JP4171552B2 - Temperature compensated crystal oscillator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to a configuration of a temperature compensated crystal oscillator for use in a communication device such as a mobile phone.
[0002]
[Prior art]
  A temperature-compensated crystal oscillator for use in communication equipment is mainly composed of a 10 MHz-band AT-cut crystal resonator as a vibration source, and a frequency compensation circuit is used for this to form an AT-cut crystal resonator. The oscillation frequency is stabilized by canceling the temperature characteristic of the cubic curve.
[0003]
  A temperature-compensated crystal oscillator is required to have frequency stability against power supply voltage fluctuation, low power consumption, etc. in addition to frequency stability against temperature change.
[0004]
  The simplest means to satisfy these requirements simultaneously is to drive the temperature compensated crystal oscillation circuit with a voltage regulator that outputs a voltage lower than the power supply voltage.
[0005]
  One example of the configuration of such a temperature compensated crystal oscillator in the prior art is shown in the block circuit diagram of FIG.
[0006]
  As shown in FIG. 6, the voltage regulator 3 drives the temperature compensated crystal oscillation circuit 1.
[0007]
  The configuration of the voltage regulator 3 includes a differential circuit 5 having a certain reference voltage A as one input, and a ratio between the reference voltage A and the drive voltage of the temperature compensated crystal oscillation circuit 1 by supplying a feedback signal to the differential circuit 5. That is, it comprises a DC load 7 for determining an amplification factor and an actuator 9 which is a direct drive unit of the temperature compensated crystal oscillation circuit 1.
  Furthermore, in the example shown in FIG. 6, the phase compensation capacitor 11 for preventing self-excited oscillation is provided between the output of the actuator 9 and the control signal, but this is not essential.
[0008]
  The DC load 7 is constituted by, for example, a series connection of a first resistor 7a and a second resistor 7b of the same type.
[0009]
  The DC load 7 is not an essential configuration. If the reference voltage A equal to the drive voltage of the temperature compensated crystal oscillation circuit 1 can be obtained, the DC load 7 can be eliminated and the output of the actuator 3 can be used as the feedback signal of the differential circuit 5 as it is.
[0010]
  In any case, by using the voltage regulator 3 to lower the drive voltage of the temperature compensated crystal oscillation circuit 1 below the power supply voltage, the power consumption of the temperature compensated crystal oscillator is reduced and the frequency is stabilized against fluctuations in the power supply voltage. And can be achieved.
[0011]
[Problems to be solved by the invention]
  However, driving a temperature-compensated crystal oscillation circuit using a voltage regulator has a problem that phase noise is worse than when driving a temperature-compensated crystal oscillation circuit directly with a power supply voltage.
[0012]
    (Object of invention)
  An object of the present invention is to provide a temperature compensated crystal oscillator that utilizes the advantages of a voltage regulator and has low phase noise.
[0013]
[Means for Solving the Problems]
  In order to achieve the above object, the configuration of the temperature compensated crystal oscillator according to the present invention is as follows.
[0014]
  That is, the configuration of the temperature compensated crystal oscillator according to the present invention is a temperature compensated crystal oscillator having a voltage regulator that drives a temperature compensated crystal oscillation circuit,The voltage regulator includes an actuator that is a direct drive unit of the temperature compensated crystal oscillation circuit, a control voltage generation circuit of the actuator, a voltage follower connected to an output of the control voltage generation circuit, and an output of the voltage follower And a switch connected in parallel with the resistor or coil, and the switch is turned on when the temperature-compensated crystal oscillator is turned on. Controlled to be in a stateIt is characterized by that.
[0015]
  Alternatively, the configuration of the temperature compensated crystal oscillator according to the present invention is a temperature compensated crystal oscillator in which a voltage regulator drives a temperature compensated crystal oscillation circuit,The voltage regulator includes an actuator that is a direct drive unit of the temperature-compensated crystal oscillation circuit, a control voltage generation circuit of the actuator, an output of the control voltage generation circuit, and a control terminal of the actuator. Alternatively, a low-pass filter comprising a coil and a capacitor, and the control power A voltage follower connected to the output of the pressure generating circuit; and a switch connected between the output of the voltage follower and the control terminal of the actuator, and the switch is turned on when the temperature-compensated crystal oscillator is turned on. Controlled asIt is characterized by that.
