JP2017040533A - Time synchronization system, reference signal transmission device, and time server device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a time synchronization system capable of, after a device requiring high-accuracy time synchronization is installed in a service place where GPS satellite radio waves or the like are unreachable, wirelessly correcting the device regularly on an easy and convenient basis.SOLUTION: A reference signal transmission device 1 comprises: a semiconductor laser emitting a laser beam toward a time server device 2; an oscillation part outputting a pulsed time synchronization signal; and a drive circuit driving the semiconductor laser by a pulsed current based on the time synchronization signal. The time server device 2 comprises: a built-in oscillator; a built-in clock performing a timing operation by oscillation output of the built-in oscillator; a light-receiving element 201 receiving the laser beam to output a light detection signal; a phase difference measurement circuit measuring a time deviation between the oscillation timing of the built-in oscillator and the light detection signal so as to provide a time correction signal to the built-in clock; and a frequency correction value calculation circuit calculating a frequency correction value based on the time deviation and the elapsed period after the last correction so as to provide a frequency correction signal to the built-in oscillator.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a time synchronization system, a reference signal transmission device, and a time server device.

  There are scenes where highly accurate time information is required in various fields. In order to realize a system that requires time synchronization accuracy in the order of microseconds or sub-microseconds, time distribution with error accuracy equal to or better than UTC (Coordinated Universal Time) is required.

  A general high-accuracy time distribution system generates an accurate time using GNSS (Global Navigation Satellite System) or PTP (Precision Timing Protocol, IEEE1588).

  The GNSS is a system including a conventional GPS (Global Positioning System) satellite, and can obtain time synchronized with UTC at a level of several tens of nanoseconds in addition to positioning such as car navigation. When performing positioning, the GPS receiver needs to acquire signals from at least four GPS satellites. However, on the assumption that the exact position (latitude / longitude / altitude) of the GPS receiver is known, UTC synchronization time can be obtained if signals from at least one GPS satellite can be captured. .

  Since the signal from the GPS satellite is weak and the signal (C / A code) used for consumer use is transmitted in an unencrypted state, there is a problem that it is easily affected by electromagnetic noise and jamming radio waves. is there. However, it is a great advantage that a highly accurate time can be obtained with an inexpensive GPS receiver. Conversely, a problem with the time synchronization system using GPS satellite radio waves is that the high-accuracy time generation system cannot be used in a state where the GPS satellite radio waves cannot be received, such as indoors / underground / underwater.

  PTP is a protocol for delivering accurate time from a GMC (Grandmaster Clock) server to clients in a wired network, and time synchronization accuracy of about 1 microsecond is obtained for GMC. Although PTP can be used even in indoor / underground / underwater conditions where GPS satellite radio waves cannot be received, in general, it is necessary to configure a server and a client corresponding to PTP in a multi-layer topology. Therefore, a large introduction cost / maintenance cost is required for system construction corresponding to PTP. Furthermore, the time synchronization accuracy greatly depends on the time synchronization accuracy of the GMC, and there is a problem that the time synchronization accuracy deteriorates as the layer is physically / logically separated from the GMC. For the purpose of ensuring the UTC time synchronization accuracy of GMC, the GMC server itself is often connected to a GPS receiver.

  On the other hand, in order to realize a small base station in a room or underground shopping center where GPS is difficult to use, a technology is disclosed in which a master station and a slave station are connected by an optical fiber, and synchronization packets used for time synchronization are multiplexed and transmitted / received. (See, for example, Patent Document 1). According to this, a high-accuracy time can be obtained on the slave station side as a timing at which the transmission delay time is corrected with respect to the reference signal held by the master station.

  Also disclosed is a technique for performing spread spectrum processing on a time synchronization signal (1 PPS (1 Pulse Per Second) signal) generated by a GPS receiver and transferring a modulated signal superimposed on a carrier wave to a reference time server through a power line. (See, for example, Patent Document 2). According to this, a time synchronization signal (1PPS signal) can be reproduced | regenerated by a demodulation process with a reference | standard time server, and a time synchronization process can be implemented.

  In addition, phase difference data with respect to the high-precision reference signal of the voltage controlled crystal oscillator is accumulated, and when the reference signal cannot be obtained (free-running state), the oscillation frequency change with time estimated from the accumulated phase difference data is corrected. Thus, a technique for obtaining a highly accurate oscillation frequency signal is disclosed (see, for example, Patent Document 3).

