JPS62125793A - Chrominance signal processing circuit for video tape recorder - Google Patents

Abstract

PURPOSE:To prevent the deterioration of a picture quality by making the frequency band of a chrominance signal processed, recorded and reproduced by a chrominance signal recording and processing circuit, a chrominance signal reproducing and processing circuit and a tape head system narrow and making substantially the chrominance signal a wide band. CONSTITUTION:Initially, during recording, an input carrier chrominance signal to a terminal 18 is demodulated to the chrominance signal of two color difference signals R-Y, B-Y by a chrominance signal demodulator 19. A sampling signal generated by the first sampling generating circuit 26 becomes a pulse sequence in which a phase is dislocated by 1/2 cycle every one field by a repeating frequency (fp). According to this sampling signal, the first sampling circuits 20, 20' are sampled by the chrominance signal. The chrominance signal in which a band is compressed by low-pass filters 27, 27' is modulated into the carrier chrominance signal by a carrier chrominance signal modulator 28, an unnecessary component is removed at a band-pass filter 29, the carrier chrominance signal in which the band is compressed is obtained and magnetically recorded on a tape by the tape head system 9.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a video tape recorder (hereinafter referred to as VTR).
The present invention relates to a color signal processing circuit.

[Prior Art] FIG. 7 is a block diagram showing a recording and reproducing system of a color signal processing circuit called a color under one type which is employed in a conventional consumer VTR.

In the figure (1) is the luminance signal and the frequency f 5c (NT
(2) is an input terminal for inputting a composite video signal containing a color signal (hereinafter referred to as carrier color signal) modulated with a color subcarrier of 3.58 MHz in the SC system, and has a band of ±500 kHz at the center frequency Esc. A bandpass filter for extracting the carrier color signal, (3) a frequency converter, and (4),
A signal generator with a frequency fc shown by the following formula, fc = fsc + fs In the VH3NTSC system, f c = 3.58 MHz + 40 f H = 3.58 M
Hz + 629 kHz Hz・= (1) Here, fsc
S color subcarrier frequency fH: horizontal scanning frequency fS: low-pass conversion The color subcarrier frequency (5) is a phase shifter, and is set to O', 90 every horizontal scan (IH) by the horizontal synchronization signal to the terminal (6). ', 180''
', 270', the phase is advanced by a channel switching signal sent to the terminal (7) to switch the channel (CH) of the head every 1 fill, and is operated to advance when it is CHI and to lag when it is CH2. (8) Among the signals from the frequency converter (3), the color signal (hereinafter referred to as low (9) is a tape head system that records and plays back the low-pass converted color signal from the low-pass filter (8); (10) is the low-pass filter that passes only the low-pass converted color signal from the low-pass filter (8); A low-pass filter that takes out the converted color signal, (11) a frequency converter that converts the reproduced low-pass converted color signal with a center frequency fs into a carrier color signal with a center frequency fsc, and (12) a band that passes only the carrier color signal. The filter (13) is a comb-shaped filter for crosstalk removal having a stop band at the horizontal scanning frequency interval, and FIG. 8 shows an example of its configuration.
15).

Next, the operation will be explained with reference to FIG. Figure 9 is a frequency spectrum diagram of the signals of each part. In the figure, a is the carrier color signal, b is the recorded low-frequency conversion color signal, black is the low-frequency conversion color signal of head channel 1 (CHI), and white is the low-frequency conversion color signal of the head channel 1 (CHI). The low-pass converted color signal of channel 2 (CH2), C is the reproduced carrier color signal of channel 1, and d is the comb filter (13
), and e indicates the carrier color signal of channel 1 after passing through the filter (13). Figure 9a from the composite video signal to terminal (1) by filter (2)
The carrier color signal shown in is extracted. This signal has a strong spectrum with fsc as the center and an interval of fH on both sides. Such a carrier color signal is supplied to a frequency converter (3). - The signal of frequency fc from the force signal generator (4) is converted to IHz by the phase shifter (5) when switching to the CH1 head.
The phase is advanced by 906 every time, and when switching to the CH2 head, the phase is delayed by 90° every IHz.

In the case of CHI, the spectrum of the signal whose phase is controlled in this way is shifted higher by 1/4・fH and becomes fc+1/4.
・f +1, and in the case of CH2, it is shifted lower by 1/4・fH and becomes fc-1/4・fH. A signal with such a spectrum is supplied as a carrier signal to the frequency converter (3), beats with the carrier color signal are taken, and unnecessary components are removed by the filter (8), resulting in the frequency shown in Figure 9. A spectral low-pass converted color signal is obtained. That is, centering on fs (40f++ in case of VHS, NTSC (7)), CHl is 1/4・fH to the upper eight, and H2 is 1/4
・fH is shifted downward, resulting in CHI and CH2
The relative frequency offset of is 1/2·fH. This low frequency converted color signal is combined with an FM luminance signal, etc., and then supplied to a tape head system (9) for recording.

