JPH0738548A - Transmitter - Google Patents

Abstract

PURPOSE:To provide a transmitter which can be stably provided with a clock signal to be a reference through a transmission line. CONSTITUTION:A clock extraction part 18 prepares an extracting clock signal 19 based on a transmission line signal 13. This signal 19 and a reference clock signal 11 are supplied to a switching part 15 and besides, the presence/absence of abnormality is monitored by respective abnormality detection parts 16 and 21. This monitored result is inputted to a switching control part 24, and the switching part 15 is controlled. When the first abnormality detection part 16 detects no abnormality, the reference clock signal 11 is outputted from the switching part 15 and supplied to a phase locked oscillation part 28, and the various kinds of clock signals 291-29N to be used inside the device are prepared. When the second abnormality detection part 21 detects no abnormality although the reference clock signal 11 gets abnormal, the extracting clock signal 19 is outputted from the switching part 15.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmission apparatus which receives a clock signal for synchronization from the outside of the apparatus and operates in synchronization with the clock signal, and more particularly to a reference even when an abnormality is detected in the received clock signal. The present invention relates to a transmission device that can secure the clock signal.

[0002]

2. Description of the Related Art In a communication system composed of a plurality of transmission devices operating in synchronization with each other, a common clock signal is used to synchronize signals between the respective transmission devices. In such an apparatus, for example, JP-A-60-7
As disclosed in Japanese Patent Laid-Open No. 0839 or Japanese Patent Laid-Open No. 1-259644, the system is provided with two-system receiving sections. When one of the receiving units detects an abnormality in the reference clock signal, the receiving unit is switched to the receiving unit of the standby system as another system to restore the normal operation of the device.

[0003]

Therefore, when the clock signal supply device itself outside the device is in an abnormal state, the received reference clock signal is abnormal in both systems, and it is not possible to cope with this by switching the receiving section. . Therefore, the reference clock signal for synchronization is not supplied to the phase locked oscillator in the transmission device, and the phase locked oscillator runs by itself. As a result, there is a problem that the phase of the signal between the opposing transmission devices is deviated, and the data sampling timing is deviated to cause a data error.

In order to solve such a problem, a supply device for generating a reference clock signal outside the device is used.
All you have to do is arrange more than one system. However, even if a plurality of reference clock signal supply devices are arranged in this way, if the common power source of these devices goes down, the reference clock signal will not exist and the same problem will occur. It was

Therefore, an object of the present invention is to provide a transmission device which can stably obtain a reference clock signal through a transmission line.

[0006]

According to a first aspect of the invention, reference clock signal monitoring means for monitoring whether or not a synchronization reference clock signal input from the outside is normal, and transmission received from the outside. Clock signal extracting means for inputting a path signal to extract a clock signal having the same frequency as the reference clock, and an extracted clock signal for monitoring whether or not the extracted clock signal extracted by the clock signal extracting means is normal The monitoring means, the clock signal selecting means for inputting the reference clock signal and the extracted clock signal to select one clock signal, and the monitoring result of the reference clock signal monitoring means and the extracted clock signal monitoring means are input to make normal operation. Clock signal selection control means for controlling the selection of the clock signal selection means so that the clock signal is output. To be provided in.

That is, according to the first aspect of the invention, in addition to the reference clock signal for synchronization input from the outside, a signal of the same frequency as the reference clock signal from the transmission line signal such as the main signal received through the transmission line is received. The extracted clock signals are generated and these clock signals are input to the clock signal selection means. On the other hand, with respect to each of the reference clock signal and the extracted clock signal, the abnormality detection unit detects whether or not an abnormality has occurred in the reference clock signal and the extracted clock signal, and the selection control of the clock signal selection unit is performed according to the detection result. I am going to do it. Therefore, for example, when an abnormality is detected in the reference clock signal, the extracted clock signal is selected instead, and the reference clock signal can be stably obtained on the transmission device side.

According to the second aspect of the present invention, the reference clock signals for synchronization input from the outside have a plurality of systems, and the clock signal selection control means has the clock signals between the reference clock signals and the extracted clock signals of the plurality of systems. It is characterized by performing selection control of. In this way, if the reference clock signals for synchronization input from the outside are multiple systems,
The clock signal can be stably obtained together with the generation of the extracted clock signal.

According to the third aspect of the present invention, the extracted clock signal is a clock signal of a plurality of systems created by the transmission path signals for each station. That is, the generation of the reference clock signal is stabilized by using the transmission path signals of different stations.

[0010]

EXAMPLES The present invention will be described in detail below with reference to examples.

FIG. 1 shows the essential parts of the structure of a transmission apparatus according to an embodiment of the present invention. This device has two input terminals, a reference clock signal input terminal 12 for inputting a reference clock signal 11 from the outside and a transmission path signal input terminal 14 for inputting a transmission path signal 13 from the outside. The reference clock signal 11 is input to one side of the switching unit 15, and is also input to the first abnormality detecting unit 16 so that the presence / absence of the abnormality is monitored.

