JPH0420180A - Detecting circuit for waveform distortion - Google Patents

Abstract

PURPOSE:To improve the S/N of a GCR signal and to efficiently remove a ghost by making the level of a video signal to be supplied to a transversal filter large with controlling a level control circuit during the period of the GCR signal. CONSTITUTION:A video signal SY from a video wave detecting circuit 1 is supplied to an A/D converter 2 through a variable gain amplifier 31 for level control and is supplied to a switch circuit 32. Besides, also the video signal SY from a D/A converter 4 is supplied to the switch circuit 32, the output signal of the switch circuit 32 is taken out by a terminal 5, the output signal of a switch circuit 33 is supplied to the amplifier 31 as the control signal of the gain of it and the gain of the amplifier is made as the fixed large gain. Then, the level of the video signal SY supplied to a transversal filter 3 is made large with controlling the gain of the amplifier 31 during the period of a reference GCR signal for ghost canceling. Thus, the improvement of the S/N of the GCR signal and efficient ghost removing are attained.

Description

[Detailed description of the invention] [Industrial application field] 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 ghost removal circuit that uses GCR
By controlling the gain of the signal period, a detection signal with a good S/N ratio can be obtained.

[Conventional technology]

In a television receiver, ghost wave components can be removed from a received video signal as follows.

That is, on the transmitting side, a reference signal for ghost cancellation (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,
This extracted GCR signal and its ghost wave component,
A ghost wave component is extracted by comparing the GCR signal formed on the receiving side, and the passage characteristics of a transversal filter, for example, are controlled so that the extracted ghost wave component is eliminated.

As the GCR signal at this time, a signal 5GCR as shown in FIG. 3 is considered.

That is, in the same figure, HD is the horizontal synchronizing pulse, BR
3T indicates a burst signal, and the first GCR signal GCR has a bar waveform located at the rear of the horizontal period, as shown in A of the same figure, and has a width of 44.7 μs and a level of 70 IRE. be done. Also, the rise characteristic is 5i
This is the ringing characteristic of nX/X.

Further, the second GCR signal pDs has a pedestal waveform (0 level), as shown in FIG.

As shown in FIG. 4A, the 8-field period of the video signal is used as a repeating period, and the first, third, sixth,
18th line or 2nd line of 8th field period
The GCR signal GCR is inserted into the 81st line, and the remaining 2nd line
, the signal PDS is inserted into the 18th line or the 281st line of the fourth, fifth, and seventh field periods, and the video signal into which the GCR signal 5GCR is inserted is transmitted.

Then, the first to eighth GCR signals 5GCR are
1 to S, if the receiving side performs the calculation shown in FIG. 1B, the result of the calculation will be the signal GCR.

Also, if there is a ghost, this calculation result will include the signal GC
I? This also includes a ghost wave component Sg.

Therefore, the signal GCI? of this operation result? (and S
Ghost removal can be performed from g).

In this case, the burst signal BRST, chrominance signal, and horizontal synchronizing pulse (10), which are separated by 8 field periods, are in phase with each other, so when calculating the signals S, ~S, the burst signal BR5T, the chrominance signal, and the horizontal synchronizing pulse 10 are in phase with each other. Sync pulse H
D cancel each other out.

Therefore, the signal GCR (and ghost wave component Sg) resulting from the calculation does not include the burst signal BR5T, the color signal, and the horizontal synchronization pulse HD, so it is difficult to remove the so-called front ghost and rear ghost, waveform equalization, etc. It can handle up to 45 microseconds.

Moreover, false detection does not occur even for long ghosts up to about 80 μsec.

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

That is, (1) shows the video detection circuit of the television receiver, and the above-mentioned GCR signal 5GCR is output from this detection circuit (1).
The color composite video signal SY to which
) is taken out to terminal (5) through the signal line.

At this time, in the detection circuit (10), the GCR
A ghost wave component Sg is detected from the signal 5GCR, and the detection output controls the passage characteristics of the filter (3) to remove the ghost wave component.

That is, the calculation shown in FIG. 4B can be rewritten as shown in FIG.
This indicates that it is sufficient to integrate the R signals 5GCR in order.

Therefore, the digitized video signal SY from the filter (3) is supplied to the gate circuit (11) to take out the CCR signal 5GCR, and this signal 5GCR is sent to the memory (
12), and the GCR signal 5GCR of that field period (including the preceding and succeeding detection periods) is held for each field period.

The GCR signal 5GCR of this memory (12) is then supplied to the arithmetic circuit (21). This arithmetic circuit (21) and the following circuits (22) to (24) are actually constructed by a microcomputer (20) and software, but are represented by hardware here.