Next, we will discuss the regeneration process. Tape head system (9)
A low-pass filter (10) extracts only the low-pass converted color signal from the reproduced signal. This signal has CHI,
When there is no guard band between CH2, crosstalk from four adjacent channels is mixed. Low-pass filter (
The low frequency converted color signal with center frequency fs from 10) is supplied to the frequency converter (11) and returned to the carrier color signal with center frequency fsc, but the carrier signal to the frequency converter (11) is Similarly, the signal is supplied through a signal generator (4) and a phase shifter (5). The output signal from the frequency converter (11) has unnecessary components removed by a bandpass filter (12).

When CHI is reproduced in this way, the spectrum of the reproduced carrier color signal is as shown in Figure 9C, where the CH2 crosstalk component has an offset of 1/2 f H with respect to the CHI spectrum centered at fsc. It's mixed in. This crosstalk component is removed by a rectangular filter (13) having the frequency characteristics shown in FIG.
A reproduced carrier color signal with the frequency spectrum shown in Figure e is obtained.

[Problems to be Solved by the Invention] The conventional V, TR color signal processing circuit is configured as described above, and the color signal is transmitted through the band filters (2) (12), the low pass filters (8) (10 ), comb filter (13), and tape head system (9) during the recording/playback process, the color signal band narrows and the image quality deteriorates.Especially when dubbing, this process is repeated twice, which further deteriorates the image quality. to degrade. In addition, as shown in the recorded video signal frequency spectrum shown in Figure 10 (in the case of VHS and NTSC), there is interference between the upper side band of the low frequency conversion color signal and the lower side band of the FM luminance signal in the overlapped part. This had problems such as deterioration of image quality.

This invention was made to solve the above-mentioned problems by substantially widening the color signal band.

The object of the present invention is to obtain a color signal processing circuit for a VTR with high image quality that can reduce deterioration in image quality due to narrow band filters and the like and interference with luminance signals.

[Means for Solving the Problems] The color signal processing circuit of the VTR according to the present invention processes the color signal at a frequency higher than its highest frequency, fIIla.
Sampling is performed using a sampling signal that has a frequency fp that is an integer multiple of fH, which is lower than twice x, and whose phase is shifted by 172 periods for each field. It is converted to a converted color signal and recorded, and during playback, the reproduced low-frequency converted color signal is converted to a color signal, and sampled with the same sampling signal as during recording, and delayed in the field memory circuit at the same period as this sampling signal. The color signal is obtained by switching and superimposing the signal of the previous field.

[Function] In this invention, a component of 1/2 fρ or less of the color signal and a component of 1/2 fp or less of the color signal modulated by the fp signal and reflected to the low frequency side as a lower sideband are used. are frequency-shifted by 172 of the field frequency and superimposed,
A color signal of 0 to f max is frequency compressed to 0 to 1/2 fp. On the other hand, during playback, the playback color signal is sampled using a recording time-like sampling signal, and a signal sampled one field before with a phase shift of 172 cycles is superimposed and an interpolated signal is used as the playback color signal. . Since the frequency of the color signal is compressed and recorded in this way, it is possible to substantially widen the band of the color signal.

[Example] Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention. In the figure, (9) is the same tape head system as in Figure 8, and (16) is the bandpass filter (2), frequency converter (3), signal generator (4), and phase shifter (5) in Figure 7. , a conventional color signal recording processing circuit consisting of a low-pass filter (8), (+
7) similarly includes a low-pass filter (10) and a frequency converter (1).
1), bandpass filter (12), comb filter (13)
(18) is a conventional color signal reproduction processing circuit consisting of 3
．． 58M +-(z (NTSC system) input terminal into which the carrier color signal is input, (19) demodulates the carrier color signal into two color difference signals R-Y, B-Y (hereinafter referred to as color signals) (20') is a first sampling circuit that samples and holds a color signal;
1) is the frequency f! (Horizontal synchronization signal input terminal of (22)
) is the frequency f under the condition that the horizontal scanning frequency fH is expressed by the following formula.
This is a frequency multiplier that multiplies p.

fp”N ftl, fmax<fp<2 fmax
- (2) where N is an integer and f max is the maximum frequency of the color signal (usually about 500 kI(z)). (23) is the phase of the pulse output from the frequency multiplier (22)
A phase shifter for delaying the period, (24) is a head channel information signal application terminal that is switched every field, (25)
The pulse signals from the frequency multiplier (22) and phase shifter (23) are switched every field according to the channel information signal from the terminal (24) and sent to the first sampling circuit (20) (20'). For example, in the case of CHI, the output from the frequency multiplier (22) is
In the case of 2, the output from the phase shifter (23) is selected.

