JP2016152468A - Reference signal generating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reference signal generating device capable of preventing a decrease in reference signal accuracy caused by a temperature change in a thermostatic oven.SOLUTION: A reference signal generating device 10 comprises a VCXO 23, an internal temperature sensor 24, and a control unit 22. The VCXO 23 is arranged a thermostatic oven 30. The internal temperature sensor 24 detects an internal temperature which is a temperature in the thermostatic oven 30. The control unit 22 calculates a phase difference by comparing a reference signal and the signal output by the VCXO 23, and controls the VCXO 23 on the basis of the phase difference and the internal temperature detected by the internal temperature sensor 24.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a reference signal generator having an oscillating portion covered with a thermostatic chamber.

  2. Description of the Related Art Conventionally, a reference signal generated by a reference signal generator is used to synchronize signal transmission timing and frequency in a mobile phone base station, a digital broadcast transmission station, and the like. The reference signal generator compares the signal output from the oscillator with a highly accurate reference signal obtained from a GNSS receiver or the like to obtain a phase difference. The reference signal generator generates a highly accurate reference signal by controlling the oscillator so that the phase difference approaches zero.

  As the reference signal generator, for example, a voltage controlled oscillator is used as shown in Patent Document 1. The voltage controlled oscillator is configured such that the oscillation frequency varies depending on the input control voltage. In addition, the oscillation frequency of the voltage controlled oscillator changes with the ambient temperature and the passage of time even if the control voltage is the same.

  Since the oscillation frequency fluctuates in this way, the frequency of the reference signal may not be temporarily stabilized even when the control based on the reference signal is performed as described above. Also, the frequency of the reference signal may not be stable even when performing free-running control that controls the oscillator without using the reference signal. Considering this point, conventionally, a crystal oscillator with a thermostat (OCXO) having a configuration in which the oscillator is covered with a thermostat and the temperature inside the thermostat is controlled to be constant is known.

  The OCXO includes a temperature sensor and a heater in a constant temperature bath, and controls the heater so that the difference between the temperature detected by the temperature sensor and the target temperature becomes zero. Thereby, the inside of a thermostat can be maintained at target temperature.

Japanese Patent No. 4050618

  However, since OCXO heats the heater after a temperature difference has occurred, the temperature in the thermostatic chamber may deviate from the target temperature by several degrees, particularly in an environment with a large external temperature change. In this case, even if control based on the reference signal or self-running control is performed, the frequency of the reference signal may not be stable.

  Further, when the external temperature is close to or exceeds the target temperature, it cannot be brought close to the target temperature even if the heater is controlled. Therefore, the reference signal generator cannot be used in such an environment.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a reference signal generator that prevents a decrease in accuracy of a reference signal due to a change in temperature in a thermostatic chamber.

Means and effects for solving the problems

  The problems to be solved by the present invention are as described above. Next, means for solving the problems and the effects thereof will be described.

  According to a first aspect of the present invention, a reference signal generator having the following configuration is provided. That is, the reference signal generator includes an oscillation unit, an internal temperature sensor, and a control unit. The oscillation unit is disposed in a thermostatic bath. The internal temperature sensor detects an internal temperature that is a temperature in the thermostatic chamber. The control unit compares a reference signal and a signal output from the oscillation unit to obtain a phase difference or a frequency difference, the phase difference or the frequency difference, and the internal temperature detected by the internal temperature sensor, The oscillation unit is controlled based on the above.

  As a result, the temperature around the oscillating unit can be accurately obtained compared to a configuration in which a temperature sensor is installed outside the thermostat, so the oscillating unit can be controlled more precisely and the frequency output by the oscillating unit can be accurately controlled. Can be improved.

  In the reference signal generator, a target temperature is set in the thermostat, and the control unit takes into account the difference between the target temperature and the internal temperature detected by the internal temperature sensor. It is preferable to control the oscillation unit.