[0016]
  In these temperature compensated crystal oscillators, the cutoff frequency of the low-pass filter is 1 Hz or less.
[0017]
  Furthermore, in these temperature compensated crystal oscillators, the stray capacitance of a switch capable of short-circuiting both ends of the resistor or the coil is 1/100 or less of the capacitance value of the capacitor constituting the low-pass filter.
[0018]
    [Action]
  A conventional low power consumption type temperature compensated crystal oscillator forms a voltage regulator with an actuator, a differential circuit, and the like, and drives the temperature compensated crystal oscillation circuit with the output of the voltage regulator.
  As a means for maintaining the constant voltage characteristic of the drive voltage, feedback control is generally used.
[0019]
  By the way, the temperature-compensated crystal oscillation circuit is a stable load in the long term, but has a characteristic that current pulsates in accordance with the phase state of oscillation in the short term.
  That is, it is a load having the property that the impedance changes in the short term.
[0020]
  When such a short-term variability load is driven by a conventional voltage regulator, the output voltage of the actuator pulsates due to the influence of the load variation, so that the signal fed back to the differential circuit also pulsates.
[0021]
  In such a case, the voltage regulator performs an operation of canceling the load fluctuation in order to keep the output voltage constant.
[0022]
  If the response speed of the voltage regulator is fast enough to follow the frequency of the temperature compensated crystal oscillation circuit, the output voltage is kept constant.
[0023]
  However, it is extremely difficult to make the differential circuit that controls the actuator in the voltage regulator fast enough to follow the temperature compensated crystal oscillation circuit in the 10 MHz band.
[0024]
  For this reason, the voltage regulator performs an operation for compensating for the load fluctuation at a lower frequency than the fluctuation in the 10 MHz band of the temperature compensated crystal oscillation circuit.
[0025]
  In other words, since the load fluctuation is faster than the speed at which the output voltage of the voltage regulator is kept constant, the output voltage cannot be kept constant, and the output voltage is lower than the fluctuation in the 10 MHz band. The characteristic combined with the variation of the frequency is shown.
[0026]
  Since the oscillation frequency of the temperature compensated crystal oscillation circuit varies depending on the drive voltage, if the output voltage of the voltage regulator varies at a certain frequency, the oscillation frequency of the temperature compensated crystal oscillation circuit is delicately modulated.
[0027]
  This subtle modulation of the oscillation frequency appears as a deterioration of phase noise.
[0028]
  In the voltage regulator in the prior art, the response possible frequency of the differential circuit is about several tens of kHz.
  In the case of such a voltage regulator, the phase noise is worsened with respect to a range where the deviation from the oscillation frequency of the temperature compensated crystal oscillation circuit is within several tens of kHz.
[0029]
  Current cellular phone specifications require low phase noise in the range of 1 Hz to 100 kHz deviation from the oscillation frequency, and conventional voltage regulators exacerbate this large range of phase noise. Will be.
[0030]
  Therefore, in order to prevent the deterioration of the phase noise in a range that is regarded as a problem by the mobile phone, the response frequency of the voltage regulator may be set to 1 Hz or less.
[0031]
  One means for reducing the response frequency of the voltage regulator to 1 Hz or less is the configuration of the present invention described above.
[0032]
  In the voltage regulator of the present invention, a low-pass filter is inserted in the control signal of the actuator, and components on the higher frequency side than the cutoff frequency of the low-pass filter are not transmitted to the actuator.
  Therefore, if the cut-off frequency of the low-pass filter is set to 1 Hz or less, the response frequency of the voltage regulator becomes 1 Hz or less.
[0033]
  Therefore, it is possible to prevent the phase noise from deteriorating in a range that the mobile phone considers problematic.
[0034]
  This is the reason why the configuration of the present invention can prevent deterioration of phase noise while mounting a voltage regulator.
