JPH0211068A - Ghost removing device - Google Patents

Abstract

PURPOSE:To prevent the picture quality deterioration due to the oscillation by changing to a non-cyclic type with the switching of a switch when a cyclic type normal ghost removing performance is reduced over the prescribed limit. CONSTITUTION:An ordinary ghost removing part 20 can be constituted to both cyclic type and non-cyclic type by the connection change based on the switching of switches 31-34 and constituted to the cyclic type at the normal time. Control parts 26-28, when they detect that the ghost removing performance is reduced over the prescribed limit while the ordinary ghost removing part 20 is constituted to the cyclic type or receives the command from the external part, reconstitutes the ordinary ghost removing part 20 to the non-cyclic type. Thus, since the part is changed to the non-cyclic type only at the time of the oscillation generation, the deterioration of the picture quality can be prevented.

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, although there are differences in degree.

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.

The ghost removal device used to remove such ghosts uses a pseudo-ghost generation circuit consisting of a transversal filter and a waveform (referred to as a "reference waveform") at a predetermined location of the received television signal. It consists of a ghost detection circuit that detects the state of occurrence of ghosts and controls the tap gain supplied to the transversal filter, and a signal synthesis circuit that synthesizes the original received television signal and the pseudo ghost generated from it. .

The ghost detection circuit holds in advance a reference waveform before being affected by ghosts contained in the television signal sent out from the broadcasting station (and also detects distortion from the actually received television signal due to the influence of ghosts). A pseudo-ghost generation circuit consisting of a transversal filter that receives this tap gain detects the influence of ghost from the relationship between the two, and generates a tap gain to remove the ghost. A pseudo-ghost is generated by simulating the mechanism of ghost generation based on multiple reflections, such as attenuation and mutual addition, using a delay circuit group, a coefficient circuit group, and an adder circuit connected in series. It is 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.

The ghosts mentioned above are close ghosts that appear almost at the same time as the original signal (including slightly ahead of it), and ghosts that appear several μ from the original signal.
Ghosts are broadly classified into normal ghosts that appear after a delay of about 2 seconds.

Further, methods for adding the pseudo ghost generated from the original television signal to the original television signal include an acyclic (feedforward) addition method and a cyclic (feedback) addition method. Conventionally, an acyclic addition method has been used to remove nearby ghosts, and a cyclic addition method has been used to normally remove ghosts.

That is, as shown in FIG. 4, the conventional ghost removal device is formed separately into a non-recursive type proximity ghost remover circuit 60 and a recursive type normal ghost remover circuit 70.

In the acyclic proximity ghost removal circuit 60, the input terminal I
The received television signal appearing at N is supplied to one input terminal of the adder 64 via the delay section 63 and is also supplied to the nearby ghost detection section 61 .

The pseudo proximity ghost generated by the pseudo proximity ghost generation section 62 according to the detection result of the proximity ghost detection section 61 is supplied to the other input terminal of the addition section 64 and added to the original received television signal. On the other hand, the normal ghost removal circuit 70
Here, the normal ghost detection section 71 detects a normal ghost from the television signal from which the proximity ghost has been removed and is output from the addition section 74 and supplies it to the pseudo normal ghost generation section 72 . The pseudo-normal ghost generating section 72 generates a pseudo-normal ghost according to the detection result of the normal ghost detecting section 71, supplies it to one input terminal of the adding section 73, and generates a pseudo-normal ghost according to the detection result of the normal ghost detecting section 71, and supplies it to one input terminal of the adding section 73, and generates a pseudo-normal ghost that is supplied to the other input terminal of the pseudo-normal ghost. Add to television signal.

In this way, the ghost removal circuit usually has a cyclic configuration. Generally, a ghost removal device generates child ghosts in order to remove a parent ghost. In this respect, the cyclic type has higher ghost removal performance than the non-cyclic type because it is capable of removing child ghosts that occur when removing parent ghosts, and grandchild ghosts that occur when removing child ghosts. Become.

On the other hand, in order to remove nearby ghosts, including pre-ghosts that appear before the original television signal, a delay circuit that delays the original television signal by the time required to detect and generate the ghost is required. For this reason, an acyclic configuration as shown in FIG. 4 must be used.