  As described above, in order to maintain time accuracy in the target device, it is necessary to supply a synchronization signal from the reference device via the network. Even if the target device side is provided with an oscillator and a watch that can run freely when the synchronization signal from the reference side is not given, the reference device and the target device regularly Must be connected to the network and a synchronization signal must be supplied for correction.

  However, there are various environments in which the target device is installed. For example, in the case of a device installed at a high position in the tunnel, it is difficult to connect by wire. Regardless of whether it is a wired connection in advance or a wired connection for each periodic correction that is not normally connected, it is costly to install and maintain. Not right. Furthermore, in the connection by the conventional wired network, the process which converts a time synchronous signal (1PPS signal etc.) into a synchronous packet, and processes, such as spread spectrum and a carrier wave superimposition, are needed. For this reason, in addition to providing functional blocks for performing these processes on the transmission / reception side, it is necessary to correct the time required for these processes. In addition, in the case of wireless connection, there are many problems in accuracy, propagation direction, etc. due to the influence of multipath signals resulting from multiple reflections from the tunnel inner wall and the like.

  The present invention has been proposed in view of the above-described conventional problems, and the object of the present invention is to install a device that requires high-accuracy time synchronization after use in a place where GPS satellite radio waves do not reach. The purpose is to easily implement periodic corrections in a non-wired manner.

  In order to solve the above problems, the present invention includes a reference signal transmission device and a time server device, and the reference signal transmission device includes a semiconductor laser that irradiates a laser beam toward the time server device; An oscillation unit that outputs a pulsed time synchronization signal; and a drive circuit that drives the semiconductor laser with a pulsed current based on the time synchronization signal; and the time server device includes an internal oscillator and an oscillation of the internal oscillator A built-in timepiece that performs a clock operation by output; a light receiving element that receives the laser beam and outputs a light detection signal; measures an oscillation timing of the built-in oscillator and a time shift of the light detection signal; A frequency correction value is calculated based on the phase difference measurement circuit that provides a time correction signal, the time lag, and the elapsed time since the previous correction, and the frequency correction is performed in the built-in oscillator. And a frequency correction value calculation circuit for providing a signal.

  In the present invention, periodic correction after installing a device that requires high-accuracy time synchronization in a place where GPS satellite radio waves or the like do not reach can be easily realized non-wired.

It is a figure which shows the example of an external appearance of the reference signal transmission apparatus and time server apparatus concerning one Embodiment of this invention. It is a figure which shows the structural example of a reference signal transmission apparatus. It is a figure which shows the structural example of a time server apparatus. It is a flowchart which shows the process example of embodiment. It is a figure which shows the example of the timing of the various signals by the side of a reference signal transmitter. It is a figure which shows the example of the timing of the various signals by the time server apparatus side. It is a figure which shows the example of the time shift which a phase difference measurement circuit measures.

  Hereinafter, preferred embodiments of the present invention will be described.

<System configuration>
FIG. 1 is a diagram showing an example of the appearance of a reference signal transmission device 1 and a time server device 2 according to an embodiment of the present invention. In FIG. 1, for example, a plurality of time server devices 2 are installed in a tunnel or the like, and supply accurate time to vibration sensors or the like that are also installed in a large number in the tunnel or the like. The vibration sensor is installed for the purpose of investigating a tunnel degradation point due to secular change from vibration propagation data, and the time information of the data acquired by the vibration sensor is required to be accurate. Since the time server device 2 gives accurate time information to the data acquired from the vibration sensor, it is necessary in principle to continue supplying time information without collecting it over a long period of year after installation. is there.

  The time server apparatus 2 includes an oscillation device, and a clock operation of a built-in real time clock is performed using a frequency signal (usually 10 MHz) output from the oscillation device. The accuracy of the time information supplied from the time server device 2 greatly depends on the frequency accuracy of the oscillation device. Although the time information and frequency are adjusted before the time server device 2 is installed, the GPS satellite radio wave cannot be corrected using the reference signal after being installed in a tunnel or the like. Because frequency and time are gradually shifted due to frequency drift (a phenomenon in which the frequency gradually shifts in one direction), in order to provide accurate time information, there is a means for periodically correcting the time and frequency. Necessary.

