JPS61265991A - Cross modulation distortion reducing device for low frequency conversion carrier chrominance signal - Google Patents

Abstract

PURPOSE:To reduce the ringing of a reproduced low frequency conversion carrier chrominance signal due to mixed modulation distortion by employing a comb- line filter which filtrates a frequency component at least twice the chrominance subcarrier frequency of the low frequency conversion chrominance signal from an input low frequency conversion carrier signal. CONSTITUTION:The low frequency carrier conversion chrominance signal of the chrominance subcarrier frequency fS reproduced from a magnetic tape by a VTR is supplied to a delay circuit 11 and an adder 12 from an input terminal 10. The delay circuit 11 and the adder 12 comprise the comb-line filter 13. Its (adder 12) output signal turns out a signal where a frequency component of 2fS being a main component for ringing is emphasized. A subtractor 15 subtracts the output signal of a limiter 14 from the input reproduced low frequency carrier chrominance signal, whereby the reproduced low frequency conversion carrier chrominance signal from which a frequency component of 2fS (cross modulation distortion causing mainly ringing) is approximately off-set and removed is outputted to an output terminal 16.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an apparatus for reducing cross-modulation distortion of a low-band converted carrier color signal, and particularly relates to a low-band converted carrier color signal obtained by frequency converting a carrier color signal to a low band. The present invention relates to a device for reducing cross-modulation distortion contained in a low-pass conversion carrier color signal reproduced from a recording medium on which a color signal is recorded.

Conventional technologyCurrent helical scan magnetic recording and reproducing equipment (VTR)
) is the standard recording/playback method (NTSC).
The method separates the luminance signal and the carrier color signal from the composite color video signal of the PAL system or S E CAM system, respectively.
A frequency-modulated luminance signal obtained by frequency modulating a luminance signal and a low-frequency converted carrier color signal obtained by frequency-converting a carrier color signal to a low frequency are frequency-division multiplexed, and the frequency-division multiplexed signal is magnetically transmitted. It is well known that this is a so-called low frequency conversion color signal recording and reproducing method in which color signals are recorded on tape and then reproduced. The frequency converter of the carrier color signal recording system of such a VTR is as follows:
Carrier color signal cos(2πfCt
) and a constant frequency signal cos(2π(fs+fc)
t) (However, frequency conversion is performed with fs<f(). As a result, if there is no cross-modulation distortion, C03(2πfct)・C08(2π(fs+fc)t
)=cos(2π(2f c + f s )t
) +C03(2π fst) is taken out from the frequency converter, and by passing it through a low-pass filter, the color subtractor of the low frequency fs shown in the second term on the right side of equation (1) is obtained. A low frequency converted carrier color signal cos(2πfst) of the carrier frequency is obtained.

Problems to be Solved by the Invention However, in general, due to the capabilities of circuit elements such as transistors that constitute a frequency converter, there are signals in addition to the signals expressed by equation (1) at the output stage of the frequency converter. Cross-modulation distortion is also generated. Figure 5 shows the frequency spectrum of the output signal of the frequency converter having this cross-modulation distortion (however, the input carrier color signal is actually fc±500k). This shows a frequency spectrum when only a single frequency fc is frequency converted.

). In Figure 5, 2fs, fc-fs, fc, fc+f3
゜f c + 2 f s are cross-modulation distortion components, of which the cross-modulation distortion with a frequency of 2 fs is shown by a broken line in the figure.
Since it is located within the pass band of the low-pass filter for the low-pass converted carrier color signal P wave, the low-pass converted carrier color signal and the cross-modulation distortion with a frequency of 2 fs are respectively extracted from this low-pass filter. .

Therefore, the output signal of the low-pass filter in this case is cos
(2πfst) + a-cos(4πfst)
=(1+a-cos(2πfst))-cos(2
πf3t)-a (7)
It can be seen from equation 0 that the low-pass conversion carrier color signal is amplitude-modulated at the frequency fs. "For this reason, in the case where there is no cross-modulation distortion, the low-pass conversion carrier color signal with a waveform as shown by the solid line in FIG. As shown, ringing occurs.

On the other hand, conventionally, a noise reduction circuit as shown in FIG. 7 is provided in the carrier color signal reproduction system to reduce the signal-to-noise ratio (S/
N) was improved. In the figure, a reproduced carrier color signal which has been returned to the original color subcarrier frequency fC by frequency converting the reproduced low-pass converted carrier color signal is input to input terminal 1, and from this, a glass delay line, etc. The signals are supplied to the adder 3 which is delayed by one horizontal scanning period (1H) by the one-day delay circuit 2 used, while the signals are directly supplied to the adder 3 without being delayed and are added there. As a result, after noise and signal components that have no line correlation are extracted from the adder 3, the amplitude is limited by the limiter 4, the noise is extracted and supplied to the subtracter 5, where it is reproduced from the input terminal 1. Subtracted from the carrier color signal. As a result, the reproduced carrier color signal whose noise has been canceled out by the subtracter 5 is output to the output terminal 6.

