JP2011077724A - Crystal oscillation circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve a crystal oscillation circuit which can reduce consumption current amount even while performing amplitude restriction. <P>SOLUTION: Between an input end and an output end of an inverter INV, a crystal oscillator XD and a resistor R are connected in parallel to each other. The input end and the output end of the inverter INV are connected to the ground by a capacitor C. A diode D is independently connected to the inverter INV, the crystal oscillator XD, the resistor R in parallel without interposing other circuit elements. In this case, an anode of the diode D is connected to the input end of the inverter INV, and a cathode of the diode D is connected to the output end of the inverter INV. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a crystal oscillation circuit that oscillates a reference signal having a predetermined frequency using a crystal resonator.

  Conventionally, an oscillation circuit using a crystal resonator, that is, a crystal oscillation circuit, is used in various fields as a reference frequency signal generation circuit.

  As a basic circuit configuration of the crystal oscillation circuit, for example, as shown in Non-Patent Document 1, an inverter, a crystal resonator connected between an input terminal and an output terminal of the inverter, and an input terminal and an output terminal of the inverter And a resistor connected in parallel to the crystal unit and a capacitor connected between each of the input and output terminals of the inverter and the ground.

  When a reference frequency signal generator for a reception system is configured using such a crystal oscillation circuit, if the excitation intensity of the crystal resonator is too strong, harmonics with respect to the reference frequency signal are propagated to other circuits in the reception system. Sometimes. Then, the reception characteristics deteriorate due to the propagation of such harmonics.

  In order to solve such a problem, it is considered to limit the amplitude of a reference frequency signal having a predetermined frequency output from a crystal oscillation circuit. For example, in Patent Document 1, in the basic circuit configuration of the above-described crystal oscillation circuit, two diodes having opposite polarities are connected in parallel to the inverter and the crystal resonator.

Japanese Examined Patent Publication No. 62-53961

By Masaomi Suzuki, “Design of Tsunemoto Junction Transistor Circuit”, CQ Publishing Co., Ltd., published first edition on December 20, 1992, issued on July 14, 2003, p. 328-p. 331

  However, in the crystal oscillation circuit of Patent Document 1, the current flows through the diode regardless of whether the amplitude of the output reference frequency signal swings from the reference level to the maximum direction or from the reference level to the minimum direction. . For this reason, a current constantly flows through one of the diodes, and the amount of current consumed as a crystal oscillation circuit increases.

  An object of the present invention is to realize a crystal oscillation circuit capable of reducing the amount of current consumption while limiting the amplitude.

  (1) A crystal oscillation circuit according to the present invention includes an inverting amplifier circuit in which the phase of an output signal is inverted with respect to an input signal, one end connected to the input terminal of the inverting amplifier circuit, and the other terminal connected to the output terminal of the inverting amplifier circuit. It is characterized by comprising a crystal resonator having ends connected thereto, and a diode connected in parallel to the crystal resonator without any other element interposed therebetween.

  In this configuration, in a crystal oscillation circuit in which a crystal resonator is connected between the input end and the output end of the inverting amplifier circuit, only a diode is further directly connected in parallel to the crystal resonator. With this configuration, when a potential difference equal to or greater than the threshold potential in the forward direction of the diode occurs between the input terminal and the output terminal of the inverting amplifier circuit, a current flows through the diode, and the level of the input signal of the inverting amplifier circuit decreases. . As a result, the amplitude of the output signal of the inverting amplifier circuit, that is, the amplitude of the reference frequency signal oscillated by the crystal oscillation circuit is suppressed and the amplitude is limited. On the other hand, when a potential difference in the reverse direction of the diode occurs between the input terminal and the output terminal of the inverting amplifier circuit, the diode is opened in a circuit. Therefore, the amplitude level of the reference frequency signal by normal oscillation can be obtained without contributing to the level change of the input signal of the inverting amplifier circuit. As described above, when this configuration is used, the amplitude is limited during the period in which the diode is forward-biased, and the normal oscillation operation is performed during the period in which the diode is reverse-biased, and the amplitude of the reference frequency signal is limited as a whole. . At this time, as in the configuration in which two diodes are connected in parallel in different directions as in the above-described conventional example, the inverting amplifier circuit is not always in the transition state, and current does not always flow, so the current consumption is reduced. .

