JPS6028391A - Television receiver - Google Patents

Abstract

PURPOSE:To reproduce stably the picture of a character multiplex broadcast by processing digitally the character signal of a received character multiplex broadcast and reading a character data. CONSTITUTION:A composite video signal via a video detecting circuit 3 is given to an A/D converter 12, where the signal is converted into a digital signal and the signal is processed digitally by a digital signal processing section 13, D/A- converted into an analog signal again and given to a video switching circuit 10. On the other hand, the detection of a clock line signal, detection of maximum and minimum value and detection of a framing code or the like are conducted by a video signal memory 14. Succeedingly, a sample value train where the automatic equalization and processing of impulse noise elimination are conducted digitally is given to a character signal separation circuit 17. Then the sample value separated into a binary value is stored in a character signal memory 18 in 1-bit per each sample value. A data is read from the sample train by a sampling circuit 19. The data obtained in this way is processed by a character signal processing circuit 9 and drives a CRT display 11 via the video image switching circuit 10.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a television receiver, and more particularly to an improvement in a television receiver capable of receiving teletext, for example.

Teletext broadcasting uses time gaps in regular TV radio waves to multiplex and transmit digitized text and graphic information, allowing viewers to select any program from among several teletext programs. This is a new broadcast service system that allows you to select a program and display information about that program on your television receiver.

FIG. 1 is a block diagram showing an example of a conventional television receiver capable of displaying teletext.

In the figure, the composite video signal received by tuner 1 is
The signal is applied to a VIP (intermediate frequency) amplifier 2 and amplified.

The output of the VIP 11 width amplifier 2 is detected by a video detection circuit 3, and then is detected by a video signal and color signal processing circuit 4. A CRT display 11 is driven via a video switching circuit 10.

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

By the way, since the character signal, which is originally a digital signal, is multiplexed with the television signal, which is an analog signal, and transmitted, various distortions occur in the waveform of the reproduced character signal depending on the transmission characteristics of the television broadcast wave. However, as described above, conventional television receivers process received character signals in an analog manner, and therefore have the drawback that reading errors in character signals occur frequently due to waveform distortion. As a result, the quality of the reproduced image of the teletext is impaired. In addition, in conventional television receivers, when converting a received character signal into a two-dominant signal, the level of the received character signal is compared with a certain reference level set in advance, and the level of the character signal is determined to be higher than that of the reference signal. Depending on whether the level is exceeded or not, it is converted into a 2-dominant number.

As described above, in the conventional television receiver, it is necessary to set the reference level in advance, which is troublesome. In addition, this reference level fluctuates due to changes in the television receiver (fin) over time, and it has to be reset, which is a hassle. It is necessary to further sample the signal and convert it into a bit-sequential 2-dominant signal.The sampling period at this time must be completely synchronized with the bit period of the character signal as a digital signal, which is difficult to set. It had the disadvantage of being.

Therefore, the main object of the present invention is to provide a television receiver that can eliminate all of the above-mentioned drawbacks and stably reproduce teletext images.

To summarize, this invention digitally processes received text signals of teletext multiplex broadcasting to read text data.

The above objects and other objects and features of the present invention will become more apparent from the following detailed description with reference to the drawings.

FIG. 2 is a schematic block diagram showing one embodiment of the present invention. Referring to the figure, this embodiment is similar to the circuit of FIG. 1 except for the following points, and corresponding parts are given the same reference numerals and their explanation will be omitted.

The output of the video detection circuit 3 is given to an A/D converter 12. The output of this A/D converter 12 is sent to a digital signal processing section 13. Automatic waveform equalizer 15d5 and video signal memory 1
given to 3. The digital signal processing section 14 is a circuit for digitally processing the luminance signal and the color signal, and its output is given to one input of the video switching circuit 10. The automatic waveform equalizer 15 is a circuit for correcting waveform distortion of character signals, and its output is given to an impulse noise removal circuit 16. The impulse noise removal circuit 16 is a circuit for removing impulse noise from character signals, and its output is given to a character signal separation circuit 17.

The output of the character signal separation circuit 17 is applied to and stored in a character signal memory 18.

