JPS60251788A - Data sampling clock generator for character broadcast - Google Patents

Abstract

PURPOSE:To obtain a data sampling pulse by generating a color burst signal in a video signal in the timing formed by dividing equally one period of a character broadcast signal into (n) and selecting said pulse and a pulse where an edge of a character broadcast signal is coincident. CONSTITUTION:A color burst signal is inputted to a waveform shaping circuit 1, and its output is connected to a phase shift circuit 3 via an APC oscillating circuit 2. Two CL1, CL2 from the phase shift circuit 3 is inputted to a sub-clock pulse generating circuit 4 comprising a shaft register circuit and a logical circuit to output 10 sets of sub-clock pulses Pa-Pj. They are given to a data selector circuit 7. D flip-flop circuits 8a-8j sample a sub-clock pulse having a timing coincident at the rise of the character broadcast signal, the clock pulse is accumulated by counter circuits 10a-10j, read by an encoder 11 and the sub-clock pulse having the highest degree of coincidence with the leading of the character broadcast signal is outputted as the sampling clock pulse.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a teletext data sampling clock generation device for generating a sampling clock pulse synchronized with a teletext signal included in a television video signal.

As shown in Figure 1, in order to extract the teletext signal from the television video signal and examine its error rate, etc., first, so-called sampling is performed, which generates a data sampling clock pulse synchronized with the teletext signal. It must be made.

In this case, the frequency of the teletext signal is 5.72 MHz, the color burst signal appearing before it is 3.57 MHz, and the frequency of the teletext signal is 1 MHz of the color/heast signal. .6 times. Several methods are already known for sampling teletext signals, such as using color burst signals, but these methods have drawbacks such as complicating processing circuitry and low reliability.

SUMMARY OF THE INVENTION An object of the present invention is to provide a data sampling clock generator for teletext broadcasting that is simple in terms of circuitry and can generate accurate data sampling clock pulses. A device for generating a data sampling clock pulse synchronized with a teletext signal included in a teletext signal, the device comprising:
One period of the teletext signal is divided into n equal parts (n is a positive integer) from the color burst signal in the video signal, and pulses are divided into n equal parts, each having a different phase and one pulse appearing during the one period. a circuit that generates a set of sub-clock pulses, a circuit that compares these sub-clock pulses with a teletext signal and detects a coincidence with an edge portion of the teletext signal for each sub-clock pulse, and a circuit that generates a matched sub-clock and a circuit for selecting a pulse as a requestable data sampling clock pulse.

The present invention will be explained in detail based on the embodiments shown in FIG. 2 and below.

Figure $2 is a circuit diagram for generating a sub-crotter pulse, in which a color burst signal is input to a shaping circuit 1, and its output is connected to a phase shift circuit 3 via an APC oscillation circuit 2. Then, from the phase shift circuit 3, two CLI, Cl3
are output, and these are input to a sub-clock pulse generation circuit 4 consisting of a shift register circuit, a logic circuit, etc.
0 set of sub-crotter pulses Pa-'Pj are output.

In other words, a color burst signal having a frequency of 3.57...MHz passes through a shaping circuit 1, and is oscillated by an oscillation circuit 2 into a frequency pulse of 8 times 28.63...MHz, which is then sent to a phase shift circuit 3. It will be done. In the phase shift circuit 3, the clock hole 1 shown in FIG. 3(a) transmitted from the oscillation circuit 2
, the clocks C1 and 2 shown in (b) whose phases are shifted by half a period are output together with C(1. These clocks C
L1. Cl3 are each input to the sub-clock pulse generation circuit 4, and are sequentially output as 10 sets of phase-shifted sub-clock pulses Pa"Pj shown in FIG. 3(C) to (1). Sub clock pulse P
The synthesized frequency of a”Pj is 28.63...φ×2−
57, 2.7...MHz, which is 10 times the focus clock pulse of the teletext signal. Therefore, the period of each sub-clock pulse Pa to Pj obtained by dividing this into ten coincides with one period of the teletext signal, as shown in FIG.

