JPS58190180A - Character broadcast receiver - Google Patents

Abstract

PURPOSE:To display of characters even under interruption of broadcasting, by switching a circuit that reads out the character information written into a picture element memory in synchronization with the horizontal and vertical synchronizing signals to an internal synchronizing circuit. CONSTITUTION:The horizontal and vertical synchronizing signals A and B and pseudo synchronizing signal B contained in a TV signal are applied to a switching circuit 11. The circuit 11 selects the signal B which is supplied from a synchronizing signal generating circuit 6 in case the TV broadcast is interrupted and no synchronizing signal exists any more. A TV signal monitor circuit 10 transmits a switch command signal C to the circuit 11 when an interruption of the TV signal is detected. The synchronizing signal D selected by the circuit 11 is supplied to a refresh counter 12. Then the character information stored in a picture element memory 13 is read out in synchronization with the signal D and supplied to a CRT15.

Description

[Detailed Description of the Invention] Regarding the teletext receiver that can be used, 7I? This invention relates to stabilizing the display during interruptions in television broadcasting.

A teletext television system uses television radio waves to transmit text information and display it on the receiver's cathode ray tube.

This is effective when transmitting and displaying text information to a large number of terminals. in this case. Character information that is sent by time-multiplexed packet transmission during any one or more horizontal scanning periods (hereinafter referred to as H) of the 10th to 2l horizontal scanning periods in the vertical retrace period of a television signal. A teletext receiver serving as a terminal receives and displays this text information. And to this teletext receiver,
Character information (including graphics) that matches the specified program number
The teletext program is sequentially captured and once written into the pixel memory, and then read out in synchronization with the horizontal and vertical scanning of the cathode ray tube, thereby displaying the desired teletext program. In this teletext receiver, horizontal and vertical synchronization signals contained in the television signal K are extracted in a synchronization separation circuit, and the synchronization signal sound separated from this television signal is used to deflect the cathode ray tube. Control and pixel memory readout control are performed 7 times.

However, in the teletext receiver with the above configuration, reading of the pixel memory and deflection control are performed using synchronization signals included in the lighting and television signals. There are many problems when displaying text information, but when displaying text information when a TV broadcast is interrupted or at the end of a TV broadcast, the synchronization signal is lost, making it impossible to display text information. There are some problems.

In particular, some teletext receivers have a program reservation function that automatically writes infrequent programs such as news or weather forecasts into the pixel memory by reserving them. These reserved programs have various problems, such as not being able to be viewed after the television broadcast ends, and making it impossible to fully utilize the program reservation function.

Therefore, it is an object of the present invention (1) to provide a teletext receiver capable of stably displaying character information stored in a pixel memory even when a television broadcast is interrupted or terminated.

In order to achieve all of these objects, the present invention provides a television signal supply monitoring circuit that monitors the supply of television signals by manually inputting the output signal of a synchronization separation circuit that separates all synchronization signals contained in a television signal. When this television signal supply monitoring circuit detects a complete interruption of the television signal, it controls the entire switching circuit and transmits a synchronization signal for pixel memory read control from the output of the synchronization separation circuit to the internal synchronization signal generation circuit. It switches to output and supplies it. The teletext receiver according to the present invention will be explained in detail with reference to the following five drawings.

FIG. 1 is a circuit diagram showing an embodiment of a teletext receiver according to the present invention. In the same figure, 1 is a tuner that receives all of the target television broadcasts and generates a video intermediate frequency signal as an input for all antenna signals supplied from the antenna 2, and 3 is an intermediate frequency signal input for signals supplied from the tuner 1. Intermediate frequency amplification and detection circuit that performs all amplification and video detection.

4 is a synchronization signal separation circuit for extracting the horizontal and vertical synchronization signals contained in the television signal sent from the intermediate frequency amplification/detection circuit 3 as a composite synchronization signal A; 5 and 14.
Oscillation circuit that generates 3MH2 clock shift 02, 6
1 is a retriggerable multivibrator circuit in which a clock/zo system 0PI is a synchronizing signal generating circuit that manually generates a pseudo composite synchronizing signal Btl, and a composite synchronizing signal A clock input from the synchronizing separation circuit 4 is input to 7.

The time constant of the operation time is determined by the resistor 8 and the capacitor 9 so that it is slightly longer than the cycle of the horizontal synchronizing signal included in the composite synchronizing signal A. Therefore, this) I
When receiving TV broadcasts, the J Gable mono multipibrator circuit 7 is repeatedly retriggered by the horizontal synchronization signal included in the composite synchronization signal, so the set output Q becomes "H" and the TV broadcast reception is determined. The signal C continues to be generated, and the television signal reception monitoring circuit 10i uses this signal to determine the presence or absence of a television signal.
Focus on composing. 11 is a switching circuit for selecting the composite sync signal generated from the sync separation circuit 4 and the pseudo composite sync signal B generated from the sync signal generation circuit 6; The pixel memory 13 is connected to a refresh counter which generates the address signal AD for the pixel memory I713K in synchronization with the synchronization signal Drc generated from the switching circuit 11;
Amplify the character signal read out from the cathode ray tube IFI
The driving video amplifying circuit 16 is a deflection circuit that deflects the cathode ray tube 15 horizontally and vertically in synchronization with the synchronizing signal DK generated from the switching circuit 11.

In the teletext receiver configured as described above, when the tuner 1 receives the target television broadcast as the full input of the antenna signals supplied from the antenna 2, the entire video intermediate frequency signal is generated and the intermediate frequency amplification/detection circuit 3 supply to. The intermediate frequency amplification and detection circuit 3 extracts a television signal by amplifying and detecting the intermediate frequency signal and supplies it to the synchronization separation circuit 4 . Then, the horizontal and vertical synchronizing signals contained in the television signal are separated and taken out by the synchronization separation circuit 4, and these two synchronization signals are generated as a composite synchronization signal.