(26) is the frequency multiplier (22) and phase shifter (23)
and a switch (25), and (27) (27') is a low-pass filter that passes only signals with frequencies below 172 fo = 1/2 fp of the sampling signal frequency fP. , (28)
is the color signal from the low-pass filter (27) (27”)
．． A carrier color signal modulator performs quadrature two-phase modulation using a 58 MHz subcarrier, (29) is a bandpass filter that removes unnecessary components, (
30) is each of the above circuits (+9) (20) (20')
(26) (27) (27”) (28) and (2
(9) is a color signal frequency compression circuit, (31) is a second color signal demodulator that demodulates the reproduced carrier color signal into color signals that are two color difference signals R-Y and B-Y, (32) (32) '
) is the second sampling circuit that samples and holds the color signal, and (33) is the first sampling signal generation circuit (
26), a frequency multiplier circuit (34) and a phase shifter (35) similar to
) and a switch (36), the second sampling signal generating circuit (37) (37') generates the sampling color signal from the second sampling circuit (32) (32') at one field period (NTSC system). field memory, (38) (38')
is a changeover switch that is switched at the same cycle as the sampling signal from the circuit (33), and (39) is a changeover switch that changes the color signal from this changeover switch (38) (38') by 3.58
A carrier color signal modulator that performs quadrature two-phase modulation using a MHz subcarrier, (40) is a bandpass filter that removes unnecessary components, and (40) is a bandpass filter that removes unnecessary components;
1) is each circuit on the playback side (31) (32) (32') (
33) (37) (37') (38) (38') (39)
and (40).

Next, the operation will be explained with reference to Figs. 2 to 6.
The figure is a frequency spectrum diagram of the signals of each part of the color signal frequency compression circuit (3o), Figure 3 is a diagram showing the sampling operation on the VTR screen, Figure 4 is a frequency spectrum diagram of the low frequency conversion signal in this embodiment, Figure 5 shows the color signal interpolation circuit (4
1) is an explanatory diagram of the operation, and FIG. 6 is an explanatory diagram of the crosstalk removal operation in this embodiment.

First, during recording, the input carrier color signal to the terminal (18) is converted into two color difference signals R-Y by the first color signal demodulator (19).
, B-Y. The frequency spectrum of the color signal is as shown in FIG. 2a, and the maximum frequency f max is about 500 kHz. −10,000 terminals (
The horizontal synchronizing signal of frequency fH from 21) is multiplied by N times by a frequency multiplier (22) to obtain a pulse signal of frequency fp. The frequency fp of this signal has the relationship shown in equation (2) above. This pulse signal is sent to the switch (25)
- contact and is also applied to the phase shifter (23), where 18o.

(172 cycles) and is applied to the other contact of the switch (25) with its phase shifted. The switch (25) is switched according to the head channel switching for each field by a channel information signal sent to the terminal (24). Therefore, the sampling signal generated by the first sampling generation circuit (26) becomes a pulse train with a repetition frequency fP and a phase shift of 172 cycles for each field.

A color signal is sampled by the first sampling circuit (20) (20.) using this sampling signal.

The frequency spectrum of this sampled color signal is as shown in FIG. 2, and consists of a color signal component shown by a solid line and a component whose amplitude is modulated by the sampling signal of frequency fp shown by a broken line. fH of the frequency spectrum in the frequency domain where these two signals overlap
FIG. 2C is an enlarged view of only the n harmonic components of . The spectrum indicated by white circles in the figure is the spectrum of the color signal, and as is well known, it is distributed at intervals of the field frequency ff on both sides with nfH at the center. On the other hand, the spectrum indicated by the black circle is the N-nth lower sideband component modulated by the sampling signal, and since the phase of the sampling signal is inverted every field period, the spectrum shown by the black circle is 172
, that is, the frame frequency f F (30 in N TSC
It is offset by F(z) and interleaved with the color signal components. Therefore, f of the color signal is in the frequency band below fo, which is 1/2 of fp.

The following low-pass components and high-frequency components above fO modulated by fP are included, and the low-pass filter (27) (27'
), as shown in FIG. 2d, even if the frequency band is limited to below fO, the entire color signal band is transmitted.