(Problem to be Solved by the Invention) In the conventional ghost removal device described above, the ghost removal circuit usually has a cyclic configuration, so it usually exhibits higher ghost removal performance than a non-cyclic type. . However, in this cyclic configuration, there is a risk that the loop gain may exceed 1 depending on the size and form of the ghost, causing oscillation, and there is a problem in that the image quality is deteriorated accordingly.

(Means for Solving the Problem) The ghost removal device of the present invention can be configured as either a cyclic type or a non-cyclic type by changing the connection based on switching between Sui and Sochi, and can be configured as a cyclic type in normal times. When the normal ghost removal section detects that the ghost removal performance has decreased beyond a predetermined limit or receives an external command when the normal ghost removal section is configured in a cyclical manner, the normal ghost removal section The controller is configured to change the configuration to the acyclic type only when oscillation occurs, thereby preventing deterioration of image quality.

According to one embodiment of the present invention, an acyclic proximity ghost removal circuit is arranged before the above-mentioned normal ghost removal circuit.

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, in which 1 is an A/D conversion circuit, 10 is a proximity ghost removal circuit, and 20 is a normal ghost removal circuit. be.

The proximity ghost removal circuit 10 includes a proximity ghost detection section 11
and a pseudo proximity ghost generation unit 12 connected in an acyclic manner.
, a delay section 13, and an addition section 14.

On the other hand, the normal ghost detection circuit 20 at the subsequent stage can be configured into either a cyclic type or a non-cyclic type by changing the connection by switches 31, 32, 33, and 34 that are switched in conjunction with each other. That is, in the connected state where the switches 31 to 34 are switched to the upper contact a side, the switch 31
, the adder 23, the normal ghost detector 21, the pseudo normal ghost generator 22, the switch 33, and the switch 34 constitute a cyclic normal ghost removal circuit. On the other hand, in the connected state in which the switches 31 to 34 are switched to the lower contact side, the switches 31 and 32
, normal ghost detection unit 21, receiving normal ghost generation unit 2
2, the switch 33, the adder 24, and the switch 34 constitute an acyclic normal ghost removal circuit. This normal ghost removal circuit 20 is normally configured in a cyclic type.

The normal ghost detection section 21 in FIG. 1 typically includes a timing signal generation section 42, a zero level detection section 43, a normalization section 44, a reference waveform holding section 45, 46, a difference calculation section 47, and a tap gain holding section. It consists of 48.

The received television signal from which the proximity ghost has been removed, which is normally supplied to the input terminal I of the ghost detection section 21, is supplied to the timing generation section 42. The timing generation section 42 extracts a synchronization signal from the television signal and generates a timing signal to be supplied to each section within the normal ghost detection section 21, such as the zero level detection section 43 and the standardization section 44.

Further, the reference waveform from which the proximity ghost has been removed is supplied to the zero level detection section 43 and the normalization section 44 . The zero level detection unit 43 detects the zero level of the reference waveform by detecting a time difference between sampling points before and after the reference waveform, and taking the average value of the amplitude of only the sampling points where this time difference is less than a predetermined value. do. The standardization unit 44 temporarily holds the sampling points of the reference waveform included in the received television signal, and standardizes each sampling point using the zero level received from the zero level detection unit 43.

The difference calculation unit 47 calculates the correspondence between the sampling points of the normalized reference waveform extracted from the received television signal and held in the reference waveform holding unit 46 and the undistorted reference waveform held in advance in the reference waveform holding unit 45. The difference from the sampling point is calculated and supplied to the tap gain holding section 48 as the tap gain of the transversal filter constituting the pseudo ghost generation section 22 in FIG.

As shown in FIG. 3, the transversal filter constituting the pseudo-ghost generation section 22 in FIG. 1 includes delay units 52 a and 52 b connected in series in multiple stages.

52c...52n, and multipliers 53a and 53b for multiplying the respective outputs of these delay devices by tap gain.
, 53C...53n and an adder 54 for adding the respective outputs of these multipliers, and an A/D converter 51 and a D/A converter 55 placed before and after these multipliers. A pseudo-normal ghost is generated based on the tap gain supplied from the section 21. The pseudo-normal ghost generated by this transversal filter is combined with the television signal in adders 23 and 24, and is canceled out by the ghost contained therein.

