JP2014060682A - Oscillator control method, reference signal generation device and oven-controlled oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oscillator control method that controls an oscillator by using an appropriate tracking rate in consideration of stability of a temperature characteristic.SOLUTION: The oscillator control method includes a signal difference calculation step, a temperature acquisition step, a tracking rate determination step and a control step. The signal difference calculation step determines a phase difference or a frequency difference between an output signal output from the OCXO or a signal based thereon and a reference signal. The temperature acquisition step acquires an ambient temperature of the OCXO. The tracking rate determination step determines a tracking rate that is the rate of reducing the phase difference or frequency difference, on the basis of the temperature acquired in the temperature acquisition step. The control step controls the OCXO so as to reduce the phase difference or frequency difference at the tracking rate determined in the tracking rate determination step.

Description

  The present invention mainly relates to a method for controlling an oscillator provided in a reference signal generator or the like.

  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 signal by controlling the oscillator so that the phase difference approaches zero. Patent Documents 1 to 4 disclose this type of reference signal generator. Hereinafter, the speed at which the phase difference is brought close to zero may be referred to as a tracking speed.

  The reference signal generator of Patent Document 1 reduces the tracking speed when the reference signal output becomes zero, and increases (returns) the tracking speed when the reference signal output returns. Thereby, the influence when the output of the reference signal becomes zero can be reduced, and the output of the oscillator can be stabilized.

  The reference signal generators of Patent Documents 2 and 3 determine the amount of operation given to the oscillator by performing processing by the IP control unit or the like based on the phase difference (following error) between the reference signal and the reference signal. As a result, the oscillator can be controlled so that the tracking error quickly approaches zero and no overshoot occurs.

  The reference signal generator of Patent Document 4 includes a temperature detection unit. The reference signal generator obtains a temperature gradient (temperature change per unit time) from the output of the temperature detection unit, and changes the tracking speed according to the temperature gradient. Specifically, the tracking speed is increased when the temperature gradient becomes equal to or higher than a predetermined threshold. When the temperature gradient is large, it is estimated that the frequency change per unit time becomes large. Therefore, the reference signal can be accurately followed by changing the follow-up speed according to the temperature gradient.

JP 7-202871 A JP 2009-17408 A International Publication No. 2012/29416 JP 2006-157302 A

  Incidentally, the oscillator has a property (temperature characteristic) in which the oscillation frequency changes according to the temperature even when the same control amount (control voltage) is given. Therefore, when the temperature changes, the oscillation frequency of the oscillator changes. Therefore, it is necessary to control the oscillator so that the oscillation frequency is restored.

  Here, since the reference signal generators of Patent Documents 1 to 3 do not perform control for changing the follow-up speed in consideration of temperature, for example, when a sudden temperature change occurs, the PLL lock is released. Sometimes. In this respect, the reference signal generator of Patent Document 4 increases the tracking speed when the temperature gradient becomes large, so that there is a possibility that the PLL lock can be maintained even if a temperature change occurs.

  However, it is known that the temperature characteristic changes in stability according to the temperature around the oscillator. That is, the oscillation frequency is greatly influenced not only by the temperature change amount (temperature gradient) but also by the stability of the temperature characteristics (see FIG. 2A and the like described later). Furthermore, if the temperature characteristics are stable, the oscillation frequency will not change much even if the temperature changes suddenly. On the other hand, if the temperature characteristics are unstable, the oscillation frequency will increase even if the temperature change is slow. Change.

  In other words, the configuration that changes the follow-up speed according to the temperature gradient does not consider the stability of the temperature change, and depending on the conditions, the phase difference from the reference signal becomes large and the PLL lock is released, disturbances, etc. It may be affected greatly.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an oscillator control method for controlling an oscillator using an appropriate tracking speed in consideration of the stability of temperature characteristics.

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 the first aspect of the present invention, the following oscillator control method is provided. That is, the oscillator control method includes a signal difference calculation step, a temperature acquisition step, a follow-up speed determination step, and a control step. In the signal difference calculating step, a phase difference or a frequency difference between an output signal output from the oscillator or a signal based thereon and a reference signal is obtained. In the temperature acquisition step, the temperature around the oscillator is acquired. In the follow-up speed determination step, a follow-up speed that is a speed for reducing the phase difference or the frequency difference is determined based on the temperature acquired in the temperature acquisition step. In the control step, the oscillator is controlled so as to reduce the phase difference or the frequency difference by using the following speed determined in the following speed determining step.