  The reference signal transmission device 1 provides a reference signal for correction in a non-wired manner when the time server device 2 is periodically corrected, and is placed on a moving means such as a vehicle. Is moved to a position in the field of view and correction processing is performed. From the reference signal transmission device 1, a parallel light beam BM driven in a pulse shape by a 1 PPS signal is emitted, and the optical axis is adjusted so that the light receiving element 201 of the time server device 2 is irradiated. The optical axis adjustment is performed by three-axis adjustment (horizontal rotation / turning angle / height) by the mounting table of the reference signal transmission device 1 and the optical system in the reference signal transmission device 1.

  On the surface of the time server device 2 on which the light receiving element 201 is provided, an LED (Light Emitting Diode) that indicates that the parallel light beam BM is properly irradiated on the light receiving element 201 and that indicates that correction is completed. ) Etc., two indicators 205a and 205b are provided. The two indicators 205a and 205b can be identified by their emission colors and lighting / flashing patterns. In addition, since the parallel light beam BM assumes infrared light and an irradiation spot cannot be visually observed, a sheet that emits visible light with respect to infrared light irradiation is pasted on the casing surface around the light receiving element 201, The confirmation of the irradiation position by visual observation can also be facilitated. It is assumed that the visual confirmation is performed through a telephoto lens when the reference signal transmission device 1 and the time server device 2 are separated.

<Configuration of reference signal transmitter>
FIG. 2 is a diagram illustrating a configuration example of the reference signal transmission device 1. In FIG. 2, the reference signal transmission device 1 includes a time information holding block 11 including a microscale atomic clock (CSAC) 12 and a built-in clock 13. The micro atomic clock 12 is assumed to be initially calibrated with an accuracy of 5e-12 for a nominal frequency of 10 MHz using the Cs frequency standard. As for the time (phase difference), it is assumed that initial calibration is performed with accuracy within 100 ns with respect to UTC using a reference signal from a GPS receiver. For example, the frequency drift characteristic of Microsemi's CSAC (SA.45s) is 3e-10 / month, and if frequency calibration is performed with an accuracy of 5e-12 using a Cs frequency standard (eg, Microsemi 5071A), The time accuracy within 1 μs can be maintained for about one full day. The built-in clock 13 performs a clock operation based on the 10 MHz frequency signal from the micro atomic clock 12.

  The reference signal transmission device 1 includes a semiconductor laser drive circuit 14, a timing adjustment circuit 15, a semiconductor laser (laser diode) 16, and a collimator lens 17. As the semiconductor laser 16, it is assumed that a vertical cavity surface emitting laser (VCSEL) for communication use (wavelength 850 nm) is used, but other semiconductor lasers may be used.

  The semiconductor laser drive circuit 14 obtains a drive current B of the semiconductor laser 16 from a time synchronization signal (1PPS signal) A output from the micro atomic clock 12. The timing adjustment circuit 15 adjusts the timing deviation caused by the processing time of the semiconductor laser driving circuit 14 and the response time of the semiconductor laser 16, and adjusts the rising edge of the 1PPS signal A and the output light intensity of the output light D of the semiconductor laser 16. The timing to rise is matched. Since the processing time of the semiconductor laser drive circuit 14 depends on circuit implementation and is not described in the specification in most cases, the time difference between the rising edges of the 1PPS signal A and the drive current B is measured in advance with an oscilloscope or the like. Ask. The response time of the semiconductor laser 16 is a nanosecond level or less and is described in the specification of the device. The timing adjustment circuit 15 also corrects the propagation time according to the distance between the reference signal transmission device 1 and the time server device 2 (for example, the time difference when the distance is 100 m is 333 ns). The light emission timing at the position reaching the time server device 2 is adjusted so as to be in phase with the time synchronization signal.

  The collimator lens 17 converts the pulsed emitted light D from the semiconductor laser 16 into parallel light. When a VCSEL device is used as the semiconductor laser 16, the emitted light D has a radiation angle of about 5 degrees to 20 degrees. However, by using a collimator lens 17 appropriately designed according to the radiation angle, a parallel beam is formed. In addition, it is possible to obtain a parallel light beam BM having a diameter of 1 cm or less even at a distance of several hundred meters or more. As a result, neither an optical fiber nor a power line is required, and spatial transmission of the time synchronization signal is possible at low cost.

<Configuration of time server device>
FIG. 3 is a diagram illustrating a configuration example of the time server device 2. 3, the time server device 2 includes a light receiving element 201, an amplifier circuit 202, a timing adjustment circuit 203, a correction circuit 204, indicators 205a and 205b, and a time information holding block 206. The time information holding block 206 includes a built-in oscillator 207, a built-in clock 208, a phase difference measurement circuit 209, and a frequency correction value calculation circuit 210.

