JPS58104576A - Ghost eliminating device - Google Patents

Abstract

PURPOSE:To improve the accuracy of ghost detection, by taking a DC voltage as a fraction of a minimum converting ragne at analog-to-digital conversion and averaging the DC voltage for a number of times equal to the reciprocal of the fraction. CONSTITUTION:A control clock H is generated at the end of data transfer with the A/D conversion of the front edge in the vertical synchronizing rate and the direct memory access. A digital-to-analog converter 15 performs voltage change one over an integer of the minimum conversion voltage ragne of the A/D converter. When one control pulse is received, a voltage corresponding to one over an integer of the minimum voltage range of the A/D converter is changed and the voltage is restored at the number of times of integer. This voltage I is summed to an input signal E clamped at an addition circuit 16, and the signal is converted into a digital value at an A/D converter 13. This digital value is averaged.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention particularly relates to a ghost signal detection portion of a ghost removal device built into a television receiver.

In recent years, when receiving television broadcasts, there has been an increase in the deterioration of received images due to various radio wave interferences, resulting in intermittent blackouts. In particular, the main reason for the increase in the height of buildings in convenient areas is the double reception of images.

Triple so-called ghost development has started to occur frequently. Countermeasures against this problem include the development of wall construction materials that prevent the reflection of radio waves from these buildings, higher directivity of receiving antennas, and diversity reception using horizontally stacked antennas, but all of these methods have operational issues. It has not become widespread due to its complexity and rising costs.

Therefore, there has been an increasing need to provide a fully automatic ghost removal system that can be built into television receivers at low cost.

First, a configuration of a television receiver and a ghost removal device in which the present invention can be implemented will be described. 1st
The figure shows a part of the configuration of the television receiver. In the figure, reference numeral 1 denotes an intermediate amplified video detection circuit which amplifies and detects the intermediate tL number tone signal from Chuchi to obtain a baseband composite video signal. This composite video signal becomes a signal of 0 to 4.2 MH2 in the NTSC system.

In a typical television receiver, this composite video signal is directly supplied to both the video signal processing amplifier circuit 3 and the chroma signal processing amplifier circuit 4. The ghost removal device 2 has a function of inputting a composite video signal, removing the ghost signal, and then supplying a ghost-free video signal to the circuit 3.4.

C shown in the figure is supplied to a video display device (such as a CRT) as a display signal without ghosts.

FIG. 2 is a more detailed block diagram of the portion of the ghost removal device 2 in FIG. 1. A feature of this device is that it uses a transversal filter 5.

As is generally known, in a television transmitting and receiving system, the transfer function in the radio wave propagation system is expressed as H(S),
If the transfer function of the propagation system due to ghosts is G (S), then the transfer function of the total signal propagation system including ghosts is H
(S)・G (S). On the other hand, since the transversal filter 5 can have an arbitrary transfer function, ghosts can be removed by controlling it to have &G'(S) between the reverse transfers of the propagation system due to ghosts.

The other parts in FIG. 2 are this transversal filter 6.
Ghost detection and calculation for automatically controlling the weighting coefficient for each tap so that G'(S) has an inverse transfer function G'(S) corresponding to the ghost at that time.

It performs operations such as generating and storing weighting coefficients. In the figure, M is an input composite video signal, B is an output composite video signal from which ghosts have been removed, and D is a synchronization signal.

Detection of a ghost in a received television signal is performed by observing the flatness of the signal before and after the beginning portion (@edge portion) of the vertical synchronization signal. Ideally, this portion of the signal can be regarded as a unit stage number, and if there is a ghost, distortion of the unit stage number is detected accordingly. For example, the location and size of a ghost is detected at each sampling point. Reference numeral 8 denotes a timing pulse generation circuit for controlling the timing pulse generating circuit, which generates a sampling pulse based on horizontal and vertical synchronizing signals in order to extract the signal of this portion.

The video signal B processed by the transversal filter 6 is applied to a clamp five-way conversion circuit 7, where it is clamped to eliminate direct current fluctuations, and then the above-mentioned sampled portion is converted by a multiple conversion circuit. Obtain ghost information, digitize it, and store it in memory 1°.

The arithmetic circuit 9 processes the ghost information stored in the memo I 710 and generates a signal for controlling the weighting coefficient when extracting the output signal from each tap of the transversal filter 6. This part is usually configured using a microcomputer.

The weighting coefficient correction circuit 6 is for actually generating and holding a weighting coefficient for each tap based on the calculation result of the calculation circuit 9, and since the output of this calculation circuit 9 is normally a digital signal, If the weighting coefficient is an analog signal, a D-me conversion circuit is required, in which case it is also included.

In addition, since this detection, calculation, and weighting is performed repeatedly using a so-called adaptive equalization method, the weighting coefficients are modified one after another many times, and the previous coefficients are stored in memory. It is necessary to store it in 1o. In addition, the sampling frequency of the five-way conversion circuit in 7 is required to be three times the band frequency since it handles video signals, and in the NTSC system, it is 10.7MHz, which is three times the number of chroma subcarrier frequencies.
is often used. Therefore, this human-to-person conversion circuit is required to be high-speed. Memo IJ10 is also often used as a high-speed one, and since a microcomputer is also used as the arithmetic circuit 9, it is not so fast, and Memo 1J10 is used only when the conversion circuit is handling the vertical synchronization signal part. Operation by so-called DM (direct memory access), which is disconnected from the 'jz microcomputer, can be performed.

In this way, this circuit device can be constructed mainly of digital circuits including a microcomputer, and since the transversal filter 6 also has variable integration using solid-state delay lines such as COD, it can be used for TVs at relatively low cost. It is possible to incorporate it into a John receiver.

