阅读说明：本技术 振荡装置 (Oscillating device ) 是由 古幡司 于 2019-03-25 设计创作，主要内容包括：本发明提供一种在使用石英振子,根据外部时钟信号来使频率稳定的振荡装置中,即便当外部时钟已中断时,也使被输出的振荡频率稳定的技术。在根据石英振子10的振荡频率及频率设定值来输出频率信号的振荡装置中,设置有求出与振荡装置的输出频率和外部时钟信号的频率差对应的差值的频率差检测部207、及温度检测部。而且,在正获取外部时钟信号的期间中,根据由频率差检测部207所求出的差值的经时变化、及检测温度的经时变化,求出老化系数(a1)与温度特性系数(a2)。进而,在延期期间中,使用老化系数(a1)与温度特性系数(a2)来算出频率校正值,并将所述频率校正值与频率设定值相加。(The invention provides a technology for stabilizing the output oscillation frequency even if the external clock is interrupted in an oscillation device using a quartz resonator and stabilizing the frequency according to the external clock signal. An oscillator that outputs a frequency signal based on the oscillation frequency of the quartz resonator 10 and a frequency set value is provided with a frequency difference detection unit 207 that obtains a difference corresponding to the frequency difference between the output frequency of the oscillator and an external clock signal, and a temperature detection unit. While the external clock signal is being acquired, the aging coefficient (a1) and the temperature characteristic coefficient (a2) are determined from the temporal change in the difference value determined by the frequency difference detection unit 207 and the temporal change in the detected temperature. Further, during the delay period, a frequency correction value is calculated using the aging coefficient (a1) and the temperature characteristic coefficient (a2), and the frequency correction value is added to the frequency set value.)

1. An oscillation device including an oscillation unit that outputs a frequency signal in accordance with a frequency set value, the oscillation unit using a quartz resonator, the oscillation device comprising:

a frequency difference detection unit that obtains a difference value corresponding to a frequency difference between an external clock signal acquired from the outside and the frequency signal output from the oscillation unit;

a temperature detection unit that detects a temperature of an environment in which the quartz resonator is disposed;

a correction value calculation unit that calculates a frequency correction value to be added to the frequency setting value so that the frequency corresponding to the frequency setting value matches the frequency of the frequency signal;

an adding unit that adds the frequency setting value input to the oscillating unit and the frequency correction value acquired from the correction value calculating unit; and

a correction coefficient calculation unit that calculates an aging coefficient indicating a rate of change in the frequency correction value per unit time and a temperature characteristic coefficient indicating a rate of change in the frequency correction value per unit temperature, based on a change in the difference value obtained by the frequency difference detection unit and a change in the detected temperature detected by the temperature detection unit with time;

the correction value calculation unit calculates the frequency correction value based on the difference detected by the frequency difference detection unit while the external clock signal is being acquired, and calculates the frequency correction value using the aging coefficient and the temperature characteristic coefficient while the external clock signal is being interrupted.

2. The oscillation apparatus of claim 1,

the oscillation section includes a phase-locked loop circuit section including a voltage-controlled oscillator, and a direct digital synthesizer that outputs a frequency signal for reference of the phase-locked loop circuit section corresponding to the frequency setting value by inputting the frequency setting value and a reference clock,

the quartz resonator is provided in an oscillation circuit that outputs the reference clock of the direct digital synthesizer.

3. The oscillation apparatus of claim 1,

the oscillation unit includes an oscillation circuit provided with the quartz resonator.

4. The oscillation apparatus according to claim 1, characterized by comprising:

a heater unit that heats an environment in which the quartz resonator is installed; and a heater control unit that adjusts an output of the heater unit so that the temperature detected by the temperature detection unit reaches a preset target temperature.

5. The oscillation apparatus of claim 1,

the frequency of the frequency signal has a rate of change of 1 ppt/sec or less with respect to the frequency corresponding to the frequency set value.

6. The oscillation apparatus of claim 1,

the correction coefficient calculation unit calculates the aging coefficient based on a change amount of the frequency correction value in an aging measurement period in which a change rate of the detected temperature in a preset time is equal to or less than a preset minimum temperature change rate.

7. The oscillation apparatus of claim 6,

the correction coefficient calculation unit calculates the temperature characteristic coefficient based on a temperature change factor frequency correction amount obtained by subtracting an aging factor frequency correction amount from a change amount of the frequency correction value in a temperature characteristic measurement period, the temperature characteristic measurement period being a period in which a change rate of the detected temperature is greater than the minimum temperature change rate, the aging factor frequency correction amount being obtained based on the aging factor calculated in the aging measurement period before the start of the temperature characteristic measurement period and an elapsed time of the temperature characteristic measurement period.

8. The oscillation apparatus of claim 1,

the correction coefficient calculation unit obtains a plurality of aging coefficients and a plurality of temperature correction coefficients by repeating the calculation of the aging coefficients and the temperature correction coefficients with the elapse of time, and the correction value calculation unit calculates the frequency correction value based on an average value of the aging coefficients and an average value of the aging coefficients.

9. The oscillation apparatus of claim 1,

comprising a temperature adjustment mechanism for changing the temperature of the environment in which the quartz resonator is disposed,

the temperature adjustment means changes the temperature of the environment in which the quartz resonator is disposed, while the correction coefficient calculation unit calculates the temperature correction coefficient to obtain the temporal change in the difference and the temporal change in the detected temperature.

