JP2616450B2 - Clock supply system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a clock supply system for supplying a clock signal, and more particularly to a clock supply system having a spare clock signal.

[0002]

[Prior art]

In some types of communication systems, in order to improve the reliability of communication, when a failure occurs in a communication device, switching to a standby communication device is performed. One of the problems that occurs when switching to a spare communication device
First, there is a shift in frame synchronization. Frame synchronization means that when data is transmitted in a frame unit composed of a predetermined amount of data, the start position of the frame recognized on the receiving side matches the start position of the frame configured on the transmitting side. Say. As an invention of a device for solving the frame synchronization deviation, a buffer memory for temporarily storing data is prepared in a spare transmission device, and data is read from the buffer memory at a timing synchronized with a frame synchronization signal of the spare transmission device. it has been proposed that you send. In this device, the buffer memory absorbs the timing difference between the frame synchronization signal of the transmitting device in which a failure has occurred and the frame synchronization signal of the backup transmitting device. Such a transmitting device is disclosed in Japanese Patent Application Laid-Open No. 3-187534.

In a synchronous communication network, a clock signal and data synchronized with the clock signal are transmitted from the transmitting side, and the receiving side takes in the data by using the transmitted clock signal. For this reason, if the clock signal is interrupted, data cannot be transmitted / received and communication is interrupted. So, monitor the clock signal,
When this is interrupted, for example, instead of switching the entire transmission device, only the clock signal generator is switched to a spare one.

FIG. 4 schematically shows a circuit configuration of a conventionally used clock supply system. This clock supply system includes a clock signal supply unit 11 that outputs two clock signals, and a clock selection unit 12 that selects any one of these two clock signals.
It is composed of The clock signal supply unit 11
Clock supply unit 13 and second clock supply unit 14
Clock supply unit. The first clock supply unit 13 and the second clock supply unit 14 are connected to the first clock signal 15 and the second clock signal 15 having the same pulse width, cycle, and phase.
, Respectively. The first clock signal 15 and the second clock signal 16 are input to a selector 17. The selector 17 receives a switching control signal 18 from a selector control unit 19. The selector 17 selects and outputs one of the first clock signal 15 and the second clock signal 16 according to the switching control signal 18.

The selector control unit 19 monitors both the first clock signal 15 and the second clock signal 16,
These disconnections are detected. When the selector control unit 19 detects that either the first clock signal 15 or the second clock signal 16 has been cut off, it outputs the switching control signal 18 and outputs the clock signal of the one which has not been cut off. Is switched to.

FIG. 5 shows signal waveforms at various parts of the clock supply system shown in FIG. First
Clock signal 15 (a in the figure) and the second clock signal 1
6 (FIG. 6B) has the same period, pulse width and phase. Until a predetermined time T ₁₁ both signals are output normally, the selector control unit 19 outputs a switching control signal 18 for selecting the first clock signal 15 up to this point (FIG c). Time T ₁₂ after this
First, it is assumed that the first clock signal 15 is disconnected. The selector control unit 19 detects the disconnection of the first clock signal 15 at the time of the elapse until the time T _13, the second clock signal 16 changes the value of the switching control signal 18 to be selectively in a time T ₁₃ . Thus, the output clock signal 21 (FIG. D) of the selector 17 is time T ₁₃ later is configured to output a second clock signal 16.

In this example, the clock signal is switched when one clock pulse has elapsed since the clock signal was cut off. However, the clock signal is normally switched only when the clock pulse does not arrive for several clocks. This is because the clock signal may be momentarily interrupted by one clock pulse due to the influence of attenuation or noise in the transmission path. The time from when the clock signal is cut off until it is detected is called the cutoff detection time.

[0009]

As described above,
A conventionally used clock supply system detects that a clock pulse does not arrive for a period of one cycle or more, and thereby determines that the clock signal has been cut off. Therefore, when a clock signal is interrupted, it takes at least one cycle of the clock signal to detect this and switch to the other clock signal. Therefore, as shown in FIG. 5, the clock pulse is lost between the time when the clock signal is cut off (time T ₁₂ ) and the time when the switching is performed (time T ₁₃ ), and the communication is momentarily interrupted. There was a problem that it would.

