JP2018007015A - Crystal oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact crystal oscillator having small stray capacitance and capable of changing an oscillation signal frequency.SOLUTION: A crystal oscillator 1 includes: a quartz vibrator X1; a plurality of capacitors C1 and C2 which are disposed between the quartz vibrator X1 and the ground; an amplifier A1 connected in parallel to the quartz vibrator X1; a first feedback resistor R1 and a second feedback resistor R2 which are connected in parallel to the amplifier A1; and a first diode D1 which is connected in series to the second feedback resistor R2 and can switch the self-diode between a conduction state and a non-conduction state.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a crystal oscillator.

  Conventionally, the oscillation of a crystal resonator has been performed by switching between oscillation by a fundamental wave and overtone oscillation. For example, Patent Document 1 has a switch for switching the oscillation of a crystal resonator to either a fundamental wave oscillation or an overtone oscillation, and a fundamental wave oscillation signal and an overtone oscillation oscillation signal A QCM (Quartz Crystal Microbalance) sensor including a crystal oscillator capable of outputting either one is disclosed.

  FIG. 4 is a diagram showing a configuration of a conventional crystal oscillator 100 described in Patent Document 1. As shown in FIG. As shown in FIG. 4, the conventional crystal oscillator 100 includes a crystal resonator 101, capacitors 102 and 103, an amplifier 104, resistors 105 and 106, and a switch 107. Capacitors 102 and 103 have one end connected to the crystal unit 101 and the other end connected to the ground. The amplifier 104 is connected to the crystal resonator 101 in parallel. Each of the resistors 105 and 106 is connected in parallel to the amplifier 104 via the switch 107. The switch 107 switches which of the resistor 105 and the resistor 106 is connected to the amplifier 104. In the conventional crystal oscillator 100, the resistance values of the resistor 105 and the resistor 106 are set as a resistance value corresponding to oscillation by the fundamental wave and a resistance value corresponding to overtone oscillation, and any one of these resistors is used as the amplifier 104. By connecting to the quartz oscillator 101, the oscillation of the crystal unit 101 can be switched to either the fundamental wave oscillation or the overtone oscillation.

JP 2004-184256 A

  A mechanical switch or an electrical switch can be applied to the switch 107 provided in the conventional crystal oscillator 100. However, when a mechanical switch is applied, the crystal oscillator 100 is increased in size, and it is difficult to reduce the size of the QCM sensor.

  As an electrical switch, a MOS analog switch is widely used. However, in order to reduce signal loss in the MOS analog switch, a certain area is required, and it is difficult to reduce the size of the QCM sensor. Further, when the area of the MOS analog switch is increased, there is a problem that a large stray capacitance of several tens of pF is generated between the MOS analog switch and the ground.

  The present invention has been made in view of these points, and an object of the present invention is to provide a crystal oscillator capable of switching the frequency of an oscillation signal that can be downsized and has a small stray capacitance.

  A crystal oscillator according to a first aspect of the present invention includes a crystal resonator, a plurality of capacitors provided between the crystal resonator and a ground, an amplifier connected in parallel to the crystal resonator, A first feedback resistor and a second feedback resistor connected in parallel to the amplifier; and a first diode connected in series to the second feedback resistor and capable of switching itself between a conductive state and a non-conductive state.

  The first diode is turned off by applying a reverse bias voltage when the crystal oscillator is oscillated with a fundamental wave, and a forward bias voltage is applied when the crystal oscillator is overtone oscillated. By doing so, it is preferable to be in a conductive state.

  The crystal oscillator may further include a damping resistor connected in series to the crystal resonator, and a second diode connected in parallel to the damping resistor and capable of switching itself between a conductive state and a non-conductive state. .

  The second diode becomes non-conductive when a reverse bias voltage is applied when the crystal resonator is oscillated with a fundamental wave, and a forward bias voltage is applied when the crystal resonator is overtone oscillated. By doing so, it is preferable to be in a conductive state.

  According to the present invention, there is an effect that it is possible to provide a crystal oscillator that can be downsized and has a small stray capacitance and that can switch the frequency of an oscillation signal.

It is a figure which shows the structure of the crystal oscillator which concerns on this embodiment. It is a figure which shows the circuit side real part impedance and circuit side load capacity of a crystal oscillator at the time of making a crystal oscillator oscillate with a fundamental wave. It is a figure which shows the circuit side real part impedance and circuit side load capacity | capacitance of a crystal oscillator at the time of carrying out an overtone oscillation of a crystal oscillator. It is a figure which shows the structure of the conventional crystal oscillator.

[Configuration of Crystal Oscillator 1]
FIG. 1 is a diagram illustrating a configuration of a crystal oscillator 1 according to the present embodiment. The crystal oscillator 1 includes a crystal resonator X1, capacitors C1 and C2, an amplifier A1, a first feedback resistor R1, a second feedback resistor R2, a first diode D1, a damping resistor R3, and a second diode D2. With.