Technical Field

The present invention relates to an oscillation device using a quartz resonator.

Background

For example, a base station of a mobile communication system of a mobile phone, a terrestrial broadcasting system, or the like requires high frequency stability. In this regard, as a technique for generating a frequency signal with higher stability, for example, patent document 1 describes an oscillation device (oscillation clock circuit) for acquiring an external clock signal (synchronization signal) with high frequency stability from a Global Positioning System (GPS) and calibrating the frequency signal (multiplied correction frequency signal) generated by using a quartz oscillator (the term described in patent document 1 is also described in parentheses).

In an oscillation device that uses such an external clock signal to achieve frequency stability, there are cases where the external clock signal (hold) cannot be received when a malfunction occurs in a device or a transmission path. If a delay occurs as described above, the external clock signal cannot be used, and thus a problem arises in generating a frequency signal with high stability.

Therefore, in the oscillation device described in patent document 1, attention is paid to a temperature change or a temporal change which is a factor affecting the stability of the frequency signal. In the delay period, a calibration signal calculated using the number of years elapsed from the crystal oscillator or the ambient temperature as a parameter is used instead of the external clock signal, and the influence of the temperature change or the temporal change is compensated for, thereby obtaining a stable frequency signal.

Patent document 2 describes an Oven Controlled crystal oscillator (OCXO) that oscillates a quartz resonator in an environment in which temperature adjustment is performed to obtain an oscillation frequency corresponding to a frequency set value. The OCXO calculates a frequency correction value for canceling temporal variation of the oscillation frequency based on a correspondence between the accumulated elapsed time of oscillation after the start of oscillation of the crystal oscillator and the oscillation frequency, and corrects a frequency set value, thereby obtaining a stable oscillation frequency.

Further, patent document 3 describes an oscillation device that oscillates a first oscillation circuit based on an external clock signal acquired from a GPS to obtain a frequency corresponding to a frequency set value. In addition, a second oscillation circuit for obtaining a frequency corresponding to the frequency setting value is provided separately from the first oscillation circuit. When the external clock signal is being received, an approximation formula for predicting the influence of the temporal change in frequency is obtained from time-series data of a difference value corresponding to the frequency difference between the frequency of the external clock signal and the frequency obtained from the second oscillation circuit. Further, the following techniques are described: when the external clock signal has been interrupted, the first oscillation circuit is oscillated using, as the internal clock signal, the frequency of the second oscillation circuit obtained by correcting the frequency setting value using the correction value calculated from the approximation equation and the elapsed time.

As described above, various techniques have been proposed for obtaining a frequency signal with high stability even during a delay period, and on the other hand, there is an increasing demand for frequency stability during this period.

Disclosure of Invention

Problems to be solved by the invention

The present invention has been made under such circumstances, and provides a technique for obtaining a frequency with higher stability even when an external clock signal is interrupted in an oscillation device in which a frequency is stabilized based on the external clock signal using a quartz resonator.

Means for solving the problems

An oscillation device according to the present invention is an oscillation device including an oscillation unit that outputs a frequency signal based on a frequency set value, the oscillation unit using a quartz resonator, the oscillation device including:

a frequency difference detection unit that obtains a difference value corresponding to a frequency difference between an external clock signal acquired from the outside and a frequency signal outputted from the oscillation unit;

a temperature detection unit that detects a temperature of an environment in which the quartz resonator is disposed;

a correction value calculation unit that calculates a frequency correction value to be added to the frequency setting value so that the frequency corresponding to the frequency setting value matches the frequency of the frequency signal;

an adding section that adds the frequency setting value input to the oscillating section and the frequency correction value acquired from the correction value calculating section; and

a correction coefficient calculation unit that calculates an aging coefficient indicating a rate of change in the frequency correction value per unit time and a temperature characteristic coefficient indicating a rate of change in the frequency correction value per unit temperature, based on a change with time of the difference value obtained by the frequency difference detection unit and a change with time of the detected temperature detected by the temperature detection unit;

the correction value calculation unit calculates a frequency correction value based on the difference detected by the frequency difference detection unit while the external clock signal is being acquired, and calculates the frequency correction value using the aging coefficient and the temperature characteristic coefficient while the external clock signal is being interrupted.

ADVANTAGEOUS EFFECTS OF INVENTION

The present invention provides an oscillation device using a quartz resonator and including an oscillation unit that outputs a frequency signal according to a frequency set value, the oscillation device including a frequency difference detection unit that obtains a difference corresponding to a frequency difference between an external clock signal input from the outside and the frequency signal output from the oscillation unit, and a temperature detection unit that detects a temperature of an environment in which the quartz resonator is disposed. In addition, while the external clock signal is being acquired, an aging coefficient indicating a rate of change in the frequency correction value per unit time and a temperature characteristic coefficient indicating a rate of change in the frequency correction value per unit temperature are determined from a temporal change in the difference value determined by the frequency difference detecting unit and a temporal change in the detected temperature. Further, in a period in which the external clock signal cannot be acquired, a frequency correction value is obtained from the aging coefficient and the temperature characteristic coefficient, and the frequency correction value is added to the frequency setting value. Therefore, even when the external clock signal cannot be received, the frequency signal output from the oscillation unit can be stabilized.