When the disconnection detection time is set to several clocks, clock pulses are lost by the number of clocks, and there is a problem that the time during which data cannot be transmitted or received is further lengthened. Further, in order to switch the clock signal, a selector control unit for detecting the disconnection of the clock signal and a selector for actually switching the clock signal are required, so that the circuit configuration is complicated and the cost is increased.

Therefore, a first object of the present invention is to provide a clock supply system capable of supplying a clock signal without an instantaneous interruption by a spare clock signal even if the clock signal is interrupted.

A second object of the present invention is to simplify the configuration of a clock supply system having a spare clock signal.

[0013]

According to the first aspect of the present invention, there are provided: (a) a plurality of optical clock signals having a repetition period of a square wave pulse equal to each other, and adding these signal levels;
The period of the pulse waveform of the calculated signal is equal to that before the addition , and
(B) optical clock signal output means for outputting a plurality of optical clock signals each having a pulse width and a phase set so that each square wave pulse before addition has an overlapping portion with each other; Output of means
These multiple optical clock signals are input and
The signal level is added at the point where
Optical clock signal adding means for outputting an added clock signal
And (c) addition after addition of the optical clock signal adding means.
A clock signal generating means for generating a <br/> clock signal cycle before the addition by binarizing the clock signal with a predetermined threshold Ru is included in a clock supply system.

That is, according to the first aspect of the present invention, a plurality of optical clock signals having the same repetition period of the square wave pulse are output by the optical clock signal output means . Further, the plurality of optical clock signals, these signals
When the signal levels are added , the period after the addition is equal to the period of each optical clock signal before the addition , and
So that there are overlapping parts of the square wave pulse
The pulse width and phase are set . These optical clock signal is being added by the optical clock signal adding means into one addition optical clock signal. Since the clock signal generation means generates a clock signal synchronized with the added optical clock signal, its cycle is equal to the cycle of each optical clock signal before addition . Even if one of the optical clock signals before the addition is interrupted, the signal level of the other optical clock signal remains in the added optical clock signal, so that the clock generation means can continuously generate the clock signal. it can. Further, since the rectangular wave pulses are set so as to have overlapping portions, the period of the added optical clock signal does not change even if any of the optical clock signals is interrupted.

[0015] In the present invention of claim 2 wherein, in (i) square-wave pulse repetition period signal obtained by adding these signal levels and a plurality of optical clock signal equal pulse
A plurality of optical clock to the period of the waveform is set equal to the previous sum, and before addition of the respective <br/> the path <br/> pulse width and phase so that portions overlapping each other in the square-wave pulse at each occurrence An optical clock signal output device for outputting a signal; (b) a plurality of optical fibers for transmitting the plurality of optical clock signals separately for each signal ; and (c) a plurality of optical clock signals transmitted by these optical fibers. Enter these time
Do not add each signal level at places where
Optical clock signal adding means for outputting an added clock signal
And (d) addition after the addition by the optical clock signal adding means.
A clock signal generator and a clock signal generating means for binarizing the clock signal with a predetermined threshold value to generate a <br/> clock signal cycle before the addition Ru is included in a clock supply system.

That is, according to the present invention, a plurality of optical clock signals are prepared separately for each of these signals.
After being individually transmitted by the optical fibers, the signal levels are added on the clock signal generator side .
Therefore, even if any failure occurs in any of the optical fibers, a clock signal can be generated based on the optical clock signal transmitted by the remaining optical fibers.

Further, according to a third aspect of the present invention, there is provided: (a) a plurality of optical clock signals having a repetition period of a square wave pulse equal to each other , and
Equal the period of the pulse waveform as the previous addition and before the addition it
There are parts that overlap each other in the respective square wave pulse
An optical clock signal output means for outputting a plurality of optical clock signals urchin pulse widths and phases are set respectively, this
A plurality of optical clocks output by the optical clock signal output means
Signal and output the added optical clock signal
And adding optical clock signal output device and an optical clock signal adding means for force, an optical fiber for transmitting the (b) adding optical clock signal output from the adder optical clock signal output device, transmission by (c) the optical fiber Ru is and a clock signal generator for generating a <br/> clock signal cycle before adding the addition optical clock signal is binarized at a predetermined threshold which is a clock supply system.

