JPS6022552B2 - White adjustment circuit for color television receivers - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a white adjustment circuit for a color television receiver.

When a black and white image is received, the white adjustment circuit has red (R), green (G), blue (B) so that a correct black and white image can be obtained.
) is a circuit that adjusts the light emission balance of the

In color picture tubes, the drive conditions for the three colors R, G, and B are adjusted in the picture tube circuit so that the gradations of white (white) from dark to bright screens can be accurately reproduced. In a primary color drive type picture tube, this is done by adjusting the voltage vs. cathode current characteristics between the cathode and the first grid so that the three colors R, G, and B are reproduced as white from dark areas to bright areas. ing.

Dark areas are performed where the cathode fin flow with the above characteristics is almost zero (cutoff adjustment), and bright areas are performed where the cathode current is relatively large (drive adjustment).
. Both of these are collectively referred to as white adjustment. 1st
The figure is a block diagram of a conventional white adjustment circuit.

After the color television signal is detected by a video detection circuit 1, it is applied to a color signal processing circuit 2 and a variable video gain circuit 3.
The color signal processing circuit 2 outputs three color difference signals R-Y, G.
-Y, B-Y (Y is a luminance signal) are output, and each R
, G, B output circuits 4, 5, and 6. On the other hand, the output of the variable video gain circuit 3 is applied to the video drive circuit 8 after the black level is clamped by the vedestal clamp circuit 7 . Video drive outputs are R, G, and B, respectively.
Three color difference signals R-Y, which are added to the output circuits 4, 5, and 6,
Mixed (matrix) with G-Y and B-Y to produce primary color signal R
, G, B outputs are obtained. These R, G, and B primary color signals are applied to each of the R, G, and B cathodes of the picture tube 9. on the other hand,
The signal applied to the picture tube 9 is the output from the vertical oscillation circuit 10 which is vertically deflected by the current obtained through the vertical deflection output circuit 11 . Further, 12 is a so-called service switch for cut-off adjustment, and when adjusting the cut-off, a part of the variable video gain circuit 3 and the vertical oscillation circuit 10 is grounded to make the video gain zero and also stop vertical oscillation. let Variable resistors for cutoff and drive adjustment are provided in the R, G, B output circuits 4, 5, 6. A conventional cutoff and drive adjustment method will be explained based on the circuit shown in FIG. First, the service switch 12 is turned on for cutoff adjustment. As a result, the gain of the variable video gain circuit 3 becomes zero, and the video signal becomes a simple DC voltage, which is fixed at the black level by the horizontal clamp circuit 7 and applied to the video drive circuit 8. At this time, since the vertical oscillation circuit is disabled, a so-called one horizontal screen in which all the scanning lines overlap in the center is obtained on the picture tube surface. Therefore, R
, G, B output circuits 4, 5, and 6 are varied to provide cutoff voltages to each of the R, G, and B cathodes of the picture tube 9. That is, the adjustment is made so that the horizontal lines on the horizontal screen begin to be seen faintly. Next, turn the service switch 12 to the OFF side and receive a normal black and white broadcast. After properly adjusting the brightness and contrast of this received image, R, G, B
Drive adjustment is performed by adjusting each of the drive adjustment variable resistors in the output circuits 4, 5, and 6. Note that since these adjustments are made in black and white broadcasting, each color difference output from the color signal processing circuit 2 is a simple DC voltage. As mentioned above, in conventional white adjustment, cutoff adjustment and drive adjustment were performed separately by switching a service switch.

Also, since these adjustments interfere with each other, it is necessary to turn the service switch ○N many times in order to adjust the white correctly.
It is necessary to repeat the OFF operation. Therefore, a considerable amount of time is required for adjustment, and a considerable amount of skill is required for accurate adjustment, making it difficult to reproduce uniform white from the edge to the bright portion of the reproduced image. Therefore, the main object of the present invention is to provide a white adjustment circuit that eliminates the above-mentioned drawbacks and can perform white adjustment accurately and in a short time.

In summary, the present invention provides a clipping circuit for clipping a part of the vertical deflection output, stops the vertical deflection for a certain period within the vertical deflection period, and makes the gain of the video output signal zero only for the certain period. To perform white adjustment, horizontal signals representing bright and dark areas appear on the picture tube at the same time, or instead of clipping part of the vertical deflection output, the vertical deflection period is set to 1 or n (n is a constant). This is a white adjustment circuit that performs white adjustment by providing a circuit that stops vertical deflection at each time.