  (2) The diode connected in parallel to the crystal resonator of the crystal oscillation circuit of the present invention is a single diode.

  This configuration shows a specific configuration of the above-described crystal oscillation circuit. This is because, for example, in a system with a low voltage level such as a mobile phone reception system, if one diode is used, it is possible to obtain a sufficient withstand voltage, and by using only one diode, The circuit is simplified and miniaturized.

  (3) Further, the diode of the crystal oscillation circuit of the present invention has an anode connected to the input terminal of the inverting amplifier circuit and a cathode connected to the output terminal of the inverting amplifier circuit.

  This configuration shows a specific configuration of the above-described crystal oscillation circuit. An inverting amplifier circuit usually has a very high input impedance. Therefore, if the diode is connected to the inverting amplifier circuit so that the input terminal side of the inverting amplifier circuit becomes the anode and the output terminal side becomes the cathode, a current flows through the diode, and even if the inverting amplifier circuit operates in the transition state, The amount of current flowing to the inverting amplifier circuit is low. Thereby, the current consumption amount as a crystal oscillation circuit can be further reduced.

  (4) Further, the inverting amplifier circuit of the crystal oscillation circuit of the present invention is an inverter circuit for rectangular wave oscillation.

  This configuration shows a specific configuration of the above-described crystal oscillation circuit. When an inverter circuit for rectangular wave oscillation is used as the inverting amplifier circuit, if only a diode is directly connected in parallel to the inverting amplifier circuit as described above, the effect of reducing the input bias to the inverter circuit can be achieved even with a rectangular wave. It is definitely obtained.

  (5) Further, the crystal resonator of the crystal oscillation circuit of the present invention is a crystal resonator having a unique contour vibration mode.

  In this configuration, a specific example of the above-described crystal resonator is shown, and if a contour resonator mode crystal resonator is used, the height can be reduced. As a result, the crystal oscillation circuit can be reduced in height.

  (6) The diode of the crystal oscillation circuit of the present invention is integrally formed on a semiconductor substrate on which an inverting amplifier circuit is formed.

  In this configuration, since the diode and the inverting amplifier circuit are integrally formed on the same semiconductor substrate, the crystal oscillation circuit can be reduced in height and size.

  According to the present invention, it is possible to realize a crystal oscillation circuit with reduced power consumption while limiting the amplitude. Furthermore, according to the present invention, it is possible to reduce the number of circuit components for limiting the amplitude as compared with the prior art, and it is possible to form a crystal oscillation circuit with an amplitude limit smaller than before.

1 is a circuit diagram of a crystal oscillation circuit 1 according to a first embodiment. FIG. FIG. 2 is a waveform diagram of the crystal oscillation circuit 1 according to the first embodiment and a waveform diagram of a conventional circuit. It is a wave form diagram of the crystal oscillation circuit which connected the diode of the 2 conventional reverse characteristics in parallel. FIG. 6 is a circuit diagram of a crystal oscillation circuit 1 ′ according to a second embodiment. It is a wave form diagram of crystal oscillation circuit 1 'concerning a 2nd embodiment.

A crystal oscillation circuit according to a first embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a circuit diagram of the crystal oscillation circuit 1 of the present embodiment, FIG. 1 (A) is a circuit diagram showing the main configuration of the crystal oscillation circuit 1, and FIG. 1 (B) is an internal circuit of the inverter INV. It is a circuit diagram in the shown state.

  2A is a waveform diagram of the input signal Vin and the output signal Vout of the inverter INV of the crystal oscillation circuit 1 of the present embodiment, and FIG. 2B is a waveform diagram of the inverter INV of the conventional circuit. FIG. 4 is a waveform diagram of an input signal Vin ′ and a waveform diagram of an output signal Vout ′. Note that the conventional circuit shown in the present embodiment has an inverter INV, a crystal resonator XD, and a resistor R connected in parallel as shown in Non-Patent Document 1, and an input terminal and an output terminal of the inverter INV are connected to a capacitor C. Shows the circuit connected to ground.

  FIG. 3 is a waveform diagram of a crystal oscillation circuit in which two conventional diodes having opposite characteristics, which are comparison targets of the crystal oscillation circuit 1 of the present embodiment, are connected in parallel.

