JP2579141B2 - Television receiver - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a television receiver, and more particularly to an improvement in a television receiver that can receive, for example, teletext broadcasting.

Teletext is a multiplex of digitized text and graphic information that is transmitted using the time gap of ordinary television waves. Is a new broadcast service system in which information of the program is displayed on a television receiver.

FIG. 1 is a block diagram showing an example of a conventional television receiver capable of displaying teletext broadcasting. In the figure, a composite video signal received by a tuner 1 is provided to a VIF (intermediate frequency) amplifier 2 and amplified. After the output of the VIF amplifier 2 is detected by the video detection circuit 3, it drives the CRT display 11 via the video signal and color signal processing circuit 4 and the video switching circuit 10.

On the other hand, the DC level of the detected composite video signal is fixed by the clamp circuit 5, and the character signal is extracted by the slice circuit 6. Character data is read from the character signal by the sampling circuit 7. The sampling clock for this reading is reproduced by the sampling clock reproducing circuit 8 from the clock synchronization signal (clock run-in) in the character signal. The read data is processed by the character signal processing circuit 9, becomes a signal displayed on the CRT display, and drives the CRT display 11 via the video switching circuit 10.

By the way, since a character signal which is originally a digital signal is multiplexed and transmitted with a television signal which is an analog signal, various distortions occur in a waveform of a reproduced character signal due to the transmission characteristics of a television broadcast wave. However, as described above, in the conventional television receiver, since the received character signal is processed in an analog manner, there has been a disadvantage that the reading error of the character signal frequently occurs due to the waveform distortion. As a result, the quality of the reproduced image of the teletext is deteriorated. In a conventional television receiver,
When converting a received character signal into a binary signal, a predetermined reference level is compared with the level of the received character signal, and a binary value is determined based on whether or not the level of the character signal exceeds the level of the reference signal. It converts it to a signal. As described above, in the conventional television receiver, it is necessary to set the reference level in advance, which is troublesome. Further, the reference level fluctuates due to a change with time of the television receiver and the like, and there is a trouble that the reference level has to be reset. Further, in a conventional television receiver, it is necessary to further sample the signal binarized as described above and convert it into a bit-sequential binary signal. The sampling period at this time must be completely synchronized with the bit period of the character signal as a digital signal.
There is a disadvantage that the setting is difficult.

SUMMARY OF THE INVENTION Therefore, a main object of the present invention is to provide a television receiver which can solve all of the above-mentioned disadvantages and can stably reproduce an image of teletext broadcasting.

In summary, the present invention converts a character signal including a clock run-in signal, a framing code, and character data of a received teletext to a digital character signal having a binary level sampled value. In addition to correcting the waveform distortion, the impulse noise included in the digital character signal is removed, and the binary digital character signal is separated into a sample value having a level higher than the reference level and a sample value having a level lower than the reference level. , Data is read from the sample values of the separated levels, and the read data is processed to display characters on a display.

The above and other objects and features of the present invention are:
It will be more apparent from the following detailed description, which proceeds with reference to the drawings.

FIG. 2 is a schematic block diagram showing one embodiment of the present invention. In this figure, this embodiment is the first except for the following points.
The circuit is the same as the circuit shown in the figure, and the corresponding parts are denoted by the same reference numerals, and description thereof will be omitted. The output of the video detection circuit 3 is
It is provided to the A / D converter 12. The output of this A / D converter 12 is
The digital signal is supplied to the digital signal processing unit 13, the automatic waveform equalizer 15, and the video signal memory 13. The digital signal processing unit 14 is a circuit for digitally processing a luminance signal and a chrominance signal, and its output is provided to one input of the video switching circuit 10. The automatic waveform equalizer 15 is a circuit for correcting waveform distortion of a character signal, and its output is provided to an impulse noise removing circuit 16. The impulse noise removing circuit 16 is a circuit for removing impulse noise from a character signal, and its output is provided to a character signal separating circuit 17. The output of the character signal separation circuit 17 is provided to a character signal memory 18 and stored. The sampling circuit 19 is a circuit for reading a character signal stored in the character signal memory 18 and reading character data, and an output thereof is given to the character signal processing circuit 9. The output of the character signal processing circuit 9 is provided to the other input of the video switching circuit 10.

FIGS. 3 (a) and 3 (b) are diagrams showing the transmission waveform of the character signal on the transmission side of the teletext broadcasting. In particular, FIG. 3 (a) shows the character signal during one horizontal scanning period,
FIG. 3B shows the clock run-in and the framing code in the header portion of the character signal in an enlarged manner.
FIG. 3 (c) shows a case where a character signal containing no waveform distortion or impulse noise is received.
Represents the sample value (digital value) of the character signal output to the graph length. Note that a sine waveform connecting the vertices of each graph indicates the output of the video detection circuit 3. FIG. 3 (c) shows sample values in the first four bits of the clock run-in described above. FIGS. 4 (a) and 4 (b) show sample values of the character signal output to points a and b in FIG. 2 when the received character signal contains waveform distortion and impulse noise, respectively. Is shown by the length of the graph.