[0035]
  By the way, in many recent mobile phones, a method of intermittently driving a temperature-compensated crystal oscillator or the like during the standby time is employed in order to reduce power consumption during the standby time.
  For example, a temperature-compensated crystal oscillator or the like is operated only for 20 msec in one second, and the power is turned off except for the timer for the remaining time.
[0036]
  As the call detection time is shorter, the integrated power consumption can be suppressed. Therefore, there is a strong demand for a temperature-compensated crystal oscillator to make the start-up as fast as possible.
  In recent specifications, for example, the oscillation frequency after 3 msec from power-on is within 0.5 ppm of the predetermined frequency.
[0037]
  As described above, since the cutoff frequency of the low-pass filter effective for reducing phase noise is 1 Hz or less, when the power is turned on while the low-pass filter is in a normal state, it takes 1 second until the output voltage of the voltage regulator stabilizes. It takes more time.
  Therefore, in order to cope with intermittent driving, means for speeding up the operation of the low-pass filter at the time of turning on the power is necessary.
[0038]
  Various means for speeding up the operation of the low-pass filter are conceivable, but it is meaningless unless the oscillation frequency changes when the low-pass filter is returned to the normal state.
  In other words, when the low-pass filter is changed from the high speed state to the normal state, the control voltage of the actuator must not be changed.
[0039]
  Therefore, in the present invention, a switch is provided in parallel at both ends of the resistor or coil constituting the low-pass filter.
[0040]
  By turning on this switch when the power is turned on, the cutoff frequency of the low-pass filter increases, the capacitor constituting the low-pass filter is charged at high speed, and quickly reaches the control voltage. At this time, since the potentials at both ends of the switch are equal, there is no potential fluctuation even if the switch is turned off thereafter.
[0041]
  However, when the stray capacitance of the switch is large, potential fluctuation due to charge redistribution when the switch is turned off cannot be ignored.
  Such a variation in oscillation frequency due to a variation in potential is practically allowed to be within about 0.1 ppm.
[0042]
  Therefore, the stray capacitance of the switch needs to be 1/100 or less of the capacitance value of the capacitor constituting the low-pass filter.
[0043]
  Furthermore, in the present invention, a voltage follower is provided between the control voltage generation circuit of the actuator and the low pass filter.
[0044]
  The control voltage generation circuit of the actuator must be a relatively high impedance circuit from the viewpoint of suppressing current consumption and preventing self-excited oscillation.
  In general, the impedance of the control voltage generation circuit is often higher than the on-resistance of a switch provided in the low-pass filter.
[0045]
  If an attempt is made to charge the capacitor constituting the low-pass filter by such a control voltage generation circuit, the charging time will be long, and the required specifications at the time of power-on cannot be satisfied.
[0046]
  One means for solving this problem is the voltage follower according to the present invention, which is used as a kind of impedance conversion circuit.
[0047]
  Since it is a voltage follower used for such a purpose, it goes without saying that its output impedance must be about the on-resistance of a switch provided in the low-pass filter or less.
[0048]
  In order to charge the capacitor constituting the low-pass filter at high speed when the power is turned on, a series connection of the voltage follower and the switch is connected in parallel with the low-pass filter, and this parallel connection is connected to the output of the control voltage generation circuit and the actuator. You may insert between these control terminals.
[0049]
DETAILED DESCRIPTION OF THE INVENTION
  In the following, an optimum embodiment of the temperature compensated crystal oscillator of the present invention will be described with reference to the drawings. First, a first embodiment of the present invention will be described.
  FIG. 1 is a block circuit diagram showing a configuration of a temperature-compensated crystal oscillator according to the first embodiment of the present invention.
[0050]
    [Description of First Embodiment: FIG. 1]
  As shown in the block circuit diagram of FIG. 1, the voltage regulator 3 drives the temperature compensated crystal oscillation circuit 1.
[0051]
  The voltage regulator 3 includes a differential circuit 5 having a certain reference voltage A as one input, a DC load 7 for supplying a feedback signal to the differential circuit 5, a DC load 7 and a temperature compensated crystal oscillation circuit 1. Between the actuator 9 to be driven, the low-pass filter 13 connected to the control terminal of the actuator 9 and composed of a resistor 13a and a capacitor 13b, the switch 15 connected in parallel to the resistor 13a, and the differential circuit 5 and the low-pass filter 13 And a voltage follower 17 connected to the.
