JP3077163B2 - Circuit for removing waveform distortion components - Google Patents

Description

The present invention relates to a circuit for removing a waveform distortion component of a video signal.

[Summary of the Invention]

According to the present invention, for example, in a ghost removal circuit, the level of an output video signal is read and fed back to prevent the video signal from overflowing in a transversal filter.

[Conventional technology]

To remove a ghost wave component from a received video signal in a television receiver, the following may be performed.

That is, on the transmission side, a ghost canceling reference signal (hereinafter, referred to as a GCR signal) is added to the video signal.

Then, on the receiving side, the received video signal is gated to extract the GCR signal and its ghost wave component,
The extracted GCR signal and its ghost wave component are compared with the GCR signal formed on the receiving side to extract the ghost wave component, and the pass characteristic of, for example, a transversal filter is changed so that the extracted ghost wave component disappears. Control.

Then, a signal SGCR as shown in FIG. 3 is considered as the GCR signal at this time.

That is, in the figure, HD is the horizontal synchronization pulse, BRST
Represents a burst signal, and the first GCR signal GCR has a bar waveform located at the rear side of the horizontal period as shown in FIG. 2A, a width of 44.7 μsec, and a level of 70 IRE. . The rising characteristic is a ringing characteristic of sinX / X.

Further, the second GCR signal PDS is, as shown in FIG.
A pedestal waveform (0 level) is set.

Then, as shown in FIG. 4A, the eight-field period of the video signal is set as a repetition period, and the eighteenth line or the eighteenth field period of the first, third, sixth, and eighth field periods is used.
The GCR signal GCR is inserted into the 281st line, and the signal PDS is inserted into the 18th line or the 281st line in the remaining second, fourth, fifth, and seventh field periods.
The video signal with the GCR inserted is transmitted.

Then, the first to eighth GCR signals SGCR are transmitted to the signals S _{1 to} S _8.
Then, if the receiving side performs an operation as shown in FIG. B, the operation result becomes a signal GCR. If there is a ghost, this calculation result also includes a ghost wave component Sg of the signal GCR.

Therefore, the ghost can be removed from the signal GCR (and Sg) of the operation result.

In this case, the burst signal BRST, the color signal, and the horizontal synchronization pulse HD which are four fields apart from each other are in phase with each other, so when calculating the signals S _{1 to} S ₈ , the burst signal BRST, the color signal, and the horizontal synchronization pulse HD Are offset each other.

Therefore, since the signal GCR (and the ghost wave component Sg) of the operation result does not include the burst signal BRST, the color signal, and the horizontal synchronization pulse HD, the so-called front ghost and rear ghost removal and waveform equalization are performed. Up to 45 μs can be handled. In addition, erroneous detection does not occur even for a long ghost up to about 80 μsec.

FIG. 5 shows an example of a ghost removal circuit using this GCR signal SGCR.

That is, (1) shows a video detection circuit of a television receiver, from which the above-described color composite video signal SY to which the GCR signal SGCR is added is extracted from this detection circuit (1), and this signal SY is converted into an A / D converter. (2) → transversal filter (3) → taken out to terminal (5) through signal line of D / A converter (4).

Then, at this time, the ghost wave component Sg is detected from the GCR signal SGCR in the detection circuit (10), and the pass characteristic of the filter (3) is controlled by this detection output to remove the ghost wave component.

That is, the operation shown in FIG. 4B can be rewritten as shown in FIG.
This indicates that the R signal SGCR should be calculated in order.

Then, the digitized video signal SY from the filter (3) is supplied to the gate circuit (11) and the GCR signal SGC
R is taken out and the signal SGCR is supplied to the memory (12), and the GCR of the field period is
The signal SGCR (including the preceding and following detection periods) is held.

Then, the GCR signal SGCR of the memory (12) is supplied to the arithmetic circuit (21). The arithmetic circuit (21) and the following circuits (22) to (24) are actually constituted by a microcomputer (20) and software, but are represented here by hardware.

Then, in the arithmetic circuit (21), the GCR signal SGCR held in the memory (12) is sequentially added or subtracted in each field period according to the equation of FIG. A certain signal GCR and a ghost wave component Sg are taken out, these signals GCR and Sg are supplied to an arithmetic circuit (22), and a reference waveform signal S (FIG. 3C) is supplied from a reference GCR signal forming circuit (23). The signal S is extracted and supplied to a subtraction circuit (22). Therefore, the ghost wave component Sg of the received signal GCR is extracted from the subtraction circuit (22).

