JPH0237155B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION FIELD OF INDUSTRIAL APPLICATION The present invention relates to a ghost removal device that can be used in television receivers.

Conventional configuration and its problems In recent years, when receiving television broadcasts,
Deterioration of received images due to various types of radio wave interference is becoming more and more problematic. In particular, so-called ghost development, in which received images become double or triple, has become more common, mainly due to the rise in the heights of buildings in urban areas. 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 horizontal stack antennas, but none of these measures are effective. It has not become widespread due to the above 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. FIG. 1 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 an intermediate frequency modulated signal from a tuner to obtain a baseband composite video signal A. This composite video signal A
is a signal of 0 to 4.2MHz in the NTSC system. In a typical television receiver, 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. The ghost removal device 2 has a function of inputting the composite video signal A, removing the ghost signal, and then supplying the ghost-free composite video signal B to the circuits 3 and 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 H(s), and the transfer function in the propagation system due to ghosts is G.
(s), the transfer function of the total signal propagation system including the ghost is H(s)·G(s). On the other hand, since the transversal filter 5 and adder circuit 12 in FIG. 2 can have any transfer function, the inverse transfer function G ^-1 of the propagation system due to ghosts
(s), ghosts can be removed.

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 ^-1 (s) corresponding to the ghost at each time. Ghost detection, calculation,
It performs operations such as generating and storing weighting coefficients. In the figure, A is an input composite video signal, B is an output composite video output from which ghosts have been removed, and D is a synchronization signal.

Ghosts in a received television signal are detected by observing the flatness of the signal before and after the beginning (leading edge) of the vertical synchronization signal. Ideally, this portion of the signal can be regarded as a unit step function, and if there is a ghost, distortion of the unit step function is detected accordingly. For example, the location and size of a ghost is detected at each sampling point. In order to extract this portion of the signal, a timing pulse generation circuit 9 generates each control pulse based on the output D of the synchronization signal generation circuit 8.

The input composite video signal A and the output of the transversal filter 5 are added together in an adder circuit 12, and the composite video signal B via the AGC circuit 13 is applied to the clamp/AD conversion circuit 7, where it is clamped to eliminate DC fluctuations and then AD The ghost information is converted into digital data and stored in the memory 11.

The arithmetic circuit 10 processes the ghost information stored in the memory 11 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. The weighting coefficient correction circuit 6 is used to actually generate and hold a weighting coefficient for each tap based on the calculation result, and since the output of this calculation circuit 10 is normally a digital signal, the weighting coefficient is an analog signal. If so, a DA converter circuit is required, and in that case it is also included.

In addition, since such detection → calculation → weighting is performed repeatedly by a so-called adaptive equalization method, the weighting coefficients are modified one after another many times, and the previous coefficient memory 11 is need to be memorized. In addition, since the sampling frequency of the AD conversion circuit in circuit 7 handles composite video signals, it is necessary to be three times the band frequency, and in the NTSC system, 10.7MHz, which is three times the chroma subcarrier frequency, is often used. , this AD conversion circuit requires high speed. The memory 11 is also often high-speed, and a microcomputer is also used as the arithmetic circuit 10, so the memory 11 is not very high-speed and can only be used from the microcomputer when the AD conversion circuit is handling the vertical synchronization signal part. An operation using so-called DMA (direct memory access) can be performed.

Further, in order to keep the amplitude of the composite video signal B from which ghosts have been removed constant, an AGC circuit 13 is provided after the adder circuit 12 to receive an appropriate sampling pulse from the timing pulse generation circuit 9 and keep the amplitude of the synchronization signal constant. .

In order to start the ghost removal operation described above,
A reset pulse E is generated from the reset circuit 14 and supplied to each block. A concrete circuit of this reset circuit 14 is shown in FIG. As seen in FIG. 4, a reset pulse E is generated by operating the manual switch SW1. Therefore, when the ghost removal device is built into a television receiver or used as an adapter, it is necessary to operate the manual switch mentioned above to restart the operation of the ghost removal device every time the reception channel of the television receiver is changed. It's quite annoying.

OBJECTS OF THE INVENTION In view of the above-mentioned problems, an object of the present invention is to provide a device that automatically detects a change in a reception channel of a television receiver and automatically performs ghost removal processing.