Then, in the arithmetic circuit (21), the GCR signal 5GCR held in the memory (12) is sequentially added or subtracted every one field period according to the second part of FIG. The signal GC which is the calculation result of
R and ghost wave component Sg are extracted, and this signal GC
R, S g are supplied to the subtraction circuit (22), and
Reference waveform signal G from the reference GCR signal forming circuit (23)
CR (FIG. 3A) is taken out and this signal GCR is supplied to the subtraction circuit (22). Therefore, the subtraction circuit (2
From 2), the ghost wave component Sg of the received signal GCR is
is taken out.

This component Sg is then supplied to the control circuit (24) and subjected to processing such as differentiation to become a predetermined control signal.This control signal is supplied to the filter (3) as a control signal for its tap gain, and the filter ( 3) GCR retrieved from
The passage characteristics of the filter (3) are controlled so that the ghost wave component Sg of the signal 5GCR is canceled out and removed.

Therefore, at this time, the ghost wave component of the video signal sy is also removed in the filter (3), and the video signal SY containing no ghost wave component is taken out at the terminal (5).

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

Document 7 1989 Journal of the National Conference of the Television Society "Ghost Cancellation Standard Signal System" [Problems to be Solved by the Invention] By the way, in the ghost cancellation circuit, the received GC
Since ghost removal information is obtained from the R signal 5GCR, the GCR signal 5GCR is obtained from the gate circuit (11).
When extracting the GCR signal 5GCR, it is desired that the S/N (S/N when converted from D/A) of the extracted GCR signal 5GCR is as good as possible. For this purpose, the GCR signal 5GCR taken out from the gate circuit (11) is
Signal level indicated by (signal level when D/A converted)
is required to be as large as possible.

Then, in order to thicken the signal level indicated by the GCR signal 5GCR taken out from the gate circuit (11),
It is sufficient to increase the level of the video signal SY supplied to the /D converter (2).

However, as shown in FIG. 3A, the level of the signal GCR among the GCR signals is 70IRE, whereas the white level of the video signal SY is 10011? E, and when there is a color component, the level is higher than that.

Therefore, the level of the video signal SY supplied to the A/D converter (2) is limited by this video signal SY and the allowable input range (dynamic range) of the A/D converter (2), and is suitable for the GCR signal 5GCR. It cannot be made to such a large level.

Therefore, the GCR taken out from the gate circuit (11)
Unable to increase the level indicated by signal 5GCR,
Sufficient S/N cannot be secured.

This invention attempts to solve these problems.

[Means to solve the problem]

For this reason, in the present invention, a variable gain amplifier circuit (31) for level control is provided on the input signal line of the transversal filter (3), and the amplifier ( 31) to increase the level of the video signal SY supplied to the transversal filter (3).

[Effect]

The S/N of the GCR signal 5GCR is improved and effective ghost removal is performed.

〔Example〕

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

Furthermore, the GCR signal 5GC from the clock forming circuit (9)
A gain control pulse Pc that is at the “1” level is extracted during the period R (including the detection period before and after it), and this pulse P
c is supplied to the switch circuit (33), and the "0" level is also supplied as an input to this switch circuit (33). Note that the pulse Pc can be formed by counting the number of horizontal synchronization pulses based on the vertical synchronization pulse.

Further, a trigger circuit (34) is provided, and a trigger pulse Pt is taken out from this trigger circuit (34) when switching channels, when power is turned on, when a user operates a ghost removal key, etc. is supplied to the time constant circuit (35) for, for example, 5 seconds from the pulse Pt, that is, the period required for the removal process of the ghost wave component.
The control signal Sc is set to “1” level, and this signal Sc
is supplied to the switch circuits (32) and (33) as their control signals.

Then, the output signal of the switch circuit (32) is sent to the terminal (5).
The output signal of the switch circuit (33) is supplied to the amplifier (31) as a control signal for its gain, and the gain of the amplifier (31) is set at the level "0" when the output signal of the switch circuit (33) is , 0dB (reference gain), “
When it is at the 1'' level, it is a predetermined large gain.

According to such a configuration, during steady state, Sc="'0"
The switch circuit (32) is connected to the D/A converter (4) side as shown in the figure. In addition, the switch circuit (33) is also 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 for its gain, so the gain of the amplifier (31) is It is said to be OdB.

Therefore, during normal operation, this ghost removal circuit has a configuration equivalent to that shown in FIG. 5, and performs the same ghost removal operation.

