JPH11271476A - Reference frequency generating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent frequency accuracy in an automatic running from being deteriorated when reception cannot be made, by accumulating phase difference data where an external reference signal is synchronously compared with an internal voltage controlled crystal oscillator(VCXO) in a normal reception state. SOLUTION: A reference frequency generating device for receiving a time signal with high accuracy from a satellite or the like is provided with, for example, an operation means 40 for calculating a steady frequency deviation, a part 45 for generating automatic run frequency correction data, and the like. Then, the part 45 for generating correction data stores frequency deviation D (n) data from the operation means 40 into a memory with time information in a normal reception state. On the other hand, when no signals can be received, the part 45 calculates the amount of transition regarding the aging of oscillation frequency focs of a VCXO 10 at each specific time based on the stored data. Automatic traveling correction data C (h) being calculated according to the operation are added to frequency control data C (n) being outputted by an operation means 23 for controlling steady frequency, and the fluctuation of the oscillation frequency focs of the VCXO 10 in an automatic traveling state is corrected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reference frequency generator which receives a radio wave from an artificial satellite having a built-in atomic frequency standard or a high-precision time signal similar to the radio signal and generates a high-precision reference frequency. . In particular, it relates to maintaining the reference frequency generated by the internal oscillator with high accuracy when the ultra-high-precision time signal cannot be obtained for a certain period of time.

[0002]

2. Description of the Related Art The prior art is disclosed in Japanese Patent Application Laid-Open No. 08-1461.
No. 66, there is a “reference frequency generator”. As shown in FIG. 5, a configuration example of the reference frequency generator includes a satellite radio receiver 11, a time interval measuring unit 12, a frequency control operation unit 13, an adder 50, and a D / A converter 14 When,
Frequency divider 15 and voltage controlled crystal oscillator (VCXO) 10
, A frequency converter A17, a frequency converter B16, and a temperature sensor 29.

According to the configuration of the prior art described above, in a state where a reference satellite wave is received, a high frequency control algorithm using a digital filter having a long time constant by an estimating operation unit in the frequency control operation means 13 is used. Accurate frequency is always output. However, when satellite radio waves cannot be received for some reason, the control data output immediately before is directly supplied to the D / A converter 14 via the adder 50. However, the fluctuation of the ambient temperature is detected by the temperature sensor 29 and the temperature is appropriately corrected, so that the frequency fluctuation relating to the ambient temperature is canceled.

[0004]

In the above-mentioned conventional configuration, if the state in which satellite radio waves cannot be received for some reason is short, the output frequency accuracy is maintained without any problem, but if the satellite radio waves cannot be received. Is longer than a certain length of time, the output frequency accuracy gradually deteriorates with the passage of time due to the aging rate fluctuation factor of the voltage-controlled crystal oscillator 10. Come. This will be described with reference to the example of FIG.

[0005] The VCXO 10 shows a very slight change in the oscillation frequency with time. FIG. 6 is an explanatory diagram showing a change in the oscillation frequency when the reception failure occurs for a long time when the ambient temperature is assumed to be constant. In the normal reception period of FIG. 6B, the feedback control state is maintained, so that the constant oscillation frequency fosc of FIG. 6A is maintained including the change with time of the VCXO 10. However, if reception becomes impossible for some reason, V
The state shifts to the self-running state by the CXO 10 itself. At this time, V
Since the CXO 10 has a change with time, a frequency shift 105 gradually occurs as time elapses over several hours. Eventually, when reception is restored, the initial oscillation frequency fosc
There is a synchronous transition period for returning to the above, and this period also has the frequency shift 106. Thereafter, the oscillation frequency is restored to the normal oscillation frequency fosc. As described above, in the conventional device configuration, if there is a long non-reception period, the frequency fluctuation becomes large, and there is a problem that the frequency accuracy is deteriorated.

[0006] Incidentally, in mobile communication base stations and the like currently in operation, there is an oscillator whose output timing shifts in a state where satellite radio waves cannot be received, for example, an oscillator of 10 μsec in 8 hours or an oscillator of 7 μsec in 24 hours. . Here, the difference between the former and the latter is due to the difference in the aging rate of the voltage-controlled crystal oscillator used.The voltage-controlled crystal oscillator used in the latter device is older than the former. The rate is about 10 times better, but the price is 2-3 times more expensive. In a communication base station or the like, if the deviation of the output timing of a reference device exceeds a certain allowable amount, the communication device may have to stop functioning. In order to reduce the downtime, it is necessary to use an expensive voltage controlled oscillator, but this is not preferable because it increases the cost of the apparatus. In a mobile communication base station that requires a low price, an expensive voltage-controlled crystal oscillator cannot be used, and downtime when a failure occurs may be long. For this purpose, the stability of the oscillator in a state where satellite radio waves cannot be received is checked in advance by a reference frequency generator or the like. However, since the reference frequency generator itself cannot receive satellite radio waves, a predetermined accuracy cannot be maintained over a long period of time. In this respect, the conventional reference frequency generator has a practical difficulty. Therefore, the problem to be solved by the present invention is to solve the problem of an internal oscillator that is in a self-running state even in a period in which a radio wave from an artificial satellite having a built-in atomic frequency standard or a similar high-precision time signal cannot be obtained. An object of the present invention is to provide a reference frequency generator capable of preventing deterioration of frequency accuracy.

[0007]

First, in order to solve the above-mentioned problems, the configuration of the present invention comprises a voltage-controlled crystal oscillator 10 which receives an ultra-high-precision reference signal from the outside and receives the above-mentioned voltage. In a reference frequency generator that controls a voltage control input terminal of the controllable crystal oscillator 10 and slowly follows an external high-precision reference signal to generate a high-precision reference frequency, in a normal reception state, The phase difference data obtained by synchronously comparing the high-precision reference signal with the internal voltage-controlled crystal oscillator 10 is stored, and in a reception disabled state,
From the accumulated phase difference data, the amount of change with time of the oscillation frequency fosc of the voltage controlled crystal oscillator 10 is specified, and from the amount of change, the voltage controlled crystal oscillator 10 in the free running state is determined.
To compensate for fluctuations over time of the oscillation frequency fosc of
A reference frequency generator characterized in that generation of a high-precision reference frequency is maintained for a long time even in a reception disabled state. According to the above invention, the output frequency of the internal oscillator in a free-running state even in a period in which a radio wave from a satellite having a built-in atomic frequency standard or a similar ultra-high-precision time signal cannot be obtained for a relatively long time. , A reference frequency generator capable of preventing the frequency accuracy from deteriorating with time can be realized.

