JPH0312829B2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a television receiver capable of displaying two screens or even more screens at the same time, especially its ABL.
It is related to circuits.

Conventional configuration and problems thereof In a conventional multi-screen television, a composite video signal into which a sub-screen has been inserted is input to a contrast control circuit and a brightness control circuit to control contrast and brightness.

On the other hand, in television receivers, the winding of the flyback transformer is used to prevent the beam current flowing through the cathode ray tube (CRT) from changing drastically due to fluctuations in the average brightness level (APL) of the video signal. Detects changes in beam current and controls brightness or contrast based on the detected output
An ABL circuit (ABL/contrast circuit) is included. However, this ABL circuit operates based on the average amount of changes in beam current, so in the case of a multi-screen TV, the size of the sub-screen is the primary factor.
Because it is smaller than the main screen (hereinafter referred to as the main screen), it is usually smaller than the main screen.
The ABL circuit operates according to changes in APL. Therefore, there is a problem in that the brightness of the child screen fluctuates due to changes in the APL of the parent screen, making it difficult to see.

Furthermore, even if it is a multi-screen TV in which the sub-screen is synthesized immediately before the CRT drive circuit, the same applies if the clamp of the sub-screen's pedestal level is tracked by changes in the pedestal level of the main screen. has the disadvantages mentioned above.

Purpose of the invention The present invention solves the above problems and
To provide a multi-screen television receiver capable of making a sub-screen easier to see by eliminating changes in brightness of the sub-screen due to changes in the sub-screen.

Structure of the Invention In the present invention, a switch circuit is provided to switch the operation of the ABL circuit, and this switch circuit is controlled by a pulse indicating the position where the sub-screen is to be synthesized. The brightness/contrast is not controlled by the beam current to prevent the brightness/contrast of the child screen from changing due to changes in the APL of the main screen.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows its configuration, in which a composite video signal A in which a parent screen and a child screen are combined is input to a contrast control circuit 1. Its output is further connected to a brightness control circuit 2. Volume 3
is for the viewer to manually adjust the contrast. Volume 4 is provided for sub-bright adjustment, and volume 7 is provided for adjusting brightness.

The winding a of the flyback transformer 11 is equipped with a CRT.
A current i flows according to an increase or decrease in the beam current. One end of winding a is connected to power source B ₁ via resistor 12 . One end of a capacitor 13 and the cathode end of a Zener diode 14 are connected to the intersection of the winding a and the resistor 12, and the other ends of the capacitor 13 and the Zener diode 14 are grounded. The Zener diode 14 is used to provide a reference potential for ABL operation, and the beam current of the CRT increases and i
As increases, the voltage drop across resistor 12 increases, and when it drops below the Zener potential, resistor 12 and winding a
The potential at the intersection of , changes depending on the increase or decrease in current i.
Capacitor 13 is provided to smooth out fluctuations. In particular, the intersection point between the resistor 12 and the winding a is also connected to one end _C2 of the switch circuit 10. One end _C3 of the switch circuit 10 is connected to the intersection of the resistor 9 and the other end of the volume 18 connected to the power source _B2 .
The other end of resistor 9 is grounded. Therefore, the voltage at _{the three} points C is a constant voltage adjusted by the volume 8.

A common end _C1 of the switch circuit 10 is connected to one end of the contrast adjustment volume 3 and the cathode of the diode 6, and the anode is connected to the brightness control circuit 2 via the resistor 5. When C ₁ and C ₂ of the switch circuit 10 are connected,
Fluctuations at the _C2 end due to changes in beam current are fed back to the contrast control circuit 1 via the volume 3, and fed back to the brightness control circuit 2 via the diode 6 and resistor 5, resulting in the so-called
ABL operations are normally performed.

When C ₁ is connected to C ₃ , a constant voltage determined by volume 8 and resistor 9 is maintained regardless of beam current fluctuations, so contrast,
Neither the brightness nor the brightness changes due to changes in beam current.

The switch circuit 10 is connected by a line L to a sub-screen synthesis position instruction pulse generation circuit 15. The child screen synthesis position instruction pulse generation circuit 15 generates the horizontal synchronization signal H and the vertical synchronization pulse V as shown in FIG.
Pulse A and pulse B are generated internally. The AND output of pulse A and pulse B is output to line l, and during that period, the switch circuit 10 is internally controlled to connect C ₁ and C ₃ , and during the remaining period, connects C ₁ and C ₂ . Made to connect.

Due to the above operation, only the insertion period of the sub screen
The ABL circuit is switched to eliminate changes in the brightness of the child screen due to changes in the APL of the main screen. Without supplying a fixed voltage to the C ₃ terminal, if you use another means to supply a variable voltage that is linked to changes in the APL of the sub-screen, it is possible to equivalently suppress changes in beam current caused only by the sub-screen. It is also possible to prevent extreme brightness changes from occurring independently between the parent screen and the child screen.

Effects of the Invention As described above, according to the present invention, the APL of the main screen
It is possible to prevent changes in the brightness and contrast of the sub screen due to ABL circuit operation caused by changes in the
A multi-screen television receiver with easy-to-see sub-screens is realized.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a multi-screen television receiver according to an embodiment of the present invention, and FIG. 2 is a front view and a waveform diagram showing an example of the screen composition position thereof.

Claims (1)

[Claims] 1. A multi-screen television in which a second or multiple television screens are compressed at a certain rate and inserted as child screens on a part of a first television screen, which is a main screen. The receiver includes an ABL circuit that receives as input a composite video signal in which the main screen and the sub-screen are combined and controls contrast and brightness according to increases and decreases in the beam current of the CRT, and a control that indicates the position where the sub-screen is inserted. signal as input, and output the sub-screen part of the composite video signal.
A multi-screen television receiver comprising: a switch circuit for switching the ABL circuit to prohibit ABL control;