JPH0161274B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a device for removing ghosts generated in a television transmission/reception system.

Conventional configuration and its problems In a television transmitting and receiving system, if the transfer function in the radio wave propagation system is H(S) and the transfer function of the propagation system due to ghosts is G(S), then the transfer function of the entire propagation system including ghosts is becomes H(S)・G(S).
It is well known that if a high-frequency signal is detected using synchronous detection as the detection method of a television receiver, the demodulated signal will not contain nonlinear elements even if the signal is transmitted using the vestigial sideband method. . Therefore, the propagation system by ghosts remains unchanged in a short time and can be regarded as a kind of linear filter. It is well known that ghosts can be removed by creating a transversal filter on the receiving side, which has a transfer function opposite to that of the ghost filter called G ^-1 (S). When the channel is switched in the receiver, the transfer function due to ghosts obviously changes. Therefore, it is necessary to modify the tap weighting coefficient of the transversal filter on the receiving side again by adaptive equalization.

FIG. 1 shows a block diagram of a conventional ghost removal device. A is a signal containing a ghost that has been synchronously detected and demodulated, and 1 is a transversal filter composed of a CCD or the like. Ghosts in received television signals are detected by using the leading edge of the vertical synchronizing signal as a reference signal and observing flatness before and after the leading edge. 4 is a clamp A/D conversion circuit that clamps the signal B that has passed through the transversal filter at the pedestal part and converts it into digital data, and only one horizontal period including the leading edge of the vertical synchronization signal is used as DMA (direct memory access). It is then transferred to memory 6. 5 is an arithmetic processing circuit consisting of a microcomputer, which calculates the position and size of the ghost based on the leading edge of the vertical synchronization signal from the waveform information transferred to the memory 6 by DMA, and performs tap correction. The information is sent to the weighting coefficient correction circuit 3. In addition,
The weighting coefficient correction circuit 3 is composed of a number of tap coefficient holding memories equal to the number of stages of the transversal filter 1 and the same number of D/A converters. 2 is a synchronization separation/timing generation circuit, which generates a sampling pulse indicating the leading edge of vertical synchronization, and 3fsc for DMA.
(10.73MHz) sampling pulse, address signal, etc.

The tap coefficient is controlled according to the following equation.

cj ⁿ⁺¹ = cj ⁿ +α・ej ⁿ cj: Tap coefficient of the jth stage ej: Ghost amount corresponding to the jth stage α: Value less than 1 n: Correction circuit Signal B passed through the transversal filter
When the control of the transversal filter is completed through adaptive equalization, a signal with ghosts removed or greatly reduced will be obtained. C is a signal indicating that the channel has been switched. Note that the tap coefficient correction operation ends when the maximum amount of ghosts, ej max, at the position corresponding to each tap becomes less than a certain value K. ej can be calculated by subtracting the digital values of adjacent sampling points and using the leading edge of vertical synchronization as the reference point.

In a ghost removal device having such a conventional configuration, the channel switching signal C notifies the arithmetic processing circuit 5 that the channel has been switched, and the tap weighting coefficient correction circuit of the transversal filter 1 is set to an initial value. The transfer function for ghost removal that was created when receiving the channel is set to G ^-1 (S) = 1, and a new ghost-based inverse transfer function is created using adaptive equalization to remove ghosts. was. However, if you continue to watch the same channel for a long time without switching channels, the ghost propagation system may be displaced due to the influence of rain, etc., and the tap weighting coefficient that was created and maintained at the time of channel switching may be affected. However, there were times when the ghosts could not be removed sufficiently. There are also devices that do not retain the tap coefficients and are configured to always perform adaptive equalization, but these have the drawback that they follow large external noises and the screen changes occasionally, making it difficult to see. It was hot.

Purpose of the Invention The present invention provides that, after switching the reception channel, the tap weighting coefficient of the transistor universal filter is once determined and held in order to remove ghosts, and even after the tap weighting coefficient is maintained, the amount of residual ghost is constantly monitored, and the amount reaches a certain value. When the above value is exceeded, the tap weighting coefficient is finely modified again even without switching the receiving channel to obtain good and stable ghost removal performance.

