JPS626395B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a teletext receiver, and more specifically, it displays an image in a part of one frame using a video signal, and displays an image in the remaining part of the frame using a character signal. This invention relates to a teletext receiver that displays .

In the prior art, in order to improve the image quality when displaying images using character signals and to simplify the configuration, when superimposing character signals on video signals, the cathode ray tube is removed from the television video circuit. A character signal is supplied and superimposed on the demodulated output given to the drive circuit. Although the brightness of the video signal can be adjusted by operating a knob provided on the outside of the receiver or by remote control, the brightness of the image due to the character signal is Regardless of the signal brightness adjustment, it was not possible to adjust it to an appropriate value.

An object of the present invention is to enable, in a teletext receiver that displays an image by superimposing a character signal on a video signal, to appropriately adjust the brightness of an image based on the character signal to a desired value. It is.

FIG. 1 is a block diagram of one embodiment of the present invention. In teletext broadcasting, a signal containing a video signal in which a character signal is multiplexed in one horizontal period or two horizontal periods during a vertical retrace period is amplified in a high frequency amplification circuit 1 and an intermediate frequency amplification circuit 2, and is amplified in a separation circuit 8. Signals and text signals and voice signals are separated. The audio signal is amplified by the amplifier circuit 6 and output from the speaker 7. The video signal from the separation circuit 8 is given to a demodulation circuit 9. The demodulated video signal is sent from line 14 to red,
The signal is divided into green and blue signals and applied to the superimposition circuit 11. A character signal is also obtained from the demodulation circuit 9 and applied to the teletext recorder 12.
The red, green and blue character signals from the teletext recorder 10 are applied to the superimposition circuit 11 via a line 21.

The signal derived from the superposition circuit 11 on line 16 has a waveform as shown in FIG. The superimposed signal derived from the line 16 is formed by superimposing the character signal 18 on the video signal 17. This superimposed signal is given to a drive circuit 12, and an image is displayed by a cathode ray tube 13 serving as a display means.

The signal from the remote control transmitter 5 is received by the remote control receiver 4 and provided to the remote control decoder 3. The remote control decoder 3 selects a receiving broadcast station based on the signal from the remote control transmitter 5,
A signal representing brightness is also derived from line 19. The pulse-amplified signal representative of brightness from line 19 is at a high level to brighten the image and at a low level to darken the image. The signal representing the brightness from this line 19 is
The signal is applied to the demodulation circuit 9 to control the level of the video signal, and is also applied to the character signal brightness adjustment circuit 20.

In the character signal brightness control circuit 20, the superimposed signal from the line 16 is connected to the line 2 via the diode 22.
3 to the emitter of transistor Q1. The character signal derived from the teletext decoder 10 on line 21 is inverted by an inverting circuit 24 and passed through a variable resistor R3 to a transistor Q1.
is connected at connection point 25 to the base of. The signal given to the variable resistor R3 from the inverting circuit 24 is
Red, green and blue signal components R, G, of the character signal
The inverted value (=+
G+B). A resistor R2 is connected to the connection point 25, and a constant current transistor Q2 and a resistor R2 are connected to the connection point 25.
6 and capacitor C2 are connected. Resistors R4, R5 and capacitor C1 are connected in conjunction with the base of transistor Q2. A signal for brightness control via a line 19 is applied from the remote control decoder 3 via a resistor R7 to the connection point between the resistor R6 and the capacitor C2, and the average value is obtained by the capacitor C2. A resistor R1 is connected to the emitter of the transistor Q1.

A superimposed signal in which a character signal is superimposed on a video signal is
As mentioned above, the peak level of this superimposed signal is derived from line 16, and the peak value of the level of this superimposed signal is
It is clipped at level 26 (see FIG. 2) determined by the base potential of 1, and its peak value is suppressed. To determine the clip level 26, the sum of character signals provided by the teletext decoder 10 is inverted by an inverting circuit 24 and connected to a resistor R.
2 and variable resistor R3, and is applied to the base of transistor Q1 in synchronization with the character signal included in the superimposed signal on line 16. The level of only the text signal 18 can be controlled by providing a variable resistor R3 outside the teletext receiver and allowing the listener to change the resistance value of the variable resistor R3. At this time, the video signal does not change due to changes in variable resistor R3. By appropriately determining the values of the resistors R4, R5, R6, and R7, the suppression control range of the peak value of the character signal can be determined. The brightness signal derived from line 19 by operation of remote control transmitter 5 changes the current value of transistor Q2. Therefore, the voltage drop across resistor R2 changes, and the voltage value at connection point 25 changes. In this way, the brightness of the video signal and character signal can be transmitted and controlled by remote control.

Capacitor C2 may be omitted when the luminance signal derived from line 19 is an analog value.

As described above, according to the present invention, the peak value of the level of a superimposed signal in which a character signal is superimposed on a video signal is suppressed in synchronization with the level of the character signal before being superimposed on the video signal. Therefore, the brightness of the image based on the character signal can be adjusted independently of the brightness adjustment of the image based on the video signal.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of one embodiment of the present invention, and FIG.
The figure shows line 23 in the embodiment shown in FIG.
FIG. 2 is a waveform diagram of a signal obtained from FIG. 1...High frequency amplification circuit, 2...Intermediate frequency amplification circuit, 3...Remote control decoder, 8...Separation circuit,
9... Demodulation circuit, 10... Teletext decoder, 11... Superimposition circuit, 12... Drive circuit, 13
...Cathode ray tube, 20...Character signal brightness control circuit.

Claims (1)

[Claims] 1. A text signal is superimposed on a video signal, an image is displayed in a part of one frame by the video signal, and an image is displayed in the remaining part of one frame by the character signal. A teletext receiver equipped with a means for suppressing and controlling a peak value of a level of a superimposed signal in which a text signal is superimposed on a video signal; A teletext receiver characterized in that it performs broadcasting in synchronization with the occurrence of.