  In general, even when the internal temperature is controlled to approach the target temperature by a heater or the like, the internal temperature deviates from the target temperature due to a control delay or the like. Therefore, the accuracy of the frequency output from the oscillating unit can be improved by controlling the oscillating unit in consideration of this deviation.

  In the reference signal generator, the control unit changes the frequency of the oscillation unit based on a change in the internal temperature when the reference signal and the signal output from the oscillation unit are synchronized. It is preferable to obtain a temperature characteristic that is

  Thereby, the temperature around the oscillation unit can be accurately acquired by detecting the internal temperature. Further, when the reference signal and the signal output from the oscillating unit are synchronized, an accurate frequency can be grasped. As described above, accurate temperature characteristics can be obtained.

  In the reference signal generator, it is preferable that the control unit obtains an apex temperature that is a temperature at which the function indicating the temperature characteristic takes an extreme value based on the obtained temperature characteristic.

  Thereby, an accurate vertex temperature can be obtained. Further, by controlling the oscillating unit using this apex temperature, the oscillating unit can be operated at a stable temperature with little frequency change, so that the frequency change can be reduced.

  In the reference signal generation device, it is preferable that the control unit controls the oscillating unit so that a change in frequency based on a time change rate of the internal temperature is removed.

  As a result, the frequency change based on the time change needs to accurately acquire the temperature around the oscillation unit, but in the above configuration, the internal temperature can be detected instead of the external temperature. Changes can be removed appropriately.

  The reference signal generator preferably has the following configuration. That is, the reference signal generator includes an external temperature sensor that detects an external temperature that is a temperature outside the thermostatic bath. The control unit acquires the external temperature detected by the external temperature sensor, acquires the internal temperature detected by the internal temperature sensor, and considers the change in the internal temperature based on the change in the external temperature. , Controlling the oscillation unit.

  Thereby, since the change of the internal temperature can be estimated based on the change of the external temperature, for example, even when the external temperature changes suddenly, the oscillation unit can be appropriately controlled.

  According to a second aspect of the present invention, a reference signal generator having the following configuration is provided. That is, the reference signal generator includes an oscillation unit, a heating unit, an internal temperature sensor, an external temperature sensor, a heating control unit, and a control unit. The oscillating unit is disposed inside a thermostatic chamber. The said heating part heats the inside of a thermostat. The internal temperature sensor detects an internal temperature that is a temperature in the thermostatic chamber. The external temperature sensor detects an external temperature that is a temperature outside the thermostat. The heating control unit compares the internal temperature detected by the internal temperature sensor with a set target temperature to obtain a temperature difference, and controls the heating unit based on the temperature difference. The control unit compares a reference signal and a signal output from the oscillation unit to obtain a phase difference or a frequency difference, and controls the oscillation unit based on the phase difference or the frequency difference. The heating control unit increases the target temperature when the external temperature detected by the external temperature sensor becomes equal to or higher than a threshold value.

  Thereby, for example, even when the external temperature becomes high and the internal temperature cannot be accurately controlled, the internal temperature can be kept constant by raising the target temperature. Therefore, it is possible to prevent the occurrence of frequency change.

  In the reference signal generator, the threshold value is preferably a temperature higher than the target temperature.

  Thereby, when the external temperature exceeds the target temperature, it becomes difficult to adjust the internal temperature to the target temperature, so that the above method can be effectively used.

  In the reference signal generation device, the control unit acquires the external temperature detected by the external temperature sensor, acquires the internal temperature detected by the internal temperature sensor, and is based on a change in the external temperature. It is preferable to control the oscillation unit in consideration of the change in the internal temperature.

  Thereby, since the change of the internal temperature can be estimated based on the change of the external temperature, for example, even when the external temperature changes suddenly, the oscillation unit can be appropriately controlled.