The sampling circuit 19 is a circuit for reading character signals stored in the above-mentioned character signal memory 18 to read character data, and its output is given to the character signal processing circuit 9. The output of this character signal processing circuit 9 is the video switching circuit 10.
is given to the other input of

FIGS. 3(a) and 3(b) are diagrams showing the sending waveforms of character signals on the transmission side of teletext broadcasting. In particular, FIG. 3(a) shows the character signals for the entire one horizontal scanning period; FIG. 3(b) shows an enlarged view of the clock run-in and framing code in the header portion of the character signal. Figure 3 (C) shows the sample value (digital value) of the character signal output at point a in Figure 2 as a graph length when a character signal containing no waveform distortion or impulse noise is received. It is expressed. Note that the sinusoidal waveform connecting the vertices of each graph indicates the output of the video detection circuit 3. This FIG. 3(C) shows the sample value at the first 4 bits of the above-mentioned clock run-in. Fourth
Figures (a) and (b) respectively show that (
The length of the graph indicates the magnitude of the sample value of the character signal output at point a and point a in FIG. 2.

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

The composite video signal subjected to video detection by the video detection circuit 3 is supplied to an A/D converter 12 and converted into a digital signal (for example, 8 bits). This digital signal is given to a digital signal processing section 131, where the luminance signal and color signal are digitally processed and converted into an analog signal again.
/A conversion and applied to the video switching circuit 10. on the other hand,
The composite video signal converted into a digital signal is also provided to the video signal memory 14. This video signal memo 1-14
, the character signal portion of the vertical blanking period (for example, the signal of one horizontal scanning period of 4f scanning line numbers 208 and 283H) is stored.

Here, data in teletext is binary NRZ
Pulse clock frequency is 3641'++=(815)
・fsc (fll is horizontal scanning frequency.

fgc is the color subcarrier frequency). therefore,
The sample frequency of A/D conversion (i-line frequency) is set to 4",
. If you select , the number of samples per 1 bit of data is 4.
/ (815), which is 2.5 times. Since 2 bits correspond to exactly 5 sample values, the I11th sample point and the m+5th sample point are the same phase points of the nth and n+2nd bits of data. now,
If the data is divided into 2 bits and 1, then fL=1.2.・・・
When a data bear number is attached to the data pair number, the data pair with the data pair number includes the n (=211-1)th bit data and the n+lth bit data.

The above relationship is illustrated in FIG. 3(C).

That is, each sample point is Pr+1i-1,2,...
lll-1, 2, 3, 4, 5), and the data bear number is incremented by 1 for every 5 simples.

The video signal memory 14 stores sample values for one running period including character signals in the order shown in FIG. 3(C). From this Zumble value sequence, there is no error.
Think about finding (16 hits, 101010...10). The detection of this clock run-in signal utilizes the aforementioned property that the m%th sample point and the In+5th sample point are the same phase points of the nth and n+2nd bits of data. In other words, the values of ... are the same among the sample values of PA (for example, P2 and P2 have the same value (same phase) at clock run-in. Therefore, the sample values of P 4 and P tray 1, that is, every 5 It is possible to sequentially compare the sample 1 shifts of , and detect that the point where the values are the same within a certain FAN range is the starting point of the clock run-in signal. Similar comparisons may be made for several sample values.

The maximum and minimum values of the clock run-in signal can then be easily determined. For example, in Figure 3 (C), P5 is the maximum value,
P! is the minimum value. Therefore, the sample value of the phase of P2 is set as the n-th data value, P
! may be adopted as the data value of the 11th+1st bit.

As described above, the framing code (8 bits, 11100101) can be easily detected following the clock run-in.

As mentioned above, detection of lock run-in signal, detection of its maximum and minimum values, detection of framing code, etc.
The video signal memory '14 is configured to have such a function as well as a storage function. That is, the blocks represented by the video signal memory 4 include structures having the above-mentioned functions in addition to ordinary digital ones.

By the way, the received character signal cannot avoid waveform distortion caused by various factors on the transmitting side, the transmission path, and the receiving side of the television signal. The appearance of waveform distortion changes depending on the broadcasting station, reception conditions, etc. The automatic waveform equalizer 15 removes this waveform distortion. Figure 4(a) shows a character signal (
This is the framing code (FC) part of sample la>. In this case, the most affected by distortion is the transition part of the 3rd bit of +=C and the 4th bit, followed by the 5th bit.
This is the transition part from bit to sixth bit. Therefore, for example, when waveform equalization evaluation (I) is taken as the li standard, the sample values of the 1st to 3rd bits and the 6th bit of C are high level and almost the same value, and the sample values of the 4th and 5th bits 1 to 1 are low. It is sufficient to consider an evaluation function that allows the best score to be expressed by the maximum or minimum value of this evaluation standard by adopting the fact that the levels are almost the same.

