JPH01268361A - Ghost eliminating device - Google Patents

Abstract

PURPOSE:To restore the pedestal level, which is shifted by the ghost level in accordance with the ghost elimination processing, to a prescribed clamp level by clamping the pedestal level not only just before the ghost elimination processing but also after this processing. CONSTITUTION:This device consists of a ghost eliminating part 10, a clamping part 11 provided between the ghost eliminating part 10 and an input terminal IN, a reclamping part 12 provided between the ghost eliminating part 10 and an output terminal OUT, and a clamp pulse generating part 13 which generates clamp pulses CP1 and CP2 to be supplied to the clamping part 11 and the reclamping part 12. The pedestal level of the reception television signal outputted from the ghost eliminating part 10 is clamped to a prescribed value again. As the result, extraction of a synchronizing signal in a picture quality improving processing part of the succeeding stage and level control in a video amplifying part or the like are surely performed, and the degradation in picture quality which occurs in a conventional device is effectively avoided.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a ghost removal device installed in a television receiver.

(Prior Art) In addition to signal components directly received by the antenna, a video signal received by a television receiver includes signal components that pass through various reflection paths from nearby trees, buildings, and moving objects such as vehicles. It also includes signal components that are received with a delay. Therefore, multiple images generally appear within the receiving screen, regardless of the degree of difference.

A signal component that causes multiple images to appear in the reception screen is called a ghost, and a phenomenon in which the multiple images become so large that they become an eyesore and the image quality deteriorates is called a ghost disturbance.

Such a ghost removal device includes a transversal filter for generating pseudo-ghosts, and detects the occurrence of ghosts from a reference waveform inserted at a predetermined position in a received television signal, and calculates the tap gain of the transversal filter. It is composed of a tap gain control circuit that controls the tap gain control circuit, and a signal synthesis circuit. This transversal filter generates pseudo-ghosts by simulating the ghost generation mechanism based on multiple reflections of signal delay, attenuation, and mutual addition using a delay circuit group, a coefficient circuit group, and an adder circuit connected in series. . This pseudo-ghost is usually generated with opposite polarity, is added to the original received television signal in a signal synthesis circuit, and is canceled out by the ghost component contained therein.

In order to improve the performance of the ghost removal device, it is necessary to extract the reference waveform in the tap gain control circuit at highly accurate timing. To achieve this highly accurate reference waveform extraction timing, it is necessary to stabilize the signal level. Conventionally, in order to stabilize the signal level, as shown in FIG. The pedestal level of the John signal is fixed at a predetermined level.

(Problems to be Solved by the Invention) In television receivers including the conventional ghost removal device described above, pedestal clamping is performed before the ghost removal section, so subsequent processing such as the video amplification section and the image quality improvement processing section is performed. In this section, the pedestal clamp was omitted again.

However, deterioration of the display screen was observed, which was thought to be due to the omission of re-clamping in the latter stage. This is considered to be a deterioration in image quality due to a change in the pedestal level due to ghost removal, as will be explained in detail later regarding the operation of the present invention.

(Means for Solving the Problems) A ghost removal device of the present invention includes a clamp section that clamps the pedestal level of a received television signal to a predetermined value, and a ghost removal process for the received television signal output from the clamp section. and a re-clamping section that re-clamps the pedestal level of the received television signal outputted from the ghost removing section to the predetermined value, and prevents deterioration of the display screen by re-clamping after the ghost removal processing. configured to prevent

Hereinafter, the operation of the present invention will be explained in detail together with examples.

(Embodiment) FIG. 1 is a block diagram showing the configuration of a ghost removal device according to an embodiment of the present invention.

This ghost removal device includes a ghost removal section 10, a clamp section 11 installed between the ghost removal section 10 and an input terminal IN, and a ghost removal section 10 and an output terminal OU.
A clamp pulse C is supplied to the re-clamping section 12 installed between the re-clamping section 12 and the clamping section 11 and the re-clamping section 12.
It is composed of a clamp pulse generation section 13 that generates P, , cpz.