If this sampling operation is made to correspond to the screen, it will become as shown in FIG. 3. In this way, the low-pass filter (27) (
27') is modulated into a carrier color signal by a carrier color signal modulator (28), unnecessary components are removed by a bandpass filter (29), and the band is compressed as shown in Figure 2e. A conveyed color signal is obtained. This carrier color signal is applied to a color signal recording processing circuit (16) similar to the conventional one shown in FIG. 7, and is converted into a low frequency conversion color signal.
It is combined with the luminance signal and magnetically recorded on a tape by a tape head system (9). The frequency spectrum of the low frequency converted color signal recorded at this time is as shown in FIG. 4, and the aliased signal spectrum of CH2 does not overlap with the offset of 172f +1 of CHI.

Next, we will discuss the regeneration process. Tape head system (9)
The reproduced carrier color signal which is reproduced by the color signal reproduction processing circuit (17) similar to the conventional one shown in FIG.
The color signal demodulator (31) converts the color signal into two color difference signals at the console and sends it to the second sampling circuit (32) (3
2'). This color signal has a spectrum approximately as shown in FIG. 2d. On the other hand, the sampling signal is exactly the same as when recording, the horizontal synchronizing signal is multiplied by a frequency multiplier (34) until fp=Nfl (this multiplied signal and a signal delayed by 172 periods by a phase shifter (35) are multiplied by 1 By switching the switch (36) for each field, the second sampling signal generating circuit (33) generates the reproduced color signal.This sampling signal causes the reproduced color signal to be sampled in the second sampling circuit (32) (32'). Retained.

The frequency spectrum of this sampled color signal is as shown in FIG. 5a, and is similar to the spectrum after sampling during recording (FIG. 2b). This sampled color signal is stored in the field memory (37) (3
7' ) and selector switch (3g) (3g') a
Supplied to the contacts. Field memory (37) (37'
), the input color signal is divided into one field 1/ f f
(1760 seconds in NTSC) and then supplies it to the b contact of the changeover switch (38) (3g'). As already shown in Figure 5, the changeover switches (38) (38') switch between the sampling points during recording indicated by white circles.
Interpolation is performed using the signal from one field before, which is indicated by a black circle. The timing of this switching is determined by the sampling signal from the sampling signal generation circuit (33).

By performing such an interpolation operation, the original 1/
A signal sampled at an interval of f p is equivalently 172f
This means that the signals are sampled at intervals of p, and according to the sampling theorem, signals up to fp can be reproduced. At this time, the frequency spectrum of the output color signal from the changeover switch (38) (38') becomes as shown in FIG. 5C, and the frequency spectrum of the recording signal is reproduced. The color signal processed as described above is subjected to quadrature two-phase modulation in a carrier signal modulator (39), and unnecessary components are removed in a bandpass filter (40) to obtain a reproduced carrier color signal.

The above reproduction operation has been described for the case where there is no crosstalk from adjacent tracks, but if crosstalk is included, the frequency spectrum of the carrier color signal obtained in the reproduction color signal conversion circuit (17) will be As shown in the figure, the crosstalk component has an offset of 1/2 f I+ from the original signal component. However, in this invention, the high frequency component of the color signal is frequency interpolated with a 30 Hz offset from the low frequency component having a strong spectrum for each fH. Therefore, as in the conventional method, crosstalk from adjacent tracks can be removed using an IH-type comb filter having the characteristics shown in Figure 6. Moreover, the high-frequency components folded back into the low frequency range of this comb-shaped filter There is almost no impact on

The frequency spectrum of the comb filter output signal is shown in Figure 6C.
The crosstalk component is removed. Therefore, if the comb filter output is processed by the color signal interpolation circuit (41) described in the above embodiment, the band can be expanded without any problem.

In the above embodiment, the second sampling circuit (32)
Although a sampling/holding circuit is used as (32'), if the field memory (37) (37') is one that processes digital signals, it can be replaced with an analog-to-digital converter or the like. In addition, in the above embodiment, the frequency-compressed color signal is first modulated into a carrier color signal, then converted to a low-pass converted color signal and recorded, and the reproduced low-pass converted color signal is converted to a carrier color signal and then demodulated to a color signal. Although it has been described that the interpolation processing is performed by using the interpolation process, the color signal may be directly converted into a recording low-band conversion color signal, or the reproduction low-band conversion color signal may be directly converted into a color signal.

In addition, 1. Second sampling signal generation circuit (26)
It is also possible to share (33).