FIG. 1 and FIG. 7 show a solution according to the present invention. Secondly, in order to solve the above-mentioned problem, the configuration of the present invention includes the voltage-controlled crystal oscillator 10 and outputs a reference timing signal UTC1ppsA every second in response to an ultra-high precision reference signal from the outside. A frequency divider (such as a frequency divider 15 or a synthesizer) for receiving the output frequency fout of the voltage-controlled crystal oscillator 10 and outputting 1 pps of a one-second signal VCXO for synchronization comparison; UTC 1ppsA and 1 second signal VC for comparison
Time interval measuring unit 12 for measuring the time interval with XO1pps
And a steady frequency control calculating means 23 for synchronizing the oscillation frequency of the voltage controlled crystal oscillator 10 from the phase difference of the time interval measuring unit 12. In the high-precision reference frequency generating apparatus which controls the voltage control input terminal of 10 and slowly synchronizes with the external high-precision reference signal, the receiving means detects the reception failure of the external reference signal. A receiving unit having a unit for outputting the disable signal 11stp, and the time interval measuring unit 12
Receiving the measurement data D1 every second from the
1 from the measured data D1 to calculate the current frequency deviation D (n) of the voltage-controlled crystal oscillator 10 and supply the calculated frequency deviation D (n) to the free-running frequency correction data generating unit 45. Firstly, an unreceivable signal 1
In the normal state where there is no 1 stp, the frequency deviation D (n) data from the steady-state frequency deviation calculating means 40 is stored in the memory together with the time information. Based on the history data of the frequency deviation D (n) stored in the memory and the time information, the amount of change of the oscillation frequency fosc of the voltage-controlled crystal oscillator 10 with time is estimated and calculated for each predetermined correction interval time Th. The self-running correction data C (h) calculated by this estimation calculation is added to the frequency control data C (n) output from the steady-state frequency control calculating means 23 at the time when reception is impossible, and the voltage control type C (h) in the self-running state is added. There is a reference frequency generation device including a free-running frequency correction data generation unit 45 that corrects a variation with time of the oscillation frequency fosc of the crystal oscillator 10.

Third, in order to solve the above-mentioned problem, the configuration of the present invention includes a voltage-controlled crystal oscillator 10 which receives an ultra-high-precision reference signal from the outside, and In a reference frequency generator that controls the voltage control input terminal and generates a high-precision reference frequency by slowly and synchronously following an external high-precision reference signal, in a normal reception state, an external high-precision reference signal The phase difference data synchronously compared with the internal voltage controlled crystal oscillator 10 is stored, and in the reception disabled state, the oscillation frequency fosc of the voltage controlled crystal oscillator 10 is calculated from the stored phase difference data.
Of the curve related to the change with time, an estimated correction curve (or estimated correction data sequence) 92 that fits the curve is obtained from this transition curve, and the voltage-controlled crystal oscillator 10 in the self-running state is obtained from the estimated correction curve. There is a reference frequency generation device which is characterized in that the variation of the oscillation frequency fosc over time is corrected, and the generation of a high-precision reference frequency is maintained for a long time even in a reception disabled state.

FIG. 8 shows a solution according to the present invention. Fourth, in order to solve the above-mentioned problem, the configuration of the present invention includes the voltage-controlled crystal oscillator 10 and outputs a reference timing signal UTC1ppsA every one second in response to an ultra-high accuracy reference signal from the outside. A frequency divider (such as a frequency divider 15 or a synthesizer) for receiving the output frequency fout of the voltage-controlled crystal oscillator 10 and outputting 1 pps of a one-second signal VCXO for synchronization comparison; UTC1ppsA and 1 second signal VCXO1pp for comparison
a time interval measuring unit 12 for measuring a time interval with s,
A stationary frequency control computing means for synchronizing the oscillation frequency of the voltage controlled crystal oscillator from the phase difference of the time interval measuring unit;
A high-precision reference frequency generator that controls the voltage control input terminal of the voltage-controlled crystal oscillator 10 to slowly follow an external high-precision reference signal. And receiving means for outputting a reception-disabled signal 11stp that has detected that the reception has failed. Upon receiving the measurement data D1 every one second from the time interval measurement unit 12 during normal reception, the measurement data D1 is stored. Then, there is provided a steady-state frequency deviation calculating means 40 for calculating the current frequency deviation D (n) of the voltage-controlled crystal oscillator 10 from the measurement data D1 and supplying the frequency deviation D (n) to the curve-fit free-running frequency correction data generation unit 120. First, in a normal state where there is no reception impossible signal 11stp, the frequency deviation D from the steady frequency deviation calculating means 40 is calculated.
(N) storing the data in the memory together with the time information;
After receiving the unreceivable signal 11stp, a transition curve obtained by low-pass filtering the history data sequence based on the history data sequence and the time information of the frequency deviation D (n) stored in the memory, that is, a data sequence or a curve. An approximation curve to be fitted is obtained, and an estimated curve or data sequence that is extended by approximating the transition curve is obtained, whereby the oscillation frequency fos of the voltage-controlled crystal oscillator 10 which is in a free-running state after receiving is disabled.
There is a reference frequency generation device including a curve-fit free-running frequency correction data generation unit 120 for estimating and correcting fluctuations due to aging of c.

The curve-fit free-running frequency correction data generating section 120 performs a low-pass filter process by a wavelet transform means to convert a fluctuation transition data sequence or a transition curve relating to a temporal change of the oscillation frequency fosc of the voltage-controlled crystal oscillator 10. The reference frequency generator described above is characterized by extracting and generating estimated correction data.
As the low-pass filter processing by the wavelet transform means, the wavelet transform is performed up to a predetermined α level number, and the data is decomposed into detailed data Hα (β) and smoothed data Lα (β) of each level number.
The reference frequency generator described above is a low-pass filter processing for performing data restoration by performing wavelet inverse transform with (β) as a zero value. The low-pass filter processing by the wavelet transform means includes a predetermined α
Wavelet transform is performed up to the level number to decompose into detailed data Hα (β) and smoothed data Lα (β) of each level number, and one of the decomposed detailed data Hα (β) is averaged for each level number. The above-mentioned reference frequency generator is characterized by low-pass filter processing for restoring data by performing an inverse wavelet transform using an average value.
Further, the wavelet transform is performed using the latest frequency deviation D (n) data of a predetermined time in the frequency deviation D (n) data group from the stationary frequency deviation calculation operation means 40. There is a reference frequency generator described above.

As a receiving means for receiving an ultra-high-precision reference signal from the outside and outputting a reference timing signal UTC 1 ppsA, a satellite for receiving and outputting a reference frequency signal by a radio wave of an artificial satellite having a built-in atomic frequency standard is used. There is the above-mentioned reference frequency generation device which is the radio wave receiver 11. The receiving means for receiving the ultra-high accuracy reference signal from the outside and outputting the reference timing signal NW1ppsA is a synchronous network clock extracting device 11c for receiving and outputting a signal distributed over a communication network or a broadcast network. There is a reference frequency generator.

Fifthly, in order to solve the above-mentioned problem, the configuration of the present invention includes a voltage-controlled crystal oscillator 10 which receives an ultra-high-precision reference signal from the outside to receive the voltage-controlled crystal oscillator 10. In a reference frequency generator that controls a voltage control input terminal and slowly follows an external high-precision reference signal to generate a high-precision reference frequency, the time-dependent change of the voltage-controlled crystal oscillator 10 is represented by a curve. A low-pass filter is applied to the past data sequence, and a curve or a data sequence that fits the curve after the reception failure is obtained from the low-pass filtered data sequence. (For example, a curve-fit free-running frequency correction data generation unit 120).

