JPS6123716B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention eliminates waveform distortion of color television signals.
This invention relates to an automatic waveform equalization device that automatically compensates on the receiving side using a test signal (VITS) superimposed on the vertical blanking period of a television video signal.

Waveform distortion in television is mainly caused by linear distortion such as amplitude distortion and delay distortion that occur in the transmission system. Conventionally, a transversal filter is used to send a test waveform such as a squared sine wave pulse, which makes it easy to see waveform distortion, from the transmitting side, and while observing the waveform on the receiving side,
A manual waveform equalizer that performs waveform equalization by manually adjusting the tap gain of the transversal filter to approximate a test waveform on the transmitting side,
Also known is a preset type automatic waveform equalization device that transmits a specific test waveform from the transmitting side during the pause period of the television signal and automatically equalizes it so as to minimize waveform distortion. However, both of the above two methods have the disadvantage that they must be performed at night when television broadcasting is suspended, and that the former manual equalizer is difficult to make precise adjustments and requires skill. are doing. Furthermore, in transmitters, fluctuation distortion caused by environmental changes in relay stations and other equipment, aging, and distortion caused by reflection of spatial waves, etc., will vary slightly depending on humidity, temperature, etc.
With respect to these temporally varying distortions, it has been difficult to always obtain good image quality using conventional waveform equalizers.

The purpose of the present invention is to solve the problems of the conventional technology by using a superimposed signal (VITS) inserted into the vertical blanking period as a test signal used in the operation of television broadcasting stations.
An object of the present invention is to provide an automatic waveform equalization device that constantly observes waveform distortion on a receiving side while transmitting a television signal and automatically adjusts a transversal filter.

According to the present invention, the part before the rise and the part before the fall of the sine wave pulse (2T bar) in the test signal (VITS) is used as the test waveform, and the distortion of the received waveform is reduced by using the points corresponding to the taps of the transversal filter. An automatic waveform equalization device that detects and sequentially adjusts the tap gain of a corresponding transversal filter with a relatively simple hardware configuration can be obtained.

Figure 1a shows the waveform structure of the vertical blanking period of a color television video signal, and Figure 1b shows the waveform structure of the vertical blanking period of a color television video signal.
This is a test signal (VITS) superimposed in a 17H period for the TV operation test for 525 lines proposed by CMTT, and it has various waveforms (2T pulse S ₂ , 2T bar S ₁ , modulated 20T pulse S ₃ , superimposed The temporal arrangement of the staircase wave _S4 , etc.) has been determined, and it is expected that it will be internationally standardized under the CMTT in the near future.

Figure 2 shows the relationship between the reference waveform of the 2T bar (solid line) and the distortion waveform of the wafer (dotted line) as an example. The waveform distortion caused by the transmission system is noticeable at the rising and falling parts of the 2T bar, and the waveform distortion before and after the rising and falling parts is as shown in the figure. This is because the linear distortion of the transmission system is a relatively low-order component in terms of frequency characteristics, and relatively high-order components are ghosts caused by reflected waves such as radio waves reflected by buildings and obstacles. Moreover, with the 2T bar arrangement proposed by CMTT, there are very few high-order components until the waveform distortions of the rising and falling parts overlap.

Using a transversal filter, the 2T bar is centered around the rising or falling center.
It is possible to configure an automatic waveform equalizer by configuring lead and lag taps, but since there are many reference points that provide reference waveforms and the 2T bar includes DC components, a special method is required to set the reference voltage. Consideration is required.

In view of the above drawbacks, the present invention uses a 2T bar having a wide range of components from relatively low frequencies to high frequencies as a test waveform, and can be realized with a relatively simple configuration.

Hereinafter, the present invention will be explained in detail with reference to the drawings. FIG. 3 is a diagram showing an embodiment of the present invention.
A color television signal enters a tapped delay line 3 from an input terminal 1. (2N+
1) tap coefficient adjusters 4 (N is a positive integer);
The polarities and outputs are adjusted in steps 5, 6, and 7, and the added signals are added in an adder 8 and outputted from the output terminal 2. On the other hand, the television input signal is branched from the center tap and guided to the control signal extraction circuit 10. Here, the color burst is extracted and reproduced from the tervision signal, and the 17H horizontal synchronization signal during the vertical blanking period is extracted. Extracted and reproduced color burst (3.58MHz) by multiplier 11
The signal is multiplied by 8/3 to become 9.47MHz, and is supplied to the timing circuit 13 through the phase shifter 12. In the timing circuit 13, the 17th horizontal synchronization pulse _S17H extracted by the control signal extraction circuit 10 causes
Count the 9.47MHz pulses at 9.47MHz intervals, and
Sample the rising and falling parts of the 2T bar in the signal. That is, at the rise of the 2T bar, the center generates a timing pulse S _-N near -N×τ (sec) in the advancing direction, and from this, sampling pulses S _-N+1 , S -N+2 , S -N+2 , and S _-N+2 are generated at intervals of τ, respectively.
..., S ₂ , S ₁ , S ₀ are generated. Further, a timing pulse S _i is generated in the vicinity delayed by τ from the falling center of the 2T bar, and from this, sampling pulses S' ₂ , S' ₃ , . . . , S' _N are generated at intervals of τ. The tap interval τ is the pulse time interval (approx.
104.7ns).