The automatic waveform equalizer 15 is composed of, for example, a transversal filter, and automatically calculates and controls its parameters so that the above-mentioned evaluation function is maximized or minimized. The FC with waveform distortion corrected becomes as shown in FIG. 4(b). Note that the automatic waveform equalizer 15 calculates parameters for automatic equalization using a framing code with a fixed bit pattern, and thereafter uses the calculated parameters to correct waveform distortion of the character signal.

Next, consider the case where impulse noise is mixed into the sample values. In the impulse noise removal circuit 416, abnormal sample values due to impulse noise are discarded and corrected to correct values by, for example, taking a majority vote of the sample values in one bit or checking the continuity of previous and subsequent sample values.

In this way, the sample value string digitally subjected to automatic equalization and impulse noise removal processing is provided to the character signal separation circuit 17. This character signal separation 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 this reference level, for example, the center value between the maximum value and the minimum value of the clock run-in signal is calculated and adopted. Therefore, there is no need to set a reference level in advance for separating two dominant signals as in the past, and there is no need for readjustment due to changes over time.

As mentioned above? The sample values separated into values are stored in a character signal memory 18 with one pit ('1 or O) for each sample value. Data is read from this sample value sequence by a sampling circuit 19. The sampling period required for data reading is determined by the fact that 2 bits of data in Section 11a is exactly 51 sample values.]
In addition, the rA start point of the data is also disturbed due to the detection of the above-mentioned framing code (FC). That is, the sampling circuit 19 reads f-events at the same phase point every five sample values, for example, from the detected starting point of f-event. However, unlike the conventional analog system, there is no need for delicate adjustment of the reading timing depending on the phase of the number printer clock, and the sample value as data can be easily read from the address of the character signal register 18. The data obtained in this way is processed by the character signal processing circuit 9 in the same way as in the past, and the image switching circuit 1
0 to drive the CRT display 11.

In the above embodiment, the clock run-in detection 6 is an example of digitally processing the received character signal.
Although the equalization of the character signal waveform and the removal of impulse noise have been described, the present invention is not limited to this, and various other digital processing may be performed.

As described above, according to the present invention, a composite video signal including a text signal of teletext broadcasting is converted into a digital signal, and the digitized composite video signal is digitally processed to read character data. With this configuration, teletext can be stably received and high-quality reproduced images can be obtained.

[Brief explanation of drawings]

FIG. 1 is a schematic block diagram showing an example of a conventional television receiver capable of receiving teletext. FIG. 2 is a schematic block diagram showing one embodiment of the present invention. 3(a) and 3(b) are diagrams showing the sending waveform of a character signal on the transmission side of teletext multiplex broadcasting. (b) shows an enlarged waveform of the clock run-in and framing code part in the header part of the character signal. Figure 3 (C) shows the sample value (digital value) of the character signal output at point a shown in Figure 2 when the received character signal does not contain waveform distortion or impulse noise. This is a diagram expressed in . Figures 4 (a) and (b) are samples of character signals output at points a and 2 in Figure 2, respectively, when the received character signal contains waveform distortion or impulse noise. It is a figure which expresses a value by the length of a graph. In the figure, 1 is a tuner, 2 is a VIP 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 10 is a character signal processing circuit, 10 is a video switching circuit, 11 is a CRT display, 12 is a Δ/D converter, 13 is a digital signal processing section,
14 is a signal video signal memory, 15 is an automatic waveform equalizer, 1
6 is an impulse noise removal circuit, 17 is a character signal separation circuit, 18 is a character signal memory, and 19 is a sampling circuit. Agent Masuo Oiwa Figure 1 Figure 2 Figure 3

Claims (5)

[Claims] (1) A television receiver capable of displaying teletext broadcasting, which is equipped with a character signal digital processing means for digitally processing received teletext character signals and reading character data. . (2) The sampling frequency when converting the decoded video signal into a digital signal is selected to be four times the color subcarrier frequency, and the character signal digital processing means converts the nth sample value and the n+5th sample value. 2. The television receiver according to claim 1, wherein the television receiver is used to perform calculations for predetermined processing. (3) The television receiver according to claim 1 or 2, wherein the character signal digital processing means includes means for automatically equalizing waveform distortion of the character signal by digital processing. (4) The automatic equalization means automatically equalizes the waveform distortion of other parts of the character signal based on the result of automatically equalizing the framing code part of the character signal. The television receiver according to item 3 of the above. (5) The television receiver according to any one of claims 1 to 4, wherein the character signal digital processing means includes means for removing impulse noise contained in the character signal by digital processing. (6) The character signal digital processing means includes a memory that stores the character signal as a digital value, and reads data from the memory at predetermined address intervals and uses it for reading the character data. A television receiver according to any one of claims 1 to 5.