JPS5952979A - Teletext receiver - Google Patents

Abstract

PURPOSE:To supply an excellent character signal to a decoder and make accurate reception possible, by compensating the frequency characteristic of an amplifier circuit for the character signal with the size of the clock signal part in a multiplexed character signal obtained from a television signal. CONSTITUTION:A sampling gate 12 fetches the clock signal part from the television signal by using the pulse from a sampling pulse generating circuit 11. The noise component of the clock signal is removed by means of a filter 13 and the size is detected by detecting the signal at a detecting circuit 14. Since the amplitude of the clock signal becomes smaller when a high band characteristic is affected worse by a tuner 1 and VIF video detecting circuit 2, the gain at the high band of the amplifier circuit 8 is controlled to increase by a frequency characteristic compensating circuit 15. Therefore, the character signal having a sufficient waveform can be supplied to the decoder 9 irrespective of the frequency characteristic up to a preceding stage and the character signal transmitted by multiplexing the TV signal can be reproduced correctly.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a device for receiving a character signal multiplexed with a television signal such as a teletext system and transmitted.

Conventional configurations and their problems In recent years, teletext broadcasting called teletext has become widespread in Europe, particularly in the United Kingdom, and there is a demand for television receivers capable of receiving the signals.

However, in conventional receiving devices, if the high-frequency components of the waveform are significantly lost due to the reception condition of the received signal, the teletext signal decoder will not perform correct signal processing, and the reproduced text information will not be processed properly. Errors were often made.

As shown in FIGS. 1a and 1b, the teletext signal used in the teletext system has a binary character signal inserted into the vertical retrace period of a general television signal. For example, the 17th, 18th and 3'3
Character signals for one line of character information are sent during each 0.331st horizontal scanning period, and 40 characters of normal size are displayed per line, with 24 lines forming one screen.

As shown in FIG. 2, for this character signal, one horizontal scanning period is divided into 444 vias and 360 bits thereof are used. A clock signal is transmitted to the first 16 bits of the 360 bits, and thereafter various control code signals based on binary code signals and character code signals for displaying characters are transmitted.

In such a receiving device for a teletext system, the video detection output of the television signal is input to the decoder section via a dedicated amplification k, where the character signal is stored and converted into a video signal for character display. ) In addition to the Nox circuit, it is displayed as characters on the cathode ray tube. However, the condition of the received signal is subject to change, and the frequency characteristics of the video detection output are often subject to variations due to variations in the chi corners, etc., and it is often difficult to correctly receive character signal components.

OBJECT OF THE INVENTION The present invention (d) is to provide a device that can accurately receive character signals of teletext broadcasting based on binary coding such as a teletext system and reproduce character information by eliminating such conventional inconveniences. ]” target.

Structure of the Invention In the present invention, the receiving state is detected by detecting the size of the clock signal portion in the character signal obtained from the television signal, and the frequency of the character signal amplifier circuit is determined from the detection output. so that it is supplied to the special coder,
This allows for accurate reception.

DESCRIPTION OF THE EMBODIMENTS FIG. 3 shows a block diagram of a teletext receiving apparatus for a teletext system according to an embodiment of the present invention. In the figure, 1 is CH, -S, and 2 is ■F.

Video detection circuit, 3 is color demodulation circuit, 4 is video amplification circuit, 5
1 is a multiplex circuit, 6 is an amplifier circuit, and 7 is a cathode ray tube, which are the same as those in a normal color television receiver, so a detailed explanation will be omitted. Reference numeral 8 denotes an amplifier circuit for amplifying character signals etc. from the video-detected television signal; 9 extracts the character signal multiplexed with the television signal, stores it in a memory, and synchronizes it with the scanning of the cathode ray tube 7; This is a decoder that reads out the data and converts it into a video signal for character display. This decoder 9 may also be of a known type. The static image signal output from the decoder 9 is applied to the 7-trix circuit 5 to reproduce character information on the cathode ray tube 7.

Here, 1o is 4? of this device? It is a compensation circuit with a small
In this circuit, first, the sampling pulse generation circuit 11 generates a second pulse.
A sampling pulse is generated at a position corresponding to the clock signal of the character signal as shown in the figure, and this is used to control the sampling gate 12.
extracts only the clock signal portion of the character signal from the television signal. The extracted clock signal r is passed through a filter 13 tuned to the lock frequency to remove noise components, and then detected by a detection circuit 14 to detect its magnitude. Chronoclay 1, which is a character signal, belongs to the higher range of television signals, so if the high range characteristics are deteriorated due to variations in the frequency characteristics of tuner 1, VIP, video detection circuit 2, etc. The amplitude of the detected clock signal becomes small. Therefore, this detection output is applied to the frequency characteristic compensation circuit 16, and the gain of the amplifier circuit 8 in the high frequency range is controlled to be more favorable as the amplitude of the detected clock signal becomes smaller. By doing this, the decoder 9 can always be supplied with a character signal with a sufficient waveform regardless of variations in frequency characteristics up to the previous stage, and can always receive and reproduce character information accurately. It is.

In the following embodiments, the clock is taken out from the input side of the amplifier circuit 8, but it goes without saying that the clock may be taken out from the output side of the amplifier circuit 8 to form a feedback loop configuration.

Effects of the Invention According to the present invention, in a device for receiving teletext multiplexed with a television signal, such as a teletext system, received characters may Even if there is variation in the signal, it can be automatically compensated for, and character signals can always be received accurately and character information can be reproduced.

[Brief explanation of the drawing]

FIGS. 1A and 1B and FIG. 2 are waveform diagrams showing examples of transmission modes of text signals, and FIG. 3 is a block diagram of a text multiplex broadcast receiving apparatus according to an embodiment of the present invention. 8...Amplifier circuit, 9...Decoder, 1
0... Auxiliary circuit, 11... Sampling pulse generation circuit, 12... Sampling gate, 13...
...Filter, 14...Detection circuit, 15.
...Frequency characteristic compensation circuit. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 3

Claims (1)

[Claims] The clock signal part of the character signal is extracted from the television signal in which the character signal with binary coding is multiplexed, and its size is detected by detection, and the detected output is used in the amplification circuit for the character signal. attached device.