[0052]
  The DC load 7 is constituted by a series connection of a first resistor 7a and a second resistor 7b of the same type.
[0053]
  In this embodiment, the differential circuit 5 is a control voltage generation circuit of the actuator 9.
[0054]
  In general, factors that cause the output voltage of the voltage regulator to deviate from a set value include power supply voltage fluctuations, device characteristic manufacturing variations, and load fluctuations.
  A means for dealing with these fluctuation factors is so-called feedback control in which the output of the actuator or its divided voltage is fed back to the differential circuit.
[0055]
  In the voltage regulator 3 shown in FIG. 1, the divided voltage of the output of the actuator 9 is fed back from the DC load 7 to the differential circuit 5. That is, the actuator 9 and the DC load 7 constitute a feedback loop.
[0056]
  By this feedback function, the output of the actuator 9 can be maintained at a constant value that is a constant multiple of the reference voltage A, regardless of variations in power supply voltage, device characteristics, and load variations.
  Such a configuration is the same as that of the prior art shown in FIG.
[0057]
  Now, since the actuator 9 drives the temperature compensated crystal oscillation circuit 1 which is a short-term variable load, the drive voltage pulsates due to the influence of the load fluctuation.
[0058]
  Therefore, the feedback signal fed back from the DC load 7 to the differential circuit 5 also pulsates, and the operating point of the differential circuit 5 varies.
  If the operation of the differential circuit 5 is sufficiently high, it can operate following the pulsation of the feedback signal, so that the fluctuation frequency of the operating point matches the oscillation frequency of the temperature compensated crystal oscillation circuit 1.
[0059]
  However, if the operation of the differential circuit 5 becomes too fast, the voltage regulator 3 will self-oscillate. Therefore, the differential circuit 5 usually does not operate at high speed by means such as reducing the current flowing through the operating circuit 5. Must do so.
[0060]
  Therefore, the differential circuit 5 cannot follow the pulsation of the feedback signal, and the maximum frequency of fluctuation of the control signal to the actuator 9 is lower than the pulsation frequency of the feedback signal, that is, the oscillation frequency of the temperature compensated crystal oscillation circuit 1. . Usually, it is about several tens of kHz.
[0061]
  In the conventional example shown in FIG. 6, since the actuator 9 is directly controlled by a control signal that varies at such a frequency, the drive voltage varies at a frequency different from the oscillation frequency of the temperature compensated crystal oscillation circuit 1, and This causes the phase noise to deteriorate within a range of several tens of kHz.
[0062]
  On the other hand, in the present invention shown in FIG. 1, the control signal from the differential circuit 5 is not directly connected to the actuator 9, but is passed through the low-pass filter 13. With this configuration, the fluctuation frequency component of the control signal of the actuator 9 is equal to or lower than the cutoff frequency of the low-pass filter 13.
[0063]
  As a result, the deterioration of the phase noise due to the voltage regulator 3 is limited to the range where the deviation from the oscillation frequency of the temperature-compensated crystal oscillation circuit 1 is not more than the cutoff frequency of the low-pass filter 13, and the phase noise in a range where the deviation is larger than this. Is equivalent to the phase noise when the temperature-compensated crystal oscillation circuit 1 is directly driven by the power supply voltage.
[0064]
  Since the specifications of the current mobile phone require that the phase noise in the range between 1 Hz and 100 kHz is a deviation from the oscillation frequency, the voltage regulator can be set by setting the cutoff frequency of the low-pass filter 13 to 1 Hz or less. Even a temperature compensated crystal oscillator using 3 can satisfy this requirement.
  The deterioration of the phase noise due to the use of the voltage regulator 3 is not a problem because the deviation from the oscillation frequency is in a range of 1 Hz or less.