The component Sg is supplied to a control circuit (24) and subjected to processing such as differentiation to obtain a predetermined control signal. This control signal is supplied to the filter (3) as a control signal for the tap coefficient (tap gain). Then, the pass characteristic of the filter (3) is controlled so that the ghost wave component Sg of the GCR signal SGCR extracted from the filter (3) is canceled and removed.

Therefore, at this time, the ghost wave component of the video signal SY is also removed by the filter (3), and the video signal SY containing no ghost wave component is extracted from the terminal (5).

Literature: The 1989 National Convention of the Institute of Television Engineers of Japan, "Ghost cancellation reference signal system" [Problems to be Solved by the Invention] By the way, as shown in FIG. 6A, the dynamic range DR of the transversal filter (3) is It is assumed that a video signal SY having substantially the same level is transmitted, but a ghost is generated in the video signal SY, and the actually received video signal SY has a waveform as shown in FIG.

Then, in the transversal filter (3), a ghost canceling signal SC as shown in FIG. C is formed, and the ghost wave component is removed by subtracting this signal SC from the received video signal SY (FIG. B). Will be.

However, in this case, as shown in FIG. C, if the DC component of the cancellation signal SC is offset, the cancellation signal SC is subtracted from the received video signal SY in the transversal filter (3). As shown by a broken line, the peak portion of the output signal SY resulting from the subtraction (this is the target video signal SY from which the ghost wave component has been removed) corresponds to the dynamic range DR of the transversal filter (3). Overflow may occur.

Then, when such an overflow occurs, the waveform of the video signal SY output to the terminal (5) is broken or the level is inverted at the overflow portion, so that the video signal is not a normal video signal.

The present invention is intended to solve such a problem.

[Means for solving the problem]

Here, considering the ghost removal processing of the microcomputer (20), the microcomputer (20) reads the waveform of the GCR signal SGCR from the output signal of the transversal filter (3), and thereby performs the next transversal filter (3). Information for correcting the tap coefficient of.

Therefore, whether or not the video signal SY passing through the transversal filter (3) exceeds the dynamic range DR can be detected based on the GCR signal SGCR.

Considering the transversal filter (3), the transversal filter can be roughly divided into a transposed type (input addition type) and a standard type (output addition type). And the latter standard type transversal filter is integrated into an IC as shown in FIG.

In these filters, D ₁ -Dn the delay circuit A _0, A ₁ .about.An an addition circuit, M ₁ to Mn multiplication circuit unit periods, Ti is the signal input terminal, To the signal output terminal, Tci Denotes a cascade input terminal, Tco denotes a cascade output terminal, and an input terminal for tap coefficients is not shown.

In this case, the cascade terminals Tci and Tco are provided for when a large transversal filter is required. In the case of a transposed transversal filter, they are connected as shown in FIG. 8A. , Standard transversal filters are connected as shown in FIG.

The present invention prevents overflow of the video signal SY in the transversal filter (3) by utilizing the above points.

That is, in the present invention, when corresponding to an embodiment described later, level comparison circuits (31) and (34) for detecting the level of the GCR signal SGCR extracted from the output signal of the transversal filter (3); A DC bias circuit (3) that applies a DC offset Vd to the transversal filter based on the output of the comparison circuit
7) to control the DC level of the video signal passing through the transversal filter according to the level of the GCR signal extracted from the output signal of the transversal filter.

[Action]

The DC level of the video signal in the transversal filter is controlled according to the level of the GCR signal to prevent overflow.

〔Example〕

In FIG. 1, circuits (31) to (37) described below
Is actually configured by a microcomputer (20) and software, like the circuits (21) to (24), but is represented by hardware here.

The GCR signal SGCR from the gate circuit (11) is supplied to digital level comparison circuits (31) and (34) for level detection, and the reference voltages + Vth and -V are supplied from the voltage sources (32) and (35). Vth is supplied to comparison circuits (31) and (34), and comparison outputs SP and SM are extracted.

In this case, the voltage ± Vth is a level corresponding to the positive and negative peak values when the cancellation signal SC is calculated into the video signal SY in the filter (3), and the comparison circuit (31)
From the signal SGCR, the part of SGCR> Vth is compared output S
P is output from the comparison circuit (34).
Among them, the part of SGCR <−Vth is extracted as the comparison output SM.