The block diagram which shows the structure of the reference signal generator which concerns on 1st Embodiment. The graph which shows the temperature characteristic of quartz. The block diagram which shows the structure of the reference signal generator which concerns on 2nd Embodiment. The block diagram which shows the structure of the reference signal generator which concerns on 3rd Embodiment. The block diagram which shows the structure of the reference signal generator which concerns on 4th Embodiment.

  Next, an embodiment of the invention will be described. First, the overall configuration of the reference signal generator 10 according to the first embodiment will be described with reference to FIG. FIG. 1 is a block diagram showing a configuration of a reference signal generator 10 according to the first embodiment.

  The reference signal generator 10 according to the present embodiment is used for a mobile phone base station, a terrestrial digital broadcasting transmitter station, a WiMAX (Worldwide Interoperability for Microwave Access) communication facility, and the like, and is connected to user equipment. Provides a reference timing signal and a reference frequency signal. Below, the structure of each part of the reference signal generator 10 is demonstrated.

  As shown in FIG. 1, the reference signal generator 10 of the present embodiment includes a GPS receiver 21, a controller 22, a VCXO (Voltage Controlled Crystal Oscillator) 23, and an internal temperature sensor 24. And a heater (heating unit) 25, a heating control unit 26, and a frequency dividing unit 27. In addition, the control unit 22, the VCXO 23, and the frequency dividing unit 27 constitute a PLL circuit 44.

  A GPS antenna (GNSS antenna) 11 is connected to the input unit 41 of the reference signal generator 10. A positioning signal received by the GPS antenna 11 from a GPS satellite (GNSS satellite) is input to the GPS receiving unit 21 via the input unit 41. The GPS receiving unit 21 generates a reference signal (one pulse signal per second) by performing positioning calculation based on the positioning signal. This reference signal is appropriately calibrated to accurately synchronize with 1 second of Coordinated Universal Time (UTC).

  The VCXO 23, the internal temperature sensor 24, and the heater 25 are disposed inside the constant temperature bath 30. The VCXO 23 is an oscillator that can change the output frequency according to the level of a voltage applied from the outside. The signal output from the VCXO 23 is supplied as a reference signal from the output unit 42 to an external device.

  The internal temperature sensor 24 is a sensor that detects the temperature (internal temperature) in the thermostatic chamber 30. The heater 25 heats the inside of the thermostatic chamber 30 with a heating wire or the like.

  The heating control unit 26 is configured to be able to set a target temperature, and controls the heater 25 so that the inside of the thermostatic chamber 30 becomes the target temperature by setting the target temperature. Specifically, the internal temperature detected by the internal temperature sensor 24 is input to the heating control unit 26. The heating control unit 26 obtains a difference between the internal temperature and the target temperature, and heats the heater 25 according to the temperature difference. With the above configuration, the periphery of the VCXO 23 can be maintained at the target temperature.

  An oscillator that covers a VCXO or the like with a thermostat and keeps the thermostat at a constant temperature is conventionally known as OCXO. However, this embodiment differs from the conventional OCXO in that the internal temperature detected by the internal temperature sensor 24 is output to the control unit 22. The control performed by the control unit 22 using the internal temperature will be described later in detail.

  The frequency divider 27 is configured to divide and convert the reference frequency signal input from the VCXO 23 from a high frequency to a low frequency, and to output the obtained phase comparison signal to the controller 22. The phase comparison signal is also output from the output unit 43 to the external user side system as a reference timing signal (1PPS signal). For example, when the reference frequency output from the VCXO 23 is 10 MHz, the frequency divider 27 divides the 10 MHz signal output from the VCXO 23 by a frequency division ratio of 1 / 10,000,000 to generate a 1 Hz phase comparison signal.

  The control unit 22 receives the reference signal and the phase comparison signal. The control unit 22 compares the phases of these signals to obtain a phase difference, and generates a signal (phase difference signal, frequency control amount) based on the phase difference.