[0065]
  As described above, according to the configuration of the present invention, even when a voltage regulator is used for reducing power consumption and countermeasures against power supply voltage fluctuations, temperature compensation does not cause deterioration of phase noise in a required deviation range. Type crystal oscillator can be provided.
[0066]
  Many modern mobile phones operate a temperature-compensated crystal oscillator for the time required to detect a call in order to reduce power consumption during the standby time, and supply most of the time to each circuit except for the timer. The intermittent drive specification is to turn off the power.
  For this reason, the temperature-compensated crystal oscillator is required to start oscillating at a predetermined frequency within a time of about 3 msec after the power is turned on.
[0067]
  Therefore, when using a low-pass filter with a cut-off frequency of 1 Hz or less as in the present invention, it takes at least 1 sec for the frequency to reach a predetermined value. A means to do is necessary.
  The switch 15 shown in FIG. 1 is one of the means.
[0068]
  That is, if the switch 15 is in the ON state, the cutoff frequency of the low-pass filter 13 is determined by the product of the ON resistance of the switch 15 and the capacitance value of the capacitor 13a.
  Accordingly, by setting the on-resistance of the switch 15 to be sufficiently low and turning on the switch 15 when the power is turned on, the oscillation frequency can be quickly raised to a predetermined value.
[0069]
  For example, if the capacitance value of the capacitor 13a is 0.01 μF, if the on-resistance of the switch 15 is set to about 10 kΩ or less, the time constant becomes 100 μsec or less, and the frequency is almost completely within 2 msec after the power is turned on. To reach.
[0070]
  The above discussion is based on the assumption that the current supply capability of the differential circuit 5 is sufficiently high, in other words, the impedance of the differential circuit 5 is sufficiently lower than the on-resistance of the switch 15.
[0071]
  However, the impedance of the differential circuit 5 cannot be made 100 kΩ or less due to power consumption restrictions. Moreover, if the impedance of the differential circuit 5 is lowered, the risk of self-oscillation increases.
[0072]
  For this reason, when the differential circuit 5 is directly connected to the low-pass filter 13, the capacitor 13b is charged by a circuit having a higher impedance than the on-resistance of the switch 15, and the oscillation frequency is set to a predetermined value when the power is turned on. It becomes difficult to start up promptly.
[0073]
  One means for solving such a problem is a voltage follower 17 shown in FIG.
[0074]
  In the voltage follower 17, the voltage values of the input and the output are equal, and the output impedance can be easily reduced.
  Therefore, by using the voltage follower 17 having a sufficiently low output impedance, the start-up speed when the power is turned on can be substantially determined only by the product of the on-resistance of the switch 15 and the capacitance value of the capacitor 13a. it can.
[0075]
  As described above, according to the configuration of the present invention, even when the low-pass filter 13 having a cutoff frequency of 1 Hz or less is used, the oscillation frequency can be quickly set to a predetermined value after the power is turned on.
[0076]
  By the way, when the temperature compensated crystal oscillator is constituted by a semiconductor integrated circuit, the switch 15 is constituted by a CMOS transistor or the like, and generally the stray capacitance cannot be made zero.
  Therefore, charge and discharge to the stray capacitance occurs as the switch 15 is turned on and off, so that it is inevitable that charge transfer occurs.
[0077]
  Such movement of electric charges slightly changes the control voltage of the actuator 9 and thereby slightly changes the oscillation frequency.
  The stray capacitance of the switch 15 must be controlled so that the fluctuation amount remains within the allowable range.
[0078]
  According to a detailed investigation by an actual device, if the stray capacitance of the switch 15 is set to 1/100 or less of the capacitance value of the capacitor 13a, the variation amount of the frequency can be within 0.1 ppm. This value is well within an acceptable range.
[0079]
  It is easy to set the stray capacitance of the switch 15 to 1/100 or less of the capacitance value of the capacitor 13a. For example, as described above, if the capacitance value of the capacitor 13a is 0.01 μF, the on-resistance of the switch 15 may be about 10 kΩ or less, but a CMOS transistor switch having an on-resistance of about 10 kΩ is 1 to 2 pF. It can be easily formed with the following stray capacitance, and since this value is 1/1000 or less of the capacitance value of the capacitor 13a, the condition of 1/100 or less is satisfied.
