JP2600595B2 - Clock distribution method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

2. Description of the Related Art In a synchronous digital transmission system, in order to efficiently process a signal over a plurality of terminal devices with a simple circuit, the operation of each terminal device is synchronized in frequency or phase. Clock distribution is required.

The present invention relates to this clock distribution system,
In particular, the present invention relates to a clock distribution method for distributing a reference clock signal generated by one reference clock source to a plurality of clock receiving devices.

[0003]

2. Description of the Related Art In an intercommunication system for a very large number of signal sources represented by public communication, a function for realizing communication is divided into a large number of devices for physical and economic reasons.
Generally, a communication system is constructed by combining a plurality of these devices. For example, in the case of a telephone communication system, a voice signal from each subscriber is accommodated in a switching device of a nearest station, and after concentrating and switching, a target communication partner is transmitted through a transmission terminal device. The information is transmitted to the exchange of the accommodating station.

Usually, a transmission station apparatus has a multiplexing function in order to effectively use an expensive transmission line, and this multiplexing function is configured to multiplex stepwise by several devices. I have. For this reason, communication signals are inevitably transmitted and received between the devices, but if the speeds of the signals input to and output from each device are exactly the same, the individual original signals can be directly converted from the multiplexed signals. The identification can be performed, and not only the signal processing performed by each device can be efficiently realized, but also the circuit of each device can be simplified.

[0005] Due to such advantages, in recent communication systems, a synchronous digital transmission system in which the operating speeds of all related devices are strictly matched has become mainstream. In a synchronous digital transmission system, a reference clock source is usually installed in a station in order to exactly match and synchronize the operation of each device, and a reference clock signal generated by this clock source is distributed to all related devices. Each device is configured to synchronize its internal operation with the received reference clock. Each station is provided with a clock supply device that generates a reference clock and distributes the reference clock to various devices.

In such a clock distribution system, a clock signal must be distributed according to each installed clock receiving device. For this reason, a station typically has a very large number of clock receivers, often in the number of thousands or more. In addition, since each device synchronizes all internal device operations with the received clock signal as a reference, if a disturbance occurs in the received clock signal, the operation of the device is immediately hindered. For this reason, sufficient consideration is necessary for ensuring the normality and reliability of the clock signal.

[0007] In order to cope with the above, each clock receiving device generally receives two clock signals of a working system and a standby system from a clock supply device. Even if a failure occurs in the clock signal of one system, the operation of the clock receiving device is not hindered by the clock signal of the other system. As a result, since each clock supply device distributes a very large number of clock signals, economical use of clock distribution means is a very important condition.

In the conventional clock distribution system, clock signals are generally distributed by electric signals mainly for economic reasons. In a system in which the output signal of one transmission circuit is connected to a plurality of reception circuits and the signal is simultaneously distributed to the plurality of reception circuits, the connection is established by attaching or detaching the reception circuit due to addition, removal, etc. of a device receiving a clock. When the number of receiving circuits changes, a change in characteristic impedance including the transmission medium of the clock signal is inevitable. For this reason, when the receiving circuit is attached or detached, harmful effects such as phase fluctuations and level fluctuations occur on signals supplied to other receiving circuits. Further, in such a clock distribution method, when one of a plurality of devices receiving the same clock output fails and, for example, a short circuit occurs, the clock supply to the other devices cannot be continued. Impossible. Therefore, even when clocks are distributed to a very large number of devices, it is common to provide the same number of clock transmitting circuits as the number of receiving circuits, and to associate one transmitting circuit with one receiving circuit.

FIG. 5 is a block diagram showing a configuration of a conventional clock distribution system. In FIG. 5, reference numeral 53 denotes a reference clock, and an associated clock receiving device 591-5
9n is a clock supply device for supplying a reference clock signal to 9n. This clock supply device has a clock generator 51 inside, and supplies a clock to each clock reception device with an electric signal. Clock receiving devices 591 to 59n receive the reference clock supplied from the clock supply device 53, respectively. The function of each of these devices is not particularly limited, but all devices operate in synchronization with the received reference clock signal. In the existing clock distribution system in Japan, the clock supply device is 64 kHz.
It provides a Z bipolar signal, a 1.544 MHz sine wave signal and a 6.312 MHz sine wave signal. The clock receiving device is configured to receive a necessary clock signal from the three types of clock signals. Therefore, when the clock receiving device requires three types of clock signals, at least three transmission media are required between the clock receiving device and the clock supply device.