  Further, the control unit 22 outputs the frequency control amount to the VCXO 23 after blocking the high frequency component of the frequency control amount and removing the noise. Thereby, the VCXO 23 can be controlled so that the phase difference approaches zero. The control unit 22 may be configured to output a comparison result between the output signal of the VCXO 23 or a signal based thereon and the reference signal, and the signal processing method is arbitrary.

  With the configuration described above, a loop of the PLL circuit 44 is configured, and the VCXO 23 is controlled so that the output signal is synchronized with the 1PPS signal as the reference signal. Therefore, as long as the GPS receiver 21 generates a 1 PPS signal and supplies it to the reference signal generator 10 and is PLL-locked with respect to the 1 PPS signal, the characteristics of the VCXO 23 are caused by changes over time, ambient temperature changes, and the like. Even if the fluctuation occurs, the reference signal of the reference signal generator 10 can be maintained with high accuracy.

  Next, a method for determining the target temperature in the thermostat 30 will be described. First, general characteristics of the crystal oscillator will be described. FIG. 2A is a graph showing temperature characteristics of quartz crystal and OCXO.

  In the graph shown in FIG. 2A, the horizontal axis indicates the temperature around the oscillator, and the vertical axis indicates the amount of change in frequency due to temperature change. As shown in FIG. 2A, the crystal itself generally has a temperature characteristic similar to a cubic function, and takes an extreme value (zero temperature coefficient point) at about 80 ° C. to 90 ° C. Hereinafter, the temperature at which the extreme value is taken is referred to as the apex temperature.

  Accordingly, when the temperature around the oscillator is near the apex temperature, the frequency change accompanying the temperature change is small (temperature characteristics are stable). On the other hand, when the temperature around the oscillator is far from the apex temperature, the frequency change accompanying the temperature change is large (temperature characteristics are unstable).

  As described above, by setting the vertex temperature as the target temperature, even if the temperature (internal temperature) in the thermostatic chamber 30 is changed, the change in frequency can be suppressed.

  Further, since the vertex temperature has individual differences for each oscillator, it is necessary to obtain the vertex temperature for each oscillator. In the conventional OCXO, the change in oscillation frequency when the temperature is changed is measured by a universal counter or the like, and the vertex temperature is obtained based on the measurement result. This method requires various inspection devices.

  On the other hand, the reference signal generator 10 of this embodiment can output a highly accurate frequency while synchronizing with the reference signal. Accordingly, the temperature characteristic can be obtained based on the control voltage output by the control unit 22 at that time while changing the temperature in the vicinity of the vertex temperature while synchronizing with the reference signal.

  Since the reference signal generator 10 uses the VCXO 23 in a portion where the temperature characteristics are stable, the internal temperature is maintained in the vicinity of the apex temperature during use. Therefore, when obtaining the temperature characteristics, it is only necessary to obtain the temperature characteristics in the vicinity of the apex temperature. Therefore, it is possible to suppress the storage capacity of the storage unit (or to store detailed temperature characteristics in the same storage unit) as compared with the method of obtaining the temperature characteristic over the entire usable temperature.

  Next, the control performed by the control unit 22 based on the internal temperature detected by the internal temperature sensor 24 will be described. Based on the internal temperature, the control unit 22 performs (1) correction based on the difference between the internal temperature and the target temperature and (2) correction considering the time change rate of the temperature.

  As described above, the inside of the thermostatic chamber 30 is maintained at the target temperature (apex temperature) by the heater 25 and the heating control unit 26, but the time from when the temperature difference occurs until the heating by the heater 25 starts, Since there is a time until the temperature in the thermostatic chamber 30 rises after the heating by the heater 25 starts, the internal temperature and the target temperature are shifted by several degrees.

  Of course, when the signal output from the VCXO 23 and the reference signal are synchronized, the control voltage is adjusted so as to eliminate the frequency difference based on the temperature difference. However, it is difficult to make the phase difference suddenly close to zero, and the accuracy of the frequency of the reference signal is temporarily reduced. Therefore, when there is a difference between the internal temperature detected by the internal temperature sensor 24 and the target temperature, the control unit 22 of the present embodiment creates a control voltage in consideration of this temperature difference. Thereby, it can suppress that the precision of the frequency of a reference signal falls. The same control can be performed during the self-running control (for details, refer to a modification example described later).