  The light receiving element (PD: Photo Detector) 201 is an element such as a phototransistor or a photodiode that receives incident light E (parallel light beam BM) from the reference signal transmission device 1 and converts it into an electrical signal. The amplification circuit 202 amplifies the PD signal (light detection signal) F of the light receiving element 201 and converts it into a pulsed 1PPS signal G. The timing adjustment circuit 203 adjusts the timing deviation caused by the amplifier circuit 202 and the like, and matches the rising edge of the output light intensity of the incident light E with the rising edge timing of the 1PPS signal H. The time difference (for example, when the distance is 100 m away) from the time synchronization signal by the propagation time until the parallel light beam BM emitted from the reference signal transmission device 1 reaches the light receiving element 201 of the time server device 2. The time difference is 333 ns), and the time difference is corrected by the timing adjustment circuit 15 on the reference signal transmission device 1 side.

  When the time average value of the PD signal F exceeds a certain level, the correction circuit 204 sends a correction start instruction signal to the time information holding block 206, and lights or blinks the indicator 205a to turn the parallel light beam BM. Is notified that the light receiving element 201 is properly irradiated. The reason why the determination is based on the time average value of the PD signal F is that the PD signal F is a pulse signal. When the correction circuit 204 receives a correction completion notification signal from the time information holding block 206, the correction circuit 204 lights or blinks the indicator 205b to notify the completion of correction.

  The built-in oscillator 207 of the time information holding block 206 outputs a 10 MHz signal to the built-in clock 208 and also outputs a 1 PPS signal I to the phase difference measuring circuit 209. The internal clock 208 performs a clock operation using a 10 MHz signal provided from the internal oscillator 207.

  The phase difference measurement circuit 209 measures the phase difference between the 1PPS signal H from the timing adjustment circuit 203 and the 1PPS signal I from the built-in oscillator 207. The phase difference measured here is the time shift of the time server device 2 with respect to the time synchronization signal. The phase difference measurement circuit 209 gives the measured time deviation to the frequency correction value calculation circuit 210 and also gives the built-in clock 208 as a time correction signal. The frequency correction value calculation circuit 210 holds the time when the previous correction was performed (previous correction time), and calculates the frequency correction value (frequency ratio) from the time lag given from the phase difference measurement circuit 209. The frequency correction signal is supplied to the built-in oscillator 207.

<Correction process>
FIG. 4 is a flowchart showing a processing example of the above embodiment. In FIG. 4, when starting the correction process, the worker in charge activates the reference signal transmission device 1 (step S1).

  FIG. 5 is a diagram showing an example of the timing of various signals on the reference signal transmission device 1 side. The micro atomic clock 12 outputs a time synchronization signal (1PPS signal) A to the semiconductor laser driving circuit 14, and the semiconductor laser driving circuit 14 outputs a drive current B. The timing of the drive current B is delayed by the processing time of the semiconductor laser drive circuit 14.

  The timing adjustment circuit 15 applies a delay application to the drive current B taking into account the processing time of the semiconductor laser drive circuit 14 and the response time of the subsequent semiconductor laser 16, and the drive current slightly advanced in timing from the 1PPS signal A. C is output to the semiconductor laser 16. As a result, the intensity of the emitted light D from the semiconductor laser 16 is aligned with the 1PPS signal A. Although not shown in FIG. 5, the timing adjustment circuit 15 has a propagation time corresponding to the distance between the reference signal transmission device 1 and the time server device 2 (for example, the time difference when the distance is 100 m is 333 ns). ) Is also corrected. The distance between the reference signal transmission device 1 and the time server device 2 can be acquired from a distance sign or the like installed in the tunnel, for example, if the distance is in the tunnel.

  Returning to FIG. 4, the worker moves the vehicle on which the reference signal transmission device 1 is mounted and moves to a place where the time server device 2 can be seen (step S <b> 2). In addition, the correction process by laser irradiation is implemented in the state stopped in the installation position vicinity of each time server apparatus 2. FIG. Besides the reason that it is difficult to carry out laser irradiation accurately while moving, the rising edge interval of the 1PPS signal that is transmitted while the reference signal transmission device 1 serving as the reference signal source is moving changes due to the Doppler effect. This is because it is necessary to eliminate the deterioration of timing accuracy due to this.

