JP3074699B2 - Waveform distortion detection circuit for ghost removal - Google Patents

Description

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

[Summary of the Invention]

The present invention provides, for example, a GCR
By controlling the gain during the signal period, a detection signal with a good S / N can be obtained.

[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 the 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, 8 field period apart the burst signal BRST, the color signal and the horizontal synchronization pulses HD, since each of phase with each other, when calculating the signal S ₁ to S _8, the burst signal BRST, the color signal and the horizontal synchronizing 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 color component video signal SY to which the above-mentioned GCR signal SGCR is added is extracted from this detection circuit (1), and this signal SY is converted into an A / D signal. The signal is taken out to a terminal (5) through a signal line of a converter (2) → transversal filter (3) → 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 accumulated 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 a subtraction circuit (22), and a reference GCR signal forming circuit (23) outputs a reference waveform signal GCR (FIG. 3C). The signal GCR is taken out 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).

Then, the component Sg is supplied to the 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 of the tap gain, and the filter (3) GCR signal S extracted from 3)
The pass characteristic of the filter (3) is controlled so that the ghost wave component Sg of the GCR 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).

Incidentally, (9) is a clock signal forming circuit, in which various clocks and timing signals synchronized with the video signal SY are formed, and these signals are supplied to the respective circuits.

Reference: 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, in the ghost removal circuit, the received GC
Since the ghost removal information is obtained from the R signal SGCR, when extracting the GCR signal SGCR from the gate circuit (11), the S / N (S / N when the D / A conversion is performed) indicated by the extracted GCR signal SGCR is performed. N) is desired to be as good as possible. For this purpose, it is required that the signal level indicated by the GCR signal SGCR extracted from the gate circuit (11) (the signal level after D / A conversion) is as high as possible.

Then, the GCR signal S extracted from the gate circuit (11)
In order to increase the signal level indicated by the GCR, the level of the video signal SY supplied to the A / D converter (2) may be increased.

However, the level of the signal GCR of the GCR signal is 70 IRE as shown in FIG.
The white level of Y is 100 IRE, and when there is a color component, the level is higher.

Therefore, the level of the video signal SY supplied to the A / D converter (2) is limited by the video signal SY and the allowable input range (dynamic range) of the A / D converter (2), and is suitable for the GCR signal SGCR. It cannot be as large as that.

Therefore, the level indicated by the GCR signal SGCR extracted from the gate circuit (11) cannot be increased, and
S / N cannot be secured.

The present invention is intended to solve such a problem.

[Means for solving the problem]

According to the present invention, a received video signal is supplied to a transversal filter, and a ghost removal reference signal (GCR) is output from the transversal filter (3).
Signal (SGCR)) and a ghost wave component from the extracted reference signal (GCR signal (SGCR)).
Based on the extracted ghost wave component, the pass characteristic of the transversal filter (3) is controlled to extract a video signal from which the ghost wave component has been removed from the transversal filter (3). 10) In the input signal line of the transversal filter (3), the reference signal (GCR signal (SGCR))
Characterized by comprising an amplifier circuit (31) that is controlled so that the level of a video signal supplied to the transversal filter (3) is increased during a period in which is detected. It is.

[Action]

The S / N of the GCR signal SGCR is improved, and effective ghost removal is performed.

〔Example〕

In FIG. 1, a video signal SY from a video detection circuit (1) passes through a variable gain amplifier (31) for level control.
It is supplied to the A / D converter (2) and to the switch circuit (32). D / A converter (4)
Is also supplied to the switch circuit (32).

Further, a gain control pulse Pc which becomes "1" level is taken out from the clock forming circuit (9) during the period of the GCR signal SGCR (including the detection period before and after the GCR signal SGCR), and this pulse Pc is supplied to the switch circuit (33). At the same time, a "0" level is also supplied to the switch circuit (32) as an input. In addition,
The pulse Pc can be formed by counting the number of horizontal synchronization pulses with reference to the vertical synchronization pulse.

Further, a trigger circuit (34) is provided. From this trigger circuit (34), a trigger pulse Pt is taken out at the time of switching channels, turning on power, operating a ghost removal key by a user, and the like. Is supplied to the time constant circuit (35) and becomes a control signal Sc which becomes "1" level for, for example, 5 seconds from the pulse Pt, that is, a period required for the ghost wave component removal processing. This signal Sc is a switch circuit ( The control signal is supplied to 32) and (33).

The output signal of the switch circuit (32) is connected to the terminal (5).
The output signal of the switch circuit (33) is supplied to the amplifier (31) as a control signal of the gain, and the gain of the amplifier (31) is set such that the output signal of the switch circuit (33) is "0".
At the level, the gain is set to 0 dB (reference gain). At the level of “1”, the gain is set to a predetermined large value.

