JP2001154625A - Crt display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of a smear in a picture and to present a clear picture on a large screen by suppressing an effect of a current detection circuit for a beam current to the minimum. SOLUTION: A black level adjustment circuit 4 sends an AKB pulse to a grid G1 of a CRT 1 during a vertical fly-back period. A drive circuit 6 keep output terminals of a photo-coupler type semiconductor switch 5 is an open state for the period when the AKB pulse is turned 'on' to flow a beam current to a current detection circuit 3. On the other hand, for the period when the AKB pulse is turned 'off', the circuit 6 keep the output terminals of the photo- coupler type semiconductor switch 5 in a conductive state to flow the beam current between the output terminals of the photo-coupler type semiconductor switch 5 and not to flow it to the current detection circuit 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CRT display device, and more particularly, to a CRT capable of suppressing generation of smear in a screen due to a beam current detection circuit for detecting a beam current of a CRT. It relates to a display device.

[0002]

2. Description of the Related Art FIG. 3 is a main part circuit diagram of an example of a conventional CRT display device. The CRT display device 500 amplifies CRT1 and three video signals corresponding to red, green, and blue, and cathodes Kr, K of the CRT1.
g, Kb, and the cathode Kr,
A current detection circuit 3 for shunting and detecting a beam current flowing from Kg and Kb to the video amplification circuit 2; and the CRT 1 for flowing a beam current during a predetermined AKB (Automatic Kinema Bias) period in a vertical blanking period. And a black level adjustment circuit 4 for generating an AKB pulse to be applied to the grid G1 and adjusting the brightness of the black level based on the beam current detected by the current detection circuit 3 at that time. The current detection circuit 3 includes a bypass capacitor C, a transistor Tr, a bias resistor R, and a load resistor RL. The current detection circuit 3 and the like have three systems corresponding to red, green and blue, but only one system is shown.

[0003]

In the conventional CRT display device 500, when the CRT 1 has a large screen, as shown in FIG. 4, a smear S (raster A 'trails and a whitish blur appears. Phenomenon) became noticeable. Therefore, an object of the present invention is to provide a CRT display device that can suppress occurrence of smear in a screen.

[0004]

According to a first aspect of the present invention, there is provided a current detecting means for detecting a beam current of a CRT, and a beam current detected by the current detecting means during a period when a video signal level is a black level. A CRT display device comprising a black level adjusting means for adjusting the brightness of the black level of the screen based on the current state, wherein the current detecting means has an effect on the beam current but can detect the beam current; There is provided a CRT display device provided with state switching means for switching between an invalid state in which the current detection means cannot detect the beam current but does not affect the beam current. The inventors of the present invention have conducted intensive studies and found that the cause of smear in the screen is the influence of a current detection circuit for detecting a beam current. Therefore, in the CRT display device of the first aspect, the state switching means is provided so that the current detecting means has an effect on the beam current but can detect the beam current, and the current detecting means detects the beam current. It has been made possible to switch to an invalid state in which the beam current cannot be changed but does not affect the beam current. Thus, for example, if the black level adjustment unit is enabled only during the period in which it operates, and the other periods are disabled, the influence of the current detection circuit on the beam current is minimized. And can be easily viewed even on a large screen.

In a second aspect, the present invention provides the CRT display device according to the first aspect, wherein the current detecting means is interposed between a cathode of the CRT and a video amplifier circuit, and the state switching means is provided. Is a switch means connected between the cathode of the CRT and the video amplifier circuit in parallel with the current detection means and having an open state and a conductive state.
In the CRT display device according to the first aspect, when the switch means is opened, the current detection means is interposed between the cathode of the CRT and the video amplifier circuit so as to detect the beam current. On the other hand, when the switch means is turned on, the current detection means is short-circuited between the cathode of the CRT and the video amplifier circuit, and the beam current cannot be detected. However, the current detection means does not affect the beam current. Will not give. Thus, for example, by setting the switch means to the open state only during the period when the black level adjusting means is operated and setting the switch means to the conductive state during the other periods, the influence of the current detection circuit on the beam current is minimized. Occurrence can be suppressed, making it easy to see even on a large screen.

