JPH0783495B2 - Chroma signal recorder - Google Patents

Description

The present invention relates to a magnetic recording / reproducing apparatus for color video signals, and is particularly suitable for suppressing other signal components mixed as sideband components, that is, contour components, of a carrier color signal. The present invention relates to a chroma signal recording device.

FIG. 1 shows the configuration of a signal processing circuit of a conventional video tape recorder (hereinafter abbreviated as VTR). First, recording will be described. The signal input from the video signal input terminal 1 is LPF2
It is divided into a luminance signal and a chroma signal by BPF7. The luminance signal is recorded by the luminance signal recording processing circuit 3, the frequency modulation circuit 4, and the HPF 5 and input to the mixing circuit 6. On the other hand, the chroma signal is a variable gain amplifier 8 and a detection circuit.
By the ACC (Automatic Chroma Signal Control) circuit consisting of 12,
The level is set so that the output signal level is always constant even if the input signal level fluctuates. After that, the chroma signal converted into the low-frequency conversion carrier color signal by the chroma signal recording processing circuits 9 and 10 and the LPF 11 is input to the mixing circuit 6.
It is superimposed on the frequency-modulated luminance signal. The recording video signal output from the mixing circuit 6 is amplified by the recording amplification circuit 13 and recorded on the magnetic tape 15 via the video head 14.
The chroma signal recording processing circuits 9 and 10 are, for example, all or part of a frequency conversion circuit, a burst emphasis circuit, and a pseudo burst addition circuit.

Next, reproduction will be described. A signal reproduced from the magnetic tape 15 via the video head 16 is amplified by the reproduction amplifier circuit 17 and divided into a luminance signal and a chroma signal by the HPF 18 and LPF 24. The frequency-modulated luminance signal is demodulated into luminance signals by the luminance signal reproduction processing circuits 19 and 21 and the demodulation circuit 20, and is input to the mixing circuit 23 through the LPF 22. On the other hand, the low-frequency conversion carrier color signal is added to the chroma signal reproduction processing circuits 26 and 28 and the comb filter 27 through the ACC circuit including the variable gain amplifier 25 and the detection circuit 29, and the low-frequency conversion carrier color signal is converted to the chroma signal. Is input to the mixing circuit 23. The luminance signal and the chroma signal are mixed by the mixing circuit 23 and output from the output terminal 30 as a reproduced video signal.

The luminance signal reproduction processing circuit 19 is, for example, a trop-out canceller circuit and a limiter circuit, and the luminance signal reproduction processing circuit 21 is a luminance signal de-emphasis circuit.
Generally, the limiter circuit should be in circuit 19. or,
The chroma signal reproduction processing circuit 26 is a circuit including at least a frequency conversion circuit, and the chroma signal reproduction processing circuit 28 is, for example, a burst de-emphasis circuit, a pseudo burst removal circuit, and an HPF.

In a conventional VTR having the above circuit configuration, the characteristics of the comb filter provided on the reproducing side play an important role. In other words, the comb filter is used as a 1H delay line (1H means a horizontal scanning period), but in reality, spurious is generated from the delay line, which causes interference on the screen and poses a problem. Further, the luminance FM signal and the low-frequency conversion carrier color signal have a partially overlapping band, and the cross torus to the low-frequency conversion carrier color signal due to the lower sideband of the luminance FM signal becomes a cross color, which becomes a problem. Further, the number of deviations of H from the adjacent track (hereinafter abbreviated as αH)
When H is 1.0H or 0.75H, the H lines are aligned (the recording positions of the horizontal synchronizing signals are adjacent to each other between adjacent tracks), and the burst signal leaks from the adjacent tracks, which becomes a problem.

An object of the present invention is to eliminate the drawbacks of the prior art and to provide a chroma signal recording apparatus in which other signal components mixed in the chroma signal are reduced.

In order to achieve the above object, the present invention is provided with an emphasis circuit that emphasizes the contour component of the carrier color signal in the chroma signal recording system. The emphasis characteristic of this emphasis circuit is set so that it increases as the contour component moves away from the center frequency, and increases as the level of the contour component increases.