According to such a configuration, Sc = “0” in the normal state, and the switch circuit (32) is connected to the D / A converter (4) as shown in the figure. In addition, switch circuit (33)
Is connected to the "0" level side as shown in the figure, and the "0" level is supplied to the amplifier (31) as a control signal of the gain, so that the gain of the amplifier (31) is set to 0 dB.

Therefore, in a steady state, this ghost removal circuit
The configuration is equivalent to that of FIG. 5, and the same ghost removal operation is performed.

However, switching of the channel at any time t _1, when the operation of the power-on or ghost removal key is performed,
A trigger pulse Pt is output from the trigger circuit (34), and the signal Sc becomes “1” level by the pulse Pt.

Therefore, from time t ₁ for example 5 seconds, the switch circuit by a signal Sc (33) is connected in reverse to the formed circuit (9) side to the figure, formed pulses Pc the switching circuit from the circuit (9) ( 33) is supplied as a gain control signal to the amplifier (31), and the gain of the amplifier (31) is determined by the pulse Pc
Increases every "1" level period, that is, every period of the GCR signal SGCR.

Therefore, the level of the GCR signal SGCR supplied to the A / D converter (2) is increased, for example, to the allowable input range of the converter (2), and such a GCR signal SGCR is supplied to the converter (2). The detection circuit (10) is supplied with a GCR signal SGCR having a sufficiently high S / N.

Then, the by GCR signal SGCR pass characteristic of the transversal filter (3) is set, this setting is completed, i.e., when the time t ₁ is 5 seconds elapses, Sc =
Since it becomes "0", it returns to the above-mentioned steady state, and the video signal SY from which the ghost wave component has been removed is taken out at the terminal (5).

In addition, for 5 seconds during which the characteristics of the filter (3) are set, Sc = “1”, and the signal Sc causes the switch circuit (32) to operate on the detection circuit (1) side, contrary to the drawing. , The video signal SY from the detection circuit (1) is output to the terminal (5) through the switch circuit (32) as it is for 5 seconds during this setting, and the level of the video signal SY is disturbed. Never.

Thus, according to the present invention, when the ghost wave component is removed using the GCR signal SGCR, the video signal SY level supplied to the A / D converter (2) is increased during the period of the GCR signal SGCR. S / N GCR signal
SGCR can be supplied to the detection circuit (10), and ghost removal without excess or deficiency can be performed.

Also, while the pass characteristic of the transversal filter (3) is being set, the video signal SY from the detection circuit (1) is output to the terminal (5) in place of the video signal SY being set. Is not output to the terminal (5), so that there is no adverse effect on the monitor receiver connected to the terminal (5).

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 (42) are configured 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).

〔The invention's effect〕

According to the present invention, when a ghost wave component is removed by using the GCR signal SGCR, A
Since the video signal SY level supplied to the / D converter (2) is increased, a sufficient S / N GCR signal SGCR can be supplied to the detection circuit (10), and ghost removal without excess or shortage can be achieved. It can be carried out.

Also, while the pass characteristic of the transversal filter (3) is being set, the video signal SY from the detection circuit (1) is output to the terminal (5) in place of the video signal SY being set. Is not output to the terminal (5), so that there is no adverse effect on the monitor receiver connected to the terminal (5).

[Brief description of the drawings]

FIGS. 1 and 2 are system diagrams of an example of the present invention, and FIGS. 3 to 5 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) is a D / A converter, (9) is a clock forming circuit,
(10) is a detection circuit, (11) is a gate circuit, (12) is a memory, (20) is a microcomputer, (31) is a variable gain amplifier, (32) and (33) are switch circuits, and (34) is A trigger circuit, (35) is a time constant circuit.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Takayu Nagamine 6-7-35 Kita Shinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation (56) References JP-A-1-300706 (JP, A) (58) ) Surveyed field (Int.Cl. ⁷ , DB name) H04N 5/21

Claims (1)

(57) [Claims] 1. A received video signal is supplied to a transversal filter, a ghost removal reference signal is extracted from an output signal of the transversal filter, and a ghost wave component is extracted from the extracted reference signal. A ghost-removing waveform distortion detection circuit for controlling a pass characteristic of the transversal filter based on the wave component and extracting a video signal from which a ghost wave component has been removed from the transversal filter; A ghost removal waveform characterized by comprising an amplifier circuit controlled to increase the level of a video signal supplied to the transversal filter during a period in which the reference signal is detected in the input signal line. Distortion detection circuit.