  Thereby, since the temperature characteristic of the oscillator changes according to the temperature, the oscillator can be controlled using the follow-up speed in consideration of the temperature characteristic.

  In the oscillator control method, it is preferable that in the follow-up speed determination step, the follow-up speed to be determined increases as temperature characteristics of the oscillator become unstable.

  As a result, when the temperature characteristics are stable, the follow-up speed is reduced to make it less susceptible to disturbances, and when the temperature characteristics are unstable, the follow-up speed is increased to follow rapid frequency changes due to temperature changes. Can do.

  In the oscillator control method, it is preferable that in the follow-up speed determination step, the follow-up speed is switched stepwise based on the temperature acquired in the temperature acquisition step.

  Thus, the oscillator can be controlled with a simple configuration and at an appropriate tracking speed in consideration of temperature characteristics.

  In the oscillator control method, the following is preferable. That is, at least the first tracking speed and the second tracking speed exist as candidates for the tracking speed determined in the tracking speed determination step. In the follow-up speed determining step, a temperature when switching from the first follow-up speed to the second follow-up speed is different from a temperature when switching from the second follow-up speed to the first follow-up speed.

  Thereby, it is possible to prevent the determined follow-up speed from being switched many times in a short time.

  In the oscillator control method, in the tracking speed determination step, the tracking speed is determined based on the phase difference or frequency difference acquired in the signal difference calculation step in addition to the temperature acquired in the temperature acquisition step. It is preferred that

  Thereby, when the phase difference or the frequency difference is large, control such as increasing the follow-up speed can be performed, so that a more appropriate follow-up speed can be determined.

  According to a second aspect of the present invention, a reference comprising: an oscillator controlled by the oscillator control method; and an output unit that outputs an output signal output from the oscillator or a signal based on the output signal as a reference signal. A signal generator is provided.

  As a result, a reference signal generator capable of controlling the oscillator at an appropriate tracking speed in consideration of temperature characteristics can be realized.

  According to a third aspect of the present invention, there is provided a thermostatic chamber comprising an oscillator controlled by the oscillator control method and covered with a thermostatic chamber, and a heating unit that heats the thermostatic chamber to a constant temperature. An attached oscillator is provided.

  Thereby, the oscillator with a thermostatic chamber which can control an oscillator with the suitable follow-up speed in consideration of the temperature characteristic is realizable.

1 is a block diagram showing a reference signal generator according to an embodiment of the present invention. The graph which shows the temperature characteristic of quartz and OCXO. The graph which shows roughly the behavior of control voltage and phase difference when disturbance occurs when the follow-up speed is low. The graph which shows roughly the behavior of control voltage and phase difference when disturbance occurs when the follow-up speed is high. A table showing the magnitude of the influence of disturbance in association with the tracking speed. The figure explaining the threshold value for changing the tracking speed of OCXO. The graph which shows a mode that a tracking speed is changed based on a phase difference.

  Next, an embodiment of the invention will be described. First, the overall configuration of the reference signal generator 10 will be described with reference to FIG. FIG. 1 is a block diagram schematically showing a reference signal generator 10 according to the present 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 (a), the reference signal generator 10 of the present embodiment includes a GPS receiver 21, a controller 22, an OCXO (Oven Controlled Crystal Oscillator) 23, and a frequency divider. 24 and a temperature sensor (temperature acquisition unit) 25. The control unit 22, OCXO 23, and frequency dividing unit 24 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).

  As shown in FIG. 1B, the OCXO 23 includes a VCO (Voltage Controlled Oscillator) 51, a temperature sensor 52, a heater control unit 53, and a heater 54.

  The VCO 51 is an oscillator that can change the output frequency according to the level of a voltage applied from the outside. Further, the VCO 51 is disposed in a constant temperature bath. The temperature sensor 52 acquires the temperature around the VCO 51 and outputs it to the heater control unit 53.

  The heater control unit 53 controls the heater 54 based on the difference between the temperature acquired from the temperature sensor 52 and a predetermined target temperature. The heater 54 heats the inside of the constant temperature bath under the control of the heater control unit 53. With the above configuration, the inside of the thermostatic chamber can be maintained at the target temperature regardless of the temperature change outside the OCXO 23.

