JPS5910088A - Color signal reproducer - Google Patents

Abstract

PURPOSE:To obtain a color signal reproducer which can improve the S/N of a reproduced color signal, by using a charge transfer element such as a CCD, etc. as a delay line to convert a signal passing through a comb-shaped filter into a low frequency in a frequency band where the CCD can be practically used in a satisfactory way. CONSTITUTION:As shown in the diagram, a reproduced color signal which received a jitter compensation and a high band conversion to its original 3.58MHz through a frequency converter 13 and a BPF15 is converted into a low frequency by a frequency converter 25, a fixed oscillator 27 and an LPF26. This color output signal is supplied to a feedback type comb-shaped filter consisting of a CCD1H delay line 29, its clock signal generator 28, an adder 16, a subtractor 18 and an attenuator 19. Thus the S/N of a color signal is improved. For the output signal of the comb-shaped filter, it is possible to obtain a color signal that received a vertical image resolution compensation carried out by an amplifier 24, a subtractor 20, a slice amplifier 21 and an adder.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a color signal recording and reproducing device, and provides a device that improves the 8/N ratio of reproduced color signals.

In general, in the carrier color signal of a color television signal such as the NTSC system, by passing it through a C-shaped comb filter, random cross color and in-band two-dimensional noise due to the high frequency component of the luminance signal can be removed.
The visual S/N improvement effect is significant.

In order to further enhance the improvement effect of this ↓ comb filter (1) 87N, a feedback comb is used that can obtain sharp amplitude frequency characteristics by feeding back part of the output of the conventional comb filter to the input side. A block diagram and frequency characteristics of this feedback comb filter are shown in Fig. 1 (A) (13). In Fig. 1, (1) is the ]H slow g-line, (2) is an adder, (3) is a subtracter, and (4) is an attenuator for feeding back the output signal. Also, the delay time of the ]H delay line (1) is assumed to be τ.

Since the feedback comb filter can change the sharpness of the amplitude frequency characteristic by changing its feedback rate K, the S/N improvement storm can be set freely, and a large S/N improvement effect can be expected. . When the feedback rate KK=o, it is equivalent to a general C-shaped comb filter without feedback.

When a color television signal is passed through these comb filters, if the line correlation of the video signal is strong, the image S/N ratio can be improved in accordance with the theoretical value.

However, it has the disadvantage that the vertical resolution of the image deteriorates in portions of the video signal where there is no line correlation.

Particularly in the case of a feedback comb filter, the vertical resolution of the image is significantly degraded in proportion to the increase in the feedback rate. For example, in the case of =0.5, the 90% response time when a signal indicating a stepwise change is input requires approximately 5H period.

Such a comb-shaped filter is used in a magnetic recording and reproducing device (hereinafter referred to as V).
When installed in the reproduction circuit of a VTR (referred to as a TR), 87N of color signals due to noise generated in the tape head system of a VTR can be removed.
Deterioration can also be greatly improved.

However, vertical resolution degradation also occurs, and unless corrected by some means, the reproduced image quality will be very poor.

FIG. 3 shows a conventional example in which a feedback comb filter and a vertical resolution correction circuit are introduced into a VTR reproducing circuit. The color television signal recording method applied to this reproduction circuit is a method in which the luminance signal is modulated by FMi, the color signal is frequency-converted to a low frequency, and this two-frequency signal is superimposed and recorded. .

In Figure 3, using a feedback comb filter, fcVT
The regeneration circuit will be explained. The two-frequency signal reproduced from the video head (5) is amplified by the head amplifier (6).
After , bypass filter (7) and low pass filter a
The signal is separated into a luminance signal frequency-modulated by the power and a chrominance signal whose carrier wave is low-frequency converted. Frequency-modulated brightness signal IJ After amplitude fluctuations are removed by the transmitter (8), the frequency is demodulated by the frequency demodulator θ9), and high-frequency noise is reduced by the de-emphasis circuit OQ.
/N is obtained as an improved signal and sent to the adder (c).