Drawings

Fig. 1 is a block diagram showing an oscillation device according to an embodiment of the present invention.

Fig. 2 is a flowchart showing a learning operation for calculating a correction coefficient.

Fig. 3 is a timing chart relating to an operation at the time of calculation of the correction coefficient.

Fig. 4 is a flowchart showing a flow of an operation of correcting the frequency set value.

Fig. 5 is a timing chart related to an operation of correcting the frequency setting value during a period in which the GPS signal is interrupted.

Fig. 6 is a block diagram showing an example of an oscillation device according to another embodiment.

Detailed Description

[ summary of embodiments ]

Before describing the embodiments of the present invention in detail, the present invention will be briefly described in the following. Fig. 1 is a block diagram showing the overall configuration of an oscillation device according to an embodiment. A portion indicated by reference numeral 200 in fig. 1 is a PLL circuit portion having an oscillation function using a Phase Locked Loop (PLL). Reference numeral 201 denotes a Direct Digital Synthesizer (DDS) that outputs a frequency signal (reference signal) for reference used in the PLL.

The reference clock for operating the DDS 201 uses the oscillation output of the first oscillation circuit 1 denoted by symbol 1 in fig. 1. Therefore, as a result, in order to improve the frequency stability of a frequency signal output from a Voltage-Controlled crystal Oscillator (VCXO) 100 as an oscillation unit, the reference clock must be stabilized.

Therefore, in the oscillation device of the embodiment, the temperature of the environment in which the first quartz resonator 10 provided in the first oscillation circuit 1 is placed is detected, the correction value is calculated using the detected temperature, and the frequency set value is added to the frequency set value of the reference clock input to the DDS 201. This stabilizes the reference signal output from the DDS 201.

In the present embodiment, a heater circuit (heater section) 5 is provided to fix the temperature of the environment in which the first quartz resonator 10 is placed, and the output Δ F of the oscillation frequency difference detection section 3 described later, which corresponds to the detected temperature, is used to control the heater circuit 5.

Further, the oscillation device according to the present embodiment has a function of acquiring a signal of 1 pulse per second (pps) (hereinafter, also referred to as a GPS signal) from the GPS as an external clock signal. During the period when the GPS signal is being acquired, the frequency of the GPS signal is compared with the frequency of the frequency signal output from the PLL circuit unit 200, a frequency correction value is calculated from a difference corresponding to the obtained frequency difference, and the frequency correction value is used to correct the frequency setting value input to the DDS 201. By using the GPS signal having high frequency stability in this manner, the frequency of the frequency signal output from the PLL circuit unit 200 (hereinafter also referred to as an output frequency) can be stabilized.

Further, the oscillation device of this example learns a frequency change (aging) due to the elapse of time from the start of use of the first quartz resonator 10 and a frequency change due to a temperature change of the environment in which the first quartz resonator 10 is disposed, while the GPS signal is being acquired. Further, correction coefficients for compensating for these frequency variations are respectively obtained. In addition, the structure is as follows: even during a delay period in which the GPS signal cannot be acquired, the frequency correction value is calculated from the learned correction coefficient, and the frequency correction value is added to the frequency setting value, thereby stabilizing the reference signal output by the DDS 201.

[ Overall description of embodiments ]

Hereinafter, a detailed configuration of the oscillation device of the present embodiment will be described. As shown in fig. 1, the oscillation device includes a first quartz resonator 10 and a second quartz resonator 20. The first quartz resonator 10 and the second quartz resonator 20 have, for example, the following configurations: two divided regions are provided on a common long quartz plate Xb, and electrodes 11 and 12 (electrodes 21 and 22) for excitation are provided on both the front and back surfaces of each divided region (vibration region).

The first and second quartz resonators 10 and 20 are connected to the first and second oscillation circuits 1 and 2, respectively. The oscillation outputs of the first and second oscillation circuits 1 and 2 are harmonics (harmonics) of the first and second quartz oscillators 10 and 20, for example. In this example, it can be said that the first quartz resonator 10 and the second quartz resonator 20 are part of the temperature detection unit, in order to use a signal corresponding to the difference in the frequencies of the two oscillation outputs as the temperature detection signal. As will be described later, the temperature detection unit is used for controlling the power supplied to the heater circuit 5 included in the oscillation device or calculating a frequency correction value in the delay period. As described above, the oscillation output from the first oscillation circuit 1 is used as the reference clock of the DDS 201.

An oscillation frequency difference detection unit 3 is provided on the rear stage side of the first oscillation circuit 1 and the second oscillation circuit 2. In summary, the oscillation frequency difference detection unit 3 is a circuit unit for extracting a difference between Δ fr and a difference between the oscillation frequency F1 of the first oscillation circuit 1 and the oscillation frequency F2 of the second oscillation circuit 2, that is, a frequency difference detection value F2-F1- Δ fr (Δ F). Δ fr is the difference between f1(f1r) and f2(f2r) at a reference temperature of, for example, 25 ℃.