On the other hand, the reference voltage generation circuit 9 continuously generates a plurality of reference voltages (DC levels) corresponding to each time interval τ before the rising center and after the falling center of the 2T bar. and the output television signal of the transversal filter are supplied to a comparator 16. Actually 2T
The reference voltages for each τ interval of the rise and fall of the bar are D ₀ , D _±1 , D _±2 , D _L as shown in Figure 4a.
Approximately set by The comparator 16 receives a train of N+1 sampling pulses delayed from the S _-N pulse from the first sampling pulse generation circuit 14 at intervals of τ _sec , and from the S ₁ pulse from the second sampling pulse generation circuit 15 at intervals of τ _sec . With the delayed N sampling pulse trains (see Figure 4b), the comparison outputs of the N+1 points in front including the 2T bar rising center and the subsequent N points not including the 2T bar falling center are directly reversible counts, respectively. Counting D/A conversion circuit 1 consisting of a circuit and a D/A converter
Added to 8. The output voltage of the counting D/A conversion circuit 18 is changed by the judgment code output signal of the comparator 16, and the corresponding tap coefficient adjusters 4-
7, the output of each tap coefficient adjuster is slightly adjusted in the direction of correcting the distortion of the test waveform.

The timing phase of the sampling pulse is determined by inputting a television signal that is almost undistorted, and selecting a sampling pulse near the center of the rising edge of the 2T bar that is delayed by N×τ (sec) from the S _-N pulse of the test waveform and sampling pulse. While observing with a synchroscope or the like, fine adjustment is made using the phase shift circuit 12 so as to align with the center. At this time, the timing phase after the falling edge is 9.47 MHz, as shown in Figure 4c, which shows the relationship between the clock and the sampling pulse, since the time interval between the rising and falling edges of the 2T bar is a fixed time that is roughly determined. A predetermined number of clock pulses are counted, and the fractional time Δt is a fixed delay line 1.
9 in series with the timing pulse _S1 , timing can be achieved. Therefore, all the sampling phases can be matched by focusing only on the sampling pulse at the center of the rising edge and matching the timing phases.

Next, the principle of automatic waveform equalization of the present invention will be explained.
In Figure 3, if the input of the equalizer is x(t),
The output y(t) is At the sampling time nτ, It can be expressed as Now, if we define the distortion by the following formula, In other words, when y ₀ = 1 at center tap C ₀ , the output distortion D is a continuous convex function of the remaining 2N taps,
C _K (K=-N,...,-1,1,
2,...,N) exists. Furthermore, when D ₀ <1 Then, ∂D _o /∂D _K , sign yk, and the output distortion D can be minimized by focusing only on the sign of the k-th tap adjustment and sequentially correcting it (zero-facing). It is.

By repeating the correction every time VITS arrives, it converges to the minimum distortion point. This operation can be realized by obtaining, for example, a 17H horizontal synchronizing signal from the control signal extraction circuit 10, dividing the frequency appropriately, and supplying the resulting number of pulses to the counting A/D conversion circuit 18.

In this example, distortion is detected before the rising center and after the falling center of the 2T bar, but it can also be realized by changing the reference voltage in combination after the 2T bar rising center and before the falling center. is clear.

In this embodiment, the sampling pulse is reproduced by extracting a color burst signal, so a color burst is not necessarily inserted when transmitting a black and white television signal.In this case, the presence or absence of a color burst is detected and the tap correction operation is stopped. It is conceivable to maintain the state just before the color burst disappears.

As explained above, according to the present invention, the squared sine wave pulse of the test signal (VITS) superimposed on the vertical blanking period ( By monitoring part of the waveform distortion before the rise and after the fall of the 2T bar), and comparing it with a predetermined reference voltage, and controlling the transversal filter, the transmission system from the transmitting station to the receiving station is The waveform distortion of the generated video signal can be automatically equalized, making it possible to always obtain good image quality.

The automatic waveform equalization device according to the present invention can be implemented, for example, in a television relay broadcasting device, and its effects are significant.

In other words, conventional television relay equipment has a preset type ghost canceling device inside it, but ghosts that appear in the received signal of the television relay broadcasting equipment are affected by their delay time, phase,
The amplitude often changes with time, and a preset type ghost canceling device cannot respond to changes in the ghost, making it impossible to completely eliminate the ghost. In contrast, according to the television relay broadcasting device equipped with the automatic waveform equalization device according to the present invention, even if there is a ghost that changes over time, it is possible to automatically eliminate it.