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings together with embodiments.

FIG. 1 is a first block diagram showing an embodiment of the present invention. In this case, in the reception disabled state, the past time-dependent change of the VCXO 10 is regarded as a linear change, and the estimation correction is performed using a straight line approximating this.
In general, after aging or operation for several hundred to several thousand hours or more, the change over time of VCXO shows a substantially linear change.

This configuration comprises a satellite radio receiver 11, switches 31, 32, a time interval measuring unit 12, a calculating means 23 for steady frequency control, a calculating means 40 for calculating steady frequency deviation, a self-running frequency correction Data generator 45 and adder 5
0, the D / A converter 14, and the voltage-controlled crystal oscillator (V
CXO) 10, a temperature sensor 29, an arithmetic unit 28 for controlling ambient temperature fluctuation, a frequency converter A17, a frequency converter B16, a frequency divider A25, and a frequency divider B26. In this configuration, the satellite radio receiver 11, the time interval measuring unit 12, the D / A converter 14, the voltage controlled crystal oscillator 10, the temperature sensor 29, and the frequency converter A17
, The frequency converter B16 and the frequency divider A25 are substantially the same components as those in the related art.

The satellite radio receiver 11 receives an ultra-high accuracy reference signal from the outside and receives a reference timing signal UTC 1 ppsA.
In this case, it receives satellite radio waves and generates an ultra-high-accuracy one-second reference timing signal UTC1ppsA included in the satellite radio waves. However, there are short-term fluctuations imparted intentionally by the military. An output function of the unreceivable signal 11stp is added to the function of the prior art. That is, it detects that the satellite radio wave cannot be received, and outputs the reception impossible signal 11stp.

The switch A is a component of the present invention,
The reference timing signal UTC 1ppsA in an undefined state is generated by the reception disabled signal 11stp from the satellite radio receiver 11.
Stop output of. In the case where the satellite radio receiver 11 has the above function, it can be deleted.

The time interval measuring unit 12 is a component similar to that of the prior art, and receives an ultra-high-precision reference timing signal UTC1ppsA every second from the satellite radio receiver 11 via the switch A, and 1-second signal VCXO1p obtained by dividing the output frequency fout output from the device to the outside by the frequency divider A25
In response to ps, the time interval between the two is measured, and this measurement data D1 is sequentially and continuously output every second.

The operating means 23 for steady-state frequency control is a component of the present invention, but is almost the same as the operating means 13 for frequency control shown in FIG. That is, using the measurement data D1 of the time interval measurement unit 12, the oscillation frequency of the voltage-controlled crystal oscillator 10 is changed to the reference timing signal UTC1ppsA generated by the satellite radio receiver 11 and the one-second signal VC.
Frequency control data C for feedback-controlling the voltage controlled crystal oscillator 10 so that XO 1 pps has the same phase relationship.
(N) is calculated and output. However, the satellite radio receiver 11
In order to remove phase noise due to radio wave propagation superimposed on the intra-satellite reference timing signal input from the satellite and noise intentionally applied for U.S. military reasons, a digital filter with a long time constant is used gently. Let them follow. still,
This calculation means is realized by a CPU, a DSP, or the like, as in the related art.
The details are described in Japanese Patent Application Laid-Open No. 08-146166, but the operation will be briefly described below. The measurement data D1 from the time interval measurement unit 12 is sequentially stored in an internal buffer memory, and the internal estimation calculation unit calls a past measurement result as needed to perform an estimation calculation. Immediately after power-on or after a long period of time when the intra-satellite reference timing is not obtained for a long time, in order to perform the frequency pull-in operation in a short time, the number N of data used for the estimation calculation is set small and the loop response time is shortened. . When the frequency pull-in operation is performed to some extent, it can be seen that the amount of change per unit time of the time interval measurement data, that is, the frequency error becomes smaller. Therefore, the number N of data used for the estimation calculation is gradually increased, and the loop response time is reduced. To go. Next, in order to convert the result of the estimation operation into frequency control data C (n) of the voltage controlled crystal oscillator 10, a proportional operation by multiplying by a constant P is performed. Immediately after the power is turned on or after the reference timing within the satellite has not been obtained for a long time, the constant P is set large in order to perform the frequency pull-in operation in a short time. When the frequency pull-in operation is performed to some extent, the amount of change in the time interval measurement data per unit time, that is, the frequency error is found to be small, so the constant P is gradually reduced. In order to convert the result of the estimation operation into the frequency control data C (n) of the voltage-controlled crystal oscillator 10, the integral operation is performed by multiplying by the constant I. Immediately after power-on or after a long period of time when the intra-satellite reference timing is not obtained, a large constant is set to perform the frequency pull-in operation in a short time. When the frequency pull-in operation is performed to some extent, it is found that the amount of change in the time interval measurement data per unit time, that is, the frequency error becomes smaller, so the constant I is gradually reduced. In the estimation calculation, when the intra-satellite reference timing generated by the satellite radio receiver 11 is a one-second signal, the time interval measurement unit 12 performs measurement at one-second intervals. The coupling is strengthened so that the voltage-controlled crystal oscillator 10 does not run free while having a long control loop time constant. A so-called feedback control like PLL control is performed. Incidentally, when the satellite radio wave cannot be received and the reception impossible signal 11stp is received, the frequency control data C (n) immediately before the reception failure is held and output.

The adder 50 is a component similar to that of the prior art, and includes a frequency control data C (n) calculated by the steady-state frequency control calculating means 23 and a free-running frequency correction data generator 45 described later. -Running correction data C (h) from
Then, the setting data D5 obtained by adding the temperature correction data D4 from the ambient temperature fluctuation control calculating means 28 to be described later is supplied to the D / A converter 14. However, when the satellite radio wave is in a normal reception state, that is, when there is no reception impossible signal 11stp, the free-running correction data C (h) is zero. Conversely, the unreceivable signal 11
If there is stp, self-running correction data C (h) is added.

The D / A converter 14 is a component similar to that of the prior art, and includes the setting data D5 from the adder 50.
And converts it into a corresponding analog DC voltage V6,
It is supplied to the voltage control input terminal of CXO10.

Voltage Controlled Crystal Oscillator (VCXO) 10
Is a high-stable voltage-controlled crystal oscillator that receives the analog DC voltage V6 and oscillates by oscillating the oscillation frequency fosc corresponding to this voltage.

The temperature sensor 29 and the calculating means 28 for controlling the fluctuation of the ambient temperature are the same as in the prior art. However, the ambient temperature fluctuation control arithmetic means 28 is an arithmetic part relating to temperature control provided in the frequency control arithmetic means 13 in the conventional configuration of FIG. The temperature sensor 29 is disposed at an appropriate portion of the voltage controlled crystal oscillator 10 to detect an ambient temperature. The operation means for controlling ambient temperature fluctuation 28 receives the signal from the temperature sensor 29, and
The temperature correction data D4 for correcting the frequency deviation of the oscillation frequency fosc of 0 accompanying the change in the ambient temperature with high accuracy is obtained and supplied to the adder 50.

