JPH0420179A - Detecting circuit for waveform distortion - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

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 prevents the video signal from overflowing within the transversal filter by reading the level of the output video signal and feeding it back in, for example, a ghost removal circuit.

[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,
The ghost wave component is extracted by comparing it with the GCR signal formed on the receiving side, and the passage characteristics of the transversal filter, for example, are controlled so that the extracted ghost wave component becomes as follows.

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
5T indicates a burst signal, and the first GCR signal GCR has a bar waveform located on the rear side of the horizontal period, as shown in A of the same figure, and has a width of 44.7 μs and a level of 701RE. be done. Also, the rise characteristic is 5i
This is the ringing characteristic of nX/X.

Furthermore, 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 set as a repetition period, and the
The GCR signal GCR is inserted into the 18th line or the 281st line of the 6th and 8th field periods, and the GCR signal GCR is inserted into the 18th line or the 281st line of the 6th and 8th field periods.
The signal PDS is inserted into the 8th line or the 281st line, and the video signal into which the GCR signal 5GCR is inserted is transmitted.

Then, the first to eighth GCR signals 5GCR are converted into a signal S
, ~S, then if the receiving side performs the calculation shown in FIG. 2B, the calculation result will be the signal GCR.

Also, if there is a ghost, this calculation result will include the signal GC
A ghost wave component Sg of R is also included.

Therefore, ghost removal can be performed from the signal GCR (and Sg) resulting from this calculation.

In this case, the burst signal BRST, color signal, and horizontal synchronization pulse HD, which are separated by 8 field periods, are in phase with each other, so when calculating the signals S and -S,
Burst signal BR5T, color signal and horizontal sync pulse HD
are canceled out respectively.

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 this GCR signal 5GCI? An example of a ghost removal circuit using .

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 the
) 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 GCR 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 field period according to the formula shown in 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, and this control signal is supplied to the filter (3) as a control signal for its tap coefficient (tap gain). The pass characteristics of the filter (3) are controlled so that the ghost wave component Sg of the GCR signal 5GCR extracted from the filter (3) 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).

Literature: 1989 National Conference Journal of the Television Society "Ghost Cancellation Standard Signal System" [Problem to be Solved by the Invention] By the way, as shown in FIG. 6A, the dynamic range OR of the transversal filter (3) is Assume that a video signal SY of approximately the same level is transmitted, but a ghost occurs in this 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 cancellation signal SC as shown in FIG.
) to remove the ghost wave component.

However, in this case, as shown in Figure C, if the DC component of the cancellation signal SC is biased, when the cancellation signal SC is subtracted from the received video signal SY in the transversal filter (3), As shown by the broken line, the peak portion of the output signal SY (this is the target video signal SY from which ghost wave components have been removed) as a result of the subtraction exceeds the dynamic range DR of the transversal filter (3). may overflow.

When such an overflow occurs, the waveform of the video signal SY output to the terminal (5) is distorted or the level is reversed in a portion of the overflow, so that the video signal is no longer a normal video signal.

This invention attempts to solve these problems.

[Means to solve the problem]

Here, considering the ghost removal process of the microcomputer (20), this microcomputer (20) reads the waveform of the GCR signal 5GCR from the output signal of the transversal filter (3), and then selects the next transversal filter (3). We have obtained the information to modify the tap coefficient of.

Therefore, using the GCR signal 5GCR, it is possible to detect whether the video signal SY passing through the transversal filter (3) exceeds the dynamic range DR.

Also, considering the transversal filter (3), it can be roughly divided into a transposed type (input addition type) and a standard type (output addition type), and the former transposed type transversal filter is shown in FIG. The latter standard type transversal filter is implemented as an IC with the configuration shown in FIG.