An embodiment of the present invention will be described below with reference to FIGS. 2 and 3. 2 and 3 show the structure of a chroma signal recording and reproducing circuit according to the present invention. The difference from the conventional example shown in FIG. 1 is that a chroma emphasis circuit 31 and a chroma de-emphasis circuit 34 are provided. In other words, when recording, a non-linear circuit called a chroma emphasis circuit is provided to enhance low-level signals for recording, and when reproducing, a chroma de-emphasis that has a complementary relationship with the input-output characteristics of the recording nonlinear circuit. By providing a circuit, the non-linear characteristic at the time of recording is removed and the original signal is restored.

In FIG. 2, of the video signals input from the input terminal 1, only the chroma signal is taken out by the BPF 7. Thereafter, the chroma signal adjusted to a constant level by the ACC circuit including the variable gain amplifier 8 and the detection circuit 12 passes through the chroma signal recording processing circuit 9 and the chroma emphasis circuit 31.
Entered in. The chroma signal emphasizing the low level signal in the chroma emphasis circuit 31 is frequency-converted to the low frequency in the next chroma signal recording processing circuit 10 and passed through the LPF 11 to the low frequency conversion carrier color signal from the output terminal 32 to the luminance signal. Is output to the mixing circuit with. The above is the chroma signal recording circuit according to the present invention.

FIG. 3 shows a reproduction circuit for a chroma signal. The signal amplified by the reproduction amplifier is input to the input terminal 33. LPF24
The chroma signal extracted by is adjusted to a constant level by the ACC circuit composed of the variable gain amplifier 25 and the detection circuit 29, and the chroma signal reproduction processing circuit 26 and the comb filter.
At 27, the low-frequency conversion carrier color signal is converted to the original chroma signal. After that, the chroma signal which has been corrected by the chroma de-emphasis circuit 34 for the non-linear characteristic performed by the chroma emphasis during recording is output from the output terminal 35 to the mixing circuit with the luminance signal through the chroma signal reproduction processing circuit 28. .

According to the present embodiment, there have been problems in the past (1) cross color interference due to crosstalk from the lower sideband of the luminance FM signal (2) spurious interference (especially burst) generated from the delay line constituting the comb filter (3) Pseudo burst interference is large. (3) Leakage of burst signals or pseudo burst signals from adjacent tracks when H lines are not aligned is suppressed, and chroma S / N is improved.

The first characteristic of FIGS. 2 and 3 is that the chroma de-emphasis circuit 34 is provided after the comb filter 27. The reason for this is to solve (2) and (3) of the above-mentioned conventional problems. That is, with respect to (2), since the burst interference depends on the output of the comb filter, the de-emphasis circuit 34 must be provided on the output side of the comb filter 27 to suppress it.

Also in (3), the effect of the de-emphasis circuit 34 can be obtained only after the crosstalk from the adjacent track is sufficiently suppressed by the comb filter 27. Therefore, the de-emphasis circuit 34 needs to be provided on the output side of the comb filter 27.

The second characteristic of FIGS. 2 and 3 is the chroma emphasis circuit.
That is, the ACC loop is configured such that the input signal (or output signal) level of 31 and the output signal (or input signal) level of the chroma de-emphasis circuit 34 are substantially equal. Both the chroma emphasis circuit 31 and the chroma de-emphasis circuit 34 are non-linear circuits, and the input signal level of the emphasis circuit 31 and the output signal level of the de-emphasis circuit 34 need to be almost equal in order for each to be an inverse circuit. .

Since the ACC circuit operates so that the input signal levels of the detection circuits 12 and 29 are constant, the ACC circuit is arranged so that the input signal of the detection circuit 12 and the input signal of the emphasis circuit 31 are almost the same, and the detection circuit 29 It is necessary to arrange so that the input signal and the output signal of the de-emphasis circuit 34 are almost equal.

Alternatively, the input signal of the detection circuit 12 is converted into the emphasis circuit 31
It is also possible to arrange so that it becomes almost the same as the output signal of. In this case, the input signal of the detection circuit 29 may be arranged to be almost the same as the input signal of the de-emphasis circuit 34.

Although the detection loop of the ACC circuit in FIG. 2 is taken out before the chroma emphasis circuit, it can be taken out after the chroma emphasis circuit.
Similarly, the detection loop in FIG. 3 can be taken out before the chroma de-emphasis circuit.