As shown in FIG. 2, the clamp section 11 and the re-clamp section 12 are supplied with a resonant circuit of a color subcarrier frequency (3.58 MHz) formed by parallel connection of a capacitor C and a coil L, and a clamp pulse generation section 13. Clamp pulse C
A switch S that is selectively closed at the pedestal level before and after the color burst in synchronization with P+ (or CPz)
and a battery E that outputs a predetermined clamp level. The television signal supplied from the input terminal I is output from the output terminal O while its pedestal level is fixed at a predetermined voltage value by the battery E.

Assume that the received television signal, that is, the original waveform, in the case where no ghost exists is shown in FIG. 3(A). It is assumed that a ghost waveform shown in FIG. 3(B) is generated from such an original waveform (A).

This ghost waveform (B) exemplifies the occurrence of a positive ghost in which the original waveform (A) appears in phase with a predetermined time delay. Therefore, in the example of FIG. 3, the waveform of the actual received television signal supplied to the clamp circuit 11 from the input terminal IN of FIG. 1 is the original waveform (A) plus the ghost waveform (
B) becomes the superimposed waveform (C). In the waveform (C) of this received television signal, its pedestal level PL
is raised above the clamp level CL due to the influence of the positive ghost.

The clamp circuit 11 applies pedestal clamping to the waveform (C) of the received television signal affected by the positive ghost by lowering its pedestal level PL to a predetermined clamp level CL. The signal is converted into the waveform (D) shown in the figure and is supplied to the ghost removal section 10. The ghost removal unit 10 converts the pedestal clamped waveform (D) into the waveform (E) shown in FIG. 3 by performing ghost removal processing on the waveform (D).

This ghost removal process is nothing but subtracting the ghost waveform (B) from the waveform (D) after pedestal clamping. Therefore, in the waveform (E) after ghost removal, the pedestal level PL is slightly lower than the ghost level than the clamp level CL. As a result, if an attempt is made to process the ghost-removed waveform as it is using a re-clamping section as in the prior art, failures will likely occur in synchronization signal extraction, level control, etc., resulting in deterioration of image quality.

On the other hand, the re-clamping section 12 of the ghost removal device shown in FIG. Perform re-clamping to raise it to CL. That is, as shown in the waveform (F) in FIG. 3, a normal television signal from which ghosts have been removed and whose pedestal level is fixed at a predetermined clamp level is output from the re-clamp section 12, and the pedestal clamp section is It is supplied to the subsequent image quality improvement processing unit and video amplification unit that do not have the same function.

The present invention has been described in detail above using the case of a positive ghost as an example, but it is clear that the configuration of the present invention can be applied to any ghost such as a negative ghost that appears in an opposite phase with a predetermined time delay from the original signal. It is.

Further, although the configuration in which the clamp section and the re-clamp section are realized by analog circuits has been illustrated, this may be realized by digital circuits.

(Effects of the Invention) As described above in detail, the ghost removal device of the present invention is configured to perform clamping immediately before the ghost removal process as well as re-clamping after the ghost removal process. The pedestal level that has shifted by the ghost level can be returned to the predetermined clamp level.

As a result, the extraction of the synchronization signal in the subsequent image quality improvement processing section, the level control in the video amplification section, etc. become reliable, and the deterioration in image quality that occurs in conventional devices can be effectively avoided.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a ghost removal device according to an embodiment of the present invention, FIG. 2 is a circuit diagram illustrating the configuration of the clamping section and re-clamping section shown in FIG. 1, and FIG. 3 is the circuit diagram shown in FIG. 1. FIG. 4 is a waveform diagram for explaining the operation of the conventional ghost removing device. FIG. 4 is a block diagram of the configuration of the conventional ghost removing device. 10... Ghost removal section, 11... Clamp section, 1
2... Re-clamp section, 13... Clamp pulse generation section, IN... Input terminal, OUT... Output terminal, PL
...Pedestal level, CL...Clamp level. Patent applicant: NEC Home Electronics Co., Ltd.

Claims (1)

[Claims] A clamp section that clamps a pedestal level of a received television signal to a predetermined value; a ghost removal section that performs ghost removal processing on the received television signal output from the clamp section; A ghost removal device comprising: a re-clamping section that re-clamps a pedestal level of an output received television signal to the predetermined value.