JPH07212617A - Video image mute circuit - Google Patents

Abstract

PURPOSE:To obtain a method to mute tentatively a pattern on a screen when disturbance of synchronization or the like takes place in a cathode ray tube display device. CONSTITUTION:The circuit is provided with a 1st transistor (TR) 1 of common emitter connection whose base receives a positive video image mute signal S1, a 2nd TR 2 of common emitter connection whose base receives a prescribed voltage being a division of a collector voltage of the TR 1, a 3rd TR 3 whose base receives a prescribed voltage being a division of a collector voltage of the TR 2, and a variable resistor VR 1 whose one fixed terminal receives a positive voltage of a collector of the TR 3, whose other fixed terminal receives a prescribed negative voltage and whose slider terminal applies a voltage to a 1st grid of a cathode ray tube. When a video mute signal is received, the TR 3 is cut off to interrupt a positive voltage to the variable resistor thereby cutting off the cathode ray tube.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video mute circuit, and more particularly to a method for temporarily erasing (muting) a screen in the case of a disturbance in synchronization in a cathode ray tube display device.

[0002]

2. Description of the Related Art Conventionally, the circuit configuration around the first grit (hereinafter referred to as "G1") of a CRT has been as shown in FIG. In the figure, a positive voltage (+ Vcc) and a negative voltage (-Vcc) are applied to both ends of a fixed end of a VR1 (bright volume) for adjusting an applied voltage to G1 of the cathode ray tube 1, and a required voltage is applied from a movable end. Is applied to the same G1. In addition, a blanking signal (horizontal and vertical) is added to G1. Conventional video muting such as when synchronization is disturbed is performed by lengthening the blanking time of the blanking signal (horizontal).

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a video mute circuit by a method different from the conventional one.

[0004]

The present invention provides a first grit of a cathode ray tube for applying a video signal to a cathode, comprising:
A variable resistor configured to apply a predetermined negative voltage to one end of the fixed end and take out a voltage to be applied to the first grit of the cathode ray tube from the movable end, and a predetermined positive voltage between the emitter and collector to change the variable resistor. A transistor provided so as to be applied to the other end of the fixed end of the resistor, and when a voltage based on a video mute signal is applied to the base end of the transistor, the emitter and collector of the transistor are turned off. An image mute circuit is provided in which the cathode voltage is cut off by cutting off the positive voltage and applying only the negative voltage to the first grid.

[0005]

[Function] A positive voltage is applied to one end of the G1 applied voltage adjusting volume (bright volume) through the transistor switch circuit. Normally, the transistor switch circuit is on. Here, when a synchronization disorder or the like occurs, a video mute signal is output from the microcomputer or the like. The transistor mute signal is used to turn off the transistor switch circuit. By this turning off, the positive voltage is cut off and only the negative voltage is applied to the volume. As a result, the G1 bias is deepened and the CRT is cut off and muted. When the video mute signal disappears, the transistor switch circuit turns on again and returns to the normal state.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A video mute circuit according to the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram of essential parts showing an embodiment of a video mute circuit according to the present invention. In the figure,
1 is a cathode ray tube (hereinafter referred to as “CRT”), S1 is a video mute signal, TR1, TR2, and TR3 are first to third transistors, VR1 is a first grid (G1) voltage adjustment volume (bright volume). ), + Vcc is a predetermined positive voltage, and -Vcc is a predetermined negative voltage.

Next, the operation of the present invention will be described. During normal operation, the video mute signal is not applied to the base end of TR1, so that it is not forward biased and TR1 is off. When TR1 is turned off, TR2 is turned on and TR3 is turned on. The collector voltage and base voltage of each TR are set by the constants of the peripheral resistance so that the above relationship is satisfied. When TR3 is turned on, + Vcc is applied to one end of VR1 via the resistor R1. On the other hand, -Vcc is applied to the other end of VR1. Adjust the same VR1 and take out the required voltage from the movable end, and use the resistor R2
And so on to G1 of CRT1. A blanking signal (horizontal, vertical) is added to G1 as in the conventional case.