  The crystal resonator X1 is, for example, an AT-cut crystal resonator, which oscillates with a fundamental wave and oscillates with a third overtone. In the present embodiment, the oscillation frequency by the fundamental wave is about 10 MHz, and the oscillation frequency by the third overtone is about 30 MHz.

  Capacitors C1 and C2 are provided as a plurality of capacitors between the crystal unit X1 and the ground. In the present embodiment, the crystal resonator X1 is provided with one electrode pair. However, the present invention is not limited to this, and two electrode pairs may be provided.

  The capacitor C1 has one end connected to the crystal unit X1 and the other end connected to the ground. The capacitor C2 has one end connected to a damping resistor R3 connected in series with the crystal resonator X1 and the other end connected to the ground. Each of the capacitors C1 and C2 is an oscillation capacitor for causing the crystal resonator X1 to oscillate.

  The amplifier A1 is connected in parallel to the crystal unit X1. Specifically, the amplifier A1 has one end connected to the crystal unit X1 and the other end connected to one end of the damping resistor R3. The amplifier A1 is, for example, an inverter, which inverts and amplifies the input signal and outputs it. An output terminal T1 for outputting an oscillation signal is provided on the output side of the amplifier A1.

  The first feedback resistor R1 and the second feedback resistor R2 are connected in parallel to the amplifier A1. The first feedback resistor R1 and the second feedback resistor R2 are used to return a part of the signal amplified by the amplifier A1 to the input side of the amplifier A1 in reverse phase. A first diode D1 is connected in series to the second feedback resistor R2. Whether or not the second feedback resistor R2 functions as a feedback resistor of the amplifier A1 is switched by switching the state of the first diode D1 between the conductive state and the non-conductive state.

  Here, the resistance value of the first feedback resistor R1 is a resistance value suitable when the crystal resonator X1 is oscillated with a fundamental wave, and the resistance value of the parallel resistance of the first feedback resistor R1 and the second feedback resistor R2. Is a resistance value suitable for overtone oscillation of the crystal unit X1.

  The first diode D1 is a PIN diode that can switch itself between a conductive state and a non-conductive state. Specifically, the first diode D1 has an anode connected to the output side of the amplifier A1, and a cathode connected to the second feedback resistor R2. Further, terminals Td11 and Td12 for applying a bias voltage to the first diode D1 are provided at both ends of the first diode D1.

  The damping resistor R3 is connected in series with the crystal unit X1. Specifically, the damping resistor R3 is provided between the crystal unit X1 and the output side of the amplifier A1. The damping resistor R3 is used to adjust the negative resistance of the oscillation circuit constituting the crystal oscillator 1.

  The second diode D2 is a PIN diode connected in parallel to the damping resistor R3 and capable of switching itself between a conductive state and a non-conductive state. Specifically, the second diode D2 has an anode connected to one end of the crystal unit X1, and a cathode connected to the output side of the amplifier A1. Terminals Td21 and Td22 for applying a bias voltage to the second diode D2 are provided at both ends of the second diode D2.

[Operation of Crystal Oscillator 1]
Next, the operation of the crystal oscillator 1 will be described.
When the crystal resonator X1 is oscillated with a fundamental wave, a reverse bias voltage is applied to the terminals Td11 and Td12 corresponding to the first diode D1, and a reverse bias voltage is applied to the terminals Td21 and Td22 corresponding to the second diode D2. Is applied. Thereby, the 1st diode D1 and the 2nd diode D2 will be in a non-conducting state.

When the first diode D1 is non-conductive, the resistance value of the feedback resistor of the amplifier A1 is the resistance value of the first feedback resistor R1 suitable for oscillating the crystal resonator X1 with a fundamental wave.
In addition, when the second diode D2 is non-conductive, the signal generated in the crystal resonator X1 passes through the damping resistor R3. Therefore, when the crystal resonator X1 is oscillated with a fundamental wave, the negative resistance of the oscillation circuit is reduced by the damping resistor R3. As a result, the negative resistance corresponding to the oscillation frequency of the third order overtone is reduced, and the third order overtone oscillation is suppressed. Although the negative resistance corresponding to the oscillation frequency of the fundamental wave is also reduced, the negative resistance corresponding to the oscillation frequency of the fundamental wave is originally large, so even if the negative resistance is reduced by the damping resistor R3, Oscillation is maintained. Thereby, the crystal unit X1 stably oscillates with the fundamental wave.

  When the crystal resonator X1 is caused to overtone oscillate, a forward bias voltage is applied to the terminals Td11 and Td12 corresponding to the first diode D1, and a forward bias voltage is applied to the terminals Td21 and Td22 corresponding to the second diode D2. Applied. Thereby, the 1st diode D1 and the 2nd diode D2 will be in a conduction state.

  When the first diode D1 is in a conductive state, the resistance value of the feedback resistor of the amplifier A1 is a resistance of a parallel resistor of the first feedback resistor R1 and the second feedback resistor R2 suitable for overtone oscillation of the crystal resonator X1. Value. In addition, when the second diode D2 is in a conductive state, the signal generated in the crystal resonator X1 does not pass through the damping resistor R3, so that the negative resistance does not decrease. Thereby, the crystal unit X1 stably oscillates overtone.