Conventional noise reduction circuits that utilize such line correlation are effective in reducing noise mixed into the reproduced carrier color signal during the recording and reproduction process, but they are effective in reducing noise mixed into the reproduced carrier color signal during the recording and reproduction process. It is not possible to reduce ringing, and there has been no effective means to reduce ringing so far.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an apparatus for reducing cross-modulation distortion of a low-frequency converted carrier color signal, which solves the above-mentioned problems by extracting the above-mentioned cross-modulation distortion component and subtracting it from the low-frequency converted carrier color signal. shall be.

Means for Solving the Problems An apparatus for reducing cross-modulation distortion of a low-pass converted carrier color signal according to the present invention has a frequency of at least 2 fs from an input low-pass converted carrier color signal.
(where, fs is the color subcarrier frequency of the low-pass conversion carrier color signal), and the input low-pass conversion carrier color signal and the output signal of the comb filter are each supplied with a frequency component of 2 fs. It consists of a suppression means for outputting a low frequency converted carrier color signal with reduced frequency components.

Operation The above comb filter converts the input low-pass converted carrier color signal into n”/
(2fs) (where n is a positive integer), and an adder that adds the input low-pass conversion carrier color signal and the output signal of the delay circuit, respectively,
At least one frequency component of 2 fs, which is cross-modulation distortion, in the input low-pass conversion carrier color signal is separated. Since the small amplitude component in the output signal of this comb filter is the above frequency component, either only this small amplitude component is extracted by a limiter and subtracted from the input low-pass conversion carrier color signal, or the comb filter is output by a slicer. Only the large amplitude component is taken out, the small amplitude component is removed, and the input low frequency transformed carrier color signal is subtracted from the output signal of the delay circuit, and added to the low frequency transformed carrier color signal that does not contain the frequency component. .

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to examples shown in the drawings.

FIG. 1 shows a block system diagram of a first embodiment of the device of the present invention. In the figure, a low frequency converted carrier color signal having a color subcarrier frequency fs, which is reproduced from a magnetic tape by the VTR, is input to an input terminal 10, and is supplied to a delay circuit 11 and an adder 12, respectively. Ru. The delay time τ0 of the delay circuit 11 is selected to be 1/(2fs), and the input low-pass conversion carrier color signal is delayed by 1/(2fs) and then output to the adder 1.
Supply to 2. That is, a delay circuit 11, an adder 12, and a comb filter 13 are configured. The frequency characteristic of this comb filter 13 exhibits a comb-like frequency characteristic, in which the pass band is at frequencies that are even multiples of the frequency t's, and the attenuation band is at frequencies that are odd multiples of the frequency fs. Therefore, the reproduced low-pass converted carrier color signal having a frequency spectrum as shown by the dashed line ■ in FIG. When the signal is supplied together with the above-mentioned cross-modulation distortion at a frequency of 2 fs, the frequency characteristic of the output signal of the comb filter 13 becomes as shown by the solid line 3 in the figure.

Therefore, the output signal of the comb filter 13 (adder 12) becomes a signal in which the 2fs frequency component, which is the main component of the ringing, is emphasized. However, 2f in this output signal
Even if the frequency component of s is emphasized, its amplitude is much smaller than that of the low-frequency conversion carrier color signal, so the limiter in the next stage extracts only the small-amplitude frequency component of 2fs and outputs the large-amplitude low-frequency conversion carrier color signal. Remove signal components. The subtracter 15 performs a subtraction operation to subtract the output signal of the limiter 14 from the input reproduced low frequency conversion carrier color signal, thereby producing a reproduced low frequency component in which the 2fs frequency component (cross modulation distortion that is the main cause of ringing) is substantially canceled out. The gamut-transformed carrier color signal is output to the output terminal 16.

Next, a second embodiment of the device of the present invention will be described with reference to FIGS. 3 and 4. In FIG. 3, the same components as those in FIG. 1 are designated by the same reference numerals, and their explanations will be omitted. In FIG. 3, the frequency characteristics of the output signal of the comb filter 13 are as shown in FIG. 4(A), which is the same as shown in FIG. , here, amplitude components smaller than a certain level indicated by the broken line V in FIG. 4(A) are removed. As a result, the frequency characteristics of the output signal of the slicer 17 become as shown in FIG. 4(B).
During this slicer, the 2fs frequency component is removed.

