JPS6246119B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a circuit for displaying a synchronization separation level on a waveform monitor when a synchronization signal is separated and extracted from a television signal. An example of an application area of the present invention is a television relay device.

A conventional general synchronous separation circuit is shown in FIG. The input TV signal IN is filtered by a low frequency filter LPF to remove noise and subcarrier components of approximately 3 MHz or higher, and is then passed through a feedback synchronous peak clamp circuit consisting of an inverting amplifier IC2, a comparator IC3, a constant current circuit Q3, and a voltage follower IC6. Added to 10. In the feedback synchronous peak clamp circuit 10, the TV signal that has passed through the LPF is inverted and amplified by IC2, and then sent to the comparator IC3.
The voltage is applied to the (+) terminal of the terminal and compared with the clamp voltage applied to the (-) terminal. For example, if the voltage level at the synchronization tip of the TV signal output of IC2 is lower than the clamp voltage, the output of IC3 becomes a low voltage level, the constant current circuit Q3 is turned off, and the charging voltage of the capacitor C36 is discharged through the resistor R21. The voltage gradually decreased starting from
Accordingly, the output of the voltage follower IC6 also gradually decreases. The output of this voltage follower IC6 is negatively fed back to the input of the first-stage inverting amplifier IC2, and the DC level of the input television signal applied from the LPF is gradually lowered, so that the DC level of the inverting output of IC2 gradually increases. Since the DC level is negatively fed back in this way, the synchronization peak level of the television signal approaches the clamp voltage, and a stable state is reached when the synchronization peak level exactly matches the clamp voltage.

The video signal whose synchronous peak portion has been clamped by the above method is supplied to the (+) terminal of the comparator IC4 and the (+) terminal of the comparator IC5.

Comparator IC5, constant current circuit Q6, voltage follower IC
8 is a feedback blanking detection circuit 12. A comparator IC5 compares the direct current level during the blanking period of the television signal, which is applied to the (+) terminal of IC5, with the synchronous peak portion clamped, and the negative feedback control voltage at the (-) terminal. For example, if the DC level during the blanking period of the TV signal at the (+) terminal of IC5 is lower than the negative air return control voltage at the (-) terminal, the constant current circuit Q6 is turned on only during the synchronous part, and the capacitor C
However, since this synchronization period is shorter than the blanking period, the charging voltage is lower than when the blanking period is being detected. This voltage is negatively fed back to the (-) terminal of IC5 through voltage follower IC8 and operates so as to approach the blanking level. When this negative feedback control voltage gradually decreases and matches the blanking level of the synchronous peak-clamped TV signal, the constant current circuit Q also applies during the blanking period.
6 is turned on and charges the capacitor C60 to increase the voltage. Therefore, this negative feedback control voltage becomes stable when it matches the blanking level.

Next, the slicing circuit slices the synchronous peak-clamped video signal applied to the (+) terminal of IC4 according to the level of the (-) terminal. A clamp voltage and a blanking level voltage are applied to the slice level variable resistor RV, and the slice point can be changed to any position in the synchronized section by turning RV.

Because of the above operation, when there is synchronous noise N in the input TV signal as shown in Figure 2, the slice level is adjusted to the level shown by the broken line.
If SL is set, an error synchronization signal will occur in the synchronization separation output, so it is necessary to change the slice level to the position shown by the solid line. If you want to quickly change the level during operation of the device, you have to measure and change the voltage at the two input terminals of the comparator IC4 separately, which is inconvenient with a 1-channel oscilloscope, so it is difficult to change it with a 2-channel oscilloscope. It is necessary to change the slice level while simultaneously displaying the slice level and the TV signal with the synchronization peak clamped on the oscilloscope. Therefore, there is a drawback that it is difficult to change the slice level flexibly. Furthermore, since the operating state of the synchronization separation circuit cannot be easily monitored during operation, there is a drawback that it is not possible to promptly deal with cases where the circuit is malfunctioning due to low S/N ratio of the input television signal.