  The output signal output from the OCXO 23 (VCO 51) is output as a reference frequency signal from the output unit 42 to the external user system and also input to the frequency dividing unit 24.

  The frequency dividing unit 24 is configured to divide and convert the reference frequency signal input from the OCXO 23 from a high frequency to a low frequency, and to output the obtained phase comparison signal to the control unit 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 OCXO 23 is 10 MHz, the frequency divider 24 divides the 10 MHz signal output from the OCXO 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 (signal difference calculation step).

  The control unit 22 outputs the phase difference signal to the OCXO 23 after blocking the high frequency component of the phase difference signal and removing noise. Thereby, the OCXO 23 can be controlled so that the phase difference approaches zero (control process). The control unit 22 may be configured to output a comparison result between the output signal of the OCXO 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 OCXO 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 to the 1 PPS signal, the characteristics of the OCXO 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.

  The temperature sensor 25 detects the temperature around the OCXO 23 (outside the thermostatic chamber) (temperature acquisition step). The temperature sensor 25 outputs the detected temperature to the control unit 22. In addition, the temperature acquisition part of this invention is not restricted to the structure which detects the temperature around OCXO23 directly like the temperature sensor 25. FIG. For example, since the heater supplied to the OCXO 23 has a higher power supply as the ambient temperature is lower, the temperature can be acquired by detecting this power. Further, a temperature sensor 52 that detects the temperature around the VCO 51 instead of around the OCXO 23 can be used as the temperature acquisition unit.

  Next, temperature characteristics will be described. FIG. 2 is a graph showing temperature characteristics of quartz and OCXO.

  First, the temperature characteristics of the crystal itself will be described. 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 a pole (zero temperature coefficient point) at about 80 ° C. to 90 ° C. Moreover, below, the temperature when taking a pole is called 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).

  Next, temperature characteristics of the OCXO 23 will be described. In the graph shown in FIG. 2B, the horizontal axis indicates the temperature around the OCXO 23 (the temperature outside the thermostat), and the vertical axis indicates the amount of change in frequency due to temperature change. In the OCXO 23 of the present embodiment, the vertex temperature is set as the target temperature. Thereby, the temperature characteristic of the oscillator can be stabilized regardless of the temperature outside the thermostat.

  However, as the temperature outside the thermostat increases, it becomes difficult to maintain the temperature inside the thermostat at the apex temperature. In the OCXO shown in FIG. 2 (b), when the temperature outside the thermostat exceeds about 75 ° C., the temperature inside the thermostat cannot be maintained at the apex temperature, and the temperature inside the thermostat also depends on the temperature outside the thermostat. It will rise. Therefore, as shown in FIG. 2 (b), OCXO has a temperature characteristic that is stable until the temperature outside the thermostatic bath reaches about 75 ° C., and the temperature characteristic becomes unstable as the temperature exceeds about 75 ° C. Have.

  Next, the influence of disturbance due to the difference in tracking speed will be described. 3 and 4 are graphs schematically showing the behavior of the control voltage and the phase difference when a disturbance occurs when the tracking speed is low and high. FIG. 5 is a table comparing the following speed and the factor of frequency fluctuation.

  FIG. 3A and FIG. 4A show a phase difference caused by the influence of a temperature change and a phase difference caused by the influence of multipath, jamming waves, and the like.

  First, a phase difference that occurs due to a temperature change will be described. When the temperature outside the thermostatic chamber changes, the temperature around the oscillator changes due to the influence, so the frequency changes depending on the temperature characteristics. The phase difference due to a temperature change usually changes slowly when the temperature characteristic is stable, and changes abruptly when the temperature characteristic is unstable.

  When a phase difference occurs due to a temperature change, it is preferable to quickly bring the phase difference close to zero. Here, when the follow-up speed is small, the control unit 22 gradually changes the control voltage (see FIG. 3B). Therefore, when the phase difference changes abruptly, the change cannot be followed quickly, and a relatively large phase difference occurs (see FIG. 3C).

  On the other hand, when the follow-up speed is high, the control unit 22 can greatly change the control voltage (see FIG. 4B). Therefore, even when the phase difference changes rapidly, the change can be quickly followed, and thus the generated phase difference can be suppressed. (See FIG. 4 (c)).