Structure of the Invention A transversal filter that receives a video detection output as an input and removes a ghost component included in the video detection output by correcting a tap coefficient, and a timing for receiving the video detection output as an input and detecting a reference signal for ghost detection. a generation circuit, an A/D conversion circuit that clamps and digitally converts the output of the transversal filter, and a fixed period of waveform information including a reference signal detected by the timing generation circuit from the output of the A/D conversion circuit. A first memory to store the ghost, and calculate the position and size of the ghost based on the reference signal from the waveform information stored in the first memory to output tap correction information, and also calculate the position and size of the ghost corresponding to each tap. an arithmetic circuit that outputs information indicating the largest amount of ghosts in the arithmetic circuit; a second memory that stores information indicative of the largest amount of ghosts output from the arithmetic circuit; a weighting coefficient correction circuit that stores tap correction information and corrects tap coefficients of the transversal filter; and means for releasing the holding of the tap correction information and restarting the tap correction operation when the amount of ghosts at positions corresponding to each tap in the second memory exceeds a predetermined amount. It is characterized by this.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG.

In FIG. 2, A is a detected signal including a ghost, B is a signal after ghost removal, and C is a signal indicating that the channel has been switched. 7 is a transversal filter having the same configuration as the transversal filter 1 shown in FIG. 1, 8 is the synchronous separation/timing generation circuit 2 shown in FIG. is the clamp shown in Figure 1.
The A/D conversion circuits 4 and 12 are the memory 6 in FIG.
and a circuit and memory each having the same configuration. 13 is a ghost amount storage memory. The arithmetic circuit 11 uses the conventional method to correct the tap coefficients, and in addition to starting and stopping the correction operation, always calculates the maximum amount of ghosts at the position corresponding to each tap.
Send ej max to ghost amount storage memory 13,
When the value of the ghost amount storage memory 13 exceeds a certain value W after the tap coefficient correction operation is completed, the tap coefficient holding memory of the weighting coefficient correction circuit 9 is configured to be corrected.

Because of this configuration, even after the tap coefficient is temporarily held after the channel is switched, even if there is a change in the ghost propagation system due to rain or the like other than the channel switching operation, the ghost removal operation is started again. Optimal ghost removal status can be obtained.

Effects of the Invention As explained above, according to the present invention, ghosts can always be removed in an optimal state, and when the ghost removal device is connected as an adapter to a television receiver having an existing video input/output terminal, the channel This is useful because the ghost removal device can be moved in response to changes in the ghost system (including when switching channels) even without a switching signal.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of a conventional ghost removal device, and FIG. 2 is a configuration diagram of an embodiment of a ghost removal device according to the present invention. 7... Transversal filter, 9... Weighting coefficient correction circuit, 10... Clamp/A/D conversion circuit, 11... Arithmetic processing circuit, 12... Memory,
13...Ghost amount memory.

Claims (1)

[Scope of Claims] 1. A transversal filter that receives the video detection output as input and removes ghost components included in the video detection output by correcting tap coefficients; a timing generation circuit that detects a signal; an A/D conversion circuit that clamps and digitally converts the output of the transversal filter; and a constant signal that includes a reference signal detected by the timing generation circuit from the output of the A/D conversion circuit. a first memory for storing waveform information of a period; and calculating the position and size of a ghost based on the reference signal from the waveform information stored in the first memory and outputting tap correction information. an arithmetic circuit that outputs information indicating the largest amount of ghosts at a position corresponding to the tap; a second memory that stores information indicating the largest amount of ghosts output from the arithmetic circuit; a weighting coefficient correction circuit that stores the tap correction information output from the arithmetic circuit and corrects the tap coefficient of the transversal filter; means for holding tap correction information when the amount of ghosts at positions corresponding to each tap in the second memory exceeds a predetermined amount; A ghost removal device characterized by having means for restarting the ghost.