  As shown in FIG. 1, the crystal oscillation circuit 1 of this embodiment includes an inverter INV, a crystal resonator XD, a diode D, a resistor R, and two capacitors C.

The output terminal of the inverter INV is a signal output terminal OUT as the crystal oscillation circuit 1.
The inverter INV includes drive power supply terminals Vdd and Vee. A predetermined drive voltage is applied to the drive power supply terminal Vdd, and the drive power supply terminal Vee is connected to the ground. As shown in FIG. 1B, the inverter INV includes an odd number of amplification stages in which a P-channel MOSFET and an N-channel MOSFET are connected in cascade. Each amplification stage is applied with a drive voltage of a predetermined level via a drive power supply terminal Vdd, and is connected to the ground via a drive power supply terminal Vee. In addition, an input bias voltage obtained by resistively dividing the drive voltage is applied to each amplification stage. The gate of the first stage of the plurality of amplification stages becomes the input terminal of the inverter INV, and the connection point between the P channel MOSFET and the N channel MOSFET of the final stage becomes the output terminal of the inverter INV. In this embodiment, the case where there are a plurality of amplification stages and an odd number is shown as an example, but the configuration of this embodiment can be realized even if there is only one amplification stage.

  Such an inverter INV is realized by an integrated circuit formed on a semiconductor substrate.

  The crystal resonator XD is connected in parallel to the inverter INV. That is, one end of the crystal unit XD is connected to the input end of the inverter INV, and the other end of the crystal unit XD is connected to the output end of the inverter INV. The crystal resonator XD uses a crystal that resonates at a reference frequency in the contour vibration mode. Although the configuration of the present application can be realized by using an AT-cut crystal, it is desirable to use a contour vibration mode crystal. As described above, by using the crystal in the contour vibration mode, the shape of the crystal unit XD can be made lower than that in the case of using the AT-cut crystal.

  For example, such a crystal resonator XD is mounted on the above-described semiconductor substrate to be connected to the inverter INV in a circuit.

  The resistor R is connected in parallel to the inverter INV and the crystal resonator XD. That is, one end of the resistor R is connected to the input end of the inverter INV, and the other end of the resistor R is connected to the output end of the inverter INV. The resistor R is a resistor that stabilizes oscillation in a so-called crystal oscillation circuit, and is set to a predetermined resistance value.

  Such a resistor R is realized by, for example, a discrete resistance element, and is connected to the inverter INV or the crystal resonator XD by being mounted on the above-described semiconductor substrate. Depending on the resistance value, the resistor R may be formed in the semiconductor substrate.

  The diode D is connected in parallel to the inverter INV, the crystal resonator XD, and the resistor R. At this time, the anode of the diode D is connected to the input terminal of the inverter INV, and the cathode of the diode D is connected to the output terminal of the inverter INV.

  Such a diode D utilizes a pn junction formed in the semiconductor substrate described above. Further, this diode D may be mounted on a semiconductor substrate as a discrete element. However, the crystal oscillation circuit 1 can be reduced in height by forming the diode D in the semiconductor substrate.

  The two capacitors C are so-called Colpitts oscillation capacitors, and each of the input terminal and the output terminal of the inverter INV is connected to the ground. The capacitor C may be a discrete element or may be formed in the semiconductor substrate. Then, by forming the capacitor C in the semiconductor substrate, the crystal oscillation circuit 1 can be reduced in height.

  With the above configuration, a so-called Colpitts-type crystal oscillation circuit can be configured. Then, by connecting a single diode D in parallel to the inverter INV and the crystal resonator XD, the following effects can be obtained.

  As described above, the diode D has an anode connected to the input terminal of the inverter INV and a cathode connected to the output terminal of the inverter INV.

  Here, immediately after the start of oscillation, since the level of the input signal of the inverter INV is low, it is below the threshold voltage level in the forward direction of the diode D, and the diode D is turned off. For this reason, the diode D functions as a resistor in terms of circuit, contributes to stable excitation together with the resistor R, and does not generate other functions in terms of circuit. Here, the threshold voltage level means a threshold voltage level at which the amount of current suddenly increases when a voltage is applied in the forward direction of the diode.