The normal ghost detection section 25 shown in FIG. 1 has the same configuration as the normal ghost detection section 21 shown in FIG. This normal ghost detection section 25 detects the normal ghost-removed television signal which is output from the normal ghost removal circuit to the output terminal OUT in a cyclical configuration as the switch 31 is switched to the contact a side. The normal ghost included in the oscillation detection section 26 is detected and supplied to one input terminal of the oscillation detection section 26. The detection result of the normal ghost detection unit 21 is supplied to the other input terminal of the oscillation detection unit 26, which is based on the normal ghost contained in the television signal before the normal ghost removal that appears before the addition unit 23. It is nothing but a detection result.

The detection result of each normal ghost supplied to the oscillation detection section 26 is the difference between the actually received reference waveform and the undistorted reference waveform held in advance. Therefore, the magnitude of both amplitudes corresponds to the magnitude of the detected ghost. The oscillation detection unit 26 averages and compares the detection results before ghost removal and the detection results after ghost removal supplied from the detection units 21 and 25 over a predetermined time width, and if the latter exceeds the former, Since the number of ghosts has increased as a result of ghost removal, it is assumed that cyclic specific oscillation has occurred, and a high signal is output onto the signal line 36.

This high signal passes through OR gate 28 and sets flip-flop 27, raising its output high. As the output of the flip-flop 27 rises to high, the contacts in each of the switches 31 to 34 are switched from the a side to the b side, and the configuration of the normal ghost removal circuit 20 changes from the conventional cyclic type to an acyclic type. Be changed. The normal ghost removal circuit 20 thereafter operates as an acyclic type, and returns to the cyclic type when the flip-flop 27 is reset by an overflow of the timer 29 activated by the high output of the oscillation determining section 26. The configuration change from the above-mentioned cyclical type to a non-cyclical type was made by the viewer who noticed the deterioration of the screen by switching the switch 3.
Open 5 and go through or gate 28 to flip flop 2
This is also done by supplying a high signal to 7.

The above has exemplified a configuration in which when the number of ghosts increases due to the cyclic normal ghost removal processing, it is assumed that oscillation has occurred and the process is changed to the non-cyclic type. However, if the ghost removal performance is lower than the typical removal performance of the acyclic type, it may be assumed that oscillation has occurred and the system switches to the acyclic type.

Further, although a configuration in which a proximity ghost removal circuit is installed before the normal ghost removal circuit has been illustrated, the installation may be omitted if deterioration of image quality due to proximity ghosts is not a problem.

In addition, although the configuration in which the zero level detection section is installed in the normal ghost detection section in Fig. 2 is illustrated, this zero level detection section may be omitted if a step waveform is used as the reference waveform instead of a pulse waveform. .

(Effects of the Invention) As described above in detail, the ghost removal device of the present invention has a configuration in which when the normal ghost removal performance of the cyclic type decreases beyond a predetermined limit, it changes to the non-cyclic type by switching a switch. Therefore, it is possible to effectively prevent image quality deterioration due to oscillation that may occur in high-performance cyclic type.

[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 block diagram illustrating the configuration of the normal ghost detection section 21 shown in FIG. 1, and FIG. FIG. 4 is a block diagram illustrating the configuration of the pseudo-normal ghost generation section 22, and FIG. 4 is a block diagram illustrating the configuration of a conventional ghost removal device. 10... Proximity ghost removal circuit, 20... Normal ghost removal circuit, 21.25... Normal ghost detection section,
22...Pseudo-normal ghost generation unit, 23.24...
Addition unit, 26... Oscillation determination unit, 27... Flip.
Flop. Patent applicant: NEC Home Electronics Co., Ltd.

Claims (2)

[Claims] (1) A normal ghost removal section that can be configured as either a cyclic type or a non-cyclic type by changing the connection based on switching of a switch, and is normally configured as a cyclic type; This normal ghost removal section is configured as a cyclic type. and a control unit that reconfigures the normal ghost removal unit to a non-cyclic type when detecting that the normal ghost removal performance has decreased beyond a predetermined limit in the state where the normal ghost removal unit is in use, or upon receiving an external command. A ghost removal device characterized by: (2) The ghost removal device according to claim 1, wherein a non-recursive proximity ghost removal device is disposed at the front stage.