JPS6138675B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic waveform equalizer that automatically equalizes waveform distortion, which is an important problem in waveform transmission of television signals, etc., and particularly relates to an equalization timing pulse extraction circuit thereof. It is.

The waveform distortion of television signals is mainly caused by amplitude distortion and linear distortion caused by delay distortion in the transmission system. Conventionally, a transversal filter is used to send out squared sine wave pulses, etc. from the transmitting side, which have easy-to-understand waveform distortion. However, on the receiving side, while observing the waveform, the tap gain of the transversal filter is manually adjusted to approximate the test waveform from the transmitting side, thereby performing waveform equalization.
Alternatively, a so-called preset type automatic waveform equalization device is known, which sends a specific test waveform from the transmitting side during the pause period of the television signal and automatically equalizes it to minimize waveform distortion. This must be done at night when the television signal is out of service. The former manual equalizer has the disadvantage that precise adjustment is difficult and requires skill. Furthermore, the appearance of fluctuating distortion caused by changes in the environment of a transmitter or equipment such as an interruption site, changes over time, and distortion caused in the process of wave propagation changes over time. Therefore, even with the preset type waveform equalizer, it is difficult to always obtain good image quality. There are adaptive automatic waveform equalizers that attempt to overcome the above drawbacks.

The object of the present invention is to improve the equalization timing pulse generation circuit in order to improve the equalization accuracy of the adaptive automatic waveform equalizer.

FIG. 1 is a diagram showing the principle of a conventional adaptive automatic waveform equalizer. The second residual sine wave pulse (2T pulse) of the superimposed signal (VITS) inserted in the 17H of the vertical blanking period, which is used as a reference waveform for the adaptive automatic waveform equalizer in the operation of television broadcasting stations. An example will be explained in which a cut pulse of an equalization pulse or the like is also used as a reference waveform. A color television signal enters a tapped delay line 3 from an input terminal 1. τsec
The polarity and level are adjusted by 2N+1 (N is a positive integer) tap coefficient adjusters 4, 5, 6, 7 provided at intervals, added by an adder 8, and outputted from an output terminal 2. On the other hand, the television input signal is branched from the center tap 18 and guided to the control signal extraction circuit 10, which extracts the 17H horizontal synchronizing signal during the vertical blanking period from the television signal. On the other hand, the clock pulse from the clock pulse oscillator 17 is applied to the timing circuit 13, and after being controlled by the timing signal of the 17H horizontal synchronization signal extracted by the control signal extraction circuit, a trigger pulse ( S- _N ) is outputted from the timing circuit 13 and applied to the sampling generation circuit 14.

This sampling pulse generation circuit 14 is delayed by an interval of τsec based on the trigger pulse S- _N .
Generates 2N+1 sampling pulse trains.

On the other hand, a signal branched from the output of the television signal is input to a comparator 15. This comparator 15
compares the 2T pulse used as the VITS test waveform from the reference voltage generation circuit 9 with the television signal in response to 2N+1 sampling pulses.
That is, in the comparator 15, the 2T pulse is compared in magnitude with the television signal at a total of 2N+1 points, including the first half N points, the second half N points centered on the center of the 2T pulse, and the center, and when it is large, it is positive. When the sign is small, a negative sign is output. The output voltage of the 2N+1 comparison outputs is changed by one step according to the positive and negative signals of the comparator outputs by a counting D/A conversion circuit 16 consisting of an up/down counting circuit 101 and a D/A converter 201. and is applied to each corresponding tap coefficient adjuster. By repeating this series of operations, the line waveform is equalized. However, this conventional adaptive automatic waveform equalizer has the following drawbacks.
The clock pulse generator is expensive, and the output signal of the clock pulse generator and the trigger pulse of the equalization sampling pulse should be generated.
Since it is asynchronous with the horizontal synchronization signal of 17H, there is a drawback that phase jitter occurs between the two signals, making it difficult to sample at the correct time. Therefore, the final equalization accuracy cannot be expected to converge to the optimal point. To solve this shortcoming,
A method has been considered in which a specific reference waveform and a burst signal for timing synchronized with the reference waveform are inserted on the transmitting side for a certain period in an appropriate LINE during the vertical blanking period (for example, E, ARNON: An Adaptive
Equalizer for Television Channels, IEEE
Transactions on Communication Technology
Vol. COM―17, No. 6, Dec. 1969). However, this method requires a special test waveform and a burst signal synchronized with it to be inserted into the vertical blanking period of the television signal on the transmitting side, so it is not universal. In the case of timing extraction, there is a drawback that it is difficult to obtain sufficient stability of the regenerated clock due to the limited period of the convolutional burst period.

