JPS5941982A - Ghost eliminating device - Google Patents

Abstract

PURPOSE:To raise ghost eliminating accuracy, by controlling the amplification gain of a signal to an A/D converter for digitally converting an output of a transversal filter, by an overflow output of the A/D converter. CONSTITUTION:When operating a position and size of a ghost basing on a digital data by A/D-converting an output E of a transversal filter, if its output exceeds a converting range of an A/D converter 11, a transistor Q5 is made to conduct by a signal of its overflow terminal OF, a collector resistance R4 of a transistor Q1 is short-circuited, and the gain of an inversional amplifier constituted of Q1 is lowered. In this way, an input to the A/D converter 11 can be made small forcibly, and the leading edge part of a synchronizing signal can be operated and detected without an error from an output digital value of the A/D converter 11.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a device for removing ghosts from a television transmission/reception system ξζ by using a transversal filter.

Conventional configurations and their problems In recent years, when receiving television broadcasts, the deterioration of received images due to various radio wave interferences has become a problem. The so-called ghost phenomenon, in which received images become double or triple, has become a frequent cause, mainly due to the rise in the heights of buildings in urban areas. Countermeasures for this 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.
However, none of them have become widespread due to operational complexity and rising costs. So, TV reception 8! There has been an increasing need to provide a fully automatic ghost removal system that can be built into a machine at a low cost.

First, a ghost removal device that can be built into a television receiver will be described. FIG. 1 shows a part of the configuration of the television receiver. In the figure, (1) is an intermediate amplified video detection circuit that amplifies and detects an intermediate frequency modulated signal from a tuner, and generates a baseband composite video signal A. This composite video signal A is NTS
In the C method, the signal is 0 to 42M11z. In a typical TV set, this composite video signal A is directly supplied to both the video signal processing amplifier circuit (3) and the chroma signal processing amplifier circuit (4). Ghost removal bag R (
2) has a function of inputting the composite video signal A, removing the ghost signal, and then supplying the ghost-free video signal B to the circuits (3) and (4). The signal C shown in the figure is supplied to a video fψ display device (such as a CRT) as a ghost-free display signal.

FIG. 2 is a more detailed block diagram of the ghost removal device +21 in FIG. 1. The features of this device are ζ
The reason is that a transversal filter (5) is used.

As is well known, in a television transmitting and receiving system, the transfer function of the radio wave propagation system (Ij) is expressed as H(S).
, :r- If the transfer function of the propagation system due to the strike 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 any transfer function, ghosts can be removed by controlling it to have the inverse transfer function G'(S) of the propagation system due to ghosts. The other parts in Fig. 2 are for automatically controlling the weighting coefficient of each tap so that the transversal filter (5) has an inverse transfer function G-''(S) depending on the ghost at each time. It performs operations such as ghost detection, calculation, weighting coefficient generation and storage.In the figure, A is the input composite video signal, B is the output composite video signal from which ghosts have been removed, and D is the synchronization signal. be.

Ghost detection in a received television signal is carried out by observing the flatness of the signal before and after the beginning (leading edge) of the vertical synchronization signal. The signal in this part can be ideally regarded as the number between unit stages, and if there is a ghost, distortion related to the unit stage is detected accordingly. For example, the location and size of a ghost is detected at each sampling point. Reference numeral (8) is a timing pulse generation circuit for controlling the timing pulse, which generates a sampling pulse based on the horizontal and vertical synchronizing signals in order to extract the signal of this part.

The video signal B processed by the transversal filter (5) is added to the clamp A/D conversion circuit (7), where it is clamped to eliminate DC fluctuations, and then the sampled portion is digitally converted by the AID conversion circuit. This is stored in the memory 01 as ghost information.

The arithmetic circuit (9) processes the ghost information stored in the memory θ (1) and generates a signal for controlling the weighting coefficient when extracting the output signal from each tap of the transversal filter (5). This part is usually configured using a microcomputer.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),
Normally, the output of this arithmetic circuit (9) is a digital signal, so if the weighting coefficient is an analog signal, a D/A conversion circuit is required, in which case it is also included.

In addition, since this process of correct detection → calculation → weighting is repeated many times using the 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 memorize the 0C mark. In addition, the sampling frequency of the A/D conversion circuit (7) in the clamp/A/D conversion circuit (7) is required to be 8 times the band frequency because it handles video signals, and in the NTSC system, it is 8 times the chroma subcarrier frequency. 10.7 MHz is often used. Therefore, this A/D conversion circuit is required to be high-speed. The same goes for memory aQ).In many cases, a high-speed memory is used, and a microcomputer is also used as the arithmetic circuit (9), so it is not that high-speed.
Only when the D conversion circuit is handling the vertical synchronization signal portion can the so-called DMA (Direct Memory Access) be used to disconnect the memory 011 from the microcomputer.

In this town, this circuit device can be mainly composed of digital circuits including a microcomputer, and the transversal filter (5) also uses a solid-state extension line such as a CCD and has variable integration, so it is relatively low cost. It is possible to incorporate a television receiver at low cost.

Next, the drawbacks of the conventional method will be explained.

Figure 8 is a specific circuit diagram of the clamp/A/D conversion circuit (7) in Figure 2, where E is the output (M) of the transversal filter (5), and transistor Q1 converts this signal to a predetermined level. Transistors Q2, Q3 and capacitor C1 clamp the signal from the collector of Ql to a point higher than the reference potential (ground potential) by the forward voltage drop of diode D1 using clamp pulse 1. )1 is used to cancel the voltage drop between the base and emitter of the transistor Q4 for output impedance conversion, and to set the pedestal level of the signal to the input terminal of the A/D converter 0υ to ground. This clamp pulse F excludes one horizontal period centered on the leading edge of the vertical synchronizing signal.

