JPS6180979A - Crt drive circuit of two screen television - Google Patents

Abstract

PURPOSE:To monitor the subsidiary screen consistently in fine condition even when the brightness of the mother TV is changed, by returning the voltage step down due to the current supplied to the second resistor to the collector of a drive-in transistor for a specified duration of time. CONSTITUTION:A video signal incorporated with the picture of subsidiary screen is inputted to a point B, and a positive pulse which specifies the position and width of subsidiary screen is inputted from a point A. Since a bias transistor Qa is set 'on' only when a transistor Qf is 'on', a potential of a point C varies following only to the video signal inputted from the point B, but keeps constant in other occasions. Now, if the mother screen is adjusted to be darker, a feed- back is not made from a point E to a point F during a picture signal of mother screen is inputted; but while a picture signal of subsidiary screen is inputted, feed-back is made from the point E to the point F by the transistor Qf, resulting in constant fine screen of the subsidiary screen.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] 2P: The invention relates to a television receiver screen ((a two-screen TV screen that displays images such as Gozuyannel, etc. in addition to the normal received image). Regarding improvements.

[Technical background of the invention and its problems]

Recently, due to requests such as wanting to see images of other channels and surveillance camera images while watching images of the channel, a sub-screen for monitoring was created within the normal screen, and two screens were created to display the above images. Television is developed and commercialized.

The image displayed on the sub-screen of this two-screen TV will be displayed with the same white and black levels and the same contrast as the image displayed on the screen other than this small screen (hereinafter referred to as the current screen). In this case, the image of the child screen becomes an eyesore for IT listeners of the main screen, and the image of the single child screen itself has a large contrast on the small screen, making it difficult to see. Originally, the sub-screen was used for monitoring rather than for viewing itself, and it is important that it be easy to view, even at the expense of image fidelity. Therefore, the signal level between the white level and the black level of the child screen image is usually narrowed, that is, the contrast is made smaller than that of the main screen image.

By the way, even in such a two-screen television, the black level etc. of the main screen can be changed depending on the viewer's image preference. However, in a conventional two-screen television, when the black level of the image on the current screen is changed, the black level of the image on the sub-screen changes accordingly. For example, if you lower the black level or brightness of the main screen image, the black level of the sub screen will also drop and the contrast will be lower than that of the uHm screen, so the sub screen will have a darker image as a whole, and conversely, the contrast between the two images on the 1st screen will be lower. If you increase the black level, the sub screen will look whitish.

This problem will be explained using a specific circuit using FIGS. 2 and 3. At point A, a barusui ear sign that becomes L in the M circle of the image of the sub-screen shown in Figure 3 is inserted, and from point B, the image signal of the sub-screen is also incorporated into the image signal of image 11. FB+ is turned on.Then, the bias transistor (Qa) is turned on when the A point level is L, and fx is
The potential at point C drops slightly.

On the other hand, it is amplified by the video signal light drive transistor (Qd) that is connected to BAK, but as mentioned above, the potential at point C is slightly lower in the image signal of the sub-screen, so the potential at point D is shown in Figure 3 (Dl). The image signal of the sub-screen changes slightly in the direction of the white level.

The brightness (brightness) is determined by the DC level of the video signal input to point B, but normally this DC level depends on the vedestal level of the horizontal synchronizing signal. The diagonally shaded portion (Dl) is displayed.

However, depending on the viewer's preference, the image on the main side is brightened, that is, the DC level of the video signal input to point B? When set in the white direction, the potential at point D in Figure 2 is as shown in Figure 3 (D2).
The image on the sub-screen becomes too dark to be seen. Also, conversely, set the main screen image darker,
In other words, if the DC level of the video signal input to point B is set toward black, the potential at point D will make the sub-screen image too bright as shown in Figure 3 (D3), making it difficult to see. . Therefore, within the range where the child screen can be clearly seen, it is not possible to vary the brightness of the main screen over a wide range.

[Departure I! Purpose]

The present invention was made in view of the above-mentioned conventional problems, and provides a CRT for a two-screen television that can always monitor the image on the sub-screen in good condition even if the brightness of the main screen is greatly changed.
According to the present invention, the above-mentioned return is performed, so that when the current screen is adjusted to darken, the main screen does not become so dark, and when the main screen is adjusted to brighten, the cloth-subscreen The brightness of the main screen can be varied over a wide range.