Structure of the Invention In the present invention, a loss of a synchronization signal is detected from a signal obtained by synchronously separating a composite video signal, a change in the amount of ghost is detected from a ghost detection section of a ghost removal device, and both detection signals are gated. Now, it detects changes in the reception channel and automatically restarts the ghost removal operation.

DESCRIPTION OF THE EMBODIMENTS A block diagram of an embodiment of the present invention is shown in FIG. Blocks in FIG. 3 that are the same as those in FIG. 2 are given the same numbers. Further, the ghost removal operation has been described in the description of the conventional example, so it will be omitted, but the difference from the conventional example is the automatic reset circuit 16.

The automatic reset circuit 16, which is a feature of this circuit, will be explained with reference to FIGS. 5 and 6. FIG. 5 is a block diagram of the automatic reset circuit 16, and FIG.
This figure is a waveform diagram for explaining the operation of FIG. 5.

First, the horizontal synchronizing signal F is supplied from the synchronizing signal generating circuit 8 to the retrigger mono multivibrator 21 at the first stage. The output is supplied to the next-stage retrigger mono-multivibrator 22, and the output pulse H
get. In other words, by designing the pulse width of the first-stage trigger mono multivibrator 21 to be longer than the horizontal synchronization period, the pulse width is normally kept at a constant level, even if the horizontal synchronization signal is lost by changing the reception channel of the television receiver (see Figure 6). A pulse can be generated during the period A of F). Further, the retrigger mono-multivibrator 22 at the next stage receives the pulse from the previous stage and widens the pulse width to obtain the horizontal synchronization signal missing detection pulse H. If only this pulse H is observed, even on the same channel, the signal may be lost for a period of several hundred microseconds, for example, when the broadcasting station's camera is switched, or there is a seam between programs, and the above-mentioned detection pulse H may occur. be. Therefore, the arithmetic circuit 10 of the ghost detection section constantly monitors changes in the ghost, and when the state of the ghost changes, generates a ghost change detection pulse G for a certain period, and generates the horizontal synchronization signal missing detection pulse H and the gate circuit 2.
3 to generate an automatic reset pulse E. By doing this, the reset pulse E necessary for the ghost removal device can be automatically obtained. The specific circuit of the block is well known and will therefore be omitted, but it can be constructed using an inexpensive integrated circuit.

Effects of the Invention As explained above, according to the present invention, the operation of the ghost removal circuit is restarted only when the receiving channel changes and the ghost changes stably for a certain period of time. The ghost removal process, which used to be a troublesome operation, can now be restarted automatically and reliably.
A more appropriate ghost removal operation can be performed.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the main parts of a television receiver including a ghost removal device, FIG. 2 is a block diagram of a conventional ghost removal device, and FIG. 3 is an overall block diagram of a ghost removal device according to an embodiment of the present invention. figure,
FIG. 4 is a circuit diagram showing a specific circuit example of a conventional reset circuit, FIG. 5 is a block diagram of an automatic reset circuit used in a device according to an embodiment of the present invention, and FIG. 6 is an operation of the circuit shown in FIG. 5. It is a waveform diagram for explanation. 5... Transversal filter, 6... Weighting coefficient correction circuit, 7... Clamp/AD conversion circuit, 8...
Synchronous signal generation circuit, 9... Timing pulse generation circuit, 10... Arithmetic circuit, 11... Memory, 12... Addition circuit, 16... Automatic reset circuit, 21, 22... Retrigger mono-multivibrator, 23... Gate circuit.

Claims (1)

[Claims] 1. An addition circuit and a transversal filter, a weighting coefficient correction circuit and an arithmetic circuit for controlling the transversal filter, an AD conversion circuit for detecting ghosts, a memory, a timing pulse generation circuit, and ghost removal means having a synchronization signal generation circuit; means connected to an output end of the synchronization signal generation circuit to detect the presence or absence of a synchronization signal; and means connected to an output end of the arithmetic circuit for detecting a change in ghost. and restarting the operation of the ghost removal means when the detection output signal of the synchronization signal presence/absence detection means indicating the lack of the synchronization signal and the detection output signal of the ghost change detection means indicating that the ghost has changed are input. What is claimed is: 1. A ghost removal device comprising means for emitting a reset signal for starting.