[0010]

However, such a conventional clock distribution system using electric signals has a number of disadvantages which are difficult to avoid as follows.

A first drawback is that the conventional clock distribution system uses an electric signal as a clock transmission means, and is essentially susceptible to electric noise. For example, electrostatic and inductive noise generated by an adjacent device and electric noise generated by various works around the device are mixed into the device or a wire for clock transmission, and a clock signal is disturbed. . In addition, when a large number of devices are installed, it may be necessary to install the devices at physically separated positions, and the ground wires of the devices may be placed in an ideal layout due to physical and electrical restrictions. It is difficult to do. In large stations where many devices are installed,
It is very difficult to always match the ground potential, especially the AC potential, between a plurality of related devices, and the potential between the clock supply device and the clock reception device often fluctuates. As a result, the electric signal corresponding to the fluctuation of the ground potential is superimposed on the clock signal, and the clock signal is disturbed. The use of an optical signal can be considered as a solution to the drawbacks caused by using such an electrical signal. However, an optical signal interface is generally extremely expensive compared to an electrical interface, and the essential conditions for the clock distribution method described above are required. Is not economical.

The second disadvantage is that, as described above, in the clock distribution system using electric signals, the transmission circuit and the reception circuit are connected to one another.
Since it is necessary to correspond to one to one, when a clock receiving device is newly added and installed, a transmitting circuit of the clock supply device is added and a transmission medium between the clock generation source and the clock receiving device is also newly installed. There is a need. For this reason, although the clock transmitting / receiving circuit is relatively inexpensive, there is a drawback that a large amount of operation work is required. In addition, in the conventional clock distribution method, a new clock supply device and a new transmission medium can be used even when the clock receiving device needs a clock signal of a different speed or a plurality of clock signals. This has the disadvantage that not only is it economically burdensome, but also that a large amount of work work is required and a large transmission medium accommodation space is required. For this reason, it is virtually impossible to change or add the type of the clock signal to be distributed. Even if the function and operation speed of the clock receiving device are improved due to technological innovation, the received clock signal must be one of the three types of clock signals described above, and the clock generator inside each clock receiving device is complicated. ,
It has to be expensive.

The third disadvantage is that, in the conventional clock distribution system, the transmission circuit and the reception circuit correspond to each other on a one-to-one basis, so that it is difficult to increase the reliability of the clock supply device itself by duplication or the like. When the clock supply device stops functioning due to a failure or the like, there is a disadvantage that the clock signal to the clock reception device is interrupted. In addition, when updating a clock supply device due to aging, performance improvement, etc., it is necessary to switch the clock receiving destination corresponding to each clock receiving device, which is extremely complicated and requires a large amount of work. There are drawbacks needed. In addition to this, there is a disadvantage that the clock signal must be temporarily interrupted at the time of renewal.

An object of the present invention is to eliminate the above-mentioned disadvantages of the conventional clock distribution system by a simple and economical configuration, not to be affected by electric disturbance, easy to construct and maintain such as expansion and removal, etc. It is an object of the present invention to provide a clock distribution method that does not require interruption of a clock signal even when a clock supply device is renewed.

[0015]

A clock distribution system according to the present invention comprises a reference clock generator for generating a reference clock composed of an electric clock signal, and an electric / optical converter for converting the electric clock signal into an optical clock signal composed of an optical signal. A clock supply device with a converter, connected to the clock supply device,
An optical fiber transmission line for transmitting an optical clock signal, an optical splitter for distributing the optical clock signal transmitted on the optical fiber transmission line to a plurality of distribution optical fiber transmission lines and transmitting the distribution light, and an optical fiber for distribution A clock receiving device connected to the transmission line and having an optical-to-electrical converter for receiving the optical clock signal and converting it to an electric clock signal.

