JPS63227280A - Synchronizing separator circuit - Google Patents

Abstract

PURPOSE:To prevent jitter from being generated in the synchronization of a video signal, by synchronizing the video signal with the horizontal synchronizing signal of an inputted composite external synchronizing signal, and setting the cycle of a vertical blanking period at 1H. CONSTITUTION:A vertical synchronizing signal is separated by inputting the output B of first monostable multivibrator 2 triggered by the horizontal synchronizing signal of the composite external synchronizing signal A and a composite synchronizing signal passing a delay circuit to a NOR gate 3. Furthermore, to the input terminal of a NOR gate 4 connected to the trigger terminal of second monostable multivibrator 5, the output signal B of the first monostable multivibrator 2 and the output signal E of the second monostable multivibrator 5 itself are inputted. And a pulse signal with a cycle of 1H is outputted from the second monostable multivibrator 5, and the horizontal synchronizing signal with the cycle of 1H through a differentiation circuit and an inverter 7 can be obtained. In such a way, it is possible to prevent the jitter from being generated in the synchronization of the video signal.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is a synchronization separation circuit used in the field of video equipment such as video cameras.

2. Description of the Related Art A conventional synchronous separation circuit, as shown in FIG.
It is formed of a separation circuit 12 and a pseudo synchronization signal generation circuit 13. When a composite synchronization signal is input to the input terminal 11 of this synchronization separation circuit, the vertical synchronization signal VD and horizontal synchronization signal HD are separated by the HD/VD separation circuit 12, but the vertical blanking period of the horizontal synchronization signal is A pseudo signal with a period determined by an external capacitor C and a resistor R is applied. Therefore, the horizontal synchronization signal during the vertical blanking period has a period different from that of the input composite synchronization signal (normal).

Problems to be Solved by the Invention When driving a video camera or the like using external synchronization, in order to simplify the connection cable for the external synchronization signal, a composite synchronization signal is used as the external synchronization signal to synchronize with a computer for image processing. I am made to do so.

On the other hand, external synchronization circuits for video cameras often use PLL circuits for synchronization. A horizontal synchronization signal HD is used as a signal to be compared and synchronized in this PLL circuit. When using a composite synchronization signal as an external synchronization signal, it is necessary to separate it into a horizontal synchronization signal HD and a vertical synchronization signal VD. The horizontal synchronization signal HD separated by the conventional synchronization separation circuit shown in FIG. The oscillation frequency fluctuates, causing jitter in the synchronization of the video signal.

Means for Solving the Problems The present invention sets the output pulse width of the first monostable multivibrator that is triggered by the horizontal synchronization signal of the composite external synchronization signal to be slightly larger than the horizontal synchronization pulse width, and
The vertical synchronization signal is separated by inputting the output of the monostable multivibrator and the composite synchronization signal passed through the delay circuit into a NOR gate, and the output pulse width is made approximately 3/4H of the width H of the horizontal synchronization pulse. Inputting the output signal of the first monostable multivibrator and the output signal of the second monostable multivibrator itself to an input terminal of a NOR gate connected to a trigger terminal of the set second monostable multivibrator. This outputs an IH period pulse signal from the second monostable multivibrator, passes the output signal of the second monostable multivibrator through a differentiating circuit and an inverter, and outputs an IH period horizontal synchronizing signal from the same inverter. This is the configuration to obtain.

According to the present invention, the pulse signal output from the second monostable multivibrator is synchronized with the horizontal synchronization signal of the input composite external synchronization signal, and the period of the vertical blanking period is also IH. Therefore, when the synchronization separation circuit of the present invention is used in a video camera, since the oscillation frequency of the VCO of the PLL circuit forming the external synchronization circuit does not vary, jitter does not occur in the synchronization of the video signal.