  Next, the worker in charge adjusts the optical axis so that the parallel light beam BM from the reference signal transmission device 1 is accurately applied to the light receiving element 201 of the time server device 2 (step S3). The optical axis adjustment is performed by three-axis adjustment (horizontal rotation / turning angle / height) by the mounting table of the reference signal transmission device 1 and the optical system in the reference signal transmission device 1.

  When a sheet or the like that emits visible light with respect to infrared light irradiation is attached to the peripheral surface of the light receiving element 201 of the time server device 2, a telephoto lens determines whether the optical axis is aligned. It is possible to confirm with the naked eye. Further, when the time average value of the PD signal F of the light receiving element 201 exceeds a certain level, the correction circuit 204 turns on or blinks the indicator 205a, so that the optical axis adjustment is confirmed visually through a telephoto lens. Can do.

  Since the parallel light beam BM having high straightness is used, even if the time server device 2 has to be installed at a high position in the tunnel or the like, the parallel light beam is accurately emitted to the light receiving element 201. It is possible to irradiate the beam BM. Further, unlike the case of using radio waves, there is an advantage that the influence of multipath signals caused by multiple reflections by the tunnel inner wall or the like can be completely eliminated. Further, regarding the level at which the light receiving element 201 determines that the 1PPS signal is being received, since the S / N ratio can be increased when using laser light, the setting is very easy.

  When the optical axis adjustment is completed, in the time server device 2, the correction circuit 204 sends a correction start instruction signal to the time information holding block 206, and a process for correction is automatically executed (step S4).

  FIG. 6 is a diagram showing an example of the timing of various signals on the time server device 2 side. The PD signal F output from the light receiving element 201 with respect to the incident light E (parallel light beam BM) from the reference signal transmission device 1. Are almost the same timing. However, the timing of the 1PPS signal G output from the amplifier circuit 202 is slightly delayed due to the delay of the amplifier circuit 202. Therefore, the timing adjustment circuit 203 performs a delay taking the delay time of the amplifier circuit 202 into account, matches the timing of the incident light E and the 1PPS signal H, and outputs the 1PPS signal H to the phase difference measurement circuit 209.

  The phase difference measurement circuit 209 measures the phase difference (time shift) Δt between the 1PPS signal H from the timing adjustment circuit 203 and the 1PPS signal I from the built-in oscillator 207, as shown in FIG. Note that the correction process is executed within a period in which Δt does not exceed 1 second, and Δt is within 1 second.

  The phase difference measurement circuit 209 gives the measured time deviation to the frequency correction value calculation circuit 210 and also gives the built-in clock 208 as a time correction signal. The built-in clock 208 performs time correction (correction within ± 1 second) based on the time correction signal.

  The frequency correction value calculation circuit 210 holds the previous correction time, calculates a frequency correction value (frequency increase / decrease ratio) from the time lag given from the phase difference measurement circuit 209, and is built in as a frequency correction signal. This is given to the oscillator 207. The built-in oscillator 207 corrects the oscillation frequency based on the frequency correction signal. At this time, the built-in oscillator 207 also adjusts the timing of the 1PPS signal I. Further, the frequency correction value calculation circuit 210 stores the correction time as a new previous correction time.

  When the time and frequency correction by the phase difference measurement circuit 209 and the frequency correction value calculation circuit 210 is completed, the time information holding block 206 sends a correction completion notification signal to the correction circuit 204. In response, the correction circuit 204 lights or blinks the indicator 205b to notify the completion of correction.

  Returning to FIG. 4, when the operator confirms the completion of the correction by turning on or blinking the indicator 205 b (step S <b> 5), the correction process for one time server device 2 is finished, and the next time server device 2 exists. In that case, the same processing is repeated from the movement of the time server device 2 (step S2).

<Summary>
As described above, according to this embodiment, periodic correction after installing a device that requires high-accuracy time synchronization in a place where GPS satellite radio waves or the like do not reach can be easily realized non-wired. be able to. That is, the time synchronization signal (1PPS signal) can be transmitted and received for correction without being connected by an optical fiber or a power line, and without performing packet conversion processing or processing (modulation) superimposed on a carrier wave.

  The present invention has been described above by the preferred embodiments of the present invention. While the invention has been described with reference to specific embodiments, various modifications and changes may be made to the embodiments without departing from the broad spirit and scope of the invention as defined in the claims. Obviously you can. In other words, the present invention should not be construed as being limited by the details of the specific examples and the accompanying drawings.