  As described above, as shown in FIG. 5, when the phase difference changes gradually due to a temperature change, the phase difference can be quickly reduced to 0 regardless of the follow-up speed (effect is small). In addition, when the phase difference changes rapidly due to a temperature change, the phase difference can be quickly reduced to 0 (the influence can be reduced) as the follow-up speed increases.

  Next, the phase difference generated due to the influence of multipath or the like will be described. When an abnormal signal is received as a reference signal due to multipath or the like, the phase difference temporarily changes significantly, and after a while, the phase difference is restored (see FIG. 3A, etc.).

  Since the phase difference due to multipath or the like is caused by the fact that a normal reference signal cannot be received, it is preferable not to bring the phase difference close to zero. Here, when the follow-up speed is low, the control voltage is gradually changed, so that the control voltage (frequency) does not change abruptly (see FIG. 3B). In addition, since overshoot does not occur after the influence of multipath or the like is eliminated, the generated phase difference can be suppressed (see FIG. 3C).

  On the other hand, when the follow-up speed is high, the control voltage (frequency) changes abruptly (see FIG. 4B). In addition, since overshoot may occur after the influence of multipath or the like is eliminated, the frequency deviates from a desired value (see FIG. 4C).

  As described above, as shown in FIG. 5, when a multipath or the like occurs, the influence can be reduced as the follow-up speed is reduced.

  Considering the points described above, it is usually desirable to control the oscillator at a small follow-up speed and increase the follow-up speed only when the phase difference changes rapidly due to a temperature change. Here, in the said patent document 4, the structure which performs control which enlarges a follow-up speed when a temperature gradient becomes large is disclosed. However, if the temperature characteristic is unstable as described above, it is necessary to increase the tracking speed even when the temperature gradient is small. If the temperature characteristic is stable, the tracking speed may remain small even when the temperature gradient is large. Therefore, in the configuration of Patent Document 4, the oscillator may be controlled at an inappropriate tracking speed.

  On the other hand, in the present embodiment, the oscillator is controlled using an appropriate tracking speed by determining the tracking speed based on the stability of the temperature characteristics, not the temperature gradient. Hereinafter, a method for determining the follow-up speed will be specifically described with reference to FIG. FIG. 6 is a diagram for explaining a threshold value for changing the tracking speed of the OCXO 23.

In this embodiment, as shown in FIG. 6A, three following speeds V ₁ to V ₃ are prepared as candidates for the following speed (V ₁ <V ₂ <V ₃ ). And the reference signal generator 10 (control part 22) determines the tracking speed used for control of OCXO23 according to the temperature outside a thermostat (following speed determination process).

As described above, since the OCXO 23 can maintain the inside of the thermostatic chamber at the apex temperature when the temperature outside the thermostatic bath is low, the temperature characteristics are stable. Therefore, the OCXO 23 is controlled using V ₁ which is the smallest following speed.

  In this way, when the temperature characteristics are stable, the tracking speed can be reduced to reduce the effects of multipath, etc., and when the temperature characteristics are unstable, the tracking speed is increased to increase the frequency change amount rapidly. Can follow any changes.

  In addition, a threshold is set in the reference signal generator 10, and the tracking speed is switched when the temperature outside the thermostatic chamber exceeds the threshold. In the present embodiment, the threshold value is different between when the temperature rises and when the temperature falls.

That is, as shown in FIG. 6B, when the follow-up speed is V ₁ , the follow-up speed is switched to V ₂ at the timing when the temperature reaches 65 ° C. On the other hand, when the follow-up speed is V ₂ , the follow-up speed is switched to V ₁ when the temperature reaches 55 ° C. Similarly, the thresholds are different when switching between V ₂ and V ₃ .

  Thereby, even when the temperature is around 55 ° C. or around 65 ° C., the follow-up speed can be prevented from being switched many times in a short time.

  Since the temperature characteristics of the oscillator have individual differences, it is preferable to obtain the temperature characteristics in advance for each individual and obtain the threshold value of the tracking speed based on the temperature characteristics.

  Next, a modification of the above embodiment will be described. FIG. 7 is a graph showing how the tracking speed is changed based on the phase difference.

  In the above embodiment, the tracking speed is switched based on the ambient temperature of the OCXO 23 (that is, the temperature characteristics of the OCXO 23). On the other hand, in this modified example, the tracking speed is switched in consideration of the phase difference detected by the control unit 22 in addition to the temperature around the OCXO 23.