The operation of the embodiment shown in FIG. 2 will be described below with reference to FIGS. 3 and 4.

The composite video signal detected by the video detection circuit 3 is supplied to an A / D converter 12 and converted into a digital signal (for example, 8 bits). The digital signal is supplied to a digital signal processing unit 13, where the luminance signal and the chrominance signal are digitally processed, D / A converted again into an analog signal, and supplied to the video switching circuit 10. On the other hand, the composite video signal converted into the digital signal is also supplied to the video signal memory 14. The video signal memory 14 stores character signal portions during the vertical blanking period (for example, the scanning line numbers 20H and 2H).
83H) is stored for one horizontal scanning period.

Here, the data in teletext broadcasting is binary NRZ.
Clock frequency pulses _{364f H = (8/5) · f} sc (f H)
Is transmitted at the horizontal scanning frequency and _fsc is the color subcarrier frequency). Therefore, if the sampling frequency (sampling frequency) of the A / D conversion is selected to be _4fsc , the number of samplings per bit of data is 4 / (8/5), which is 2.5. Since two bits correspond to exactly five sample values, the m-th sample point and the (m + 5) -th sample point are the same phase point at the n-th bit and the (n + 2) -th bit of the data. If two data bits are combined into one set and given a data pair number such as l = 1, 2,..., The data pair given a certain data pair number l has the n (= 2l−1) th bit And the data of the (n + 1) th bit are included. FIG. 3 (c) illustrates the above relationship. That is, each sample point is defined as ▲ P ^l _m
（(L = 1,2,..., M = 1,2,3,4,5), and the data pair number 1 is incremented by one for every five samples.

In the video signal memory 14, sample values for one scanning period including a character signal are stored in the order shown in FIG. 3 (c). First, consider finding a clock run-in signal (16 bits, 101010... 10) from this sample value sequence.
The detection of the clock run-in signal utilizes the above-mentioned property that the m-th sample point and the (m + 5) -th sample point are the same phase point at the n-th bit and the (n + 2) -th bit of the data. That is, the same value (the same phase) in ▲ P ^l _m ▼ values m between the sample values are the same thing (e.g. ▲ P ¹ ₂ ▼ and ▲ P ² ₂ ▼ the clock run-in. Thus,
▲ P ^l _m ▼ , Ie, every five sample values are sequentially compared, and it can be detected that the point recognized as the same value within a certain error range is the point at which the clock run-in signal starts. Here, in order to increase the certainty, a similar comparison may be made for several subsequent sample values.

Next, the maximum and minimum values of the clock run-in signal can be easily obtained. For example, in FIG. 3 (c), ＰP ^l ₂ ▼ is the maximum value and ＰP ^l ₄ is the minimum value. Therefore ▲ P ^l ₂ ▼ phase sample values n bit data values, ▲ P ^l ₄ ▼ a may be adopted as the data value of the n + 1 th bit.

As described above, the detection of the framing code (8 bits, 11100101) can be easily performed after the clock run-in.

The detection of the clock run-in signal, the detection of the maximum value and the minimum value thereof, the detection of the framing code, and the like as described above are configured so that the video signal memory 14 has such a function together with the storage function. That is, the block represented by the video signal memory 14 includes a configuration having the above function in addition to the ordinary digital memory.

By the way, the received character signal is transmitted on the TV signal transmitting side,
Waveform distortion caused by various factors on the transmission path and the receiving side cannot be avoided. Also, the state of the waveform distortion changes depending on the broadcasting station, reception conditions, and the like. The automatic waveform equalizer 15 removes this waveform distortion. FIG. 4A shows a framing code (FC) portion of a character signal (sample value) containing the above-described waveform distortion. In this case, the most affected by distortion is the transient portion of the third to fourth bits of FC, and then the fifth to sixth bits of FC.
This is the bit transition part. Therefore, for example, as the evaluation criterion for waveform equalization, the sample values of the first to third bits and the sixth bit become almost the same value at the high level, and the fourth and fifth bits become the same.
By adopting that the bit sample value becomes almost the same value at the low level, an evaluation function that can express the best point by the maximum value or the minimum value of this evaluation criterion may be considered. The automatic waveform equalizer 15 is composed of, for example, a transversal filter, and automatically calculates and controls its parameters so that the above evaluation function becomes maximum or minimum. The FC with the corrected waveform distortion is as shown in FIG. 4 (b). In addition,
The automatic waveform equalizer 15 calculates a parameter for automatic equalization using a framing code having a predetermined bit pattern. Thereafter, the waveform distortion of the character signal is corrected using the calculated parameter.