On the other hand, 1 oscillation circuit 5 U 14.3 MHz clock pulse CP always oscillates, and synchronous signal generation circuit 6t
j This clock pulse CP all inputs and 1. horizontal and vertical sync signals? A pseudo composite synchronization signal B having the following characteristics is generated j7.

Here, when receiving a television broadcast, the composite sync signal A is generated from the sync separation circuit 4 as described above, and is included in the composite sync signal A in the retriggerable multivibrator circuit 7. The horizontal synchronizing signal shown in FIG. 2(a) causes repeated tripping. In this case, the retriggerable multivibrator circuit 7 is retriggered by the horizontal synchronizing signal, so that the retriggerable multivibrator circuit 7 is set so that its operating period is somewhat shorter than the period of the horizontal synchronizing signal. Then, the TV broadcast reception discrimination signal C generated from the set W power Q is in the @H” state as shown in FIG. .

When the television broadcast reception determination signal C becomes H”.

Select all the composite synchronization signals in the switching circuit 11 and enter the synchronization number m.
! :L, refresh counter 12 and deflection circuit 1
Supply to 6. Therefore, the address signal AD is fully generated in synchronization with the synchronization signal separated from the refresh counter 12U television signal, and the character signal stored in the pixel memo 1713 is read out using this address signal ADi and output as a video signal. The video signal generated in this manner is amplified in the video amplification circuit 14 and then supplied to the cathode ray tube 15 where character information is displayed. In this case, the deflection circuit 16 also inputs the synchronization signal supplied from the switching circuit 11, and generates horizontal and vertical deflection signals synchronized with the synchronization signal I)K to direct the deflection coil provided in the cathode ray tube 15. Since the character signal read out from the 1-pixel memory 13 and the deflection are synchronized with each other, character information is stably displayed on the cathode ray tube 15Kt'j.

Next, if the TV broadcast reception is interrupted for some reason, or the teletext receiver is turned on when the TV broadcast ends.

The composite synchronization signal generated from the synchronization separation circuit 4 is disconnected. As a result, the retrigger multi/ζ isolator circuit 7 is no longer triggered, and accordingly, the TV broadcast reception determination signal C generated from the set output terminal Q is in the "L" state, and TV broadcast reception is continuously performed. I will show you the grapes. Then, the switching circuit 11 which receives the television broadcast reception discrimination signal C as the conference control input selects the pseudo composite synchronization signal B which is constantly generated from the synchronization signal generation circuit 6 and generates it as the synchronization signal (2).

Therefore, when a television broadcast is being received and is in a strong state, the output of the internally provided synchronizing signal generating circuit 6 is supplied to the refresh counter 12 and the deflection circuit I6, thereby transmitting the character information stored in the pixel memory 13. For this reason, when viewing programs such as news or weather forecasts with a small number of MUs stored in the pixel memo I+ 13 using the reservation function, or when watching the end of a television broadcast, etc. It becomes valid.

As explained above, the teletext receiver according to the present invention has the following features:
A television signal supply monitoring circuit that determines whether or not a television broadcast is being received, and a switching circuit that uses its output as a switching control input are provided. The output signal of the separation circuit is supplied to the refresh counter and deflection circuit that address the pixel memory, and when TV broadcasting is not being received, all switching circuits are switched to output the synchronization signal generation circuit provided inside the teletext receiver. It selects the signal and supplies it to the refresh counter and deflection circuit.

Therefore, even if the television signal is interrupted or the television broadcast ends due to some reason.

This has an excellent effect of stably displaying the character information stored in the pixel memory.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of a teletext receiver according to the present invention, and FIG. 2 (aHbl is a waveform diagram of each part of the circuit shown in FIG. 1. 1... tuner, 2... Antenna, 3...Intermediate frequency amplification and detection circuit, 4...Synchronization separation circuit, 5...Oscillation circuit, 6...Synchronization signal generation circuit, 7...IJ)
IJ gable multivibrator circuit, 10... Television signal reception monitoring circuit, 11... Switching circuit, 12.
...Refresh counter, 13...pixel memory. 14...Video amplification circuit, 15...Cathode ray tube. 16...Deflection circuit. Agent: Patent attorney Akio Suzuki.

Claims (1)

[Claims] (1) In a teletext receiver that receives and displays text information that is multiplexed and sent during the vertical retrace period of television broadcasting, the synchronization signal included in the received and demodulated composite video signal is separated. a synchronization separation circuit that extracts a composite synchronization signal from the synchronization separation circuit; a synchronization signal generation circuit that receives the clock pulses supplied from the single oscillation circuit as an input and generates a pseudo composite synchronization signal; and a synchronization signal generation circuit that receives the composite synchronization signal generated from the synchronization separation circuit as an input. and a reception monitoring circuit that determines whether television broadcasting is being received. By using the output signal of this reception monitoring circuit as a switching control input, the composite sync signal generated from the sync separation circuit is selected when television broadcasting is received, and the composite sync signal generated from the sync signal generation circuit is generated when no television signal is received. It is equipped with a switching circuit that selects a pseudo composite synchronization signal to be generated and supplies it to the pixel memo IJ address glue fresh counter and deflection circuit, and when the television broadcast is not being received, the internal synchronization signal generation circuit does not generate the signal. What is claimed is: 1. A teletext receiver characterized in that character information sounds stored in a pixel memory are displayed in synchronization with a pseudo-composite synchronization signal that is transmitted.