[0018] That is, in the invention of claim 3, wherein the optical black
Input a plurality of optical clock signals output from the clock signal output means.
An added optical clock signal obtained by adding these signals is transmitted through an optical fiber and input to a clock generating means. By transmitting an added optical clock signal obtained by adding a plurality of optical clock signals in this manner, a plurality of optical clock signals can be transmitted by one optical fiber.

[0019] In the invention of claim 4, wherein the phase of a plurality of optical clock signal are different from each other. For example, when the clock generation means generates a clock signal in synchronization with the rising edge of the added optical clock signal, the clock signal becomes a clock signal synchronized with the optical clock signal having the most advanced phase.
Therefore, even if a large number of optical clock signals are added, the jitter of the generated clock signal is affected only by the phase fluctuation of one optical clock signal having the most advanced phase.

Furthermore the invention of claim 5, most pulse width long optical clock signal having a pulse width as a square wave pulse of the remaining optical clock signal is contained in a square wave pulse
And the phase are set. Thus, the pulse width of the addition optical clock signal is equal to the longest pulse width of the optical clock signal before summing. As a result, the interval between the pulses does not become short even after the addition .

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to embodiments.

FIG. 1 shows an outline of the configuration of a clock supply system according to an embodiment of the present invention. This clock supply system includes a combined clock supply unit 31 that supplies a clock signal, an optical fiber 32 that transmits the combined optical clock signal, and a transmission device 33 that uses the clock signal. Synthetic clock supply unit 3
1 includes two optical clock signal supply units, a first optical clock signal supply unit 34 and a second optical clock signal supply unit 35. The first optical clock signal 36 output from the first optical clock signal supply unit 34 and the second optical clock signal 37 output from the second optical clock signal supply unit 35 are both input to the optical combiner 38.

The optical combiner 38 combines the first and second optical clock signals 36 and 37 and outputs one optical signal. The term "combination" used here means to add (overlap) the signal levels of the input optical clock signals.
It means to make two optical clock signals. In this embodiment,
Will be expressed by the term synthesis. As the light combiner, a directional optical coupler can be used when the wavelengths of the lights to be combined are equal. If the wavelengths are different, a multiplexer can be used. The optical signal output from the optical combiner 38 is referred to as a combined optical clock signal 39.

The combined optical clock signal 39 is input to the clock signal generator 41 of the transmission device 33 via the optical fiber 32. The clock signal generator 41 outputs the clock signal 4 as an electric signal based on the synthesized optical clock signal 39.
2 is generated. The clock signal 42 output from the clock signal generation unit 41 is guided to the inside of the transmission device 33 for use as, for example, a clock signal serving as a reference for data transmission timing.

FIG. 2 shows waveforms of signals of various parts in the clock supply system shown in FIG. First
The optical clock signal 36 of FIG.
0% optical clock signal. The phase of the second optical clock signal 37 (b in the figure) is shifted from the first optical clock signal 36 by 60 degrees. Further, the pulse width of the second optical clock signal 37 is set to one third of the pulse width of the first clock signal 36. A combined optical clock signal 39 obtained by combining these optical clock signals (FIG. 3c)
The light intensity of the portion 51 where the pulse of the first optical clock signal 36 and the pulse of the second optical clock signal 37 overlap is high.

The pulse width and phase of the first optical clock signal 36 and the second optical clock signal 37 are set so as to satisfy the following conditions when they are combined by the optical combiner 38. That is, the pulses of each cycle of the two optical clock signals do not become independent pulses when they are combined, and the cycles are the same as before the combination even after the combination, and the pulses of each optical clock signal overlap when they are combined. That part can be. In particular, the conditions become important when three or more optical clock signals are combined. For example, when combining three optical clock signals, there are portions where the pulses of the first and third optical clock signals overlap the pulses of the second optical clock signal, and the first and third optical clock signals are combined. Are not overlapped. In this case, if the second optical clock signal is interrupted, the frequency of the combined optical clock signal is doubled because the pulses of the first and third optical clock signals do not overlap. This does not occur if the pulses of the first to third optical clock signals are set to overlap each other.