The frequency converter A17 is a component similar to that of the prior art. The frequency converter A17 receives the oscillation frequency fosc from the voltage-controlled crystal oscillator 10, receives digital data, and converts it to a desired output frequency fout. For example, there are a frequency synthesizer and a frequency divider.

The frequency converter B16 is a component similar to that of the prior art. The frequency converter B16 receives the output frequency fout from the frequency converter A17, and counts the count clock CLOCK used by the time interval measuring unit 12, for example, several tens of MHz. Output clock. This can be achieved, for example, by a frequency synthesizer. If necessary, this frequency converter B16
May be deleted and the output frequency fout from the frequency converter A17 may be directly supplied to the time interval measuring unit 12.

The frequency divider A25 is a component similar to that of the prior art. The frequency divider A25 converts the output frequency fout into a VCXO1 pps obtained by dividing the output frequency fout into a clock in units of one second.
Feed to 2.

The frequency divider B26 receives the reference timing signal UT
It outputs a clock in units of one second synchronized with C1ppsA. It is a new component and has an output frequency fout.
Is divided into clocks in units of one second.
1 is receiving the radio wave, the output UTC1 of the frequency divider B
In order to output ppsB in the same phase as UTC 1 ppsA, in the frequency dividing process, ppsB is synchronously reset by a 1-second reference timing signal UTC 1 ppsA output from the satellite radio receiver 11. If the satellite radio wave receiver cannot receive the satellite radio wave, the UTC 1ppsA is stopped by the switch A.
Outputs 1 ppsB. This component is not essential and may be deleted as desired.

The calculating means 40 for calculating the steady frequency deviation is an important component of the present invention. This is because, in case the satellite radio receiver 11 cannot receive the satellite radio wave, it receives the measurement data D1 every second from the time interval measurement unit 12, accumulates this data, and detects the fluctuation of the accumulated measurement data D1. ,
Current frequency deviation D (n) of voltage controlled crystal oscillator 10
Is calculated and supplied to the free-running frequency correction data generator 45. In this case, in order to remove phase noise due to radio wave propagation and superimposed noise intentionally applied for military reasons in the United States, a moving average process described below using a large number of continuous past measurement data D1 is used. Is performed.
The calculation of the frequency deviation D (n) is based on the measurement data D1
It is calculated each time it is received, but if desired, when it receives the unreceivable signal 11stp output by the satellite radio receiver 11,
Using the stored past measurement data D1 group, the frequency deviation D required by the free-running frequency correction data generation unit 45 is calculated.
(N) may be calculated and output.

A specific example of the calculation of the frequency deviation D (n) output from the stationary frequency deviation calculating means 40 will be described below. Here, as shown in FIG.
The measurement data D1 output by the time interval measurement unit 12 in (1) is p (1), and thereafter, every one second, the time t
The measurement data D1 in (2) is p (2), and the time t
Assume that the measurement data D1 in (n) is p (n).
Here, n is a variable in units of one second indicating a certain measurement time point.
First, using a plurality of continuous M measurement data D1,
This average value q (n) is sequentially obtained and stored in the memory together with the time information. This is a process for increasing the time resolution of the time interval measurement unit 12, improving the measurement accuracy, and reducing the variation. That is, the calculation of the average value q (n) is performed as shown in FIG.
As shown in (a), an average value of a plurality of continuous sample numbers M, for example, M = 20 pieces of measurement data D1 is obtained at predetermined update intervals S, for example, S = 10 second intervals. More specifically, the calculation of the average value for the first time is based on the above p (1) to p (2
A value obtained by adding a plurality of continuous M = 20 pieces to 0) is calculated as an average value q (1), and is stored in the memory together with time t (1) information corresponding to the measurement data. Next S = 10
Seconds later, the average value q (2) calculated from p (1 + 10) to p (20 + 10) and the corresponding time t (2) are stored. After the next 2 × S = 20 seconds, p (1+ (2 × 1
0)) to p (20+ (2 × 10)), and store the average value q (3) and the corresponding time t (3). Thereafter, when the data is sequentially stored in the same manner, a plot of the average value q (n) is obtained as shown in FIG. Further, FIG. 2C shows an envelope plotting a large number of data groups of the average value q (n). In this figure, the fluctuation amount W3 is mainly a fluctuation component due to the above-described phase noise due to the radio wave propagation and the superimposed noise that is intentionally applied. On the other hand, since the fluctuation component related to the temporal change of the target VCXO 10 is small, it cannot be accurately detected due to the influence of the large fluctuation amount W3. Therefore, the next step is performed. In addition, by increasing the number M of the number to be averaged, FIG.
The fluctuation amount W3 shown in (c) is reduced.

Secondly, the change per unit time related to the VCXO 10, that is, the frequency deviation D (n) is calculated based on the time-series data of the plurality of average values q (n). VCXO1
Paying attention to the fact that the value of the variation amount of the fluctuation component related to the time-dependent change of 0 becomes longer as the time becomes longer, for example, as the time interval T, using a long time interval value of T = 24 hours, the frequency deviation D (n Find out). First, as shown in FIG. 3, the change amount Δ between the average value q (n) data of the time interval T which is separated for a long time.
For q (n), a sufficiently large variation is obtained. as a result,
The fluctuation amounts W1 and W2 components are practically negligible. Since the frequency deviation D (n) is the amount of change per unit time, that is, the slope, the formula is D (n) = {q (i) -q (j)} / T, which is calculated from this. This is determined by a predetermined update interval S = 10
It is calculated every second and stored in the memory sequentially. Specifically, in the first frequency deviation D (1), D (1) =
It is calculated as {q (i) -q (j)} / T, and is calculated as the following frequency deviation D (2) = {q (i + 1) -q (j + 1)} / T. Here, q (i) is the average value q (n) data stored in the memory 24 hours ago, and q (j)
Is the current average value q (n) data. The frequency deviation D (n) obtained above is supplied to the free-running frequency correction data generator 45 every 10 seconds. If the average value q (n) of T = 24 hours before has not been accumulated yet, a value of the frequency deviation D (n) = 0 is output.

The free-running frequency correction data generator 45 is an important component of the present invention. First, when satellite radio waves are normally received, the frequency deviation D (n) calculated by the steady-state frequency deviation calculating means 40 is stored in the memory together with the time information. . Second,
After receiving the non-reception signal 11stp from the satellite radio receiver 11, based on the history of the stored frequency deviation D (n) data and the frequency deviation D (n) immediately before the generation of the non-reception signal 11stp, The predetermined correction interval time Th,
For example, self-running correction data C (h) is calculated every Th = 60 seconds and output to the adder 50 via the switch 32. Specific calculation means of the self-running correction data C (h) will be described below.

