JPH0514772A - Ghost eliminator device - Google Patents

Abstract

PURPOSE:To prevent the deterioration of an S/N after eliminator ghost at the time of a relatively intense close ghost, in a ghost eliminator device using a GCR signal. CONSTITUTION:This device is equipped with a frequency characteristic calculating part 5 which calculates a frequency characteristic from a compared result obtained by comparing the GCR signal fetched from the output of an A/D converter 7, and obtained through a GCR signal detecting circuit 1, and a synchronizing adding part 2 with a reference GCR signal 6. Moreover, this device is equipped with a frequency characteristic control part 8 which corrects the frequency characteristic of an input video signal to the A/D converter 7 based on the calculated result. Thus, the characteristic of the input video signal to the A/D converter 7 can be preliminarily corrected by an analog part, so that the deterioration of the S/N can be reduced.

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ghost removal apparatus for removing ghosts using a GCR signal inserted into a video signal.

[0002]

2. Description of the Related Art In recent years, there has been a tendency for television receivers to increase in size.
There is a demand for higher image quality. Among them, ghost cancellation has received a great deal of attention, and GCR signaling has been proposed and introduced. The GCR signal is reported in "Television Society Technical Report ROFT89-4, pp19-24".

A conventional ghost eliminator will be described below. FIG. 3(a) is a block diagram showing the configuration of a conventional ghost removing apparatus. In FIG. 3(a), 31 is an A/D converter for digitizing a video signal, 32 is a transversal filter for removing ghosts, and 33
D returns the ghost-removed video signal to an analog signal.
A/A converter, 35 a memory for fetching the GCR signal inserted in the video signal, 34 a switch for fetching data into the memory 35, 36 a CPU, 38 a timing generator, and 37 a ROM. CPU 36 is connected to provide tap coefficients to transversal filter 32 . The timing generator circuit 38 has fV, fH, 2
From the timing signal of fH, G
It is configured to generate a GCR gate signal for extracting the CR signal and to notify the CPU 36 of the timing of the GCR gate. The GCR signal is shown in FIG. 4(a)
, the WRB signal and the 0 pedestal signal are connected to WR
B signal→0 pedestal signal→WRB signal→0 pedestal signal→0 pedestal signal→WRB signal→0 pedestal signal→WRB signal. The GCR signal shown in FIG. 4(b) can be obtained by performing the calculation shown in (Equation 1) for these 8-field signals. However, Fn (n=1 to 8) represents the n-th field signal.

[0004]

[Number 1]

[0005] If the GCR signal in FIG. 4(b) is subtracted by one sampling clock, the waveform shown in the lower part of the figure is obtained. When this waveform is enlarged, the SIN as shown in Fig. 4(c) is obtained.
The (x)/x waveform has a flat frequency component up to about 4.2 MHz as shown in the figure if there is no distortion such as a ghost. However, the waveform shown in FIG. 4(c) represents an ideal GCR signal, which is extracted from the video signal processed by the television receiver.
As already mentioned, the CR signal is not a little distorted by the influence of the radio wave transmission system, the tuner's bandpass filter, etc., and does not have an ideal waveform. A ghost eliminator is a device that detects and eliminates ghosts using GCR signals, and various methods such as the MSE method and the ZF method have been proposed as ghost eliminator methods (algorithms). However, in either method, the GCR signal waveform in the input video signal is basically controlled to be the same as the ideal GCR signal waveform. As an example, the ZF (Zero Forcing) method is used to describe the process of obtaining the tap coefficients of the transversal filter 32. FIG. In FIG. 3A, if the output signal of the transversal filter is {Yk}, the reference signal is {Rk}, and the difference signal between the output signal of the transversal filter and the reference signal is {Ek}, The n-th tap coefficient C{i}{n} of the transversal filter is corrected based on (Equation 2) in the ZF method. However, α is a coefficient for determining the amount of correction for one time.

[0006]

[Number 2]

The CPU 36 in FIG. 3(a) performs the synchronous addition and field sequence processing shown in (Equation 1).
By performing the operation of (Equation 2), the tap coefficients are repeatedly corrected until the amount of residual ghost becomes sufficiently small. Here, the reference GCR signal is written in the ROM 37 of 37 . The original GCR signal is taken in by setting the switch 34 to the terminal 1 side by the GCR gate signal generated by the timing generating circuit 38, and setting it to the terminal 2 side to switch the transversal filter 32. The output is captured in memory 35 . As a result, the waveform of the GCR signal inserted into the video signal input to the A/D converter 31 becomes substantially the same as the waveform of the reference GCR signal, and the ghost disturbance that the television signal received on the transmission line is eliminated. , antenna mismatch, frequency characteristics, phase characteristics, etc. in the tuner and image detection stage are improved.

[0008] In the process of the ghost removal process described above, ghost detection is performed as shown in FIG. 3(b). Fig. 3(b)
1 is a block diagram showing an example of a conventional ghost detection method; FIG. In the figure, 41 is a GCR signal containing a ghost, which is captured by the GCR gate signal. 42 is fee
46 is a reference GCR signal; 43 is a subtractor which subtracts the reference GCR signal 46 from the data of the synchronous adder 42; A ghost detect signal 44 is produced. In this example, since the ghost removal algorithm performs ghost detection on the time axis, the comparison between the synchronously added GCR signal and the reference GCR signal is a subtraction. Since both the signal and the reference GCR signal are Fourier transformed, the subtractor 43 performs division by complex numbers.

