JPH0447864A - Waveform distortion elimination circuit - Google Patents

Abstract

PURPOSE:To amplify a main signal while eliminating its waveform distortion by giving a tap coefficient of the main signal in terms of a sinX/X wave pulse having a frequency band of a video signal among tap coefficients of a transversal filter. CONSTITUTION:Let one sample period of a digital video signal SY, that is, a delay time tau of a delay circuit be tau=1/(4Xchrominance subcarrier frequency) 69.78nsec, then the maximum frequency able to be processed by a transversal filter 5 is 1/(2tau) 7.16MHz based on the sampling theorem. Since the maximum frequency of a video signal of the NTSC system is 4.2MHz, the video signal SY is not lost even when the filter 5 has a low pass characteristic whose cut-off frequency is 4.2MHz by selecting the tap coefficient of the filter 5 in this way. A tap coefficient for a main signal among tap coefficients of the filter 5 is given on a sinX/X wave by using the sinX/X wave pulse having a band of 4.2MHz in the setting of the tap coefficient of the filter 5 to obtain a gain for the main signal in the transversal filter.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a circuit for removing waveform distortion of a video signal.

[Summary of the Invention] According to the present invention, a gain can be obtained by selecting a tap coefficient of a main signal of a transversal filter in, for example, a ghost removal circuit.

[Prior Art] In a television receiver, ghost wave components can be removed from a received video signal in the following manner.

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, GC of the received video signal is performed.
The waveforms of the R signal (which includes a ghost wave component) and the GCR signal formed on the receiving side are compared to extract the ghost wave component, and the filter is passed through a transversal filter, for example, so that the extracted ghost wave component is eliminated. Control characteristics.

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 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 701RE. be done. Also, the rise characteristic is si
This is the ringing characteristic of nX/χ.

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 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 4th, 5th, and 7th field periods,
A video signal with this GCR signal 5GCR inserted is transmitted.

Then, the first to eighth GCR signals 5GCR are converted into a signal S
, ~S8, if the receiving side performs the calculation shown in FIG. 3B, the result of the calculation 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, the chrominance signal, and the horizontal synchronizing pulse HD, which are separated by 8 field periods, are in phase with each other. The synchronization pulses HD are each canceled out.

Therefore, the signal GCR (and ghost wave component Sg) resulting from the calculation does not include the burst signal BRST, color signal, and horizontal synchronizing pulse, so it is difficult to eliminate so-called front and rear ghosts and waveform equalization. It can be used for 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 0 is added is taken out, and this signal SY is supplied to the A/D converter (2), where one sample is converted into, for example, an 8-bit digital video signal SY, and this signal SY is sent to the delay circuit. (3) and is delayed by a predetermined time, and this delayed video signal SY is supplied as a main signal to an adder circuit (4).

Further, the video signal SY from the converter (2) is supplied to a transversal filter (5) of, for example, 640 stages (640 taps) to form a cancellation signal SC having an opposite phase to the ghost wave component. is supplied to the adder circuit (4).

Therefore, in the adder circuit (4), the video signal SY
Since the ghost wave component included in the signal SC is canceled out by the signal SC, the adder circuit (4) outputs the video signal SY from which the ghost wave component has been removed.

This signal SY is then supplied to a D/A converter (6) and converted into the original analog video signal SY, and this signal SY is taken out to a terminal (7).

At this time, in the detection circuit (10), the GCR
A ghost wave component 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 adder circuit (4) is supplied to the gate circuit (11) to take out the GCR signal 5GCR (including the previous and subsequent detection periods), and this signal 5GCR is transferred to the buffer memory (12 ), and the GCR signal 5GCR of that field period is held every one field period.

Then, the GCR signal 5GCR of this memory (12) is
It is supplied to an arithmetic circuit (21). This calculation circuit (21)
Although the following circuits (22) to (25) are actually constructed by the microcomputer (20) and software, they are expressed by hardware here.