  Next, correction in consideration of the time change rate of temperature will be described. It is known that a crystal oscillator has a frequency characteristic having hysteresis. That is, in the above description, the frequency is changed by changing the temperature. Specifically, even if the temperature is the same, the temperature is increased to reach the temperature or the temperature is decreased. The temperature characteristics are slightly different depending on whether the temperature is reached (see FIG. 2B). In order to perform correction in consideration of frequency characteristics having hysteresis, it is necessary to grasp in detail the temperature change around the oscillator. Therefore, the configuration capable of accurately detecting the internal temperature as in the present embodiment can appropriately perform this correction.

  As described above, the control unit 22 performs control using the internal temperature detected by the internal temperature sensor 24, so that a reference signal with higher accuracy can be output. In many cases, manufacturers that manufacture the reference signal generator purchase OCXO as a unit. Therefore, it is difficult to take out the internal temperature detected by the temperature sensor inside the OCXO, and it cannot be easily conceived. In this regard, the applicant of the present application was able to conceive the configuration of the present application by preparing and assembling the thermostat 30 and the internal temperature sensor 24 themselves.

  Next, a second embodiment will be described with reference to FIG. FIG. 3 is a block diagram showing a configuration of the reference signal generator 10 according to the second embodiment. In the description of the reference signal generator 10 of the second embodiment, the same or similar members as those of the above-described embodiment may be denoted by the same reference numerals in the drawings, and description thereof may be omitted.

  Unlike the first embodiment, the reference signal generator 10 of the second embodiment does not output the internal temperature detected by the internal temperature sensor 24 to the control unit 22. In addition to the configuration of the first embodiment, the external temperature sensor 28 is newly provided.

  The external temperature sensor 28 detects the temperature outside the thermostat 30 (external temperature). The external temperature detected by the external temperature sensor 28 is output to the heating control unit 26.

  The heating control unit 26 performs control to change the target temperature based on the external temperature. This will be specifically described below. As described above, the heating control unit 26 can bring the internal temperature close to the target temperature by controlling the heater 25 to perform heating. However, when the external temperature is equal to or higher than the target temperature, the internal temperature cannot be adjusted close to the target temperature because the internal temperature cannot be adjusted by heating with the heater 25. In addition, although it is not impossible to cool the thermostat 30 using a Peltier device etc., it is not realistic from a viewpoint of cost. Therefore, in such a high temperature environment, the internal temperature is not stable, so the oscillation frequency of the VCXO 23 is not stable.

  In this regard, in the reference signal generator 10 of the second embodiment, control is performed to increase the target temperature when the external temperature detected by the external temperature sensor 28 is equal to or higher than a threshold value. Although the temperature used as a threshold value is arbitrary, vertex temperature (target temperature) can be made into a threshold value, for example. By increasing the target temperature, the fluctuation of the internal temperature can be reduced by the heater 25 and the heating control unit 26. Of course, the stability of the temperature characteristic shown in FIG. 2A is lowered, but the fluctuation of the internal temperature is small, so that the frequency of the reference signal can be relatively stabilized.

  Although it is possible to perform control to increase the target temperature even when performing self-running control, it is preferable to perform this control when synchronizing with the reference signal from the viewpoint of the accuracy of the reference signal.

  Next, a third embodiment will be described with reference to FIG. FIG. 4 is a block diagram showing a configuration of the reference signal generator 10 according to the third embodiment.

  In the reference signal generator 10 of the third embodiment, the internal temperature detected by the internal temperature sensor 24 is output to the control unit 22. Further, the external temperature detected by the external temperature sensor 28 is output to the control unit 22 and the heating control unit 26.