According to the clock distribution system of the present invention, a plurality of clock supply devices and optical clock signals transmitted from the plurality of clock supply devices are optically coupled to each other so as to be transmitted to an optical fiber transmission line. An optical coupler disposed between the apparatus and the optical fiber transmission line, and at least one optical clock signal among the optically coupled optical clock signals is received by the optical-electrical converter.

Further, each of the plurality of clock supply devices transmits the same optical clock signal, and each of the optical-to-electrical converters provided in the clock reception device transmits each optical clock signal from all of the plurality of clock supply devices. Even when a signal is transmitted, even when there is no transmission of an optical clock signal from at least one of the plurality of clock supply devices, the optical reception sensitivity is set to be receivable. I have.

In the above-mentioned configuration, at least one of the plurality of optical clock signals comprises an optical signal having a wavelength different from that of the other optical clock signals, and the plurality of optical clock signals are provided in a clock receiving device. The optical demultiplexer is demultiplexed into a plurality of demultiplexed optical clock signals for each wavelength, and one of the demultiplexed optical clock signals is selected and converted into an electric clock signal by an optical / electrical converter.

[0019]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a first embodiment of the clock distribution system according to the present invention.
It is a lineblock diagram of an Example of a. The first embodiment shows an example in which a single clock supply device is used. The clock generator 13 includes a reference clock generator 11 for generating a clock signal and an electric / electrical converter for converting the clock signal into an optical clock signal.
An optical converter is provided. The clock supply device 13 is connected to an optical fiber transmission line 15, and an optical clock signal is sent out to the optical fiber transmission line 15.

The optical clock signal transmitted through the optical fiber transmission line 15 is split by the optical splitter 16 and distributed to each of the clock receiving devices 191 to 19n. The optical clock signal input to each clock receiving device is re-converted into a clock signal composed of an electric signal by each of the optical-to-electrical converters 171 to 17n.
8n. This clock signal is used as a clock signal for synchronizing clock generators 181 to 18.
It is transmitted from n as needed.

FIG. 2 shows a second embodiment of the clock distribution system according to the present invention.
FIG. 3 is a configuration diagram showing an example of the embodiment. In the second embodiment, the number of clock supply devices is not two but two. In FIG. 2, reference numerals 23a and 23b denote first and second clock supply devices, respectively, which generate a reference clock,
It has a function of supplying a clock signal to various devices.
Here, each of the clock supply devices 23a and 23b includes a reference clock generator 21a or 21b and the reference clock generators 21a and 21b, as in the first embodiment.
Have electrical / optical converters 22a and 22b for converting the reference clock signal of the electrical signal generated in the above into an optical clock signal. An optical coupler 24 receives optical clock signals from the two clock supply devices 23a and 23b and sends out both signals to the same optical fiber. here,
The optical coupler 24 has two outputs according to the number of outputs of the clock supply device.
The two clock supply devices 23a and 23b are installed in the immediate vicinity, and for example, as shown in FIG.
In the case of output, one unit is installed, and when there are two outputs of the clock supply device, two units are installed.

Reference numeral 26 denotes an optical splitter that splits the optical clock signal transmitted and transmitted to the optical fiber transmission line 25 by the optical coupler 24 into multiple branches by the number of the clock receivers and distributes them to the respective clock receivers. Also called a star coupler. The optical splitter 26 is installed near a plurality of clock receiving devices 291 to 29n to which the reference clock is distributed. The number of branches is the sum of the intensities of the optical clock signals input from the optical coupler 24, the transmission path loss, the loss occurring at the time of branching, the sensitivity of the optical / electrical converters 271 to 27n in the clock receiving devices 291 to 29n, and the like. Is determined by the following parameters. Here, in consideration of these factors, each parameter is selected such that the number of branches is about several tens. The optical coupler 24 and the optical splitter 26 are usually composed of only optical components, and do not use any active elements. Therefore, it is not necessary to supply power or the like.
No adjustment is required, and the life is semi-permanent.

The internal configuration of each of the clock receiving devices 291 to 29n is the same as in the first embodiment. The functions of these clock receiving devices are not particularly limited, but all devices operate in synchronization with the received reference clock.