<Correspondence between Terms in Embodiment and Terms in Claims>
The reference signal transmission device 1 is an example of a “reference signal transmission device”. The time server device 2 is an example of a “time server device”. The semiconductor laser 16 is an example of a “semiconductor laser”. The micro atomic clock 12 is an example of an “oscillator”. The semiconductor laser drive circuit 14 is an example of a “drive circuit”. The built-in oscillator 207 is an example of “built-in oscillator”. The built-in clock 208 is an example of “built-in clock”. The light receiving element 201 is an example of a “light receiving element”. The phase difference measurement circuit 209 is an example of a “phase difference measurement circuit”. The frequency correction value calculation circuit 210 is an example of a “frequency correction value calculation circuit”.

  The timing adjustment circuit 15 is an example of a “timing adjustment circuit”. The correction circuit 204 is an example of a “correction circuit”. The timing adjustment circuit 203 is an example of a “second timing adjustment circuit”. The collimator lens 17 is an example of a “collimator lens”. The indicators 205a and 205b are examples of “indicators”.

DESCRIPTION OF SYMBOLS 1 Reference signal transmitter 11 Time information holding block 12 Micro atomic clock 13 Built-in clock 14 Semiconductor laser drive circuit 15 Timing adjustment circuit 16 Semiconductor laser 17 Collimator lens 2 Time server apparatus 201 Light receiving element 202 Amplifying circuit 203 Timing adjustment circuit 204 Correction circuit 205a, 205b Indicator 206 Time information holding block 207 Built-in oscillator 208 Built-in clock 209 Phase difference measurement circuit 210 Frequency correction value calculation circuit BM Parallel light beam

JP 2010-206327 A JP 2004-150892 A JP 11-271476 A

Claims (8)

A reference signal transmission device and a time server device;
The reference signal transmitter is
A semiconductor laser for irradiating a laser beam toward the time server device;
An oscillation unit that outputs a pulse-shaped time synchronization signal;
A drive circuit for driving the semiconductor laser with a pulsed current by the time synchronization signal;
The time server device is:
A built-in oscillator;
A built-in clock that performs a clock operation by the oscillation output of the built-in oscillator;
A light receiving element that receives the laser beam and outputs a light detection signal;
A phase difference measuring circuit that measures the time difference between the oscillation timing of the built-in oscillator and the light detection signal, and gives a time correction signal to the built-in clock;
A time synchronization system comprising: a frequency correction value calculation circuit that calculates a frequency correction value based on the time lag and an elapsed period from the previous correction and provides a frequency correction signal to the built-in oscillator. The reference signal transmitter is
A timing adjustment circuit is provided that adjusts the timing of the current of the driving circuit by delaying so that the light emission timing at the position where the laser beam reaches the time server device is in phase with the time synchronization signal. The time synchronization system according to claim 1. The time server device is:
3. The time synchronization system according to claim 1, further comprising a correction circuit that issues a correction start instruction when the light detection signal reaches a predetermined level. The time server device is:
A second timing adjustment circuit that adjusts the timing of the photodetection signal by delaying the timing so that the timing of the photodetection signal applied to the phase difference measurement circuit is in phase with the time synchronization signal; The time synchronization system according to any one of claims 1 to 3, wherein the time synchronization system is characterized in that: The reference signal transmitter is
The time synchronization system according to any one of claims 1 to 4, further comprising a collimator lens that converts light emitted from the semiconductor laser into parallel light. The time server device is:
The time synchronization system according to any one of claims 1 to 5, further comprising an indicator that displays a progress state of correction processing for the internal clock and the internal oscillator. A semiconductor laser that emits a laser beam toward the time server device;
An oscillation unit that outputs a pulse-shaped time synchronization signal;
A reference signal transmission device comprising: a drive circuit for driving the semiconductor laser with a pulsed current by the time synchronization signal. A built-in oscillator;
A built-in clock that performs a clock operation by the oscillation output of the built-in oscillator;
A light receiving element that receives a laser beam from a reference signal transmission device and outputs a light detection signal;
A phase difference measuring circuit that measures the time difference between the oscillation timing of the built-in oscillator and the light detection signal, and gives a time correction signal to the built-in clock;
A time server apparatus comprising: a frequency correction value calculation circuit that calculates a frequency correction value based on the time lag and an elapsed period from the previous correction and provides a frequency correction signal to the built-in oscillator.

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