  Thus, the control unit 22 can perform detailed control by outputting the internal temperature and the external temperature to the control unit 22. When the external temperature changes, the internal temperature changes with a slight delay under the influence. That is, a change in the internal temperature can be estimated by referring to the external temperature. For this reason, for example, when the external temperature rises greatly, it is conceivable that the internal temperature also rises and the oscillation frequency error becomes large. In this case, the control unit 22 can quickly make the oscillation frequency error zero by increasing the follow-up speed.

  Next, a fourth embodiment will be described with reference to FIG. FIG. 5 is a block diagram showing a configuration of the reference signal generator 10 according to the fourth embodiment.

  The reference signal generator 10 of the fourth embodiment is configured to be able to execute self-running control (holdover control). The self-running control is performed when an appropriate reference signal cannot be acquired from the GPS receiver 21, and is a control for outputting a highly accurate reference signal without using the reference signal.

  The reference signal generation device 10 includes a self-running control unit (control unit) 51 and a switch 52 as a configuration for performing self-running control.

  The frequency control amount output from the control unit 22 is input to the self-running control unit 51. When the self-running control unit 51 is in a synchronized state as performed by the control unit 22 in the first embodiment, the correspondence between the temperature detected by the internal temperature sensor 24 and the frequency of the signal output by the VCXO 23 (Temperature characteristics) is stored. The self-running control unit 51 corrects the frequency control amount output by the control unit 22 in consideration of the internal temperature detected by the internal temperature sensor 24 and the temperature characteristics obtained above. In this way, by using the internal temperature detected by the internal temperature sensor 24, the frequency control amount can be appropriately corrected even when the internal temperature is deviated from the target temperature.

  The frequency control amount output by the control unit 22 and the frequency control amount corrected by the self-running control unit 51 are input to the switch 52. The switch 52 outputs the frequency control amount output by the control unit 22 when an appropriate reference signal is available, and outputs the frequency control amount output by the self-running control unit 51 when an appropriate reference signal is not available. To do.

  The frequency control amount output from the self-running control unit 51 is determined in consideration of environmental changes (specifically, temperature changes). An accurate reference signal can be continuously output.

  In addition, the self-running control unit 51 of the present embodiment can perform the correction considering the time change rate of the temperature described in the first embodiment. In addition, the heating control unit 26 of the present embodiment can perform control to increase the target temperature based on the external temperature described in the second embodiment. In addition, the self-running control unit 51 of the present embodiment can perform control for predicting the internal temperature based on the external temperature and changing the follow-up speed and the like described in the third embodiment.

  As described above, the reference signal generator 10 of the present embodiment includes the VCXO 23, the internal temperature sensor 24, and the control unit 22. The VCXO 23 is disposed in the constant temperature bath 30. The internal temperature sensor 24 detects an internal temperature that is the temperature in the thermostat 30. The control unit 22 compares the reference signal and the signal output from the oscillation unit to obtain a phase difference, and controls the VCXO 23 based on the phase difference and the internal temperature detected by the internal temperature sensor 24.

  As a result, the temperature around the VCXO 23 can be accurately obtained as compared with a configuration in which a temperature sensor is installed outside the thermostat 30, so that the frequency of the reference signal output by the VCXO 23 can be controlled more accurately. Accuracy can be improved.

  The preferred embodiment of the present invention has been described above, but the above configuration can be modified as follows, for example.

  The oscillation unit constituting the reference signal generator 10 may not be the VCXO 23. For example, TCXO (temperature compensation type crystal oscillator) or OCXO may be used. In this case, instead of the peak temperature, a performance upper limit temperature is obtained as necessary (or the performance upper limit temperature is examined based on specifications, etc.) and set as a target temperature in the heating control unit 26. The oscillation unit may be a DCO (digitally controlled oscillator) such as an atomic oscillator (rubidium oscillator) other than quartz or an NCO (numerically controlled oscillator).