The self-running correction data C (h) is
Is the correction data for correcting a linear temporal change 102 related to the oscillation frequency fosc of the VCXO 10 which includes the oscillation frequency fosc itself or peripheral circuits.
The correction is performed by adding data to the data supplied to the A converter 14. Here, the oscillation frequency fosc of the VCXO 10
When a change with time when the ambient temperature change is constant is represented by a general function formula, it can be expressed as y (x) = r (x) + G · x + y0. In the function formula of the temporal variation, x is a temporal variable with the self-running start time as a zero value. The r (x) term is a random AC fluctuation component like white noise caused by the crystal oscillator itself and peripheral circuits, which cannot be corrected and its value is considered to be small, and r (x) = 0 far. The G term is a gradient coefficient of the amount of change over time to be corrected and executed in the present invention, and is a term of a linear function that changes linearly. The term y0 is a constant offset value, and corresponds to a deviation amount (offset) from the ideal oscillation frequency fosc which completely matches the reference timing of the satellite radio receiver 11 immediately before the start of the self-running. This is a value obtained by multiplying the value of the deviation D (n) by a certain coefficient, but in a normal normal tracking control state, it can be set to y0 ≒ 0 because it is almost close to zero. Using the above-mentioned function equation of the temporal variation, the self-running correction data C (h) can be expressed as C (h) = KGGx. In this equation, K represents the self-running correction data C (h)
This is a sensitivity coefficient corresponding to the data given to the setting register of the / A converter 14, and varies depending on the amount of change in the oscillation frequency with respect to the control voltage of the VCXO 10, the voltage resolution output by the D / A converter 14, and the like. Since the sensitivity coefficient K differs for each device, it is determined in advance for each device.

The improvement effect of the self-running correction data C (h) will be described with reference to FIG. The vertical axis is the D / A set value, and the horizontal axis is the time axis. The linear change with time 102 having a slope is a change in the D / A set value that needs correction with the change with time of the VCXO 10. First, the section from the beginning of the time axis to the point A in FIG. 4 is a normal reception period, and the control data C (n) value subjected to the feedback control by the steady frequency control calculating means 23 is given. Is corrected and matched on the transition line of the time-dependent change 102, and the original high-precision accuracy of the oscillation frequency fosc is maintained and secured. Second, the section from FIG. 4A to FIG.
This is a non-reception period, and as a result of adding the above-described self-running correction data C (h) of the present invention, correction is performed substantially along the transition line of the temporal change 102. Actually, as shown at the time point in FIG. 4B, a slight correction error 103 may occur, but practically, a sufficiently stable and excellent accuracy of the oscillation frequency fosc is maintained. Note that this slight correction error 103
Although it depends on the length of the non-reception period, there is obtained a great advantage that it is greatly reduced to 1/10 to 1 / tens of tens in comparison with the conventional case without correction. As a result, there is obtained an advantage that the operation can be performed with practical accuracy for several hours or more. Third, in the section after the time point of FIG.
Is corrected by the self-running correction data C (h), and as a result, the change of the temporal change 102 is a difference of only a slight correction error 103. Therefore, the feedback frequency converges from this slight difference state in a short time and returns to the original high-accuracy state oscillation frequency fosc. This slight correction error 103
The time required for convergence depends on the period during which reception is not possible, but there is also a great advantage that it is greatly reduced to 1/10 to 1 / tens of tens in comparison with the conventional case without correction. In this respect, the effect of the present invention is obtained.

The switch 32 is a component of the present invention, and is turned off when the satellite radio receiver 11 is receiving satellite radio waves, and outputs a zero value to the adder 50.
If there is an unreceivable signal from the satellite radio receiver 11,
The switch 32 is turned on, and supplies the self-running correction data C (h) to the adder 50. The self-running frequency correction data generator 4
If 5 has the above function, it can be deleted.

According to the configuration of the present invention described above, the reference frequency generator that has achieved excellent frequency stability using satellite radio waves, after the state where satellite radio waves cannot be received,
By having a means that can correct the fluctuation of the oscillation frequency due to the temporal change of the free-running oscillation frequency of the crystal oscillator,
Since a stable oscillation frequency can be output for a longer time than before, an effect that excellent frequency stability can be maintained for a long time can be obtained.

The means for realizing the present invention is not limited to the above embodiment. For example, in the case of FIG. 1, the satellite radio receiver 11 uses a satellite radio wave as a reference time signal. However, the present invention is not limited to this. The used signal source may be used as the reference time signal. Specifically, as shown in the configuration example shown in FIG. 7, the satellite radio receiver 1 shown in FIG.
There is a configuration example in which 1 is replaced with a synchronous network clock extracting device 11c and a frequency distributed in a subordinate synchronous network adopted in a communication network or a broadcast network is used as a reference signal. In the case of communication networks and broadcasting networks, in particular, despite the fact that the distribution source generates stable short-, medium-, and long-term frequencies with the atomic frequency standard, multiple long-distance transmission cables and microwave relay lines are used. If the distribution is repeated and transmitted, short-term phase fluctuations are superimposed on the route (path). As a result, the distribution destination cannot accurately reproduce the frequency of the distribution source. In addition, since the reference frequency distribution in the subordinate synchronous network uses the same line as the information data, it is scrambled as a discontinuous PCM signal such as an AMI code and the like. , It is necessary to use an extraction circuit such as a PLL or a resonance circuit. However, even with this extraction circuit, there is a disadvantage that short-term phase fluctuations are likely to be superimposed, and reception may be temporarily disabled. Therefore, as shown in FIG.
A continuous reference signal is reproduced from a reference signal in the form of an M signal by a clock extracting circuit, and is divided into a 1 second reference timing signal NW1ppsA by a frequency divider to generate a time interval measuring unit 12.
As described above, a stable oscillation frequency can be output for a long time as described above. When the interruption of the input PCM signal is detected, the reception disable signal 11stp similar to the above is output. According to the configuration of the present invention described above, it is possible to generate a reference signal with excellent frequency accuracy in response to a signal distributed in the subordinate synchronous network, and to stop the reference signal from the subordinate synchronous network line for some reason. However, there is an advantage that a sufficiently stable frequency or timing can be continuously generated and supplied for a long time.

In the above-described invention means,
Change amount Δq at time interval T = 24 hours shown in FIG.
Since (n) is a sufficiently large change amount, the fluctuation amount W
Although the description has been made on the assumption that the W1 and W2 components are practically ignored, a process for further removing the fluctuation amounts W1 and W2 components may be added if desired. That is, first, in order to reduce and eliminate the fluctuation W1 fluctuation of the average value q (i) 24 hours ago, the average value q (i) which is data for a predetermined time section before q (i) time point A, for example, 1 hour section data. The values obtained by further averaging the data of 360 points i) to q (i-360) are represented by q (i
i), and secondly, the fluctuation amount W2 at the time of reception failure
In order to reduce and eliminate fluctuations, average values q (j) to q (j-36), which are predetermined one-hour interval data before time point B of q (j).
The value obtained by further averaging the data of the 360 points of 0) is determined as q (jj), and the frequency deviation at the time of non-reception is D (n) = {q (ii) -q (jj)} / It may be calculated as T. In this case, as a result of removing the fluctuation amounts W1 and W2 almost, there is an advantage that the frequency deviation can be satisfactorily corrected even when the time interval T = 24 hours is set to a relatively short time interval of, for example, about 5 hours. .

