JPH0312833B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a brightness adjustment device used in color television receivers, monitor televisions, CRT display devices, and the like.

Conventional configurations and their problems In recent years, CRTs have been recognized for their expressive capabilities, resolution, and visibility, and have been used not only as television receivers but also as teletext receivers, personal computer terminals, and even game terminals. It has come to be widely used. This application ranges from general household use to
It is used in everything from moving means of transportation.

This indicates that devices that were conventionally used only for reproducing one video signal are now becoming multipurpose devices that can reproduce multiple video signals. In other words, it is now more necessary than ever to adjust the brightness depending on the purpose, fatigue, and visibility.
It became necessary to solve this problem.

A conventional example of the brightness adjustment device shown in FIG. 1 is shown.
In the figure, 1 is a video signal such as a television signal or a video signal. As a result, the R, G, B, and Y signals are reproduced by the video/chroma demodulation circuit 2 and applied to the analog switch circuit 7.

On the other hand, R, G, and B signals 10, 11, and 12 (hereinafter referred to as
TxR, TxG, TxB) pass through each amplifier circuit 13, 14, 15 and are applied to one of the analog switches 7. Since each Tx signal is input as only an alternating current component, a direct current regeneration circuit 16 performs direct current regeneration and offsets the direct current component to each amplifier 13, 14, 15. The switching signal 17 controls the switching of the analog switch 7, and is generally a logic "H" signal.
(high level) and “L” (low level). The signal selected by the analog switch 7 is applied to the CRT 9 via the video drive circuit 8 and displayed as an image.

In this device, the brightness adjustment is artificially performed by a variable resistor _R1 , and the variable DC component obtained thereby passes through the line 18 on one side and the line 19 on the other side, and is passed through the video/chroma demodulation circuit. The brightness is changed by changing the DC offset of No. 2 and the DC offset of the DC regeneration circuit 16.

However, in this device, the two amplification systems (i.e., 2 and 13, 14, 15) have different amplification degrees and DC regeneration amounts, so when controlled by the DC bias obtained by variable resistor _R1 , Another drawback is that the CRT 9 does not have the same brightness in both amplification systems, and the variable resistor R ₁ must be constantly adjusted in response to changes in the ambient light of the environment in which it is used.

Purpose of the Invention The present invention solves the above-mentioned problems, and is capable of adapting to the selection of multiple video signals and changes in the surrounding environment, and is capable of adjusting the visibility of the display to the optimum brightness. The purpose is to provide a device that responds to

Structure of the Invention The present invention applies different DC bias voltages corresponding to the first and second amplification systems to
The brightness of the signal does not change depending on the signal selection. Furthermore, in the present invention, the brightness is automatically changed in response to changes in ambient light, thereby improving visibility.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. 1 to 17 shown in the figure are the same as in the conventional example. In this device, a first amplification system including a video/chroma demodulation circuit 2 and an amplification circuit 1
3 to 15, a different DC bias is applied to the line 1, corresponding to the second amplification system including the DC regeneration circuit 16.
8 and 19 to each amplification system, so that the brightness of the CRT does not change even depending on the selection of the video signal.

The control switching signal 17 for selecting the video signal is
Controls transistor _Q1 on/off. _R1 is a variable resistor for brightness adjustment. When transistor Q ₁ is off, the bias applied to the base of transistor Q ₂ is determined by variable resistor R ₁ . The base voltage of this transistor _Q2 is impedance-converted and output to the resistor _R4 , and then divided between the resistors _R7 and _R8 . The divided DC bias is applied to the video/chroma demodulation circuit 2 via line 18. On the other hand, amplifier circuits 13, 14, 15 DC regeneration circuit 16
A DC bias divided by resistors R ₅ and R ₆ is applied via line 19 to . Resistors R ₇ , R ₈ and R ₅ ,
_R6 is a resistor for matching the DC amplification degrees of the two amplification systems.

Resistor R ₉ is an external light sensor (e.g. silicon photodiode), and transistor Q ₃
The base potential of is supplied by R ₁₀ /R ₉ . By controlling the base potential of the transistor _Q3 , the DC impedance from the collector to the emitter of the transistor _Q3 is changed, and the potential of the line 18 and the line 19 are controlled according to external light, thereby changing the brightness.

The same result can be obtained by using a stitch instead of a sensor with this resistor _R9 . In this case, transistor Q ₃ operates as a switching transistor, and when transistor Q ₃ is off, line 1
The emitter potential of transistor Q ₂ is directly added to the potentials of lines 8 and 19, and when transistor Q ₃ is on, the potentials of lines 18 and 19 R ₇ /R ₈ and R ₅ /R ₆
It is added at partial pressure.

When the control switching signal 17 is "H", the transistor _Q1 is turned on, and the voltage divided by the resistors _R1 and _R3 is applied to the base of the transistor _Q2 .

This is the DC amplification degree of the two signal amplification systems.
Even if R ₇ /R ₈ and R ₅ /R ₆ are made to match, the amount of DC regeneration is still different, so both are made to match.

In this way, it is possible to respond to changes in brightness due to the environment and to unify brightness by selecting a plurality of signals.

Effects of the Invention As described above, according to the present invention, it is possible to match the DC amplification degrees of two amplification systems, and also match the amount of DC regeneration, so that the CRT can be used even if the input signals are different. It can always be driven to the same brightness. In addition, the brightness can be automatically changed depending on the ambient light, making it more convenient in practice.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a conventional brightness adjustment device, and FIG. 2 is a circuit diagram of a brightness adjustment device according to an embodiment of the present invention. 2... Video chroma demodulation circuit, 7... Switch, 8... Drive circuit, 9... Cathode ray tube, 1
3, 14, 15...Amplification circuit, _Q1 , _Q2 ...Transistor, _R5 , _R6 , _R7 , _R8 ...Voltage dividing resistor.

Claims (1)

[Claims] 1: a video chroma demodulation circuit that demodulates and amplifies a first video signal; an amplifier that amplifies a second video signal different from the first video signal; a switch circuit that switches between the output video signal of the demodulation circuit and the output video signal of the amplifier and supplies the same to the cathode ray tube via the drive circuit; a DC regeneration circuit that performs DC regeneration of the second video signal in the amplifier; A brightness adjustment volume for changing the brightness of the first video signal and the second video signal by changing the DC offset of the video/chroma demodulation circuit and the DC offset of the DC regeneration circuit, and a switch circuit for switching control. a first transistor that is turned on and off by inputting a control switching signal; the brightness adjustment volume is connected to the base of the transistor, and the base is connected to the output terminal of the first transistor through a first resistor; A second transistor, a third transistor having a base circuit connected to an element whose impedance changes depending on the brightness of external light, and a series circuit of second and third voltage dividing resistors, A fourth circuit with a different divided voltage from the circuit,
A fifth series circuit of voltage dividing resistors is connected in parallel and inserted between the output terminal of the second transistor and the output terminal of the third transistor, and a connection point of the second and third voltage dividing resistors is connected. is connected to the DC regeneration circuit, and the connection points of the fourth and fifth voltage dividing resistors are connected to the video chroma demodulation circuit to match the DC amplification of the video chroma demodulation circuit and the amplifier, and to adjust the amount of DC regeneration. A brightness adjustment device characterized in that the brightness adjustment device matches each other.