  In this modification, a threshold value for the phase difference is set, and the follow-up speed is changed based on whether or not the phase difference detected by the control unit 22 exceeds this threshold value. Note that the phase difference caused by multipath and the like has a characteristic that it temporarily increases greatly and then immediately returns to its original state, so that the tracking speed can be increased when a state exceeding the threshold continues for a predetermined time. preferable. If the phase difference does not decrease even when the follow-up speed is increased, control for further increasing the follow-up speed may be performed.

  On the other hand, when decreasing the follow-up speed, it is preferable that the phase difference is stabilized in the vicinity of zero. Further, by gradually reducing the tracking speed, the phase difference can be brought close to zero quickly while preventing overshoot.

  As described above, the oscillator control method of the present embodiment includes a phase difference calculation step, a temperature acquisition step, a follow-up speed determination step, and a control step. In the phase difference calculation step, the phase difference between the output signal output from the OCXO 23 or a signal based thereon and the reference signal is obtained. In the temperature acquisition step, the temperature around the OCXO 23 is acquired. In the follow-up speed determining step, a follow-up speed that is a speed for reducing the phase difference is determined based on the temperature acquired in the temperature acquiring step. In the control process, the OCXO 23 is controlled using the tracking speed determined in the tracking speed determination process so as to reduce the phase difference.

  Thereby, since the temperature characteristic of OCXO23 changes according to temperature, OCXO23 can be controlled using the follow-up speed in consideration of the temperature characteristic.

  The preferred embodiments and modifications of the present invention have been described above, but the above configuration can be modified as follows, for example.

  The oscillator constituting the reference signal generation device 10 may not be OCXO. For example, (Temperature Compensated Crystal Oscillator, temperature compensated crystal oscillator) may be used, or an atomic oscillator other than crystal (rubidium oscillator) may be used.

  In the said embodiment and modification, although it is the structure which switches a follow-up speed to three steps, two steps may be sufficient and four steps or more may be sufficient. Further, a configuration in which the follow-up speed is continuously changed instead of stepwise can be adopted.

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

  A configuration in which the tracking speed is switched in consideration of not only temperature (stability of temperature characteristics) but also a temperature gradient may be employed.

  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.

DESCRIPTION OF SYMBOLS 10 Reference signal generator 21 GPS receiving part 22 Control part 23 OCXO
24 Dividing part 41 Input part 42, 43 Output part 44 PLL circuit

Claims (7)

A signal difference calculating step for obtaining a phase difference or a frequency difference between an output signal output from the oscillator or a signal based thereon and a reference signal;
A temperature acquisition step of acquiring the ambient temperature of the oscillator;
Based on the temperature acquired in the temperature acquisition step, a tracking speed determination step for determining a tracking speed that is a speed for reducing the phase difference or the frequency difference;
A control step of controlling the oscillator so as to reduce the phase difference or the frequency difference using the tracking speed determined in the tracking speed determination step;
An oscillator control method comprising: The oscillator control method according to claim 1, comprising:
In the tracking speed determining step, the determined tracking speed is increased as the temperature characteristic of the oscillator becomes unstable. The oscillator control method according to claim 1 or 2,
In the follow-up speed determination step, the follow-up speed is switched stepwise based on the temperature acquired in the temperature acquisition step. The oscillator control method according to claim 3, wherein
There are at least a first following speed and a second following speed as candidates for the following speed determined in the following speed determining step,
In the follow-up speed determination step, a temperature when switching from the first follow-up speed to the second follow-up speed is different from a temperature when switching from the second follow-up speed to the first follow-up speed. Oscillator control method. An oscillator control method according to any one of claims 1 to 4, comprising:
In the tracking speed determination step, the tracking speed is determined based on the phase difference or frequency difference acquired in the signal difference calculation step in addition to the temperature acquired in the temperature acquisition step. Control method. An oscillator controlled by the oscillator control method according to any one of claims 1 to 5,
An output unit that outputs an output signal output from the oscillator or a signal based on the output signal as a reference signal;
A reference signal generation device comprising: An oscillator controlled by the oscillator control method according to any one of claims 1 to 5 and covered with a thermostatic chamber,
A heating unit for heating the inside of the thermostatic chamber to a constant temperature;
An oscillator with a thermostatic bath, comprising:

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