JPH05191679A - Ghost removing device - Google Patents

Abstract

PURPOSE:To improve an S/N after removing ghost at the ghost removing device using GCR signals. CONSTITUTION:After video signals extracted from the front step of an A/D converter 10 are delayed by a delay line 18, they are synthesized with the output signals of a D/A converter 14 by an adder 19 so as to obtain video outputs, and the input signals of the D/A converter 14 are limited to the output signals of the adder 16 not to contain any output signals of a delay line 13. Thus, the S/N can be improved since a main signal to pass through the delay line 18 is not quantized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ghost removing device for removing a ghost by using a GCR signal inserted in a video signal.

[0002]

2. Description of the Related Art In recent years, television receivers have tended to become large in size, and there is a demand for higher image quality together with the start of clear vision broadcasting. Among them, the ghost elimination has received great attention, and the GCR signal system has been proposed and introduced. The GCR signal has been reported in "Technical Report of the Television Society ROFT 89-4, pp 19-24".

A conventional ghost removing device will be described below. FIG. 2 is a block diagram showing the configuration of a conventional ghost removing device. In FIG. 2, 20 is an A / D converter for digitizing a video signal, 21 is a transversal filter for removing near-field ghosts, 22 is a transversal filter for removing normal ghosts, and 23.
Is a delay line for forming a main tap in the transversal filter 21, 24 is a D / A converter for converting a ghost-removed video signal into an analog signal, and 25 is a ghost for capturing a GCR signal inserted in the video signal. Is a CPU circuit that performs processing such as setting coefficients in the transversal filters 21 and 22 after performing detection for ghost removal and performing calculation for ghost removal. 26 is an adder for adding the outputs of the transversal filters 21 and 22, and 27 is an adder for adding the outputs of the adder 26 and the delay line 23.

The operation of the conventional ghost removing device configured as described above will be described with reference to the block diagram. The ghost removing device is a device for detecting and removing a ghost by using a GCR signal, and various methods such as the MSE method, the ZF method, and the division method have been proposed as algorithms for removing the ghost, but any of these methods can be used. The GCR signal waveform in the input video signal is basically controlled to be the same as the ideal GCR signal waveform. The video signal including the ghost is digitized by the A / D converter 20, and when the GCR signal inserted in the video signal is taken in and the 8-field sequence of the GCR signal is processed and an appropriate synchronous addition process is performed, noise is generated. Can be removed and the basic GCR signal and ghost signal can be detected. The GCR signal is defined as an impulse response of a filter having a flat frequency characteristic up to 4.2 MHz, and its waveform is a SINC function. When the GCR signal is modeled with a vertical line having an amplitude of 1.0 to explain the operation, the input video signal shown in FIG. 3 is obtained. Here, the ghost signal is modeled similarly to the GCR signal, and is represented by ghost 1 and ghost 2 in FIG. Ghost 1 is a positive ghost having a proximity ghost of D / U = 6 dB and a delay time of tn, and ghost 2 is a normal ghost having a normal ghost of D / U = 6 dB and a delay time of tn ′. The transversal filter 21 takes charge of a ghost with a short delay time which is generally called a proximity ghost,
The transversal filter 22 takes charge of a ghost having a long delay time, which is usually called a ghost. When the ghost is removed by the CPU 25 using any one of the algorithms, the tap coefficients of the transversal filters 21 and 22 are generated as shown in FIG. Here, the delay times tn and tn ′ of the ghosts 1 and 2 are integer multiples of the sampling period. Since the ghost 1 is removed by the transversal filter 21, tap coefficients other than tn are 2tn and 4tn.
This is because the grandchild ghost of the ghost at the position of tn occurs at the positions of 2tn and 4tn. A grandchild ghost at a position of 4tn also occurs at a position of 8tn, but the transversal filter 21 has a limitation on the number of taps.
Ghosts at position n cannot be removed. The transversal filter 22 takes charge of the ghost at the position of 8tn, as shown in FIG.
If a tap coefficient such as is set, it can be removed together with the ghost 2. In the transversal filter 22, since the transversal filter is of a feedback type, grandchild ghost does not occur. The resulting tap coefficient is as shown in FIG. 3, where the coefficient 1.0 represents the main tap of the transversal filter 21, and the delay line 23 functions as the main tap of the coefficient 1.0. Therefore, the main tap coefficient of the transversal filter 21 may be set to a value obtained by subtracting 1.0 from the generated main tap coefficient. In the example of FIG. 3, the main tap coefficient of the transversal filter 21 is 0. Delay line 23
The delay time is determined by the position of the main tap of the transversal filter 21, that is, the range in which the ghost signal can be removed from the preceding ghost which is ahead of the desired signal in time, and is usually 1 μS to 2 μS. It is a degree.