In addition, in these filters, D, ~Dn are delay circuits for a unit period, Ao, A+-An are adder circuits, and M, ~Dn are delay circuits for a unit period.
Mn is a multiplication circuit, Ti is a signal input terminal, To is a signal output terminal, Tci is a cascade input terminal, Tco is a cascade output terminal, and the tap coefficient input terminal is not shown.

In this case, the cascade terminals Tci and Tco are prepared when a large transversal filter is required, and in the case of a transposed transversal filter, they are connected as shown in Figure 8A. , in the case of a standard type transversal filter, they are connected as shown in FIG.

The present invention utilizes the above points to prevent overflow of the video signal SY in the transversal filter (3).

That is, in this invention, in correspondence with the embodiments described later, level comparison circuits (31) and (34) for detecting the level of the GCR signal 5GCR extracted from the output signal of the transversal filter (3); Based on the output of the comparator circuit, the transversal filter is supplied with a DC offset (Vd).
A DC bias circuit (37) is provided to control the DC level of the video signal passing through the transversal filter in accordance with the level of the GCR signal extracted from the output signal of the transversal filter.

[Effect]

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 (3I) to (37) described below
.

Although, like the circuits (21) to (24), are actually configured by the microcomputer (20) and software, they are expressed by hardware here.

Then, the gate circuit (11) to (7) GCR signal 5G
CR is a digital level comparison circuit (31) for level detection.
), (34) as well as a voltage source (32),
From (35), the reference voltages +vth and -vth are the comparator circuit (
31) and (34), and comparison outputs SP and SM are taken out.

In this case, the voltage ±vth is a level corresponding to the positive and negative peak values when the cancellation signal SC is calculated on the video signal SY in the filter (3), and
31), of the 5GCR signals, 5GCR>V
th portion is taken out as a comparison output sp, and from the comparison circuit (34), 5GCR<- of the signal 5GCR
A portion of V th is taken out as a comparison output SM.

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

According to such a configuration, a transversal filter (
When the level of the GCR signal 5GCR extracted from the output signal of 3) exceeds the reference value ±vth, the DC offset of the transversal filter (3) is changed by the DC voltage Vd. , even if the cancellation signal SC is calculated on the video signal SY, its peak value will not exceed the dynamic range of the filter (3).

Therefore, regardless of the size of the ghost, it is possible to obtain an image without waveform collapse or level inversion, and in which the ghost is removed.

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), the video signal SY from which the long ghost wave component has 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).

At this time, since the DC voltage Vd from the bias circuit (37) is supplied to the cascade input terminals Tci of the filters (42) and (44), the filter (42)
).

Overflow of the video signal SY in (44) is prevented.

〔Effect of the invention〕

According to this invention, when the level of the GCR signal 5GCR extracted from the output signal of the transversal filter (3) 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 on the video signal SY in the transversal filter (3),
The peak value never exceeds the dynamic range of the filter (3).

Therefore, regardless of the size of the ghost, it is possible to obtain an image without waveform collapse or level inversion, and in which the ghost is removed.

[Brief explanation of drawings]

FIGS. 1 and 2 are system diagrams of an example of the present invention, and FIGS. 3 to 8 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, (10) is a detection circuit,
(11) is a gate circuit, (12) is a memory, (20) is a microcomputer, (21) is an arithmetic circuit, (23)
(24) is a control circuit, (31) and (34) are level comparison circuits, and (37) is a DC bias circuit. Agent Hidemori Matsukuma Figure 1 Equivalent circuit diagram

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 waveform distortion component is extracted from the extracted GCR signal, and a waveform distortion component is extracted from the extracted waveform distortion component. In the waveform distortion component removal circuit, the waveform distortion component removal circuit controls the pass characteristics of the transversal filter based on the above transversal filter and extracts the video signal from which the waveform distortion component has been removed from the transversal filter. and a DC bias circuit that applies a DC offset to the transversal filter based on the detection output of the detection circuit, The waveform distortion detection circuit is configured to control the DC level of the video signal passing through the transversal filter according to the level of the GCR signal.