Here, an example of the difference between f1 and f2 is, for example, several MHz. In this example, it is established by calculating Δ F, which is the difference between the value (F2-F1) corresponding to the difference between F1 and F2 and the value (F2 r-F1 r) corresponding to the difference between F1 and F2 at a reference temperature of, for example, 25 ℃, by using the oscillation frequency difference detecting unit 3. In the present embodiment, more specifically, the value obtained by the oscillation frequency difference detection unit 3 is { (f 2-f 1)/f1} - { (f2 r-f 1r)/f1r }. However, the output of the oscillation frequency difference detection unit 3 is not shown in the figure.

An adder unit 6 is provided downstream of the oscillation frequency difference detection unit 3. The adder 6 acquires a temperature set value (target temperature) from a microcomputer 90 described later, and calculates a difference between the temperature set value and the frequency difference detection value Δ F. As shown in fig. 1, a loop filter 61 corresponding to an integrating circuit unit is provided at a stage subsequent to the adder unit 6. Further, a Pulse Width Modulation (PWM) interpolation unit 62 that converts a digital signal into a Pulse signal of a fixed time is provided at a stage subsequent to the loop filter 61. A Low Pass Filter (LPF) 63 is provided at a stage subsequent to the PWM interpolation section 62, and outputs from the PWM interpolation section 62 are averaged to input a dc voltage corresponding to the number of pulses as the output to the heater circuit 5. The digital signal corresponding to the detected temperature output from the loop filter 61 is input to a microcomputer 90 described later. The loop from the oscillation frequency difference detection section 3 to the LPF 63 constitutes a heater control section of this example.

The PLL circuit section 200 compares the phase of the reference signal output from the DDS 201 with the phase of the clock obtained by dividing the output of the VCXO 100 by the frequency divider 204 by the phase comparison section 205, and simulates the phase difference as the obtained comparison result by the charge pump 202. The simulated signal is input into the loop filter 206 and controlled in a PLL-stable manner. The DDS 201 inputs the oscillation output from the first oscillation circuit 1 as a reference clock. As will be described later, the DDS 201 is configured to input the corrected frequency setting value to which the frequency correction value is added by the adder 42.

The oscillation device of the present embodiment includes, for example, a frequency difference detection unit 207, and the frequency difference detection unit 207 detects a frequency difference between a GPS signal of 1pps, which is an external clock signal, and an output frequency output from the VCXO 100. The frequency difference detection unit 207 is configured, for example, as follows: the frequency signal output from the VCXO 100 is divided, and the frequency difference between the divided frequency signal and the GPS signal is output to the microcomputer 90 as a difference. For example, when the frequency setting value is 10MHz, the frequency signal from the VCXO 100 is divided by one hundred thousand, and frequency difference detection is performed with respect to the GPS signal (1 pps). If sufficient resolution is obtained, the frequency difference detection unit 207 may multiply the GPS signal by, for example, 10MHz instead of dividing the frequency signal, and detect the frequency difference.

As shown in fig. 1, the microcomputer 90 includes: a correction value calculation unit 92, a correction coefficient calculation unit 93, a memory 94, and a timer 95. Reference numeral 91 in fig. 1 denotes a bus. The oscillation device of the present example calculates a frequency correction value from a GPS signal acquired from the GPS and corrects the frequency setting value, but as described above, a delay in interruption of the GPS signal may occur.

On the other hand, there is an increasing demand for stabilizing the output frequency also during the delay period. For example, when the output frequency is 10MHz as described above, it is required that the phase shift amount is stable to about 1.5 μ s or less even when the delay lasts for 24 hours. This corresponds to a rate of change of the output frequency with respect to the frequency set value (more specifically, "frequency corresponding to the frequency set value") of 17.35 ppt/sec or less.

Therefore, as described above, in the oscillation device of the present example, the correction coefficient calculation unit 93 calculates the correction coefficient for calculating the frequency correction value used in the delay period in which the GPS signal is not acquired, during the period in which the GPS signal is being acquired. In this case, conventionally, frequency change due to aging is compensated for. However, it is known that in order to perform extremely high-precision frequency correction of 1 ppt/sec or less, it is necessary to calculate a frequency correction value that can compensate for a frequency change accompanying a minute temperature change due to slowness of control, shaking, or the like even in an environment in which temperature control is being performed by the heater circuit 5.

From the above viewpoint, the correction coefficient calculation unit 93 of the present example has a function of obtaining an aging coefficient (a1) for compensating for a change in the frequency correction value due to aging of the first quartz resonator 10 and a temperature characteristic coefficient (a2) for compensating for a change in the frequency correction value due to a change in the temperature of the first quartz resonator 10. The aging coefficient (a1) and the temperature characteristic coefficient (a2) calculated by the correction coefficient calculation unit 93 are stored in the memory 94.

While the GPS signal is being acquired, the correction value calculation unit 92 calculates a frequency correction value from the difference output from the frequency difference detection unit 207. In the delay period in which the GPS signal is not acquired, the correction value calculation unit 92 calculates the frequency correction value from the detected temperature T acquired by the loop filter 61 and the elapsed time τ measured by the timer 95 using the aging coefficient (a1) and the temperature characteristic coefficient (a2) stored in the memory 94.

The microcomputer 90 outputs the temperature set value to the adder 6.