The clock signal generator 41, the intensity of light of the combined light clock signal 39 into an electric signal, and outputs an electrical signal by the period voltage that has become greater than or equal to the set threshold value of the converted electric signal It has become. For example,
The composite optical clock signal 39 is received by the PIN photodiode and converted into an electric signal. And the output is
Current-voltage conversion is performed using an amplifier. The converted voltage signal is compared with a predetermined reference voltage by a comparator, and the voltage signal output from the comparator is output as a clock signal. Thus, the clock signal generator 4
1 can be configured. In this embodiment, the reference voltage is set so that the comparator is turned "ON" when the light intensity of the combined optical clock signal becomes higher than the level indicated by the dotted line 52 shown in FIG.

[0028] When both of the 2 and the first optical clock signal 36 the second optical clock signal 37 is output normally, that is, until the time T ₂₁ combined optical clock signal by superimposing these lights 39 Are output from the photosynthesizer 38. T and from T ₂₂ from clock generator 41
A clock signal 42 having a pulse width corresponding to ₂₃ is output. Now, a first optical clock signal 36 is assumed to have a cross-sectional time T _24. At this time, the combined optical clock signal 39 is only the component of the second optical clock signal 37. Correspondingly, the clock signal 42 output from the clock signal generator 41 also has the same waveform as the second optical clock signal 37.

As described above, even if one of the optical clock signals is interrupted, the component of the other optical clock signal remains in the composite optical clock signal 39. 41 can output the clock signal 42 continuously. Further, since the switching of the clock signal is not performed, the configuration of the clock supply system can be simplified. Further, it is not necessary to set the disconnection detection time when switching the clock signal. That is, in the conventional method of switching the clock signal,
Although it is necessary to set the disconnection detection time in consideration of the instantaneous interruption of the clock signal, the apparatus according to the present embodiment does not switch the clock signal, so that it is not necessary to determine whether the instantaneous interruption occurs. Also, since two optical clock signals are combined, even if one optical clock signal is momentarily interrupted, a clock signal can be generated by the other optical clock signal, and the clock signal is not instantaneously interrupted. rare. Also, if the combined optical clock signal 39 after being combined by the optical combiner 38 is branched into a large number and used, the transmission / reception device only needs to individually include the clock signal generation unit 41, which simplifies the system configuration. can do.

By the way, in the clock supply system of this embodiment, the first optical clock signal 36 is disconnected from the state where the first and second optical clock signals 36 and 37 are combined as shown in FIG. When this happens, the phase of the generated clock signal is shifted by 60 degrees as compared with the case up to that time. That is, if the first optical clock signal 36 is not interrupted, a pulse should be output from the clock signal generation unit 41 at time T ₂₄ , but is output at time T ₂₅ because it has been interrupted. However, this phase shift can be absorbed by various methods. For example, the clock signal 42 output from the clock signal generation unit 41 is converted to a PLL (Phase
Locked Loop) is input as a reference signal to be subjected to phase comparison. When the phase of the input reference signal changes, the PLL circuit changes the phase of the output signal so as to follow the change. If the PLL circuit is set so that this phase tracking is performed gently, the phase of the clock signal output from the PLL circuit can be rapidly shifted by 60 degrees even when the first optical clock signal 37 is cut off. It changes slowly without. In this way, it can be sufficiently used as a clock signal that is a reference for the timing of transmitting and receiving data.

By shifting the phase of the first optical clock signal 36 and the phase of the second optical clock signal 37 by 60 degrees, the clock signal 4
2 is reduced. The clock signal generator 41 generates a clock signal in synchronization with the rising edge of the combined optical clock signal 39. Therefore, the first
If the phases of the optical clock signal 36 and the second optical clock signal 37 are shifted from each other, the jitter of the generated clock signal 42 is affected only by the phase fluctuation of the first optical clock signal 36 whose phase is advanced. .