Next, the operation of the clock distribution system of the present invention having the configuration according to the second embodiment will be described. The reference clock signal generated by the reference clock generators 21a and 21b inside the clock supply device 23a or 23b is:
After being converted into an optical clock signal by the electrical converters 22a and 22b in the same device, the signal is output to the optical coupler 24 that is installed in the nearest place. The optical clock signal received from one clock supply device and the optical clock signal received from the other clock supply device are optically coupled by the optical coupler 24 and transmitted to one and the same optical fiber transmission line 25.

The optical splitter 26 converts the transmitted optical clock signal into each of the clock receivers 29 requiring a reference clock.
It branches into 1 to 29n and supplies. Here, the optical splitter 2
6 is installed near the clock receivers 291 to 29n. For example, even when a new clock receiver 29x is installed, the clock receiver 29x and the optical splitter 2
The required clock signal can be received only by laying a very short fiber between the clock signals 6 and 6, and it is not necessary to install a new optical fiber between the clock supply device and the clock reception device as in the related art. As a result, even if the clock supply device and the clock reception device are physically far apart, once the optical fiber is laid between the optical coupler 24 and the optical splitter 26, such a complicated operation will be performed thereafter. Work requiring a large amount of operation is unnecessary, and the operation of the work is greatly reduced. Further, even when a large number of clock receiving devices are installed, only one expensive electric / optical converter 22a needs to be provided in the clock supply device. In addition, an expensive optical fiber can be used alone, which is not only economical, but also greatly reduces the cable accommodation space in the office building. In the above description, the case where the number of clock supply devices is two has been described. However, if the optical coupler 24 has multiple inputs, the optical clock signals transmitted from more clock supply devices can have the same configuration. It will be clear that distribution can be made to a plurality of clock receivers in a similar manner.
Further, as will be described later, if a plurality of clock supply devices are provided, the clock generation side becomes redundant, and there is also an effect of improving the reliability of the entire device as compared with the configuration of the first embodiment.

The optical clock signal (ie, the output signal of the clock supply device) input to the optical coupler 24, which is a component of the clock supply system, is as follows.
Two schemes are conceivable: a case where the optical wavelengths of the two optical clock signals are different and a case where the optical wavelengths of the two optical clock signals are equal. Hereinafter, these two cases will be described in more detail.

FIG. 3 shows an example of a clock distribution system according to the present invention in which two clock supply devices are installed and optical clock signals of different optical wavelengths are input to the optical couplers from the respective clock supply devices. FIG. In FIG. 3, reference numerals 33a and 33b denote clock supply devices for generating optical clock signals, respectively. The optical wavelength of the optical clock signal generated by both clock supply devices is λ1.
And λ2. Reference numeral 34 denotes an optical coupler similar to that of the second embodiment. Reference numerals 391 to 39n denote clock receiving devices. In the case of this configuration, optical demultiplexers 301 to 30n for separating only a clock signal of a desired optical wavelength are added to the clock receiving point. This is different from the clock receiving apparatus of the embodiment. Needless to say, in the case where the optical / electrical converters 371 to 37n of the clock receiving devices 391 to 39n operate selectively with respect to the wavelength of the input optical signal, for example, the optical receivers 371 to 37n can When a filter that transmits only a specific wavelength is added, it is not necessary to install an optical demultiplexer.

In FIG. 3, the first clock supply device 3
An optical clock signal with an optical wavelength of λ ₁ is sent from 3a, an optical clock signal with an optical wavelength of λ ₂ is sent from a second clock supply device 33b, and sent from the optical coupler 24 to the same optical fiber transmission line 35. . These optical signals have wavelengths λ ₁ and λ
An optical signal obtained by combining the _two lights. As described above, the optical signal transmitted through the optical fiber transmission line 35 is multi-branched by the optical branching device 36, and the mixed signal of the optical wavelengths λ1 and λ2 is distributed to the clock receiving devices 391 to 39n. You. Optical demultiplexers 301 to 30n are added to the reception points of the clock supply devices 391 to 39n, respectively. In this drawing, the clock reception device 391 receives the clock signal of the optical wavelength λ ₂ and the clock reception device 39n Is the optical wavelength λ ₁
Is selectively received. As described above, since each clock receiving device can selectively receive only the optical clock signal of the desired optical wavelength, it is possible to distribute clock signals of different speeds for each optical wavelength of the optical clock signal on the same medium. it can. For example, the clock signal of the speed f ₁ by the light wavelength lambda ₁ of the optical signal, a clock signal of the speed f ₂ is kept to be supplied by the light wavelength lambda ₂ of the optical signal. In each clock receiving device, if a clock signal convenient for each device is appropriately selected by the optical demultiplexer from the clock signals of these two speeds according to the internal operation, a great deal of cost and construction operation will be required. It is possible to easily receive the desired clock of each device without laying a new transmission medium requiring