Next, the operation of the oscillation device including the above-described structure will be described. First, an operation during a period in which a GPS signal is being acquired will be described. When the power supply of the oscillation device is turned on to start the oscillation device, the first quartz resonator 10 and the second quartz resonator 20 oscillate and obtain oscillation outputs, respectively. The microcomputer 90 outputs a frequency set value, the DDS 201 operates based on the oscillation output (reference clock) from the first oscillation circuit 1 and the frequency set value, and the DDS 201 outputs a reference signal. Then, the frequency of the VCXO 100 is controlled based on the result of phase comparison between the reference signal from the DDS 201 and the frequency signal from the VCXO 100.

Here, the oscillation device of this example compares the frequency signal (actually, the frequency-divided signal obtained by frequency-dividing the frequency signal) output from the PLL circuit unit 200 with the frequency of the GPS signal of 1pps, using the frequency difference detection unit 207. At this time, although the frequency control is being performed by the PLL circuit unit 200, when the frequency difference is detected, the reference signal to be compared with the frequency signal may be shifted from the frequency corresponding to the frequency setting value. The reasons for this phenomenon include: the first quartz resonator 10 for outputting the reference clock has an influence of aging, a change in oscillation frequency due to delay in temperature control by the heater circuit 5, or the like.

On the other hand, while the GPS signal is being acquired, the frequency difference from (the frequency-divided signal of) the frequency signal from the PLL circuit unit 200 can be determined using an extremely stable GPS signal of 1 pps. Therefore, the actual frequency of the frequency signal being output from the PLL circuit section 200 is obtained from the frequency difference (difference), and the frequency set value is corrected so that the offset is cancelled from the offset between the actual frequency and the frequency corresponding to the frequency set value. This makes it possible to obtain a stable frequency signal regardless of the influence of aging or temperature change on the first quartz resonator 10 side.

The correction value calculation unit 92 calculates a frequency correction value based on the above-mentioned findings, and outputs the frequency correction value to the addition unit 42. The frequency setting value and the frequency correction value are added by the addition unit 42 and input to the DDS 201. As a result, the influence of the frequency offset on the reference clock side is eliminated, and a frequency signal of an accurate frequency corresponding to the frequency set value can be output.

In contrast to the above operation, if a factor causing a frequency shift on the reference clock side and the degree of influence of each factor are incorrectly grasped during a delay period in which a GPS signal cannot be acquired, a frequency correction value with high accuracy cannot be calculated. Therefore, the oscillation device of the present example performs a learning operation of acquiring the correction coefficient (the aging coefficient (a1) and the temperature characteristic coefficient (a2)) for calculating the frequency correction value in the delay period in advance during the period in which the GPS signal is being acquired.

The correction value calculation unit of this example calculates the frequency correction value using, for example, a linear sum of linear equations represented by the following equation (1).

Δh＝(a1)×(Δτ)+(a2)×(ΔT)…(1)

Where Δ h is a change amount of the frequency correction value, a1 is an aging coefficient (a change rate of the frequency correction value per unit time), Δ τ is an elapsed time, a2 is a temperature characteristic coefficient (a change rate of the frequency correction value per unit temperature), and Δ T is a change amount of the detected temperature (temperature change amount).

The correction coefficient calculation unit 93 of this example learns the aging coefficient (a1) during an aging measurement period in which the influence of temperature changes is small. Further, a period in which the temperature change occurs is referred to as a temperature characteristic measurement period, and the temperature characteristic coefficient is learned using the aging coefficient that has been learned in the aging measurement period.

The learning operation will be described below with reference to the flowchart of fig. 2. First, when the oscillation device is started, the device stands by for, for example, 6 hours without learning the correction coefficient for the initial aging (step S11). As shown in equation (1), the correction value calculation unit 92 uses a linear equation of the correction coefficient (aging coefficient, temperature characteristic coefficient) and each variable (elapsed time, temperature change amount) when calculating the frequency correction value. On the other hand, immediately after the power supply of the oscillation device is turned on, the relationship between the elapsed time due to the aging of the first quartz resonator 10 and the frequency correction value may not be the relationship expressed by the linear expression. Therefore, the standby time is about 6 hours after the power is turned on (initial aging standby period).

When waiting for a predetermined time, the change in the frequency correction value corresponding to the elapsed time is approximately related to the change in the frequency correction value by a linear expression.

Next, a determination is made as to whether or not a GPS signal is being acquired (step S12). At this time, if the GPS signal is not acquired, the system stands by until the GPS signal can be acquired (step S12; NO).

Then, if the GPS signal can be acquired (step S12; YES), it is determined whether or not the predetermined aging measurement period Deltat has elapsed (step S13). If the aging measurement period Δ t has not elapsed (step S13; no), the apparatus waits while checking the state in which the GPS signal is being acquired (step S12; yes → step S13; no).

Here, the following description will be made with reference to fig. 3 as well as step S13. Fig. 3 is a timing chart showing temporal changes in the frequency correction value and the detected temperature after the GPS signal is acquired. Time t0 in fig. 3 represents the start time of step S13.

As shown in fig. 2, when the aging measurement period Δ T (denoted as Δ T1 in fig. 3) has elapsed (step S13; yes), the period (the change rate of the detected temperature per unit time (| Δ T/Δ T |) in the aging measurement period Δ T) is obtained, and it is determined whether or not the minimum temperature change rate Tmin that becomes the threshold value has been exceeded (step S14).