FIG. 5 shows the subclock pulse P obtained in this way.
This circuit generates a sampling clock pulse using a-Pj. Each sub-clock pulse Pa-Pj is connected to the data selector circuit 7 and input to the D terminal of each D flip-flop circuit 8a to 8j, and the T terminal of these D flip-flop circuits 8a to 8j is connected to an AND terminal. The outputs of all the circuits 9 are connected in common. The AND circuit 9 receives a data extraction signal based on a prediction signal based on the television video signal shown in FIG. 1 and a color burst signal generated from a circuit not shown in the drawing. The outputs Q of the D flip-flop circuits 8a to 8j are input to the T terminals of the counting circuits 10a to 10j, respectively, and the outputs thereof are connected to the priority encoder circuit 11. The output of the encoder circuit 11 is sent to the data selector circuit 7 via the latch circuit 12, and the reset signal of the encoder circuit 11 causes each counting circuit 10a to
10j is reset, and the latch circuit 12 is held.

That is, at the same time that television video signal data is input to the AND circuit 9 as shown in FIG.
A data extraction signal for extracting only the teletext signal portion shown in (C) is input and a logical product is performed, and as shown in (C), only the teletext signal is extracted from each D flip-flop circuit 8a to 8a.
Commonly sent to the T terminal of 8j. Since the suck lock pulses Pa-Pj are input to the D terminals of the D flip-flop circuits 8a to 8j, respectively, the sub-clock pulses having timings that coincide with the rising edge of the teletext signal are sampled, and the sub-clock pulses of the corresponding D flip-flop circuits are sampled. The output of the Q terminal will change. Each counting circuit 10a to 10
j is the Q of each D flip-flop circuit 8a to 8j
The number of output changes of the terminals is accumulated and read by the priority encoder circuit 11 after a certain period of time, and a signal is sent to the latch circuit 12 to specify the sub-clock pulse that most closely matches the rising edge of the teletext signal. Based on the signal transmitted from the latch circuit 12, the data selector circuit 7 selects a corresponding one of the ten sets of sub-clock pulses Pa-Pj input to the data selector circuit 7 and outputs it as a sampling clock pulse. At the same time, the encoder circuit 11 sends a reset signal to the counting circuits 10a to 10j and a hold signal to the latch circuit 12 to start counting again, and a sampling clock pulse based on new data is generated.

It goes without saying that the above-described embodiment is merely an example, and that other circuit configurations may be adopted as appropriate. In addition,
Considering the circuit configuration, it is appropriate to have the number of sub-clock pulse sets as in the embodiment, but if the number is increased, the resolution will further deteriorate and the reliability of the obtained sampling clock pulses will also increase. Furthermore, although the embodiment uses the rising portion of the teletext signal for detection, it may be the falling portion, or both the rising portion and the falling portion may be used without any problem.

As described above, the data sampling link clock generator for teletext broadcasting according to the present invention can obtain a rotator sampling clock pulse that faithfully matches the timing of an edge portion such as a rising portion of a teletext signal with a relatively simple circuit configuration. There are advantages.

[Brief explanation of drawings]

Figure 1 is a waveform diagram of a television video signal, Figure 2 is a block circuit configuration diagram of a circuit that generates a sub-crotter pulse,
Figure 3 is a timing chart, Figure 4 is a waveform diagram showing the relationship between teletext signals and subclock pulses, and Figure 5 is a block circuit diagram of a circuit that generates sampling clock pulses using subclock pulses. , FIG. 6 is a timing chart diagram of the AND circuit. 1 is a shaping circuit, 2 is an oscillation circuit, 3 is a phase shift circuit, 4 is a sub-clock pulse generation circuit, 7 is a data selector circuit, 8a to 8j are D flip-flop circuits, 9 is an AND circuit, and 10a to 10j are counters. 11 is an encoder circuit, and 12 is a latch circuit. Patent Applicant: Nippon Television Network Corporation Toshiba Corporation

Claims (1)

[Scope of Claims] 1. A device for generating a data sampling clock pulse synchronized with a teletext signal included in a television video signal, the device generating one of the teletext signals from a color burst signal in the video signal. A circuit that generates n sets of subclock pulses in which a pulse whose period is divided into n equal parts (n is a positive integer) has different phases and each pulse appears during one cycle, and these subclock pulses. and a teletext signal, and a circuit for detecting a match with an edge portion of the teletext signal for each sub-clock pulse, and a circuit for selecting the matched sub-clock pulse as a requestable data sampling clock pulse. A data sampling clock generator for teletext broadcasting, characterized in that: 2. The teletext data sampling clock generator according to claim 1, wherein the selected sub-clock pulse has the highest degree of coincidence with the teletext signal within a predetermined period. 3. The teletext data sampling clock generator according to claim 1, wherein the integer n is 10.