As described above, when two clock signals are received from the clock supply device, the conventional clock supply method always requires two clock signals for one clock reception device.
In the clock distribution system of the present invention, the clock signal of one system (for example, the working system) is used for the optical wavelength λ ₁ , and the clock signal of the other system (for example, the standby system) is used for the optical wavelength λ _2. By doing so, it is possible to transmit by one optical fiber, and it is possible to greatly reduce costs and reduce cable space. In the following description, the case in which the number of clock supply devices is two has been described. However, it is apparent that the present invention can be applied to the case where more clock supply devices are installed by the same configuration and the same method. .

Next, the second example of the application of the clock distribution method of the present invention when the optical wavelengths of the optical clock signals input to the optical coupler from the plurality of clock supply devices are equal.
This will be described with reference to the implementation of the above. Taking the case where two clock supply devices are installed as an example, the configuration is as shown in FIG. 4A and 4B are waveform diagrams showing the operation of each unit of the present configuration. FIG. 4A shows the output signal waveform of the first clock supply device, and FIG. 4B shows the output signal waveform of the second clock supply device. Each signal waveform is shown. (A)
Fault occurs at time t _1, the time t ₁ later shows the case where the clock signal is disrupted. Also, FIG.
Shows the input signal waveform of each clock receiving device.

In this embodiment, since the two optical clock signals input to the optical coupler 24 have the same optical wavelength, the intensity of the output signal is the same as the intensity of the optical clock signals input from both clock supply devices 23a and 23b. Is added. Now, it is assumed that the clock supply devices 23a and 23b have their output clock signals phase-synchronized by appropriate means, and that their signal waveforms are both rectangular waves having an intensity of one. In this state, when the optical clock signal shown in FIGS. 4A and 4B is input to the optical coupler 24, the output signal of the optical coupler 24 becomes the first clock supply device 23a
Time t when clock supply is interrupted after a failure occurs
Before ₁ , the signal becomes a rectangular wave clock signal with a light intensity of 2.
The time t ₁ subsequent to the clock supply is disrupted from the second clock supply unit 23b, the light intensity is 1 square-wave clock signal. Since this signal is n-branched by the optical branching device 36, each of the clock receiving devices 291 to 29n has a time t _1.
Previously, light intensity 2 / n, the time t ₁ thereafter the light intensity is 1
/ N is distributed as a rectangular wave clock signal.

Here, if the intensity of the optical clock signal transmitted from the clock supply device or the reception determination level R of the optical / electrical converter 271 in each clock receiving device is set to a value satisfying the expression (1), 0 <R < 1 / n (1) Even after the time t _{1 when} the first clock supply device fails and its output signal is interrupted, each clock receiving device receives the clock signal without any influence. You can continue. In the above description, the optical clock signals of the two clock supply devices are inserted into the optical coupler 24 in advance, but usually, the optical clock signal is supplied from one clock supply device to the optical coupler 24, When updating the supply device, a new clock supply device is installed in advance. Then, after supplying the optical clock signal of the new clock supply device to the optical coupler 24, the method of removing the clock supply device that was operating up to that time is used, so that the clock can be received without affecting the clock reception device at all. The supply device can be renewed.