Embodiment FIG. 1 shows a synchronous separation circuit of the present invention, in which 1 is a composite external synchronous signal input terminal, 2 is a first monostable multivibrator, 3 and 4 are NOR gates, and 5 is a second monostable multivibrator. , 6°7 is an inverter. FIG. 2 shows signal waveforms at various parts of the synchronization separation circuit shown in FIG. 1 during the vertical blanking period.

A detailed explanation will be given below with reference to the signal waveforms shown in FIG.

When the composite synchronization signal A is input to the input terminal 1, the first monostable multivibrator 2 is triggered by the horizontal synchronization signal, and the timing capacitor C1 and the resistor R+
A pulse signal B having a pulse width determined by the time constant of the product C+R+ is output. The time constants of C and R are set so that the pulse width of pulse signal B is slightly larger than that of the horizontal synchronizing signal. The composite synchronization signal input to input terminal 1 is the product C2R2 of capacitor C2 and resistor R2.
The trigger input of the first monostable multivibrator 2 is delayed by the delay time of the first monostable multivibrator 2 through a delay circuit having a time constant of , and is then input to the NOR gate 3. Since the output signal B of the first monostable multivibrator 2 is input to the other input terminal of the NOR gate 3, the output of the NOR gate 3 becomes a pulse signal C with the vertical synchronization part separated. . When the output signal C of the NOR gate 3 is input to the inverter 6 via an integrating circuit consisting of a capacitor C3 and a resistor R3, the inverter 6 outputs a vertical synchronizing signal.

On the other hand, the output signal B of the first monostable multivibrator 2
is input to one input terminal of the NOR gate 4, and the second
Trigger the monostable multivibrator 5. The output pulse width of the second monostable multivibrator 5 is approximately 3/4
Timing capacitor C4 and resistor R4 so that
is set. This pulse signal E is applied to the NOR gate 4.
By feeding back to the other input terminal of the second monostable multivibrator 5, the second monostable multivibrator 5 is triggered only at periods longer than 3/4H. Therefore, as shown in the pulse signal E in FIG. 2, since the second monostable multivibrator 5 is triggered at the IH period even during the vertical blanking period, its output signal E is It is synchronized with the signal and becomes a pulse signal with an IH cycle.

The output signal E of the second monostable multivibrator 5 is input to the inverter 7 via a differentiating circuit consisting of a capacitor C5 and a resistor R5. The constants c, , R5 of this differentiation circuit
is set so that the output pulse width of the inverter 7 is about 5 μS. Therefore, the output terminal of the inverter 7 outputs a horizontal synchronizing signal F with a pulse width of approximately 5 μs and an IH period.

Effects of the Invention According to the present invention, the horizontal synchronization signal output from the synchronization separation circuit is compared with the horizontal synchronization signal internally oscillated by the phase comparison circuit of the PLL circuit, and the period of the horizontal synchronization signal from the synchronization separation circuit is kept constant. Therefore, the oscillation frequency of the vCO connected to the phase comparison circuit becomes stable. The video signal of the video camera is formed using the signal output from the VCO. Therefore, when a video camera to which the sync separation circuit of the present invention is applied is driven by a composite external sync signal, jitter does not occur in the video signal.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a synchronous separation circuit according to an embodiment of the present invention, FIG. 2 is a signal waveform diagram of each part of FIG. 1, and FIG. 3 is a circuit diagram of a conventional synchronous separation circuit. 1...Composite external synchronization signal input terminal, 2
・・・・・・First monostable multivibrator, 3, 4
...NOR gate, 5...second monostable multivibrator, 6,7...inverter.

Claims (1)

[Claims] A first monostable multivibrator which receives a horizontal synchronization pulse of a composite synchronization signal as a trigger input, and a second monostable multivibrator which receives a trigger input with a logical composite signal of the output signal of the first monostable multivibrator and its own output signal. an inverter that inputs, via an integrator circuit, a logical composite signal of the output signal of the first monostable multivibrator and the delayed signal from the composite synchronization signal delay circuit; and a second monostable multivibrator. A synchronous separation circuit that consists of an inverter that inputs the output signal of the 2000 through a differentiating circuit.