  While the excitation progresses and the inverter INV is in the transition state, the amplitude level of the excitation signal corresponding to the crystal resonator XD, that is, the input signal and output signal of the inverter INV gradually increase. At this time, the excitation signal is a signal that alternately swings in the positive voltage direction and the negative voltage direction with respect to the reference bias potential. Then, assuming that the diode D is not present and the excitation progresses to a predetermined level or higher and the inverter INV is in a saturated state operation, the Hi level potential on the positive voltage side and the Low level potential on the negative voltage side with respect to the reference bias potential. It becomes a rectangular wave signal that repeats.

  In such an oscillation process, the diode D of the present embodiment is present, and the potential in the period in which the oscillation signal (strictly speaking, the excitation signal) swings to the positive voltage side is equal to or higher than the forward threshold voltage level of the diode D. Then, the diode D is turned on. As a result, a current flows from the input terminal of the inverter INV via the diode D, and the input bias voltage of the inverter INV decreases. As a result, even if an input signal is input to the inverter INV, it is not amplified, and the period during which the excitation signal swings to the positive voltage side is output without being amplified.

  On the other hand, during the period in which the oscillation signal swings to the negative voltage side, the diode D remains in the OFF state, and the input bias voltage of the inverter INV does not decrease. As a result, the inverter INV functions normally and becomes saturated, and the input signal is amplified to the low level potential on the negative voltage side and output. As described above, when the configuration of the present embodiment is used, the input signal is not amplified during the period in which the input signal swings to the positive voltage side, but is amplified in the period in which the input signal swings to the negative voltage side with respect to the reference potential. An oscillation signal is obtained.

  Thereby, an input signal Vin and an output signal Vout having waveforms as shown in FIG. That is, the output signal Vout that is an oscillation signal (reference frequency signal) as the crystal oscillation circuit 1 is not amplified when the input signal Vin swings to the positive voltage side with respect to the reference potential, and is negative with respect to the reference potential. When it swings to the voltage side, it becomes an amplified waveform.

  On the other hand, as shown in FIG. 2B, the input signal Vin ′ and the output signal Vout ′ of the crystal oscillation circuit that does not use a conventional diode are positive with respect to the reference potential according to the amplification capability of the inverter INV. Both the negative voltage side and the negative voltage side have a waveform in which the voltage level swings to the maximum amplitude level. FIG. 2B uses an AT-cut quartz crystal. When the above-described contour vibration mode quartz crystal is used and the diode D is not used, the oscillation occurs when the amplitude level exceeds a certain level. It stops and no oscillation signal can be obtained.

  Thus, by using the configuration of the present embodiment, it is possible to limit the amplitude of the oscillation signal while stably oscillating.

  Furthermore, in the crystal oscillation circuit disclosed in Patent Document 1 shown in the prior art, diodes whose characteristics are opposite to each other are connected in parallel to the inverter INV. In such a configuration, the amplitude is limited in both the period in which the input signal swings positively and negatively with respect to the reference potential, and a waveform as shown in FIG. 3 is obtained. At this time, the inverter INV is in a transition state both in the period in which the input signal is swinging positive with respect to the reference potential and in the period in which the input signal is swinging negative, and current always flows.

  However, if the configuration of this embodiment is used, the period during which the input signal swings positive with respect to the reference potential is in the transition state, but the period during which the input signal swings negative with respect to the reference potential is in the saturated state. Become. For this reason, current flows only during a period in which the input signal swings positive with respect to the reference potential, and the amount of current consumption as the crystal oscillation circuit can be reduced.

  Further, in the configuration of the present embodiment, since only one diode is used, the number of components as a crystal oscillation circuit can be reduced and the size can be reduced.

Next, a crystal oscillation circuit according to a second embodiment will be described with reference to the drawings.
FIG. 4 is a circuit diagram of the crystal oscillation circuit 1 ′ of the present embodiment. FIG. 5 is a waveform diagram of an input signal Vin and an output signal Vout of the inverter INV of the crystal oscillation circuit 1 ′ of this embodiment.

