JPH04127678A - Double screen television reciver - Google Patents

Abstract

PURPOSE:To prevent doming by using an ABL signal showing the brightness of an entire screen including master and slave screens by providing a first luminance control circuit for the master screen, second luminance control circuit for the slave screen, slave screen inserting circuit, cathode ray tube and control means to control the luminance control circuits. CONSTITUTION:When the screen is dark, the luminance of the slave screen is controlled to be lowered on the screen of the cathode ray tube for preventing doming. When the screen is bright, the luminance of the master screen is lowered by an ABL operation 28' and the luminance of the slave screen is increased in a video chroma circuit 19. By matching the pedestal levels of the slave and master screens, however, the luminance of the master screen starts lowering and is lowered a little on the screen of the cathode ray tube. This lowering amount of the luminance is set to be worked even when adding the increase of the luminance of the slave screen in the slave screen inserting circuit. Thus, when the master screen of the cathode ray tube is dark, the slave screen on the screen of the cathode ray tube is made dark as well so that the generation of doming can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to a two-screen television receiver (two-screen TV).

(b) Prior Art A two-screen TV called picture-in-picture is well known. FIG. 3 shows a schematic block diagram. (10)
1 is a video signal input terminal for the main screen, (12) is a video chroma circuit for the main screen, (14) is a sub-screen insertion circuit, and (16) is a cathode ray tube (braun tube).

(18) is a video signal input terminal for the child screen, (19) is a video chroma circuit for the child screen, and (20) is a picture-in-picture system circuit for reducing the video signal for the child screen.

(22) is a control CPU. (24) is Y, R-
This is a matrix circuit that converts Y, BY signals into RGB signals.

(26) is a flyback transformer circuit which supplies high voltage to the cathode ray tube (16) and outputs an ABL signal corresponding to the brightness of the screen created from the beam current. Note that since the area of the child screen is small, the value of this ABL signal approximately corresponds to the brightness of the main screen. (!1) is a signal path, which connects the ABL signal to the main screen and the deochroma circuit (!1).
2), and when the angle of view is bright, brightness, contrast, etc. are controlled to darken the main screen. or,
If the screen is bright, brighten the main screen. In addition, since the child screen insertion circuit (14) matches the pedicle levels of the RGB signals of the child screen and the main screen and inserts them into the main screen,
As the brightness of the parent screen changes, the brightness of the child screen also changes.

(28) is an ABL signal inversion circuit provided to prevent this. This circuit (28) controls the brightness and contrast of the deochroma circuit (19) for the child screen in the opposite direction to that of the main screen in order to cancel the change in brightness of the child screen.

Thereby, even if the brightness of the main screen changes, the brightness of the child screen is always constant. In addition, a TV that maintains the brightness of the sub-screen in this way is disclosed in Japanese Patent Application Laid-Open No. 171875-1986.
(HO4N 5/45).

(c) Problems to be Solved by the Invention By the way, in such a two-screen TV, as shown in Figure 4, when the brightness of the sub-screen is high, an excessive beam current exceeding the dynamic range of the cathode ray tube is generated. The doming phenomenon (a phenomenon in which a large beam current flows and the shadow mask is warmed and deformed, causing the electron beam to not correctly hit the phosphor and cause the color to change) as shown in FIG. 5 occurs on the sub-screen.

In order to prevent this doming, Japanese Patent Laid-Open No. 2-67086 discloses that the brightness levels of the main screen and the child screen are detected separately, and the brightness of the main screen and the child screen are controlled based on the values of both sides.
(HO4N 5/45).

However, this TV requires a detection circuit that detects the brightness of the main screen and the child screen.

The present invention uses the conventional ABL signal, which indicates the brightness of the entire screen including the parent and child, to prevent doming6.
It is.

(d) Means for Solving the Problems The present invention provides a first brightness control circuit (12) for a main screen;
a second brightness control circuit (19) for the child screen;
A child screen insertion circuit (14) provided after the second brightness control circuit (12) (19), and a child screen insertion circuit (14) provided after the second brightness control circuit (12) (19).
4) a cathode ray tube (16) for projecting a signal from the cathode ray tube (16), and a first control means for controlling the first brightness control circuit (12) using an ABL signal corresponding to the amount of beam current of the cathode ray tube (16). and the second brightness control circuit (19) detects when the screen is dark based on the ABL signal and lowers the brightness of the sub-screen on the screen of the cathode ray tube (16).
), and a second control means (28°) for controlling the angle.