Examples of the chroma emphasis circuit and the chroma de-emphasis circuit are shown in FIGS. 4 and 5. The chroma emphasis circuit of FIG. 4 divides the chroma signal input from the input terminal 36 into a system path through the limiter circuit 37 and a system path of the original signal, and adds and mixes them in the adder circuit 38 to output them. Is output from. The limiter circuit 37 outputs a signal whose amplitude is limited with respect to a large-amplitude signal. The characteristic of the chroma emphasis circuit in FIG. 4 is that the low-level signal is linearly enhanced to a large-level signal. Will be restricted. The chroma de-emphasis circuit shown in FIG. 5 is a negative feedback type reverse circuit characteristic of the circuit shown in FIG. The reproduced chroma signal input from the input terminal 40 is subtracted by the subtractor circuit 41 from the signal fed back from the output terminal 42 through the limiter 37, and output to the output terminal 42. That is, if the transfer function H ₁ (ω) of the limiter circuit 37 in FIG. 4 is used, the transfer function R (ω) of the chroma emphasis circuit is given by the following equation.

R (ω) = 1 + H ₁ (ω) The transfer function P (ω) of the chroma de-emphasis circuit shown in FIG. 5 is given by the following equation.

P (ω) = 1 / {1 + H ₁ (ω)} Therefore, if the transfer functions H ₁ (ω) of the limiter circuits for emphasis and de-emphasis are equal, emphasis,
The transfer characteristic of the total de-emphasis is R (ω) · P (ω) = {1 + H ₁ (ω)} / {1 + H ₁ (ω)} = 1, and the non-linear characteristic of the emphasis circuit is corrected by the de-emphasis circuit. The signal can be restored almost completely.

Other examples are shown in FIGS. 6 and 7. The difference from FIGS. 4 and 5 is that a chroma signal side band extracting circuit 43 having the characteristics shown in FIG. 8 is provided in the path of the limiter circuit. That is, the emphasis is performed only on the side band of the chroma signal. The side band of the chroma signal is a high frequency band with a low level and is susceptible to noise. Therefore, performing sideband emphasis during recording and performing sideband deemphasis during reproduction improves the S / N of the chroma signal, and a good quality reproduced image can be obtained.

In FIG. 6, a carrier color signal (FIG. 11B) in which the burst signal is controlled to a predetermined level by the ACC circuit is input to the input terminal 36, and is supplied to the sideband extracting circuit 43. Since the sideband extracting circuit 43 has the frequency characteristic shown in FIG. 8, it suppresses the center frequency of the carrier color signal shown in FIG. 11 (a) to obtain the carrier color signal as shown in FIG. 11 (b). Extract only the contour component. Figure 11 (a)
As is apparent from (b), the contour component is larger as the level change of the carrier color signal is larger. The limiter circuit 37 is the 11th
A large amplitude exceeding a predetermined limit level is limited in the contour component of the carrier color signal shown in FIG. 11B, and a signal as shown in FIG. 11C is output. This signal is added by the adder circuit 38 to the original carrier color signal (Fig. 11 (a)), and the output terminal 39 outputs the signal
The signal shown in Fig. 11 (d) is obtained. In this emphasis circuit, the contour component of large amplitude is level-limited by the limiter circuit 37 and added to the original carrier color signal.
The emphasis action on the contour component is performed at a constant rate from the dew to the limit level, and the emphasis action decreases as the contour component increases beyond the limit level.