FIG. 8 is a second block diagram showing an embodiment of the present invention. In this case, in the unreceivable state, the past time-dependent change of the VCXO 10 is regarded as a curvilinear variation, and a past curve fit curve approximating this is used to perform estimation correction after the unreceivable. As a result, it is possible to maintain the generation of a highly accurate reference signal for a long time equal to or longer than that described above.

This configuration is different from the configuration shown in FIG.
But the others are the same.

The curve-fit self-running frequency correction data generation section 120 is provided with the self-running frequency correction data generation section 45 described above.
For example, using a multi-resolution analysis method using a wavelet transform for the linear estimation correction method based on
(N) is used to remove an unnecessary high-frequency noise component in a change transition of this data group by using a past data group of huge frequency deviation D (n) stored in an internal memory;
A self-running correction data C (h), which generates an approximate curve that fits the curve relatively gently and generates correction data for estimation correction after reception failure, is sequentially supplied to the adder 50 via the switch 32.

First, a wavelet transform, in particular, a Haar
A so-called low-pass filter function for removing unnecessary high-frequency noise components using a wavelet transform will be briefly described. It should be noted that the Haar wavelet transform method itself is a well-known technique, and it is known that the wavelet transform has an operation in the decomposition direction and a reversible operation in the restoration direction.

FIG. 9 shows an example of the process of calculating the decomposition direction of the wavelet transform using the Haar basis function. In this figure, for ease of explanation, the input data string
This is an example of the number of samples, where 3 levels (hierarchy)
Can be decomposed into One of the decomposed Lα (β) is used as smooth data (Smooth Data), and the other Hα (β) is used as detail data (Detail Data). Here, α is a multiresolution analysis level (level number), and β is a time series number of the input data sequence. Level 1 based on the input data strings a1 and a2 (α =
The operation on the detail data H1 (1) side of 1) is H1 (1) =
According to (a1-a2) / 2. This is a change value between two consecutive data and has a meaning of a high frequency component.
The calculation on the level 1 (α = 1) smoothed data L1 (1) side is based on L1 (1) = (a1 + a2) / 2. This is an average value between two consecutive data and has a meaning of a low frequency component. Similarly, receiving the input data strings a3 to a8, the level 1 decomposition operation is performed, and the detailed data H1
(Β) and smoothed data L1 (β) are obtained. The first-stage smoothed data L1 (β) is a low-pass filter (L
PF) is obtained as time-series data having the effect.

Next, at the level 2 (α = 2), the smoothed data L1 (β) obtained at the level 1 is received and the detailed data H2 (β) and the smoothed data L2 (β) are received in the same manner as described above.
Is calculated.

Finally, at level 3 (α = 3), the smoothed data L2 (β) obtained at level 2 is received and the detailed data H3 (β) and the smoothed data L3
The calculation of (β) is performed. Note that this last smoothed data L3
(1) is the average value of all the input data string data a1 to a8, and if necessary, this average value data is self-propelled correction data C for performing the estimation correction by the straight line in FIG.
(H) may be used.

By the way, the wavelet transform has reversibility that the inverse of the decomposition direction, that is, the inverse wavelet transform can be performed. Next, a state in which the inverse operation is performed in the reverse order of level 3, level 2, and level 1 shown in FIG. 10 from the smoothed data and the detailed data decomposed in FIG. By this operation, the same restored output data string as the original input data strings a1 to a8 is obtained. A desired low-pass filter is realized by utilizing the feature that can perform the inverse wavelet transform. That is, when performing the inverse operation in FIG. 10, the low-pass filter can be realized by performing the inverse wavelet transform operation with the detailed data up to the desired level number as zero or an average value. In other words, a low-pass filter having desired characteristics can be realized depending on which level number up to which detailed data is set to zero or an average value. Here, the average value is a value obtained by adding and averaging the detailed data of the level number.

For example, high-frequency components are removed by performing a restoration operation with the level 2 detailed data H 2 (β) and level 1 detailed data H 1 (β) shown in FIG. It will be obtained as the time series data obtained. The deeper the level number is, the stronger the low-pass filter characteristic up to lower frequency components is.

In the above description, the input data string is an example of 8 samples. However, the actual number of data used for the Haar wavelet transform depends on the limitation of the memory capacity. For example, the input data string of 216 = 65536 words is used. Use In this case, the exponent is 16, that is, the multiresolution analysis level of level α = 16.

Based on the above wavelet transform,
The operation of the curve-fit free-running frequency correction data generator 120 will be described below.

First, the section from point A to point B on the time axis of FIG. 11 is a normal reception period of several tens of hours. During this long period, the frequency deviation D (n) sequentially output from the steady-state frequency deviation calculating means 40 is stored in the internal memory. If desired, a predetermined plurality of words may be added and averaged and stored as average value data. FIG.
D is a plot of the past transition over a long period of time, and is an example in which the temporal change of the VCXO 10 gradually transitions in a curved manner, including a short-term fluctuation. In FIG. 11D, elements that fluctuate up and down in the short term are phase noise due to radio wave propagation, superimposed noise intentionally applied for military reasons in the United States, and the like, and need to be removed.

Secondly, the section from point B to point C in FIG. 11 is a non-reception period. In this period, a past data string 91 (FIG.
H), the past data string 91 is extended, and an estimated correction curve 92 (FIG. 11J) that continuously fits the curve is obtained, and self-running correction data C based on the estimated correction curve 92 is obtained.
(H) are sequentially supplied to the adder 50 in a predetermined time unit.
As a result, the hatched portion in FIG. 11M is estimated and corrected. For this purpose, a wavelet transform up to a predetermined level number is performed based on the stored data of FIG. 11D obtained during the normal reception period. Here, assuming that data is received every 10 seconds,
It is assumed that 17280 points in the past 48 hours from point A to point B have been stored in the internal memory. In this case, the number of data used for the wavelet transform is 163 of the exponent 14
Since the number of words is 84, the data of the latest 16384 words (for example, section K in FIG. 11) existing immediately before the reception is disabled is used.

First, FIG. 11F is a plot of a data string resulting from filtering up to level number 2, for example, FIG. 11G is a plot of a data string resulting from filtering processing to level number 4, for example, and FIG. , For example, is a plot of a data string as a result of filtering up to level number 6. In this figure, it can be seen that the plot of FIG. 11H is a desirable curve from which short-term fluctuations have been removed, and this filtered data sequence 91 is used as a reference. Alternatively, an approximate curve fit curve may be obtained instead of the data sequence 91 and used as a reference.