[Embodiments of the invention]

Examples of the present invention will be described below. FIG. 1 shows the configuration of an embodiment of the present invention. (21) v'i,, the collector of the CRT transistor (Qd) is connected to the power supply +Vd (for example, 200V) via an auxiliary resistor (Rd) to 15, for example.
The base of this transistor (Qd) (point B) receives a video signal containing the image of the sub-screen. In addition, a resistor (Rc) of, for example, 160Ω is connected to the emitter of this transistor (Qd), and in addition to this resistor, 9□M is connected to the emitter of the bias transistor (Qa), and is 1/fi, for example, IKΩ. The resistance (
Rb) Full valve and positive power supply (+Vb) (12V in row)
K-connected vine.

The base of the bias transistor (Q, a) is, for example, 3
To the above power supply (+Vb) via the Krl resistor (R1),
Also, for example, connect it through a 680Ω resistor (R2),
Furthermore, it is connected to the collector of the transistor (Qf) via a resistor (R4) of, for example, 910Ω. The collector of the bias transistor (Qa) is the transistor (Qf)
The emitter of V is connected to the V and connected via a bias resistor (lRk) of, for example, 17Ω. Also, transistor 9 (Qf) o heat 6c is 'hjei'fl
A resistor (R3) of OKΩ is connected, and a positive pulse train is input to the other end of this resistor at point A, which turns on the transistor (Qf) only when the image signal of the sub-screen is input to point B. be done.

Note that the emitter, collector, and base f-1 of the bias transistors (Q, a) are assumed to be point C, point E, and point F, respectively.

Next, the operation of the CRT drive circuit of this embodiment will be explained using FIG. 4.

First, we will discuss the case where the brightness is set to normal. As mentioned above, a positive pulse train with a waveform like 44'1ACAt is input to point A, while a video signal incorporating the image of the sub-screen shown in the same figure (Bl) is input to point B. (Qa) is on when the transistor (Qf) is on, so the potential at point C changes following the video signal input from point B only when it is an image signal of the sub screen, and is constant in other parts. It has a potential.

On the other hand, although the amplitude of the potential at point E is small, it changes with great force following point B. At other times, the transistors (Q, f) are off, and feedback from point E to point F is not possible, so this potential maintains a constant potential determined by the values of resistors (R1) and (R2). As mentioned above, the potential at the KC point is lowered only when the image signal is on the sub-screen, so the BAK
The input video signal is inverted and amplified and appears at point D, but as shown in FIG. 934 (Dl), the image signal of the sub-screen has a waveform slightly pushed toward the white level.

By the way, suppose that the brightness is adjusted so that the main screen image becomes darker according to the preferences of the viewer of the dual-screen television. In this case, the DC V level of the video signal input to the B terminal is shifted toward the white level. When the image signal of the main screen is input to point B, the transistor (Qf
) is turned off, and no feedback is applied from point E to point F.

However, when the image signal of the sub-screen is input, feedback from the point E to the point F by the transistor (Qf) is heard. When adjusted so that it becomes dark as in this case, the potential at point B becomes relatively high, the current (Ik) flowing through the resistor <RJC> increases, the point E becomes high, and the potential at point F increases due to the feedback path. , the potential at point C also increases. Therefore, the emitter potential of the drive transistor (Qd) increases, making it difficult for the video signal input to point B to pass through, and looking at the potential at point D, the image signal of the sub-screen is
It will change in the direction shown by the arrow (22) in Figure (D2). After all, this means that even if you darken the image on the parent screen, the image on the seed screen will not darken.

On the other hand, when the viewer adjusts the brightness so that the main screen image becomes brighter, the current (Ik) flowing through the resistor (Rk)
becomes small, and the voltage drop due to this current is fed back to point F when the image signal of the sub-screen is input, so the drop in potential at point C is not so large. Therefore, at this time, the image signal of the sub-screen input from point B passes through the drive transistor (Qd) more easily, and as shown in FIG. 4 (D3), the image signal of the sub-screen changes in the direction shown by the arrow (23). do. That is, even if the main screen is brightened, the brightness of the child screen is not that bright.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an embodiment of the present invention, and FIG. 2 is a circuit diagram of a conventional C
FIG. 3 is a waveform diagram for explaining the circuit operation of FIG. 2, and FIG. 4 is a waveform diagram for explaining the circuit operation of FIG. 1. 11.21...CRT, Qd...drive transistor fi, Qa...bias transistor. R, 1, about 2. FL3. R, 4, Rk, Rh, 几c, R
+d... resistance. Agent Patent Attorney Noriyuki Chika Figure 1: 10% Figure 3

Claims (1)

[Claims] A drive transistor that is input based on a video signal incorporating an image signal of a sub-screen and drives a CRT that displays images on two screens, and a second resistor that is connected to the emitter of this transistor via a first resistor. and means for feeding back a voltage drop caused by the current flowing through the resistor to the collector of the bias transistor only when an image signal of a sub-screen is input to the base of the drive transistor. CRT drive circuit.