  In the above embodiment, a PLL circuit that compares phase differences is used, but an FLL circuit that compares frequency differences can also be used. In this case, the tracking speed indicates a speed at which the frequency difference is brought close to zero.

  The above embodiment and the modification are configured to generate a reference signal based on a signal from a GPS satellite, but can be appropriately changed as long as the configuration uses a GNSS (Global Navigation Satellite System). For example, it can be changed to a configuration in which a reference signal is generated based on a signal from a GLONASS satellite or a GALILEO satellite. Further, it may be configured to acquire a reference signal from an external device.

  The GPS receiving unit 21 can be changed to a configuration that generates a signal other than 1 Hz such as PP2S as a reference signal instead of 1PPS. Further, the GPS receiver 21 may be arranged outside the reference signal generator 10 instead of inside.

  Each unit included in the reference signal generation device 10 may be configured by software instead of being configured as hardware.

10 Reference Signal Generator 21 GPS Receiver 22 Control Unit 23 VCXO (Oscillator)
24 Internal temperature sensor 25 Heater (heating part)
26 Heating Control Unit 27 Frequency Dividing Unit 28 External Temperature Sensor 30 Constant Temperature Bath

Claims (9)

An oscillating unit disposed in a thermostat;
An internal temperature sensor that detects the internal temperature, which is the temperature in the thermostat,
A reference signal and a signal output from the oscillating unit are compared to obtain a phase difference or frequency difference, and the oscillation is based on the phase difference or frequency difference and the internal temperature detected by the internal temperature sensor. A control unit for controlling the unit,
A reference signal generation device comprising: The reference signal generator according to claim 1,
A target temperature is set in the thermostat, and the control unit controls the oscillation unit in consideration of a difference between the target temperature and the internal temperature detected by the internal temperature sensor. A characteristic reference signal generator. The reference signal generator according to claim 1 or 2,
The control unit obtains a temperature characteristic that is a change in the frequency of the oscillation unit based on a change in the internal temperature when the reference signal and a signal output from the oscillation unit are synchronized. Reference signal generator. The reference signal generator according to claim 3, wherein
The control unit obtains an apex temperature that is a temperature at which the function indicating the temperature characteristic takes an extreme value based on the obtained temperature characteristic. The reference signal generator according to any one of claims 1 to 4, wherein
The reference signal generator according to claim 1, wherein the control unit controls the oscillating unit so that a change in frequency based on a temporal change rate of the internal temperature is removed. A reference signal generator according to any one of claims 1 to 5,
Equipped with an external temperature sensor that detects the external temperature, which is the temperature outside the thermostat,
The control unit acquires the external temperature detected by the external temperature sensor, acquires the internal temperature detected by the internal temperature sensor, and considers the change in the internal temperature based on the change in the external temperature. A reference signal generator for controlling the oscillation unit. An oscillating unit disposed inside the thermostat;
A heating unit for heating the inside of the thermostat;
An internal temperature sensor that detects the internal temperature, which is the temperature in the thermostat,
An external temperature sensor that detects an external temperature that is the temperature outside the thermostat; and
A heating control unit that compares the internal temperature detected by the internal temperature sensor with a set target temperature to obtain a temperature difference, and controls the heating unit based on the temperature difference;
A reference signal and a signal output from the oscillating unit to obtain a phase difference or a frequency difference, and a control unit that controls the oscillating unit based on the phase difference or the frequency difference;
With
The reference signal generator according to claim 1, wherein the heating control unit increases the target temperature when the external temperature detected by the external temperature sensor becomes equal to or higher than a threshold value. The reference signal generator according to claim 7,
The reference signal generator according to claim 1, wherein the threshold is a temperature higher than the target temperature. The reference signal generator according to claim 7 or 8,
The control unit acquires the external temperature detected by the external temperature sensor, acquires the internal temperature detected by the internal temperature sensor, and considers the change in the internal temperature based on the change in the external temperature. A reference signal generator for controlling the oscillation unit.

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