[0005]

In the ghost removing apparatus having the above-described structure and used as the conventional example, an A / D converter having an 8-bit precision is often used. This is because the price of the converter is reasonable. As for the ghost removing device, it is general to use an A / D converter having 8-bit precision. However, in the ghost elimination device, the video signal including the ghost signal is
Since the D / D conversion is performed, it depends on how strong the ghost is to be supported. For example, if a D / U ghost with 0 dB is used, a video signal without a ghost signal has an 8-bit precision. Even if the A / D converter is used, the accuracy is 7 bits, which is a major factor of S / N deterioration. A /
Since the S / N of the D converter can be expressed by (Equation 1) with the quantization bit number being n, the S / N is degraded by 6 dB when the A / D converter is used with 7-bit precision.

[0006]

[Equation 1]

As described above, the ghost removing device has a problem that the S / N is not good even if the ghost can be removed.

[0008]

In order to solve the above problems, a ghost removing apparatus of the present invention includes an A / D converter for A / D converting a video signal and a ghost in a digitized video signal. A ghost removing section, a D / A converter for converting the output signal of the ghost removing section into an analog signal, and
A delay line for delaying the input signal to the / D converter,
It is characterized by comprising an adder for adding the output signal of the delay line and the output signal of the D / A converter.

[0009]

According to the present invention, since most of the video signal output from the ghost removing device can be a signal that has passed through the delay line with the above-described structure, the A / D converter and the D / A converter can be The influence of noise due to quantization can be reduced, and a video signal with a good S / N can be provided.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A ghost removing device according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a ghost removing device according to an embodiment of the present invention. In FIG. 1, 10 is an A / D converter for digitizing a video signal, 11 is a transversal filter for removing a proximity ghost, 12 is a transversal filter for removing a normal ghost, and 13 is a transversal filter 11 A delay line for forming a main tap on the input terminal, a D / A converter for returning a ghost-free video signal to an analog signal, and a ghost for detecting a ghost by capturing a GCR signal inserted in the video signal. This is a CPU circuit that performs processing such as setting coefficients in the transversal filters 11 and 12 after performing calculation for removal. 16 is a transversal filter 1
An adder for adding the outputs of 1 and 12, 17 is an adder for adding the outputs of the adder 16 and the delay line 13, and 18 is an analog delay line for delaying the video signal,
An analog adder 19 adds the output of the D / A converter 15 and the output of the delay line 18.

The operation of the ghost removing device of the embodiment constructed as described above will be described with reference to the block diagram. In FIG. 1, the delay line 18, adder 19, D / A
The part excluding the converter 14 is exactly the same as the conventional example of FIG. 2, and the CPU circuit 15 operates in the same manner as the conventional example, and therefore its description is omitted. Unlike the conventional example, the signal to the D / A converter 14 does not include the video signal coming through the delay line 13 when it is output from the adder 16,
A signal having a polarity opposite to that of the ghost signal is D / A converted, and a waveform without a main signal is output from the D / A converter 14 like the output waveform of the D / A converter in FIG. After the main signal is D / A converted, the input signal to the A / D converter 10 is combined by the adder 19 through the delay line 18. Therefore, the delay line 18 has the same function as the delay line 13. Of course, delay line 1
The delay time of 8 is A in addition to the delay time of the delay line 13.
The delay time must include the delay time of the / D converter 10 and the D / A converter 14. Since most of the video signal can be a signal that has passed through the delay line in this way, the influence of noise due to the quantization of the A / D converter and the D / A converter can be reduced, and the S / N ratio can be reduced. It is possible to obtain a good video signal.

[0012]

As described above, the ghost removing apparatus of the present invention includes an A / D converter for A / D converting a video signal, a ghost removing section for removing a ghost in a digitized video signal, and a ghost. A D / A converter that converts the output signal of the removing unit to an analog signal, a delay line that delays the input signal to the A / D converter, and an output signal of the delay line and an output signal of the D / A converter With such a configuration, most of the video signal output from the ghost removing device can be a signal that has passed through the delay line, and thus the A / D converter and the D / D converter can be used. A
The influence of noise due to the quantization of the converter can be reduced, and a video signal with a good S / N can be provided.

[Brief description of drawings]

FIG. 1 is a block diagram of a ghost removing device according to an embodiment of the present invention.

FIG. 2 is a block diagram of a conventional ghost removing device.

3A is a modeled input video signal waveform diagram, FIG. 3B is a diagram showing tap coefficients for removing ghosts, and FIG. 3C is a ghost removed output video signal waveform diagram. FIG. Output waveform diagram

[Explanation of symbols]

 10 A / D converter 11 Transversal filter 12 Transversal filter 13 Delay line 14 D / A converter 15 CPU circuit 16 Adder 17 Adder 18 Delay line 19 Adder

Claims (1)

[Claims] 1. An A / D converter for A / D converting a video signal, a ghost removing section for removing a ghost in a digitized video signal, and a D for converting an output signal of the ghost removing section into an analog signal. A / A converter, a delay line that delays an input signal to the A / D converter, and an adder that adds an output signal of the delay line and an output signal of the D / A converter.