JPS61120583A - Synchronizing separation and clamping device - Google Patents

Abstract

PURPOSE:To attain excellent synchronizing signal separation by amplifying a video signal before being fed to a comparator and clipping a large-level part of the video signal after being clamped. CONSTITUTION:An amplifier 4 is provided after a clamp amplifier 2, and after the tip of a synchronizing signal of an output signal is clamped by a clamp circuit 5, the clamp circuit 10 clips the large level and supplies the result to a comparator 6. When a signal 12 is fed to an input terminal 12, a signal 13 appears at the output of the circuit 5. The circuit 10 clips a part of the signal 13 larger than the E and applies it to the comparator 6. Since the portion from the B to the E of the signal 13 is applied to the signal input of the comparator 6, the level is decreased remarkably in comparison with the case of no clip, the comparator 6 acts normally, the synchronizing signal portion is amplified and the synchronizing signal is separated stably.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a synchronization signal separation/clamping device that can be used to separate synchronization signals and clamp the signals in video equipment such as VTRs and TVs.

Conventional technology Figure 3 shows an example of a conventional synchronous signal separation/clamp circuit.
FIG. 4 shows the waveforms of each part. In FIG. 3, 1 is a video signal input terminal, 2 is a clamp amplifier, 3 is a clamped video signal output terminal, 6 is a clamp circuit, e is a comparator, T is a sample and hold circuit, 8 is a differential amplifier, 9 is a synchronization signal output terminal. The video signal applied to the terminal 1 is amplified and clamped by the clamp amplifier 2, then led to the clamp circuit 5, where it is clamped at the tip of the synchronizing signal, and the comparator 6 outputs the signal as shown by the broken line in FIG. A synchronizing signal is obtained at terminal 9. On the other hand, the output video signal from terminal 3 is guided to sample and hold circuit A, and the potential at the pedestal is detected by the sample pulse created from the synchronization signal at terminal 9, and differential amplifier 8
The difference from the reference potential (ground in the figure) is amplified, and the clamp amplifier 2 is controlled by the output voltage.

The clamp amplifier 2 works in such a way that, for example, when the output potential of the amplifier 8 increases, the output potential of the terminal 3 decreases, and if the gain of the differential amplifier 8 is sufficiently large, the output potential of the sample and hold circuit 7 and the differential amplifier 8 The reference potential of the other input of the two input terminals is controlled so that they match, and as a result, a video signal clamped to a constant potential is obtained at the terminal 3. The input video signal is as shown in Fig. 4-12 when switched by a switch, etc.
There may also be a case where the DC potential of the synchronizing signal changes as shown in FIG. Without the clamp circuit 5, in such a case, a normal synchronizing signal would not be output to the output 9 of the comparator 6, so the loop of the clamp amplifier 2 would not work properly and would not follow. Therefore, the clamp circuit 6 is connected to the clamp amplifier 2.
Set it so that the response is faster than the loop of
If a response is made to indicate a busy schedule, a normal synchronization signal is output to the terminal 9 after the response, and the loop can be followed. However, this method has the following problems. Fourth
As shown in A of FIG. 11, when an overshoot or the like occurs in the video signal and enters the synchronization signal section, this overshoot portion is erroneously output to the output of the comparator 6, causing the synchronization Not only does the signal become abnormal, but sample and hold 7 detects the potential at the wrong point, controlling the loop in the wrong direction, which disturbs the video signal at terminal 3. This creates a vicious cycle in which an incorrect synchronization signal is output.

In order to prevent this, the reference potential shown by the broken line in Figure 4-11 should be set as close to the synchronization tip as possible, but it will become unstable with respect to DC fluctuations in the signal and beat noise will be added to the synchronization tip. If you do, it will be more likely to malfunction.

SUMMARY OF THE INVENTION An object of the present invention is to provide a device that performs good synchronization separation and clamping even if there is overshoot or beat noise in a video signal.

Means for Solving the Problems The synchronizing signal separating/clamping device of the present invention is equipped with a clipping circuit that clips the high level portion of the video signal.

Effect: The present invention amplifies and clamps the video signal before providing it to the comparator, and then clips the high level part of the video signal, so it is possible to increase the margin when separating the synchronizing signal by the comparator. Malfunctions due to over differential input of the comparator can be eliminated, and good synchronization signal separation can be achieved.

Embodiment FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 shows signal waveforms for explaining its operation.

In FIG. 1, the same numbers as in FIG. 3 represent the same things and perform the same operations. 4 is an amplifier, and 1o is a clip circuit. As a method to solve the problem described in FIG. 3, the video signal is amplified before being provided to the comparator 6,
There is a method of setting the reference potential below the overshoot and above the beat of the synchronizing signal section to provide some margin when comparing with the reference potential. At this time, an excessive signal is applied to the input of the comparator 6. There is a limit to the differential input level of the comparator, and if this limit is exceeded, the reference input side will be swayed, the output will be distorted, and normal operation will not occur. From the above points, the present invention provides an amplifier 4 after the clamp amplifier 2.
A clamp circuit 6 clamps the leading end of the synchronizing signal of the output signal No. 7, and a clip circuit 10 clips the high level portion before supplying it to the comparator 6. When a signal as shown in FIG. 2 is applied to the input terminal 1, a signal as shown in FIG. 13 appears at the output of the clamp circuit 6.

In FIG. 13, a portion having a higher level than E is clipped by a clipping circuit 1o and provided to a comparator e. In this way, comparator 6
Since only the portions B to E in Fig. 2 13 are applied to the signal input of , it can be much smaller than in the case of no clipping (B to C in 13), and the comparator 6 functions normally and , the synchronizing signal section is amplified compared to the case of FIG. 3, and the synchronizing signal can be stably separated.

In this embodiment, the clamp circuit 5 has been described as one that clamps the leading end of the synchronizing signal, but any other method other than one that clamps the pedestal may be used.

In addition, the loop of the clamp amplifier 2 and the 2 loop of the clamp circuit S
The present invention is also effective in systems that do not have two clamps, but simply rely on one clamp circuit (regardless of loop type 'C' or not). Further, the clipping level is not limited to E in FIG. 2, but may be any level as long as the synchronizing signal can be separated and the input level of the comparator 60 does not become excessive.

Effects of the Invention As described above, according to the present invention, it is possible to perform good synchronization signal separation and clamping even when the potential of the input video signal changes, or when there is overshoot or beat noise.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an embodiment of the present invention, Fig. 2 is a signal waveform diagram for explaining its operation, Fig. 3 is a block diagram showing a conventional example, and Fig. 4 is a waveform diagram of each part thereof. . 2... Clamp amplifier, 4... Amplifier, 5... Clamp circuit, 6... Comparator, 7... Sample hold circuit, 8...
・Differential amplifier, 1o... Clip circuit. Name of agent: Patent attorney Toshio Nakao and 1 other person Figures 3 and 4

Claims (1)

[Claims] When a video signal is clamped by a clamp circuit and the clamped video signal is compared with a reference potential by a comparison means to separate a synchronization signal, a large level portion of the video signal is A synchronizing signal separating/clamping device characterized in that it is configured to be clipped by a clipping circuit.