The minimum temperature change rate Tmin is a temperature change rate per unit time that can be determined that the change in the detected temperature is almost negligible, and is stored in the memory 94, for example. An example is a case where the minimum temperature change rate Tmin is set to a value of, for example, 0.1 ℃/hour or less. Then, when the change rate of the detected temperature per unit time does not exceed the minimum temperature change rate Tmin (| Δ T/Δ T | < Tmin) (step S14; NO), the aging factor is calculated (step S15).

The aging factor (a1) is calculated using the frequency correction value Δ h1 during the time Δ t1 from the time t0 to the time ta, as shown in fig. 3, for example. In the interval 1 from the time t0 to the time ta, it is determined that the change in the detection temperature (aging measurement period) is almost negligible. Therefore, even when the oscillation frequency of the first quartz resonator 10 has changed, it can be determined that the change in the oscillation frequency is caused by aging. Therefore, it can be said that the change Δ h1 in the frequency correction value in the period of the section 1 is also caused by the aging of the first quartz resonator 10.

As shown in equation (1), in this example, the frequency correction value of the first quartz resonator 10 that depends on aging is approximated by a linear expression using the amount of change in the elapsed time and the detected temperature as variables. As described above, the change in the detection temperature can be ignored during the aging measurement period. Therefore, by substituting the amount of change Δ h1 in the frequency correction value and the elapsed time Δ t1 into equation (1) and performing a modification with the second term on the right set to zero, the aging coefficient (a1) indicating the rate of change in the frequency correction value per unit time can be calculated from equation (2) below.

a1＝Δh1/Δt1…(2)

The correction coefficient calculation unit 93 performs the calculation, and updates the aging coefficient (a1) already stored in the memory 94, for example (step S15). Also, the GPS signal is acquired, and the action is repeated as long as the rate of change of the detected temperature does not exceed the minimum rate of change of temperature (| Δ T/Δ T | < Tmin) (step S12; YES → step S13; YES → step S14; NO → step S15).

Then, when it is determined that the change rate of the detection temperature is equal to or greater than the minimum temperature change rate (| Δ T/Δ T | ≧ Tmin), the temperature characteristic coefficient is learned with the view of the start of the temperature characteristic measurement period (step S14; YES). For example, in the section 2 from the time ta to the time tb in fig. 3, since the detection temperature changes, | Δ T1/Δ T1| ≧ Tmin, this corresponds to the temperature characteristic measurement period.

On the other hand, since the temperature change of the environment in which the first quartz resonator 10 is placed may depend on the temperature change of the external environment, it may not be possible to predict when the temperature characteristic measurement period ends. In this case, for example, after waiting for a predetermined measurement waiting time Δ T ' (step S16), a change rate (| Δ T/Δ T ' |) of the detected temperature per unit time in the measurement waiting time Δ T ' is obtained, and it is determined whether or not the minimum temperature change rate Tmin is exceeded (step S17).

When the temperature change rate is equal to or greater than the minimum temperature change rate Tmin (| Δ T/Δ T' | ≧ Tmin) (step S17; yes), the temperature change of the environment in which the first quartz resonator 10 is placed continues, and the temperature characteristic measurement period continues, so that the standby state is maintained (step S17; yes → step S16).

After that, as shown in fig. 3, the detection temperature is fixed at the time tb, for example, after a time Δ t2 elapses from the time ta. In this case, the minimum temperature change rate is less than Tmin, and the temperature characteristic measurement period ends (step S17; NO). Then, the temperature characteristic coefficient (a2) is calculated using the amount of change Δ h2 in the frequency correction value acquired during the temperature characteristic measurement period in the section 2 (step S18).

In an environment in which the temperature rise and fall of the environment in which the first quartz resonator 10 is placed occur continuously, the determination regarding the change rate of the detected temperature may be performed, or the temperature characteristic coefficient may be calculated at each timing of the temperature rise process and the temperature fall process by determining the positive and negative values of the temperature change amount (Δ T).

As described above, the oscillation device of the present example stabilizes the oscillation frequency of the first oscillation circuit by heating the environment in which the first quartz resonator 10 is placed by the heater circuit 5 and controlling the temperature. However, the temperature of the environment in which the first quartz resonator 10 is placed may vary due to delay in temperature control or the like when a rapid temperature change in the ambient temperature occurs. As a result, when the oscillation frequency of the first oscillation circuit 1 (the reference clock of the DDS 201) changes, a frequency difference may occur between the frequency-divided frequency signal of the output frequency and the GPS signal of 1pps, and a change in the frequency correction value may occur. It can be understood that the variation of the frequency correction value in the section 2 (temperature characteristic measurement period) shown in fig. 3 includes the variation of the frequency correction value due to aging of the first quartz resonator 10 (aging factor frequency correction amount) and the variation of the frequency correction value due to the temperature change (temperature change factor frequency correction amount).

Here, for example, in a relatively short period of about several hours or several days, the value of the aging coefficient (a1) may not change greatly and may be stable over time. In the case where the period from the section 1 to the section 2 shown in fig. 3 corresponds to such a period in which the aging coefficient is stable over time, the aging factor frequency correction amount in the period of the section 2 can be estimated using the aging coefficient calculated in the section 1. Therefore, the aging factor frequency correction amount in the period is subtracted from the change amount Δ h2 of the frequency correction value in the section 2, thereby obtaining the temperature change factor frequency correction amount between the time ta and the time tb.