Next, there are three correction modes for generating the self-running correction data C (h) to be sequentially supplied to the adder 50 from the filtered data string 91 or the approximate curve fit curve 91. The first correction mode is a method in which the filtered data string 91 is applied as it is to the estimated correction data string as the estimated correction data string 92, and the filtered data string 91 is used as it is as free-running correction data C (h).
Are sequentially supplied to the adder 50. Note that the self-running correction data C (h) output at the beginning at the time of FIG. 11B is output by holding the frequency control data C (n) immediately before reception by the steady-state frequency control calculating means 23, so that the zero value is set to zero. It goes without saying that the offset processing is performed so as to be the initial value. In the second correction mode, the filtered data sequence 91
This is a method of applying a result obtained by calculating the estimated correction data sequence 92 on the extension line that fits the above. The third correction mode is a method in which a curve fit curve 91 obtained by extending the curve fit curve 91 obtained above is applied as an estimated correction data sequence 92.

The change over time of the VCXO 10 is not limited to the change shown in FIG. 11, but shows different characteristics for each device. FIG. 12 shows an example of a curve of another past data string. A curve 201 is an example of a transition to a convergence tendency, and FIG.
1, the curve 202 is an example that changes almost linearly, the curve 203 is an example that changes divergently, and the curve 2
04 is an example of transition to a periodic fluctuation tendency. Any of these can be estimated and corrected by the above-described three correction modes. Each shaded portion in FIG. 12M indicates a correction amount to be estimated and corrected.

In the above wavelet transform, Haar
Although a specific example of implementing a low-pass filter by the wavelet transform has been shown and described, other wavelet transforms or FFTs that can receive an input data sequence and output a data sequence converted into a desired low-pass filter characteristic as desired are described. You may implement using processing. Also, in the frequency deviation D (n) data group received from the steady frequency deviation calculating means 40, the latest frequency deviation D (n) data of the latest predetermined time, for example, about 5 to 10 hours is used. Wavelet transform may be performed.

According to the configuration of the present invention described above, the reference frequency generator that has achieved excellent frequency stability using satellite radio waves, after the state where satellite radio waves cannot be received,
By providing a means for compensating fluctuations in the oscillation frequency due to the time-dependent change in the free-running oscillation frequency of the crystal oscillator, excellent frequency stability can be achieved even when the time-dependent change related to the VCXO10 changes nonlinearly. Can be maintained over a long period of time. Note that the realizing means of the present invention is not limited to the configuration of FIG. 8 in which the above-described curve is used to estimate and correct, and as described above, the frequency distributed in the subordinate synchronous network employed in a communication network or a broadcast network is used. The present invention is also applicable to a configuration used as a reference signal.

[0057]

According to the present invention, the following effects can be obtained from the above description. As described in the above embodiment, the present invention uses a signal source, such as a satellite radio wave or a subordinate synchronous network, which includes a large amount of short-term phase fluctuation but is stable for a long time as a reference time signal. Means that the reference frequency generator that has achieved excellent frequency stability can correct fluctuations in the oscillation frequency due to the temporal change in the free-running oscillation frequency of the crystal oscillator after the state in which the reference time signal cannot be received. Is provided, a stable oscillation frequency can be output for a longer time than before, so that there is a great advantage that excellent frequency stability can be maintained for a long time. Therefore, the technical effect of the present invention is great, and the industrial economic effect is also great.

[Brief description of the drawings]

FIG. 1 is a configuration example of a reference frequency generation device according to the present invention.

2A and 2B are diagrams illustrating calculation of an average value and a diagram illustrating fluctuation of the average value according to the present invention.

FIG. 3 is a diagram illustrating calculation of a frequency deviation according to the present invention.

FIG. 4 is a diagram illustrating calculation of self-running correction data according to the present invention.

FIG. 5 is a configuration example of a conventional reference frequency generator.

FIG. 6 is a diagram illustrating a conventional change in oscillation frequency due to reception failure.

FIG. 7 is a configuration example of another reference frequency generation device according to the present invention.

FIG. 8 is a configuration example of another reference frequency generation device according to the present invention.

FIG. 9 is an explanatory diagram of a decomposition operation process by a wavelet transform according to the present invention.

FIG. 10 is an explanatory diagram of a restoration operation process by wavelet inverse transform according to the present invention.

FIG. 11 is an explanatory diagram for obtaining an approximate curve to be estimated and corrected from a plot of a past fluctuation transition by the configuration of FIG. 8;

FIG. 12 is a graph showing an example of a change with time of VCXO.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 voltage controlled crystal oscillator (VCXO) 11 satellite radio receiver 11 c synchronous network clock extraction device 12 time interval measurement unit 13 frequency control operation unit 14 D / A converter 15 frequency divider 16 frequency converter B 17 frequency converter A 23 Steady frequency control arithmetic means 25 Divider A 26 Divider B 28 Ambient temperature fluctuation control arithmetic means 29 Temperature sensor 31, 32 switch 40 Steady frequency deviation calculating arithmetic means 45 Self-running frequency correction data generator 50 Adder 120 Curve fit free-running frequency correction data generator

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[Procedure amendment]

[Submission date] February 17, 1999

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0018

[Correction method] Change

[Correction contents]

The switch 31 is a component of the present invention, and is a non-reception signal 11st from the satellite radio receiver 11.
The reference timing signal UTC1p in an undefined state is determined by p.
Stop psA output. In the case where the satellite radio receiver 11 has the above function, it can be deleted.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0019

[Correction method] Change

[Correction contents]

The time interval measuring section 12 is a component similar to that of the prior art, and receives an ultra-high-precision reference timing signal UTC1ppsA per second from the satellite radio receiver 11 via the switch 31 and outputs the received signal. 1 second signal VCXO obtained by dividing the output frequency fout output from the device to the outside by the frequency divider A25
Receiving 1 pps, the time interval between the two is measured, and this measurement data D1 is successively output every second.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0028

[Correction method] Change

[Correction contents]

The frequency divider B26 receives the reference timing signal UT
It outputs a clock in units of one second synchronized with C1ppsA. It is a new component and has an output frequency fout.
Is divided into clocks in units of one second.
1 is receiving the radio wave, the output UTC1 of the frequency divider B
In order to output ppsB in the same phase as UTC 1 ppsA, in the frequency dividing process, ppsB is synchronously reset by a 1-second reference timing signal UTC 1 ppsA output from the satellite radio receiver 11. Further, when the satellite radio wave receiver can not receive the satellite radio waves, in order UTC1ppsA is stopped by the switch 31, UT in the final phase when the radio is receiving
Outputs C1ppsB. This component is not essential and may be deleted as desired.