  2 and 3 show impedance characteristics in the crystal oscillator 1. FIG. 2 is a diagram illustrating the circuit-side real part impedance and the circuit-side load capacitance of the crystal oscillator 1 when the crystal resonator X1 is oscillated with a fundamental wave. FIG. 2 is a diagram showing the circuit-side real part impedance and the circuit-side load capacitance of the crystal oscillator 1 when the crystal resonator X1 is subjected to third-order overtone oscillation. 2 and 3, the solid line indicates the circuit-side real part impedance, and the broken line indicates the circuit-side load capacitance.

  When the crystal resonator X1 is oscillated with a fundamental wave, as shown in FIG. 2, the negative resistance near 10 MHz corresponding to the fundamental wave frequency is about 1000Ω, whereas the third overtone. It can be confirmed that the negative resistance in the vicinity of 30 MHz corresponding to the above frequency disappears. Further, it can be confirmed that the load capacitance corresponding to the frequency of the fundamental wave is about 7 pF.

  When the quartz resonator X1 is oscillated in the third overtone, as shown in FIG. 3, the negative resistance near the fundamental frequency disappears, and the negative resistance near the third overtone frequency disappears. It can be confirmed that the resistance is about 200Ω. Also, it can be confirmed that the load capacitance corresponding to the frequency of the third overtone is about 12 pF.

[Effect of this embodiment]
As described above, the crystal oscillator 1 according to the present embodiment includes the first diode D1 connected in series to the second feedback resistor R2 and capable of switching itself between a conductive state and a non-conductive state. In addition, the crystal oscillator 1 includes a second diode D2 that is connected in parallel to the damping resistor R3 and can switch itself between a conductive state and a non-conductive state.

  By doing so, the crystal oscillator 1 changes the value of the negative resistance at each oscillation frequency when the crystal oscillator X1 is oscillated with the fundamental wave and when it is overtone oscillated, and the crystal oscillator X1 Can be switched between oscillation with a fundamental wave and overtone oscillation. In addition, since the switching of the negative resistance value is switched by a diode, the area of the switch can be reduced and the stray capacitance can be reduced as compared with the case where a mechanical switch or a MOS analog switch is used.

  As mentioned above, although this invention was demonstrated using embodiment, the technical scope of this invention is not limited to the range as described in the said embodiment. For example, in the above-described embodiment, when the first diode D1 and the second feedback resistor R2 are connected in series and the crystal resonator X1 is oscillated with the fundamental wave, the first diode D1 is turned off, and the crystal resonator When X1 is caused to overtone oscillate, the resistance value of the feedback resistor of the amplifier A1 is switched by bringing the first diode D1 into a conductive state, but this is not restrictive.

  For example, the resistance value of the parallel resistance of the first feedback resistor R1 and the second feedback resistor R2 is set to a suitable resistance value when the crystal resonator X1 is oscillated with a fundamental wave, and the resistance value of the first feedback resistor R1 is A resistance value suitable for overtone oscillation of the crystal resonator X1 is set. When the crystal resonator X1 is oscillated with a fundamental wave, the first diode D1 is turned on, and the crystal resonator X1 is overtone oscillated. In this case, the first diode D1 may be turned off.

  In addition, it will be apparent to those skilled in the art that various modifications or improvements can be added to the above embodiment. It is apparent from the scope of the claims that the embodiments added with such changes or improvements can be included in the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 1 ... Crystal oscillator, X1 ... Crystal oscillator, C1, C2 ... Capacitor, A1 ... Amplifier, R1 ... 1st feedback resistance, R2 ... 2nd feedback resistance, D1 ... -1st diode, R3 ... Damping resistor, D2 ... 2nd diode, T1 ... Output terminal, Td11, Td12, Td21, Td22 ... Terminal

Claims (4)

A crystal unit,
A plurality of capacitors provided between the crystal resonator and the ground;
An amplifier connected in parallel to the crystal unit;
A first feedback resistor and a second feedback resistor connected in parallel to the amplifier;
A first diode connected in series to the second feedback resistor and capable of switching itself between a conductive state and a non-conductive state;
A crystal oscillator comprising: The first diode is turned off by applying a reverse bias voltage when the crystal oscillator is oscillated with a fundamental wave, and a forward bias voltage is applied when the crystal oscillator is overtone oscillated. It becomes a conduction state by being
The crystal oscillator according to claim 1. A damping resistor connected in series to the crystal resonator;
A second diode connected in parallel to the damping resistor and capable of switching itself between a conductive state and a non-conductive state;
The crystal oscillator according to claim 1 or 2. The second diode becomes non-conductive when a reverse bias voltage is applied when the crystal resonator is oscillated with a fundamental wave, and a forward bias voltage is applied when the crystal resonator is overtone oscillated. It becomes a conduction state by being
The crystal oscillator according to claim 3.

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