The emitter of Q4 is the signal input terminal V of the A/D converter 0υ
connected to S. Vref is a conversion reference voltage. The digital output terminal of A/D converter 09 is VDO~VDN
until memory O via tri-state buffer 7(2)
Connected to [). When performing DMA, G is connected to the A/D converter Q via the tri-state buffer (2).
This is a pulse for connecting the timing pulse 1) to the memory OQ, and is generated by the timing pulse generation circuit (8) shown in FIG.

With such a configuration, AGC at the video intermediate frequency stage does not work for television signals that include close negative ghosts, and the negative ghost portion becomes larger than the specified level, causing the A/D converter αυ exceeds the conversion range of FIG. 4 shows this state. (6) shows the leading edge of the vertical synchronization signal in the case of a television signal that does not include ghosts. (di is the case where a positive ghost is included. In the case of (A) and (D), the AG at the top of the synchronization signal
When C is applied, the A/D conversion range will not be exceeded. (C) is a case of close negative ghosts, and the top part of the synchronization signal with such a narrow width is middle 1. In the AGC detection section of the inter-frequency stage, the peak is not held, but the remaining part is actively held, and as shown in the figure, the area near the leading edge of the vertical synchronization signal exceeds the conversion range of the A/D converter θυ. It ends up. The location and size of the ghost is A
/D converted digital data, but if the vertical synchronization n'1NPt part exceeds the conversion range, its leading edge cannot be found from the digital data. It's gone.

In general, there are various types of A/T) converters, but those with one overflow terminal φ so that they can be used in parallel with an Al1) converter to increase the number of bits. be. In such an A/D converter having one overflow terminal, when overflow occurs, data outputs other than the overflow output become 01. Therefore, if the A/D converter Qυ is an A/D converter with one overflow terminal, the overflow terminal will be °1" and the other data outputs will be "'0", and the calculation will be difficult. Mistakes occur.

Purpose of the Invention The present invention provides a ghost removal device using a transversal filter that calculates the position and size of a ghost based on the digital data by A/D converting the output of the transversal filter. When I did Tegaku-sama, the AGC was not fully plowed due to the ghost Al1)
The conversion range of the converter is exceeded, and the overflow output of the A/D converter is 1'1" and other data outputs are °'0.
The purpose is to prevent calculation errors from occurring.

Structure of the Invention The present invention has a transversal filter to which a composite video signal is applied to its input, and calculates the position of a ghost based on data obtained by digitally converting the output of the transversal filter with an A/D converter. The configuration is configured to calculate the magnitude and modify the weighting coefficient of the transversal filter to obtain a ghost-removed video signal from the output of the transversal filter, and performs A/D conversion based on the overflow output of the A/D converter. It is characterized by controlling the amplification gain of the signal applied to the input of the amplifier.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described based on FIG. 6. Components similar to those in FIG. 8 are given the same reference numerals and their explanations will be omitted.

In FIG. 5, an overflow terminal OF of the A/D converter θη is connected to the base of a transistor Q5 via a resistor R5, and a resistor R6 is connected between the base of Qs and ground. When the conversion range of the A/D converter 01) is exceeded, use the signal at the overflow one terminal OF to make Qs conductive, and short-circuit the collector resistor R4 of transistor Q1. f is used to lower the gain of the inverting amplifier.

With this kind of configuration, even if the AGC as described above works, the situation where the conversion range is exceeded due to ghosting can be avoided.
The overflow of the D converter α9 is detected by the terminal OF, and the input to the A/D converter Oυ can be forcibly reduced. can be detected by calculation from the output digital value.

As described in the detailed description of the invention, according to the present invention, in order to control the amplification gain of the signal to the A/D converter that digitally converts the output of the transversal filter by the overflow output of the A/D converter, the synchronization signal is Be sure to check the leading edge of A/D.
Calculation can be detected from the output digital value of the converter. In addition, AGC of the video intermediate frequency stage of a television digital receiver is generally performed by detecting the top of the synchronizing signal, but since it is not possible to completely hold the peak, if a signal containing a negative ghost in the vicinity is received, the specified Although AGC cannot be applied to the level, according to the present invention, the position and size of the ghost are always calculated from the digital data transferred by DMA with the leading edge of the vertical synchronization signal as a reference, so AGC is sufficient. It is possible to stably remove ghosts from television signals, including ghosts such as those that do not work, and in normal cases, the input level to the A/D converter should be kept high. Since it is possible to do this, detection accuracy is also important, and ghost removal accuracy is also important.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of a ghost removal device built into a television receiver, and Fig. 2 is a configuration diagram of a conventional ghost removal device.
8 is a specific configuration diagram of the main part of FIG. 2, FIG. 4 is an explanatory diagram of the conversion range and input signal level of the A/D converter, and FIG. 5 is an illustration of an embodiment of the ghost removal device of the present invention. It is a specific configuration diagram of main parts. (5)...Transversal filter, (6)...
Add'M coefficient correction circuit, (7)...Clamp/Al1
) conversion 11j 1 path, (8)...timing pulse generation circuit, (9)...ri14 arithmetic circuit, (11...memory, (10...A/D converter, overflow terminal for OF) , Q1-Q5...transistor, R3R4
Rs Re... Resistance agent Yoshihiro Moriki Figure 3 CK Figure 1

Claims (1)

[Claims] 1. It has a transversal filter to which a composite video signal is applied to the input, and the output of this transversal filter is converted into digital data using an A/D converter. Based on the data obtained, the degree of deterioration of the ghost is estimated. The configuration is configured to calculate a weighting coefficient of the transversal filter to obtain a ghost-removed video signal from the output of the transversal filter, and to obtain a ghost-removed video signal from the output of the transversal filter. applied to the input (
A ghost removal device that controls the amplification gain of r48.