[0009]

However, FIG.
In the configuration shown in (a), all distortions, including ghosts, received in the signal transmission system are transferred to the A/D converter 31 and the D/A converter 3.
3 is corrected by the transversal filter 32. That is, since ghost removal is performed by A/D-converted digital signal processing, depending on the type of ghost, S/N deterioration after ghost removal may be large, which may pose a problem. FIG. 5 shows the frequency characteristics up to the input of the A/D converter in such a state. Especially when the frequency characteristics of FIG. 5 are like the characteristic line 2 or the characteristic line 4, the frequency characteristic is corrected to the characteristic like the characteristic line 1 when the ghost is removed, but the S/N is reduced by the amount that the frequency characteristic rises. to degrade. In the case of frequency characteristics such as characteristic line 3, there is no direct effect on the S/N, but since the rise in the high frequency range is large, overshoot and undershoot in the video signal may affect the input level of the A/D converter. Care must be taken to exceed When the frequency characteristic up to the input of the A/D converter undulates greatly in this manner, the S/N and the dynamic range of digital signal processing are greatly affected, and the performance after ghost removal is significantly affected. A frequency characteristic such as that shown in FIG. 5 is generated by a strong proximity ghost of about several 100 nS or by VSWR caused by mismatching of the antenna system.

[0010]

In order to solve the above-mentioned problems, the ghost removal apparatus of the present invention converts the GCR signal inserted into the A/D converted video signal into an 8-field sequence GCR signal. Means for adding according to the contents of transmission, means for comparing the added GCR signal with a reference GCR signal, means for calculating a frequency characteristic correction value based on the output of the comparison means, and A/D conversion according to the content of the correction value. means for controlling the frequency characteristic of a frequency characteristic control circuit connected to the device.

[0011]

According to the above configuration, even if the frequency characteristics of the video signal before A/D conversion fluctuate greatly, the frequency characteristics can be controlled to some extent by the frequency characteristics control circuit connected to the preceding stage of the A/D converter. can be corrected, the degradation of the S/N can be reduced by the amount of the correction performed by the analog circuit, and a high-quality image can be provided. Also, even if the signal has a raised high frequency characteristic, overshoot and undershoot can be reduced to some extent in the stage preceding the input of the A/D converter, so the input level to the A/D converter can be reduced as a result. It can be increased, and the S/N can be improved.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A ghost removing apparatus according to an embodiment of the present invention will now be described with reference to the drawings. FIG. 1 shows a block diagram of a ghost detector of a ghost eliminator according to an embodiment of the present invention. The configuration of the ghost removing device is the same as that of FIG. In FIG. 1, 1 is G containing a ghost.
In the CR signal detection circuit, the GCR is detected by the GCR gate signal.
A signal is captured. Reference numeral 2 denotes a synchronous addition section for performing field sequence processing and improving S/N, 6 denotes a reference GCR signal, and 3 denotes a comparator for the synchronous addition section 2 and the reference GC.
A ghost detection signal 4 is produced by comparing the output signals of the R signal source 6 . Reference numeral 5 denotes a frequency characteristic calculation section for calculating frequency characteristics based on the output result of the comparator 3, and 8 denotes a frequency characteristic calculation section 5.
A/D converter 7 is provided with a video signal whose frequency characteristic is corrected by a frequency characteristic control section for controlling the frequency characteristic of the video signal according to the result of (1).

FIG. 2 shows a specific example of the frequency characteristic control section 8 in FIG. In FIG. 2, 21 and 22 are delay lines with a delay time of td, and their inputs and outputs are multipliers 23, 24,
25 is connected. 26 is an adder, and multipliers 23 and 2
4 and 25 are added and supplied to the A/D converter 7 . Coefficients C0, C1 and C2 are supplied to the other inputs of multipliers 23, 24 and 25, respectively, based on the results of frequency characteristic calculator 5, so the block diagram of FIG. It's becoming Although the number of taps is three in this example, the number of taps may be increased if it is necessary to finely control the frequency characteristics.

The operation of the circuit constructed as above will be described. Let G(S) be the Fourier transform of the output of the synchronous adder 2 in FIG. 1, and R be the Fourier transform of the reference GCR signal.
When putting (S)

[0015]

[Number 3]

H(S) represented by ##EQU1## represents the transfer function of the ghost generation system, and its reciprocal is the transfer function H@-1 (S) of the ghost correction system. Since this inverse Fourier transform h@-1 (t) becomes the impulse response of the correction system, the ghost generation system can be corrected by giving the impulse response as it is as the tap coefficient of the transversal filter. This way of thinking is the basic way of thinking of the division method, which is the batch conversion method of the ghost removal algorithm. Instead of giving the tap coefficients thus obtained to the transversal filter, the frequency characteristic control unit 8 connected to the front stage of the A/D converter 7 in FIG.
When given to 0, C1, and C2, it is possible to correct the frequency characteristic for three tap coefficients. Of course, since only three tap coefficients are given, sufficient correction cannot be performed, and DC
Since the gain also changes, correction for it is also required.

The reason why the S/N can be improved by the above concept is that the S/N of analog is better than that of a general A/D converter. Since 8-bit A/D converters, which are widely used in clear vision, etc., are the mainstream, if the A/D converter is 8-bit and used with a 6 dB input margin in the ghost removal device, the S/N digital will be low.

[0018]

[Formula 4]

On the other hand, S/N unlog

Claims (1)

[Claims] [Claim 1] G inserted into an A/D converted video signal
means for adding the CR signal to the GCR signal transmission contents of the 8-field sequence;
means for comparing the R signal with a reference GCR signal; means for calculating a frequency characteristic correction value based on the output of the comparing means;
A ghost eliminator comprising means for controlling the frequency characteristic of a frequency characteristic control circuit connected to an A/D converter according to the content of the correction value.