Then, in the arithmetic circuit (21), the GCR signal 5GCR held in the memory (12) is sequentially added or subtracted every 1 field period according to the formula shown in FIG. The resulting signal GC
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, from the subtraction circuit (22), the received signal G
A ghost wave component Sg of CR is extracted. Note that this ghost wave component Sg is also an error component from which the ghost cannot be removed.

Since the signal GCR has a bar waveform, in order to make it a pulse response, the ghost wave component Sg is supplied to a differentiating circuit (24) to form a differentiated pulse Pg, and this pulse Pg is supplied to a converting circuit (25).

In this conversion circuit (25), the pulse Pg is converted into a signal ST representing the correction amount of the tap coefficient (tap gain) of the filter (5), and this signal ST is supplied to the filter (5). The filter ( 5) The passage characteristics are controlled.

From then on, as such processing is repeated, the characteristics of the transversal filter (5) are adjusted little by little, and gradually converge to the characteristics that remove the ghost wave component Sg of the GCR signal 5GCR (.

When the characteristics of the filter (5) converge sufficiently, the ghost wave component Sg of the GCR signal 5GCR from the adder circuit (4) becomes small to a negligible level, but at this time, the ghost wave component of the original video signal SY is also at a negligible level.

Therefore, the video signal SY from which the ghost wave component has been removed is taken out at the terminal (7).

By the way, when the transversal filter (5) is an output addition type (standard type), it is implemented as an IC with a configuration as shown in FIG.

However, D −N ” D 0 to DM are delay circuits of one sample period (for example, N + M = 639),
CN-'' CO~C, 4 is a multiplier circuit, Ao is an adder circuit, Ti is an input terminal, and To is an output terminal.

The circuit for setting tap coefficients is omitted.

Therefore, as shown in FIG. 8A, delay circuits D-N to D
o-Ds, the output of the delay circuit D0 at the position corresponding to the delay time of the delay circuit (3) is supplied to the addition circuit (4), and the output of the filter (5) is supplied to the addition circuit (4).
This corresponds to circuits (3) to (5) in FIG.
) connection.

Furthermore, in FIG. 8A, if the tap coefficient (multiplier) of the multiplier circuit M0 corresponding to the delay circuit D0 is "1" (full gain), the output of the delay circuit D0 is directly passed through the multiplier circuit C0 to the adder circuit. Since the filter (5) in FIG. 8A can be expressed as shown in FIG. 8B. This state is equivalent to adding the output of the delay circuit D0 and the output of the adder circuit A0 in the adder circuit (4) in FIG.

Therefore, if the tap coefficient of the multiplier circuit C0 of the transversal filter (5) is set to "1", the delay circuit (3)
is the delay circuit 11. -D, and the adder circuit (4) can also be used as the adder circuit, so the removal circuit in FIG. 5 can be configured as shown in FIG. 7, and the delay circuit in FIG.
3) and the adder circuit (4) can be omitted.

That is, if the tap coefficient of the multiplier circuit C8 is set to "1" and the main signal is taken out from the delay circuit D0, the delay circuit (3) and the adder circuit (4) can be omitted as shown in FIG.

Literature: 1989 National Conference Journal of the Television Society of Japan "Ghost Cancellation Standard Signal System" [Problem to be Solved by the Invention] By the way, as mentioned above, the tap coefficient of the multiplier circuit C0 is
1” means that the gain for the main signal is OdB.
That's what it means.

However, depending on the state of the ghost, it may be necessary to increase the level of the main signal, and if the level of the main signal cannot be increased, it may not be possible to cancel the ghost wave. Alternatively, it is necessary to prepare an external amplifier to cancel ghost waves.

This invention attempts to solve these problems.

[Means to solve the problem]

Now, if one sample period of the digital video signal SY, that is, each delay time τ of the delay circuit D-N''D0 to DM, is τ=1/(4X color subcarrier frequency)', 69.8 ns, then From the sampling theorem, the highest frequency that the transversal filter (5) can handle is 1/(2r
) 'i7.16MHz.

On the other hand, for example, the highest frequency of an NTSC video signal is 4.2 MHz.