(e) Function In the present invention, when the screen is dark, doming is prevented by controlling the brightness of the sub-screen to be lowered on the screen of the cathode ray tube (16). Also, when the screen is bright, the conventional A
The brightness of the main screen is lowered by the BL operation, and the brightness of the sub-screen is increased by the video chroma circuit (19), but since the sub-screen has the same basic level as the main screen, the sub-screen insertion circuit (14) The brightness on the cathode ray tube (16) screen drops slightly due to the drop in brightness on the main screen.

(F) Embodiment An embodiment of the present invention will be described with reference to FIGS. 1 to 3. In Figure 1, (28'') is an ABL signal inversion circuit. (R1) to (R5) are resistors, (CI) (C2
) is a capacitor. (19) is a deochroma circuit for the sub screen, (19a) is a contrast control terminal,
(19b) is a bright control terminal. (Tr+) is a transistor. (V R1) (V R2) are sub-variable volumes for bright/contrast control.

FIG. 2 shows the relationship between the A, BL signals input to the input terminal (28a') in FIG. 1 and the values of the bright contrast control signal output from the point (28b'). The ABL signal of this TV is about 3.7V when the screen of the cathode ray tube is completely black, and about 6.0V when all songs are played.

Note that the slope and value of the bright/contrast control voltage for the sub-screen in Figure 2 are such that when the main screen is bright, the brightness output from the video chroma circuit for the sub-screen is reduced by the drop in brightness of the main screen. Although the bell rises, the brightness of the sub-screen on the screen is set to fall. When the main screen is dark, the brightness level of the child screen is set so that the video chroma circuit output and the screen also fall together.

Incidentally, setting the bright contrast control voltage for the child screen in this manner is performed by the resistor shown in FIG. For example, the upper limit (10.8V) is set for the resistors (R2) and (R3). Also, resistors (R4) and (R5) are at ABL which starts to fall.
Set the voltage value, resistor (R1)) transistor (T r
) to select the slope.

In other words, as can be seen from the characteristics shown in FIG. 2, the blacker the screen, the higher the value of the control signal. Then, the brightness and contrast of the video chroma circuit (19) of the sub-screen are controlled to lower the brightness. The amount of reduction in brightness is set so that even if an increase in the brightness of the child screen in the child screen insertion circuit (14) is added, the amount of reduction in brightness still decreases. Therefore, a cathode ray tube (1
6) When the main screen becomes black, the sub-screen on the cathode ray tube screen also becomes dark to prevent doming from occurring. Note that if the parent screen is dark and the child screen is also dark, the child screen will become darker, but we focused on preventing doming.

(G) Effects of the Invention As described above, according to the present invention, doming can be prevented without providing a main screen brightness detection means and a sub screen brightness detection means.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the present invention. FIG. 2 is a diagram for explaining the operation. FIG. 3, FIG. 4, and FIG. 5 are diagrams for explaining conventional examples. (12)...Video chroma circuit (first brightness control circuit), (19)...Video chroma circuit (second brightness control circuit), (14)...Sub screen insertion circuit, (16) ... Braun tube (cathode ray tube), (21)...
・Signal path (first control means), (28”)...ABL
Signal inversion circuit (second control means). 1 -□Owl Ton#

Claims (1)

[Claims] (1) A first brightness control circuit (12) for the main screen, a second brightness control circuit (19) for the child screen, and the first and second brightness control circuits.
a sub-screen insertion circuit (14) provided after the brightness control circuits (12) and (19); a cathode-ray tube (16) for projecting the signal from the sub-screen insertion circuit (14); ABL corresponding to the beam current amount of (16)
a first control means (l_1) for controlling the first brightness control circuit (12) using a signal; and a first control means (l_1) for controlling the first brightness control circuit (12) using the ABL signal; A two-screen television receiver comprising: second control means (28') for controlling the second brightness control circuit (19) to lower the brightness of the screen.