JPS63141471A - Ringing reducing device - Google Patents

Abstract

PURPOSE:To automatically decrease ringing by detecting two points of a transient part of a rectangular waveform added at a frame or a field synchronization, subtracting the result from a normal level and using the result as a phase correction data for a VCO (voltage controlled oscillator). CONSTITUTION:A television signal being converted into a digital signal by an A/D converter 14 is outputted from an output terminal 19 and fed to a phase detection circuit 15 and a frame pulse detection circuit 110. The frame pulse detection circuit 110 detects the transient part of the rectangular wave of a frame period added to the input signal and sends the result to the ringing detection circuit 111. The ringing detection circuit 111 subtracts the output of the frame pulse detection circuit 110 from the output of a comparison signal generating circuit 112 to detect the ringing of each sampling point and outputs a data correcting it if any ringing exists. The correction data is subtracted and added from/to the output of the phase detection circuit 15 by the adder/subtractor 16 to be formed into a control signal for the VCO 18.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is directed to a television receiver in which a television 2''-
The present invention relates to a circuit that reduces ringing in a collision signal.

2. Description of the Related Art When transmitting a wideband video signal such as a high-definition television signal, methods of band compression of the video signal are being considered. One of them is the so-called MUSE (MuJ
2tipfie 5ubnyquist Sample
ngEncading) method has been proposed. The details of the content are shown in, for example, "Satellite one-channel transmission system for high-definition television (MUSE) I," written by Tasuku Ninomiya et al., IEICE technical report, IE84-72.1984.

An outline of this transmission method is shown in FIG. On the transmitting side, a video signal obtained by a high-quality camera, VTR, etc. 41 is converted into a digital signal by an A/D converter 42, subjected to subsampling processing by a subsampling circuit 43, passed through a transmission matching filter 44, and then converted into a digital signal by a subsampling circuit 43. The /A converter 45 reconverts the signal into an analog signal, and the FM modulator 46 performs FM modulation and transmits the signal.

On the receiving side, this signal is received, demodulated by an FM demodulator 473, converted to a digital signal by an A/D converter 48,
A subsampling circuit 49 performs subsampling. Further, a two-dimensional interpolation circuit 410 performs interpolation processing, a D/A converter 411 converts the signal into an analog signal, and the signal is displayed on a high-quality display 412.

Here, in order to synchronize the receiver side and the transmitter side, a horizontal synchronization signal 51 is added to the video signal on the transmitter side as shown in FIG. On the receiving side, the horizontal synchronization signal after A/D conversion is calculated by (level at point b + level at point 0) -2X level at point a, and if this result is zero, the phase of the sampling clock is correct. If it is negative, it is determined that the phase is delayed, and if it is positive, it is determined that the phase is advanced, and control is performed so that the phases match.

However, even if the phases of the sampling clocks are matched in this manner, the sampling position of the video signal may still shift and ringing may occur.

The reason for this is that overshoot or undershoot has occurred in the horizontal synchronization signal, that point a cannot be detected correctly due to distortion in the transmission path, or that the phase characteristics of the transmission path are not completely linear, causing horizontal synchronization with the video signal. There are cases where the relative position of the signal changes and the video signal cannot be sampled at the correct position.

In this way, if the sampling position of the video signal shifts,
The A/D converted signal on the receiving side is different from the subsampled signal on the transmitting side, resulting in a waveform with ringing distortion, and ringing also occurs in the image.

This means that the signal that has been D/A converted on the transmitting side is converted into A/A on the receiving side.
When D-converting, the input signal causes frequency ringing, which is determined by the transmission path. However, as shown in Figure 6 a and b, if the sampling phases on the transmitting and receiving sides match, the center of the ringing waveform The original waveform can be reproduced regardless of ringing, whereas
This is because, as described above, if the phase of subsampling on the receiving side is shifted, ringing distortion will occur as shown in FIG. 6C.

5/ Next, the basic configuration of a conventional sampling clock and phase control circuit is shown in FIG. A signal input to an input terminal 71 is demodulated by an FM demodulator 72, band-limited by a low-pass filter 73, and converted into a digital signal by an A/D converter 74. The phase detection circuit 75 outputs the result of the above calculation as a phase error of the synchronization signal, and the adder 76 adds the phase error of the previous synchronization signal and the addition data 710, and outputs the phase error of the video signal. Next, this is integrated by an integrator 47 to absorb sudden changes.

A voltage-controlled oscillator (VCO) 78 generates a sampling clock for the A/D converter 74, and controls the phase of the sampling clock using the integrator 77Ω output.

75 is an output terminal. Note that the addition data 710 is A/
This data is used to adjust the phase of the sampling clock of the D converter 74, and can be varied using a switch.

Problems to be Solved by the Invention However, in the above configuration, it is necessary to minimize ringing each time the input video signal is switched or the characteristics of the transmission path change. I had to manually adjust the subsampling phase on the receiver side.

The present invention can automatically control the sampling clock phase of the A/D converter on the receiving side to obtain an image with less ringing even when the input video signal is switched or the transmission path characteristics change. A ringing reduction circuit is provided.