The present invention provides such a ghost removal device in which tap correction information of the transversal filter is obtained from data obtained by amplifying and digitalizing the output of the transversal filter, which performs analog-to-digital conversion with fewer pings. The objective is to provide an inexpensive and highly accurate ghost removal device that can achieve the same ghost detection accuracy as using an analog-to-digital converter with a larger number of bits even when using a digital converter. be.

FIG. 3 shows the configuration of an analog-to-digital converter in a conventional ghost removal device. The human input signal is the output of the transversal filter 5 and is supplied to the clamp circuit 12 via the capacitor 11. The clamp circuit 12 uses a clamp pulse F to clamp the pedestal portion to a predetermined DC voltage value in a horizontal period except for the leading edge portion of the vertical synchronizing signal. The reason for excluding the leading edge of the vertical synchronizing signal is to prevent it from being affected by the clamp pulse, since the leading edge of the vertical synchronizing signal is regarded as an impulse and used for detecting ghost information. The clamped signal is transferred to an analog-to-digital converter (hereinafter referred to as MU/D converter) 13.
It is connected to the.

G is the output of the Mu/G converter 13.

In such a configuration, the ghost detection limit is determined by the 130-bit number of the mu/D converter used. Figure 4 shows this state. This shows a slight ghost that is in phase with the leading edge of the vertical synchronization signal. Do ha mu/D
The voltage is N times the minimum conversion range of the converter 13. 1 indicates a sampling point. Naturally, ghosts within the minimum conversion range as shown in FIG. 4 cannot be detected. For example, even if the conversion range is used to the maximum, the 6-bit MU/D converter 13 cannot detect ghosts smaller than 5 edB. Seven bits are required to discriminate about 40 dB. Therefore, if you want to detect ghosts with high precision, that is, if you want to remove ghosts sufficiently, it is necessary to use a MU/D converter with a corresponding number of bits.

In view of this point, the present invention provides a means for equivalently improving ghost detection accuracy even when using a MU/D converter with a small number of bits.

FIG. 6 shows an embodiment of the present invention. Input signal E.

The capacitor 11, clamp circuit 12, and clamp pulse F are the same as those shown in FIG. The control clock H is a pulse that is generated at the vertical synchronization rate every time the leading edge M/D conversion and data transfer by direct memory access (DMA) are completed. The converter 15 causes the gutter voltage to change within the minimum conversion voltage range (11, SB) of the Mu/D converter as the minimum change. Therefore, if the control pulse is applied once, the voltage corresponding to 114'I-SB of the M/D converter will be changed, and it will return to the original value after four times. This voltage I is added to the clamped input signal X by an adder circuit 16, and the signal is converted into a digital value by a MU/D converter 13. By averaging the digital values converted in this way, it is possible to obtain the same accuracy as using a mu/D converter equivalently having a large number of bits.

FIG. 6 is a diagram when electrons are changed by 1/4L S B. This shows a state in which the number increases by 1ALSB every vertical period. DMA for each vertical sync
The leading edge of vertical synchronization is determined from the data,
It is averaged by performing synchronous addition and dividing it that number of times.

FIG. 7 shows six vertical periods of the input signal E, and FIG. 8 shows the output of the D/MU converter 15. FIG. 9a shows an enlarged view of one horizontal period before and after the leading edge of vertical synchronization, and shows changes in the DMA timing b and the control pulses H and output of the I/M converter 16.

Sampling points of the Mu/D converter in FIG.

1+j and 1+j+1. In other words, the j-th and j+1 from the leading edge
If the th data differs by more than LSB, it is recognized as a ghost.

In the above embodiment, the pure case of the minimum conversion range has been described, but it may be divided by an arbitrary integer and averaged a number of times that is an integer multiple.

As described above, according to the configuration of the present invention, it is possible to obtain a ghost removal device with good removal performance even when using a human/D converter with a small number of bits. Furthermore, high-speed M/D converters are generally of the parallel converter type, and if the P/D can be reduced, the cost can be reduced, and an inexpensive ghost canceling device can be provided.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a television receiver to which the ghost removal device of the present invention can be applied, FIG. 2 is a basic block diagram of the ghost removal device, and FIG. 3 is a detailed block diagram of a part thereof. Figure 4 is a waveform diagram explaining the operation, and Figure 5 is a waveform diagram explaining the operation.
The figure is a block diagram of a ghost removal device according to an embodiment of the present invention, and FIGS. 6, 7, 8, and 9 are waveform diagrams illustrating its operation. 5...Transversal filter, 6...
・Weighting coefficient correction circuit, 7... Clamp/I
ff conversion circuit, B... timing pulse generation circuit, 9... arithmetic circuit, 1o... memory, 11... capacitor, 12...・Clamp circuit, 13・Old... Mu/D converter, 14...
・Counter, 15...D/mu converter, 16...
...Addition circuit. Name of agent: Patent attorney Toshio Nakao and one other person II
I Figure 2 Figure 3 Fi! J Fig. 4 Nt3 ・---------1-------t-iy
s + lr + '1t (Figure 5 Figure 6'''':: 2 cho ' -7, =---, te・2---part iψ1
1+7&su J meeting f

Claims (1)

[Claims] A video signal is input to a transversal filter, and a ghost signal is removed by modifying the weighting coefficient of the signal taken out from a plurality of taps of the transversal filter and synthesized, and the output signal of the transversal filter is removed. The weighting coefficient correction information of the tap is obtained by applying a DC voltage that changes in vertical synchronization to the signal and converting the signal from analog to digital.The DC voltage is an integer of the minimum conversion range in the analog to digital conversion. A ghost removal device characterized in that by averaging the number of times equal to an integer, an analog-to-digital converter with a small number of bits is used to equivalently perform analog-to-digital conversion with a large number of bits. .