Therefore, by selecting the tap coefficients of the transversal filter (5), even if the filter (5) has a low-pass characteristic with a cutoff frequency of 4.2 MHz,
The video signal SY is not impaired.

The present invention focuses on such points and provides a transversal filter in which a gain can be obtained for the main signal.

That is, in this invention, in correspondence with the embodiments described later, the transversal filter (5) only needs to pass the video signal SY of up to 4.2 MH2 as the main signal, so the tap coefficient of the filter (5) When setting, consider a sin

[Effect]

Gain can be obtained for the main signal in the transversal filter.

[Embodiment] In FIG. 1, a video signal SY from a video detection circuit (1) is supplied to an A/D converter (2), and one sample is converted into, for example, an 8-bit digital video signal SY. For example, SY is 640 steps (640 tamps)
The original analog video signal S is supplied to the D/A converter (6) through the transversal filter (5) of
Y, and this signal SY is taken out to the terminal (7).

Further, the signal SY from the filter (5) is transmitted to the circuit (11
), (12), and (20), a signal ST is taken out, and this signal ST is supplied to the filter (5) as a signal representing the correction amount of the tap coefficient.

Here, if the tap coefficient of filter (5) is given in 10 bits in two's complement format, its maximum value is "111111111" since its MSB is the sign focus.
'=511.

Therefore, the tap coefficient "1" of the multiplier circuit C0 in FIGS. 8 and 7 corresponds to 511" of 10-bit data, so in reality, as shown in FIG. This means that the tap coefficient was "511".

In contrast, in the present invention, as shown in FIG. 2B, the tap coefficient of the multiplier circuit C0 is set to "300".

Furthermore, the tap coefficients of the multiplier circuits C-1, -C-1, and C5 - CI5 before and after the multiplier circuit C0 are set to the values indicated by the circles in FIG. 2B (the values are 10 bits and 2 (complement representation), that is, the value on the waveform of sinX/X.

According to such a configuration, the multiplication circuits C-15~00~C
The video signal passing through the IS becomes the main signal, and the level of this main signal is the same as in the cases of FIGS. 8 and 7.

Then, the transversal filter (5) outputs the video signal SY from which the ghost wave component has been removed.

In this case, the multiplier circuit C that takes out the main signal
The tap coefficient of 0 is “300”, which is “511”
is 58.7% (!=i3001511), so the gain for the main signal is 1.7 times (!=i511/300
), that is, the main signal can be amplified up to 1.7 times.

〔Effect of the invention〕

Thus, according to the present invention, in a ghost removal circuit using an FIR type transversal filter, the main signal is extracted through the transversal filter, and the tap coefficient of the multiplication circuit for extracting the main signal is set to the waveform of sinX/X. Since the above value is set, the main signal can be amplified in the transversal filter.

Therefore, even if a ghost wave would normally require an external amplifier, the ghost wave can be removed without providing such an amplifier.

Furthermore, since it is only necessary to select tap coefficients for the amplification, there is no increase in cost.

Furthermore, by setting the tap coefficients, the transversal filter has a low-pass characteristic with a cutoff frequency of 4.2 MHz, so noise components outside the band of the video signal SY can be removed, resulting in improvements in image quality. Obtainable.

The delay circuit (3) and adder circuit (4) in FIG.
) is also unnecessary.

[Brief explanation of drawings]

FIG. 1 is a system diagram of an example of the present invention, and FIGS. 2 to 8 are diagrams for explaining the same. (1) is a video detection circuit, (2) is an A/D converter, (
5) is a transversal filter, (6) is a D/A converter, (10) is a detection circuit, (11) is a gate circuit,
(12) is a buffer memory, and (20) is a microcomputer.

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 removal circuit, the pass characteristic of the transversal filter is controlled based on the above-mentioned transversal filter, and a video signal from which waveform distortion components have been removed is extracted from the transversal filter. A waveform distortion removal circuit in which a tap coefficient of a signal is given by a sinX/X wave pulse having a frequency band of the video signal.