Means for Solving the Problems In order to solve the above problems, the present invention provides two
A frame pulse detection circuit that detects a point, a comparison signal generation circuit that generates a normal level of the pulse, and a ringing detection circuit that takes the difference between these two signals and outputs data for correcting the phase of a VCO (sampling clock), It has a structure that automatically reduces ringing.

Effect of the Invention With the above-described configuration, the present invention corrects the phase of vC○ by detecting the ringing of the frame pulse even if the state of ringing changes by changing the input signal, and manually creates an image with less ringing. can be obtained automatically without any adjustment.

Embodiment Hereinafter, a ringing reduction circuit according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a block diagram of a ringing reduction circuit in one embodiment of the present invention. Here, 11 is a video input terminal, 12 is an FM demodulator, 13 is a low-pass filter, 14 is an A/D converter, 15 is a phase detection circuit, 16 is an adder/subtractor, 17 is an integrator, 18 is a VCO 119 is a two-dimensional This is an output terminal to a signal processing circuit for interpolation, etc., and these are similar in configuration to the conventional example. In the present invention, further,
Frame pulse detection circuit 110, ringing detection circuit 1
11, a comparison signal generation circuit 112 is provided.

The operation of the ring reduction circuit configured as described above will be described below with reference to FIGS. 1 and 2. First, FIG. 2a is a waveform diagram of a frame pulse line, which is inserted into the video signal for one horizontal period in one frame. Here, 21 is a frame pulse, and a rectangular wave with a width of 1611& is repeated in 117.5 pairs at a 100% level.

This frame pulse waveform originally samples each sampling point a, b, c, etc. in Figure 3a, but as mentioned above, it has ringing distortion, and the sampling points of the frame pulse are as shown in Figure 3C. At each sample point a, b, c
...Sample h. Therefore, in order to improve accuracy, the frame pulse detection circuit 110 detects each sample point at least twice and outputs the average level of each sample point.

Next, the comparison signal generating circuit 112 outputs the levels at each sampling point a, b, c, . . . h of the original frame pulse free of ringing distortion as shown in FIG. 3a.

The ringing detection circuit 111 subtracts the output of the frame pulse detection circuit 110 from the output of the comparison signal generation circuit 112 to detect ringing at each sampling point as shown in FIG. If the ringing at the q point is negative, the phase of the sampling clock is delayed, so data to correct this is output.Similarly, if the ringing at the 0 point is positive and the ringing at the q point is negative, Since the phase of the sampling clock is ahead, data to correct this is output.
If the f points are in a combination other than the above, the correction data is set to zero. The correction data outputted from the ringing detection circuit 111 is added to the phase error data outputted from the phase detection circuit 15, and this is integrated in the same way as in the conventional case, and the voltage controlled oscillator (VCO) 18.7, that is, A/D conversion The phase of the sampling clock of the device 14 is controlled to obtain an image with less ringing.

As described above, according to this embodiment, by providing the frame pulse detection circuit 1101, the comparison signal generation circuit 112, and the ringing detection circuit 111, even when the input signal is switched or the transmission path characteristics change, to A/D
By controlling the sampling clock phase of the converter, images with less ringing can be obtained at all times.

1. Effects of the Heno Invention As described above, the present invention provides a claim (field) pulse detection circuit for detecting at least two points in the transient portion of a rectangular wave added in a frame or field period, and a regularization of the pulse. By providing a comparison signal generation circuit that generates a level and a ringing detection circuit, even when the input signal is switched or the transmission path characteristics change, there is no need to manually adjust while watching the playback screen, and the ringing detection circuit is always automatically adjusted. The sampling clock of the A/D converter can be controlled to a point with less ringing, and the ringing of the reproduced image can be reduced to the right.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a ringing reduction device according to an embodiment of the present invention, Fig. 2 is a waveform diagram of the frame pulse used, Fig. 3 is a waveform diagram for explaining the operation of the device, and Fig. 4 is a high-quality waveform diagram. A block diagram showing the transmission configuration of the television system, Fig. 5 is a waveform diagram of its horizontal synchronizing signal, Fig. 6 is a waveform diagram showing the relationship between sampling and sampling, and Fig. 7 is a waveform diagram of the conventional example. It is a block diagram showing the configuration. 11... input terminal, 12... FM demodulator,
13...Low pass filter, 14...
A/D converter, 15... Phase detection circuit, 16...
... Adder/subtractor, 17... Integrator, 18...
・VC○ (voltage controlled oscillator), 19...output terminal, 110...frame pulse detection circuit, 11
1... Ringing detection circuit, 112...
Comparison signal generation circuit. Name of agent: Patent attorney Toshio Nakao and 1 other person City: 0 areas: City:

Claims (1)

[Claims] an analog-to-digital converter into which a television signal is input; means for detecting a phase error of a sampling clock of the analog-to-digital converter using a horizontal synchronizing signal added to the input signal; means for detecting at least two points in a transient part of a rectangular wave or the like of a frame or field period to generate a normal level of the pulse; and comparing the detected rectangular wave and the normal level to output phase correction data. and the means to
A ringing mitigation device characterized by comprising means for adding and integrating the phase error and the phase correction data and applying the resulting value to a voltage controlled oscillator to control the phase of a sampling clock.