... Output driver, 3 ... Temperature compensation voltage generation circuit, C ... Capacitance (capacitor), L ... Coil, Q ... Transistor, R ... Resistance, X ... Crystal oscillator

Claims (6)

A crystal oscillation circuit having a crystal resonator that oscillates a specific frequency and a transistor that amplifies the frequency oscillated by the crystal resonator,
An extension coil is connected between one end of the crystal resonator and the base of the transistor, a collector of the transistor is connected to the base via a first resistor, and an oscillation circuit power supply is connected to the collector at the second Connected through a resistor, the collector is connected to the other end of the crystal resonator, the other end is connected to one end of a first capacitor and the other end is grounded, and the base of the transistor is connected to a second When one end of the capacitor is connected, the other end is grounded, the emitter of the transistor is grounded, and an additional capacitor is connected in parallel to the crystal unit ,
The additional capacitor, crystal oscillator circuit, characterized that you have been set so that the phase inversion due to the series arm of the equivalent circuit when the equivalent constant circuit the crystal oscillator is generated only at a specific oscillation frequency.   2. The crystal oscillation circuit according to claim 1, wherein the first capacitor is a variable capacitor.   2. The crystal oscillation circuit according to claim 1, wherein the second capacitor is a variable capacitor.   2. The crystal oscillation circuit according to claim 1, wherein both the first capacitor and the second capacitor are variable capacitors.   5. A temperature compensation voltage generating circuit for detecting a temperature in the circuit and generating a control voltage for the variable capacitor so that the oscillation frequency becomes constant according to the detected temperature fluctuation. Or a crystal oscillation circuit. 6. The crystal oscillation circuit according to claim 1, wherein the value of the additional capacitor is 0.4 pF to 1.0 pF .

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