Specifically, the aging factor frequency correction amount for the section 2 is obtained by multiplying the time Δ t2 for the section 2 by the aging coefficient (a1) updated in the section 1, which has been stored in the memory 94. Further, using the relationship of equation (1), the temperature-change-factor frequency correction amount in the section 2 is obtained by subtracting the aging-factor frequency correction amount (Δ t2) × (a1) from the frequency correction amount Δ h2 in the period. When these values are transformed in place of the formula (1), the temperature characteristic coefficient (a2) is obtained by the following formula (3).

a2＝{Δh2－(Δt2)×(a1)}/ΔT…(3)

The correction coefficient calculation unit 93 performs the calculation and updates the temperature characteristic coefficient (a2) already stored in the memory 94.

Thereafter, in the section 3 from time tb to time tc shown in fig. 3, since the detected temperature is substantially constant, it is determined that the above-described operation of calculating the aging factor is performed during the aging measurement period (step S12 to step S15).

According to the operation described above, the aging coefficient and the temperature characteristic coefficient used in the delay period are calculated using the frequency correction value obtained based on the result of comparison with the GPS signal.

Next, an operation of outputting a frequency signal from the oscillation device including the use of the aging coefficient and the temperature characteristic coefficient will be described with reference to the flowchart of fig. 4 and the timing chart of fig. 5.

After the start of the oscillation device (start), in a period in which the GPS signal can be acquired (step S21; yes), a frequency correction value is calculated from a frequency difference (difference) between the frequency signal output from the PLL circuit unit 200 and the GPS signal of 1pps, and the frequency correction value is added to the frequency set value (step S27).

On the other hand, if the GPS signal acquisition is not possible (step S21; no), it is checked whether or not the correction coefficients (aging coefficient and temperature characteristic coefficient) calculated during the GPS signal acquisition period can be used (step S22). The usable judgment reference is, for example, a judgment as to whether or not the correction coefficient is stored in the memory 94. In addition, when the average value of the correction coefficients calculated a plurality of times is used as described later, it is determined whether or not the number of correction coefficients used for calculation of the average value reaches a preset number.

When it is determined that the aging factor or the temperature characteristic factor cannot be used (no in step S22), the correction is performed using, for example, the frequency set value of the frequency correction value acquired immediately before the period in which the GPS signal cannot be acquired (step S28), and the process returns to the acquisition confirmation of the GPS signal (step S21).

On the other hand, when the aging factor and the temperature characteristic factor can be used (step S22; yes), the acquisition of the GPS signal and the availability of the correction factor are checked before the predetermined correction value adjustment time (i.e., elapsed time) Δ τ elapses (step S23; no → step S21; no → step S22; yes). Then, when the correction value adjustment time (elapsed time) Δ τ has elapsed, it is determined whether or not the rate of change (| Δ T/Δ τ |) of the detected temperature per unit time exceeds the minimum temperature change rate Tmin, based on the amount of change Δ T of the detected temperature in the correction value adjustment time (elapsed time) Δ τ (step S24).

For example, the section 4 from the time td to the time te shown in fig. 5 is "| Δ T/Δ τ | < Tmin", the change in the detected temperature is small, and Δ T can be regarded as zero. The correction value adjustment time Δ τ may be set to a period shorter than the aging measurement period and the temperature coefficient measurement period Δ t described above, and the operation of calculating and setting the frequency correction value may be repeated little by little. However, in order to facilitate understanding of the knowledge of the frequency correction value calculation, the correction value adjustment time (elapsed time) Δ τ 4 to the correction value adjustment time (elapsed time) Δ τ 6 shown in fig. 5 are indicated by intervals of the same degree as the aging measurement period, the temperature coefficient measurement period Δ t1 to the aging measurement period, and the temperature coefficient measurement period Δ t3 described with reference to fig. 3.

In this way, when the temperature change is small (step S24; no), the frequency correction value is calculated by substituting the correction value adjustment time (elapsed time) Δ τ 4 into only the first term of the above-described equation (1) obtained using the aging coefficient (a1) and the temperature characteristic coefficient (a2) that have been read from the memory 94. Thereby, a frequency correction value using only the aging coefficient is calculated (Δ h4 in fig. 5), and the frequency correction value is used for correction of the frequency setting value (step S25).

On the other hand, when the ambient temperature of the first quartz resonator 10 changes as in the section 5 from the time te to the time tf shown in fig. 5, it is determined that the change rate of the detection temperature per unit time is equal to or greater than the minimum temperature change rate (| Δ T2/Δ τ 5| ≧ Tmin) (step S24; yes). In this case, the frequency correction value is calculated by substituting both the correction value adjustment time (elapsed time) Δ τ 5 and the temperature change amount Δ T2 into equation (1) obtained using the aging coefficient (a1) and the temperature characteristic coefficient (a2) that have been read out from the memory 94.

Thus, a frequency correction value (Δ h5 in fig. 5) using both the aging coefficient and the temperature characteristic coefficient is calculated, and the frequency correction value is sent to the adding unit 42 to be used for correction of the frequency set value.

Further, in the section 6 from the time tf to the time tg shown in fig. 5, since the temperature is fixed, the frequency correction value Δ h6 is calculated from the correction value adjustment time (elapsed time) Δ τ 6 and the aging factor (a1) of the section 6, taking the temperature change amount Δ T as zero.