On the other hand, the transmission path signal 13 is supplied to the clock extraction unit 1
A clock signal (hereinafter referred to as an extracted clock signal) 19 that is the same as the reference clock signal is input to the signal source 8 and extracted. The extracted clock signal 19 is supplied to the other input terminal of the switching unit 15 and is also supplied to the second abnormality detecting unit 21 so that the presence / absence of the abnormality is monitored. These first and second abnormality detectors 1
The detection result signals 22 and 23 indicating the detection results of 6 and 21 are
It is adapted to be input to the switching control unit 24. The switching control section 24 outputs a switching control signal 26 to the switching section 15 based on these detection result signals 22 and 23 to perform the switching control.

The reference clock signal 27 output from the switching unit 15 is supplied to the phase locked oscillator 28 as a synchronizing signal. Based on this, the phase-locked oscillating unit 28 outputs various clock signals 29 _{1 to} 29 _N for operating the respective units in this transmission device.

A reference clock signal is supplied to each of the same stations in the transmission device having such a configuration. The switching control unit 24 is composed of a logic circuit that takes the logic of the two detection result signals 22 and 23, and the logic is as follows.

First, when the first abnormality detecting unit 16 does not detect the abnormality of the reference clock signal 11, the switching control unit 24 controls the switching unit 15 to select the reference clock signal 11. It has become. At this time, the reference clock signal 11 is supplied to the phase locked oscillator 28 as the reference clock signal 27. The phase-locked oscillator 28 generates various clock signals 29 _{1 to} 29 _N used in the apparatus by appropriately dividing the reference clock signal 27.

When the first abnormality detecting unit 16 detects the abnormality of the reference clock signal 11 and the second abnormality detecting unit 21 does not detect the abnormality of the extracted clock signal 19, the switching control unit 24. Controls the switching unit 15 so as to select the extracted clock signal 19 side generated by the clock extraction unit 18 as a measure in the event of an abnormality. At this time, the extracted clock signal 19 is supplied to the phase-locked oscillator 28 as the reference clock signal 27, and various clock signals 29 _{1 to} 29 _N are generated based on this.

In the embodiment described above, the case where one system of the reference clock signal is prepared outside the transmission device has been described, but the present invention can be applied to the case where a plurality of systems of the reference clock signal are prepared. The present invention can also be applied to the case where a plurality of transmission path signals are input.

For example, when two systems of reference clock signals are prepared for the transmission line, the logics of the detection results of the abnormality detection units of these and one type of transmission line signal are taken and the switching unit is switched and controlled. Good. Also, when a plurality of transmission path signals are received, even if an abnormality occurs in the transmission path signal of one station (for example, a local station), another station (for example, a remote station) In many cases, the transmission line signal of) is normal. Therefore, if the clock signal is extracted based on this normal transmission line signal, the phase-locked oscillator can operate normally even when the reference clock signal cannot be received normally.

[0019]

As described above, according to the present invention, in addition to the reference clock signal for synchronization input from the outside, the reference clock signal from the transmission path signal such as the main signal received through the transmission path is received. Since an extracted clock signal with the same frequency as the above is generated, even if an abnormality occurs in the reference clock signal, the phase of each transmission device shifts and the signal phase between the devices shifts, causing a data error. The situation can be avoided. Further, even if the external clock supply source is only one system, it is possible to use a plurality of systems, and the reliability of the device can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing a main part of a transmission device according to an embodiment of the present invention.

[Explanation of symbols]

11 Reference Clock Signal 12 Reference Clock Signal Input Terminal 13 Transmission Line Signal 14 Transmission Line Signal Input Terminal 15 Switching Section 16 First Abnormality Detection Section 18 Clock Extraction Section 21 Second Abnormality Detection Section 24 Switching Control Section 29 _{1 to} 29 _N Various clock signals

Claims (3)

[Claims] 1. A reference clock signal monitoring means for monitoring whether or not a synchronization reference clock signal input from the outside is normal, and a transmission line signal received from the outside to input the same frequency as the reference clock. A clock signal extracting means for extracting the clock signal, an extracted clock signal monitoring means for monitoring whether the extracted clock signal extracted by the clock signal extracting means is normal, and the reference clock signal and the extracted clock signal. Clock signal selecting means for inputting and selecting one clock signal, and clock signal selecting means for inputting the monitoring results of the reference clock signal monitoring means and the extracted clock signal monitoring means and outputting a normal clock signal And a clock signal selection control means for controlling the selection of the transmission device. 2. The reference clock signals for synchronization input from the outside have a plurality of systems, and the clock signal selection control means controls the selection of clock signals between the plurality of systems of reference clock signals and the extracted clock signals. The transmission apparatus according to claim 1, which is performed. 3. The transmission device according to claim 2, wherein the extracted clock signal is a clock signal of a plurality of systems created by a transmission line signal for each station.