However, if the channel is switched, the power is turned on, or the ghost removal key is operated at any time t1,
A trigger pulse Pt is output from the trigger circuit (34),
This pulse Pt brings the signal Sc to the "1 Pa level."

Therefore, for example, for 5 seconds from time t, the signal Sc causes the switch circuit (33) to switch to the formation circuit (9), contrary to the diagram.
Since the pulse Pc from the forming circuit (9)
is supplied to the amplifier (31) as a gain control signal through the switch circuit (33), and the gain of the amplifier (31) changes every “1” level period of the pulse Pc, that is,
The GCR signal increases every 5GCR periods.

Therefore, the GC supplied to the A/D converter (2)
The level of the R signal 5GCR is increased to, for example, the allowable input range of the converter (2), and such a GCR signal 5GCR is supplied to the converter (2), so the detection circuit (10) has a sufficient S/N ratio. Good GCR signal 5GCR
is supplied.

Then, the pass characteristic of the transversal filter (3) is set by this GCR signal 5GCR, and when this setting is completed, that is, when 5 seconds have passed from time tl,
Since Sc="0", the system returns to the steady state described above, and the video signal SY from which the ghost wave component has been removed is taken out from the terminal (5).

Note that during the 5 seconds during which the characteristics of this filter (3) are set, Sc=“1”, and this signal Sc allows
Since the switch circuit (32) is connected to the detection circuit (1) side contrary to the diagram, the detection circuit (1) is connected for 5 seconds during this setting.
), the video signal SY from the switch circuit (3
2) to the terminal (5), and the level of the video signal SY will not be disturbed.

Thus, according to the present invention, when removing ghost wave components using the GCR signal 5GCR, the video signal SY level supplied to the A/D converter (2) is increased during the period of the GCR signal 5GCR. Therefore, the GCR signal 5GCR with sufficient S/N can be supplied to the detection circuit (10), and ghost removal can be performed with just the right amount.

Also, while setting the pass characteristics of the transversal filter (3), the video signal SY from the detection circuit <1) is output to the terminal (5) instead of the video signal SY being set. The video signal SY having a disturbed level is not outputted to the terminal (5), and therefore does not have an 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 s from the A/D converter (2)
y is supplied to the first subtraction circuit (41), and
The signal is supplied to the subtraction circuit (41) through the first 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 this subtraction circuit (43) is passed through the second transversal filter (44) to the subtraction circuit. (43), and the output signal of this subtraction circuit (43) is sent to the D/A converter (4).
supplied to

Further, the detection signal from the detection circuit (10) is transmitted through the filter (
42) and (44) as a control signal for their pass characteristics.

Therefore, since the subtraction circuit (41) and filter (42) are configured in a feedforward type loop,
A video signal SY from which adjacent ghost wave components including front ghosts have been removed is taken out from the subtraction circuit (41).

In addition, since the subtraction circuit (43) and the filter (44) are configured in a feedback type loop, the subtraction circuit (43)
43), a video signal Sy from which long ghost wave components have been removed is extracted.

Therefore, the video signal SY from which the close ghost wave component and the long ghost wave component have been removed can be taken out at the terminal (5).

〔Effect of the invention〕

According to this invention, when removing a ghost wave component using the GCR signal 5GCR, the video signal SY level supplied to the A/D converter (2) is increased during the period of the GCR signal 5GCR. Therefore, the GCR signal 5GCR with sufficient S/N can be supplied to the detection circuit (10), and ghost removal can be performed without excess or deficiency.

Also, while setting the pass characteristics of the transversal filter (3), the video signal SY from the detection circuit (1) is output to the terminal (5) instead of the video signal SY being set. The video signal SY having a disturbed level is not outputted to the terminal (5), and therefore does not have an adverse effect on the monitor receiver connected to the terminal (5).

[Brief explanation of drawings]

FIGS. 1 and 2 are system diagrams of an example of the present invention, and FIGS. 3 to 5 are diagrams for explaining the same. (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, (34) is a trigger circuit, and (35) is a time constant circuit. Agent Hidemori Matsukuma

Claims (1)

[Claims] A received video signal is supplied to a transversal filter, a GCR signal is extracted from the output signal of the transversal filter, a ghost wave component is extracted from the extracted GCR signal, and a ghost wave component is extracted from the extracted ghost wave component. In the ghost wave component removal circuit which controls the pass characteristic of the transversal filter based on the above-mentioned signal and extracts the video signal from which the ghost wave component has been removed from the transversal filter, a level is applied to the input signal line of the transversal filter. A waveform distortion detection circuit comprising a control circuit, wherein the level control circuit is controlled to increase the level of the video signal supplied to the transversal filter during the period of the GCR signal.