The above objects and other objects and features of the invention will become more apparent from the following detailed description with reference to the drawings.

FIG. 2 is a block diagram showing essential parts of an embodiment of the present invention, and FIG. 3 is a waveform diagram of each part explaining the operation of FIG. 2.

In the embodiment shown in FIG. 2, a clip circuit 13 is connected to the vertical deflection output circuit 11, and a pulse shaping circuit 1 is connected between the clip circuit 13 and the variable video gain circuit 3.
4 and that the service switch 12 is connected only to the clip circuit 13. Note that the clip circuit 13 does not operate until the service switch 12 is turned on and grounded. Normally, the service switch 12 is turned off, and the output waveform of the vertical deflection output circuit 11 in this case is as shown in FIG. 3a.

Turn this service switch 12 to O for white adjustment.
When set to the N side, the clip circuit 13 operates to make the normal output waveform a of the vertical deflection output circuit 11 as shown in FIG. This waveform signal of FIG. 3b is also applied to the vertical deflection circuit 11.
The clip circuit operates to drive the picture tube 9 as an output. The pulse shaping circuit 14 generates a substantially rectangular pulse signal as shown in FIG. 3c based on the signal shown in FIG. The video signal gain of the video gain variable circuit 3 is set to 1 (indicated by T in FIG. 3c). The video signal subjected to such waveform manipulation further passes through the vedestal clamp circuit 7 and is applied to the video drive circuit 8.
The signal output from this video drive circuit 8 is shown in Fig. 3d.
The waveform is as shown in . Under the above structure and operation, the screen that appears on the picture tube has a white screen with a narrow vertical deflection width and a dark area that gives a cut-off state where the vertical deflection stops, as shown in Figure 4, for example. The horizontal line shown appears at the same time.

Therefore, in this state, the variable resistor is adjusted so that the horizontal lines can be seen faintly and the white of the white screen does not change color even when the brightness is changed. In this way, cutoff adjustment and drive adjustment, that is, white adjustment, can be easily performed by simply switching the service switch once. In addition, as another embodiment, instead of using the clipping circuit and the pulse shaping circuit as described above, the vertical deflection may be stopped every vertical synchronization period, or a certain fixed number n may be determined, and the vertical deflection may be stopped every n vertical synchronization periods. A vertical deflection output control circuit may be provided behind the vertical deflection output circuit and the variable video gain circuit so as to stop the deflection.

The state of the screen that appears in this case is as shown in FIG. 5, with a uniform white screen and a Fujiichi screen approximately in the center. As described above, by switching the service switch only once, the complicated and delicate white adjustment that is conventionally performed by switching the service switch many times can be easily and accurately performed in a short time.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a conventional white adjustment circuit. FIG. 2 is a block diagram showing essential parts of a white adjustment circuit showing an embodiment of the present invention. FIG. 3 is a waveform diagram of each part explaining the operation of the embodiment of the present invention. The mother diagram is an example of a screen obtained when the white adjustment circuit shown in FIG. 2 is activated. FIG. 5 is an example of a screen obtained by another embodiment of the invention. In the figure, the same reference numerals indicate the same or equivalent parts, 3 is a variable video gain circuit, 8 is a video drive circuit, 9 is a color picture tube, 11 is a vertical deflection output circuit, 12 is a service switch, 13 is a clip circuit, 14 indicates a pulse shaping circuit. Figure 2 Figure 4 Figure 1 Figure 3 Figure 5

Claims (1)

[Scope of Claims] 1. A variable video gain circuit that varies the gain of a video signal subjected to video detection, means for deriving a primary color signal based on the output of the variable video gain circuit and the video detection output, and a vertical oscillation circuit; a vertical deflection output circuit that receives a vertical synchronization pulse from the vertical oscillation circuit; a plurality of electron guns that are individually energized according to the primary color signals; and energized according to the deflection output from the vertical deflection output circuit. a color television receiver comprising a color picture tube having controlled deflection means, a switch for white adjustment, for forcing a vertical deflection output signal to a certain DC level for a certain period of time in response to operation of said switch; A white adjustment circuit for a color television receiver, comprising: means for reducing the gain of the variable video gain circuit to zero for the certain period of time. 2. The color according to claim 1, wherein the certain period is within one cycle of the vertical deflection output, and the forcing means includes a clip circuit that clips the output of the vertical deflection output circuit. White adjustment circuit for television receivers. 3. The white adjustment circuit for a color television receiver according to claim 1, wherein the certain period is every n (n is 1 or more) vertical deflection periods.