JPS61120585A - Synchronizing signal separating and clamping circuit - Google Patents

Abstract

PURPOSE:To attain excellent synchronizing separation and clamping by passing a video signal through an amplifier having a dynamic range where the synchro nizing signal part to be clamped before being fed to a comparator is not suppressed even when a DC potential of the synchronizing signal is fluctuated before the video signal is fed to the comparator. CONSTITUTION:An amplifier 4 is provided after a clamp amplifier 2, the tip of the synchronizing signal being its output signal is clamped by a clamp circuit 5, the result is fed to the comparator 6, and the amplifier 4 has the dynamic range from B to E so as to be activated at a low power supply voltage and small current consumption. When the amplifier 4 has a dynamic range lower than F and an input signal changes from a period T1 to a period T2, a correct synchronizing signal does not appear at the output of the comparator 6 and the loop of the amplifier 2 is not operated normally. When the input signal c changes from the period T1 to the period T1, since the circuit 5 clamps the tip of the synchronizing signal because the upper dynamic range of the amplifier 4 is E, the level responds to a level shown in a signal 13 and then normal synchronizing signal is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a sync signal separation and clamping device that can be used to separate sync signals and clamp video 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, 6 is a comparator, 7 is a sample and hold circuit, 8 is a differential amplifier, and 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 synchronization signal is obtained at terminal 9. On the other hand, terminal 3
The output video signal of is led to the sample hold circuit 7,
The potential of the pedestal is detected by the sample pulse generated from the synchronization signal at terminal 9, and is guided to the differential amplifier 8, where the difference from the reference potential (ground in the figure) is amplified, and the output voltage is used to connect the clamp amplifier. 2 is controlled.

The clamp amplifier 2 works in such a way that, for example, when the output potential of the differential amplifier 8 increases, the output potential of the terminal 3 decreases.
If the gain of the differential amplifier 8 is sufficiently large, the output potential of the sample-and-hold circuit 7 and the reference potential of the other input of the differential amplifier 8 will match, and as a result, the terminal 3 will be clamped to a constant potential. A video signal can be obtained. As for the input video signal, there may be a case where the DC potential of the synchronizing signal changes as shown in FIG. 4, such as when the input video signal is changed by a switch. Without the clamp circuit 6, in such a case, a normal synchronizing signal would not be output to the output 9 of the comparator 6, and the loop of the clamp amplifier 2 would not work properly and would not follow. For this reason, the clamp circuit 6 is set to have a faster response than the loop of the clamp amplifier 2, and when it responds as shown in FIG. can be made to follow. As shown in Fig. 4-11A, when an overshoot occurs in the video signal and enters the synchronization signal section, this overshoot portion is erroneously output to the output of the comparator θ. , not only does the synchronization signal become abnormal, but the potential at the wrong point is detected in the sample hold 7, and the loop is controlled in the wrong direction.As a result, the video signal at terminal 3 is disturbed, and therefore the voltage at terminal 9 is This creates a vicious cycle in which an erroneous synchronization signal is further output.

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 this will result in instability due to DC fluctuations in the signal and beat noise will be added to the synchronization tip. If you do this, it will be more likely to malfunction.

SUMMARY OF THE INVENTION An object of the present invention is to provide a device that can perform 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 separation/franging device of the present invention allows the synchronizing signal to be supplied to the comparator even if the DC potential of the synchronizing signal in the video signal fluctuates before the video signal is supplied to the comparator. It is passed through an amplifier with a dynamic range such that the portion of the synchronization signal that was previously clamped is not suppressed.

Operation The present invention has a configuration in which the above-described configuration increases the margin when separating synchronizing signals by the comparator, and reduces the dynamic range of the amplifier to save current.

Embodiment@1 Figure 1 is a schematic diagram of an embodiment of the present invention, and the second example has the same operation. 4 is an amplifier. As a method to solve the problem described in Fig. 3, the video signal is amplified before being supplied to the comparator 6, and the reference potential is set at a portion above the beat of the sync signal section under overshoot. There is a method to provide a margin when comparing with a reference potential. At this time, if we consider the case where a signal as shown in Figure 2 12 is input to terminal 1, in order to faithfully amplify the signal, the output of amplifier 4 must be as shown in Figure 2 1.
A dynamic range from B to D of 3 is required.

However, for this purpose, it is necessary to increase the power supply voltage, and the current consumption also increases. From the above points, the present invention provides an amplifier 4 after the clamp amplifier 2, clamps the leading end of the synchronizing signal of the output signal with the amplifier circuit 5, and supplies it to the comparator 6. At least, Fig. 2 1
It has a dynamic range from B to E of 3, which can be achieved with low power supply voltage and current consumption. Assuming that the amplifier 4 does not have a dynamic range below F in FIG. As a result, the loop of the clamp amplifier 2, which outputs a correct synchronizing signal at the output of the comparator 6, does not operate normally. Therefore, the dynamic range under the amplifier 4 is limited to B in FIG. 13. In addition, the input signal is transferred from the T2 section in FIG. 2 to the T1 section.
Since the tip of the dyna signal above the amplifier 4 is clamped, it responds as shown in FIG. 2, and after that a normal synchronization signal can be obtained.

In addition, in this embodiment, when clamping the force ζ pedestal described in the case where the clamp circuit 5 clamps the tip of the synchronizing signal, the dynamic range of the amplifier 4 is set at least from G to D in FIG. Just do it.

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 drawings]

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, 6... Clamp circuit, 6... Comparator, 7... Sample hold circuit, 8...
・Differential amplifier.

Claims (1)

[Claims] Clamping the video signal by a first clamp circuit using a sample pulse created from the separated synchronization signal,
This clamped video signal is supplied to a comparison means via a second clamp circuit and compared with a reference potential to separate the synchronization signal, and before the video signal is provided to the comparison means, A synchronous signal separation/clamping device characterized in that the synchronous signal is passed through an amplifier having a dynamic range such that at least a portion of the synchronous signal that is clamped by the second clamp circuit is not suppressed even if the DC potential of the synchronous signal fluctuates. .