  The crystal oscillation circuit 1 ′ of the present embodiment is different from the crystal oscillation circuit 1 shown in the first embodiment in the connection direction of the diode D, and the other configurations are the same. The anode of the diode D of this embodiment is connected to the output terminal of the inverter INV, and the anode of the diode D is connected to the input terminal of the inverter INV.

  With such a configuration, as shown in FIG. 5, during the period in which the input signal swings to the positive voltage side with respect to the reference potential, the inverter INV is saturated and normal oscillation is performed. On the other hand, during the period in which the input signal swings to the negative voltage side with respect to the reference potential, the inverter INV remains in the transition state and the amplitude is limited. Thereby, an oscillation signal whose amplitude is limited as a whole can be obtained.

  In the case of this embodiment, since the inverter INV is in a saturated state during the period in which the input signal swings to the positive voltage side with respect to the reference potential, there is almost no current consumption of the inverter INV, which is the same as in the first embodiment. In addition, the amount of current consumption as the crystal oscillation circuit can be reduced.

  As shown in the second embodiment, the diode D is connected to the input terminal of the inverter INV and the anode is connected to the output terminal of the inverter INV. The amount of current can be reduced and an oscillation signal can be output stably. However, if the configuration of the first embodiment described above is used, the amount of current consumption as the crystal oscillation circuit can be further reduced. This is because the input impedance of the inverter INV is usually high, so that the anode of the diode D is connected to the input terminal of the inverter INV and the cathode is connected to the output terminal of the inverter INV as in the first embodiment. Even if a current flows through the diode D and the inverter INV operates in the transition state, the amount of current flowing through the inverter INV becomes low. Thereby, the current consumption amount of the inverter INV is reduced, and the current consumption amount as the crystal oscillation circuit can be further reduced.

  Further, in each of the above-described embodiments, an example in which only one diode D is connected in parallel to the inverter INV and the crystal resonator XD has been described. However, a configuration may be used in which a diode circuit in which a plurality of diodes D having the same characteristic direction are connected in series is connected, and the diode circuit is connected in parallel to the inverter INV and the crystal unit XD. However, as shown in each of the above-described embodiments, if only one diode is connected in parallel, circuit components can be reduced and the crystal oscillation circuit can be further downsized. In the case of a reception system circuit of a normal mobile terminal, a sufficient breakdown voltage can be obtained even if a single diode is used. Therefore, with the configuration of each of the embodiments described above, it is possible to realize a smaller crystal oscillation circuit having a practically sufficient oscillation function.

  In addition, if only the above-mentioned diode D is connected in parallel to the inverter INV and the crystal resonator XD, the amplitude is reliably limited even when the rectangular wave oscillation signal as described above is obtained. can do. This is because, for example, if a circuit element such as a capacitor having another impedance component other than the diode D is connected in series to the diode D, the waveform of the rectangular wave is distorted and the amplitude cannot be reliably limited. And since it is not necessary to provide such an extra circuit element, a crystal oscillation circuit can be comprised more compactly.

  In each of the embodiments described above, the inverter INV has been described as an example. However, if the phase of the input signal and the output signal is opposite (180 ° phase difference) and the inverting amplifier circuit has a predetermined amplification factor, The above-described configuration can be applied, and the above-described effects can be obtained.

1,1'-crystal oscillator circuit, INV-inverter, D-diode, XD-crystal oscillator, R-resistor, C-capacitor

Claims (6)

An inverting amplifier circuit in which the phase of the output signal is inverted with respect to the input signal;
A crystal resonator having one end connected to the input end of the inverting amplifier circuit and the other end connected to the output end of the inverting amplifier circuit;
A diode connected in parallel to the crystal unit without any other elements;
Crystal oscillation circuit with   The crystal oscillation circuit according to claim 1, wherein the diode connected in parallel to the crystal resonator is a single diode.   The crystal oscillation circuit according to claim 2, wherein the diode has an anode connected to the input terminal and a cathode connected to the output terminal.   4. The crystal oscillation circuit according to claim 1, wherein the inverting amplifier circuit is an inverter circuit for rectangular wave oscillation.   The crystal oscillation circuit according to claim 1, wherein the crystal resonator is a crystal resonator having a unique contour vibration mode.   6. The crystal oscillation circuit according to claim 1, wherein the diode is integrally formed on a semiconductor substrate on which the inverting amplifier circuit is formed.

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