On the other hand, the output signal of the delay circuit 11 in the comb filter 13 and the input reproduced low-pass conversion carrier color signal are each supplied to a subtracter 18, where they are subtracted to produce a frequency that is an odd multiple of the frequency t's. The signal is given a comb-like frequency characteristic that becomes an attenuation region at frequencies that are even multiples of the passband 9 frequency fs, and is extracted. Therefore, the frequency characteristics of the output signal of the subtracter 18 are as shown in FIG. 4(C). The output signal of the subtracter 18 and the output signal of the slicer 17 are respectively supplied to an adder 19, which receives two signals from the input reproduction low-pass conversion carrier color signal.
A reproduced low-pass conversion carrier color signal having a frequency characteristic shown in FIG. 4(D) with the frequency component of fs reduced is extracted and output to the output terminal 20.

In this way, a reproduced low-pass converted carrier color signal with reduced ringing is obtained at the output terminal 16. Since the signal is also output, the S/N is also improved based on the same principle as the conventional noise reduction circuit using line correlation.

In addition, since the carrier color signal is separated from the composite color video signal band-sharing multiplexed into the high frequency region of the luminance signal and then low-pass converted, the luminance signal component is contained in the low-pass converted carrier color signal. This may have an adverse effect on image quality (this is referred to as cross color), but along with the suppression of the 2rs frequency component, cross color is also reduced.

Note that the present invention is not limited to the above embodiment, and for example, the delay time τ0 of the delay circuit 11 is n/(2fs).
(However, n may be a positive integer.) In short, it is sufficient that at least a frequency component of a frequency of 2 fs is outputted from the comb filter 13 as a P wave. In addition, although the application to a VTR has been described, a low-pass conversion carrier color signal reproduction system for a video disc in which a low-pass conversion carrier color signal is band-shared multiplexed and recorded in the high frequency region of a band-limited luminance signal. It can also be applied to Furthermore, it is also possible in principle to apply it to a recording system for low-frequency conversion carrier color signals.

Effects of the Invention As described above, according to the present invention, it is possible to reduce the cross-modulation distortion of the low-pass conversion carrier color signal, thereby suppressing the ringing caused by the cross-modulation distortion, and it is also possible to suppress the ringing caused by the cross-modulation distortion of the low-frequency conversion carrier color signal. Based on the same principle, it is possible to improve the S/N ratio of the reproduced low-frequency conversion carrier color signal, and it also has the advantage of reducing cross color.

[Brief explanation of drawings]

1 and 3 are block system diagrams showing respective embodiments of the device of the present invention, FIG. 2 is a characteristic diagram for explaining the operation of the main parts in the block system shown in FIG. 1, and FIG. FIG. 5 is a frequency spectrum diagram showing the cross-modulation distortion that occurs during low-band conversion; FIG. 6 is a diagram showing each waveform of the low-band conversion carrier color signal; FIG. The figure shows an example of a conventional noise reduction circuit. 10...Low frequency conversion carrier color signal input terminal, 11...Delay circuit, 12.19...Adder, 13...Comb filter, 14...Limiter, 15.18...Subtraction device, 16.20...Low frequency conversion carrier color signal output terminal, 17
...Slicer. Patent applicant: Victor Japan Co., Ltd. Figure 1 Figure 2 Figure 3 Figure 4 (C) (D) Field 7a! Song → Figure 6 Figure 7

Claims (3)

[Claims] (1) An input low-pass conversion carrier color signal with a color subcarrier frequency fs is supplied, and consists of a delay circuit with a delay time n/(2fs) (where n is a positive integer) and an adder, and a frequency component with a frequency of at least 2fs. a comb filter for filtering the input low-pass converted carrier color signal from the input low-pass converted carrier color signal; 1. A cross-modulation distortion reduction device for a low-band converted carrier color signal, comprising a suppressor for outputting a low-band converted carrier color signal with a reduced frequency component of 2 fs. (2) The suppression means extracts the small amplitude component of the output signal of the comb filter as it is, and includes a limiter that limits the amplitude of the large amplitude component, and subtracts the output signal of the limiter from the input low-pass conversion carrier color signal. 2. A cross-modulation distortion reduction device for a low-pass conversion carrier color signal according to claim 1, further comprising a subtracter. (3) The suppression means includes a slicer that extracts only amplitude components of a predetermined level or higher from the output signal of the comb filter;
It is characterized by comprising a subtracter that subtracts the output signal of the delay circuit in the comb filter from the input low-pass conversion carrier color signal, and an adder that adds and outputs both output signals of the slicer and the subtracter. An apparatus for reducing cross-modulation distortion of a low frequency conversion carrier color signal according to claim 1.