JPH0746430A - Blanking mask circuit - Google Patents

Abstract

(57) [Summary] [Purpose] To eliminate blanking signals from video signal input after color demodulation. [Constitution] The video signal in which the horizontal blanking period erase signal is inserted is connected to one fixed terminal of the switch, the constant voltage source is connected to the other fixed terminal, and the blanking pulse signal is connected to the switch control terminal. During the blanking signal, the movable contact of the switch is switched to the fixed terminal on the constant voltage source side, and during the video signal, the movable contact of the switch is switched to the fixed terminal on the video signal side. To do so.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is intended for facilitating A / D conversion processing and the like by removing a blanking signal in the horizontal and vertical blanking periods of a video signal, which is carried out in television signal processing. It relates to a blanking mask circuit.

[0002]

2. Description of the Related Art Conventionally, a video signal input to a cathode ray tube of a television set may be output by inserting a horizontal blanking period erasing signal (blanking signal) into the horizontal blanking period of the video signal. In such a case, when it is necessary to perform A / D conversion of the video signal as a display means other than the cathode ray tube, such as a plasma display (PDP) device, the blanking signal is also A / D together with the video signal.
This results in D conversion, which causes a problem that the blanking signal level is added to the A / D converted video signal level, which increases the video signal level of the plasma display (PDP) device. .

[0003]

As described above, conventionally, when a video signal on which a blanking signal is superimposed is A / D converted, the level of the blanking signal is added to the video signal level during this conversion. There was a problem that the signal level of was raised. In view of such a problem, the present invention is to provide a blanking mask circuit capable of removing a blanking signal from a video signal input of an A / D converter.

[0004]

In order to solve the above problems, the present invention connects a video signal in which a horizontal blanking period erasing signal is inserted to one fixed terminal of a switching device and fixes it to the other fixed terminal. Connect a voltage source, connect a blanking pulse signal to the switching control terminal, and switch the movable contact of the switching device to the fixed terminal on the constant voltage source side during the blanking signal period, and during the video signal period. Inside, the movable contact of the switch is switched to the fixed terminal side on the video signal side.

[0005]

With the above construction, in the blanking mask circuit according to the present invention, the movable contact of the switch is switched to the fixed terminal on the constant voltage source side during the blanking signal, and the blanking signal is Make it masked. Further, since the movable contact of the switch is switched to the fixed terminal side on the video signal side during the video signal period, only the video signal level is applied to the A / D converter.

[0006]

Embodiments of the blanking mask circuit according to the present invention will be described in detail with reference to the drawings. In the embodiment of FIG. 1, an NPN transistor 12 and an emitter follower circuit composed of a constant current source 14 and a resistor 16
A video signal is output from a video output terminal 20 through an emitter follower circuit composed of a PN transistor 13 and a resistor 15. Next, from the blanking pulse input terminal 6, a horizontal blanking period pulse 25 is input in synchronization with the horizontal blanking period of the video signal 21 shown in FIG. I will describe the case. In FIG. 1, when a blanking pulse is input to the blanking pulse input terminal 6, the NPN transistor 1
9 becomes the operating state. When the NPN transistor 19 operates, a current flows through the collector of the NPN transistor 19. This current is supplied from the NPN transistor 12 and passes through the resistor 16, so that the voltage at the point 18 drops and the second
The waveform is similar to that of 25 in FIG.
Is saturated. The voltage at point 18 is the NPN in the saturated state.
The voltage between the collector and the emitter of the transistor 19 (about 0.2 V) is fixed. The resistor 17 is a protection resistor that limits the base current to the saturation state of the NPN transistor 19. The signal at the point 18 is the NPN transistor 13,
It is output from the video output terminal 20 through the emitter follower circuit composed of the resistor 15. Through the above operation, the video signal in which the blanking signal is inserted in the horizontal blanking period of the video signal similar to 25 in FIG. 2 is output to the video output terminal 20. When this output is A / D converted, the black level of the video signal is added to the A / D converted video signal level. Therefore, a blanking mask circuit shown in a block 21 surrounded by a broken line in FIG. 1 is added. . In the same block, reference numeral 1 is a switch, which inputs a video signal in which the horizontal blanking period erase signal is inserted to one fixed terminal 2 of the switch and connects a constant voltage source 4 to the other fixed terminal 3. . The movable contact 5 of the switch is connected to the input of the A / D converter, and the switch is switched by the blanking pulse from the blanking pulse input terminal 6. The delay circuit composed of the resistor 8, the capacitor 9 and the diode 7 widens the pulse width of the blanking pulse signal to stabilize the switching timing of the switch.

Next, the operation of the blanking mask circuit according to the present invention will be described with reference to FIG. In the figure, 21
Is a waveform of the video signal 24 in which the horizontal synchronizing signal 23 and the horizontal blanking period erasing signal 22 are inserted, and is input to the blanking mask circuit. A horizontal blanking period erase signal 25 is created based on this signal and input to the blanking pulse input terminal, and a delay signal 27 is created via a delay circuit composed of a resistor, a capacitor and a diode. In this case, the rising edge of the input of the blanking pulse is delayed by the delay circuit, so that the beard-like pulse generated at the time of switching can be removed by this signal, and the operation of the switching circuit can be stabilized. This signal is input to the control terminal of the switch through the NOT gate 10 of FIG. Since the constant voltage source 4 is connected to one fixed terminal of the switch, the voltage of the constant voltage source 4 is output from the switch during the period when the switching signal is negative. The signal waveform becomes the waveform 30 in FIG. 2, and blanking is masked.

[0008]

As described above, according to the blanking mask circuit of the present invention, the blanking pulse can be removed from the video signal output. The signal level can be lowered by the ranking pulse signal level,
It is possible to perform normal clamping during A / D conversion.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a blanking mask circuit according to the present invention.

FIG. 2 is an explanatory diagram of waveforms of a blanking mask circuit according to the present invention.

[Explanation of symbols]

 1 Switching device 2 Fixed terminal 3 Fixed terminal 4 Constant voltage source 5 Moving contact 6 Input terminal 7 Diode 8 Resistor 9 Capacitor 10 Gate 11 Input terminal 12 Transistor 13 Transistor 14 Constant current source 15 Resistor 16 Resistor 17 Resistor 18 point 19 Transistor 20 Output Terminal 21 Blanking mask circuit

Claims (2)

[Claims] 1. A video signal in which a horizontal blanking period erase signal is inserted is connected to one fixed terminal of a switch, and a constant voltage source is connected to the other fixed terminal of the switch, and the switch of this switch is switched. A blanking mask circuit in which a signal obtained by delaying a blanking pulse is connected to a control terminal. 2. A signal input side of the blanking pulse is input to a delay circuit composed of a resistor, a capacitor and a diode, an anode of the diode is connected to one end of the resistor on the signal input side, and the other end of the resistor is connected. The blanking mask circuit according to claim 1, wherein a cathode is connected to the blanking mask circuit.