JPS61255167A - Synchronizing separator circuit - Google Patents

Abstract

PURPOSE:To separate a stable and highly accurate composite synchronizing signal from a weak composite signal or a strong signal by using a comparator so as to allow its threshold voltage to be changed in response to the amplitude of an inputted video composite signal. CONSTITUTION:A means potential of a television composite signal is nearly at a common potential at a point A by selecting the time constant C1R1 larger the pulse width of a vertical synchronizing signal. A gate of an analog switch 2 is opened during the synchronizing signal period to charge a capacitor C2. A potential (point B) of the capacitor C2 keeps a negative peak voltage (synchronizing signal voltage), which is divided by a resistor through a voltage follower 3 to form a threshold voltage of a comparator 4. The threshold voltage (at point C) has a value between the potential of the synchronizing signal and a common potential, it is used as a reference voltage and the synchronizing signal is separated by the comparator 4. The analog switch 2 is switched again by using the separated synchronizing signal. The time constant C2R2 is set to a value far larger than the period of the horizontal synchronizing signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a highly accurate synchronization separation circuit that can accommodate a wide range of changes in the amplitude of a video composite signal.

[Prior art]

FIG. 1 shows a commonly used synchronous separation circuit. In this circuit, in order for the transistor to conduct, a base-emitter voltage of -α1v is required for a silicon transistor or a germanium transistor, and accordingly, a large amplitude of the input composite signal is required. Furthermore, since the reverse current of the transistor changes depending on the surrounding temperature, it has been difficult to perform synchronous separation with weak signals.

〔the purpose〕

The present invention eliminates these drawbacks and aims to separate a stable and highly accurate composite synchronization signal from both weak cosaposite signals and strong signals.

〔overview〕

The present invention is a synchronization separation circuit using a comparator, the threshold voltage of which changes in accordance with the amplitude of an input video composite signal.

[% example]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the drawings showing one embodiment.

FIG. 2 shows an example of a synchronous separation circuit constructed by applying the present invention. In this example, the video composite signal reaches its lowest potential during the same signal period.

Since the time constants O and R1 in the figure are larger than the pulse width of the vertical synchronizing signal, the average potential of the television composite signal at point A is approximately the ground potential.

During the synchronization signal period, the gate of analog switch 2 is open and capacitor 0. to charge. Capacitor 0. potential (B
The point) maintains a negative peak voltage (synchronizing signal voltage), passes it through the voltage follower 3, and then divides it with a resistor to become the threshold voltage of the comparator 4. (0 point) The threshold voltage is a value between the potential of the synchronizing signal and the ground potential, and the synchronizing signal is separated by a comparator using this as a reference voltage. The analog switch 2 is opened and closed again using the separated synchronization signal. Here, the time constants O and R are set to values much larger than the period of the horizontal synchronizing signal.

〔effect〕

As is clear from the above embodiments, according to the present invention, it is possible to configure a highly accurate synchronization separation circuit that can respond to a wide range of changes in the amplitude of the Eirin composite signal.

[Brief explanation of drawings]

FIG. 1 is an example of a conventional synchronous separation circuit. FIG. 2 shows an embodiment of a synchronous separation circuit constructed using the present invention. 1...Eirin composite signal input terminal 2...Analog switch 3...Voltage follower 4...Comparator 5...Composite synchronization signal output terminal and above

Claims (1)

[Claims] A synchronous separation circuit using a comparator, the threshold voltage of which changes according to the amplitude of an input video composite signal.