JPS6243399B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a color display monitor using a color cathode ray tube and inputting primary color signals of red, green, and blue. The present invention relates to a device for erasing a raster of a desired color.

Raster erasing on general-purpose television receivers is
As shown in Fig. 1, no special circuit is employed, and variable resistors 2R, 2G, and 2B are used to adjust the screen voltage, which are used to adjust the cut-off of the red, green, and blue electron guns of the cathode ray tube 1. Either erase the raster of the desired color by reducing the screen voltage of the electron beam of the color you want to erase, or use the video output transistor 3R connected to the cathode of each red, green, and blue electron gun. Many are used to erase a raster of a desired color by changing the cathode voltage of the electron beam of the color to be erased in the cut-off direction using variable resistors 4R, 4G, and 4B for bias adjustment of 3G and 3B. ing.

In such a raster erasing circuit, there is an inconvenience in that in order to change the final adjusted screen voltage or cathode voltage, the screen voltage or cathode voltage of the erased electron gun must be final adjusted again. However, this is generally used in general-purpose television receivers where the frequency and necessity of raster erasing is low, as it is inexpensive, but R. In color display monitors using the G/B input method, rasters of arbitrary colors are often erased, and the above method is inconvenient.

On the other hand, as an example of improving such drawbacks, devices shown in FIGS. 2 and 3 are used.

In the one in Figure 2, the red, green, and
The first grid of each blue electron gun is not directly connected to ground, and the raster erase switch 5R,
It is connected to ground via 5G and 5B. In addition, the other terminals of switches 5R, 5G, and 5B are connected to a specially created negative voltage (-200V in the one in Figure 2). Sufficient negative voltage is applied to the first grid of the electron gun to cut off the electron beam and erase the raster.

However, when using this type of circuit, it is necessary to create a special negative voltage to be applied to the first grid for the raster of the color to be erased, and its value remains the same even when the primary color signal applied to the cathode is at its maximum. The inconvenience is that the raster must be made large enough to be erased.

In addition, in the case shown in Figure 3, red, green,
The second grid of each blue electron gun is not directly connected to the variable resistors 5R, 2G, 2B for adjusting the screen voltage, but is connected to the switches 6R, 6 for raster erasing.
It is connected to variable resistors 2R, 2G, and 2B via G and 6B. The other terminals of the switches 6R, 6G, and 6B are connected to ground, and when the switch for raster erasure of a desired color is turned OFF, the second grid voltage of the electron gun becomes O _V. Erase the raster by cutting off the electron beam. However, even when this circuit is used, the raster erase switches 6R, 6G, and 6B are required to have high voltage resistance, making it difficult to downsize.
The drawback is that it is not easy.

SUMMARY OF THE INVENTION An object of the present invention is to provide a raster erasing device that can overcome all of the above-mentioned drawbacks of the conventional art.One embodiment of the present invention will be described below with reference to the drawings.

FIG. 4 shows an embodiment of the raster erasing device according to the present invention, and particularly shows in detail the circuit for erasing the blue raster. In this circuit,
The small blue primary color signal applied to the input terminal 7 is amplified by a differential amplifier 10 made up of transistors 8 and 9 and a transistor 11 in the next stage, and then a pulse signal made of transistors 12, 13, 14, a capacitor 15, etc. A clamp circuit 16 performs pedestal clamping to regenerate the DC component, a video output transistor 17 amplifies it to a required large amplitude, and supplies it to the cathode of the blue electron gun of the cathode ray tube 1. In addition, 18
19 is a clamp pulse input terminal, and a variable resistor 20 for adjusting the clamp level is a blanking signal input terminal.

Furthermore, for raster cancellation, the differential amplifier 1
A transistor 21 is provided between the base of the transistor 9 of 0 and the ground, and an interlocking eraser is provided between the base of the transistor 21 and the ground, and between the emitter of the pedestal clamp transistor 13 and the ground. switch 22,2
There are 3.

Although this figure only shows the circuit portion related to the blue signal, similar circuits are provided for the other red and green signals.

With this configuration, if you want to erase the blue raster now, press the raster erase switch 2.
Set 2 and 23 to the “OFF” side. Differential amplifier 10
Since the transistor 21 connected to the base of the transistor 9 becomes cut off, the base bias of the transistor 9 rises to almost the power supply voltage, transistor 9 becomes conductive, and the transistor 8 becomes cut off, causing the blue primary color signal to be turned off. It is cut off and is no longer supplied to the next stage transistor 11. Therefore, a blue image is no longer displayed on the screen of the cathode ray tube 1, but the blue electron beam is still not completely cut off, so a raster appears. In order to further erase this, the switch 23 for raster erasure is also turned "OFF". Then, this is variable resistor 1 for clamp level adjustment.
9 and when the switch 23 is turned OFF, the clamp level is lowered to the ground level and the cathode potential is changed in the direction of cutting off the blue electron gun.This completely cuts off the blue raster. Can be erased.

In the illustrated embodiment, a double-throw raster erase switch is used, but a single-throw switch may be used by inserting a diode into one of the switches. The same is true for erasing the other red and green rasters.

As is clear from the above description, according to the present invention,
Since the signal of the color to be erased is cut off and the clamp level is switched, the raster of the desired color can be erased using a simple low voltage switch without adding any special circuit.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram of a screen adjustment circuit and cathode potential adjustment circuit used in a conventional television receiver, Figures 2 and 3 are circuit diagrams of a conventional raster erasing device, and Figure 4 is a circuit diagram of the present invention. FIG. 2 is a circuit diagram of a raster erasing device in one embodiment. 1... Cathode ray tube, 7... Primary color signal input terminal,
8, 9...transistor, 10...differential amplifier,
11, 12, 13, 14...transistor, 15
... Capacitor, 16 ... Pedestal clamp circuit, 17 ... Video output transistor, 18 ...
Clamp pulse input terminals, 22, 23...switch.

Claims (1)

[Claims] 1 The primary color signals of red, green, and blue are applied to the cathode ray tube, and the signal of the color to be erased among the red, green, or blue rasters is cut off by a switching circuit, and the output circuit of each color is A raster eraser characterized in that a pulse clamp circuit is provided, and a raster of a desired color is erased by changing the clamp level of the pulse clamp circuit and changing the cathode potential of the cathode ray tube in the cut-off direction. Device.