In addition, the reproduced color signal whose carrier wave has been low-pass converted is made into a constant amplitude by the automatic color gain adjuster (2), and then outputted by the frequency converter 0 from V C004 having the same jitter component as the color signal. The frequency is converted by The output signal is applied to a bandpass filter 06 to convert the color signal carrier back to its original frequency. And a vertical line consisting of an adder QQ1 delay line α, a subtracter, a feedback comb filter consisting of the subtractor the, a slice amplifier Qυ, an adder, and an amplifier. A reproduced color signal with a good S/N ratio is obtained by passing through a resolution deterioration correction circuit, mixed with a reproduced luminance signal of the OQ output of the DF 21 circuit in an adder, and output as a reproduced video signal to an output terminal.

In the reproducing circuit of Figure 3, a feedback comb filter consisting of an adder αQ1 delay line α range adder θ~, attenuator 09), a subtractor wall, a slice amplifier 11 adder, and an amplifier ( 24) The operation of the vertical resolution deterioration correction circuit composed of '! This is done using the s4 diagram. Note that the color television signal system below is the NTSC system, so the delay line αη
The delay time is one horizontal scanning period (hereinafter referred to as 1H).

In Fig. 4, N T of the feedback comb filter input
8 C color signal (3.58 MHz in fs)'l
, (a), there is no burst signal or color signal up to (n+2)H, and the operation will be explained assuming that there is information on burst signals and color signals that are continuous from (n+3)H and have the same amplitude V. do. (bl is a feedback comb filter output signal waveform diagram, and is the output signal of the subtracter section in FIG. 3.

For the (n+3)Hth signal, since there is no signal at the (n+2)Hth signal, the lH delayed output signal of the sH delay line 0η does not appear, and only the direct signal to the sH delay line 0η is output.

At the same time, the amplitude V of this output signal is attenuated by an attenuator H at a predetermined ratio. Now, the feedback rate =0.5 is added to the input signal by the calculator OQ, and a signal of -v is supplied to the lH delay line Oη. At the (n+4)Hth, the input signal is (n+3)H
It must be the same signal as the th, and the subtracter θ~ has an amplitude V (
(n+4)th signal and the output signal of IH delay man.
A signal with amplitude -V having the +3)th information is supplied,
The output becomes output signal 2 of 1'-■. At the same time, the output signal is fed back and lH delayed MQη
A signal of -vX O,5+v = -v is supplied to the human power of 4.

In this way, by constructing a loop in which the output signal is fed back to the input υ, when the signal changes stepwise, the output signal amplitude increases every 11 times, and the final stable amplitude is -
5-KvO value, when K-0,5, the output signal is 4
It becomes stable at the amplitude of v. In the several H interval until such a stable amplitude is reached, amplitude changes as shown in FIG. 4(b) occur.

In such a state, a sudden change in information in the line direction of the signal cannot be obtained immediately, and the vertical resolution becomes extremely poor. In this way, when the feedback factor is -0.5, the output signal of the comb filter has an amplitude four times the amplitude of the input signal. On the other hand, the mixed noise does not increase in the same way because it is a random signal and there is no line correlation between the noises.
As shown in FIG. 2, the S/N improvement degree of the output color signal is 6 dB.

By configuring the feedback comb filter in this way, an 8/N improvement can be achieved, but the vertical resolution deteriorates. This correction method will also be explained with reference to the waveform diagram in FIG.

In FIG. 4, (C) is one input signal of the subtracter and is the output signal of the amplifier. The gain of this amplifier () has the same gain as the feedback comb filter (77-).

Therefore, when K -0.5, it has an amplitude of 4V. This fourth
By subtracting the output signal of Fig. 4(C1) and the output signal of the comb filter of Fig. 4(b), the output signal of Fig. 4(d) is obtained. This signal has information, and even if the signal (d) is directly added to υ with the comb filter output signal in Figure 4 (b) using an adder, the vertical resolution degradation will not be corrected. However, if this is done, noise will also be added in the same way, so it is natural that the S/N improvement effect will not be obtained.

Therefore, the signal applied to the adder □□□ needs to be a signal that has information about the vertical resolution degradation and does not have noise components in other horizontal sections. Figure 4(e) is the fourth
This diagram is an enlarged view of the waveform in Figure (d) in the amplitude direction, and includes information on noise and vertical resolution deterioration. By passing such a signal through a slice flip filter that blocks signals below a certain level, a signal is obtained in which signals at a level below the dashed line in the figure are not output. This output signal is sent to an adder (2
) and the comb filter output signal, it is possible to correct the deterioration of vertical resolution without affecting 8/N.