9 and 10 show a case where the chroma processing circuit of the present invention is used for both recording and reproduction. In FIG. 9, the recording / reproducing changeover switch 47 plays an important role. First, recording will be described. Only the chroma signal of the video signal is input to the input terminal 44. Recording / playback switch 47 for recording
Is at the position shown in the figure, and the variable gain amplifier 8 and the detection circuit 12 operate as an ACC circuit for recording. The chroma signal whose level has been adjusted by the ACC circuit passes through the chroma signal recording processing circuit 9 and is input to the chroma emphasis circuit 31 to emphasize the low level signal. The chroma signal is further frequency-converted into the low frequency band by the chroma signal recording processing circuit 10 and output to the output terminal 45. Next, reproduction will be described. Only the chroma signal of the reproduced video signal is input to the input terminal 44 common to the recording. During reproduction, the recording / reproduction changeover switch 47 is switched to a position opposite to that shown in the drawing, and the gain amplifier 8 and the detection circuit 12 operate as an ACC circuit for reproduction. The chroma signal passed through the ACC circuit is processed by the chroma signal reproduction processing circuit 26 and the comb filter 27.
Thus, the low-frequency conversion carrier color signal is converted to the original chroma signal. After that, in the chroma de-emphasis circuit 34,
The chroma signal whose characteristics are corrected by the emphasis circuit at the time of recording is output from the output terminal 46 through the chroma signal reproduction processing circuit 28. By providing the recording / playback switch 47 as described above, the ACC for recording and playback is set.
The circuit can be combined.

FIG. 10 shows an example in which the loop of the ACC detection circuit is different from the case of FIG. 9. In the case of recording, it is returned to the detection circuit 12 after the chroma emphasis circuit 31 and in the case of reproduction, the chroma It is designed to be returned from the front of the de-emphasis circuit.

Although the chroma emphasis and the chroma de-emphasis are all explained with the carrier color signal, of course, it is also possible to perform the emphasis and the de-emphasis with the low frequency conversion color signal.

Moreover, the emphasis may be only the emphasis of the chroma sideband.

According to the present invention, noise mixed in a chroma signal can be reduced, so that the chroma S / N of a reproduced image can be improved.

In particular, the effect of the present invention is extremely large with respect to spurious interference of the delay line that constitutes the comb filter, cross color interference from the luminance FM signal, burst signal leakage from adjacent tracks, and chroma interference of the pilot signal for ATF.

Further, according to the present invention, the recording emphasis circuit and the reproducing de-emphasis circuit can be simply reversed circuits, and the restoration is extremely good.

[Brief description of drawings]

FIG. 1 is a block diagram of a conventional signal processing circuit, FIG. 2 is a block diagram of a chroma signal recording process using the present invention, FIG. 3 is a block diagram of a chroma signal reproducing process using the present invention, and FIG. , FIG. 5 is a block diagram showing a chroma emphasis circuit and a chroma de-emphasis circuit, and FIGS. 6 and 7 are block diagrams showing another emphasis circuit and a de-emphasis circuit.
FIG. 8 is a characteristic diagram showing sideband emphasis characteristics,
9 and 10 are configuration diagrams showing an example in which the ACC circuit is commonly used for recording and reproduction, and FIG. 11 is a waveform diagram showing signal waveforms of respective portions in FIG. 8,25 ...... Variable gain amplifier, 12, 29 ...... Detection circuit, 31 ...... Chroma emphasis circuit, 34 ...... Chroma de-emphasis circuit, 27 ...... Comb filter, 37 ...... Limiter circuit, 38 ...... Adder circuit, 41 …… Subtractor circuit, 43 …… Chroma signal sideband extraction circuit, 47 …… Recording / playback switching circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Noboru Kojima, 292 Yoshida-cho, Totsuka-ku, Yokohama, Kanagawa Prefecture Home Appliances Research Laboratory, Hitachi, Ltd. (72) Inventor Asami Kuroyanagi 292, Yoshida-cho, Totsuka-ku, Yokohama Home Appliance Research Laboratory, Hitachi, Ltd. (56) Reference JP-A-58-80990 (JP, A)

Claims (2)

[Claims] 1. A chroma signal recording in which a carrier color signal is frequency-converted into a frequency band on the low frequency side of a frequency-modulated luminance signal and which can be disturbed by a low-frequency component of the frequency-modulated luminance signal and recorded on a recording medium. The apparatus is provided with an emphasis circuit that non-linearly emphasizes the carrier color signal, and the amount of emphasis by this emphasis circuit increases with distance from the center frequency in the frequency band of the carrier color signal for input signals of the same level. Chroma signal recording device characterized in that it is set so that the input signal of increasing frequency and the same frequency becomes larger as the level becomes smaller. 2. The emphasis circuit includes a limiter circuit for a transfer function H (ω) (ω is an angular frequency of the carrier color signal), and has an overall characteristic of a transfer function 1 + H (ω). The chroma signal recording apparatus according to claim 1.