In order to solve this problem, the present invention utilizes a color burst signal that is always superimposed on a color television signal, and provides a timing pulse generation circuit for stable automatic waveform equalization on the receiving side.

FIG. 2 shows one embodiment of an equalization timing pulse extraction circuit according to the present invention. This will be explained below with reference to FIGS. 1 and 2. The color television signal branched from the center tap 18 in FIG. 1 is applied to the color burst signal (3.58MHz) extraction circuit 21 and control signal extraction circuit 25 in FIG. A continuous sine wave synchronized with is output, and multiplier 22 at the next stage appropriately multiplies it (for example, by 8/3) to obtain a clock pulse with a period equal to the sampling interval τsec. The multiplied pulse is subjected to phase control by the phase shift circuit 22 and then applied to the timing circuit 13. On the other hand, a 17H horizontal synchronizing signal is extracted from the color television signal applied to the control signal extraction circuit 25 and applied to the timing circuit 13 as a trigger pulse. The timing circuit 13 uses the 17H horizontal synchronizing pulse _S17H from the control signal extraction circuit 25 as a trigger pulse to count the output signal pulses of the phase shift circuit 23, and calculates the timing around τX(-N) sec from the 2T pulse center of the VITS. Outputs pulse S- _N .

In order to explain the present invention more specifically, FIG.
FIG. 3 is a diagram showing the relationship between VITS and sampling pulses. In FIG. 3a, the color burst signal of the color television signal is extracted and reproduced into a continuous wave in order to equalize the waveform as the waveform of the vertical blanking period. FIG. 3c shows the reproduced waveform. This reproduced waveform is synchronized with the 17-line horizontal synchronizing signal and the 2T pulse on the transmitting side. Therefore, since a signal obtained by multiplying the reproduced waveform is used as the equalization sampling pulse, there is no phase jitter between the 2T pulse and the equalization sampling pulse, improving equalization accuracy. Figure 3 d is a 2T pulse,
Figure e shows an equalization sampling pulse.

As described above, the conventional drawbacks can be solved by the configuration of the present invention. That is, the present invention focuses on the fact that the color burst signal in the color television signal, the 17H horizontal synchronizing pulse signal, and the 2T pulse as a reference waveform are transmitted in advance from the transmitting side in synchronization, and the timing pulse A major feature of this method is that it uses a reproduction pulse synchronized with the color burst signal. Therefore, since the equalization timing pulse and the 17H horizontal synchronization pulse signal are always synchronized, the phase jitter that had a large effect on equalization accuracy in the conventional method is eliminated, and the drawbacks of the conventional method can be completely resolved. .

[Brief explanation of the drawing]

FIG. 1 is a circuit configuration diagram showing a conventional transversal automatic waveform equalizer, and FIG. 2 is an embodiment showing an equalization timing pulse extraction circuit according to the present invention.
3a to 3e are diagrams showing the relationship between VITS and sampling pulses according to the present invention. 1...Input terminal, 2...Output terminal, 3...Delay line with tap, 4, 5, 6, 7...Tap coefficient adjuster, 8...Adder, 9...Reference voltage generator, 10
... Control signal extraction circuit, 13 ... Timing circuit, 14 ... Sampling pulse generation circuit, 15
... Comparator, 16 ... Counting D/A conversion circuit, 17
... Clock pulse generator, 18 ... Center tap, 25 ... Control signal extraction circuit, 21 ... Color burst extraction circuit, 22 ... Multiplier, 23 ...
Phase shifter, 13... timing circuit, 24... timing circuit output terminal.

Claims (1)

[Claims] 1. A filter provided with a reference waveform superimposed on a color television signal sent from a transmitting side and provided with a plurality of signal extraction taps, means for generating a sampling pulse for sampling the reference waveform, and a predetermined filter. a reference voltage generating means for generating a reference amplitude voltage at a sampling time, a reference voltage generating means for generating a reference amplitude voltage at a sampling time; A subcarrier signal is extracted from the color television signal extracted from the center tap of the transversal filter in an automatic waveform equalizer having a coefficient adjustment circuit that generates a tap coefficient adjustment signal for the transversal filter. subcarrier extraction means to extract; means for multiplying the output frequency of the subcarrier extraction means; means for adjusting the phase of the output signal of the multiplication means; and generation timing of the sampling pulse generation means in synchronization with the output signal of the multiplication means. An automatic waveform equalizer comprising control pulse generation means for providing a trigger signal for control.