Note that signals below the slice level, such as the (n+6)Hth correction signal in el in Figure 4, are not supplied to the adder (2), so complete resolution correction is not achieved, but low-level vertical resolution deterioration may occur. is visually acceptable.

In this way, by combining the feedback comb filter and the vertical resolution deterioration correction circuit and introducing the combination into the color reproduction signal processing system of the VTR, reproduction color 8/N can be improved and good image quality can be obtained. However, various problems occur at the stage of circuit design when this method is introduced, which will be explained below.

According to the configuration shown in FIG. 3, the signal used is NT
Since it is an SC color signal, the carrier color frequency is 3.58
It is MH2. A charge transfer element such as 3.58M [(Usually an ultrasonic delay line is used as a means for delaying the z signal by an IH delay line. A charge transfer element such as CCI in place of the ultrasonic delay line) is also considered, but 3.58MHz As an IH delay element for high-frequency signals such as the above, there is no commercially available product for home use, and an ultrasonic delay line is generally used. However, the ultrasonic delay line has problems such as the passband width, the phase characteristics within the band, and the generation of spurious components. In particular, especially when configuring a feedback comb filter, the sharpness component basically becomes unsightly in terms of image quality unless it is at a sufficiently low level. Further, due to variations in phase characteristics, the desired comb characteristic cannot be obtained over the entire band, and the S/N improvement effect due to the comb shape also decreases. Also, as can be seen from the configuration in Figure 3, many circuits such as adders, subtracters, amplifiers, etc. are required, but the total cost is 3.58M.
When adding or subtracting Hz color signals, it is necessary to maintain the input signals in a constant phase relationship. However, 3
．． High frequency signals such as 5sMf (z) tend to cause phase rotation due to base input capacitance, collector output capacitance, etc. even when an amplifier is configured.A buffer amplifier etc. is always connected to each adder and subtracter. Therefore, if a signal phase rotation occurs, the input phase conditions of each arithmetic unit will change, making it impossible to perform the specified operation.Therefore, in order to maintain the input signal phase relationship of each arithmetic unit, a phase correction circuit, etc. is required. na p1
Circuit design becomes extremely difficult.

When configuring a feedback comb filter and vertical resolution correction circuit using high-frequency signals such as NT8C color signals, problems such as suppressing the spurious component of the ultrasonic delay line and correcting signal phase rotation in the circuit system must be solved. Therefore, it is extremely difficult to obtain a desired performance in circuit design.

The present invention aims to solve the design problems of the conventional example, and uses a charge transfer element such as a CCU as a delay line, and the signal passing through the comb filter is 3.58M.
Unlike high frequencies such as Hz9, the frequency is converted to a low frequency that is within a frequency band that is sufficiently usable for CCDs and is less likely to cause signal phase rotation in circuits such as arithmetic units. The purpose of? This has been achieved.

An embodiment of the present invention will be described below based on the drawings. Fifth
The figure is a block diagram of a VTR color signal reproducing circuit showing the configuration of a feedback comb filter and a vertical resolution correction circuit for improving the S/N of a VTR reproduced color signal according to the present invention. Note that blocks having the same functions as those in FIG. 3 are designated by the same reference numerals.

In FIG. 5, the jitter is corrected and the frequency converter a1
, BPFθ6), the original 3. The reproduced color signal high-frequency converted to ssMHz is processed by a frequency converter■, a fixed oscillator (
2η, converted to a low frequency by a low-pass filter. This low frequency converted color output signal is sent to a feedback comb filter consisting of a CCDIH delay line 4, its clock signal generator (c), an adder OQ, a subtractor, an attenuator, and an attenuator. This improves the color signal S/N. Also, the comb filter output signal is sent to an amplifier (C) and a subtractor (E).
, slice amplifier e1), and adder (a) perform vertical resolution correction to obtain a color signal.