[0080]
  Next, the configuration of the low pass filter 13 used in the temperature compensated crystal oscillator of the present invention will be described.
[0081]
  In the example shown in FIG. 1, the resistor 13a and the capacitor 13b form a low-pass filter. If the respective values are R (Ω) and C (F), the cutoff frequency is 1 / 2πRC. Each value may be selected so as to be 1 Hz or less.
  For example, the resistor 13a may be about 100 MΩ and the capacitor 13b may be about 0.01 μF. Of course, there is no problem in making the cutoff frequency lower.
[0082]
  As shown in FIG. 1, the low-pass filter used in the present invention must be a passive filter composed of only passive devices, and not an active filter using active devices.
[0083]
  This is because the active filter is configured to exhibit its performance by feedback control and basically has a noise component similar to that of the voltage regulator of the conventional example.
  In other words, the low-pass filter itself for removing the noise component produces a noise component.
[0084]
  The passive device includes a coil in addition to the resistor and the capacitor, and the resistor 13a may be replaced with a coil.
[0085]
  Next, a second embodiment of the present invention will be described. FIG. 2 is a block circuit diagram showing the configuration of the temperature compensated crystal oscillator according to the second embodiment of the present invention.
[0086]
    [Description of Second Embodiment: FIG. 2]
  As shown in the block circuit diagram of FIG. 2, the voltage regulator 3 drives the temperature compensated crystal oscillation circuit 1.
[0087]
  The configuration of the voltage regulator 3 includes a differential circuit 5 having a reference voltage A as one input, a DC load 7 for supplying a feedback signal to the differential circuit 5, and a DC load under the control of the differential circuit 5. A low-pass filter comprising a resistor 13a and a capacitor 13b connected to the control terminal of the second actuator 9b, a second actuator 9b for driving the temperature-compensated crystal oscillation circuit 1, and a second actuator 9b for driving the temperature-compensated crystal oscillation circuit 1. 13, a switch 15 connected in parallel to both ends of the resistor 13a, a voltage follower 17 connected between the control terminal of the first actuator 9a and the low-pass filter 13, and a control terminal and an output terminal of the first actuator 9a And a phase compensation capacitor 11 connected to the.
[0088]
  The DC load 7 is constituted by a series connection of a first resistor 7a and a second resistor 7b of the same type. The low-pass filter 13 is composed of only passive elements, for example, a high resistance 13a and a capacitor 13b. These configurations are the same as those of the first embodiment shown in FIG.
[0089]
  The first actuator 9a and the second actuator 9b shown in FIG. 2 are configured by the same type of device.
[0090]
  In this example, the differential circuit 5, the DC impossibility 7, the first actuator 9a, and the phase compensation capacitor 11 are the control voltage generation circuit of the second actuator 9b.
  The phase compensation capacitor 11 is not essential.
[0091]
  In the example shown in FIG. 2, the temperature-compensated crystal oscillation circuit 1 and the second actuator 9b that drives the temperature-compensated crystal oscillation circuit 1 are outside the feedback loop, and the second actuator 9b receives the control signal of the first actuator 9a. Therefore, it seems that the low-pass filter 13 is not necessary.
[0092]
  However, the temperature-compensated crystal oscillation circuit 1 fluctuates not only the drive voltage of the second actuator 9b but also the power supply voltage. As a result, the feedback signal fed back to the differential circuit 5 is fluctuated.
  For this reason, fluctuations that worsen the phase noise are superimposed on the control signal of the first actuator 9a.
[0093]
  Even in such a case, if the cutoff frequency of the low-pass filter 13 is set to 1 Hz or less, it is possible to prevent the deterioration of the phase noise within the frequency deviation range required by the mobile phone.
[0094]
  The reason for providing the switch 15 and the voltage follower 17 is the same as that of the first embodiment shown in FIG.
[0095]
  As in the second embodiment shown in FIG. 2, the configuration in which the low-pass filter 13 is provided outside the feedback loop has a greater filter effect than that provided in the feedback loop.