[Effects of the Invention] As described above, according to the present invention, the high frequency component of the color signal is
/2 f Fold back to the low frequency side with an offset of f,
It is configured to frequency interleave with the low frequency component, and the frequency band of the color signal processed, recorded and played back by the color signal recording processing circuit, the color signal reproduction processing circuit and the tape head system can be narrowed, and the color signal can be substantially reduced. Since the band is widened, it is possible to prevent deterioration in image quality due to the narrow band of a filter, etc., and there is also less interference with the FM luminance signal, and the deterioration of frequency characteristics during dubbing can be significantly improved. Note that it also has the effect of being able to remove crosstalk caused by the conventional comb filter.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIG.
3, 4, 5, and 6 are explanatory diagrams of the operation of this embodiment. FIG. 7 is a block diagram showing a conventional VTR color signal processing circuit. FIG. 8 is a comb filter. FIG. 9 is a block diagram showing an example of the operation of the conventional circuit.
FIG. 0 is a diagram showing a frequency spectrum of a recorded video signal of a conventional circuit. In the figure, (9) is a tape head system, (16) is a color signal recording processing circuit, (17) is a color signal reproduction processing circuit, (
19) is the first color signal demodulator, (20) (20')
is the first sampling circuit, (26) is the first sampling signal generation circuit, (27) (27') is the low-pass filter, and (28) is the first carrier color signal modulator (recording color signal output circuit). , (30) is a color signal frequency compression circuit, (31)
is the second color signal demodulator (regenerated color signal input circuit), (3
2) (32') is the second sampling circuit, (33')
) is the second sampling signal generation circuit, (37) (3
7') is a field memory, (38) (38') is a changeover switch, and (39) is a second carrier color signal modulator. The same reference numerals in the drawings indicate the same or corresponding parts.

Claims (4)

[Claims] (1) Color of a video tape recorder equipped with a color signal recording processing circuit that converts an input signal into a low-band conversion color signal for recording, and a color signal reproduction processing circuit that converts the playback low-band conversion color signal into a desired output signal. In the signal processing circuit, a color signal demodulator demodulates an input carrier color signal into a color signal, which has a frequency that is an integer multiple of a horizontal scanning frequency that is higher than the highest frequency of this color signal and lower than twice it, and is used for each field. The phase is 1/2
a first sampling signal generation circuit that generates a sampling signal with a period shift; a first sampling signal generation circuit that samples the demodulated color signal using the sampling signal generation circuit from this circuit;
a sampling circuit, a low-pass filter that blocks signals with a frequency of 1/2 or more of the sampling signal frequency from the signal sampled by this circuit, and an output signal from this filter that is directly or converted into a desired signal to output the color signal. a color signal frequency compression circuit including a recording color signal output circuit that applies the input signal to the recording processing circuit; a reproduction color signal input circuit that inputs the output signal from the color signal reproduction processing circuit as the color signal; a second sampling signal generation circuit that generates the same sampling signal as the sampling signal generation circuit; and a second sampling signal generation circuit that samples the color signal from the reproduced color signal input circuit with the sampling signal from the second sampling signal generation circuit. Sampling circuit, the signal sampled by this sampling circuit is
a field memory for field delay; a changeover switch for switching and outputting the signal from the second sampling circuit and the signal delayed by one field from the field memory at the same cycle as the sampling signal from the second sampling generation circuit; , and a color signal interpolation circuit having a carrier color signal modulator that modulates a signal from this circuit into a carrier color signal. (2) The color signal recording processing circuit converts the input signal into a low-frequency converted color signal, and also converts the low-frequency converted color signals recorded on adjacent tracks of the recording tape so that their frequency spectra are at the line frequency. The color signal reproduction processing circuit is a circuit that performs processing to have an offset of 1/2 of
The video according to claim 1, which is a circuit comprising a comb filter having a stop band at horizontal scanning frequency intervals and removing crosstalk components from adjacent tracks after converting the reproduced low frequency conversion color signal into an output signal. Color signal processing circuit for tape recorder. (3) The input signal of the color signal recording processing circuit and the output signal of the color signal reproduction processing circuit are carrier color signals, and the recording color signal output circuit of the color signal frequency compression circuit converts the low-pass filter output signal into the carrier color signal. This is a carrier color signal modulator that modulates the carrier color signal into a carrier color signal that is an input signal of the recording color signal conversion circuit, and the reproduction color signal input circuit of the color signal interpolation circuit converts the carrier color signal from the reproduction color signal conversion circuit into a color signal. 3. A color signal processing circuit for a video tape recorder according to claim 1, which is a color signal demodulator for demodulating a color signal. (4) Color signal processing in a video tape recorder according to claim 1, 2 or 3, in which the first sampling signal generation circuit and the second sampling signal generation circuit are shared by one circuit. circuit.