Claims (11)

[Claims] A voltage-controlled crystal oscillator which receives a reference signal from the outside, controls a voltage-controlled input terminal of the voltage-controlled crystal oscillator, and synchronously follows an external high-precision reference signal. In a reference frequency generator that generates an accurate reference frequency, in a normal reception state, phase difference data obtained by synchronously comparing an external reference signal with an internal voltage-controlled crystal oscillator is stored, and in a reception disabled state, From the accumulated phase difference data, the amount of transition related to the change over time of the oscillation frequency of the voltage-controlled crystal oscillator is specified, and from this amount of change, the change related to the change over time of the oscillation frequency of the voltage-controlled crystal oscillator in the free-running state is determined. A reference frequency generation device that corrects and maintains the generation of a highly accurate reference frequency for a long time even in a reception disabled state. 2. A voltage controlled crystal oscillator, receiving means for receiving a reference signal from the outside and outputting a reference timing signal every second, and receiving an output frequency of the voltage controlled crystal oscillator for synchronous comparison. Frequency dividing means for outputting a one-second signal for the comparison, the one-second reference timing signal and the one-second signal for the comparison.
Equipped with a time interval measuring unit that measures the time interval with the second signal,
A constant-frequency control calculating means for synchronizing the oscillation frequency of the voltage-controlled crystal oscillator from the phase difference of the time interval measuring unit, wherein the constant-frequency control calculating means connects the voltage control input terminal of the voltage-controlled crystal oscillator to A reference frequency generator that controls and gently and synchronously follows an external high-precision reference signal, wherein the receiving means includes a means for detecting and outputting an inability to receive a reference signal from the outside; Receiving measurement data every second from the time interval measurement unit,
Calculating means for accumulating the measurement data, calculating the current frequency deviation of the voltage-controlled crystal oscillator from the measurement data, and supplying the frequency deviation to the free-running frequency correction data generating unit; In the normal state where there is no disable signal, the frequency deviation data from the calculating means for calculating the steady-state frequency deviation is stored in a memory together with the time information. Based on the deviation history data and time information, the amount of change in the oscillation frequency of the voltage-controlled crystal oscillator over time is estimated and calculated for each predetermined correction interval, and self-running correction data calculated by this estimation calculation is received. Addition to the frequency control data output by the steady-state frequency control calculation means at the time of the impossibility, and the variation with time of the oscillation frequency of the voltage-controlled crystal oscillator in the free-running state A reference frequency generator comprising: a free-running frequency correction data generator that corrects the following. 3. A voltage-controlled crystal oscillator which receives a reference signal from the outside, controls a voltage-controlled input terminal of the voltage-controlled crystal oscillator, and synchronously follows an external high-precision reference signal. In a reference frequency generator that generates a frequency, in a normal reception state, phase difference data obtained by synchronously comparing an external high-precision reference signal with an internal voltage-controlled crystal oscillator is stored, and in a reception disabled state, From the accumulated phase difference data, a transition of a curve related to a temporal change of the oscillation frequency of the voltage-controlled crystal oscillator is specified, an estimated correction curve that fits the curve is determined from the transition curve, and the self-running state is obtained from the estimated correction curve. It is characterized in that the fluctuation of the oscillation frequency of the voltage-controlled crystal oscillator over time is corrected, and the generation of a high-precision reference frequency is maintained for a long time even in a reception disabled state. The reference frequency generator. 4. A voltage-controlled crystal oscillator, receiving means for receiving a reference signal from the outside and outputting a reference timing signal every one second, and receiving the output frequency of the voltage-controlled crystal oscillator for synchronous comparison. Frequency dividing means for outputting a one-second signal for the comparison, the one-second reference timing signal and the one-second signal for the comparison.
Equipped with a time interval measuring unit that measures the time interval with the second signal,
A constant-frequency control calculating means for synchronizing the oscillation frequency of the voltage-controlled crystal oscillator from the phase difference of the time interval measuring unit, wherein the constant-frequency control calculating means connects the voltage control input terminal of the voltage-controlled crystal oscillator to A reference frequency generator that controls and gently and synchronously follows an external high-precision reference signal, wherein the receiving means includes a means for detecting and outputting an inability to receive a reference signal from the outside; Receiving measurement data every second from the time interval measurement unit,
Calculating means for accumulating the measurement data, calculating a current frequency deviation of the voltage-controlled crystal oscillator from the measurement data, and supplying the current frequency deviation to the curve-fit free-running frequency correction data generating unit; In a normal state where there is no unreceivable signal, the frequency deviation data from the above-mentioned steady frequency deviation calculating means is stored in a memory together with time information, and secondly, after receiving the unreceivable signal, the data is stored in the memory. Based on the history data sequence of the frequency deviation and the time information, a transition curve obtained by low-pass filtering the history data sequence, that is, an approximation curve that fits the data sequence or the curve is obtained, and an estimated curve or an approximation curve that extends to approximate the transition curve or A data string is obtained, and a variation related to a temporal change of the oscillation frequency of the voltage-controlled crystal oscillator in a free-running state after reception is disabled is estimated and corrected. A reference frequency generator comprising: a curve-fit self-running frequency correction data generator; 5. A curve-fit free-running frequency correction data generating unit extracts and estimates a fluctuation transition data sequence or a transition curve relating to a temporal change of an oscillation frequency of a voltage-controlled crystal oscillator by low-pass filtering by a wavelet transform unit. 5. The reference frequency generator according to claim 4, wherein the reference frequency generator generates correction data. 6. The low-pass filter processing by the wavelet transform means performs wavelet transform up to a predetermined level number and decomposes it into detailed data Hα (β) and smoothed data Lα (β) of each level number.
6. The reference frequency generator according to claim 5, wherein low-pass filter processing for performing data restoration by performing wavelet inverse transform with (β) as a zero value. 7. The low-pass filter processing by the wavelet transform means is performed by performing a wavelet transform up to a predetermined level number and decomposing it into detailed data Hα (β) and smoothed data Lα (β) of each level number.
6. The reference frequency generator according to claim 5, wherein the average value of (β) is obtained for each level number, and the average value is used to perform a wavelet inverse transform to perform data restoration to perform low-pass filter processing. 8. The criterion according to claim 5, wherein the wavelet transform is performed by using the latest frequency deviation data for a predetermined time in the frequency deviation data group from the calculation means for steady frequency deviation calculation. Frequency generator. 9. A receiving means for receiving a reference signal from the outside and outputting a reference timing signal is a satellite radio receiver for receiving and outputting a reference frequency signal based on radio waves of an artificial satellite having a built-in atomic frequency standard. Item 5. The reference frequency generator according to item 2 or 4. 10. A synchronous network clock extracting device for receiving a reference signal from outside and outputting a reference timing signal is a synchronous network clock extracting device for receiving and outputting a signal distributed on a communication network or a broadcast network. Reference frequency generator as described. 11. A voltage-controlled crystal oscillator which receives a reference signal from the outside, controls a voltage-control input terminal of the voltage-controlled crystal oscillator, and synchronously follows an external high-precision reference signal. In a reference frequency generator for generating a frequency, a time-dependent change of the voltage-controlled crystal oscillator is regarded as a curve change, a past data sequence is low-pass-filtered, and a curve fit after reception is impossible from the low-pass-filtered data sequence is performed. A reference frequency generation device for obtaining a curve or a data string and estimating and correcting a change with time of the voltage-controlled crystal oscillator after reception failure.