JPS6157752B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a television receiver used as a receiving device for a teletext system, etc., and is capable of displaying thick and clear vertical lines when displaying character information. The object of the present invention is to provide a receiver with good characteristics that does not cause any adverse effects when displaying television images.

The teletext system put into practical use in the UK multiplexes and transmits data signals for displaying characters and simple graphics during the vertical blanking period of the television signal, and on the receiving side sends the data to the television receiver. By adding a processing circuit for text reception, creating a character signal for character display based on the received data signal, and applying this character signal to the cathode ray tube in place of the video signal for normal television image display. It is designed to display character images. However, when displaying a character image on such a receiver, if the character includes vertical lines, the frequency contained in the character signal for display will reach a very high frequency. However,
The video amplification circuit that amplifies these character signals and adds them to the CRT usually has a bandwidth of only about 4.5MHz, which is required to display general television images, and the high frequency components mentioned above are Even if a character signal containing up to
It can only pass components up to about 4.5MHz. For this reason, for example, when displaying a "T" as shown in Figure 1A, a pulse character signal as shown in Figure 1B is supplied from the character signal generation circuit to display the vertical line of the "T". Even if it is, a signal with a rough waveform with high-frequency components removed, as shown in C in the same figure, is added to the CRT, and if the coloring level of the CRT is the level shown by the dashed line, then
The displayed vertical line becomes narrow, as shown in D in the figure, and becomes difficult to see.

Therefore, the present invention solves such conventional drawbacks, and even in the case of a character image having vertical lines, it is possible to display the vertical lines with a sufficient width in an easy-to-understand manner, and moreover, when displaying a normal television image, The purpose of this invention is to provide a television receiver that does not cause any problems.

EMBODIMENT OF THE INVENTION Hereinafter, the present invention will be described in detail with reference to the drawings showing one embodiment thereof.

FIG. 2 shows its circuit diagram. Here, 1 is
A video signal generation circuit that generates video signals for displaying regular television images on a CRT, such as the video detection circuit of a television receiver. The video signal is passed through a switch circuit 2 to a video amplifier circuit 3.
In addition to the base of transistor 4 for class A amplifier,
Take out the amplified output from that collector and
Add to CRT cathode.

On the other hand, 5 is a character signal generation circuit that generates a character signal for displaying a character image on a CRT. For example, it receives and stores a data signal of a teletext signal, and further generates a character signal by a character generator based on the data signal. A processing circuit or the like that generates this is used. The character signal generating circuit 5 generates a character signal at the output terminal a, and at the output terminal b, the level is set to high only when displaying a character image, and when displaying other television images. Generates a low level switching signal.

The character signal is added to the base of transistor 7 of buffer amplifier 6, taken out from its emitter, and applied to the base of transistor 4 of video amplification circuit 3 via diode 8. At the base of this transistor 7 are resistors 9 and 10 for voltage division, a bias power supply 11 for limiting the white peak, and a diode 12.
are connected. Further, the switching signal is applied to the base of the transistor 14 of the switching buffer circuit 13, taken out from its emitter and applied to the switching terminal of the switch circuit 2, and also applied to the base of the transistor 7 via the diode 15.

In this configuration, first, when displaying a normal television image on a CRT, a low level switching signal is generated from the output terminal b of the character signal generating circuit 5, the emitter output of the transistor 14 is set to a low level, and the switch is activated. Turn on the switch of circuit 2 and transfer the video signal from video signal generation circuit 1 to the CRT.
supply to. At this time, since the emitter of the transistor 14 is at a low level, the diode 15 is cut off, and since the output of the output terminal a of the character signal generating circuit 5 is fixed at the base level and is set to the ground level, the emitter of the transistor 7 is cut off. The base voltage becomes R ₉ /R ₉ +R ₁₀ Vcc, and the emitter voltage of transistor 7 becomes E ₁ . At this time, the emitter voltage _E1 at this base level is set to a level lower than the black level of the video signal, and its magnitude is determined so that the diode 8 will not conduct.

Next, when displaying a character image on a CRT,
A character signal having a pulse waveform as shown in FIG. At the same time, a high-level switching signal is generated from the output terminal b to make the transistor 14 conductive, and a high-level voltage is taken out from its emitter, thereby cutting off the switch of the switch circuit 2. This high-level voltage is then applied as a bias to the base of the transistor 7 via the diode 15. As a result, the signal at the base of transistor 7, which would be as shown by the dashed line in FIG. become. That is, the base level of the character signal moves toward the white side. however,
Since the bias power supply 11 and the diode 12 are provided, the white peak level of the character signal is maintained at the same level as before movement. Then, when it is taken out from the emitter of transistor 7 and applied to the cathode of the CRT via diode 8 and transistor 4, the high-frequency component disappears and the result is shown in Figure D.
become that way.

Here, the luminescence level on the CRT is set to l in D.
If we assume that the level is below that level, it will be displayed brightly on the CRT, and if there is no bias voltage mentioned above, the vertical lines of the character image will become narrower, as shown in the broken line shown in Figure E. By applying a bias voltage through diode 15, the signal to the cathode of the CRT becomes like a solid line, exceeding the light emission level from the root of the pulse, and is clearly displayed in a sufficiently wide state. become. Therefore, even if a video amplifying circuit 3 having a not very wide frequency band is used, character images can be displayed in an easy-to-understand manner. Moreover, even if the base level of the character signal is moved in the direction of the white level in this way, the white peak level of the character signal is maintained at a constant level by the bias power supply 11 and the diode 12.
It is possible to prevent the white peak level of the character signal applied to the CRT from becoming too high.
Even in a wide display area such as the horizontal line part of a "T", vertical lines can be displayed satisfactorily while preventing blooming or the like from occurring.

As is clear from the above description, according to the present invention, in a television receiver that receives text information such as in a teletext system, the frequency bandwidth of the video amplification circuit that amplifies the signal applied to the CRT is too wide. Even if the character image is not displayed, the vertical lines of the character image can be made sufficiently wide by applying a bias voltage to the character signal at a stage before the bias power supply and diode for controlling the white peak level of the character signal only when displaying the character image. It is an excellent receiver that can display images in a wide and easy-to-understand manner, and when displaying normal television images, there is no risk of adversely affecting the video signal by removing the bias voltage, and has good characteristics in any display. This is something that can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a waveform diagram for explaining the operation of a conventional television receiver, FIG. 2 is a circuit diagram of a television receiver according to an embodiment of the present invention, and FIG. 3 is a waveform diagram for explaining the operation. FIG. 1... Video signal generation circuit, 2... Switch circuit, 3... Video amplification circuit, 4... Transistor,
5... Character signal generation circuit, 6... Buffer amplifier, 7... Transistor, 8... Diode,
9, 10...Voltage dividing resistor, 11...Bias power supply,
12...Diode, 13...Switching buffer circuit, 14...Transistor, 15...Diode.

Claims (1)

[Claims] 1 a video signal generation circuit that generates a video signal for displaying a normal television image on a cathode ray tube; a character signal generation circuit that generates a character signal for displaying, the video signal is applied to the video amplification circuit via a switch circuit, and the character signal is applied to the video amplification circuit via a diode, A diode and a bias power supply are provided to limit the white peak level of the character signal, and a DC current of a predetermined value is used to move the base level of the character signal toward the white level only when the character signal is applied to the video amplification circuit. A television receiver characterized in that means for applying a bias voltage is provided before the white peak level limiting diode and the bias power source are installed.