A television relay broadcasting device equipped with an automatic waveform equalization device according to the present invention will be described below with reference to FIG. In FIG. 5, 20 is a receiving antenna, 21 is an input filter, 22 is a converter, and 23 is a
IF video/audio separation circuit, 24 is a video demodulation circuit, 2
5 is a transversal automatic waveform equalizer according to the present invention, 26 is a control circuit, 27 is a video modulation circuit, 28
is an IF video and audio synthesis circuit, 29 is a converter,
30 is a power amplifier, 31 is an output filter, 32
is the transmitting antenna. The signal received by the reception antenna 20 passes through an input filter 21 and is applied to a converter 22 where it is converted into an intermediate frequency band. The intermediate frequency signal is processed by the IF video/audio separation circuit 23.
It is separated into an audio IF signal component and a video IF signal component. The video IF signal component is demodulated by the video demodulator 24 and becomes a video signal. The video signal is processed by a transversal automatic waveform equalizer 25 and a control circuit 26.
The waveform is equalized by That is, ghosts are erased. The output signal of the transversal automatic waveform equalizer 25 is modulated by the video modulator 27, and the output signal is converted into a video signal again.
It becomes an IF signal and is converted into an IF signal by the IF video/audio synthesis circuit 28.
It is combined with the audio IF signal component which is the output of the video/audio separation circuit 23. The output signal of the video/audio synthesis circuit 28 is converted into a transmission channel band signal by a converter 29, further amplified by a power amplifier 30, and supplied to a transmission antenna 32 via an output filter 31.

An example of a video waveform is shown in FIG. 6 to help understand the ghost cancellation effect of the television relay broadcasting apparatus shown in FIG. 5. In Figure 6, a is the transmission waveform at the master station, b is the video waveform at the receiving point of the television relay broadcasting device with ghosts, and c is the video waveform at the transmission output point of the television relay broadcasting device after waveform equalization. . Waveform c is ideally equalized to a waveform that is exactly the same as waveform a. That is, the ghost signal is eliminated.

As explained above, by configuring the intermediate frequency stage of the television relay broadcasting device to include a video and audio separation circuit, a video demodulator, a video band transversal automatic waveform equalizer, a video modulator, and a video and audio synthesis circuit, Ghosts that occur in the radio wave propagation path from the master station to the TV relay broadcasting device can be automatically erased according to changes in the ghosts.

[Brief explanation of the drawing]

Figure 1a shows the waveform of the vertical blanking period of the television signal, Figure 1b shows the superimposed test signal (VITS) inserted into 17H, and Figure 2 shows the waveform distortion of the 2T bar. In the diagram to explain, the solid line is the standard 2T bar,
The broken line shows the distorted 2T bar, Figure 3 is a circuit diagram of an automatic waveform equalizer according to an embodiment of the present invention, and Figure 4a shows the relationship between the test waveform (2T bar) and the reference voltage according to the present invention. FIG. 4b is a diagram showing the sampling pulse trains 1 and 2, FIG. 4c is a diagram showing the relationship between the clock and the sampling pulse train 2, and FIG. Figure 6 is a diagram showing the configuration of the broadcasting device, and is a video waveform diagram to help understand the operation of the television relay broadcasting device shown in Figure 5, where a is a transmission waveform diagram at the master station, and b is a diagram with a ghost. The waveform diagram c is a waveform diagram whose waveform has been equalized. In the figure, 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, 11...
12... Phase shifter, 13... Timing pulse generation circuit, 14... Sampling pulse generation circuit, 15... Sampling pulse generation circuit,
16... Comparator, 18... Counting D/A conversion circuit, 1
9...Fixed delay line, 20...Receiving antenna, 21...
...Input filter, 22...Converter, 23
... IF video and audio separation circuit, 24 ... video demodulation circuit, 25 ... video band transversal automatic waveform equalizer, 26 ... control circuit, 27 ... video modulation circuit, 28 ... IF video and audio synthesis circuit, 29...Converter, 30...Power amplifier, 31...Output filter, 32...Transmission antenna.

Claims (1)

[Claims] 1 Automatic waveform equalization device for video signals that uses a transversal filter to use the squared sine wave pulse (2T bar) of the test signal (VITS) superimposed on the vertical blanking period of a color television signal as the test waveform. and before the rising center and after the falling center of the 2T bar, or after the rising center and before the falling center of the 2T bar, which are generated in synchronization with the 2T bar obtained from a predetermined tap of the transversal filter. and respective reference voltage generating means corresponding to predetermined sampling times before the rising center and after the falling center of the 2T bar, or after the rising center and before the falling center of the 2T bar, respectively. and means for sequentially comparing with the reference voltage at the time of generation of the sampling pulse to generate an error code; and using the error code, the system of the adjusted taps of the transversal filter is successively changed by a minute amount in a direction to correct waveform distortion. 1. An automatic waveform equalization device comprising: means for generating control information for controlling the waveform.