SUMMARY OF THE INVENTION Accordingly, the present invention aims to improve the above-mentioned drawbacks of the prior art, and its features include means for generating a clamp voltage for clamping the synchronization leading edge of an input television signal, and a means for generating a clamp voltage for clamping the synchronization leading edge of an input television signal; A clamp circuit for clamping, means for generating a blanking level voltage of an input television signal, means for generating an arbitrary slice level between the clamp voltage and the blanking level voltage, and an input television clamped according to the slice level. a slicing circuit for extracting a sync signal from a signal; means for generating an arbitrary slicing level between a clamping voltage and a blanking level voltage; and a slicing circuit for extracting a sync signal from an input television signal clamped according to the slicing level. In the synchronization separation circuit having a clamped input television signal, a switching circuit is provided which switches the slice level to output the synchronization signal period of every two scanning lines of the clamped input television signal, and outputs the input television signal during other periods. , the output of the switching circuit is supplied to a waveform monitor, and the slice level and the input television signal are superimposed on the waveform monitor. With this configuration, the slice level can be changed reliably and quickly. Examples will be described below with reference to the drawings.

FIG. 3 shows an embodiment of the present invention, and parts that overlap with those in FIG. 1 are given the same reference numbers. Additional circuit section
These circuits are IC10, IC11, IC12, and IC15. The TV signal with the synchronous peak clamped at the (+) input of IC3 and the slice voltage signal become inverted voltage follower signals at IC11 and IC10, respectively, and are switched by switch 18 and output through buffer circuit IC12 for slice level monitoring. Becomes a signal (SL monitor). The switching gate signal of the switching switch 18 is generated by shaping the waveform of the synchronously separated SYNC signal by the waveform shaping circuit IC15. The switching sequence is such that, for example, the signal is switched to the slice voltage signal (output signal of the IC 10) for each interlaced scanning line and only in an interval including the sync signal period of the sync peak-clamped input television signal. As a result, the slice level monitor signal (SL monitor) has a waveform as shown in FIG. That is, the input television signal is output in the synchronous peak-clamped section of one scanning line, and the slice voltage signal is output in the synchronous peak-clamped section of the next scanning line. Therefore, when this part is observed on a TV signal waveform monitor, scanning appears alternately, and the input TV signal and slice level are displayed simultaneously and visually overlapping on the waveform monitor, making it easy to change the slice level. can be performed quickly and accurately in response to disturbances in the input signal. In addition, the synchronization of scanning of the waveform monitor at this time is
It is necessary to use the scanning trigger at the output of the SYNC signal, not the output of the SL monitor.

As described above, since the present invention has a slice level monitor circuit, when applied to a television relay device having a synchronization separation circuit, it can be used to promptly deal with deterioration in transmission conditions.

[Brief explanation of the drawing]

FIG. 1 shows a conventional general sync separation circuit, FIG. 2 shows an input television signal with synchronous noise, FIG. 3 shows a sync separation circuit according to the present invention, and FIG.
3 is a time chart showing each output signal of the circuit shown in the figure. IN; input television signal, 10; clamp voltage generation circuit, 12; blanking level generation circuit, 1
4; Slice circuit; 16; Slice level generation circuit; 18; Selector switch.

Claims (1)

[Scope of Claims] 1. Means for generating a clamp voltage for clamping the synchronization tip portion of an input television signal, a clamp circuit for clamping the input television signal in accordance with the clamp voltage, and a blanking level voltage of the input television signal. A sync separation circuit comprising: means for generating a slice level; means for generating an arbitrary slice level between a clamp voltage and a blanking level voltage; and a slice circuit for extracting a synchronization signal from an input television signal clamped according to the slice level. In the clamped input television signal, the slice level is set at the synchronization signal period part of every two scanning lines,
A switching circuit that switches to output the input television signal during other periods is provided, the output of the switching circuit is supplied to a waveform monitor, and the slice level and the input television signal are superimposed on the waveform monitor. A television signal synchronization separation level display circuit characterized by: