JPS63189055A - Ghost eliminator - Google Patents

Abstract

PURPOSE:To perform the elimination of a ghost satisfactorily without shortening a sampling cycle, by attaching a delay time equivalent to the deviation of a timing between a sampling time and an origin in a tap gain control part on a pseudo ghost signal. CONSTITUTION:An origin deciding part 12 in the tap gain control part 1 monitors the output television signal of an A/D converter 11, and detects a sampling point nearest to each center part of a reference waveform and a ghost waveform, and decides it as the origin. The origin deciding part 12 calculates the deviation of the timing between the sampling time and the origin. The origin deciding part 12 controls the delay quantity of a variable delay circuit 6 by a time corresponding to the deviation. A tap gain corresponding to the ghost outputted from the tap gain control part 1 is inputted to a transversal filter which constitutes a pseudo ghost generating part 2. The output of the pseudo ghost generating part 2 is delayed by the delay time corresponding to the above stated deviation of the timing by the delay circuit 6, and is outputted to an adder 4 for offsetting the ghost.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a ghost removal device used in a television receiver.

Conventional technology In television receivers, delayed signals are superimposed on the signals directly received by the antenna, which are received after passing through various reflection paths from nearby terrain, buildings, and moving objects such as vehicles. Ru. For this reason, multiple images generally appear within the receiving screen, regardless of the degree of difference. The delayed signal that causes this multiple image to appear is called a ghost, and the phenomenon that this ghost becomes so large that it becomes an eyesore and deteriorates the image quality is as follows.
It is called ghost disorder.

Conventionally, in order to remove the above-mentioned ghosts, a ghost removing apparatus having the configuration shown in the professional diagram of FIG. 3 has been developed.

That is, in the pseudo-ghost generation circuit 2 composed of a transversal filter, signal processing is performed on the television signal on the input terminal 2 by a combination of delay and addition to generate a pseudo-ghost that is in opposite phase to the ghost. It is supplied to one input terminal of the adder 4. The other input terminal of the adder 4 is supplied with the television signal on the input terminal l via the delay circuit 3. Therefore, the television signal from which the ghost has been removed while being canceled out by the pseudo-ghost of the opposite phase is output from the adder 4, and is supplied to the subsequent stage via the output terminal 0.

As shown in the block diagram of FIG. 4, the pseudo ghost generation circuit 2 includes a plurality of delay devices 21a and 21 connected in series.
b...21n, multipliers 22a, 22b...22n that multiply the outputs of these delay devices by tap gains, respectively, and an adder 23 that mutually adds the outputs of these multipliers. It is made up of.

-i, ghosts change from time to time depending on various factors such as changes in the wavelength of received radio waves due to channel switching and traffic conditions of moving objects such as vehicles, aircraft, and ships passing nearby. Therefore, in the transversal filter constituting the pseudo-ghost generation circuit 2, it is necessary to simulate the ever-changing ghost by dynamically controlling the delay time and tap gain. The gain control circuit 1 in FIG. 3 that controls this delay time and tap gain is as follows:
It is equipped with an A/D converter 11, a base point determination circuit 12, a memory 13, and a difference calculation circuit 14, and calculates the delay time and tap gain to be dynamically controlled based on the ghost actually included in the television signal. These are register 5 and signal b?
The signal is supplied to the pseudo ghost generation circuit 2 via f24.25.

FIG. 5 is a conceptual diagram for explaining the operating principle of the ghost removal device shown in FIG. 3.

The tap gain control circuit 1 uses the television signal before and after the fall of the vertical synchronization signal shown in waveform (A) in FIG. 5 as a reference signal, detects ghosts from this reference signal, and detects ghosts.1. Determine the tap gain control signal and delay time. That is, when the falling portion of the vertical synchronizing signal is enlarged, as shown in waveform (B), an anti-phase ghost is generated that is delayed by a certain time τ and rises stepwise by g. This waveform (B)
is sampled at a predetermined period by the A/D converter 11 of the tap gain control circuit 1 and converted into a digital signal having an amplitude as shown in waveform (C).

Known base point determination unit 12. Memory 13 and difference calculation section 14
By subtracting the amplitude of the previous sampling point from the amplitude of each sampling point in the above waveform (C), a difference signal as exemplified in waveform (D) is created, and this is used as the tap gain to register 5. The signal is supplied to the pseudo ghost generation circuit 2 via the signal.

Having received this tap gain, the pseudo-ghost generation circuit 2 creates a pseudo-ghost with an opposite phase as shown in waveform (E) and supplies it to the adder 4. As a result, from the adder 4, the waveform (F)
As illustrated in , a television signal in which the ghost is canceled out and removed by a pseudo-ghost having an opposite phase is output.

Problems to be Solved by the Invention In the conventional ghost removal device shown in FIG. 3, if the sampling period of the A/D converter 11 is not shortened sufficiently, a discrete delay time approximated by an integral multiple of the sampling period will occur. and the actual continuous delay time can no longer be ignored,
There is a problem in that the ghost cannot be completely offset.

In order to shorten the sampling period sufficiently, a high-speed and expensive digital circuit is required, which increases the cost of the device.

Means for Solving the Problems A ghost removal device according to the present invention includes a tap that generates a pseudo ghost having a discrete delay time that is an integral multiple of a predetermined sampling period to simulate a ghost contained in a television signal. Variable gain transversal
a digital tap gain control unit that controls a tap gain to be set in the variable tap gain transversal filter based on a ghost contained in a television signal; and sampling and pulling points in the digital tap gain control unit; It is equipped with a variable delay circuit that adds a delay time corresponding to the timing deviation with the base point to the pseudo ghost or television signal, and is configured to achieve good ghost removal characteristics without significantly shortening the sampling period. .

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, where ■ is an input terminal, 1 is a tap gain control circuit, 2 is a pseudo-ghost generation circuit, and 3 is a delay circuit. , 4 is an adder, 5 is a register, 6 is a variable delay circuit, and 0 is an output terminal.

A specific waveform selected in the original television signal for ghost detection is referred to as a reference waveform, and the falling portion of the vertical synchronization signal as shown in FIG. 2(A) is used as such reference waveform. and set its amplitude to the standard value 1. Assume that a ghost waveform delayed by τ and whose amplitude is reduced to g appears in phase with respect to this reference waveform, as illustrated in waveform (B) of FIG. 2. Analog television signals containing the above reference waveforms and ghost waveforms are
The A/D converter 11 of the tap gain control circuit 1 samples the signal at a predetermined period T and converts it into a digital signal.

The base point determination unit 12 monitors the time change of the digital signals outputted from the A/D converter 11 and sequentially written into the memory 13, and determines the reference waveform and the ghost waveform that are closest to their center portions. A sampling point is detected and determined as a base point.

That is, taking the case of the ghost waveform (B) in FIG. 2 as an example and illustrating its enlarged waveform (C), the base point determination unit 12 first detects the center P0 of the falling portion by an appropriate method. For example, this center P0 is defined as the intersection of a downward-sloping straight line α that approximates the slope of the falling part and the midpoint β of the level between the sampling points sufficiently far away from the falling part. . Next, the base point determining unit 12 determines the sampling point g0 closest to the center P0 determined as described above as the base point. Base point g determined in this way. , and in front of it is a school of sampled fish g- with a predetermined sampling period T.
r, g-z... are defined, and the sampling fish school g with the same sampling period is also behind. l+g. 2...
is defined.

The subsequent difference calculation circuit 14 calculates a difference series ΔS-2 between adjacent sampling points based on the base point in the ghost waveform defined as described above and the sampled fish schools before and after the base point.
ΔS−1, ΔSo, ΔS * 1 + ΔS. 2...
are calculated and supplied to the register 5 as tap gains to be set to each tap of the transversal filter constituting the ghost generation circuit 2.

The base point determining unit 12 determines the timing shift Δt between the center P0 and the base point 50 when determining the base point in the ghost waveform.
Similarly, when determining the base point of the reference waveform, the timing shift Δt' between the center and the base point is calculated. The base point determination unit 12 calculates the difference between the discrete delay time approximated by an integral multiple of the sampling period and the actual continuous delay time τ, that is, the timing shift, by adding up the timing shifts for each of the base points. (Δt+Δt') is calculated. The base point determination unit 12 determines the timing deviation (Δt+
By controlling the delay amount of the variable delay circuit 6 by a time corresponding to Δt''), a delay time corresponding to the timing shift is added to the output of the pseudo-ghost generation circuit 2.

Therefore, a ghost created by the pseudo ghost generation circuit 2 as having a discrete delay time of an integral multiple of the sampling period is added with a delay time corresponding to the deviation in the variable delay circuit 6, and becomes the actual continuous delay time. The resulting ghost signal is supplied to the adder 4 as a ghost, and is superimposed on the television signal. As a result, the ghost in the television signal is completely canceled out and removed by the pseudo ghost.

Above, the configuration in which the double-delay circuit is installed after the pseudo-ghost generation circuit 2 has been illustrated, but it may also be installed before the pseudo-ghost generation circuit 2.
stomach. Further, by installing a variable delay circuit before or after the delay circuit 3, it is possible to have a configuration in which the timing on the vision signal side rather than on the pseudo ghost side can be varied.

Effects of the Invention As explained in detail above, the ghost removal device of the present invention generates a signal having a discrete delay time of an integral multiple of the sampling period from a reference waveform using a transversal filter and superimposes it on a television signal. The configuration is such that a delay time corresponding to the timing shift between the sampling point of the digital tap gain control section and the base point is added to the pseudo ghost component or this television signal.
The effect is that good ghost removal characteristics can be achieved without significantly shortening the sampling period.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a ghost removing device according to an embodiment of the present invention, FIG. 2 is a waveform diagram for explaining the present invention in detail, and FIGS. 3 and 4 are conventional ghost removing devices. FIG. 5 is a waveform diagram for explaining the operating principle of a general ghost removal device. ■...Input terminal, 1...Tap gain control circuit, 2...
...Pseudo-ghost generation circuit, 3...Delay circuit, 4...
・Adder, 5...Register, 6...Variable delay circuit,
11... A/D converter, 12... Base point determination unit, 13
...Memory, 14...Difference calculating section, O...Output terminal. Patent applicant: NEC Home Electronics Co., Ltd. (1 other person)

Claims (1)

[Scope of Claims] A variable tap gain transversal filter that generates a pseudo-ghost having a discrete delay time that is an integral multiple of a predetermined sampling period to simulate a ghost contained in a television signal; A digital tap gain control section that controls the tap gain set in the variable tap gain transversal filter based on the ghost included in the signal, and a timing difference between the sampling point and the base point in this digital tap gain control section. a variable delay circuit that adds a delay time to the pseudo ghost or television signal.