Next, consider a case where impulse noise is mixed in the sample value. The impulse noise elimination circuit 16 discards an abnormal sample value due to impulse noise and corrects it to a correct value by, for example, taking a majority decision of sample values in one bit or checking the continuity of sample values before and after.

In this way, a sample value sequence digitally processed for automatic equalization and impulse noise removal is provided to the character signal separation circuit 17. The character signal separating circuit 17 separates the signal into two values, a sample value larger than a certain reference level and a sample value smaller than a certain reference level. As the standard level, for example, a central value between the maximum value and the minimum value of the clock run-in signal is calculated and adopted. Therefore, unlike the related art, there is no need to set a reference level for binary signal separation in advance, and there is no need for readjustment due to aging or the like.

The sample values separated into two values as described above are stored in the character signal memory 18 of 1 bit (1 or 0) for each sample value. Data is read from the sample value sequence by the sampling circuit 19. The sampling period required for data reading is determined because two bits of the data are exactly five sample values, and the starting point of the data is also the framing code (F
It is known by the detection of C). That is, the sampling circuit 19 reads the data at the same phase point every five sample values from the start point of the detected data. Therefore, unlike the conventional analog system, fine adjustment of the read timing by the phase of the sampling clock is not required, and a sample value as data can be easily read from the address of the character signal memory 18. The data thus obtained is processed by the character signal processing circuit 9 in the same manner as in the prior art, and drives the CRT display 11 via the video switching circuit 10.

In the above embodiment, as an example of digitally processing a received character signal, detection of clock run-in,
Although the equalization of the character signal waveform and the removal of the impulse noise have been described, the present invention is not limited to this, and various other digital processes may be performed.

As described above, according to the present invention, the received character signal including the clock run-in signal, the framing code, and the character data of the character multiplex broadcasting is converted into the digital character signal of the binary level sample value, and the converted digital signal is converted. While correcting the waveform distortion of the character signal and removing the impulse noise, the binary digital character signal is separated into a sample value of a higher level than the reference level and a sample value of a lower level than the reference level, Since the data is read from the sample values at the separated levels and the characters are displayed on the display, a text broadcast can be received stably and a high-quality reproduced image can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram showing an example of a conventional television receiver capable of receiving teletext broadcasting. FIG. 2 is a schematic block diagram showing one embodiment of the present invention. FIGS. 3 (a) and 3 (b) are diagrams showing the transmission waveform of the character signal on the transmission side of the teletext broadcasting, and FIG. 3 (a) shows the character signal during one horizontal scanning period. (B) shows an enlarged waveform of the clock run-in and the framing code part in the header part of the character signal. FIG. 3 (c) shows the sample value (digital value) of the character signal output at point a shown in FIG. 2 when the received character signal does not include waveform distortion or impulse noise. FIG. FIGS. 4 (a) and 4 (b) show points a and b in FIG. 2 when the received character signal includes waveform distortion and impulse noise, respectively.
FIG. 6 is a diagram showing sample values of character signals output to the graph length. In the figure, 1 is a tuner, 2 is a VIF amplifier, 3 is a video detection circuit, 4 is a video signal and color signal processing circuit, 5 is a clamp circuit, 6 is a slice circuit, 7 is a sampling circuit, 8 is a sampling clock circuit, 9 Is a character signal processing circuit, 10 is a video switching circuit, 11 is a CRT display, 12 is A
/ D converter, 13 is a digital signal processor, 14 is a signal video signal memory, 15 is an automatic waveform equalizer, 16 is an impulse noise elimination circuit, 17 is a character signal separation circuit, 18 is a character signal memory, and 19 is sampling 1 shows a circuit.

Claims (3)

(57) [Claims] 1. A television receiver capable of displaying teletext broadcasts on a display, comprising a binary level sampled character signal containing a received clock run-in signal, a framing code, and text data of the teletext broadcast. Conversion means for converting the digital character signal into a digital character signal, waveform distortion correction means for correcting waveform distortion of the digital character signal converted by the conversion means, and noise for removing impulse noise contained in the digital character signal output from the waveform distortion correction means. Removing means for comparing a binary level digital character signal from which impulse noise has been removed by the noise removing means with a reference level, and separating the sampled value into a sample value having a level higher than the reference level and a sample value having a level lower than the reference level; Separating means for separating data from the sample values of the levels separated by the separating means. Read data reader, and the data read by processing data read by the unit with a character signal processing means for displaying characters on the display, a television receiver. 2. The conversion means converts the received text multiplex broadcast text signal to a digital signal at a sampling frequency four times the color subcarrier frequency, and further converts the digital text signal converted by the conversion means. And a video signal memory for storing the clock run-in signal and the framing code using the n-th sample value and the (n + 5) -th sample value for one scanning period. The television receiver according to claim 1. 3. The apparatus according to claim 2, wherein said waveform distortion correction means equalizes the framing code output from said video signal memory and corrects said character data based on the equalized framing code. 3. The television receiver according to claim 2.