[0034]

As described above in detail, in the clock distribution system of the present invention, a plurality of clock supply devices generate a reference clock signal, convert the reference clock signal into an optical signal, and connect the reference clock signal to an optical signal immediately before the clock supply device. The optical coupler is once coupled by an installed optical coupler, transmitted through a single optical fiber to an optical coupler provided immediately adjacent to the clock receiving device, and then multi-branched by the optical coupler. This allows
In addition to being essentially unaffected by external disturbances such as noise and ground potential fluctuations, there is no need to use a large number of expensive electro-optical converters and optical fibers, and the cable space in the office can be greatly reduced. . In addition, when installing or adding a clock receiver, it is possible to supply a clock simply by installing an extremely short connecting fiber between the nearest optical branching device and the clock receiver. Since the installation work of transmission media can be greatly simplified,
There is an effect that an extremely economical clock distribution system can be realized. Furthermore, even when the clock receiving device requires a clock signal having a different speed or a plurality of clock signals, an optical clock signal having an optical wavelength different from the conventional one is inserted into the optical coupler installed immediately adjacent to the clock supply device. By installing an optical demultiplexer at the input point of the clock receiving device and selecting an optical clock signal having an optical wavelength of a required signal, it is possible to easily supply a new clock signal without laying a new transmission medium. There is. In addition, in the event of a failure, maintenance, or renewal of the clock supply device, the clock supply can be continued without affecting the clock reception device at all, so that not only the quality and reliability of the clock signal can be improved, but also the clock supply can be improved. There is also an effect that the maintenance of the device is facilitated.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the principle of a first embodiment of a clock distribution system according to the present invention.

FIG. 2 is a block diagram showing the principle of a second embodiment of the clock distribution system according to the present invention.

FIG. 3 shows a third embodiment of the clock distribution system according to the present invention;
FIG. 3 is a block diagram showing a configuration in a case where a plurality of clock supply devices transmit optical clock signals having different optical wavelengths.

FIG. 4 shows a third embodiment of the clock supply device according to the present invention;
FIG. 9 is a waveform chart showing the operation of each unit when transmitting an optical clock signal having the same optical wavelength.

FIG. 5 is a block diagram showing a configuration of a conventional clock distribution system.

[Explanation of symbols]

11, 21a, 21b, 31a, 31b, 51 Reference clock generator 12, 22a, 22b, 32a, 32b, 52 Electrical / optical converter 13, 53 Clock supply device 23a, 33a First clock supply device 23b, 33b 2 clock supply devices 24, 34 Optical couplers 15, 25, 35 Optical fiber transmission lines 16, 26, 36 Optical splitters 171-17n, 271-27n, 27x, 371-3
7n optical-electrical converter 181-18n, 281-28n, 381-38n, 5
81-58n, 28x device internal clock generator 191-19n, 291-29n, 29x, 391-3
9n, 591 to 59n clock receiving device 301 to 30n Optical demultiplexer 551 to 55n Line

Claims (3)

(57) [Claims] A clock supply device comprising: a reference clock generator for generating a reference clock composed of an electric clock signal; an electric / optical converter for converting the electric clock signal into an optical clock signal composed of an optical signal; An optical fiber transmission line connected to a clock supply device and transmitting the optical clock signal; and an optical branch for distributing and transmitting the optical clock signal transmitted through the optical fiber transmission line to a plurality of distribution optical fiber transmission lines. A clock receiving system comprising: an optical-to-electrical converter connected to the distribution optical fiber transmission line and receiving the optical clock signal and converting the optical clock signal into an electric clock signal; The optical fiber transmission line, comprising a plurality of the clock supply devices, wherein each optical clock signal transmitted from the plurality of the clock supply devices is optically coupled. An optical coupler disposed between each of the clock supply devices and the optical fiber transmission line, and transmitting at least one optical clock signal among the optically coupled optical clock signals to the optical / electrical The optical-to-electrical converter provided in the clock receiving device is capable of receiving when the optical clock signal is transmitted from all of the plurality of clock supply devices, and From at least one of the clock supply devices Clock distribution system, characterized in that even the light reception sensitivity so as to be received is set if thrown of the optical clock signal. 2. The clock distribution device according to claim 1, wherein each of the plurality of clock supply devices transmits the same optical clock signal. 3. At least one of the plurality of optical clock signals is composed of an optical signal having a wavelength different from that of another optical clock signal, and the plurality of optical clock signals are optical signals provided in the clock receiving device. A plurality of demultiplexed optical clock signals are demultiplexed for each wavelength by a demultiplexer, and one of the demultiplexed optical clock signals is selected and converted into an electric clock signal by the optical / electrical converter. Item 1. The clock distribution method according to Item 1.