Next, this output signal is high-frequency converted by the frequency converter (7), the fixed oscillator (a) used for the low-frequency conversion, and the bandpass filter mark), and a 3.58 MHz NTSC color output signal is obtained. The adder (A) in FIG. 3 mixes it with the reproduced luminance signal to obtain a video output signal. The carrier frequency of this low-band conversion signal can be arbitrarily selected, but it should at least be selected at a frequency that does not reduce the color signal band by low-band conversion. The color signal band must be at least ±500 KHz. For example, if this low-band conversion color signal carrier frequency is 700 KHz,
The low frequency conversion color signal band is 7001 GIz±500 KHz, and this signal is supplied to the comb filter and its correction circuit.

According to the configuration shown in FIG. 5, the signal band passing through the feedback comb filter and its correction circuit is low frequency (for example, 70
0 KHz ± 500 KHz), unlike conventional processing using high-frequency signals, signal synchronization is longer, and the phase of the input signal to two or more human-powered arithmetic circuits such as adders and subtracters is controlled by the amplifier. The influence of phase rotation in circuits such as the above is extremely reduced, making it easier to match.

In addition, since a CCD is used as the delay element of the IH delay line, it is possible to obtain a delayed signal with high precision and less spurious, and it can be displayed on a television monitor unlike the conventional method using an ultrasonic delay line. There is no possibility that the sugeria component will appear and result in an unsightly 1Iill image.

In the circuit shown in Fig. 5, the fixed oscillator (2) that performs frequency conversion for the comb filter and the clock signal generator (5) for the CCDIH delay line are both composed of fixed frequency oscillators;
Since the frequency is ~5 MHz, it is also possible to configure the same frequency. In this case, the delay time of the CCDIH delay line is 'rL! nbx7″cwnb: Number of bits, fcw: Clock.The signal frequency for frequency conversion can be arbitrarily selected as long as it has a sufficient low conversion color signal band, so the frequency that should be shared is determined by the above formula. It is possible to make a selection while paying attention to the following.

According to the invention described above, it is possible to configure a highly accurate and stable feedback comb filter and vertical resolution correction circuit, without creating a circuit that is difficult to make one calculation and has many fluctuations as in the past. , it is possible to obtain a VTR reproduced color image with less interference and a good SIN ratio.

[Brief explanation of the drawing]

Figure 1 shows the basic configuration of a feedback comb filter and its frequency converter. Figure 2 1-i: S/I of a feedback comb filter.
Figure 3 shows the relationship between the N improvement effect and the feedback rate.
A TR regeneration block diagram, FIG. 4 is an explanatory diagram of the operation of FIG. 3, and FIG. 5 is a V'rR regeneration block diagram of the feedback comb filter and its correction circuit according to the present invention. j... Frequency converter, ati u7) a→4... Feedback comb filter,... υ(2) (C)... Vertical resolution deterioration correction circuit, (C)... Adder, (c)...
Frequency converter, (4)...Low pass filter, (a)
... fixed oscillator, wire ... clock signal generator, ... CCDIH delay line, cl ... frequency converter, field)
... Nokundo Pass Filter Agent Yoshihiro Moriki Figure 1 (/4) -4 and 4th? figure

Claims (1)

[Claims] 1. A color television signal consisting of a luminance signal and an amplitude-modulated modulated color signal is frequency-modulated in a high frequency band by a method of recording and reproducing it to generate an fcF'M signal and a lower side band of the FM signal. In a magnetic recording/playback device that frequency-multiplexes the KUI 4-color signal in the wave side frequency band and records it on a recording medium, during playback, the modulated color signal, which has been jitter-corrected and inversely frequency-converted to a high frequency band, is sent to a fixed oscillator. The signal is converted to a low frequency band by the fixed oscillator, processed by a feedback comb filter circuit having a delay line that delays by an integral multiple of one horizontal scanning period, and inversely converted to a high frequency band by the fixed oscillator to produce a reproduced modulated color signal. A color signal reproducing device designed to obtain 2. C as a delay line that delays by an integral multiple of one horizontal scanning period.
A special rf characterized by using a charge transfer device such as a CD
A color signal reproducing device according to claim 1. 3. The power 2-signal reproducing device according to claim 2, characterized in that the fixed oscillator for frequency conversion and the clock signal of the CCDIH delay line are shared.