Further, the pulse of the second optical clock signal 37 is included in the pulse of the first optical clock signal 36. As a result, the duty ratio of the synthesized optical clock signal 39 obtained by synthesizing these optical clock signals is the first.
50% which is the same as that of the optical clock signal 36 of FIG. For this reason, even if the waveform of the combined optical clock is rounded during transmission, the drop of the clock pulse is unlikely to occur, and a high-frequency clock signal can be used.

Modification

In the embodiment shown in FIG. 1, the light combiner 38 is included in the combined clock supply unit 31 side, but the light combiner 38 may be included in the transmission device 33 side.

FIG. 3 schematically shows the configuration of such a clock supply system as a modification of the present invention. The same parts as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be appropriately omitted. This clock supply system includes a clock signal generation unit 61 and first and second optical fibers 6.
2 and 63 and a transmission device 33. The transmission device 33 includes a light combiner 38 and a clock signal generator 41. With this configuration, even if any failure occurs in one optical fiber, the clock signal generation unit 41 can generate the clock signal 42 using the component of the other optical clock signal.

In the embodiments and the modified examples described above, the phase difference between the first optical clock signal and the second optical clock signal is set to 60 degrees, but the phase difference is not limited to this. If the phase difference is reduced as much as possible, the phase fluctuation of the clock signal output by the clock signal generation unit can be reduced even when one of the optical clock signals is interrupted. In the embodiment and the modified example, two optical clock signals are combined to generate a combined optical clock signal.
It goes without saying that three or more optical clock signals may be used.

[0037]

As described above, according to the first aspect of the present invention, the signal levels of a plurality of optical clock signals are changed.
Signal added by the signal adding means to add one added optical clock signal
Is generated, and the added clock signal after the addition is set to 2 by a predetermined threshold value.
Generates a clock signal with a period before addition
Some of these optical clock signals
Even after the addition, the added clock signal by the remaining optical clock signal
The clock signal can be generated by binarizing the signal with a predetermined threshold . This allows the clock signal to be supplied without interruption even when the optical clock signal is interrupted.
And reliability of communication can be improved. Furthermore, since the addition of the optical clock signal is performed,
Optical clock signal necessary for switching is rather name, it is possible to simplify the configuration of the clock supply system, failure of the device itself reduces the reliability is improved. Further, since an optical signal is used, there is almost no influence of noise.

According to the second aspect of the present invention, a plurality of
Optical clock signal adding means for adjusting the signal level of the optical clock signal
To create one added optical clock signal,
The added clock signal after the addition is binarized with a predetermined threshold and added.
It generates a clock signal with a period before calculation
So, even if some of these optical clock signals are interrupted,
The added clock signal by the remaining optical clock signal is
A clock signal can be generated by binarizing with a threshold . Thus, even when the optical clock signal is the cross-sectional, be fed without interruption clock signal
It is possible to improve communication reliability. Also,
Each optical clock signal before addition was prepared individually
Since the transmitted using an optical fiber, even if one of the optical fibers fails, the clock generation apparatus using the components of the remaining <br/> optical clock signal (signal component after addition) 2
A clock signal can be generated by the value processing .
Thereby, the reliability of communication can be further improved.

Further, according to the third aspect of the present invention, a plurality of
The signal level of the optical clock signal
Addition by stages to create one added optical clock signal
Then, the added clock signal after addition is binarized by a predetermined threshold value.
To generate a clock signal of the cycle before addition
So, some of these optical clock signals are interrupted
The additional clock signal from the remaining optical clock signal.
A clock signal can be generated by binarizing with a fixed threshold value . Thus, even when the optical clock signal is the cross-sectional, supply child without interruption clock signal
And the reliability of communication can be improved. Further, since the optical clock signal output device and the clock signal generation device are connected by one optical fiber, the transmission path can be simplified. Further, since signal levels of a plurality of optical clock signals are added to one optical fiber, branching of the added optical signals is easy,
An optical clock signal can be easily supplied to a large number of clock signal generation devices, and the cost of the system can be reduced.