In a third aspect, the present invention provides the CRT display device according to the second aspect, wherein the switch means is a semiconductor switch whose input and output are isolated. I do. In the CRT display device according to the third aspect, since the input and output of the switch are isolated, it is possible to prevent the switch itself from affecting the beam current. Further, since a semiconductor switch is used, high-speed operation and silent operation are possible.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. Note that the present invention is not limited by this. FIG. 1 shows C according to an embodiment of the present invention.
FIG. 3 is a main part circuit diagram of the RT display device. This CRT
The display device 100 includes a CRT 1, a video amplifying circuit 2 for amplifying three video signals corresponding to red, green, and blue and sending the video signals to cathodes Kr, Kg, and Kb of the CRT 1, and the cathode Kr, Kg, and Kb. A current detection circuit 3 for shunting and detecting a beam current flowing to the video amplification circuit 2;
AK applied to the grid G1 of the CRT1 in order to allow a beam current to flow during a predetermined AKB period in the vertical blanking period
A B pulse is generated and the current detection circuit 3
A black level adjusting circuit 4 for adjusting the brightness of the black level based on the beam current detected in the step (a), and a photo-coupler having an output terminal connected in parallel with the current detecting circuit 3 between the cathode of the CRT 1 and the video amplifying circuit 2. Coupler type semiconductor switch 5
And a drive circuit 6 that drives an input terminal of the photocoupler-type semiconductor switch 5 so as to switch between output terminals of the photocoupler-type semiconductor switch 5 to an open state or a conductive state. The current detection circuit 3 includes a bypass capacitor C and a transistor T
r, a bias resistor R, and a load resistor RL. Further, the drive circuit 6 includes the AK
When the B pulse is "ON", the output terminals of the photocoupler-type semiconductor switch 5 are made open, and when the AKB pulse is "OFF", the output terminals of the photocoupler-type semiconductor switch 5 are made conductive. The current detection circuit 3, the photocoupler type semiconductor switch 5, the drive circuit 6, etc. have three systems corresponding to red, green and blue, but only one system is shown.

According to the CRT display device 100, the output terminals of the photocoupler type semiconductor switch 5 are open during the AKB period in which the beam current needs to be detected, and the beam current flows through the current detection circuit 3. The current detection circuit 3 can detect the beam current. On the other hand, during the non-AKB period in which it is not necessary to detect the beam current, the output terminals of the photocoupler-type semiconductor switch 5 become conductive, and the beam current flows between the output terminals of the photocoupler-type semiconductor switch 5. This is equivalent to the absence of the circuit 3, and can prevent the current detection circuit 3 from affecting the beam current. That is, as shown in FIG.
The occurrence of smear (S in FIG. 4) in the screen can be prevented.

[0009]

According to the CRT display device of the present invention, it is necessary to make the current detection circuit which causes smear in the screen effective during the period when the beam current needs to be detected, and to detect the beam current. Since the period during which no current is detected can be invalidated, the influence of the current detection circuit on the beam current can be minimized. Therefore, the occurrence of smear in the screen can be suppressed, and the image can be easily viewed even on a large screen.

[Brief description of the drawings]

FIG. 1 is a main part circuit diagram of a CRT display device according to an embodiment of the present invention.

FIG. 2 is a schematic diagram of a display screen of the CRT display device of FIG.

FIG. 3 is a main part circuit diagram of an example of a conventional CRT display device.

FIG. 4 is a schematic diagram of a display screen of the CRT display device of FIG. 3;

[Explanation of symbols]

 Reference Signs List 100 CRT display device 1 CRT 2 Video amplification circuit 3 Current detection circuit 4 Black level adjustment circuit 5 Photocoupler type semiconductor switch 6 Drive circuit C Bypass capacitor R Bias resistance RL Load resistance Tr, Q1, Q2 Transistor

Claims (3)

[Claims] 1. A current detecting means for detecting a beam current of a CRT, and a black level for adjusting a brightness of a black level of a screen based on the beam current detected by the current detecting means during a period when the video signal level is a black level. CR with adjusting means
A T display device, wherein the current detecting means has an effect on the beam current but can detect the beam current, and an invalid state in which the current detecting means cannot detect the beam current but does not affect the beam current. A CRT display device comprising state switching means for switching between a state and a state. 2. The CRT display device according to claim 1, wherein said current detecting means is interposed between a cathode of the CRT and a video amplifier circuit, and said state switching means is connected to a cathode of the CRT and a video amplifier. A CRT display device comprising switch means connected in parallel with the current detection means between circuits and having an open state and a conductive state. 3. The CRT display device according to claim 2, wherein said switch means is a semiconductor switch whose input and output are isolated.
Display device.