JP2614638B2 - Ghost removal device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a ghost removal device installed in a television receiver.

(Prior Art) In addition to a signal component directly received by an antenna, a video signal received by a television receiver undergoes some reflection paths through various reflection paths by nearby moving objects such as trees, buildings, and vehicles. Signal components received with a delay are also included. Therefore, aside from the degree of difference, multiple images generally appear in the reception screen. A signal component that causes a multiplex image to appear in the reception screen is called a ghost, and a phenomenon in which the multiplex image becomes so large as to be unsightly and deteriorates the image quality is called a ghost disorder.

Such a ghost elimination device detects a ghost occurrence state from a transversal filter for generating a pseudo ghost and a reference waveform inserted at a predetermined portion of a received television signal, and detects a tap gain of the transversal filter. , And a signal synthesis circuit. This transversal filter generates a simulated ghost by simulating the mechanism of ghost generation based on multiple reflections such as signal delay, attenuation and mutual addition by cascaded delay circuits, coefficient circuits, and addition circuits. I do. This pseudo ghost is
Normally, the signal is generated with the opposite polarity, added to the original received television signal in the signal synthesis circuit, and canceled out with 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 a highly accurate timing. In order to realize this highly accurate reference waveform extraction timing, it is necessary to stabilize the signal level. Conventionally, in order to stabilize such a signal level, as shown in FIG. 4, a clamp unit 22 and a clamp pulse generating unit 23 are provided in front of a ghost removing unit 21 so that a receiving television set to be subjected to ghost removal is provided. The pedestal level of the John signal is fixed at a predetermined level.

(Problems to be Solved by the Invention) In the above-described television receiver including the ghost removing device, since the pedestal clamp is performed in the preceding stage of the ghost removing unit, the subsequent processes such as the video amplifying unit and the image quality improving processing unit are performed. The department omitted the pedestal clamp again.

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

(Means for Solving the Problems) A ghost elimination device according to the present invention includes a clamp unit for clamping a pedestal level of a received television signal to a predetermined value, and a ghost elimination process for the received television signal output from the clamp unit. A ghost removing unit to be applied and a re-clamping unit for re-clamping the pedestal level of the received television signal output from the ghost removing unit to the predetermined value, thereby preventing the display screen from deteriorating due to the re-clamp after the ghost removing process. It is configured to be.

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

(Embodiment) FIG. 1 is a block diagram showing a configuration of a ghost removing apparatus according to one embodiment of the present invention.

The ghost removing device includes a ghost removing unit 10, a clamp unit 11 installed between the ghost removing unit 10 and the input terminal IN, and a re-clamp installed between the ghost removing unit 10 and the output terminal OUT. It comprises a unit 12 and a clamp pulse generation unit 13 that generates clamp pulses CP ₁ and CP ₂ to be supplied to the clamp unit 11 and the re-clamp unit 12.

As shown in FIG. 2, the clamp unit 11 and the re-clamp unit 12 are supplied from a resonance circuit of a color subcarrier frequency (3.58 MHz) by connecting a capacitor C and a coil L in parallel, and a clamp pulse generation unit 13. Clamp pulse CP ₁ (or CP ₂ )
And a switch S that is selectively closed at pedestal levels before and after the color burst in synchronism with the above, and a battery E that outputs a predetermined clamp level. Input terminal I
Is output from the output terminal O while the pedestal level is fixed at a predetermined voltage value by the battery E.

It is assumed that the received television signal when no ghost exists, that is, the original waveform is (A) in FIG. It is assumed that a ghost waveform shown in FIG. 3 (B) is generated from such an original waveform (A). This ghost waveform (B)
Illustrates the occurrence of a positive ghost in which the original waveform (A) appears in phase with a delay of a predetermined time. Therefore, the third
In the example of the figure, the waveform of the actual received television signal supplied from the input terminal IN of FIG. 1 to the clamp circuit 11 is the waveform (C) in which the ghost waveform (B) is superimposed on the original waveform (A).
Becomes In the waveform (C) of the received television signal,
The pedestal level PL is higher than the clamp level CL due to a positive ghost.

The clamp circuit 11 performs a pedestal clamp on the waveform (C) of the received television signal affected by the positive ghost by lowering the pedestal level PL to a predetermined clamp level CL, thereby performing the pedestal clamp. The signal is supplied to the ghost removing unit 10 while being converted into the waveform (D) shown in FIG. The ghost removing unit 10 performs a ghost removing process on the pedestal clamped waveform (D),
This is converted into the waveform (E) in FIG. This ghost removal processing is nothing but subtracting the ghost waveform (B) from the waveform (D) after the pedestal clamp. Therefore,
In the waveform (E) after ghost removal, the pedestal level PL is lower than the clamp level CL by the ghost level. As a result, if it is attempted to process the ghost-removed waveform without re-clamping as in the past,
Failure to extract the synchronization signal, control the level, and the like is likely to occur, resulting in deterioration of image quality.

On the other hand, the re-clamp unit 12 of the ghost removing device of FIG. 1 sets the pedestal level PL of the television signal waveform (E) after the ghost removal output from the ghost removing unit 10 to a predetermined clamp level. Perform re-clamping to lift to CL. That is, as shown in the waveform (F) of FIG. 3, a normal television signal in which the ghost is removed and the pedestal level is fixed to the predetermined clamp level is output from the re-clamp unit 12, and the pedestal clamp unit is turned on. It is supplied to the image quality improvement processing unit and video amplification unit at the subsequent stage that do not have it.

As described above, the operation of the present invention has been described by taking the case of a positive ghost as an example, but it is apparent that the configuration of the present invention can be applied to any ghost such as a negative ghost that appears in antiphase while being delayed by a predetermined time from the original signal. It is.

Further, the configuration in which the clamp unit and the re-clamp unit are realized by an analog circuit has been illustrated, but this may be realized by a digital circuit.

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

As a result, the extraction of the synchronization signal in the image quality improvement processing section at the subsequent stage, the level control in the video amplification section, and the like are ensured, and the deterioration of the image quality that occurs in the conventional apparatus can be effectively avoided.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of a ghost removing apparatus according to one embodiment of the present invention, FIG. 2 is a circuit diagram illustrating the configuration of a clamp unit and a re-clamp unit in FIG. 1, and FIG. And FIG. 4 is a block diagram showing the configuration of a conventional ghost removing device. 10 Ghost removal unit, 11 Clamp unit, 12 Reclamp unit, 13 Clamp pulse generation unit, IN Input terminal, OUT Output terminal, PL Pedestal level, CL
... clamp level.

Claims (1)

(57) [Claims] 1. A clamp section for clamping a pedestal level of a received television signal to a predetermined value, a ghost removing section for performing a ghost removing process on a received television signal output from the clamp section, and an output from the ghost removing section. A re-clamp unit for re-clamping the pedestal level of the received television signal to the predetermined value.