[0096]
  Next, a third embodiment of the present invention will be described. FIG. 3 is a block circuit diagram showing a configuration of a temperature compensated crystal oscillator according to the third embodiment of the present invention.
[0097]
    [Explanation of Third Embodiment: FIG. 3]
  As shown in the block circuit diagram of FIG. 3, the voltage regulator 3 drives the temperature compensated crystal oscillation circuit 1.
[0098]
  The voltage regulator 3 is configured by driving a constant current load 19 and a diode-connected first actuator 9a, a second actuator 9b for driving the temperature-compensated crystal oscillation circuit 1, and a control of the second actuator 9b. A low-pass filter 13 comprising a resistor 13a and a capacitor 13b connected to the terminals; a switch 15 connected in parallel to both ends of the resistor 13a; and a voltage follower connected between the control terminal of the first actuator 9a and the low-pass filter 13. 17.
[0099]
  The output voltage of the first actuator 9a becomes a substantially constant value under a certain power supply voltage above a certain level, and this is the control voltage of the actuator 9b. Therefore, the third embodiment is configured to control the second actuator 9b with a constant voltage, and the low-pass filter 13 is unnecessary unless the constant voltage varies.
[0100]
  However, since the temperature compensated crystal oscillation circuit 1 fluctuates the power supply voltage, the output voltage of the first actuator 9a also fluctuates. Therefore, if the second actuator 9b is directly controlled by this output voltage, the phase noise also deteriorates. End up.
[0101]
  Even in such a case, it is possible to prevent the deterioration of the phase noise by removing the high frequency component from the output voltage of the first actuator 9a by the low pass filter 13.
[0102]
  In the case of the third embodiment shown in FIG. 3, there is no risk of self-excited oscillation in the control voltage generation circuit, but the current value of the constant current load 19 must be limited to suppress power consumption. Therefore, the impedance is higher than the on-resistance of the switch 15.
[0103]
  Therefore, it is necessary to provide the voltage follower 17 for high-speed operation when the power is turned on, as in the first embodiment.
[0104]
  Next, a fourth embodiment of the present invention will be described. FIG. 4 is a block circuit diagram showing a configuration of a temperature compensated crystal oscillator according to the fourth embodiment of the present invention.
[0105]
    [Description of Fourth Embodiment: FIG. 4]
  As shown in the block circuit diagram of FIG. 4, the voltage regulator 3 drives the temperature compensated crystal oscillation circuit 1.
[0106]
  The voltage regulator 3 includes a differential circuit 5 having a certain reference voltage A as one input, a DC load 7 for supplying a feedback signal to the differential circuit 5, a DC load 7 and a temperature compensated crystal oscillation circuit 1. An actuator 9 to be driven, a low-pass filter 13 connected between the output of the differential circuit 5 and the control terminal of the actuator 9 and composed of a resistor 13a and a capacitor 13b, and a voltage follower 17 connected to the output of the differential circuit 5; The switch 15 is connected between the output of the voltage follower 17 and the control terminal of the actuator 9.
[0107]
  The DC load 7 is constituted by a series connection of a first resistor 7a and a second resistor 7b of the same type.
[0108]
  In this embodiment, the differential circuit 5 is a control voltage generation circuit of the actuator 9.
[0109]
  The difference between the fourth embodiment shown in FIG. 4 and the first embodiment shown in FIG. 1 is that the connection destination of one terminal of the resistor 13a constituting the low-pass filter 13 is basically a voltage follower. 17 is the difference between input and output.
[0110]
  In either case, when the power is turned on, the voltage follower 17 charges the capacitor 13b through the switch 15 at high speed. Therefore, if the voltage follower 17 has no offset, the operation is the same in either configuration.
[0111]
  In the second embodiment or the third embodiment, it is possible to configure the connection destination of one terminal of the resistor 13a as an input of the voltage follower 17, but details thereof are omitted. To do.
[0112]
  Next, the degree of improvement in phase noise according to the configuration of the present invention will be described.
  FIG. 5 is a graph showing measured values of the phase noise of the temperature compensated crystal oscillator of the present invention and the phase noise of the temperature compensated crystal oscillator of the conventional configuration.