The red, green and blue cathodes (Kr,
Since video signals of each color are applied to Kg, Kb), the voltage of each cathode changes in the range from the white level to the cutoff level. The G1 voltage is generally set to maintain a negative voltage with respect to the cathode voltage in order to prevent the grid current from flowing even when the cathode voltage becomes the lowest (white peak). FIG. 3 illustrates the voltage relationship between the grid and the cathode. Vbw in the figure is a video contrast, and the G1 voltage is set to a voltage lower than the minimum value of the cathode voltage. The G1 voltage changes within a predetermined range between + Vcc and -Vcc (VR1), and as it approaches -Vcc, the bias to the cathode becomes deeper to limit the CRT anode current. Then, when a certain negative voltage is exceeded, the anode current does not flow and a cut-off state occurs. Therefore, if a negative voltage necessary for cutting off only for a certain period is applied to G1, the image is muted.

When the synchronization is momentarily disturbed, such as when switching video signals, a video mute signal is output from a microcomputer or the like. This video mute signal S1 is applied to the base of TR1 with positive polarity. TR1 is turned on by the mute signal S1, the collector voltage is lowered, and TR2 is turned off. This off increases the collector voltage of TR2 (hence TR3
The base voltage also rises), and TR3 turns off. When TR3 is turned off, + Vcc is cut off, and G1 becomes a negative voltage of about -Vcc to cut off CRT1. This cutoff is maintained during the pulse width of the video mute signal S1. When the mute signal S1 disappears, TR1 is turned off again and TR3 is turned on to return to the normal state. Although FIG. 1 shows an example in which the video mute signal S1 has a positive polarity, in the case of a negative polarity, TR1 to TR3 types (PN
The same mute operation is achieved by combining (P, NPN).

[0010]

As described above, according to the present invention, video muting can be performed by a method different from the conventional method using the cutoff characteristic of the first grid (G1) of the cathode ray tube. In addition, the circuit configuration is simple and does not require expensive parts. Therefore, the present invention is a new system of video mute which is an essential process for momentary synchronization disturbance.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a main part showing an embodiment of a video mute circuit according to the present invention.

FIG. 2 is a circuit diagram of a main part showing an example of a conventional video mute circuit.

FIG. 3 is a voltage relationship diagram of a cathode ray tube cathode, a first grid, and the like.

[Explanation of symbols]

 1 cathode ray tube (CRT) TR1 first transistor TR2 second transistor TR3 third transistor VR1 G1 voltage adjustment potentiometer + Vcc positive voltage −Vcc negative voltage

Claims (3)

[Claims] 1. A first grit of a cathode ray tube for applying a video signal to a cathode, wherein a predetermined negative voltage is applied to one end of a fixed end, and a voltage applied to the first grit of the cathode ray tube is taken out from a movable end. And a transistor provided so that a predetermined positive voltage is applied to the other end of the fixed end of the variable resistor via the emitter and collector, and a video mute signal is provided at the base end of the transistor. When a voltage based on is applied, the emitter and collector of the transistor are turned off to cut off the positive voltage, and the cathode is cut off by applying only the negative voltage to the first grid. Video mute circuit characterized by. 2. A grounded-emitter connected NPN-type first transistor to which a positive video mute signal is input to the base end, and a predetermined voltage obtained by dividing the collector voltage of the first transistor at the base end. An applied grounded-emitter connected NPN-type transistor, and a PNP to which a predetermined positive voltage is applied to the emitter end and a predetermined voltage obtained by dividing the collector voltage of the second transistor is applied to the base end. Type third transistor, and a positive voltage from the collector of the third transistor is applied to one end of the fixed end, a predetermined negative voltage is applied to the other end of the fixed end, and the first end of the cathode ray tube is applied from the movable end. A variable resistor for supplying a voltage to the grid, and when the video mute signal is input, the third transistor is turned off to shut off the positive voltage to the variable resistor. A video mute circuit characterized in that 3. A NPN type first transistor with a grounded emitter connection to which a negative video mute signal is input to a base terminal, and a predetermined voltage obtained by dividing the collector voltage of the first transistor at a base terminal. An applied NPN-type second transistor of grounded-emitter connection, a predetermined positive voltage is applied to the collector end, and a predetermined voltage obtained by dividing the collector voltage of the second transistor is applied to the base end. Type third transistor, and a positive voltage from the emitter of the third transistor is applied to one end of the fixed end and a predetermined negative voltage is applied to the other end of the fixed end. A variable resistor for supplying a voltage to the grid, and when the video mute signal is input, the third transistor is turned off to shut off the positive voltage to the variable resistor. A video mute circuit characterized in that