According to the fourth aspect of the present invention, the signal
The phases of the plurality of optical clock signals to be added with the bell are different from each other. For example, if clock generation means is added
When the clock signal is generated in synchronization with the rise of the arithmetic optical clock signal, the clock signal is synchronized with the optical clock signal having the most advanced phase. Therefore, even if the the sum of the number of optical clock signal, the jitter of the clock signal to be generated only undergo only the influence of the phase fluctuation of the most advanced one optical clock signal of the phase. Therefore, the signal levels of a large number of optical clock signals are added and this is
Even if the threshold value is binarized , a high quality clock signal can be obtained.

According to the fifth aspect of the present invention, when the signal levels of the plurality of optical clock signals are added , the remaining optical clock signals are converted into a square wave pulse having the longest pulse width among the optical clock signals before the addition. A square wave pulse of the clock signal is included. That is, the pulse width of the optical clock signal by the addition does not become longer than the longest pulse width before the addition . Accordingly, even if the waveform is slightly reduced during transmission of the optical clock signal by the addition, the possibility that a pulse is lost is reduced, and a clock signal with a high frequency can be supplied.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an outline of a configuration of a clock supply system according to an embodiment of the present invention.

FIGS. 2A and 2B are various waveform diagrams showing waveforms of respective parts of the clock supply system shown in FIG.

FIG. 3 is a block diagram illustrating an outline of a configuration of a clock supply system according to a modification of the present invention.

FIG. 4 is a block diagram showing an outline of a configuration of a conventionally used clock supply system.

FIG. 5 is a diagram showing various waveforms representing waveforms of various parts of a conventionally used clock supply system.

[Description of Signs] 34, 35 Optical clock signal supply unit 38 Optical combiner 32 Optical fiber 41 Clock signal generation unit

Claims (5)

(57) [Claims] [Claim 1] A plurality of optical clock signal repetition period is equal to the square-wave pulses of these signals level
Equal before adding the period of the pulse waveform of the addition signal, and
And an optical clock signal output means for outputting a plurality of optical clock signal pulse width and phase are respectively set <br/> constant such that portions overlapping each other in each of the square-wave pulse before the addition exists, this light These multiple lights output by the clock signal output means
Input clock signals, and when they overlap in time,
Addition clock signal obtained by adding each signal level
An optical clock signal adding means for outputting, adding the clock signal after the addition of the optical clock signal adding means
A clock signal generating means for binarizing the signal with a predetermined threshold to generate a clock signal having a cycle before addition . 2. A plurality of optical clock signals having a repetition period of a square wave pulse equal to each other, and these signal levels are
Equal before adding the period of the pulse waveform of the addition signal, and
An optical clock signal output device that outputs a plurality of optical clock signals each having a pulse width and a phase set so that each of the square wave pulses before addition has an overlapping portion; and of a plurality of optical fibers for transmitting divided optical clock signal to the signal by, those of temporally enter multiple optical clock signal transmitted by the optical fiber
Addition by adding each signal level at overlapping points
Optical clock signal adding means for outputting an arithmetic clock signal;
The added clock signal after addition by the optical clock signal adding means.
A clock signal generating device having a clock signal generating means for generating a clock signal of a period before addition by binarizing the signal with a predetermined threshold value . 3. A plurality of optical clock signals having a repetition period of a square wave pulse equal to each other, and their signal levels are
Equal before adding the period of the pulse waveform of the addition signal, and
And an optical clock signal output means for outputting a plurality of optical clock signal pulse width and phase are respectively set <br/> constant such that portions overlapping each other in each of the square-wave pulse before the addition exists, this light Output by clock signal output means
Addition light obtained by inputting multiple optical clock signals and adding them
And adding optical clock signal output device and an optical clock signal adding means for outputting a clock signal, and an optical fiber for transmitting the summed optical clock signal output from the adder optical clock signal output device, summing transmitted by the optical fiber A clock supply system comprising: a clock signal generation device that binarizes an optical clock signal with a predetermined threshold to generate a clock signal having a period before addition . 4. The clock supply system according to claim 1, wherein the plurality of optical clock signals have different phases from each other. Wherein said plurality of optical clock signals, these
The pulse width and phase must be set so that when the signal levels are added, the square wave pulse of the optical clock signal having the longest pulse width among these includes the square wave pulse of the remaining optical clock signal. The clock supply system according to claim 1, 2 or 3, wherein