JPS5927551B2 - Automatic waveform equalization control method for television signals - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for automatically performing waveform equalization using a test signal (hereinafter referred to as a VIT signal) superimposed during the vertical blanking period of a television signal.

In a system that samples the VIT signal of a television signal and performs tap control of a transversal filter using detected waveform distortion information to perform automatic waveform equalization of the television signal, A problem arises when receiving. That is, depending on the type of broadcasting station or program, the VIT signal is not superimposed on the television signal, and in such cases, if you try to perform waveform equalization by sampling the VIT signal, the equalizer control system
will emanate. Therefore, the present invention solves the above-mentioned problems of the prior art, and quickly detects that the VIT signal is not superimposed and stops automatic equalization control, and when the VIT signal is restored, the automatic equalization control is stopped. Automatic equalization control 5 This is to restart the automatic equalization control and stabilize the control.

The present invention will be explained in detail below using the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention, in which numeral 10 represents a transversal type '0 automatic waveform equalizer. This waveform equalizer 10 has a line 1
A transversal filter equalizes the F-band or baseband television signal sent through the line 14 and sends out the equalized television signal through the line 14. The following is simply 1
A sampling circuit that samples a predetermined part of the VIT signal (for example, a 2T pulse part) inserted into the VIT signal (referred to as 7H) and compares the level of the sampled VIT signal with a normal level to obtain digital error '0' of waveform distortion. A discriminator circuit that generates a discriminator, a shift register to which the word difference information from the discriminator circuit is sent, and a shift register that integrates the digital error information sent from each stage of the shift register, and weights the gain for each tap of the transversal filter. A gain adjustment circuit 15 is provided for adjusting the gain. The configuration of a waveform equalizer as described above is well known and is therefore not shown in FIG. In addition, the waveform equalizer 10 includes a horizontal synchronization signal drawing circuit that draws the horizontal synchronization signal of 17H in the television signal and sends it out through the line 16, and when a logic signal of "1" is sent through the line 18. Open the gate to perform waveform equalization control,
A gate circuit that closes the gate and controls waveform equalization when a logic "00" signal is sent is provided, for example, at the input or output section of the shift register described above. Since the gate circuit described above is well known and can be implemented very easily by a person skilled in the art, it is purposely not shown in FIG. 1. In FIG. This is a demodulation circuit that modulates the received television signal to baseband when it is in the IF band.

However, this demodulation circuit 20 is omitted if the television signal sent via line 12 is baseband. 1, 22 is a limiter amplifier circuit, and as shown in FIG. 2A, the VIT signal a superimposed on 17H of the television signal is limited by the threshold value b of this limiter amplifier circuit 22, and the second A signal c having a waveform as shown in FIG. B is obtained. In addition, A in FIG. 2A. is VIT
It represents a 2T pulse in the signal. Pulse generation circuit 2
4 forms two types of pulses from the horizontal synchronizing signal d of 17H as shown in FIG.

In other words, the 2T pulse A rises after a predetermined time delay from the horizontal synchronization signal d and falls after a predetermined duration. The 2T pulse extraction pulse e as shown in FIG. 2c, where the logic becomes ``1'' only around A read clock pulse f as shown in FIG. Such a pulse can be easily formed by a combination of a counter circuit that starts counting from the horizontal synchronizing signal d and a monostable multivibrator circuit. The formed 2T pulse take-out pulse e is sent via line 26 to one input terminal of NAND circuit 28, and the readout clock pulse f is sent via line 30 to the clock input terminal of D-type flip-flop 32, respectively. The pulse generating circuit 24 further sends the horizontal synchronizing signal d directly to the reset input terminal of an S-R flip-flop 36 via a line 34. By sending the output signal c of the limiter amplifier circuit 22 to the other input terminal of the NAND circuit 28, the output signal g as shown in FIG.
is obtained from the NAND circuit 28, and the S-R flip-flop 36 is set at the falling edge of the output signal g. This flip-flop 36 receives a horizontal synchronizing signal d of 17H.
Therefore, its Q output h is as shown in Fig. 2F.
The waveform will be as shown in . The Q output h of the flip-flop 36 is sent to the D input terminal of the D-type flip-flop 32, so that the Q output h of the flip-flop 36 becomes
The logic ``1-''O'' of the output h is determined, and the output signal i of the D-type flip-flop 32 as shown in FIG. 2H is obtained.

That is, when a 2T pulse exists, the S-R flip-flop 36 is set, so the output signal 1 of the D-type flip-flop 32 becomes a logic "1", and when a 2T pulse does not exist, it becomes a logic "0". This output signal 1 is sent to the waveform equalizer 10 via the line 18, so that waveform equalization control is performed when a 2T pulse is superimposed on the TV signal, and when a 2T pulse is not superimposed on the TV signal. Waveform equalization control immediately stops and divergence can be prevented. This waveform equalization control stopping operation is performed in the next 17H.
The process continues until it is detected that a 2T pulse is superimposed at . In addition, in the above embodiment, VIT
Although the presence or absence of signal superimposition is detected by the presence or absence of 2T pulse superimposition, this may be any other VIT signal. As explained in detail above, according to the method of the present invention, the automatic waveform equalization operation is stopped when the VIT signal is not superimposed, so that the TV signal on which the VIT signal is not superimposed is This eliminates the risk of distortion due to unnecessary waveform equalization operations, making it possible to
An automatic waveform equalization system can be formed that can be commonly applied to television signals from programs.

[Brief explanation of drawings]

Fig. 1 is a block diagram of one embodiment of the present invention, and Fig. 2 is a block diagram of an embodiment of the present invention.
FIG. 3 is a signal waveform diagram of each part in the figure. 10... Transversal type automatic waveform equalizer,
20... Demodulation circuit, 22... Limiter amplifier circuit, 24... Pulse generation circuit, 28...
...Sand circuit, 32...D type flip-flop, 36...S-R type flip-flop.

Claims (1)

[Claims] 1. In a method of detecting waveform distortion of a television signal using a test signal inserted in the vertical blanking period of the television signal and performing automatic waveform equalization, detecting whether or not the test signal is superimposed on the television signal. An automatic waveform equalization control method for television signals, characterized in that the automatic waveform equalization operation is stopped when the test signal is not superimposed.