[0113]
    [Description of phase noise: Fig. 5]
  The phase noise graph indicates that the lower the line, the lower the phase noise.
[0114]
  As is apparent from FIG. 5, the phase noise of the temperature compensated crystal oscillator according to the configuration of the present invention is considerably lower than the phase noise of the temperature compensated crystal oscillator of the conventional configuration.
[0115]
  Although the present invention has been specifically described based on the embodiments as described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the present invention. Needless to say.
[0116]
  For example, in the above embodiment, the differential circuit and the actuator are configured by MOS transistors, but may be configured by junction FETs.
[0117]
  In addition, the low-pass filter is composed of a single-stage resistor and capacitor, but may be composed of a plurality of stages of resistors and capacitors.
[0118]
【The invention's effect】
  As described above, the temperature-compensated crystal oscillator of the present invention includes a low-pass filter having an operation acceleration means at power-on, and drives the temperature-compensated crystal oscillation circuit with a voltage regulator whose response frequency is lowered by the low-pass filter. By adopting such a configuration, it is possible to provide a temperature-compensated crystal oscillator that can start up quickly and consume low power while preventing deterioration of phase noise.
[0119]
  Therefore, if the present invention is applied to a temperature-compensated crystal oscillator especially mounted on a mobile phone, the effect is extremely great.
[Brief description of the drawings]
FIG. 1 is a block circuit diagram showing a configuration of a temperature-compensated crystal oscillator according to a first embodiment of the present invention.
FIG. 2 is a block circuit diagram showing a configuration of a temperature compensated crystal oscillator according to a second embodiment of the present invention.
FIG. 3 is a block circuit diagram showing a configuration of a temperature compensated crystal oscillator according to a third embodiment of the present invention.
FIG. 4 is a block circuit diagram showing a configuration of a temperature compensated crystal oscillator according to a fourth embodiment of the present invention.
FIG. 5 is a graph showing an example of phase noise comparison between a temperature compensated crystal oscillator according to an embodiment of the present invention and a temperature compensated crystal oscillator having a conventional configuration.
FIG. 6 is a block circuit diagram showing a configuration of a temperature compensated crystal oscillator in the prior art.
[Explanation of symbols]
  1: Temperature compensated crystal oscillation circuit 3: Voltage regulator
  5: Differential circuit 7: DC load
  9: Actuator 13: Low-pass filter
  15: Switch 17: Voltage follower

Claims (4)

A temperature compensated crystal oscillator having a voltage regulator for driving a temperature compensated crystal oscillation circuit,
It said voltage regulator includes a actuator is a direct drive unit of the temperature compensated crystal oscillator circuit,
A control voltage generating circuit of this actuator,
A voltage follower connected to the output of the control voltage generating circuit,
There between the control terminal of the output and the actuator of the voltage follower, a low-pass filter consisting of the resistor or a coil and a capacitor,
And a switch connected in parallel to a resistor or a coil , wherein the switch is controlled to be turned on when the temperature-compensated crystal oscillator is turned on . A temperature compensated crystal oscillator having a voltage regulator for driving a temperature compensated crystal oscillation circuit,
It said voltage regulator includes a actuator is a direct drive unit of the temperature compensated crystal oscillator circuit,
A control voltage generating circuit of this actuator,
There between the control terminal of the output and the actuator of the control voltage generating circuit, a low-pass filter consisting of a resistor or a coil and a capacitor,
A voltage follower connected to the output of the control voltage generating circuit,
And a switch connected between the control terminal of the output and the actuator of the voltage follower, the switch temperature compensated, characterized in that is controlled to be turned on at the time of power-on of the temperature compensated crystal oscillator Crystal oscillator. The cutoff frequency of the low-pass filter is
The temperature compensated crystal oscillator according to claim 1, wherein the temperature compensated crystal oscillator is 1 Hz or less. The stray capacitance of the switch is
The temperature compensated crystal oscillator according to claim 1 or 2, wherein the temperature compensation crystal oscillator is 1/100 or less of a capacitance value of a capacitor constituting the low-pass filter.

Images