According to the above embodiment, in the oscillation device which outputs a frequency signal based on a frequency set value using the oscillation frequency of the first quartz resonator 10 as a reference clock, the frequency difference detection unit 207 which obtains a difference corresponding to the frequency difference between (the frequency-divided signal of) the output frequency of the oscillation device and the GPS signal of 1pps is provided. Further, the temperature of the environment in which the first quartz resonator 10 is placed is detected. While the GPS signal is being acquired, an aging coefficient (a1) for calculating a correction value for correcting frequency variation caused by aging of the first quartz resonator 10 and a temperature characteristic coefficient (a2) for calculating a correction value for correcting frequency variation caused by temperature change of the first quartz resonator 10 are obtained. In the delay period, a frequency correction value is calculated using the aging coefficient and the temperature characteristic coefficient, and the frequency correction value is added to the frequency setting value. Therefore, even during a delay period in which the GPS signal cannot be acquired, the output frequency can be stabilized.

Here, in the learning using the aging coefficient or the temperature characteristic coefficient described in fig. 2, the correction coefficient (a2) repeatedly calculated in the past may be stored in the calculation step of the correction coefficient (the aging coefficient or the temperature characteristic coefficient) (step S15, step S18) a plurality of times in the latest order. Further, the frequency correction value may be calculated using an average value of a plurality of correction coefficients including the newly calculated correction coefficient and the correction coefficient calculated in the past. The frequency correction value can be calculated by using the average value of the aging coefficient and the temperature characteristic coefficient calculated for a plurality of times, so that the correction accuracy of the output frequency can be improved.

The present invention is not limited to the embodiments described with reference to fig. 1 to 5, and can be applied to any oscillation device that uses a quartz resonator and obtains an oscillation output based on a frequency set value.

Fig. 6 shows an example of an oscillation device 500 according to another embodiment. The oscillation device 500 of the present example uses an oscillator (oscillation unit) 501 provided with a quartz resonator (not shown) and outputs a frequency signal corresponding to an inputted frequency set value. In the oscillator 501, an environment in which the quartz resonator is placed is heated to a fixed temperature by a heater circuit (heater portion) 502. Therefore, the oscillation device 500 including the oscillator 501 is an OCXO.

Examples of the oscillator 501 include: the oscillator includes an oscillation circuit including a Colpitts circuit (Colpitts circuit), and an oscillator to which a control voltage of the Colpitts circuit is input via a variable capacitance diode. In this case, the control voltage corresponds to a frequency set value, and the output frequency of the oscillator 501 is adjusted in accordance with the control voltage. The oscillation device 500 includes the microcomputer 90 having the functions of the correction value calculation unit and the correction coefficient calculation unit described above, and a frequency difference detection unit 207.

For example, the frequency difference detecting section 207 acquires a frequency difference (difference) between the frequency signal (frequency-divided signal) that has been output from the oscillator 501 and the GPS signal of 1pps, and inputs the frequency difference into the microcomputer 90. The oscillator 501 includes a temperature detector 503, and the detected temperature obtained by the temperature detector 503 is input to the microcomputer 90. The microcomputer 90 adjusts the output of the heater circuit 502 in accordance with the detected temperature to fix the temperature of the oscillator. In the oscillation device 500 having such a configuration, a stable frequency signal can be output by performing the learning operation using the correction coefficient (aging coefficient, temperature characteristic coefficient) described with reference to fig. 2 and the calculation and setting operation using the frequency correction value described with reference to fig. 4.

In addition, the present invention can be configured as follows: when the temperature characteristic coefficient (a2) is obtained, the temperature of the environment in which the quartz resonator (fig. 1 and 6) is placed can be varied by the temperature adjustment means such as the heater unit (heater circuit 502) described above. When the temperature characteristic coefficient (a2) is obtained, the accuracy of the obtained temperature characteristic coefficient may be deteriorated even when the temperature change of the quartz resonator is small. Further, in an oscillation device having a high resolution of frequency change with respect to temperature change, a frequency signal may appear to oscillate with respect to a slight temperature change, and accuracy of a calculated temperature characteristic coefficient may deteriorate. Therefore, the accuracy of the temperature characteristic coefficient can be improved by obtaining the temperature characteristic coefficient by applying a constant temperature difference or more to the quartz resonator, for example, by applying a temperature change of 1 ℃ or more by the above-mentioned temperature adjusting mechanism or the like.

When the temperature characteristic coefficient (a2) is obtained by applying a forced temperature change, for example, in the oscillation device shown in fig. 1, a temperature set value for calculating the temperature characteristic coefficient (a2) for changing the temperature of the environment in which the first quartz resonator 10 is disposed by 1 ℃. Further, the case where the operations of step S14, step S16 to step S18 in fig. 2 are executed during the period in which the temperature is changing can be exemplified.

In the above example, when the frequency correction value is calculated in the delay period, a linear expression using the aging coefficient (a1) and the temperature characteristic coefficient (a2) is used, but the expression used for calculating the frequency correction value is not limited to the linear expression. More preferably, the frequency correction value may be calculated from a linear sum of each correction coefficient and a logarithmic function or an exponential function of the elapsed time (Δ τ) or the temperature change amount (Δ T).