JPH01293727A - Pcm optical transmission equipment - Google Patents

Abstract

PURPOSE:To reproduce receive data without any trouble even when no video signal exists by providing an input stop detecting circuit and a means to impress a control voltage, by which a frequency in a VCO goes to the one in a filter passing band when an input is stopped, to the VCO for an optical transmitting part. CONSTITUTION:An original clock signal generated by a VCO1 is divided by a dividing circuit 2, made into a low-speed clock signal, inputted to a digital phase comparator 3, and phase-compared with a horizontal synchronizing signal separated from the video signal by a horizontal synchronizing signal separating circuit 6 at this comparator 3. The output of the comparator 3 is inputted through an LPF4 to a control voltage switching circuit 5, and a control voltage V, which is previously set so that the frequency in the VCO1 can be a prescribed oscillation frequency, is also inputted to the circuit 5. An input stop detecting circuit 7 detects the existence of the horizontal synchronizing signal all the time and sends a signal to the circuit 5 when no horizontal synchronizing signal exists. The circuit 5 switches so as to impress the output of the LPF4 to the VCO1 when the signal is not inputted from the circuit 7 and to impress the voltage V to the VCO1 when the signal is inputted from the circuit 7.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a PCM optical transmission device that uses a digital phase comparator to control an original clock signal generator. It is often used in PCM transmission equipment, etc. because it is suitable for use and can be mass-produced at low cost. Conventional PC that transmits video signals using PCML light
In M-optical transmission equipment, a digital phase comparator compares the phase of the horizontal synchronizing signal of the video signal and a low-speed clock signal frequency-divided from the transmission equipment's original clock signal generator (for example, a VCO, etc.), and a VCOH phase comparator Its oscillation frequency and phase are controlled by a control voltage from the oscilloscope.

Furthermore, in the optical receiving section, a high-speed clock signal is extracted using a surface acoustic wave filter or the like, and the received data is identified and reproduced.

Problems to be Solved by the Invention However, in such conventional methods, when no video signal is input, the horizontal synchronizing signal is not input to the digital phase comparator, so the output voltage of the phase comparator, that is, the oscillation frequency of the VCO The control voltage that controls the phase comparator is either the maximum or minimum voltage that the phase comparator has. This control voltage greatly changes the oscillation frequency of the VCO, which may deviate from the passband of the surface acoustic wave filter in the optical receiver, making it impossible to extract the clock signal and reproduce the received data. If data is multiplexed and transmitted in addition to the video signal, problems may occur, such as the data not being able to be received.

The present invention has been made in view of the above, and an object of the present invention is to provide a POM optical transmission device that can reproduce received data without any problem even when there is no video signal.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention provides a means for detecting an input disconnection of a horizontal synchronizing signal of a video signal input to a digital phase comparator, and a means for detecting an input disconnection of a horizontal synchronizing signal. The optical transmitter is provided with means for applying to the VCO a control voltage that, when detected, has a frequency within the passband of the surface acoustic wave filter of the optical receiver.

Effect of the Invention With the above-described configuration, the present invention detects the interruption of input of the horizontal synchronizing signal when the video signal is no longer input.

When an input disconnection is detected, the control voltage from the digital phase comparator applied to the VCO is cut off, and the control voltage is changed so that the oscillation frequency of the VCO is within the passband of the surface acoustic wave filter in the optical receiver. is set in advance and applied to the VCO. Therefore, even when the video signal is lost,
Received data can be played back without any problems.

Embodiment FIG. 1 is a block diagram showing an embodiment of the present invention. In Figure 1, 1FiVco, 2 is a frequency dividing circuit, 3 is a digital phase comparator, 4 is an LPF, es is a control voltage switching circuit, 6 is a horizontal synchronizing signal separation circuit, and 7Fi is an input disconnection detection circuit. The original clock signal is frequency-divided by the frequency divider circuit 2 and becomes a low-speed clock signal, which is sent to the digital phase comparator 3.
Here, the phase of the signal is compared with the horizontal synchronization signal separated from the video signal by the horizontal synchronization signal separation circuit 6.

The output of the digital phase comparator 3 is input to the control voltage switching circuit 5 via the LPF 4. The control voltage switching circuit 6 also receives a control voltage V that is set in advance so that VCOl has a predetermined oscillation frequency. The input disconnection detection circuit 7 constantly detects the presence or absence of a horizontal synchronization signal, and sends a signal to the control voltage switching circuit 5 when the horizontal synchronization signal disappears.

The control voltage switching circuit 6 applies the output of the LPF 4 to vCol if there is no input from the input disconnection detection circuit 7, and changes it to a preset control voltage v12vco1 if there is an input from the input disconnection detection circuit 7. Switch to apply.

The control voltage switching circuit 6 can be easily constructed using a relay, an analog switch, or the like. In addition, the input disconnection detection circuit 7 can use an integrating circuit and a comparator to detect the average value of the horizontal synchronizing signal and compare it with the reference value using the comparator.
This can be easily realized because the output of the comparator is inverted when the horizontal synchronization signal disappears. In this embodiment, when the control voltage V is applied to vcol, the oscillation frequency may change due to the temperature characteristics of the VCO1, but the VCO1 may be placed in a thermostatic oven.

FIG. 2 is a block diagram showing a second embodiment of the invention. Components having the same functions as those in FIG. 1 are designated by the same numbers as in FIG. 1, and explanations thereof will be omitted.

In FIG. 2, 8 is an input switching circuit, and 9 is a reference crystal oscillator. The horizontal synchronization signal separated by the horizontal synchronization signal separation circuit 6 and the output of the reference crystal oscillator 9 are connected to the manual switching circuit 8, and when a video signal is input, the horizontal synchronization signal is subjected to digital phase comparison. When the video signal is no longer input, the output of the reference crystal oscillator 9 is input to the digital phase comparator 3 in response to a signal from the input disconnection detection circuit 7. In either case, a phase-locked loop (PLL) including VCOl is formed, and if the temperature of the reference crystal oscillator 9 is compensated, the oscillation frequency of VCOl will be extremely stable.

Effects of the Invention As described above, according to the present invention, even if the input to the digital phase comparator is lost, the original clock signal generator of the transmission device can operate without any problem, resulting in highly reliable PCTM. An optical transmission device can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a first embodiment of the present invention;
The figure is a block diagram showing the second embodiment. 1... VCO12... Frequency divider circuit, 3.
...Digital phase comparator, 4...LPF
, 5... Control voltage switching circuit, 6...
Horizontal synchronization signal separation circuit, 7... Input disconnection detection circuit, 8... Input switching circuit, 9... Reference crystal oscillator. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
figure

Claims (2)

[Claims] (1) PLL that compares the phase of the horizontal synchronization signal of the video signal and the clock signal from the VCO using a digital phase comparator
in an optical transmission device comprising an optical transmitting unit that digitizes and transmits a video signal, and an optical receiving unit that includes a surface acoustic wave filter that extracts a clock signal; The control voltage that has a frequency within the passband of the surface acoustic wave filter when the input is cut off is set to the V
A POM optical transmission device, characterized in that the optical transmitter is provided with means for applying CO. (2) In an optical transmission device, a means for detecting input disconnection of a horizontal synchronizing signal, and a means for inputting an output from an oscillator having an oscillation frequency that is an integer fraction of the oscillation frequency of the VCO to a digital phase comparator when the input is disconnected. 2. A PCM optical transmission device according to claim 1, wherein said optical transmitter is provided with said optical transmitter.