These comparison outputs SP and SM are stored in memory (33),
(36) is held until the next comparison output SP and SM is obtained, and is also supplied to the DC bias circuit (37). The bias circuit (37) outputs the level corresponding to the comparison output SP and SM. DC voltage Vd is taken out, and this voltage Vd is applied to the cascade input terminal of the transversal filter (3).
Supplied to Tci.

According to such a configuration, when the level of the GCR signal SGCR extracted from the output signal of the transversal filter (3) exceeds the reference value ± Vth, the DC offset of the transversal filter (3) is reduced by the DC voltage Vd. In the transversal filter (3),
Even if the cancellation signal SC is calculated for the video signal SY, its peak value does not exceed the dynamic range of the filter (3).

Accordingly, it is possible to obtain an image free from ghost removal without waveform collapse or level inversion regardless of the size of the ghost.

FIG. 2 shows another connection example of the transversal filter (3).

That is, the video signal SY from the A / D converter (2)
Is supplied to the first subtraction circuit (41), and the first
Is supplied to a subtraction circuit (41) through a transversal filter (42).

The output signal of the subtraction circuit (41) is further supplied to a second subtraction circuit (43), and the output signal of the subtraction circuit (43) is passed through a second transversal filter (44). (43), and the output signal of the subtraction circuit (43) is supplied to the D / A converter (4).

Further, a detection signal from the detection circuit (10) is supplied to the filters (42) and (44) as a control signal of the pass characteristic.

Therefore, since the subtraction circuit (41) and the filter (42) are configured as a feedforward loop, the video signal SY from which the nearby ghost wave component including the previous ghost has been removed is extracted from the subtraction circuit (41). .

Further, since the subtraction circuit (43) and the filter (44) are formed in a feedback loop, the subtraction circuit (4
From 3), the video signal SY from which the long ghost wave component has been removed is extracted.

Therefore, the video signal SY from which the near ghost wave component and the long ghost wave component have been removed can be extracted from the terminal (5).

At this time, the DC voltage Vd from the bias circuit (37) is connected to the cascade input terminals of the filters (42) and (44).
Since the video signal SY is supplied to the Tci, overflow of the video signal SY in the filters (42) and (44) is prevented.

〔The invention's effect〕

According to the present invention, a transversal filter (3)
The level of the GCR signal SGCR extracted from the output signal of
When the voltage exceeds the reference value ± Vth, the DC offset of the transversal filter (3) is changed by the DC voltage Vd. Therefore, even if the cancellation signal SC is calculated for the video signal SY in the transversal filter (3), its peak is not changed. The value does not exceed the dynamic range of the filter (3).

Accordingly, it is possible to obtain an image free from ghost removal without waveform collapse or level inversion regardless of the size of the ghost.

[Brief description of the drawings]

FIGS. 1 and 2 are system diagrams of an example of the present invention, and FIGS. 3 to 8 are diagrams for explanation thereof. (1) is a video detection circuit, (2) is an A / D converter,
(3), (42) and (44) are transversal filters,
(4) D / A converter, (10) detection circuit, (11) gate circuit, (12) memory, (20) microcomputer, (21) arithmetic circuit, (23) reference GCR signal A formation circuit, (24) is a control circuit, (31) and (34) are level comparison circuits, and (37) is a DC bias circuit.

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Takayu Nagamine 6-7-35 Kita Shinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation (56) References JP-A-58-170285 (JP, A) JP-A JP-A-58-101576 (JP, A) JP-A-61-192174 (JP, A) JP-A-60-55771 (JP, A) JP-A-2-113469 (JP, U) (58) Fields investigated (Int) .Cl. ⁷ , DB name) H04N 5/21 H04B 1/10

Claims (1)

(57) [Claims] 1. A method according to claim 1, further comprising the steps of:
A video signal in which first and second GCR signals having different levels are repeatedly inserted is supplied to a transversal filter, and first and second GCR signals are extracted from an output signal of the transversal filter, and the extracted signals are extracted. The first and second GCR signals are calculated for each field period to obtain a signal including waveform distortion in the reference GCR signal, and the reference GCR signal is subtracted from the signal to extract a waveform distortion component. A waveform distortion component removal circuit configured to control a pass characteristic of the transversal filter based on the component to extract a video signal from which the waveform distortion component has been removed from the transversal filter; First and second level detection circuits for detecting respective levels of the first and second GCR signals extracted from the signals And a DC bias circuit for providing a DC offset to the transversal filter based on the detection outputs of the first and second level detection circuits, and a first and a second extracted from the output signal of the transversal filter. Wherein the DC level of the video signal passing through the transversal filter is controlled according to the level of the GCR signal.